Bryophytes cover large territories in cold biomes, where they control soil temperature regime, and therefore permafrost, carbon and nutrient dynamics. The mechanisms of this control remain unclear. ...We quantified the dependence of soil temperature fluctuations under bryophyte mats on the interplay of bryophyte heat conductance traits, mat thickness, density and moisture regimes. For seventeen predominant bryophytes in six typical subarctic ecosystems, we assessed in situ soil temperature dynamics under bryophyte mats in comparison with bryophyte‐removal patches and per‐species mat field moisture. In a complimentary laboratory investigation, we studied how per‐species bryophyte thermal conductivity and volumetric heat capacity depend on mat density and moisture content. Subsequently, we tested whether heat transfer through bryophyte mats could be modelled as a function of mat thickness, thermal conductivity and volumetric heat capacity, the latter two being determined by mat density and field moisture content. Laboratory assessment revealed that bryophyte thermal conductivity and volumetric heat capacity were independent of mat density, and depended linearly on mat moisture content, but the dependencies were not species‐specific. In the field, bryophytes reduced amplitudes of soil temperature fluctuations and freeze–thaw frequency during the growing season, but not mean soil temperature. These effects differed between species and between ecosystems, being strongest in Sphagnum fuscum‐dominated dry tundra, but were well explained by bryophyte mat thickness and field moisture content as affecting thermal conductivity and volumetric heat capacity. We suggest that reduction in soil temperature amplitudes is a generic feature in (sub) arctic ecosystems and should be considered as an important mechanism of bryophyte control on carbon and nutrient turnover. Although heat transfer through bryophyte mats differs greatly among species and ecosystems, species differences are fully explained by differences in mat thickness and moisture content and generally comply with physical laws, without deviations due to biological processes. These results imply that in global vegetation models of carbon and nutrient cycling, the heat transfer through bryophyte mats can be modelled without taking into consideration bryophyte species composition, but considering bryophyte mat depth and moisture availability only. This will allow us to enhance modelling precision through an improved representation of the soil temperature regime.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Soil carbon in permafrost ecosystems has the potential to become a major positive feedback to climate change if permafrost thaw increases heterotrophic decomposition. However, warming can also ...stimulate autotrophic production leading to increased ecosystem carbon storage—a negative climate change feedback. Few studies partitioning ecosystem respiration examine decadal warming effects or compare responses among ecosystems. Here, we first examined how 11 years of warming during different seasons affected autotrophic and heterotrophic respiration in a bryophyte‐dominated peatland in Abisko, Sweden. We used natural abundance radiocarbon to partition ecosystem respiration into autotrophic respiration, associated with production, and heterotrophic decomposition. Summertime warming decreased the age of carbon respired by the ecosystem due to increased proportional contributions from autotrophic and young soil respiration and decreased proportional contributions from old soil. Summertime warming's large effect was due to not only warmer air temperatures during the growing season, but also to warmer deep soils year‐round. Second, we compared ecosystem respiration responses between two contrasting ecosystems, the Abisko peatland and a tussock‐dominated tundra in Healy, Alaska. Each ecosystem had two different timescales of warming (<5 years and over a decade). Despite the Abisko peatland having greater ecosystem respiration and larger contributions from heterotrophic respiration than the Healy tundra, both systems responded consistently to short‐ and long‐term warming with increased respiration, increased autotrophic contributions to ecosystem respiration, and increased ratios of autotrophic to heterotrophic respiration. We did not detect an increase in old soil carbon losses with warming at either site. If increased autotrophic respiration is balanced by increased primary production, as is the case in the Healy tundra, warming will not cause these ecosystems to become growing season carbon sources. Warming instead causes a persistent shift from heterotrophic to more autotrophic control of the growing season carbon cycle in these carbon‐rich permafrost ecosystems.
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Leaf traits related to the performance of invasive alien species can influence nutrient cycling through litter decomposition. However, there is no consensus yet about whether there are consistent ...differences in functional leaf traits between invasive and native species that also manifest themselves through their “after life” effects on litter decomposition. When addressing this question it is important to avoid confounding effects of other plant traits related to early phylogenetic divergences and to understand the mechanism underlying the observed results to predict which invasive species will exert larger effects on nutrient cycling. We compared initial leaf litter traits, and their effect on decomposability as tested in standardized incubations, in 19 invasive-native pairs of co-familial species from Spain. They included 12 woody and seven herbaceous alien species representative of the Spanish invasive flora. The predictive power of leaf litter decomposition rates followed the order: growth form > family > status (invasive vs. native) > leaf type. Within species pairs litter decomposition tended to be slower and more dependent on N and P in invaders than in natives. This difference was likely driven by the higher lignin content of invader leaves. Although our study has the limitation of not representing the natural conditions from each invaded community, it suggests a potential slowing down of the nutrient cycle at ecosystem scale upon invasion.
