552 publications from this institution
The allelopathic effects of vegetative and flowering plants of the annual/biennial pasture weed Senecio jacobaea L. (ragwort) against Lolium perenne L. (pe
Although a handful of studies have shown how interspecific interactions may influence plant shoot to root ratios, the issue of how these interactions influence biomass partitioning among coexisting plant species remains largely unexplored. In this study, we determined whether a given plant species could induce other plant species to allocate relative biomass to each of four zones (aboveground, and three soil depth layers) in a different manner to what they would otherwise, and whether this may influence the nature of competitive or facilitative interactions amongst coexisting plant species. We used a glasshouse study in which mixtures and monocultures of ten grassland plant species were grown in cylindrical pots to determine the effects of plant species mixtures versus monocultures on the production of shoots and of roots of other species for each of three soil depths. Across all experiments, stimulation of production in mixtures was far less common than suppression of production. Different plant species shifted their allocation to shoots or roots at different depths, suggesting that interspecific interactions can either: (1) increase the ratio of deep to shallow roots, perhaps because competition reduces root growth in the uppermost part of the soil profile; or (2) decrease this ratio by reducing plant vigour to such an extent that the plant cannot produce roots that can reach deep enough to exploit resources at lower depths. Further, these results suggest that there are instances in which competition may have the potential to enforce resource partitioning between coexisting plant species by inducing different species to root at different depths to each other.
Summary Despite recent progress in characterizing the within‐species variability ( WSV ) of plant functional traits, the importance of this WSV in driving ecological processes such as leaf litter decomposability within species or at the whole community level is poorly understood. We ask whether leaf and litter functional traits vary within species to form a spectrum of variability analogous to the leaf economics spectrum that occurs among species. We also ask whether this spectrum of trait variation within species is an important driver of leaf litter decomposability. To address these questions, we quantified both WSV and between‐species variation of leaf and litter traits and litter decomposability of 16 co‐occurring temperate rain forest plant species along soil toposequences characterized by strong shifts in soil nutrient status in N ew Z ealand. We found considerable WSV of both leaf and litter traits for all species, and a within‐species spectrum of coordinated trait variation for 11 species. The WSV of leaf and to a lesser extent foliar litter C to N and C to P values were often strongly related to soil C to N and C to P ratios across plots. Further, in many cases, WSV and its covariation with species turnover contributed significantly to the community‐level aggregate trait response to variation in soil fertility. Contrary to our expectations, the WSV in leaf and litter traits did not generally predict within‐species variation in leaf litter mass loss, nor N and P release, during decomposition. Further, inclusion of WSV did not improve predictions of leaf litter decomposability using community‐level trait measures. Synthesis . Our findings support the view that WSV of plant functional traits is an important component of plant community responses to environmental factors such as soil fertility. However, the apparent decoupling of WSV of leaf economic traits from WSV of ecological processes such as litter decomposability suggests that consideration of WSV may not be necessary to understand the contributions of trait variation to determining the breakdown of plant litter and therefore, potentially, ecosystem processes.
Michelsen et al. (1995) present results of an experiment in which aqueous leaf extracts of three arctic woody plant species were found to inhibit growth an
One way of mitigating global climate change is protecting and enhancing biosphere carbon stocks. The success of mitigation initiatives depends on the long-term net balance between carbon gains and losses. The biodiversity of ecological communities, including composition and variability of traits of plants and soil organisms, can alter this balance in several ways. This influence can be direct, through determining the magnitude, turnover rate, and longevity of carbon stocks in soil and vegetation. It can also be indirect through influencing the value and therefore the protection that societies give to ecosystems and their carbon stocks. Biodiversity of forested ecosystems has important consequences for long-term carbon storage, and thus warrants incorporation into the design, implementation, and regulatory framework of mitigation initiatives.
No abstract is provided for this article.
