| 1. |
|
|
| 2. |
|
|
| 3. |
- Bergkvist, Bo, et al.
(författare)
-
Pools and fluxes of carbon in three Norway spruce ecosystems along a climatic gradient in Sweden
- 2008
-
Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 89:1, s. 7-25
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents an integrated analysis of organic carbon (C) pools in soils and vegetation, within-ecosystem fluxes and net ecosystem exchange (NEE) in three 40-year old Norway spruce stands along a north-south climatic gradient in Sweden, measured 2001-2004. A process-orientated ecosystem model (CoupModel), previously parameterised on a regional dataset, was used for the analysis. Pools of soil organic carbon (SOC) and tree growth rates were highest at the southernmost site (1.6 and 2.0-fold, respectively). Tree litter production (litterfall and root litter) was also highest in the south, with about half coming from fine roots (< 1 mm) at all sites. However, when the litter input from the forest floor vegetation was included, the difference in total litter input rate between the sites almost disappeared (190-233 g C m(-2) year(-1)). We propose that a higher N deposition and N availability in the south result in a slower turnover of soil organic matter than in the north. This effect seems to overshadow the effect of temperature. At the southern site, 19% of the total litter input to the O horizon was leached to the mineral soil as dissolved organic carbon, while at the two northern sites the corresponding figure was approx. 9%. The CoupModel accurately described general C cycling behaviour in these ecosystems, reproducing the differences between north and south. The simulated changes in SOC pools during the measurement period were small, ranging from -8 g C m(-2) year(-1) in the north to +9 g C m(-2) year(-1) in the south. In contrast, NEE and tree growth measurements at the northernmost site suggest that the soil lost about 90 g C m(-2) year(-1).
|
|
| 4. |
- Björk, Robert G., 1974, et al.
(författare)
-
A Climate Change aspect on root dynamics and nitrogen partitioning in a tundra landscape
- 2005
-
Ingår i: Sediment budgets and rates of sediment transfer across cold environments in Europe. 3rd Workshop of the ESF Network SEDIFLUX, Durham, UK, 15 – 19 December 2005..
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Arctic Climate Impact Assessment (ACIA) recently reported that Arctic is rapidly changing due to Climate Change. Likewise, the mountains of Europe are going to experience large shifts in plant composition and 41-56% of the alpine species might be on the edge of extinction according to the 1st synthesis of the Global Observation Research Initiative in Alpine Environments (GLORIA). Although the tundra ecosystems are subjected to dramatical changes as a result of Climate Change, there is little knowledge of the effect on root dynamics and its implication on the nitrifying and denitrifying microbial community. Here, we compare nitrification enzyme activity (NEA) and denitrification enzyme activity (DEA) rates along an altitudinal gradient with the effects of climatic warming using Open Top Chambers (OTCs) in consideration with root dynamics and architecture. This study was conducted at Latnjajaure Field Station (LFS) located in the midalpine region in northern Sweden. LFS is the Swedish field site for the International Tundra Experiment (ITEX), established in 1993. This gives an opportunity to investigate long-term effects of climatic warming by OTCs and an altitudinal gradient (1000m to 1365m), both within a very small geographical range. The OTCs used at LFS increases the soil surface temperature by approximately 1.5ºC whereas air temperatures normally falls with 0.6ºC with every hundred meter of increased altitude. To analyse the NEA and DEA we used an anaerobic incubation technique, based on acetylene inhibition technique, resulting in N2O as the only end product, which then were analysed by gas chromatography. Soil cores were additionally sampled in the OTCs to study the effects of climatic warming on the root system. The specific root length, root length density and root biomass were determined for the different root fractions. The results from NEA and DEA contradict each other. The gradient study show decreased NEA and DEA rates with falling altitude, whereas the warming experiment show a slight non significant increase due to the temperature enhancement by OTCs. The preliminary results from the root sampling indicate that there is a plant community specific response in root architecture, which has an output on root biomass and particularly in the fraction of fine roots, although, climatic warming did not have any significant affect on the root biomass. The fact that altitudinal temperature decline did not reduce NEA and DEA rates might in part be explained of the variables measured here, although they are not conclusive.
|
|
| 5. |
- Björk, Robert G., 1974, et al.
