| 1. |
- Adomas, Aleksandra, et al.
(författare)
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Comparative analysis of transcript abundance in Pinus sylvestris after challenge with a saprotrophic, pathogenic or mutualistic fungus
- 2008
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 28:6, s. 885-897
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Tidskriftsartikel (refereegranskat)abstract
- To investigate functional differences in the recognition and response mechanisms of conifer roots to fungi with different trophic strategies, Pinus sylvestris L. was challenged with a saprotrophic fungus Trichoderma aureoviride Rifai. The results were compared with separate studies investigating pine interactions with a pathogen, Heterobasidion annosum (Fr.) Bref. sensu stricto and an ectomycorrhizal symbiont, Laccaria bicolor Maire (Orton). Global changes in the expression of 2109 conifer genes were assayed 1, 5 and 15 days after inoculation. Gene expression data from a cDNA microarray were analyzed by the 2-interconnected mixed linear model statistical approach. The total number of genes differentially expressed compared with the uninfected control was similar after challenge with the pathogen and the ectomycorrhizal symbiont, but the number of differentially expressed genes increased over time, for H. annosum, and decreased for L. bicolor. Inoculation of pine roots with T aureoviride resulted overall in a much lower number of genes with changed transcript levels compared with inoculation with H. annosum or L. bicolor. Functional classification of the differentially expressed genes revealed that the ectomycorrhizal fungus triggered transient induction of defence-related genes. The response and induction of defence against the pathogen was delayed and the magnitude increased over time. Thus, there were specific transcriptional responses depending on whether the conifer roots were challenged with mutualistic, saprotrophic or pathogenic fungi. This suggests that pine trees are able to recognize diverse fungal species and specifically distinguish whether they are pathogenic, neutral or beneficial microbial agents.
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| 2. |
- Ahonen-Jonnarth, Ulla, et al.
(författare)
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Growth and nutrient uptake of ectomycorrhizal Pinus sylvestris seedlings treated with elevated Al concentrations and decreased levels of base cations
- 2003
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 23:3, s. 157-167
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Tidskriftsartikel (refereegranskat)abstract
- Models of the effects of elevated concentrations of aluminum (Al) on growth and nutrient uptake of forest trees frequently ignore the effects of mycorrhizal fungi. In this study, we present novel data indicating that ectomycorrhizal mycelia may prevent leaching of base cations and Al. Mycorrhizal and non-mycorrhizal Pinus sylvestris L. seedlings were grown in sand obtained from the B-horizon of a local forest. In Experiment 1, non-mycorrhizal seedlings and seedlings inoculated with Hebeloma cf. longicaudum (Pers.: Fr.) Kumm. ss. Lange or Laccaria bicolor (Maire) Orton were provided with nutrient solution containing 2.5 mM Al. Aluminum did not affect growth of non-mycorrhizal seedlings or seedlings inoculated with L. bicolor. Seedlings colonized by H. cf. longicaudum had the highest biomass production of all seedlings grown without added Al, but the fungus did not tolerate Al. Shoots of seedlings colonized by L. bicolor had the lowest nitrogen (N) concentrations but the highest phosphorus (P) concentrations of all seedlings. The treatments had small but significant effects on shoot and root Al concentrations. In Experiment 2, inoculation with L. bicolor was factorially combined with the addition of a complete nutrient solution, or a solution lacking the base cations K, Ca and Mg, and solutions containing 0 or 0.74 mM Al. Seedling growth decreased in response to 0.74 mM Al, but the effect was significant only for non-mycorrhizal seedlings. Mycorrhizal seedlings generally had higher P concentrations than non-mycorrhizal seedlings. Aluminum reduced P uptake in non-mycorrhizal plants but had no effect on P uptake in mycorrhizal plants. Mycorrhizal colonization increased the pH of the soil solution by about 0.5 units and addition of Al decreased the pH by the same amount. We conclude that the presence of ectomycorrhizal mycelia decreased leaching of base cations and Al from the soil.
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| 3. |
- Arnerup, Jenny, et al.
(författare)
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The pathogenic white-rot fungus Heterobasidion parviporum triggers non-specific defence responses in the bark of Norway spruce
- 2011
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Ingår i: Tree Physiology. - : Oxford University Press. - 0829-318X .- 1758-4469. ; 31:11, s. 1262-1272
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Tidskriftsartikel (refereegranskat)abstract
- Norway spruce [Picea abies (L.) Karst.] is one of the economically most important conifer species in Europe. The major pathogen on Norway spruce is Heterobasidion parviporum (Fr.) Niemelä & Korhonen. To achieve a better understanding of Norway spruce's defence mechanisms, transcriptional responses in bark to H. parviporum infection were compared with the response to wounding using cDNA-amplified fragment length polymorphism. The majority of the recovered transcript-derived fragments (TDFs) showed a similar expression pattern for infection and wounding treatment, although inoculated samples showed an enhanced reaction. Genes related to systemic acquired resistance, e.g., PR1, accumulated after H. parviporum infection. Simultaneously, several transcripts involved in various aspects of jasmonic acid (JA)- and ethylene (ET)-mediated signalling accumulated. Genes involved in the ubiquitin/proteasome system were also regulated. Expression patterns have been confirmed by quantitative polymerase chain reaction. The expression patterns of the isolated TDFs suggest that infection with H. parviporum in Norway spruce induces a broad defence, with many similarities to non-specific defence responses in angiosperms. The parallel induction of salicylic acid- and JA/ET-mediated pathways implies spatially separated responses in different cell layers, with and without hyphal contact. A set of TDFs were analysed in an independent experiment with unrelated material treated with wounding or with inoculation with H. parviporum or Phlebiopsis gigantea, verifying the original observations and underlining the non-specific defence responses. In addition, our data suggest that rerouting of carbon in secondary metabolism is an integral part of Norway spruce induced defence. We report the sequences of three 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase genes (PaDAHP1, PaDAHP2 and PaDAHP3) and their relative expression in response to wounding and infection with H. parviporum and P. gigantea. The results clearly indicate differential regulation of the three DAHPs in the induced defence responses in Norway spruce. This study gives insights into the central mechanisms in the induced defences in Norway spruce.
