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Extreme climatic events are likely to intensify under climate change and can have different effects on ecosystems depending on their timing and magnitude. Understanding how productivity responds to extreme precipitation patterns requires assessing stability and vulnerability during critical growing periods at the plant community level. In this study, we experimentally imposed two contrasting types of extreme precipitation patterns, including extreme drought (excluding all rainfall for 30 consecutive days) during early-, mid-, and late-stages of the growing season, and heavy rainfall (adding 14.1 mm of rainfall every day for 20 consecutive days) during mid- and late-stages of the growing season over four years (2013–2016) in a steppe community in Inner Mongolia, China. We found that extreme drought and heavy rainfall had no effect on community aboveground net primary productivity (ANPP), species richness, and dominance at any stage of the growing season. Community stability in response to extreme drought was mainly driven by compensation among species and the stability of dominant species, while the compensatory effect among species and functional groups, and the stability of dominant species contributed to the community stability in response to heavy rainfall. Overall, our findings indicate that the responses of the ecosystem to intra-seasonal contrasting extreme precipitation patterns can be driven by similar stability mechanisms and suggest that semiarid temperate steppe communities may have strong initial resistance to more frequent extreme climatic events in the future. [ABSTRACT FROM AUTHOR]

Summary: Heavy rainfall events are expected to increase in frequency and severity in the future. However, their effects on natural ecosystems are largely unknown, in particular with different seasonal timing of the events and recurrence over multiple years.We conducted a 4 yr manipulative experiment to explore grassland response to heavy rainfall imposed in either the middle of, or late in, the growing season in Inner Mongolia, China. We measured hierarchical responses at individual, community and ecosystem levels.Surprisingly, above‐ground biomass remained stable in the face of heavy rainfall, regardless of seasonal timing, whereas heavy rainfall late in the growing season had consistent negative impacts on below‐ground and total biomass. However, such negative biomass effects were not significant for heavy rainfall in the middle of the growing season. By contrast, heavy rainfall in the middle of the growing season had greater positive effects on ecosystem CO2 exchanges, mainly reflected in the latter 2 yr of the 4 yr experiment. This two‐stage response of CO2 fluxes was regulated by increased community‐level leaf area and leaf‐level photosynthesis and interannual variability of natural precipitation.Overall, our study demonstrates that ecosystem impacts of heavy rainfall events crucially depend on the seasonal timing and multiannual recurrence. Plant physiological and morphological adjustment appeared to improve the capacity of the ecosystem to respond positively to heavy rainfall. [ABSTRACT FROM AUTHOR]

Increasing heavy rainfalls can strongly affect ecosystem nitrogen (N) cycling processes and thereby alter soil N fluxes and pools. However, the effects of heavy rainfalls on soil N fluxes and pools are poorly understood, particularly with regards to high rainfall timing under field conditions. We conducted a 3-year (2014–2016) manipulative experiment in which heavy rainfall was imposed in middle (plant peak growing stage) or late (plant senescent growth stage) growing season in a semiarid grassland of Inner Mongolia, China to explore the responses of N 2 O fluxes and soil total N contents and the underlying microbial mechanisms. Mid-season heavy rainfall promoted soil N 2 O emissions by 65% on average across the three years, attributable mainly to increases in denitrifying nirK and nirS abundances induced large denitrification at higher soil water contents. However, archaeal and bacterial amoA and narG genes did not change significantly due probably to counteracting effects of increased soil water content (positive) and soil pH (negative). Mid-season heavy rainfall led to 17% reduction in soil total N by the end of the last year of the study (2016), partly due to the enhanced accumulated N 2 O emissions over the three years. In contrast, late-season heavy rainfall did not change N 2 O emissions and soil total N contents even though soil water content, soil pH and nirK and nirS abundance were significantly increased, perhaps due to limitation by low temperature. Timing of the heavy rainfall events during the plant growing season strongly influenced their impacts on soil N fluxes and pools and heavy rainfalls in the peak stage of plant growth may potentially cause a positive feedback to global warming and exacerbate N limitation in terrestrial ecosystems. • N 2 O flux and soil total N responses to heavy rainfall depended on seasonal timing. • Mid-season heavy rainfall increased N 2 O flux by 65% due to higher denitrification. • Enhanced N 2 O emissions coincided with 17% of reduction in soil total N. • Late-season heavy rainfall did not change N 2 O emissions and soil total N contents. [ABSTRACT FROM AUTHOR]