Elevational gradients are useful for predicting how plant communities respond to global warming, because communities at lower elevations experience warmer temperatures. Fine root traits and root trait variation could play an important role in determining plant community responses to warming in cold‐climate ecosystems where a large proportion of plant biomass is allocated belowground. Here, we investigated the effects of elevation‐associated temperature change on twelve chemical and morphological fine root traits of plant species and plant communities in a Swedish subarctic tundra. We also assessed the relative contributions of plant species turnover and intraspecific variation to the total amount of community‐level root trait variation explained by elevation. Several root traits, both at the species and whole community levels, had significant linear or quadratic relationships with elevation, but the direction and strength of these relationships varied among traits and plant species. Further, we found no support for a unidirectional change from more acquisitive root trait values at the lower elevations towards trait values associated with greater nutrient conservation at the higher elevations, either at the species or community level. On the other hand, root trait coefficients of variation at the community level increased with elevation for several root traits. Further, for a large proportion of the community‐level traits we found that intraspecific variation was relatively more important than species turnover, meaning that trait plasticity is important for driving community‐level trait responses to environmental factors in this tundra system. Our findings indicate that with progressing global warming, intraspecific trait variation may drive plant community composition but this may not necessarily lead to shifts in root resource–acquisition strategy for all species.
The proposed calibration equations for quantifying microbial biomass carbon were considered and variability associated with these methods was assessed., The fumigation-incubation (FI) method depends on a k c factor for biomass C determination. Three k c are commonly in use, i.e. 0.41, 0.45 and 0.50, but these all have an associated degree of variability. However, values of k c may also vary between certain soil treatments and between soil types. Substrate-induced respiration (SIR) has been calibrated against FI but the strength of the relationship between the two methods is uncertain in most instances because SIR measures glucose-responsive microbial biomass while FI measures chloroform-susceptible biomass. ATP and ninhydrin-extractable N analysis may show strong relationships with FI but only in specific circumstances. Fumigation-extraction (FE) demonstrates uncertain relationships when calibrated against SIR, possibly because FE measures chloroform-susceptible biomass. Calibrations of FE against FI also appear to be uncertain probably because k c and k ec values vary differently across soil types.
An enormous recent research effort focused on how plant biodiversity (notably species richness) influences ecosystem functioning, usually through experiments in which diversity is varied through random draws of species from a species pool. Such experiments are increasingly used to predict how species losses influence ecosystem functioning in ‘real’ ecosystems. However, this assumes that comparisons of experimental communities with low vs high species richness are analogous to comparisons of natural communities from which species either have or have not been lost. I explore the validity of this assumption, and highlight difficulties in using such experiments to draw conclusions about the ecosystem consequences of biodiversity loss in natural systems. Notably, these experiments do not mimic what happens in real ecosystems either when local extinctions occur or when species losses are offset by gains of new species. Despite limitations, this single experimental approach for studying how biodiversity loss affects ecosystems has often been advocated and implemented at the expense of other approaches; this limits understanding of how natural ecosystems respond to biodiversity loss. I conclude that a broader spectrum of approaches, and more explicit consideration of how species losses and gains operate in concert to influence ecosystems, will help progress this field.
Following the creation of new land surfaces, there is an initial build-up phase of ecosystem development, but after a prolonged absence of major disturbance a retrogressive (decline) phase often follows due to reduced nutrient availability over time. Although many studies have considered how the soil community changes during the build-up phase, the response of this community to the retrogressive phase is poorly known. We measured litter and soil communities of microfauna and macrofauna along the Franz Josef Glacier chronosequence in New Zealand that spans ca. 120,000 years, and includes well-established build-up and retrogressive stages. We aimed to assess whether the abundances, community structure and diversity of these groups show the same pattern across the sequence as that for vegetation. With regard to microfaunal abundances, litter-dwelling microbe-feeding nematodes were most abundant in the first stage of the chronosequence, but several other groups of microfauna in both the soil and litter increased sharply during the first few stages and declined sharply during the last (retrogressive) stages. The ratios of bacterial- to fungal-feeding nematodes in both soil and litter were lowest for the final stages of the chronosequence, and (in the case of soil) for some of the early stages, pointing to domination by the fungal-based energy channel at those stages for which soil organic matter content or quality were lowest. This is consistent with the fungal-based energy channel being better adapted than the bacterial-based channel for resource-poor conditions. The main groups of macroinvertebrates typically had their lowest abundances at the very early and late stages of the chronosequence, although the relative abundances of different taxa differed during the intermediate stages. Taxonomic diversity of nematodes and macroinvertebrates in both litter and soil varied strongly with chronosequence stage but differed among taxa; diversity of only one group (macroinvertebrates in litter) declined significantly during retrogression. Diversity of nematodes and macroinvertebrates along the sequence did not closely match tree diversity or soil chemical properties, but community composition of these groups was often related to tree community composition and ratios of soil C to N, C to P and N to P. Different groups of soil invertebrates show contrasting responses to chronosequence stage, probably because they differ in their relative response to bottom-up and top-down controls. However, the abundance of most groups increased during the build-up phase and declined during retrogression. As such, the build-up and decline phases observed for plant communities and ecosystem processes across long-term chronosequences also apply to soil communities, pointing to the importance of resource availability as a major driver of soil biota during long-term ecosystem change.