Plant litter decomposition is key to carbon and nutrient cycling in terrestrial ecosystems. Soil fauna are important litter decomposers, but how their contribution to decomposition changes with ...alterations in plant composition and climate is not well established.
Here, we quantified how soil mesofauna affect decomposition rate interactively with climate and leaf and root traits. We conducted an in situ decomposition experiment using eight dominant tree species per forest site across four elevations (50, 400, 600 and 1,000 m a.s.l.) in northern Japan. We used litterbags with different mesh sizes to control litter accessibility to soil mesofauna.
We found stronger effects of plant litter quality on both decomposition rates and faunal contribution thereto, and perhaps of local variation in soil nutritional and moisture regimes, than climatic effects of elevation. This suggests that changing climate likely alters forest litter decomposition rates indirectly through shifts in tree community composition more than directly through changing abiotic regimes. Considering both leaves and roots as litter resources enlarged the overall contribution of variation in litter quality to decomposition rates and faunal effects thereupon, because litter quality and decomposition rate varied more between leaves and roots overall than among leaves within and across elevations.
The contribution of mesofauna to litter decomposition was larger in nutrient‐rich litter than in recalcitrant litter across the elevational gradient, suggesting amplification of the effect of litter traits on decomposition through preference of soil fauna for their food resources.
Our findings highlight the importance of considering synergistic influences of soil faunal activities with litter traits of both leaves and roots for better understanding biogeochemical processes across environmental gradients over space or time.
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Cooperative interactions among species, termed mutualisms, have played a crucial role in the evolution of life on Earth. However, despite key potential benefits to partners, there are many cases in ...which two species cease to cooperate and mutualisms break down. What factors drive the evolutionary breakdown of mutualism? We examined the pathways toward breakdowns of the mutualism between plants and arbuscular mycorrhizal fungi. By using a comparative approach, we identify ∼25 independent cases of complete mutualism breakdown across global seed plants. We found that breakdown of cooperation was only stable when host plants (i) partner with other root symbionts or (ii) evolve alternative resource acquisition strategies. Our results suggest that key mutualistic services are only permanently lost if hosts evolve alternative symbioses or adaptations.
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Soil pH varies by several units among ecosystems. While soil pH is known to be a key driver of plant species composition, we still have a poor understanding of how it affects carbon cycling ...processes. For instance, soil pH, or its associated chemistry in terms of base cations and organic acids, may affect decomposition rates of dead matter directly, by controlling decomposer composition and activity and, indirectly, by controlling the traits of the plant species and thereby the afterlife effects of those traits on litter decomposition. Leaf and litter pH may play a role in this control. Based on the very limited empirical data available, we hypothesized that variation in species traits including leaf (litter) pH, within and between ecosystems contrasting in soil pH, would have stronger effects on leaf litter decomposition rates than variation in soil chemistry would.
We tested this hypothesis by carrying out a ‘common garden’ litterbed experiment in subtropical SW China, in which leaf litters of the 30 predominant plant species from mid‐successional forest on acidic sandstone (soil pH around 4.0) and calcareous soil (pH around 7.5), respectively, were incubated and their decomposition rates measured over two harvests in 14 months, both in soil plus litter matrix from their ‘home’ forest and in those from the ‘away’ forest.
We found that leaf (litter) trait variation among species and plant functional types, headed by species' dry matter content but also including tissue pH, was the strongest driver of variation in leaf litter decomposition rates. Surprisingly, however, while these effects of interspecific trait variation were very strong among species from the same site, there was no overall difference in litter decomposability between the species from the acidic versus calcareous site. Equally surprising was that this strong difference in pH of soil substrate plus litter matrix from an acidic sandstone site versus a calcareous karst site did not directly affect leaf litter decomposition rates across a given species set.
This first attempt to disentangle the multiple potential direct and indirect ways in which soil and leaf (litter) acidity might be related to litter decomposition rates has important implications for our understanding of soil–plant feedbacks. Based on our forest‐based study, we predict that soil–plant feedbacks via acidity are unlikely to be strong in ecosystems with wide‐ranging species in terms of their leaf functional traits, including leaf pH.
A free Plain Language Summary can be found within the Supporting Information of this article.
A free Plain Language Summary can be found within the Supporting Information of this article.
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Wildfires play an important role in vegetation composition and structure, nutrient fluxes, human health and wealth, and are interlinked with climate change. Plants have an influence on wildfire ...behaviour and predicting this feedback is a high research priority. For upscaling from leaf traits to wildfire behaviour we need to know if the same leaf traits are important for the flammability of 1) individual leaves, and 2) multiple leaves packed in fuel beds. Based on a conceptual framework, we hypothesised that fuel packing properties, through airflow limitation, would overrule the effects of individual leaf morphology and chemistry.