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| 4. |
- Asiegbu, Frederick
(författare)
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Response of living tissues of Pinus sylvestris to the saprotrophic biocontrol fungus Phlebiopsis gigantea
- 2011
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 31, s. 438-451
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Tidskriftsartikel (refereegranskat)abstract
- The saprotrophic fungus Phlebiopsis gigantea has been used for several years as a biocontrol agent against the conifer pathogen Heterobasidion annosum. Although the effectiveness of P. gigantea in biocontrol has been shown empirically, the long-term effect on living conifer trees as well as the mechanism underlying its antagonistic activity is still unknown. An additional concern is the potential of P. gigantea to acquire a necrotrophic habit through adaptation to living wood tissues. By using a combination of histochemical, molecular and transcript profiling (454 sequencing), we investigated under in vitro conditions the necrotrophic capability of P. gigantea and induced localized resistance as a mechanism for its biocontrol action. Pinus sylvestris seedlings (10 years old) were challenged on the xylem surface with P. gigantea or H. annosum. Both fungi provoked strong necrotic lesions, but after prolonged incubation, P. gigantea lesions shrank and ceased to expand further. Tree seedlings pre-treated with P. gigantea further restricted H. annosum-induced necrosis and had more lignified cells. The 454 sequencing revealed elevated transcript levels of genes important for lignification, cell death regulation and jasmonic acid signalling. The results suggest that induced localized resistance is a contributory factor for the biocontrol efficacy of P. gigantea, and it has a limited necrotrophic capability compared with H. annosum.
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| 5. |
- Aye, Tin Nwe, 1989-, et al.
(författare)
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Prediction of tree sapwood and heartwood profiles using pipe model and branch thinning theory
- 2022
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Ingår i: Tree Physiology. - : Oxford University Press. - 0829-318X .- 1758-4469. ; 42:11, s. 2174-2185
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Tidskriftsartikel (refereegranskat)abstract
- Estimates of tree heartwood and sapwood profiles are important in the pulp industry and for dynamic vegetation models, in which they determine tree biomechanical stability and hydraulic conductivity. Several phenomenological models of stem profiles have been developed for this purpose, based on assumptions on how tree crown and foliage distributions change over time. Here, we derive estimates of tree profiles by synthesizing a simple pipe model theory of plant form with a recently developed theory of branch thinning that from simple assumptions quantifies discarded branches and leaves. This allows us to develop a new trunk model of tree profiles from breast height up to the top of the tree. We postulate that leaves that are currently on the tree are connected by sapwood pipes, while pipes that previously connected discarded leaves or branches form the heartwood. By assuming that a fixed fraction of all pipes remain on the trunk after a branching event, as the trunk is traversed from the root system to the tips, this allows us to quantify trunk heartwood and sapwood profiles. We test the trunk model performance on empirical data from five tree species across three continents. We find that the trunk model accurately describes heartwood and sapwood profiles of all tested tree species (calibration; R2: 84-99%). Furthermore, once calibrated to a tree species, the trunk model predicts heartwood and sapwood profiles of conspecific trees in similar growing environments based only on the age and height of a tree (cross-validation/prediction; R2: 68-98%). The fewer and often contrasting parameters needed for the trunk model make it a potentially useful complementary tool for biologists and foresters.
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| 6. |
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| 7. |
- Bizjak, Tinkara, et al.