Alpine tundra ecosystems such as those which are dominated by ericaceous dwarf shrubs in northern Scandinavia are characterised by low productivity, and this is due in part to low availability of nutrients and retardation of those microbial processes required for nutrient cycling. We conducted an eight‐year field experiment in an alpine tundra in northern Sweden, in which eleven treatments aimed at alleviating possible stresses were applied to field plots; these included addition of various forms of nitrogen and other nutrients, addition of lime, addition of available carbon, and reduction of possible adverse effects of secondary metabolites produced by the dwarf shrub Empetrum hermaphroditum . Nearly all of the treatments had statistically significant effects on at least some of the plant species present in the experiment. Addition of nitrogen and liming both had important effects in reducing E. hermaphroditum cover and in these treatments Deschampsia flexuosa rapidly became dominant. Manipulations that reduced E. hermaphroditum or its effects frequently also stimulated Vaccinium myrtillus and V. vitis‐idaea . Fertilisation and liming treatments also often caused decreases in the mosses Dicranum sp. and Pleurozium schreberi , and the lichen Cladina spp. Ordination analysis revealed that vascular plant community structure was most significantly altered by treatments involving mineral nitrogen addition and liming, moss community structure by treatments involving addition of available carbon and lichen community structure by treatments involving addition of some forms of nitrogen, lime and reduction of effects of E. hermaphroditum . Nearly all treatments significantly reduced total plant diversity (species richness) and several treatments reduced diversity of each of the vascular plant, lichen and moss groups. This reduction in diversity was frequently associated with monopolisation of plots by D. flexuosa . Decomposition rates of litter added to the plots were generally only weakly influenced by treatments, but several treatments (most notably those involving nitrogen addition) induced litter nitrogen immobilisation and increased litter microbial biomass levels. Humus nitrogen and microbial levels were also sometimes enhanced by the nitrogen addition treatments. This suggests that those plots dominated by D. flexuosa were likely to result in greater conservation of nitrogen in the litter relative to those dominated by E. hermaphroditum . An important exception to this pattern was the effects of the liming treatment which, although responsible for an increase in D. flexuosa , caused net losses of nitrogen and reduced microbial biomass both in the litter and the humus. Our data therefore suggest that treatments which have vastly differing consequences for humus properties and the decomposer subsystem (and ultimately conservation of nitrogen in the soil), but which alleviate an inherent stress, have similar consequences above‐ground, e.g. E. hermaphroditum decline, D. flexuosa enhancement, and associated reductions of plant diversity.
Decomposition of organic matter in high latitude biomes makes a significant contribution to global fluxes of nutrients and carbon and is expected to accelerate due to climate change. The majority of studies have focused on decomposition during the growing season, but winter climate is expected to change dramatically. Furthermore, knowledge of the drivers of organic matter decomposition, such as litter chemical composition, has primarily been tested across the growing season so it is unknown whether these drivers are also important during the winter. Given that the depth of snow cover insulates the sub-nivean climate from the much colder air, it is an important control on winter decomposition and is expected to be influenced by climate change, we experimentally manipulated snow cover to simulate impacts of different winter precipitation scenarios on soil processes. Our results show that despite snow reduction negatively affecting decomposer abundance (by 99%) and bulk soil respiration (by 47%), litter decomposition rates showed little to no response. Furthermore, variation in winter decomposition rates among litter types was unrelated to nutrient status, indicating that our current understanding of drivers of litter decomposition may not hold during winter months. Despite very large reductions in decomposer fauna due to snow removal, litter decomposition rates were not consistently responsive, indicative of decoupled responses of soil organisms and soil processes to winter climate change.
Plant species and functional groups are known to drive the community of belowground invertebrates but whether their effects are consistent across environme
Over the past half century, ecologists have tried to unravel the factors that drive species richness patterns in ecological communities. One influential theory is island biogeography theory (IBT), which predicts that island or habitat area and isolation are drivers of species richness. However, relatively few studies testing IBT have considered invertebrate or belowground communities, and it is unclear as to whether the predictions made by IBT hold for these communities. Other theories predict that habitat characteristics such as vegetation diversity may be important drivers of invertebrate species richness. To investigate patterns of invertebrate density and species richness across gradients of area, isolation, and vegetation diversity, we used a system of 30 lake islands in the boreal zone of northern Sweden. We assessed density and taxonomic richness of ground‐dwelling spiders, web‐building spiders, beetles, collembolans, mites, and nematodes, for all islands during two consecutive summers. For all invertebrate groups, both density and taxonomic richness were either neutrally or negatively related to island size, and either neutrally or positively related to island isolation. Meanwhile the density and taxonomic richness for several groups was positively related to vegetation diversity (i.e. habitat heterogeneity). In multiple regression analyses, island size was often the single best predictor for both invertebrate density and taxonomic richness, but in some cases island size and isolation in combination explained more variation than each factor considered singly. Contrary to IBT predictions, invertebrate density and richness was never positively related to island size or negatively related to island isolation. Instead, our results suggest that plant diversity (and thus habitat heterogeneity) was the main driver of the patterns that we found, although other factors could have some influence. We conclude that several factors, but not necessarily those predicted as important by IBT, are important in determining invertebrate abundance and species richness in island systems.
