Catarina S. C. Martins

Grasslands are integral to maintaining biodiversity and key ecosystem services and are under threat from climate change. Plant and soil microbial diversity, and their interactions, support the provision of multiple ecosystem functions (multifunctionality). However, it remains virtually unknown whether plant and soil microbial diversity explain a unique portion of total variation or shared contributions to supporting multifunctionality across global grasslands. Here, we combine results from a global survey of 101 grasslands with a novel microcosm study, controlling for both plant and soil microbial diversity to identify their individual and interactive contribution to support multifunctionality under aridity and experimental drought. We found that plant and soil microbial diversity independently predict a unique portion of total variation in above- and belowground functioning, suggesting that both types of biodiversity complement each other. Interactions between plant and soil microbial diversity positively impacted multifunctionality including primary production and nutrient storage. Our findings were also climate context dependent, since soil fungal diversity was positively associated with multifunctionality in less arid regions, while plant diversity was strongly and positively linked to multifunctionality in more arid regions. Our results highlight the need to conserve both above- and belowground diversity to sustain grassland multifunctionality in a drier world and indicate climate change may shift the relative contribution of plant and soil biodiversity to multifunctionality across global grasslands.

Grasslands are integral to maintaining biodiversity and key ecosystem services under climate change. Plant and soil biodiversity, and their interactions, support the provision of multiple ecosystem functions (multifunctionality). However, whether plant and soil biodiversity explain unique, or shared, contributions to supporting multifunctionality across global grasslands remains virtually unknown. Here, we combine results from a global survey of 101 grasslands with a novel microcosm study, controlling for both plant and soil microbial diversity to identify their individual and interactive contribution to support multifunctionality under aridity and experimental drought. We found that, plant and soil microbial diversity independently predict a unique portion of variation in above- and belowground functioning, suggesting both types of biodiversity complement each other. Interactions between plant and soil microbial diversity regulated primary productivity, nutrient storage, and plant productivity. Our findings were also context dependent, since soil fungal diversity was strongly associated to multifunctionality in less arid regions, while plant diversity was strongly linked to multifunctionality in more arid regions. Our results highlight the need to conserve both above- and belowground diversity to sustain grassland multifunctionality in a drier world and indicate climate change may shift the relative contribution of plant and soil biodiversity to multifunctionality across global grasslands.

Free‐air carbon dioxide enrichment (FACE) experiments in terrestrial ecosystems have demonstrated ecological responses of key ecosystem processes to rising atmospheric carbon dioxide (CO₂). However, CO₂ fertilization responses in field conditions have seldom included methane (CH₄) and nitrous oxide (N₂O), particularly in natural and mature forests, which are expected to have an important role in climate change mitigation. Herein, we aimed to capture the effect of elevated CO₂ (eCO₂; ambient vs. +150 ppm) on long‐term temporal dynamics of CH₄ and N₂O fluxes, followed by identification of climo‐edaphic factors explaining feedback responses. To achieve this, continuous monitoring of greenhouse gas (GHG) fluxes using a manual chamber technique, over a 3‐year period was implemented in a mature dryland Eucalypt forest FACE (EucFACE) facility in Australia. The relationship between CH₄ and N₂O fluxes with rainfall indices and soil properties was also explored since they directly impact the microbial communities in the soil responsible for CH₄ and N₂O net emissions. Our results showed that in 3 years of eCO₂ treatment, the amount and frequency of rainfall predicted GHG emissions in this native forest. We also found a significant reduction in CH₄ sink (15%–25%) for some of the years as well as an overall treatment effect index reduction in N₂O emissions under eCO₂. Higher frequency of rain events with lower intensity led to highest CH₄ sink followed by lowest N₂O emissions due to fewer wet–dry cycles. Of all the environmental variables included, soil moisture, rainfall and pH were the main predictors of net CH₄ and N₂O emissions. Methane flux was also strongly influenced by soil texture. Our findings highlight the need to account for reduced forest CH₄ sink under eCO₂ in dryland ecosystems, which has implications for GHG budget predictions under future climate conditions. A free Plain Language Summary can be found within the Supporting Information of this article.

Atmospheric concentrations of carbon dioxide ( CO ₂ ), methane ( CH ₄ ) and nitrous oxide (N ₂ O) are predicted to increase as a consequence of fossil fuel emissions and the impact on biosphere–atmosphere interactions. Forest ecosystems in general, and forest soils in particular, can be sinks or sources for CO ₂ , CH ₄ , and N ₂ O. Environmental studies traditionally target soil temperature and moisture as the main predictors of soil greenhouse gas ( GHG ) flux from different ecosystems; however, these emissions are primarily biologically driven. Thus, little is known about the degree of regulation by soil biotic vs. abiotic factors on GHG emissions, particularly under predicted increase in global temperatures, and changes in intensity and frequency of precipitation events. Here we measured net CO ₂ , CH ₄ and N ₂ O fluxes after 5 years of experimental warming (+3.4°C), and 2 years of ≈45% summer rainfall reduction, in two forest sites in a boreal–temperate ecotone under different habitat conditions (closed or open canopy) in Minnesota, USA . We evaluated the importance of microbial gene abundance and climo‐edaphic factors (soil texture, canopy, seasonality, climate, and soil physicochemical properties) driving GHG emissions. We found that changes in CO ₂ fluxes were predominantly determined abiotically by temperature and moisture, after accounting for bacterial abundance. Methane fluxes on the other hand, were determined both abiotically, by gas diffusivity (via soil texture) and microbially, by methanotroph pmoA gene abundance, whereas, N ₂ O emissions showed only a strong biotic regulation via ammonia‐oxidizing bacteria amoA gene abundance. Warming did not significantly alter CO ₂ and CH ₄ fluxes after 5 years of manipulation, while N ₂ O emissions were greater with warming under open canopy. Our findings provide evidence that soil GHG emissions result from multiple direct and indirect interactions of microbial and abiotic drivers. Overall, this study highlights the need to include both microbial and climo‐edaphic properties in predictive models in order to provide improved mechanistic understanding for the development of future mitigation strategies. A plain language summary is available for this article.