(författare)
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Presence and activity of nitrogen-fixing bacteria in Scots pine needles in a boreal forest : a nitrogen-addition experiment
- 2023
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Ingår i: Tree Physiology. - : Oxford University Press. - 0829-318X .- 1758-4469. ; 43:8, s. 1354-1364
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Tidskriftsartikel (refereegranskat)abstract
- Endophytic nitrogen-fixing bacteria have been detected and isolated from the needles of conifer trees growing in North American boreal forests. Because boreal forests are nutrient-limited, these bacteria could provide an important source of nitrogen for tree species. This study aimed to determine their presence and activity in a Scandinavian boreal forest, using immunodetection of nitrogenase enzyme subunits and acetylene-reduction assays of native Scots pine (Pinus sylvestris L.) needles. The presence and rate of nitrogen fixation by endophytic bacteria were compared between control plots and fertilized plots in a nitrogen-addition experiment. In contrast to the expectation that nitrogen-fixation rates would decline in fertilized plots, as seen, for instance, with nitrogen-fixing bacteria associated with bryophytes, there was no difference in the presence or activity of nitrogen-fixing bacteria between the two treatments. The extrapolated calculated rate of nitrogen fixation relevant for the forest stand was 20 g N ha-1 year-1, which is rather low compared with Scots pine annual nitrogen use but could be important for the nitrogen-poor forest in the long term. In addition, of 13 colonies of potential nitrogen-fixing bacteria isolated from the needles on nitrogen-free media, 10 showed in vitro nitrogen fixation. In summary, 16S rRNA sequencing identified the species as belonging to the genera Bacillus, Variovorax, Novosphingobium, Sphingomonas, Microbacterium and Priestia, which was confirmed by Illumina whole-genome sequencing. Our results confirm the presence of endophytic nitrogen-fixing bacteria in Scots pine needles and suggest that they could be important for the long-term nitrogen budget of the Scandinavian boreal forest.
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| 8. |
- Brum, Mauro, et al.
(författare)
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Ecophysiological controls on water use of tropical cloud forest trees in response to experimental drought
- 2023
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Ingår i: Tree Physiology. - : Oxford University Press. - 0829-318X .- 1758-4469. ; 43:9, s. 1514-1532
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Tidskriftsartikel (refereegranskat)abstract
- Tropical montane cloud forests (TMCFs) are expected to experience more frequent and prolonged droughts over the coming century, yet understanding of TCMF tree responses to moisture stress remains weak compared with the lowland tropics. We simulated a severe drought in a throughfall reduction experiment (TFR) for 2 years in a Peruvian TCMF and evaluated the physiological responses of several dominant species (Clusia flaviflora Engl., Weinmannia bangii (Rusby) Engl., Weinmannia crassifolia Ruiz & Pav. and Prunus integrifolia (C. Presl) Walp). Measurements were taken of (i) sap flow; (ii) diurnal cycles of stem shrinkage, stem moisture variation and water-use; and (iii) intrinsic water-use efficiency (iWUE) estimated from foliar δ13C. In W. bangii, we used dendrometers and volumetric water content (VWC) sensors to quantify daily cycles of stem water storage. In 2 years of sap flow (Js) data, we found a threshold response of water use to vapor pressure deficit vapor pressure deficit (VPD) > 1.07 kPa independent of treatment, though control trees used more soil water than the treatment trees. The daily decline in water use in the TFR trees was associated with a strong reduction in both morning and afternoon Js rates at a given VPD. Soil moisture also affected the hysteresis strength between Js and VPD. Reduced hysteresis under moisture stress implies that TMCFs are strongly dependent on shallow soil water. Additionally, we suggest that hysteresis can serve as a sensitive indicator of environmental constraints on plant function. Finally, 6 months into the experiment, the TFR treatment significantly increased iWUE in all study species. Our results highlight the conservative behavior of TMCF tree water use under severe soil drought and elucidate physiological thresholds related to VPD and its interaction with soil moisture. The observed strongly isohydric response likely incurs a cost to the carbon balance of the tree and reduces overall ecosystem carbon uptake.
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| 9. |
- Businge, Edward, et al.
(författare)
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A possible biochemical basis for fructose-induced inhibition of embryo development in Norway spruce (Picea abies)
- 2014
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 34, s. 657-669
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Tidskriftsartikel (refereegranskat)abstract
- Sugars play an important role in various physiological processes during plant growth and development; however, the developmental roles and regulatory functions of hexoses other than glucose are still largely unclear. Recent studies suggest that blocked embryo development in Norway spruce (Picea abies (L.) Karst) is associated with accumulation of fructose. In the present study, the potential biochemical regulatory mechanism of glucose and fructose was studied during development of somatic embryos of Norway spruce from pro-embryogenic masses to mature embryos. The changes in protein fluorescence, a marker of the Maillard reaction, were monitored in two cell lines of Norway spruce that were grown on media containing sucrose (control), glucose or fructose. Manual time-lapse photography showed that growth of embryogenic cultures on medium containing sucrose was characterized by normal development of mature embryos whereas the embryogenic cultures that were grown on media containing glucose or fructose did not develop mature embryos. The biochemical analyses of embryogenic samples collected during embryo development showed that: (i) the content of glucose and fructose in the embryogenic cultures increased significantly during growth on each medium, respectively; (ii) the accumulation of Maillard products in the embryogenic cultures was highly correlated with the endogenous content of fructose but not glucose; and (iii) the embryogenic cultures grown on fructose displayed the highest protein carbonyl content and DNA damage whereas the highest content of glutathione was recorded in the embryogenic cultures that had grown on sucrose. Our data suggest that blocked development of embryos in the presence of fructose may be associated with the Maillard reaction.
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| 10. |
- Businge, Edward, et al.
