Researchers agree that climate change factors such as rising atmospheric CO₂ and warming will likely interact to modify ecosystem properties and processes. However, the response of the microbial ...communities that regulate ecosystem processes is less predictable. We measured the direct and interactive effects of climatic change on soil fungal and bacterial communities (abundance and composition) in a multifactor climate change experiment that exposed a constructed old-field ecosystem to different atmospheric CO₂ concentration (ambient, +300 ppm), temperature (ambient, +3°C), and precipitation (wet and dry) might interact to alter soil bacterial and fungal abundance and community structure in an old-field ecosystem. We found that (i) fungal abundance increased in warmed treatments; (ii) bacterial abundance increased in warmed plots with elevated atmospheric CO₂ but decreased in warmed plots under ambient atmospheric CO₂; (iii) the phylogenetic distribution of bacterial and fungal clones and their relative abundance varied among treatments, as indicated by changes in 16S rRNA and 28S rRNA genes; (iv) changes in precipitation altered the relative abundance of Proteobacteria and Acidobacteria, where Acidobacteria decreased with a concomitant increase in the Proteobacteria in wet relative to dry treatments; and (v) changes in precipitation altered fungal community composition, primarily through lineage specific changes within a recently discovered group known as soil clone group I. Taken together, our results indicate that climate change drivers and their interactions may cause changes in bacterial and fungal overall abundance; however, changes in precipitation tended to have a much greater effect on the community composition. These results illustrate the potential for complex community changes in terrestrial ecosystems under climate change scenarios that alter multiple factors simultaneously.
Plant biodiversity is often correlated with ecosystem functioning in terrestrial ecosystems. However, we know little about the relative and combined effects of above- and belowground biodiversity on ...multiple ecosystem functions (for example, ecosystem multifunctionality, EMF) or how climate might mediate those relationships. Here we tease apart the effects of biotic and abiotic factors, both above- and belowground, on EMF on the Tibetan Plateau, China. We found that a suite of biotic and abiotic variables account for up to 86% of the variation in EMF, with the combined effects of above- and belowground biodiversity accounting for 45% of the variation in EMF. Our results have two important implications: first, including belowground biodiversity in models can improve the ability to explain and predict EMF. Second, regional-scale variation in climate, and perhaps climate change, can determine, or at least modify, the effects of biodiversity on EMF in natural ecosystems.
Temperature is a primary driver of the distribution of biodiversity as well as of ecosystem boundaries. Declining temperature with increasing elevation in montane systems has long been recognized as ...a major factor shaping plant community biodiversity, metabolic processes, and ecosystem dynamics. Elevational gradients, as thermoclines, also enable prediction of long-term ecological responses to climate warming. One of the most striking manifestations of increasing elevation is the abrupt transitions from forest to treeless alpine tundra. However, whether there are globally consistent above- and belowground responses to these transitions remains an open question. To disentangle the direct and indirect effects of temperature on ecosystem properties, here we evaluate replicate treeline ecotones in seven temperate regions of the world. We find that declining temperatures with increasing elevation did not affect tree leaf nutrient concentrations, but did reduce ground-layer community-weighted plant nitrogen, leading to the strong stoichiometric convergence of ground-layer plant community nitrogen to phosphorus ratios across all regions. Further, elevation-driven changes in plant nutrients were associated with changes in soil organic matter content and quality (carbon to nitrogen ratios) and microbial properties. Combined, our identification of direct and indirect temperature controls over plant communities and soil properties in seven contrasting regions suggests that future warming may disrupt the functional properties of montane ecosystems, particularly where plant community reorganization outpaces treeline advance.