(författare)
-
Long-term warming effects on root morphology, root mass distribution, and microbial activity in two dry tundra plant communities in northern Sweden
- 2007
-
Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 176:4, s. 862-873
-
Tidskriftsartikel (refereegranskat)abstract
- center dot Effects of warming on root morphology, root mass distribution and microbial activity were studied in organic and mineral soil layers in two alpine ecosystems over > 10 yr, using open-top chambers, in Swedish Lapland. center dot Root mass was estimated using soil cores. Washed roots were scanned and sorted into four diameter classes, for which variables including root mass (g dry matter (g DM) m(-2)), root length density (RLD; cm cm(-3) soil), specific root length (SRL; m g DM-1), specific root area (SRA; m(2) kg DM-1), and number of root tips m(-2) were determined. Nitrification (NEA) and denitrification enzyme activity (DEA) in the top 10 cm of soil were measured. center dot Soil warming shifted the rooting zone towards the upper soil organic layer in both plant communities. In the dry heath, warming increased SRL and SRA of the finest roots in both soil layers, whereas the dry meadow was unaffected. Neither NEA nor DEA exhibited differences attributable to warming. center dot Tundra plants may respond to climate change by altering their root morphology and mass while microbial activity may be unaffected. This suggests that carbon may be incorporated in tundra soils partly as a result of increases in the mass of the finer roots if temperatures rise.
|
|
| 6. |
- Björk, Robert G., 1974, et al.
(författare)
-
Nitrification and Denitrification Enzyme Activity: a successful tool in Arctic and Alpine soil ecology
- 2007
-
Ingår i: The 14th ITEX workshop, Falls Creek, Victoria, Australia, 2–6 February 2007..
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Nitrogen is consideration to be a limiting factor for plants and microbes in arctic and alpine ecosystems and the rates of mineralization, nitrification, and denitrifi¬cation are known to be generally low. However, Climate Change is expected to alter the nitrogen availability and dynamics and, as a consequence, affect plant community composition and production. The general consensus today is that increased temperature will lead to greater microbial activity and more plant-available nitrogen. Nevertheless, nitrification and denitrification are restricted by a number of environmental factors such as low tem¬perature and low pH. The C/N ratio and the water content of the soils also play an important role in determining the rates of nitrification and denitrification. Since 2002 microbial studies has been undertaken at Latnjajure, and comprise several microbial techniques, e.g. Nitrification Enzyme Activity (NEA), Denitrification Enzyme Activity (DEA), Phospholipid fatty acid analysis (PFLA), and Temperature Gradient Gel Electrophoresis (TGGE). These studies focuses on the interaction between plants and microbes along natural environmental gradients, both within plant communities and within the landscape, but also entails the OTCs used in the ITEX studies at Latnjajaure. Here we present the techniques NEA and DEA and give some brief results from how these have been successfully applied at Latnjajaure. In ecosystems with low nitrification activity, small amounts of NO3-/NO2- will be formed and it is thus difficult to measure low fluxes. However, NO3-/NO2- can be converted to N2O and then analysed by gas chromatography, whereby the detection limit is increased at least 1000 times compared to the spectroscopical technique. These techniques are referred to Nitrification (NEA) and Denitrification Enzyme Activity (DEA) and give a potential measure on the nitrification and denitrification rates, which goes back to the actual populations of nitrifiers and denitrifiers in the soil. For instance, NEA has been proved to better correlate with extractable NH4+ concentration than net nitrification does, and still after twelve weeks show a strong correlation with the initial extractable NH4+ concentration. Therefore, these variables, in particular NEA, have the advantage of being a much more stable variable than, for instance, extractable N concentrations and net nitrification, and NEA and DEA are therefore suitable when working in fringe environments with restricted logistics like the Latnjajaure catchment. NEA is measured using a two-step incubation technique; first by incubate the soil with a nutrient solution for 24 hours in darkness, at room temperature on a rotary shaker. Sub-samples are then withdrawn after a specified time schedule. The second step allows NO3- to be reduced to N2O by adding a modified denitrifying bacterium, Pseudomonas chlororaphis ATCC 43928, together with a carbon source. This strain of bacteria lacks the enzyme to reduce N2O to N2. The samples are then again incubated in darkness, at room temperature for 24 hours, and analysed by gas chromatography. This