(författare)
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Metabolite profiling reveals clear metabolic changes during somatic embryo development of Norway spruce (Picea abies)
- 2012
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 32, s. 232-244
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Tidskriftsartikel (refereegranskat)abstract
- Progress on industrial-scale propagation of conifers by somatic embryogenesis has been hampered by the differences in developmental capabilities between cell lines, which are limiting the capture of genetic gains from breeding programs. In this study, we investigated the metabolic events occurring during somatic embryo development in Norway spruce to establish a better understanding of the fundamental metabolic events required for somatic embryo development. Three embryogenic cell lines of Norway spruce (Picea abies (L.) Karst) with different developmental capabilities were studied during somatic embryo development from proliferation of proembryogenic masses to mature somatic embryos. The three different cell lines displayed normal, aberrant and blocked somatic embryo development. Metabolite profiles from four development stages in each of the cell lines were obtained using combined gas chromatography-mass spectrometry. Multivariate discriminant analyses of the metabolic data revealed significant metabolites (P < 0.05) for each development stage and transition. The results suggest that endogenous auxin and sugar signaling affects initial stages of somatic embryo development. Furthermore, the results highlight the importance of a timed stress response and the presence of stimulatory metabolites during late stages of embryo development.
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| 11. |
- Børja, Isabella, et al.
(författare)
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Stand age and fine root biomass, distribution and morphology in a Norway spruce chronosequence in southeast Norway
- 2008
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 28:5, s. 773-784
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Tidskriftsartikel (refereegranskat)abstract
- We assessed the influence of stand age on fine root biomass and morphology of trees and understory vegetation in 10-, 30-, 60- and 120-year-old Norway spruce stands growing in sandy soil in southeast Norway. Fine root (< 1, 1–2 and 2–5 mm in diameter) biomass of trees and understory vegetation (< 2 mm in diameter) was sampled by soil coring to a depth of 60 cm. Fine root morphological characteristics, such as specific root length (SRL), root length density (RLD), root surface area (RSA), root tip number and branching frequency (per unit root length or mass), were determined based on digitized root data. Fine root biomass and morphological characteristics related to biomass (RLD and RSA) followed the same tendency with chronosequence and were significantly higher in the 30-year-old stand and lower in the 10-year-old stand than in the other stands. Among stands, mean fine root (< 2 mm) biomass ranged from 49 to 398 g m–2, SLR from 13.4 to 19.8 m g–1, RLD from 980 to 11,650 m m–3 and RSA from 2.4 to 35.4 m2 m–3. Most fine root biomass of trees was concentrated in the upper 20 cm of the mineral soil and in the humus layer (0–5 cm) in all stands. Understory fine roots accounted for 67 and 25% of total fine root biomass in the 10- and 120-year-old stands, respectively. Stand age had no affect on root tip number or branching frequency, but both parameters changed with soil depth, with increasing number of root tips and decreasing branching frequency with increasing soil depth for root fractions < 2 mm in diameter. Specific (mass based) root tip number and branching density were highest for the finest roots (< 1 mm) in the humus layer. Season (spring or fall) had no effect on tree fine root biomass, but there was a small and significant increase in understory fine root biomass in fall relative to spring. All morphological characteristics showed strong seasonal variation, especially the finest root fraction, with consistently and significantly higher values in spring than in fall. We conclude that fine root biomass, especially in the finest fraction (< 1 mm in diameter), is strongly dependent on stand age. Among stands, carbon concentration in fine root biomass was highest in the 30-year-old stand, and appeared to be associated with the high tree and canopy density during the early stage of stand development. Values of RLD and RSA, morphological features indicative of stand nutrient-uptake efficiency, were higher in the 30-year-old stand than in the other stands.
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| 12. |
- Castaño Soler, Carles
(författare)
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Insect defoliation is linked to a decrease in soil ectomycorrhizal biomass and shifts in needle endophytic communities
- 2020
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 40, s. 1712-1725
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Tidskriftsartikel (refereegranskat)abstract
- Insect outbreaks of increasing frequency and severity in forests are predicted due to climate change. Insect herbivory is known to promote physiological changes in forest trees. However, little is known about whether these plant phenotypic adjustments have cascading effects on tree microbial symbionts such as fungi in roots and foliage. We studied the impact of defoliation by the pine processionary moth in two infested Pinus nigra forests through a multilevel sampling of defoliated and non-defoliated trees. We measured tree growth, nutritional status and carbon allocation to chemical defenses. Simultaneously, we analysed the putative impact of defoliation on the needle endophytes and on the soil fungal communities. Higher concentrations of chemical defenses were found in defoliated trees, likely as a response to defoliation; however, no differences in non-structural carbohydrate reserves were found. In parallel to the reductions in tree growth and changes in chemical defenses, we observed shifts in the composition of needle endophytic and soil fungal communities in defoliated trees. Defoliated trees consistently corresponded with a lower biomass of ectomycorrhizal fungi in both sites, and a higher alpha diversity and greater relative abundance of belowground saprotrophs and pathogens. However, ectomycorrhizal alpha diversity was similar between non-defoliated and defoliated trees. Specific needle endophytes in old needles were strongly associated with non-defoliated trees. The potential role of these endophytic fungi in pine resistance should be further investigated. Our study suggests that lower biomass of ectomycorrhizal fungi in defoliated trees might slow down tree recovery since fungal shifts might affect tree-mycorrhizal feedbacks and can potentially influence carbon and nitrogen cycling in forest soils.
