Warming and altered precipitation rarely alter N addition effects on soil greenhouse gas fluxes:a meta-analysis

Background Changes in soil greenhouse gas(GHG)fluxes caused by nitrogen(N)addition are considered as the key factors contributing to global climate change(global warming and altered precipitation regimes),which in turn alters the feedback between N addition and soil GHG fluxes.However,the effects of N addition on soil GHG emissions under climate change are highly variable and context-dependent,so that further syntheses are required.Here,a meta-analysis of the interactive effects of N addition and climate change(warming and altered precipitation)on the fluxes of three main soil GHGs[carbon dioxide(CO_(2)),methane(CH_(4)),and nitrous oxide(N_(2)O)]was conducted by synthesizing 2103 observations retrieved from 57 peer-reviewed articles on multiple terrestrial ecosystems globally.Results The interactive effects of N addition and climate change on GHG fluxes were generally additive.The combination of N addition and warming or altered precipitation increased N_(2)O emissions significantly while it had minimal effects on CO_(2)emissions and CH_(4)uptake,and the effects on CH_(4)emissions could not be evaluated.Moreover,the magnitude of the combined effects did not differ significantly from the effects of N addition alone.Apparently,the combined effects on CO_(2)and CH_(4)varied among ecosystem types due to differences in soil moisture,which was in contrast to the soil N_(2)O emission responses.The soil GHG flux responses to combined N addition and climate change also varied among different climatic conditions and experimental methods.Conclusion Overall,our findings indicate that the effects of N addition and climate change on soil GHG fluxes were relatively independent,i.e.combined effects of N addition and climate change were equal to or not significantly different from the sum of their respective individual effects.The effects of N addition on soil GHG fluxes influence the feedbacks between climate change and soil GHG fluxes.

Drought decreases the positive impact of warming on an alpine grassland community

Temperature and precipitation are the main factors determining plant community succession and aboveground net primary productivity(ANPP)in natural grasslands.However,most climate manipulative experiments have mainly focused on their impacts in isolation,especially in alpine regions.Here we explored the relative effects and interaction of warming and precipitation alteration on succession and ANPP using a 7-year experiment involving warming with precipitation alteration(increase(IP)or decrease(DP))in precipitation relative to ambient precipitation(AP)on the Tibetan Plateau.Our results showed that warming and warm-wet conditions increased species richness,diversity index,height and cover of overall species.Conversely,decreasing precipitation reduced them,but increased S.purpurea and the rate of change in community composition.Importantly,warming mitigated the impacts of decreased precipitation on plant community composition,and the interactive effects of warming and altered precipitation on cover,height and plant ANPP varied with year and plant species.Generally,warming increased community ANPP through increases in forb ANPP or non-dominant species ANPP and biodiversity regardless of change in precipitation.However,decreased precipitation reduced community ANPP via decreases in the ANPP of sedges and forbs and biodiversity.Precipitation alteration affected the relationship between biodiversity and community ANPP regardless of warming(IP<AP<DP).Therefore,generally warming and decreased precipitation have opposite effects on ANPP in the alpine grassland,suggesting that warming mitigated the negative impacts of drought on the ANPP of the alpine grassland.