1. Though co-occurrence of invasive plant species is common, few studies have compared the community and ecosystem impacts of invaders when they occur alone and when they co-occur. Prioritization of ...invasive species management efforts requires sufficient knowledge of impacts – both among individual invasive species and among different sets of co-occurring invaders – to target resources towards management of sites expected to undergo the largest change. 2. Here, we observed differences in above- and below-ground impacts of two invasive woody shrubs, Lonicera maackii and Ligustrum sinense, among plots containing both shrubs (mixed), each species singly or lacking both species (control). 3. We found additive and non-additive effects of these co-occurring invasives on plant communities and soil processes. Mixed plots contained two times more subdominant invasive plant species than L. maackii or L. sinense plots. Compared to control plots, mixed plots had three times the potential activity of β-glucosidase, a carbon-degrading extracellular soil enzyme. L. maackii plots and mixed plots had less acidic soils, while L. sinense plots had higher soil moisture than control plot soils. Differences in soil properties among plots explained plant- and ground-dwelling arthropod community composition as well as the potential microbial function in soils. 4. Synthesis and applications. Our study highlights the importance of explicitly studying the impacts of co-occurring invasive plant species singly and together. Though Lonicera maackii and Ligustrum sinense have similar effects on ecosystem structure and function when growing alone, our data show that two functionally similar invaders can have non-additive impacts on ecosystems. These results suggest that sites with both species should be prioritized for invasive plant management over sites containing only one of these species. Furthermore, this study provides a valuable template for future studies exploring how and when invasion by co-occurring species alters above- and below-ground function in ecosystems with different traits.
The extent to which ectomycorrhizal (ECM) fungi enable plants to access organic nitrogen (N) bound in soil organic matter (SOM) and transfer this growth-limiting nutrient to their plant host, has ...important implications for our understanding of plant–fungal interactions, and the cycling and storage of carbon (C) and N in terrestrial ecosystems. Empirical evidence currently supports a range of perspectives, suggesting that ECM vary in their ability to provide their host with N bound in SOM, and that this capacity can both positively and negatively influence soil C storage. To help resolve the multiplicity of observations, we gathered a group of researchers to explore the role of ECM fungi in soil C dynamics, and propose new directions that hold promise to resolve competing hypotheses and contrasting observations. In this Viewpoint, we summarize these deliberations and identify areas of inquiry that hold promise for increasing our understanding of these fundamental and widespread plant symbionts and their role in ecosystem-level biogeochemistry.
Aims Variation in tree litter inputs and understory vegetation caused by human disturbances and climate change in forest plantations can extend to alter forest stability and productivity over time. ...Here, we explore how tree litter inputs interact with understory plant management to influence belowground processes in a managed forest plantation. Methods We conducted a two-factor nested experimental manipulation of pine litter and understory vegetation in a nutrient-poor Pinus sylvestris var. mongolica plantation. Three levels of tree litter manipulation (ambient litter, litter removal and litter addition) were nested in two levels of understory manipulation (understory intact and understory removal). After two years of manipulation, mineral soils were analyzed for total and extractable C, N and P concentrations, N mineralization, enzyme activities, as well as the microbial community structure (as indicated by phospholipid fatty acids). Results Litter removal had little impact on and nutrient cycling as well as microbial biomass and community structure in this low nutrient pine plantation; however, litter addition and the removal of the understory vegetation had large impacts on these processes. Litter addition elevated soil microbial biomass, acid phosphatase and β-1, 4-glucosidase activities, by a much greater degree when the understory vegetation was intact than when the understory was removed Litter addition also reduced soil available P by 39% when the understory vegetation was intact, and reduced sou available P by 74% and NO₃⁻-N by 45% when the understory was removed Litter addition significantly reduced the ratio of Gram-positive to Gramnegative bacteria as well as the ratio between PLFA markers cy17:0 and 16:1ω7. Understory removal reduced the ratio of PLFA markers cy17:0 to 16:1ω7. Conclusions Our study results show that, in this managed pine plantation, soil microbial community structure and function were more sensitive to an increase rather than to a decrease in pine litter inputs. Further, we found that the presence of understory vegetation can increase soil microbial biomass and alleviate the reduction in available N and P concentrations induced by pine litter addition. Thus, preservation of the understory vegetation is an effective way to maintain the functional stability of managed forests on nutrient-poor soils.
▶ Taxon-specific responses to climate change result in shifts in community structure ▶ Multiple climate change factors interact in affecting soil microarthropod communities ▶ Changes in soil moisture ...content outweigh direct effects of temperature and CO2.
Long-term ecosystem responses to climate change strongly depend on how the soil subsystem and its inhabitants respond to these perturbations. Using open-top chambers, we studied the response of soil microarthropods to single and combined effects of ambient and elevated atmospheric CO2, ambient and elevated temperatures and changes in precipitation in constructed old-fields in Tennessee, USA. Microarthropods were assessed five years after treatments were initiated and samples were collected in both November and June. Across treatments, mites and collembola were the most dominant microarthropod groups collected.