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| 13. |
- Crouse, Kristine, et al.
(författare)
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Acclimation of light and dark respiration to experimental and seasonal warming are mediated by changes in leaf nitrogen in Eucalyptus globulus
- 2017
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 37:8, s. 1069-1083
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Tidskriftsartikel (refereegranskat)abstract
- Quantifying the adjustments of leaf respiration in response to seasonal temperature variation and climate warming is crucial because carbon loss from vegetation is a large but uncertain part of the global carbon cycle. We grew fast-growing Eucalyptus globulus Labill. trees exposed to +3 °C warming and elevated CO2 in 10-m tall whole-tree chambers and measured the temperature responses of leaf mitochondrial respiration, both in light (RLight) and in darkness (RDark), over a 20–40 °C temperature range and during two different seasons. RLight was assessed using the Laisk method. Respiration rates measured at a standard temperature (25 °C – R25) were higher in warm-grown trees and in the warm season, related to higher total leaf nitrogen (N) investment with higher temperatures (both experimental and seasonal), indicating that leaf N concentrations modulated the respiratory capacity to changes in temperature. Once differences in leaf N were accounted for, there were no differences in R25 but the Q10 (i.e., short-term temperature sensitivity) was higher in late summer compared with early spring. The variation in RLight between experimental treatments and seasons was positively correlated with carboxylation capacity and photorespiration. RLight was less responsive to short-term changes in temperature than RDark, as shown by a lower Q10 in RLight compared with RDark. The overall light inhibition of R was ∼40%. Our results highlight the dynamic nature of leaf respiration to temperature variation and that the responses of RLight do not simply mirror those of RDark. Therefore, it is important not to assume that RLight is the same as RDark in ecosystem models, as doing so may lead to large errors in predicting plant CO2 release and productivity.
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| 14. |
- Decker, Vicki Huizu, et al.
(författare)
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Aspen phenylpropanoid genes’ expression levels correlate with genets’ tannin richness and vary both in responses to soil nitrogen and associations with phenolic profiles
- 2017
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 37:2, s. 270-279
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Tidskriftsartikel (refereegranskat)abstract
- Condensed tannin (CT) contents of European aspen (Populus tremula L.) vary among genotypes, and increases in nitrogen (N) availability generally reduce plants’ tannin production in favor of growth, through poorly understood mechanisms. We hypothesized that intrinsic tannin production rates may co-vary with gene expression responses to soil N and resource allocation within the phenylpropanoid pathway (PPP). Thus, we examined correlations between soil N levels and both expression patterns of eight PPP genes (measured by quantitative-reverse transcription PCR) and foliar phenolic compounds (measured by liquid chromatography–mass spectrometry) in young aspen genets with intrinsically extreme CT levels. Monitored phenolics included salicinoids, lignins, flavones, flavonols, CT precursors and CTs. The PPP genes were consistently expressed more strongly in high-CT trees. Low N supplements reduced expression of genes throughout the PPP in all genets, while high N doses restored expression of genes at the beginning and end of the pathway. These PPP changes were not reflected in pools of tannin precursors, but varying correlations between gene expression and foliar phenolic pools were detected in young and mature leaves, suggesting that processes linking gene expression and the resulting phenolics vary spatially and temporally. Precursor fluxes suggested that CT-related metabolic rate or sink controls are linked to intrinsic carbon allocation strategies associated with N responses. Overall, we found more negative correlations (indicative of allocation trade-offs) between PPP gene expression and phenolic products following N additions in low-CT plants than in high-CT plants. The tannin-related expression dynamics suggest that, in addition to defense, relative tannin levels may also be indicative of intraspecific variations in the way aspen genets respond to soil fertility.
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| 15. |
- Dewar, R. C., et al.
(författare)
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Why does leaf nitrogen decline within tree canopies less rapidly than light? An explanation from optimization subject to a lower bound on leaf mass per area
- 2012
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 32:5, s. 520-534
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Tidskriftsartikel (refereegranskat)abstract
- A long-established theoretical result states that, for a given total canopy nitrogen (N) content, canopy photosynthesis is maximized when the within-canopy gradient in leaf N per unit area (N-a) is equal to the light gradient. However, it is widely observed that N-a declines less rapidly than light in real plant canopies. Here we show that this general observation can be explained by optimal leaf acclimation to light subject to a lower-bound constraint on the leaf mass per area (m(a)). Using a simple model of the carbon-nitrogen (C-N) balance of trees with a steady-state canopy, we implement this constraint within the framework of the MAXX optimization hypothesis that maximizes net canopy C export. Virtually all canopy traits predicted by MAXX (leaf N gradient, leaf N concentration, leaf photosynthetic capacity, canopy N content, leaf-area index) are in close agreement with the values observed in a mature stand of Norway spruce trees (Picea abies L. Karst.). An alternative upper-bound constraint on leaf photosynthetic capacity (A(sat)) does not reproduce the canopy traits of this stand. MAXX subject to a lower bound on m(a) is also qualitatively consistent with co-variations in leaf N gradient, m(a) and A(sat) observed across a range of temperate and tropical tree species. Our study highlights the key role of constraints in optimization models of plant function.
