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| 2. |
- Asplund, Johan, et al.
(författare)
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Changes in functional traits of the terricolous lichen Peltigera aphthosa across a retrogressive boreal forest chronosequence
- 2015
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Ingår i: Lichenologist. - 0024-2829 .- 1096-1135. ; 47, s. 187-195
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Tidskriftsartikel (refereegranskat)abstract
- Changes in the functional traits of the terricolous lichen Peltigera aphthosa with declining soil fertility during ecosystem retrogression were investigated. A well-documented retrogressive chronosequence of 28 forested islands in northern Sweden that differ greatly in fire history and which spans 5000 years was used. The abundance of cephalodia increased, indicative of higher N-2-fixation rates resulting from lower N availability. Thallus C-13 values increased with ageing soils, in line with declining C-13 values of the humus substratum along this gradient. However, C-13 values were also driven by variation in factors that were at least partly independent of soil ageing. As such, C-13 values were mostly related to specific thallus mass (STM), possibly because a higher STM gives a thicker cortical layer and thus greater resistance to CO2 diffusion, leading to higher C-13 values. STM and other measured traits (i.e. thallus N, P, secondary compounds and water-holding capacity) were unresponsive to the gradient, despite these traits being very responsive to the same gradient in epiphytic lichen species.
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| 3. |
- Asplund, Johan, et al.
(författare)
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Contrasting changes in palatability following senescence of the lichenized fungi Lobaria pulmonaria and L. scrobiculata
- 2012
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Ingår i: Fungal Ecology. - : Elsevier BV. - 1754-5048 .- 1878-0083. ; 5, s. 710-713
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Tidskriftsartikel (refereegranskat)abstract
- Epiphytic lichens can contribute significantly to ecosystem nutrient input because they efficiently accumulate atmospheric mineral nutrients and, in the case of cyanolichens, also fix nitrogen. The rate at which carbon and other nutrients gained by lichens enters the ecosystem is determined by lichen litter decomposability and by invertebrate consumption of lichen litter. In turn, these processes are driven by the secondary compounds present in senesced lichens. Therefore, we explored how lichen palatability and concentrations of secondary compounds change with tissue senescence for Lobaria pulmonaria, a green algal lichen with cyanobacterial cephalodia, and L. scrobiculata, a cyanobacterial lichen. During senescence both lichens lost 38-48% of their stictic acid chemosyndrome, while m-scrobiculin and usnic acid in L. scrobiculata remained unchanged. Snails preferred senesced rather than fresh L. pulmonaria, while senesced L. scrobiculata were avoided. This provides evidence that species with labile secondary compounds will have higher turnover rates, through consumption and decomposition, than those producing more stable secondary compounds.
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| 4. |
- Asplund, Johan, et al.
(författare)
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How lichens impact on terrestrial community and ecosystem properties
- 2017
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Ingår i: Biological Reviews. - : Wiley. - 1464-7931 .- 1469-185X. ; 92, s. 1720-1738
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Forskningsöversikt (refereegranskat)abstract
- Lichens occur in most terrestrial ecosystems; they are often present as minor contributors, but in some forests, drylands and tundras they can make up most of the ground layer biomass. As such, lichens dominate approximately 8% of the Earth's land surface. Despite their potential importance in driving ecosystem biogeochemistry, the influence of lichens on community processes and ecosystem functioning have attracted relatively little attention. Here, we review the role of lichens in terrestrial ecosystems and draw attention to the important, but often overlooked role of lichens as determinants of ecological processes. We start by assessing characteristics that vary among lichens and that may be important in determining their ecological role; these include their growth form, the types of photobionts that they contain, their key functional traits, their water-holding capacity, their colour, and the levels of secondary compounds in their thalli. We then assess how these differences among lichens influence their impacts on ecosystem and community processes. As such, we consider the consequences of these differences for determining the impacts of lichens on ecosystem nutrient inputs and fluxes, on the loss of mass and nutrients during lichen thallus decomposition, and on the role of lichenivorous invertebrates in moderating decomposition. We then consider how differences among lichens impact on their interactions with consumer organisms that utilize lichen thalli, and that range in size from microfauna (for which the primary role of lichens is habitat provision) to large mammals (for which lichens are primarily a food source). We then address how differences among lichens impact on plants, through for example increasing nutrient inputs and availability during primary succession, and serving as a filter for plant seedling establishment. Finally we identify areas in need of further work for better understanding the role of lichens in terrestrial ecosystems. These include understanding how the high intraspecific trait variation that characterizes many lichens impacts on community assembly processes and ecosystem functioning, how multiple species mixtures of lichens affect the key community- and ecosystem-level processes that they drive, the extent to which lichens in early succession influence vascular plant succession and ecosystem development in the longer term, and how global change drivers may impact on ecosystem functioning through altering the functional composition of lichen communities.