method was first used by Lensi et al. (1985, 1986), to study nitrification potentials in forest soils. Furthermore, the method has been developed for soils with low pH and small amounts of NO3- and the analysis makes the quantification without interference of organic matter, which makes it suitable for arctic and alpine ecosystems. To analyse DEA an anaerobic incubation technique is used, based on acetylene inhibition of the N2O-reductase resulting in N2O as the only end product. The soil sample is evacuated and flushed with N2. Thereafter acetylene is inserted to a final acetylene concentration of 10%, and the samples are shaken continuously and gas samples are withdrawn after a specified time schedule, which is then analysed by gas chromatography. This provides an estimate of the maximum concentration of functional denitrifying enzymes in the soil. Denitrifiers, in contrast to nitrifiers, are heterotrophs and can switch from using NO3- as an alternative electron acceptor to O2 under aerobic conditions. This makes other factors in the soil important determinants of DEA, e.g. availability of oxygen and C. Hence, the presence of denitrifiers is rarely a limitation for denitrification and they usually make up a reasonably large fraction of the soil bacteria. At Latnjajaure NEA shows a larger differentiation across plant communities than DEA. However, the spatial variability in the landscape, at the meso-scale, was in the same range in both variables and increased with altitude from 1000 to 1365 m a.s.l, particularly in heath plant communities. This result suggests that the decrease in mean annual temperature with altitude (0.6ºC with every one hundred meters) did not reduce nitrification and denitrification rates, as one might have expected. None of the other variable studied could explain the altitudinal increase in all cases, and the factors controlling the nitrification and denitrification rates seem to vary with the vegetation type. Furthermore, neither NEA nor DEA exhibited any changes between the ambient and warmed plots in the warming experiments. However, the warming experiment in the dry heath exhibited a change in root morphology via increased specific root length (SRL; m gDM-1) and specific root area (SRA; m2 kgDM -1). As both heterotrophic microbes and plants out-compete nitrifiers for NH4+, a change in root morphology, as seen in the warming experiment, may also explain the increased activity of nitrifying and denitrifying microbes with altitude.
|
|
| 7. |
- Björk, Robert G., 1974, et al.
(författare)
-
Root architecture and nutrient allocation in tundra plants
- 2005
-
Ingår i: ESA-INTECOL 2005 Joint Meeting – Ecology at multiple scales, Montreal, Canada, 7 – 12 August 2005..
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Arctic Climate Impact Assessment (ACIA) recently reported that the Arctic is rapidly changing due to Climate Change. Likewise, the mountains of Europe are going to experience large shifts in plant composition and 41-56% of the alpine species might be on the edge of extinction according to the 1st synthesis of the Global Observation Research Initiative in Alpine Environments (GLORIA). Although the tundra ecosystems are subjected to dramatical changes as a result of Climate Change, there is little knowledge of the effect on root dynamics. Roots are crucial for soil development and nutrient cycling in most ecosystems. The further out in the root system a single root is located, the faster the root turns over. The fine roots are also having a lower C:N ratio than more developed and supporting roots. The aim of this study is to investigate the dynamic of root architecture and how tundra plants allocate carbon and nitrogen between root and shoot biomass and, moreover, how the plants respond to climatic warming. The dominant plant species (e.g. Cassiope tetragona, Vaccinium vitis-idaea and Diapensia lapponica for the dry heath) within each of four plant communities at Latnjajaure Field Station, in northern Swedish Scandes, were sampled and divided into shoot and root. To study the effects of climatic warming on the root system, soil cores were as well sampled in Open Top Chambers (OTCs) that was established in 1993. The root architecture was analysed by observing the degree of branching, colour, consistency etc. of the roots, which then were cut and sorted by diameter. To determine the C and N allocation within the plants we also quantified the shoot:root ratio. The preliminary results indicate that there is a difference between plant species in root biomass and particularly in the fraction of fine roots. As a result of a greater amount of root exudates from fine roots, these results imply that plant distribution has a great impact on the soil microbial community and activity. The large spatial variability often seen in microbial measurement within plant communities may be due to a sampling procedure, in that samples are taken from different plants’ root systems.