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| 16. |
- Dobrowolska, Izabela, et al.
(författare)
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Metabolome and transcriptome profiling reveal new insights into somatic embryo germination in Norway spruce (Picea abies)
- 2017
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 37, s. 1752-1766
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Tidskriftsartikel (refereegranskat)abstract
- Transcriptome, metabolome and histological profiling were performed on normal and aberrant somatic embryo germinants of Norway spruce (Picea abies L. Karst) providing a simplistic systems biology description of conifer germination. Aberrant germinants (AGs) formed periderm-like tissue at the apical pole and lacked shoot growth above the cotyledons. Transcriptome profiling (RNA-Sequencing) revealed a total of 370 differentially expressed genes at >= 1 or <=-1 log(2)-fold change, where 92% were down-regulated in AGs compared with normal germinants (NGs). Genes associated with shoot apical meristem formation were down-regulated in AGs, or not differentially expressed between AGs and NGs. Genes involved in hormone signaling and transport were also down-regulated. Metabolite profiling by gas chromatography-mass spectrometry (MS) and liquid chromatography-MS revealed biochemical difference between AGs and NGs, notably increased levels of sugars including glucose in AGs. Genes involved in glucose signaling were down-regulated and genes involved in starch biosynthesis were up-regulated, suggesting involvement of sugar signaling during late embryo development and germination. The overall results provide new data enabling further studies to confirm potential markers for a normal germination process in conifers.
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| 17. |
- Doweler, Fabian, et al.
(författare)
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High light-induced photoinhibition is not limiting seedling establishment at abrupt treeline ecotones in New Zealand
- 2021
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Ingår i: Tree Physiology. - : Oxford University Press. - 0829-318X .- 1758-4469. ; 41:11, s. 2034-2045
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Tidskriftsartikel (refereegranskat)abstract
- Seedlings of New Zealand's treeline-forming Fuscospora cliffortioides (Hook.f.) perform poorly beyond the established canopy, limiting treeline advance. To test the long-standing assumption that photoinhibition impairs regeneration in the subalpine belt of New Zealand's Southern Alps, we assessed photosystem II (PSII) performance of seedling-sized individuals and microclimate variation. We performed diurnal, non-invasive chlorophyll-a-fluorescence measurements on exposed and canopy-sheltered individuals at two sites in New Zealand's Southern Alps during summer and winter. Diurnal recordings of the effective (Phi PSII) and optimal (F-v/F-m) photosynthetic quantum yield were supplemented with light response curves and micro-temperature recordings. Phi PSII returned to near-optimal values around 0.8 after 30 min of shading, which rules out accumulative or long-term photoinhibition effects. The maximum electron transport rate derived from rapid light curves was significantly higher (+12%) in exposed compared with canopy-shaded individuals. Summer temperature fluctuated widely on the scree (-0.5 to 60.5 degrees C) and near seedlings (-2 to 26.5 degrees C). Our results revealed a remarkable level of light adaptation and contradict previous studies hinting at high light-induced photoinhibition as a treeline-limiting factor in the Southern Alps. By linking low Phi PSII on winter mornings, and large, sudden temperature drops in summer, we suspect that cold-induced photoinhibition might occur but the rapid recovery of Phi PSII seen across a wide temperature range makes lethal photo-oxidative damage rather unlikely. Given the demonstrably low summer frost tolerance of F. cliffortioides, cold-related damage resulting from frost events during the growing season or embolism induced by frost drought may offer more plausible explanations for the poor seedling establishment. Duration and frequency of these events could diminish with global warming, which may promote treeline advance.
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| 18. |
- Duursma, R. A., et al.
(författare)
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Contributions of climate, leaf area index and leaf physiology to variation in gross primary production of six coniferous forests across Europe: a model-based analysis
- 2009
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 1758-4469 .- 0829-318X. ; 29:5, s. 621-639
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Tidskriftsartikel (refereegranskat)abstract
- Gross primary production (GPP) is the primary source of all carbon fluxes in the ecosystem. Understanding, variation in this flux is vital to understanding variation in the carbon sink of forest ecosystems, and this would serve as input to forest production models. Using GPP derived from eddy-covariance (EC) Measurements, it is now possible to determine the most important factor to scale GPP across sites. We use long-term EC measurements for six coniferous forest stands in Europe, for a total of 25 site-years, located oil a gradient between Southern France and northern Finland. Eddy-derived GPP varied threefold across the six sites, peak ecosystem leaf area index (LAI) (all-sided) varied from 4 to 22 m(2) m(-2) and mean annual temperature varied from - 1 to 13 degrees C. A process-based model operating at a half-hourly time-step was parameterized with available information for each site, and explained 71-96% in variation between daily totals of GPP within site-years and 62% of annual total GPP across site-years. Using the parameterized model, we performed two simulation experiments: weather datasets were interchanged between sites, so that the model was used to predict GPP at some site using data from either a different year or a different site. The resulting bias in GPP prediction was related to several aggregated weather variables and was found to be closely related to the change in the effective temperature sum or mean annual temperature. High R(2)s resulted even when using weather datasets from unrelated sites, providing a cautionary note on the interpretation of R-2 ill model comparisons. A second experiment interchanged stand-structure information between sites. and the resulting bias was strongly related to the difference in LAI, or the difference in integrated absorbed light. Across the six sites. variation in mean annual temperature had more effect on simulated GPP than the variation in LAI. but both were important determinants of GPP. A sensitivity analysis of leaf physiology parameters showed that the quantum yield was the most influential parameter on annual GPP, followed by a parameter controlling the seasonality of photosynthesis and photosynthetic capacity. Overall, the results are promising for the development of a parsimonious model of GPP.