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| 5. |
- Asplund, Johan, et al.
(författare)
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Lichen Specific Thallus Mass and Secondary Compounds Change across a Retrogressive Fire-Driven Chronosequence
- 2012
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- In the long-term absence of major disturbances ecosystems enter a state of retrogression, which involves declining soil fertility and consequently a reduction in decomposition rates. Recent studies have looked at how plant traits such as specific leaf mass and amounts of secondary compounds respond to declining soil fertility during retrogression, but there are no comparable studies for lichen traits despite increasing recognition of the role that lichens can play in ecosystem processes. We studied a group of 30 forested islands in northern Sweden differing greatly in fire history, and collectively representing a retrogressive chronosequence, spanning 5000 years. We used this system to explore how specific thallus mass (STM) and carbon based secondary compounds (CBSCs) change in three common epiphytic lichen species (Hypogymnia phsyodes, Melanohalea olivacea and Parmelia sulcata) as soil fertility declines during this retrogression. We found that STMs of lichens increased sharply during retrogression, and for all species soil N to P ratio (which increased during retrogression) was a strong predictor of STM. When expressed per unit area, medullary CBSCs in all species and cortical CBSCs in P. sulcata increased during retrogression. Meanwhile, when expressed per unit mass, only cortical CBSCs in H. physodes responded to retrogression, and in the opposite direction. Given that lichen functional traits are likely to be important in driving ecological processes that drive nutrient and carbon cycling in the way that plant functional traits are, the changes that they undergo during retrogression could potentially be significant for the functioning of the ecosystem.
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| 6. |
- Asplund, Johan, et al.
(författare)
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Removal of secondary compounds increases invertebrate abundance in lichens
- 2015
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Ingår i: Fungal Ecology. - : Elsevier BV. - 1754-5048 .- 1878-0083. ; 18, s. 18-25
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Tidskriftsartikel (refereegranskat)abstract
- We investigated how lichen carbon-based secondary compounds (CBSCs) affect abundance of invertebrates in five lichen species growing on the forest floor (Cladonia rangiferina, Cladonia stellaris) or on tree trunks (Evernia prunastri, Hypogymnia physodes, Pseudevemia furfuracea). To do this, CBSCs were removed by rinsing lichen thalli in acetone (which has no adverse effects on the lichens) and the lichens were re-transplanted in their natural habitat. After 4 months there was higher abundance of mites, springtails and spiders in the three epiphytic lichens that had their CBSC concentrations reduced. The increase in predatory spiders following CBSC reduction suggests that the compounds have multitrophic consequences. The acetone treatment reduced the number of nematodes in four of the lichen species. Given that lichens serve as important habitats for a diverse range of invertebrates, increased knowledge of how lichen CBSCs may regulate their abundance helps us to better understand the role that lichens and their defence compounds play in structuring forest food webs. (C) 2015 Elsevier Ltd and The British Mycological Society. All rights reserved.
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| 7. |
- Asplund, Johan, et al.