|
|
| 8. |
- Børja, Isabella, et al.
(författare)
-
Stand age and fine root biomass, distribution and morphology in a Norway spruce chronosequence in southeast Norway
- 2008
-
Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 28:5, s. 773-784
-
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.
|
|
| 9. |
- Finér, L., et al.
(författare)
-
Variation in fine root biomass of three European tree species : Beech (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.)
- 2007
-
Ingår i: Plant Biosystems. - : Informa UK Limited. - 1126-3504 .- 1724-5575. ; 141:3, s. 394-405
-
Tidskriftsartikel (refereegranskat)abstract
- Fine roots (< 2 mm) are very dynamic and play a key role in forest ecosystem carbon and nutrient cycling and accumulation. We reviewed root biomass data of three main European tree species European beech, (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.), in order to identify the differences between species, and within and between vegetation zones, and to show the relationships between root biomass and the climatic, site and stand factors. The collected literature consisted of data from 36 beech, 71 spruce and 43 pine stands. The mean fine root biomass of beech was 389 g m(-2), and that of spruce and pine 297 g m(-2) and 277 g m(-2), respectively. Data from pine stands supported the hypothesis that: root biomass is higher in the temperate than in the boreal zone. The results indicated that the root biomass of deciduous trees is higher than that of conifers. The correlations between root biomass and site fertility characteristics seemed to be species specific. There was no correlation between soil acidity and root biomass. Beech fine root. biomass decreased with stand age whereas pine root biomass increased with stand age. Fine root biomass at tree level. correlated better than stand level root biomass with stand characteristics. The results showed that there exists a strong relationship between the fine root biomass and the above-ground biomass.
|
|
| 10. |
- Gaudinski, JB, et al.
(författare)
-
Use of stored carbon reserves in growth of temperate tree roots and leaf buds : analyses using radiocarbon measurements and modeling
- 2009
-
Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 15:4, s. 992-1014
-
Tidskriftsartikel (refereegranskat)abstract
- Characterizing the use of carbon (C) reserves in trees is important for understanding regional and global C cycles, stress responses, asynchrony between photosynthetic activity and growth demand, and isotopic exchanges in studies of tree physiology and ecosystem C cycling. Using an inadvertent, whole-ecosystem radiocarbon ((14)C) release in a temperate deciduous oak forest and numerical modeling, we estimated that the mean age of stored C used to grow both leaf buds and new roots is 0.7 years and about 55% of new-root growth annually comes from stored C. Therefore, the calculated mean age of C used to grow new-root tissue is similar to 0.4 years. In short, new roots contain a lot of stored C but it is young in age. Additionally, the type of structure used to model stored C input is important. Model structures that did not include storage, or that assumed stored and new C mixed well (within root or shoot tissues) before being used for root growth, did not fit the data nearly as well as when a distinct storage pool was used. Consistent with these whole-ecosystem labeling results, the mean age of C in new-root tissues determined using 'bomb-(14)C' in three additional forest sites in North America and Europe (one deciduous, two coniferous) was less than 1-2 years. The effect of stored reserves on estimated ages of fine roots is unlikely to be large in most natural abundance isotope studies. However, models of root C dynamics should take stored reserves into account, particularly for pulse-labeling studies and fast-cycling roots (< 1 years).
|
|
