552 publications from this institution
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.
While there has been much recent interest about the relationships between plant diversity and plant productivity, much remains unknown about how the diversity of mycorrhizal fungi affects plant productivity. We investigated the effects of ectomycorrhizal fungal community composition and diversity on the productivity and growth characteristics of seedlings of two tree species ( Pinus sylvetris and Betula pendula ) as well as their interactions with each other. This involved setting up a mycorrhizal fungal diversity gradient from one to eight species using a design previously demonstrated to be able to separate diversity effects from compositional effects. We found that the eight mycorrhizal fungal species differed in their effects on seedling productivity and that the nature of effects was determined by the fertility of the substrate. Fungal species richness effects were also important in affecting seedling productivity over and above what could be explained by “sampling effect” but only in some situations. For B. pendula in a low fertility substrate there were clear positive causative effects between fungal species richness and productivity with the eight species treatment having over double the productivity of any of the eight monoculture treatments; no diversity effects were, however, detected in a high fertility substrate. For P. sylvestris in a high fertility substrate there were significant negative effects of fungal diversity on productivity while in a low fertility substrate no effects were apparent. The possible mechanistic bases for these results are discussed. The growth of P. sylvestris relative to that of B. pendula when grown in combination was unaffected by mycorrhizal treatments. Our results provide clear evidence that effects of mycorrhizal fungal diversity on productivity are context dependent and may be positive, negative or neutral depending on the situation considered.
No abstract is provided for this article.
No abstract is provided for this article.
1. The effects of the grass species Lolium perenne L. and nine dicotyledonous grassland species, grown in monocultures and two-species mixtures, on (i) the soil microbial biomass, (ii) the respiration: biomass ratio and (iii) plant litter decomposition was investigated in a glasshouse experiment. 2. Microbial biomass was sometimes greater and sometimes less in the two-species mixtures than could be explained in terms of the additive effects of the two component species grown singly; this variation was independent of differences in below-ground plant productivity between monoculture and mixture treatments. 3. The microbial respiration: biomass ratios and plant litter decomposition rates in the two-species mixture treatments were either greater or less than expected based on the monoculture treatments; these differences were dependent on the combinations of species present. Because the respiration: biomass ratio is a measure of ecosystem stability, it is here proposed that stability does not respond predictably to shifts in species diversity. 4. These results provide evidence that increasing plant species richness (from one to two species) has the potential to influence soil processes positively or negatively in a non-additive way. The possible ecological implications of this are discussed.
There has been a growing recent interest in how foliar herbivory may indirectly affect the belowground sub‐system, but little is known about the belowground consequences of the identity, species composition or diversity of foliar herbivores. We performed an experiment, utilising model grassland communities containing three plant species, in which treatments consisted of addition of each of eight aphid species in single and in two‐ four‐ and eight‐species combinations, as well as an aphid‐free treatment. While aphid species treatments did not affect total plant biomass or productivity, aphid species identity had important effects on the relative abundance of the three plant species. This in turn affected the abundances of each of three groups of secondary consumers in the soil food web (bacterial‐ and fungal‐feeding nematodes, and enchytraeids) but not primary consumers (microbes, herbivorous nematodes) or tertiary consumers (predatory nematodes). The fact that some trophic levels responded to treatments while others did not is consistent with trophic dynamic theory. Aphid species treatments also affected the community composition within each of the herbivorous, microbe‐feeding and top predatory nematode groups, as well as diversity within the first two of these groups. However, aphid species diversity per se had few effects. There were specific instances in which specific aboveground and belowground response variables in two aphid species combinations differed significantly from those in both of the corresponding single aphid species treatments (apparently as a consequence of resource use complementarity between coexisting aphid species), but no instance in which increasing aphid diversity beyond two species had any effect. Our results provide evidence that the identity of aboveground consumers can have effects that propagate through multiple trophic levels in soil food webs in terms of consumer abundance, and composition and diversity within trophic levels.
Summary 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 B etula 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.
Feather mosses form a thick ground layer in boreal forests that can intercept incoming litter fall. This interception may influence the decomposition of in
Plants affect terrestrial ecosystem functioning by performing the primary production that energetically sustains heterotrophic organisms, and by shaping the microenvironment. However, the influence of plant diversity and community composition on ecosystem functioning through their effects on energy flow into food webs has been little studied, especially for soil food webs that channel most of the plant-derived energy. Applying a food web energetics approach, we show that the resource economics of dominant tree species control soil food web multifunctionality across European forests. Specifically, tree communities dominated by resource acquisitive species promoted faster rates of multiple soil trophic functions simultaneously than did those dominated by resource conservative species. This was primarily driven by their production of plant litter with higher nutritional quality and their warmer forest microclimate, leading to a higher metabolic activity of soil organisms. Tree species mixing had rather weak and negative effects on soil food web multifunctionality, mostly due to a shift in the resource-based energy channeling from living plant fine roots to litter and a cooling effect on the forest microclimate. Tree diversity effects were largely outweighed by community compositional effects, which were of similar magnitude to the effects of biogeographic differences among locations. Our findings emphasize the importance of plant functional traits related to resource economics as drivers of plant community effects on soil food web functioning5,9 and highlight the consequences that climate-driven shifts in tree community composition could have for forest soil functioning.
While several studies have shown that invasive plant effects on soil biota influence subsequent plant performance, corresponding studies on how invasive animals affect plants through influencing soil biota are lacking. This is despite the fact that invasive animals often indirectly alter the below-ground subsystem. We studied 18 offshore islands in northern New Zealand, half of which have been invaded by rats that are predators of seabirds and severely reduce their densities, and half of which remain non-invaded; invasion of rats thwarts seabird transfer of resources from ocean to land. We used soil from each island in a glasshouse experiment involving soil sterilization treatments to determine whether rat invasion indirectly influences plant growth through the abiotic pathway (by impairing seabird-driven inputs to soil) or the biotic pathway (by altering the soil community). Rat invasion greatly impaired plant growth but entirely through the abiotic pathway. Plant growth was unaffected by the soil community or its response to invasion, meaning that the responses of plants and soil biota to invasion are decoupled. Our results provide experimental evidence for the powerful indirect effects that predator-instigated cascades can exert on plant and ecosystem productivity, with implications for the restoration of island ecosystems by predator removal.
We describe a simple gravimetric technique for measuring the standing crop or production of carbohydrate-rich solutions such as honeydew or nectar. Simulated honeydew was sampled by absorbing droplets of solutions of known concentration and volume with dried and weighed pieces of filter paper. The change in mass of the paper after redrying provides an estimate of the total solution carbohydrates. This method was compared with a widely-used technique, whereby the volume and concentration of droplets is measured with microcapillary tubes and a sugar refractometer. A factor was derived to convert gravimetric refractometer readings (g sucrose 100 g -1 solution) to volumetric carbohydrate concentration (g carbohydrate 100 ml -1 solution) for the simulated honeydew solutions. There was no difference in the ratio of measured-to-expected carbohydrate mass between the two techniques, showing that the quick, easy, and accurate filter-paper method is appropriate for measuring carbohydrate-rich solutions.