We did not detect any treatment effects on microarthropod abundance. In November, but not in June, microarthropod richness, however, was affected by the climate change treatments. In November, total microarthropod richness was lower in dry than in wet treatments, and in ambient temperature treatments, richness was higher under elevated CO2 than under ambient CO2. Differential responses of individual taxa to the climate change treatments resulted in shifts in community composition. In general, the precipitation and warming treatments explained most of the variation in community composition. Across treatments, we found that collembola abundance and richness were positively related to soil moisture content, and that negative relationships between collembola abundance and richness and soil temperature could be explained by temperature-related shifts in soil moisture content.
Our data demonstrate how simultaneously acting climate change factors can affect the structure of soil microarthropod communities in old-field ecosystems. Overall, changes in soil moisture content, either as direct effect of changes in precipitation or as indirect effect of warming or elevated CO2, had a larger impact on microarthropod communities than did the direct effects of the warming and elevated CO2 treatments. Moisture-induced shifts in soil microarthropod abundance and community composition may have important impacts on ecosystem functions, such as decomposition, under future climatic change.
As the diversity of plants increases in an ecosystem, so does resource competition for soil nutrients, a process that mycorrhizal fungi can mediate. The influence of mycorrhizal fungi on plant ...biodiversity likely depends on the strength of the symbiosis between the plant and fungi, the differential plant growth responses to mycorrhizal inoculation, and the transfer rate of nutrients from the fungus to plant. However, our current understanding of how nutrient-plant-mycorrhizal interactions influence plant coexistence is conceptual and thus lacks a unified quantitative framework. To quantify the conditions of plant coexistence mediated by mycorrhizal fungi, we developed a mechanistic resource competition model that explicitly included plant-mycorrhizal symbioses. We found that plant-mycorrhizal interactions shape plant coexistence patterns by creating a tradeoff in resource competition. Especially, a tradeoff in resource competition was caused by differential payback in the carbon resources that plants invested in the fungal symbiosis and/or by the stoichiometric constraints on plants that required additional, less-beneficial, resources to sustain growth. Our results suggested that resource availability and the variation in plant-mycorrhizal interactions act in concert to drive plant coexistence patterns. Applying our framework, future empirical studies should investigate plant-mycorrhizal interactions under multiple levels of resource availability.
To maximize limited conservation funds and prioritize management projects that are likely to succeed, accurate assessment of invasive nonnative species impacts is essential. A common challenge to ...prioritization is a limited knowledge of the difference between the impacts of a single nonnative species compared to the impacts of nonnative species when they co-occur, and in particular predicting when impacts of co-occurring nonnative species will be non-additive. Understanding non-additivity is important for management decisions because the management of only one co-occurring invader will not necessarily lead to a predictable reduction in the impact or growth of the other nonnative plant. Nonnative plants are frequently associated with changes in soil biotic and abiotic characteristics, which lead to plant–soil interactions that influence the performance of other species grown in those soils. Whether co-occurring nonnative plants alter soil properties additively or non-additively relative to their effects on soils when they grow in monoculture is rarely addressed. We use a greenhouse plant–soil feedback experiment to test for non-additive soil impacts of two common invasive nonnative woody shrubs, Lonicera maackii and Ligustrum sinense, in deciduous forests of the southeastern United States. We measured the performance of each nonnative shrub, a native herbaceous community, and a nonnative woody vine in soils conditioned by each shrub singly or together in polyculture. Soils conditioned by both nonnative shrubs had non-additive impacts on native and nonnative performance. Root mass of the native herbaceous community was 1.5 times lower and the root mass of the nonnative L. sinense was 1.8 times higher in soils conditioned by both L. maackii and L. sinense than expected based upon growth in soils conditioned by either shrub singly. This result indicates that when these two nonnative shrubs co-occur, their influence on soils disproportionally favors persistence of the nonnative L. sinense relative to this native herbaceous community, and could provide an explanation of why native species abundance is frequently depressed in these communities. Additionally, the difference between native and nonnative performance demonstrates that invasive impact studies focusing on the impact only of single species can be insufficient for determining the impact of co-occurring invasive plant species.
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