Current theory (e.g., consumer‐controlled theory) predicts that nutrient enrichment typically amplifies herbivory and thereby suppresses the growth and expansion of invasive plants. Herbivores can facilitate plant regrowth in the native community by stimulating complementary growth or ameliorating habitat conditions (e.g., by increasing soil oxygen and nutrient availability), but whether they have similar positive effects on invasive plants, especially under nutrient enrichment, remains unknown. Using a field nitrogen (N)‐enrichment × crab exclusion experiment, we evaluated and compared the effects of both N enrichment and crab herbivory on the growth performance of a global invasive cordgrass, Spartina alterniflora, and a co‐occurring native plant, Phragmites australis. We found that crabs consistently suppressed P. australis by density and aboveground biomass regardless of N enrichment. In contrast, for S. alterniflora, the negative effects of crabs under ambient N were replaced by positive effects under N enrichment, with crabs stimulating complementary increases in density and aboveground biomass. The differing effects between the N treatments were driven by crab burrowing activity, which increased soil N availability, and the nutrient‐use efficiency of S. alterniflora. Our findings revealed that native herbivores can have opposing effects on native and invasive plants, which broadens our understanding of how exotic plants can achieve dominance in a changing world.

Recent discoveries of methyl-coenzyme M reductase–encoding genes ( mcr ) in uncultured archaea beyond traditional euryarchaeotal methanogens have reshaped our view of methanogenesis. However, whether any of these nontraditional archaea perform methanogenesis remains elusive. Here, we report field and microcosm experiments based on 13 C-tracer labeling and genome-resolved metagenomics and metatranscriptomics, revealing that nontraditional archaea are predominant active methane producers in two geothermal springs. Archaeoglobales performed methanogenesis from methanol and may exhibit adaptability in using methylotrophic and hydrogenotrophic pathways based on temperature/substrate availability. A five-year field survey found Candidatus Nezhaarchaeota to be the predominant mcr -containing archaea inhabiting the springs; genomic inference and mcr expression under methanogenic conditions strongly suggested that this lineage mediated hydrogenotrophic methanogenesis in situ. Methanogenesis was temperature-sensitive , with a preference for methylotrophic over hydrogenotrophic pathways when incubation temperatures increased from 65° to 75°C. This study demonstrates an anoxic ecosystem wherein methanogenesis is primarily driven by archaea beyond known methanogens, highlighting diverse nontraditional mcr -containing archaea as previously unrecognized methane sources.

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<p>Microbial respiration is the main process contributing to soil carbon (C) loss and is simultaneously regulated by changes in mean temperature and temperature fluctuation. The magnitude of the feedback between soil microbial respiration and increased mean temperature may decrease (i.e., thermal adaptation) or increase over time, and accurately representing this feedback within models improves predictions of soil C loss rates. However, climate change entails changes not only in mean thermal conditions but also in the patterns of temperature fluctuation, and whether temperature fluctuation could also cause thermal adaptation has never been addressed. Here, we collected soil samples from 6 sites along a 2,000-km-long west-east transect extending across subtropical forests in China and used them in an incubation experiment involving various temperature regimes to explore how temperature fluctuation influences the thermal response of soil microbial respiration and the underlying mechanisms of this process. We revealed that soil biomass-specific microbial respiration (<em>R</em><sub>mass</sub>) was significantly lower with increasing temperature fluctuation during incubation regardless of the assay temperature, while a positive relationship between <em>R</em><sub>mass</sub> and temperature was observed under increased constant incubation temperature. Structural equation modelling further indicated that increased bacterial species turnover and reduced substrate affinity (<em>K</em><sub>m</sub>) promoted the decrease in<em> R</em><sub>mass</sub> associated with greater temperature variation. Our results demonstrate that if such an adaptive response of soil microbial respiration occurs under greater temperature variation, the stimulatory effect of climate warming may be less than that predicted and thus may not increase atmospheric CO<sub>2</sub> concentrations as much as anticipated.</p>