Global changes and human disturbances can strongly affect the quantity of aboveground litter entering soils, which could result in substantial cascading effects on soil biogeochemical processes in forests. Despite extensive reports, it is unclear how the variations in litter depth affect soil carbon and nitrogen cycling. The responses of soil carbon and nitrogen to the variability of litter inputs were examined in a coniferous–broadleaf mixed forest of Central China. The litter input manipulation included five treatments: no litter input, natural litter, double litter, triple litter, and quadruple litter. Multifold litter additions decreased soil temperature but did not affect soil moisture after 2.5 years. Reductions in soil pH under litter additions were larger than increases under no litter input. Litter quantity did not affect soil total organic carbon, whereas litter addition stimulated soil dissolved organic carbon more strongly than no litter input suppressed it. The triggering priming effect of litter manipulation on soil respiration requires a substantial litter quantity, and the impacts of a slight litter change on soil respiration are negligible. Litter quantity did not impact soil total nitrogen, and only strong litter fluctuations changed the content of soil available nitrogen (nitrate nitrogen and ammonium nitrogen). Litter addition enhanced soil microbial biomass carbon and nitrogen more strongly than no litter input. Our results imply that the impacts of multifold litter inputs on soil carbon and nitrogen are different with a single litter treatment. These findings suggest that variability in aboveground litter inputs resulting from environmental change and human disturbances have great potential to change soil carbon and nitrogen in forest ecosystems. The variability of aboveground litter inputs needs to be taken into account to predict the responses of terrestrial soil carbon and nitrogen cycling to environmental changes and forest management.

Multitrophic interactions can strongly influence the structure and functioning of ecosystems, but how plant diversity influences the direction and predictability of multitrophic interactions across agricultural and natural ecosystems remains unclear. Using 149 field studies across five continents, we found that, on average, increasing plant diversity tended to exert differential top-down and bottom-up effects in croplands versus grasslands and forests. Organic and nonorganic croplands exhibited 846 and 148% higher invertebrate natural enemy-to-herbivore abundance ratios under increased plant diversity, consistent with top-down control patterns where predator gains cause herbivore declines, enhancing crop outcomes. In grasslands and forests, increasing plant diversity was associated with bottom-up effects where enhanced productivity increased both herbivore and predator populations, with the enemy-to-herbivore ratio increasing 4.73% for grasslands and 21.2% for forests. Our findings suggest that biodiversity effects on productivity are not solely explained by direct plant-plant interactions and the resulting biodiversity-productivity relationship. Rather, they reveal patterns consistent with the framework of top-down and bottom-up effects, the relative balance of which may vary depending on ecosystem and management type. The magnitude of the effects of diversified farming on crop pests suggests that crop diversification may be an important avenue for managing crop pests preventatively and thereby enhancing agricultural sustainability.

Reconciling agricultural productivity with greenhouse gas (GHG) mitigation remains a pivotal challenge for achieving climate-smart food systems. This study evaluates the capacity of legume-based crop rotations to balance economic viability, yield stability, and GHG reduction in the North China Plain. A two-year randomized complete block field experiment compared six cropping systems: conventional wheat–maize (WM) rotations and legume-integrated systems (wheat–soybean, WS; wheat–soybean–maize, WSM), under fertilized and unfertilized regimes. Results revealed that nitrogen fertilization increased cumulative N₂O emissions and global warming potential (GWP), with seasonal peaks occurring post-fertilization. Legume systems enhanced CH₄ uptake but showed no significant effect on N₂O emissions compared to conventional systems. N₂O fluxes correlated positively with soil moisture and soil temperature, while CH₄ uptake increased with soil moisture alone. Soybean phases reduced short-term yields by 32–52% relative to the maize yield of conventional systems, but boosted subsequent wheat/maize productivity by 2–47% through hydraulic redistribution and N priming. The wheat–soybean rotation with 200 kg N ha⁻¹ (WS200) achieved optimal sustainability, delivering the highest net profit (8061.56 USD ha⁻¹) alongside a 9% reduction in global warming potential (3980.21 kg CO_2-eq ha⁻¹) versus conventional systems. These findings provide actionable insights for sustainable intensification in global cereal systems, demonstrating that strategic legume integration can advance both food security and climate goals.