To test this hypothesis we compared the results of two experiments, respectively addressing individual leaf flammability and monospecific fuel bed flammability of 25 perennial species from eastern Australia.
Across species, fuel bed packing ratio and bulk density scaled negatively with fire spread and positively with maximum temperature and burning time. Species with ‘curlier’ leaves, higher specific leaf area, lower tannin concentrations and lower tissue density promoted faster fire spread through fuel beds.
We found that species with shorter individual leaf ignition times had a faster fire spread, shorter burning times and lower temperatures in fuel beds. Leaf traits that affect the flammability of individual leaves (e.g. specific leaf area), continue to do so even when packed in fuel beds.
While previous studies have focused on either flammability of individual plant particles or fire behaviour in fuel beds, this is the first time that an overarching combination of the two approaches was made for a wide range of species. Our findings provide a better understanding of fuel bed flammability based on interspecific variation in morphological and some chemical leaf traits. This can be a first step in linking leaf traits to fire behaviour in the field.
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Background and aims Higher than expected litter decomposition rates have been observed in dry, sunny environments due to photochemical or physical degradation. However, our understanding of carbon ...and nutrient fluxes of standing and buried litters compared to surface litter in such areas is still scarce. Methods We sampled leaf litters from 51 species in a semiarid dune ecosystem and incubated them in three positions: surface, sand-buried and simulated standing. Results Decomposition was much faster in buried litter and somewhat faster in simulated standing litter than in surface litter. This pattern was independent of the incubation period, phylogenetic group or growth form. Litter position and incubation period significantly impacted litter nutrient dynamics. The nitrogen (N) and phosphorus (P) losses were faster in buried and simulated standing litters than in surface litter. The N loss was slower than P loss in 6-month decomposed litter but the former was relatively faster than the latter in the second phase up to 12 months of incubation. Conclusions Our study shows that substantial mass and nutrient losses in simulated standing and buried litters can be a candidate explanation why drylands have higher carbon and nutrient fluxes than expected based on surface litter decomposition data alone.
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BFBNIB, DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NMLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Nutrient resorption and leaching resistance, through their roles in reducing nutrient losses, are important determinants of plant nutrient economy. However, the contributions of fine-stem and ...fine-root resorption, as well as leaf leaching resistance, have largely been overlooked. We quantified the relative contributions of these processes to nutrient depletion of these organs during their senescence using 40 subarctic vascular species from aquatic, riparian and terrestrial environments. We hypothesized that interspecific variation in organ nutrient resorption and leaf leaching would be linked to the species' nutrient acquisitive-conservative strategies, as quantified for a set of common-organ nutrient/carbon economics traits. The subarctic flora generally had both high resistance to leaching and high internal nutrient recycling. Average nutrient resorption efficiencies were substantial for leaves (nitrogen (N), 66 ± 3% SE; phosphorus (P), 63 ± 4%), fine stems (N, 48 ± 4%; P, 56 ± 4%) and fine roots (N, 27 ± 7%; P, 57 ± 6%). The link between nutrient resorption and other nutrient/carbon economics traits was very weak across species, for all three organs. These results emphasize the potential importance of resorption processes for the plant nutrient budget. They also highlight the idiosyncrasies of the relationship between resorption processes and plant economics, which is potentially influenced by several plant physiological and structural adaptations to environmental factors other than nutrient stress.
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The functional traits of organisms within multispecies assemblages regulate biodiversity effects on ecosystem functioning. Yet how traits should assemble to boost multiple ecosystem functions ...simultaneously (multifunctionality) remains poorly explored. In a multibiome litter experiment covering most of the global variation in leaf trait spectra, we showed that three dimensions of functional diversity (dispersion, rarity, and evenness) explained up to 66% of variations in multifunctionality, although the dominant species and their traits remained an important predictor. While high dispersion impeded multifunctionality, increasing the evenness among functionally dissimilar species was a key dimension to promote higher multifunctionality and to reduce the abundance of plant pathogens. Because too-dissimilar species could have negative effects on ecosystems, our results highlight the need for not only diverse but also functionally even assemblages to promote multifunctionality. The effect of functionally rare species strongly shifted from positive to negative depending on their trait differences with the dominant species. Simultaneously managing the dispersion, evenness, and rarity in multispecies assemblages could be used to design assemblages aimed at maximizing multifunctionality independently of the biome, the identity of dominant species, or the range of trait values considered. Functional evenness and rarity offer promise to improve the management of terrestrial ecosystems and to limit plant disease risks.
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