(författare)
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Secondary compounds can reduce the soil micro-arthropod effect on lichen decomposition
- 2013
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 66, s. 10-16
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Tidskriftsartikel (refereegranskat)abstract
- Phenolic compounds have been shown in several studies to have important 'carryover effects' on litter decomposition, microbial nutrient immobilization and nutrient availability. These effects arise in part because of the adverse effect they have on the feeding activities of litter-feeding invertebrates such as micro-arthropods that drive decomposition processes. However, the interactive effects of phenolic compounds and soil micro-arthropods on litter decomposition are poorly understood. Phenolic compounds can easily be removed by acetone rinsing from living lichens, allowing us to specifically test the role that phenolic compounds (and their removal) have in controlling the effects of micro-arthropods on the decomposition of their litter. We performed a litter-bag experiment aimed at exploring how lichen litter mass loss and nutrient release during decomposition was affected by phenolics (by using acetone rinsed and non-rinsed lichen material) and micro-arthropod activity (by using different mesh sizes to allow or exclude entry by micro-arthropods) for each of six contrasting lichen species (Cladonia rangiferina, Cladonia stellaris, Evernia prunastri, Hypogymnia physodes, Pseudevernia furfuracea and Usnea dasypoga). Both the removal of phenolic compounds and the presence of micro-arthropods accelerated mass and nutrient release overall, but not for either of the two Cladonia species. Removal of phenolics also had an overall positive effect on the effects of arthropods on the loss of P, but not mass and N, from the decomposing lichens. Further, for U. dasypoga, but not the other species, natural levels of phenolic compounds deterred micro-arthropods from accelerating mass loss, and the removal of these compounds enabled micro-arthropods to enhance its decomposition. Our findings that lichen phenolic compounds can sometimes interact with micro-arthropods to influence lichen litter mass loss and nutrient release during decomposition assists our understanding of how lichens and their consumers may impact on organic matter dynamics, biochemical nutrient cycling and other related ecosystem processes. (c) 2013 Elsevier Ltd. All rights reserved.
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| 8. |
- Asplund, Johan, et al.
(författare)
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The impact of secondary compounds and functional characteristics on lichen palatability and decomposition
- 2013
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 101, s. 689-700
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Tidskriftsartikel (refereegranskat)abstract
- There has been much recent interest in understanding how functional traits of vascular plant species drive ecological processes such as herbivory and litter decomposition. In plants, these two processes are often driven by the same or similar suites of traits and therefore correlate across species. However, few studies have considered how traits of plant-like life forms such as lichens determine species differences in their effects on ecological processes. This is despite the significant contribution of lichens to carbon and nutrient cycling in many environments. We collected 28 lichen species that differed in their growth form, substrate type and capacity to fix N, and determined key traits for each species. For each species, we performed a feeding bioassay using the generalist snail Cepaea hortensis and carried out a laboratory bioassay to assess decomposability. We did these tests both with intact lichen material containing natural concentrations of carbon-based secondary compounds (CBSCs), and material that had been acetone rinsed to reduce concentrations of CBSCs, to evaluate the effect of CBSC on palatability and decomposability. We found that reducing CBSC concentrations greatly increased palatability for 17 species, and decomposability of 10 species. However, decomposability was correlated with several lichen traits while palatability was not, regardless of whether or not CBSCs were removed, and we therefore found no relationship between decomposability and palatability across species. Decomposability and palatability both varied, but in contrasting directions, among N-fixing vs. non-fixing lichens, lichens with different growth forms and those from contrasting substrate types. As such, N-fixing lichens had higher decomposition rates but lower consumption rates than non-fixing lichens, while foliose species had higher decomposition rates but lower consumption rates than fruticose species. Synthesis: We have shown that lichen CBSCs regulate key processes such as lichenivory and decomposition, that lichen decomposability but not palatability are related to traits, and that these two processes are unrelated across species. These results highlight the potential role of lichen species differences in influencing ecosystem processes relating to decomposition and nutrient cycling and the role that grazers may play in driving this.