Summary Above the alpine tree line, bryophytes cover much of the tundra soil surface in dense, often monospecific carpets. Therefore, when climate warming enables tree seedling establishment above the tree line, interaction with the bryophyte layer is inevitable. Bryophytes are known to modify their environment in various ways. However, little is known about to which extent and by which mechanisms bryophytes affect the response of tree seedlings to climate warming. We aimed to assess and understand the importance of bryophyte species identity and traits for tree seedling performance at tree line temperatures and their response to warmer conditions. Seedlings of two common, tree line‐forming tree species ( Betula pubescens and Pinus sylvestris ) were planted into intact cushions of eight common tundra bryophyte species and bryophyte‐free soil and grown for 18 weeks at current (7·0 °C) and near‐future (30–50 years; 9·2 °C) tree line average growing‐season temperatures. Seedling performance (biomass increase and N‐uptake) was measured and related to bryophyte species identity and traits indicative of their impact on the environment. Tree seedlings performed equally well or better in the presence of bryophytes than in bryophyte‐free soil, which contrasts to their usually negative effects in milder climates. In addition, seedling performance and their response to higher temperatures depended on bryophyte species and seedlings of both species grew largest in the pan‐boreal and subarctic bryophyte Hylocomium splendens . However, B. pubescens seedlings showed much stronger responses to higher temperatures when grown in bryophytes than in bryophyte‐free soil, while the opposite was true for P. sylvestris seedlings. For B. pubescens , but not for P. sylvestris , available organic nitrogen of the bryophyte species was the trait that best predicted seedling responses to higher temperatures, likely because these seedlings had increased N‐demands. Synthesis . Climatically driven changes in bryophyte species distribution may not only have knock‐on effects on vascular plant establishment, but temperature effects on seedling performance are themselves moderated by bryophytes in a species‐specific way. Bryophyte traits can serve as a useful tool for understanding and predicting these complex interactions.
Fertilizer experiments aid understanding of the role of nutrient limitation in tundra ecosystems, and of the effects that global change may exert on them through enhancing nutrient availability. However, little is known about whether fertilizer additions influence tundra ecosystem properties directly, or indirectly through altering plant community composition. To separate these direct and indirect effects, we used an ongoing fertilization experiment in subalpine tundra in northern Sweden initiated in 1989. Here, the slow‐growing dwarf shrub Empetrum hermaphroditum (hereafter Empetrum ) dominates, but fertilization causes its replacement by the fast‐growing grass Deschampsia flexuosa (hereafter Deschampsia ). Therefore, in 1999, we set up three subplots in every plot of the fertilizer experiment subjected to different treatments, i.e., regular removal of Empetrum or of Deschampsia , or no removal. An interactive effect between fertilizer and removal treatments means that fertilization indirectly influences ecological properties through its effects on the dominant species whereas no interactive effect means that fertilization effects are more likely direct. We measured plant community properties four times between 1999 and 2010, and belowground properties in 2010. Fertilization exerted large effects on nearly all variables aboveground (i.e., vascular plant community properties, bryophyte and lichen cover) and belowground (i.e., measures of nutrient availability, mass of humus and major elements per area, microbial community properties). Meanwhile, loss of either Deschampsia or Empetrum reduced total vascular plant cover, with greatest effects in those fertilization treatments where they otherwise had the most mass. Deschampsia removal affected several other plant community properties, but mostly independently of fertilizer treatment; Empetrum removal had little effect on any other plant community variable. Belowground, both removal treatments reduced humus mass per area but had no effect on any other variable. Our finding of few interactive effects of fertilizer and removal treatments aboveground and none belowground means that fertilizer effects on most community and ecosystem properties operate independently of even large shifts in the plant community. These results also point to a decoupling between aboveground and belowground communities in tundra, and therefore offer insights about the mechanistic basis through which global change impacts on soil nutrient availability may transform tundra ecosystems.