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| 19. |
- Eckert, Diana, et al.
(författare)
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CO2 refixation is higher in leaves of woody species with high mesophyll and stomatal resistances to CO2 diffusion
- 2021
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Ingår i: Tree Physiology. - : Oxford University Press. - 0829-318X .- 1758-4469. ; 41:8, s. 1450-1461
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Tidskriftsartikel (refereegranskat)abstract
- The percentage of respiratory and photorespiratory CO2 refixed in leaves (P-r) represents part of the CO2 used in photosynthesis. The importance of P-r as well as differences between species and functional types are still not well investigated. In this study, we examine how P-r differs between six temperate and boreal woody species: Betula pendula, Quercus robur, Larix decidua, Pinus sylvestris, Picea abies and Vaccinium vitis-idaea. The study covers early and late successional species, deciduous broadleaves, deciduous conifers, evergreen conifers and evergreen broadleaves. We investigated whether some species or functional types had higher refixation percentages than others, whether leaf traits could predict higher P-r and whether these traits and their impact on P-r changed during growing seasons. Photosynthesis CO2 response (A/C-i)-curves, measured early, mid and late season, were used to estimate and compare P-r, mesophyll resistance (r(m)) and stomatal resistance (r(s)) to CO2 diffusion. Additionally, light images and transmission electron microscope images were used to approximate the fraction of intercellular airspace and cell wall thickness. We found that evergreens, especially late successional species, refixed a significantly higher amount of CO2 than the other species throughout the entire growing season. In addition, r(m), r(s) and leaf mass per area, traits that typically are higher in evergreen species, were also significantly, positively correlated with P-r. We suggest that this is due to higher r(m) decreasing diffusion of (photo) respiratory CO2 out of the leaf. Cell wall thickness had a positive effect on P-r and r(m), while the fraction of intercellular airspace had no effect. Both were significantly different between evergreen conifers and other types. Our findings suggest that species with a higher r(m) use a greater fraction of mitochondria-derived CO2, especially when stomatal conductance is low. This should be taken into account when modeling the overall CO2 fertilization effect for terrestrial ecosystems dominated by high r(m) species.
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| 20. |
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| 21. |
- Franklin, Oskar, et al.
(författare)
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Modeling carbon allocation in trees : a search for principles
- 2012
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 32:6, s. 648-666
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Forskningsöversikt (refereegranskat)abstract
- We review approaches to predicting carbon and nitrogen allocation in forest models in terms of their underlying assumptions and their resulting strengths and limitations. Empirical and allometric methods are easily developed and computationally efficient, but lack the power of evolution-based approaches to explain and predict multifaceted effects of environmental variability and climate change. In evolution-based methods, allocation is usually determined by maximization of a fitness proxy, either in a fixed environment, which we call optimal response (OR) models, or including the feedback of an individual's strategy on its environment (game-theoretical optimization, GTO). Optimal response models can predict allocation in single trees and stands when there is significant competition only for one resource. Game-theoretical optimization can be used to account for additional dimensions of competition, e.g., when strong root competition boosts root allocation at the expense of wood production. However, we demonstrate that an OR model predicts similar allocation to a GTO model under the root-competitive conditions reported in free-air carbon dioxide enrichment (FACE) experiments. The most evolutionarily realistic approach is adaptive dynamics (AD) where the allocation strategy arises from eco-evolutionary dynamics of populations instead of a fitness proxy. We also discuss emerging entropy-based approaches that offer an alternative thermodynamic perspective on allocation, in which fitness proxies are replaced by entropy or entropy production. To help develop allocation models further, the value of wide-ranging datasets, such as FLUXNET, could be greatly enhanced by ancillary measurements of driving variables, such as water and soil nitrogen availability.
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| 22. |
- Fransson, Peter, 1988-, et al.
(författare)
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A tree’s quest for light : optimal height and diameter growth under a shading canopy
- 2021
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 41:1, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- For trees in forests, striving for light is matter of life and death, either by growing taller toward brighter conditions or by expanding the crown to capture more of the available light. Here, we present a mechanistic model for the development path of stem height and crown size, accounting for light capture and growth, as well as mortality risk. We determine the optimal growth path among all possible trajectories using dynamic programming. The optimal growth path follows a sequence of distinct phases: (i) initial crown size expansion, (ii) stem height growth toward the canopy, (iii) final expansion of the crown in the canopy and (iv) seed production without further increase in size. The transition points between these phases can be optimized by maximizing fitness, defined as expected lifetime reproductive production. The results imply that to reach the canopy in an optimal way, trees must consider the full profile of expected increasing light levels toward the canopy. A shortsighted maximization of growth based on initial light conditions can result in arrested height growth, preventing the tree from reaching the canopy. The previous result can explain canopy stratification, and why canopy species often get stuck at a certain size under a shading canopy. The model explains why trees with lower wood density have a larger diameter at a given tree height and grow taller than trees with higher wood density. The model can be used to implement plasticity in height versus diameter growth in individual-based vegetation and forestry models.
