No abstract is provided for this article.
There has been a rapidly increasing recent interest in the effects of biological diversity on ecosystem properties, and while some studies have recently concluded that biodiversity improves ecosystem function, these views are based almost entirely on experiments in which species richness of live plants has been varied over all the species diversity treatments. However, most net ecosystem primary productivity eventually enters the decomposition subsystem as plant litter where it has important afterlife effects. Weconducted a field experiment in which litter from 32 plant species (i.e. effects. We conducted a field experiment in which litter from 32 plant species (i.e. eight species of each of four plant functional groups with contrasting litter quality) was collected and placed into litter-bags so that each litter-bag contained between one and eight species; the species which were included in the multiple (>2) species litter-bags were randomly selected. This litter diversity gradient was created within each functional group and across some functional groups. We found large non-additive effects of mixing litter from different species on litter decomposition rates, litter nitrogen contents, rates of nitrogen release from litter and the active microbial biomass present on the litter. The patterns and directions of these non-additive effects were dependent upon both plant functional group and time of harvest, and these effects could be predicted in some instances by the initial litter nitrogen content and the degree of variability of nitrogen content of the component species in the litter-bag. There was no relationship between litter-bag species richness and any of the response variables that we considered, at least between two and eight species. Within plant functional groups our results provide some support for the species redundancy and idiosyncratic hypotheses about how biodiversity alters ecosystem function, but no support for the ecosystem rivet hypothesis or the view that species richness of plant litter is important for ecosystem function. We suggest that increased species diversity of plant litter is less important than that of live plants for determining ecosystem properties (and provide possible reasons for this) and conclude that perceived relationships between biodiversity and ecosystem function may be of diminished significance when the ecological importance of plant litter is fully appreciated.
'Relevance of Interactions amongst Soil Microorganisms to Soil Biological Fertility' published in 'Soil Biological Fertility'
Experiments addressing the role of plant species diversity for ecosystem functioning have recently proliferated. Most studies have focused on plant biomass
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 E arth'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.
When the litter of a given species decomposes, it will often break down in the proximity of litters from other species. We investigated the effects of litters of 10 different species in a boreal forest of northern Sweden on each others' decomposition and N release rates; this was done through the use of litterbags containing two compartments separated by single mesh partition. Different litters could be placed on opposite sides of this mesh so that they were in contact with each other. Treatments consisted of all the possible pairwise combinations of the 10 species, with members of each pair placed in different compartments of the same litterbag. Litterbags were harvested after 1, 2 and 4 years in the field. Species differed significantly in their effects on decomposition and N loss rates of associated litters. Generally, litters from feather mosses and lichens showed the greatest promotion of decomposition on associated litters, while some vascular plant species, notably Empetrum hermaphroditum, showed the least. At year four, feather mosses also had the greatest positive effects on N loss from the litters of associated species. There were several instances in which litter of a given species decomposed at different rate when litter from its own species, rather than that of a different species, was placed in the adjacent litterbag compartment. This was particularly apparent in the second year, when across the entire data set, litters decomposed fastest when associated with their own litters. Generally, slowly decomposing litters had the greatest positive effects on decomposition of associated litters. It is proposed that in boreal forests slow decomposing litters (particularly those of feather mosses) may contribute to enhancing moisture attention in the litter layer, which in turn promotes the decomposition and N release of associated litters. Further, while litter mixing effects were clearly demonstrated in our study, they were also shown to be of secondary importance to the effects of species identity on decomposition.
<p>Changes in fire regime of boreal forests are predicted to alter plant and soil community structure and cause elevated tree mortality, increased loss of soil organic matter and reduced survival and functioning of soil microbial communities. While the impact of wildfire disturbance on plant mortality and post-fire successions in boreal forests has been studied extensively, little is known about how changes in soil properties after fire, including biotic and abiotic properties, individually and interactively impact tree seedling regeneration. The aim of this study was therefore to disentangle how tree seedling performance is independently and interactively controlled by soil biotic versus abiotic properties following wildfire.</p><p>We performed two greenhouse experiments in which seedlings of <em>Betula pendula</em>, <em>Pinus sylvestris</em> and <em>Picea abies</em> were grown in soils collected from forest stands in east-central Sweden that had been subjected to three burn severities (high, low and unburnt) following a large-scale wildfire. The first experiment consisted of live soil originating from every stand in each burn severity class crossed with each tree species. The second experiment was similar, except that all soil was first sterilized, and then was crossed with live soil inoculum originating from each of the burn severity classes and grown with each tree species. The results showed that tree seedlings subjected to live soil grew best in soil from unburnt stands (experiment 1), and that <em>P. abies </em>and <em>P. sylvestris</em> seedlings increased growth when planted in soil inoculated with biota from low burn severity stands compared to high burn severity or unburnt stands (experiment 2). In contrast, <em>B. pendula</em> was not responsive to soil inoculum treatments, but instead was driven by post-fire abiotic properties of soils. These results indicate that fire disturbances may lead to reduced regeneration of conifers, unless soil biota is maintained or has recovered, and further suggests that soil from high burn severity stands may constrain seedling regeneration, whereas soil biota from low burn severity stands promotes growth and regeneration of conifers. Our study also shows that different seedling species respond differently to abiotic and biotic soil properties altered by different burn severities, which is relevant because burn probability and fire intensity are projected to increase and become more common in many parts of the boreal region as the climate warms.</p>
No abstract is provided for this article.