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| 9. |
- Asplund, Johan, et al.
(författare)
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The influence of tree-scale and ecosystem-scale factors on epiphytic lichen communities across a long-term retrogressive chronosequence
- 2014
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 25, s. 1100-1111
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Tidskriftsartikel (refereegranskat)abstract
- Questions: We tested the relationship between total cover, species richness and composition of epiphytic lichens on trunks of Betula pubescens and ecosystem retrogression (i.e. prolonged absence of major disturbance). We then investigated how the relationships changed when also accounting for tree-scale factors (aspect, height and bark characteristics) and ecosystem-scale factors (e. g. light transmission, tree species diversity and soil fertility).Location: Thirty forested islands in northern Sweden differing in fire history, which collectively represent a retrogressive chronosequence spanning ca. 5000 yr.Results: Total lichen cover responded negatively to long-term absence of major disturbance, but only at exposed positions on the tree trunk, indicating that lichen cover on substrates with more favourable microclimates is less susceptible to environmental change at the ecosystem scale. Further, although there was no overall effect of island size on lichen species richness, we did find a significant interactive effect between island size and height on trunk on species richness. This emerged because species richness decreased with retrogression for lichen communities at breast height, but showed a hump-shaped response to retrogression at the trunk base. Shifts in ecosystem properties with retrogression explained some of the variation in lichen community composition, but most of the variation could be explained by tree-scale factors, notably height on the trunk.Conclusions: While it has frequently been shown that lichens increase in abundance and richness during the first two or three centuries of succession, our results highlight that over a much longer time scale, encompassing soil aging and declining soil fertility, the lichen flora can be negatively affected. However, these effects are heavily mediated by tree-scale factors. These changes in the lichen community may be of potential importance for ecosystem processes and higher trophic level interactions driven by lichen communities.
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| 10. |
- Asplund, Johan, et al.
(författare)
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Within-species variability is the main driver of community-level responses of traits of epiphytes across a long-term chronosequence
- 2014
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Ingår i: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 28, s. 1513-1522
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Tidskriftsartikel (refereegranskat)abstract
- There has been growing recent interest in the relative importance of within-species trait variation vs. across-species trait variation in vascular plants in determining total community-level trait variation across communities and environmental gradients. Recent studies on plant communities have generally found across-species variation to be more important than within-species variation, but comparable studies involving other functionally important biota, such as lichens, are largely lacking.We used a fire-driven chronosequence involving 30 lake islands in northern Sweden to study how declining soil fertility during retrogression affects the functional traits of each of the dominant epiphytic lichen species growing on the trunks of the tree Betula pubescens. We measured several functional traits for the commonest lichen species on each island and used community-weighted measures to study the community-level responses of lichens to the gradient.We found that as retrogression proceeds and soil fertility declines, thallus N and P concentrations and specific thallus mass (STM) increase, both within species and at the community level. Lichen secondary compounds showed contrasting within-species responses and were non-responsive at the whole community level.By decomposing community-level measures of these traits across the gradient, we showed that for the three most responsive traits (N, P and STM), within-species variation was substantially more important than across-species variation. This emerges in part because lichen species composition was not very responsive to ecosystem retrogression, and because unlike vascular plants, lichens easily absorb elements over their entire surface, meaning that nutrient concentrations within lichen species are likely to more closely reflect nutrient availability.We found that within-species variability drove the changes in community-weighted measures of lichen traits across a strong environmental gradient, which contrasts strongly with what we know from studies of vascular plants where across-species variation and species turnover is much more important. To understand how lichen functional traits at the community level respond to environmental factors, it is therefore essential to consider the responses of individual species, and the application of traits-based approaches to lichen communities needs to account for their considerable intraspecific variability.10.1111/(ISSN)1365-2435
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