skip to main content


Title: Emergent properties of microbial communities drive accelerated biogeochemical cycling in disturbed temperate forests
Abstract

Despite ever‐increasing availability of detailed information about microbial community structure, relationships of microbial diversity with ecosystem functioning remain unclear. We investigated these relationships at the Coweeta Hydrologic Laboratory, where past forest disturbances (e.g., clear‐cut) have altered both ecosystem processes (e.g., increased N export) and microbial communities (e.g., increased bacterial diversity). We sampled soils from disturbed and adjacent reference forests, characterized resident microbial communities, and measured several microbial C‐cycle and N‐cycle process rates. Microbial communities from historically disturbed soils exhibited altered ecosystem functioning, including generally higher rates of C‐ and N‐cycle processes. Disturbed soil microbial communities also exhibited altered ecosystem multifunctionality, a composite variable consisting of all measured process rates as well as extracellular enzyme activities. Although we found few relationships between ecosystem functions and microbial alpha diversity, all functions were correlated with microbial community composition metrics, particularly r:K strategist ratios of bacterial phyla. Additionally, for both ecosystem multifunctionality and specific processes (i.e., C‐ and N‐mineralization), microbial metrics significantly improved models seeking to explain variation in process rates. Our work sheds light on the links between microbial communities and ecosystem functioning and identifies specific microbial metrics important for modeling ecosystem responses to environmental change.

 
more » « less
NSF-PAR ID:
10360531
Author(s) / Creator(s):
 ;  ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Ecology
Volume:
102
Issue:
12
ISSN:
0012-9658
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Ecosystem functions and services are under threat from anthropogenic global change at a planetary scale. Microorganisms are the dominant drivers of nearly all ecosystem functions and therefore ecosystem-scale responses are dependent on responses of resident microbial communities. However, the specific characteristics of microbial communities that contribute to ecosystem stability under anthropogenic stress are unknown. We evaluated bacterial drivers of ecosystem stability by generating wide experimental gradients of bacterial diversity in soils, applying stress to the soils, and measuring responses of several microbial-mediated ecosystem processes, including C and N cycling rates and soil enzyme activities. Some processes (e.g., C mineralization) exhibited positive correlations with bacterial diversity and losses of diversity resulted in reduced stability of nearly all processes. However, comprehensive evaluation of all potential bacterial drivers of the processes revealed that bacterial α diversity per se was never among the most important predictors of ecosystem functions. Instead, key predictors included total microbial biomass, 16S gene abundance, bacterial ASV membership, and abundances of specific prokaryotic taxa and functional groups (e.g., nitrifying taxa). These results suggest that bacterial α diversity may be a useful indicator of soil ecosystem function and stability, but that other characteristics of bacterial communities are stronger statistical predictors of ecosystem function and better reflect the biological mechanisms by which microbial communities influence ecosystems. Overall, our results provide insight into the role of microorganisms in supporting ecosystem function and stability by identifying specific characteristics of bacterial communities that are critical for understanding and predicting ecosystem responses to global change.

     
    more » « less
  2. Biodiversity increases ecosystem functions underpinning a suite of services valued by society, including services provided by soils. To test whether, and how, future environments alter the relationship between biodiversity and multiple ecosystem functions, we measured grassland plant diversity effects on single soil functions and ecosystem multifunctionality, and compared relationships in four environments: ambient conditions, elevated atmospheric CO2, enriched N supply, and elevated CO2 and N in combination. Our results showed that plant diversity increased three out of four soil functions and, consequently, ecosystem multifunctionality. Remarkably, biodiversity-ecosystem function relationships were similarly significant under current and future environmental conditions, yet weaker with enriched N supply. Structural equation models revealed that plant diversity enhanced ecosystem multifunctionality by increasing plant community functional diversity, and the even provision of multiple functions. Conserving local plant diversity is therefore a robust strategy to maintain multiple valuable ecosystem services in both present and future environmental conditions. 
    more » « less
  3. Summary

