Drought effects are pervasive in terrestrial ecosystems, yet there is limited understanding of how drought impacts the transformation of plant carbon (C) inputs to mineral‐associated organic matter (MAOM)—the largest and slowest‐cycling pool of soil organic carbon (SOC). In a 12‐week 13 C‐CO 2 greenhouse labeling experiment, we tracked the formation of MAOM derived from the two dominant sources of plant C input to the mineral...

Continued current emissions of carbon dioxide (CO 2 ) and methane (CH 4 ) by human activities will increase global atmospheric CO 2 and CH 4 concentrations and surface temperature significantly. Fields of paddy rice, the most important form of anthropogenic wetlands, account for about 9% of anthropogenic sources of CH 4 . Elevated atmospheric CO 2 may enhance CH 4 production in rice paddies, potentially reinforcing the increas...

Summary Mineral‐associated microbes drive many critical soil processes, including mineral weathering, soil aggregation and cycling of mineral‐sorbed organic matter. To investigate the interactions between soil minerals and microbes in the rhizosphere, we incubated three types of minerals (ferrihydrite, kaolinite and quartz) and a native soil mineral fraction near roots of a common Californian annual grass, Avena barbata , grow...

While interactions between roots and microorganisms have been intensively studied, we know little about interactions among root‐associated microbes. We used random matrix theory‐based network analysis of 16S rRNA genes to identify bacterial networks associated with wild oat ( Avena fatua ) over two seasons in greenhouse microcosms. Rhizosphere networks were substantially more complex than those in surrounding soils, indicating...

The interface between roots and soil, known as the rhizosphere, is a dynamic habitat in the soil ecosystem. Unraveling the factors that control rhizosphere community assembly is a key starting point for understanding the diversity of plant‐microbial interactions that occur in soil. The goals of this study were to determine how environmental factors shape rhizosphere microbial communities, such as local soil characteristics and...

The rapid increase in microbial activity that occurs when a dry soil is rewetted has been well documented and is of great interest due to implications of changing precipitation patterns on soil C dynamics. Several studies have shown minor net changes in microbial population diversity or abundance following wet‐up, but the gross population dynamics of bacteria and fungi resulting from soil wet‐up are virtually unknown. Here we...

Summary Arbuscular mycorrhizal fungi ( AMF ) perform an important ecosystem service by improving plant nutrient capture from soil, yet little is known about how AMF influence soil microbial communities during nutrient uptake. We tested whether an AMF modifies the soil microbial community and nitrogen cycling during litter decomposition. A two‐chamber microcosm system was employed to create a root‐free soil environment to contr...

The source of microbial C is thought to impact its stability in soil due to variations in cellular biochemistry. It has been hypothesised that a fungal‐dominated community stabilises more C than a bacterial‐dominated community, in part due to chemical recalcitrance of their non‐living biomass, particularly cell wall components and pigments. We compared the turnover of 13 C‐labelled (99.9 atom %) temperate and tropical microbia...

Summary Nitrification and denitrification processes are crucial to plant nutrient availability, eutrophication and greenhouse gas production both locally and globally. Unravelling the major environmental predictors for nitrification and denitrification is thus pivotal in order to understand and model environmental nitrogen (N) cycling. Here, we sampled five plant community types characteristic of interior Alaska, including bla...

Summary Rapidly fluctuating environmental conditions can significantly stress organisms, particularly when fluctuations cross thresholds of normal physiological tolerance. Redox potential fluctuations are common in humid tropical soils, and microbial community acclimation or avoidance strategies for survival will in turn shape microbial community diversity and biogeochemistry. To assess the extent to which indigenous bacterial...

We report that iron‐reducing bacteria are primary mediators of anaerobic carbon oxidation in upland tropical soils spanning a rainfall gradient (3500–5000 mm/yr) in northeast Puerto Rico. The abundant rainfall and high net primary productivity of these tropical forests provide optimal soil habitat for iron‐reducing and iron‐oxidizing bacteria. Spatially and temporally dynamic redox conditions make iron‐transforming microbial c...

Humid tropical forests are generally characterized by the lack of nitrogen (N) limitation to net primary productivity, yet paradoxically have high potential for N loss. We conducted an intensive field experiment with 15 NH 4 and 15 NO 3 additions to highly weathered tropical forest soils in Puerto Rico to determine the relative importance of N retention and loss mechanisms. Over one‐half of all the NH 4 + produced was rapidly...

Plant invasions have dramatic aboveground effects on plant community composition, but their belowground effects remain largely uncharacterized. Soil microorganisms directly interact with plants and mediate many nutrient transformations in soil. We hypothesized that belowground changes to the soil microbial community provide a mechanistic link between exotic plant invasion and changes to ecosystem nutrient cycling. To examine t...

The impact of elevated CO 2 on terrestrial ecosystem C balance, both in sign or magnitude, is not clear because the resulting alterations in C input, plant nutrient demand and water use efficiency often have contrasting impacts on microbial decomposition processes. One major source of uncertainty stems from the impact of elevated CO 2 on N availability to plants and microbes. We examined the effects of atmospheric CO 2 enrichm...