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| 23. |
- Ghelardini, Luisa
(författare)
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Bud dormancy release in elm (Ulmus spp.) clones-a case study of photoperiod and temperature responses
- 2010
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 30, s. 264-274
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Tidskriftsartikel (refereegranskat)abstract
- Dormancy release as influenced by duration of outdoor winter chilling in Florence (Italy) was studied under different photoperiodic and temperature treatments in collected twigs of two European (Ulmus glabra Huds. and Ulmus minor Mill.) and four Asian (Ulmus pumila L., Ulmus parvifolia Jacq., Ulmus macrocarpa Hance and Ulmus villosa Brandis) elm clones. Photoperiod had no effect on dormancy release, and there was no evidence that photoperiod affected bud burst during quiescence in the studied elm clones. Thermal time (day degrees >0 degrees C) to bud burst decreased in all the clones with increasing Outdoor chilling. Although all the clones exhibited a rather weak dormancy, they significantly differed from each other. Dormancy was released earlier in the Asian than in the European clones, and the clones could be ranked from the U. pumila clone (very weak and short dormancy) to the U. minor clone (relatively stronger and longer dormancy), the other clones being intermediate. In all the clones except U. minor, the observed decrement in thermal time to bud burst was efficiently explained as an inverse exponential function of the number of chill days <= 5 degrees C received outdoor in autumn and winter. Endodormancy, as measured by the single-node cuttings test, was weak and short in all the clones. The latter result suggests that correlative inhibitions were largely responsible for preventing bud burst during winter in these elm clones.
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| 24. |
- Gratz, Regina, et al.
(författare)
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Organic nitrogen nutrition: LHT1.2 protein from hybrid aspen (Populus tremula L. x tremuloides Michx) is a functional amino acid transporter and a homolog of Arabidopsis LHT1
- 2021
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 41, s. 1479–1496-
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Tidskriftsartikel (refereegranskat)abstract
- The contribution of amino acids (AAs) to soil nitrogen (N) fluxes is higher than previously thought. The fact that AA uptake is pivotal for N nutrition in boreal ecosystems highlights plant AA transporters as key components of the N cycle. At the same time, very little is known about AA transport and respective transporters in trees. Tree genomes may contain 13 or more genes encoding the lysine histidine transporter (LHT) family proteins, and this complicates the study of their significance for tree N-use efficiency. With the strategy of obtaining a tool to study N-use efficiency, our aim was to identify and characterize a relevant AA transporter in hybrid aspen (Populus tremula L. x tremuloides Michx.). We identified PtrLHT1.2, the closest homolog of Arabidopsis thaliana (L.) Heynh AtLHT1, which is expressed in leaves, stems and roots. Complementation of a yeast AA uptake mutant verified the function of PtrLHT1.2 as an AA transporter. Furthermore, PtrLHT1.2 was able to fully complement the phenotypes of the Arabidopsis AA uptake mutant lht1 aap5, including early leaf senescence-like phenotype, reduced growth, decreased plant N levels and reduced root AA uptake. Amino acid uptake studies finally showed that PtrLHT1.2 is a high affinity transporter for neutral and acidic AAs. Thus, we identified a functional AtLHT1 homolog in hybrid aspen, which harbors the potential to enhance overall plant N levels and hence increase biomass production. This finding provides a valuable tool for N nutrition studies in trees and opens new avenues to optimizing tree N-use efficiency.
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| 25. |
- Gruffman, Linda, et al.
(författare)
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Plant nitrogen status and co-occurrence of organic and inorganic nitrogen sources influence root uptake by Scots pine seedlings
- 2014
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 34, s. 205-213
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Tidskriftsartikel (refereegranskat)abstract
- Insights into how the simultaneous presence of organic and inorganic nitrogen (N) forms influences root absorption will help elucidate the relative importance of these N forms for plant nutrition in the field as well as for nursery cultivation of seedlings. Uptake of the individual N forms arginine, ammonium (NH4+) and nitrate (NO3-) was studied in Scots pine (Pinus sylvestris (L.)) seedlings supplied as single N sources and additionally in mixtures of NO3- and NH4+ or NO3- and arginine. Scots pine seedlings displayed a strong preference for NH4+-N and arginine-N as compared with NO3--N. Thus, NO3- uptake was generally low and decreased in the presence of NH4+ in the high-concentration range (500 mu M N), but not in the presence of arginine. Moreover, uptake of NO3- and NH4+ was lower in seedlings displaying a high internal N status as a result of high N pre-treatment, while arginine uptake was high in seedlings with a high internal N status when previously exposed to organic N. These findings may have practical implications for commercial cultivation of conifers.
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