    Despite the abundance of studies demonstrating the effects of drought on soil microbial communities, the role of land use legacies in mediating these drought effects is unclear. To assess historical land use influences on microbial drought responses, we conducted a drought‐rewetting experiment in soils from two adjacent and currently forested watersheds with distinct land use histories: an undisturbed ‘reference’ site and a ‘disturbed’ site that was clear‐cut and converted to agriculture ~60 years prior. We incubated intact soil cores at either constant moisture or under a drought‐rewet treatment and characterized bacterial and fungal communities using amplicon sequencing throughout the experiment. Bacterial alpha diversity decreased following drought‐rewetting while fungal diversity increased. Bacterial beta diversity also changed markedly following drought‐rewetting, especially in historically disturbed soils, while fungal beta diversity exhibited little response. Additionally, bacterial beta diversity in disturbed soils recovered less from drought‐rewetting compared with reference soils. Disturbed soil communities also exhibited notable reductions in nitrifying taxa, increases in putative r‐selected bacteria, and reductions in network connectivity following drought‐rewetting. Overall, our study reveals historical land use to be important in mediating responses of soil bacterial communities to drought, which will influence the ecosystem‐scale trajectories of these environments under ongoing and future climate change.

     
    more » « less
  4. Abstract

    Human activities have led to increased deposition of nitrogen (N) and phosphorus (P) into soils. Nutrient enrichment of soils is known to increase plant biomass and rates of microbial litter decomposition. However, interacting effects of hydrologic position and associated changes to soil moisture can constrain microbial activity and lead to unexpected nutrient feedbacks on microbial community structure–function relationships. Examining feedbacks of nutrient enrichment on decomposition rates is essential for predicting microbial contributions to carbon (C) cycling as atmospheric deposition of nutrients persists. This study explored how long‐term nutrient addition and contrasting litter chemical composition influenced soil bacterial community structure and function. We hypothesized that long‐term nutrient enrichment of low fertility soils alters bacterial community structure and leads to higher rates of litter decomposition especially for low C:N litter, but low‐nutrient and dry conditions limit microbial decomposition of high C:N ratio litter. We leveraged a long‐term fertilization experiment to test how nutrient enrichment and hydrologic manipulation (due to ditches) affected decomposition and soil bacterial community structure in a nutrient‐poor coastal plain wetland. We conducted a litter bag experiment and characterized litter‐associated and bulk soil microbiomes using 16S rRNA bacterial sequencing and quantified litter mass losses and soil physicochemical properties. Results revealed that distinct bacterial communities were involved in decomposing higher C:N ratio litter more quickly in fertilized compared to unfertilized soils especially under drier soil conditions, while decomposition rates of lower C:N ratio litter were similar between fertilized and unfertilized plots. Bacterial community structure in part explained litter decomposition rates, and long‐term fertilization and drier hydrologic status affected bacterial diversity and increased decomposition rates. However, community composition associated with high C:N litter was similar in wetter plots with available nitrate detected, regardless of fertilization treatment. This study provides insight into long‐term fertilization effects on soil bacterial diversity and composition, decomposition, and the increased potential for soil C loss as nutrient enrichment and hydrology interact to affect historically low‐nutrient ecosystems.

     
    more » « less
  5. Abstract

    Nitrogen (N) deposition increases soil carbon (C) storage by reducing microbial activity. These effects vary in soil beneath trees that associate with arbuscular (AM) and ectomycorrhizal (ECM) fungi. Variation in carbon C and N uptake traits among microbes may explain differences in soil nutrient cycling between mycorrhizal associations in response to high N loads, a mechanism not previously examined due to methodological limitations. Here, we used quantitative Stable Isotope Probing (qSIP) to measure bacterial C and N assimilation rates from an added organic compound, which we conceptualize as functional traits. As such, we applied a trait‐based approach to explore whether variation in assimilation rates of bacterial taxa can inform shifts in soil function under chronic N deposition. We show taxon‐specific and community‐wide declines of bacterial C and N uptake under chronic N deposition in both AM and ECM soils. N deposition‐induced reductions in microbial activity were mirrored by declines in soil organic matter mineralization rates in AM but not ECM soils. Our findings suggest C and N uptake traits of bacterial communities can predict C cycling feedbacks to N deposition in AM soils, but additional data, for instance on the traits of fungi, may be needed to connect microbial traits with soil C and N cycling in ECM systems. Our study also highlights the potential of employing qSIP in conjunction with trait‐based analytical approaches to inform how ecological processes of microbial communities influence soil functioning.

     
    more » « less