Summary Despite widespread focus on interspecific variation in trait‐based ecology, there is growing evidence that intraspecific trait variability can play a fundamental role in plant community responses to environmental change and community assembly. Here, we quantify the strength and direction of inter‐ and intraspecific plant community trait responses along a 900 m elevation gradient spanning alpine and subalpine plant communities in southern New Zealand. We measured five commonly used leaf traits (i.e. dry matter content, N and P concentrations, leaf area and specific leaf area) on all 31 dominant and subordinate species recorded along the gradient, and examined their species‐specific and community‐level responses to elevation using both abundance‐weighted and nonweighted averages of trait values. By decomposing the variance of community‐level measures of these traits across the gradient, we showed that the contribution of interspecific variation to the response of plant assemblages to elevation was stronger than that of intraspecific variation, for all traits except specific leaf area. Further, the relative contributions of interspecific effects were greater when abundance‐weighted rather than nonweighted measures were used. We also observed contrasting intraspecific trait responses to the gradient among species (particularly for leaf N and P concentrations), and found both positive and negative covariation between inter‐ and intraspecific effects on community‐level trait values. The weak community‐average trait responses to elevation, as found for specific leaf area ( SLA ) and leaf N and P concentrations, resulted from strong but opposing responses among vs. within species, which are not typically accounted for in species‐based measures of plant community responses. For instance, increasing elevation (and associated factors such as a decrease in soil nutrient availability) favoured the dominance of species with relatively high leaf nutrient concentrations while simultaneously triggering an intraspecific decrease in the leaf nutrient concentrations of these species. The context dependency of positive and negative covariation between inter‐ and intraspecific trait variability, and the species‐specific nature of intraspecific shifts in functional trait values, reveal highly complex plastic responses of plants to environmental changes, and highlights the need for greater consideration of the role that intraspecific variation plays in community‐level processes.
Snow fungi are often visibly abundant on tundra and forest understory vegetation immediately after snow melt in Nordic regions. Fungal hyphae are a common food source for many terrestrial arthropods and snow fungi could therefore be a potentially important component of an as of yet unexplored winter food web. We compared the abundance of soil arthropods (Acari and Collembola) from paired patches with and without dense infections of snow fungi in the forest understory of a northern Swedish boreal forest after snow melt. Although we did not find increased abundance of these animals when snow fungi were present, Collembola and Acari were sustained on a diet of snow fungi for six months. The isotope signature of the snow fungi clearly differed from humus and other fungal types from literature values obtained from similar boreal forests, suggesting that these fungi may occupy a novel N niche during winter in northern boreal forests. Our study shows for the first time that snow fungi are a potential food source for micro-arthropods during winter and spring. Potentially, snow fungi may represent the basis of an unexplored sub-nivean winter food web but further work is required to assess their importance for community development and winter litter decomposition.
Summary form only given. Silica fibers exhibit a Raman gain that is of the same order of magnitude as the gain of parametric processes. A full analysis of stimulated Raman scattering (SRS) in fibers must therefore include the four-wave-mixing coupling between the pump, the red-shifted Stokes, and the blue-shifted anti-Stokes frequencies. In this communication, we provide a measurement of the ratio between the anti-Stokes and the Stokes intensities in the strong phase-mismatched regime and demonstrate an excellent agreement with the theory.
Aim To compare the ability of island biogeography theory, niche theory and species–energy theory to explain patterns of species richness and density for breeding bird communities across islands with contrasting characteristics. Location Thirty forested islands in two freshwater lakes in the boreal forest zone of northern Sweden (65°55′ N to 66°09′ N; 17°43′ E to 17°55′ E). Methods We performed bird censuses on 30 lake islands that have each previously been well characterized in terms of size, isolation, habitat heterogeneity (plant diversity and forest age), net primary productivity (NPP), and invertebrate prey abundance. To test the relative abilities of island biogeography theory, niche theory and species–energy theory to describe bird community patterns, we used both traditional statistical approaches (linear and multiple regressions) and structural equation modelling (SEM; in which both direct and indirect influences can be quantified). Results Using regression-based approaches, area and bird abundance were the two most important predictors of bird species richness. However, when the data were analysed by SEM, area was not found to exert a direct effect on bird species richness. Instead, terrestrial prey abundance was the strongest predictor of bird abundance, and bird abundance in combination with NPP was the best predictor of bird species richness. Area was only of indirect importance through its positive effect on terrestrial prey abundance, but habitat heterogeneity and spatial subsidies (emerging aquatic insects) also showed important indirect influences. Thus, our results provided the strongest support for species–energy theory. Main conclusions Our results suggest that, by using statistical approaches that allow for analyses of both direct and indirect influences, a seemingly direct influence of area on species richness can be explained by greater energy availability on larger islands. As such, animal community patterns that seem to be in line with island biogeography theory may be primarily driven by energy availability. Our results also point to the need to consider several aspects of habitat quality (e.g. heterogeneity, NPP, prey availability and spatial subsidies) for successful management of breeding bird diversity at local spatial scales and in fragmented or insular habitats.