A study reveals that increasing aridity alters the balance of carbon, nitrogen and phosphorus in dryland soils, providing insight into how global climate change will affect soil fertility and ecosystem services. See Letter p.672 It is thought likely that climatic change, such as the increased aridity predicted for many drylands, could disrupt the biogeochemical cycles of carbon, nitrogen and phosphorus during the twenty-first century. These elements are essential nutrients for biomass production in terrestrial ecosystems. This study finds that aridity has a negative effect on the concentration of global dryland soil organic carbon and nitrogen, but a positive effect on the concentration of inorganic phosphorus. This suggests a decoupling of nutrient cycles in response to an increase in aridity that could have a negative impact on biogeochemical reactions that control key ecosystem functions such as primary productivity.
1 The development of general principles regarding biotic interactions involving plants, or plant species effects in ecosystems, is best achieved through simultaneous evaluation of several species. We utilized a comparative approach involving 20 dicotyledonous herbaceous species, to explore possible relationships between several plant ecophysiological traits and plant litter decomposition, interactions involving competition and herbivory, and plant species effects on soil properties. 2 Decomposition rates of plant stem and leaf litter were negatively related to plant mass, time until flowering and vegetative growth rate, and positively related to stem nitrogen content. Root decomposition was also related to several traits. Multiple regression relationships showed that 74% and 84% of the variation across species for stem and root litter decomposition, respectively, could be predicted by plant traits; this suggests that plant traits may be powerful predictors of decomposition and have potential as alternative predictors to the litter quality characteristics that previous studies have concentrated on. 3 Palatability of both seedlings and leaf discs by the invertebrate herbivores Deroceras reticulatum and Listronotus bonariensis were frequently related to plant traits. Those traits that showed the strongest relationships with the palatability data included various vegetative growth characteristics and (for the leaf disc data) nitrogen concentrations of flowering plant stems. 4 Competitive effects of the dicotyledonous species against a phytometer species, the grass Lolium perenne , were negatively related to leaf nitrogen concentration, and multiple regression relationships involving this trait in combination with others explained over 50% of the variation across species. The competitive response of both plant mass and total seed production to L. perenne was poorly related to plant traits. 5 The effects of plant species on soil properties including microbial biomass and activity, pH, nitrate concentration and total nitrogen were often closely related to various plant traits. Multiple regression relationships revealed that combinations of several traits were often important in determining these effects; the strongest relationships found were for effects of senescent plants on soil respiration and for the effects of flowering plants on soil nitrate. Plant traits were therefore clearly important in determining plant species effects on soils. 6 Our study emphasizes the importance of plant traits in understanding (and predicting) species interactions and effects in communities and ecosystems, and shows that properties considered at the whole plant level have the potential to manifest themselves over much larger scales. We therefore conclude that there are clear linkages between plant ecophysiological traits, biotic interactions involving plants, and ecosystem level properties and processes.
1. Despite recent interest in linkages between above- and belowground communities and their consequences for ecosystem processes, much remains unknown about their responses to long-term ecosystem change. We synthesize multiple lines of evidence from a long-term ‘natural experiment’ to illustrate how ecosystem retrogression (the decline in ecosystem processes due to long-term absence of major disturbance) drives vegetation change, and thus aboveground and belowground carbon (C) sequestration, and communities of consumer biota. 2. Our study system involves 30 islands in Swedish boreal forest that form a 5000 year fire-driven retrogressive chronosequence. Here, retrogression leads to lower plant productivity and slower decomposition, and a community shift from plants with traits associated with resource acquisition to those linked with resource conservation. 3. We present consistent evidence that aboveground ecosystem C sequestration declines, while belowground and total C storage increases linearly for at least 5000 years following fire absence. This increase is driven primarily by changes in vegetation characteristics, impairment of decomposer organisms and absence of humus combustion. 4. Data from contrasting trophic groups show that during retrogression, biomass or abundance of plants and decomposer biota decreases, while that of aboveground invertebrates and birds increases, due to different organisms accessing resources via distinct energy channels. Meanwhile, diversity measures of vascular plants and aboveground (but not belowground) consumers respond positively to retrogression. 5. We show that taxonomic richness of plants and aboveground consumers are positively correlated with total ecosystem C storage, suggesting that conserving old growth forests simultaneously maximizes biodiversity and C sequestration. However, we find little observational or experimental evidence that plant diversity is a major driver of ecosystem C storage on the islands relative to other biotic and abiotic factors. 6. Synthesis. Our study reveals that across contrasting islands differing in exposure to a key extrinsic driver (historical disturbance regime and resulting retrogression), there are coordinated responses of soil fertility, vegetation, consumer communities, and ecosystem C sequestration, which all feed back to one another. It also highlights the value of well replicated natural experiments for tackling questions about aboveground-belowground linkages over temporal and spatial scales that are otherwise unachievable.
Boreal forest ecosystems are important drivers of the global carbon (C) cycle by acting as both sinks and sources of atmospheric CO 2 . While several factors have been proposed as determining the ability of boreal forest to function as C sinks, little is known about their relative importance. In this study, we applied structural equation modelling to a previously published dataset involving 30 boreal-forested islands that vary greatly in their historic fire regime, in order to explore the simultaneous influence of several factors believed to be important in influencing above-ground, below-ground and total ecosystem C accumulation. We found that wildfire was a major driver of ecosystem C sequestration, and exerted direct effects on below-ground C storage (presumably through humus combustion) and indirect effects on both above-ground and below-ground C storage through altering plant-community composition. By contrast, plant diversity influenced only below-ground C storage (and even then only weakly), while net primary productivity and decomposition had no detectable effect. Our results suggest that while boreal forests have great potential for storing significant amounts of C, traits of dominant plant species that promote below-ground C accumulation and the absence of wildfire are the most important drivers of C sequestration in these ecosystems.
Pleurocarpous feather mosses host di-nitrogen (N2) fixing cyanobacteria, and this association serves as an important source of N input to late-successional natural boreal forests. However, little is known about how forest management affects feather mosses and their associated N2-fixation rates, or how these rates change during post-logging stand development. We established a chronosequence of 32 forest stands used for commercial wood production to better understand how stand development after clear-cutting drives changes in biomass and N2-fixation rates of the two dominant feather mosses, Pleurozium schreberi and Hylocomium splendens. These stands included eight replicate stands of each of four stand types: (1) recently clear-cut and newly planted stands (CC, 4years); (2) pre-commercial thinning stands (PCT, 16years); (3) first thinning stands (T1, 34years); and (4) mature uncut forest (MF, 123years), all dominated by Pinus sylvestris. We found that clear-cutting did not reduce moss biomass relative to the uncut forest. Further, biomass of P. schreberi (but not of H. splendens) increased twofold from CC stands to PCT stands, and remained high throughout the T1 stands. Di-nitrogen fixation capacity, determined as the amount of N fixed per unit moss mass, was ca. six and three times larger in PCT stands compared to the other stand types for P. schreberi and H. splendens respectively. Correlation analyses showed that N2-fixation capacity associated with both moss species increased with increasing Empetrum hermaphroditum biomass, and that N2-fixation capacity of P. schreberi declined with increasing NH4 + availability. Further, correlation analysis showed that N2-fixation capacity of H. splendens declined with increasing tree biomass and decreasing light transmission. The total amount of N fixed at the stand level was highest in the PCT stands (1.0kgha−1 year−1 of N), and was associated with both high moss biomass and high N2-fixation capacity. The contribution of N2-fixation to total N accrual per hectare during stand development was ca. 9%, and across the chronosequence N2 was fixed on average at rates of 0.4kgha−1 year−1. Our results show that N2-fixation rates in feather moss communities were promoted by the conditions at the PCT stands approximately 16years after clear-cutting, while N2-fixation rates were lowest under conditions at the newly clear-cut and mature stands. Further, it suggests that mosses and associated N2-fixation can be important in maintaining a long-term N balance, and that this source of N input should be accounted for when modeling N balance in N-limited managed boreal forests.
No abstract is provided for this article.
