Effects of climate warming on carbon fluxes in grasslands— A global meta‐analysis

Abstract

Climate warming will affect terrestrial ecosystems in many ways, and warming‐induced changes in terrestrial carbon (C) cycling could accelerate or slow future warming. So far, warming experiments have shown a wide range of C flux responses, across and within biome types. However, past meta‐analyses of C flux responses have lacked sufficient sample size to discern relative responses for a given biome type. For instance grasslands contribute greatly to global terrestrial C fluxes, and to date grassland warming experiments provide the opportunity to evaluate concurrent responses of both plant and soil C fluxes. Here, we compiled data from 70 sites (in total 622 observations) to evaluate the response of C fluxes to experimental warming across three grassland types (cold, temperate, and semi‐arid), warming methods, and short (≤3 years) and longer‐term (>3 years) experiment lengths. Overall, our meta‐analysis revealed that experimental warming stimulated C fluxes in grassland ecosystems with regard to both plant production (e.g., net primary productivity (NPP) 15.4%; aboveground NPP (ANPP) by 7.6%, belowground NPP (BNPP) by 11.6%) and soil respiration (Rs) (9.5%). However, the magnitude of C flux stimulation varied significantly across cold, temperate and semi‐arid grasslands, in that responses for most C fluxes were larger in cold than temperate or semi‐arid ecosystems. In semi‐arid and temperate grasslands, ecosystem respiration (Reco) was more sensitive to warming than gross primary productivity (GPP), while the opposite was observed for cold grasslands, where warming produced a net increase in whole‐ecosystem C storage. However, the stimulatory effect of warming on ANPP and Rs observed in short‐term studies (≤3 years) in both cold and temperate grasslands disappeared in longer‐term experiments (>3 years). These results highlight the importance of conducting long‐term warming experiments, and in examining responses across a wide range of climate.

Multiple‐scale negative impacts of warming on ecosystem carbon use efficiency across the Tibetan Plateau grasslands

“…The higher sensitivity of GEP than ER to warming in this study has been well documented for temperate grasslands (Niu et al., 2008), alpine meadows (Zhu et al., 2017) and global vegetation (Wang et al., 2019). The SSWE and SWE observations of this study found that the downward slopes of GEP along rising temperature gradients were steeper than those of ER.…”

“…Even considering the interannual variability of environmental factors, our previous study reported that the responses of ER to variations in precipitation and temperature were weaker in HW than in LW treatments (N. Chen, Zhang, et al., 2019). Over longer time periods, accelerated decomposition may decrease soil organic carbon and nitrogen pools as a new ecosystem balance is approached (Lu et al., 2013; Wang et al., 2019). Moreover, shifts in soil microbial CUE and community structure may reduce the temperature sensitivity of R h after long‐term warming (J. Zhou et al., 2011).…”

Biotic rescaling reveals importance of species interactions for variation in biodiversity responses to climate change

“…This is because many different environmental factors influence biotic interactions through the same underlying biological mechanisms, and these diverse environmental factors should then be reflected in the same biological variables. For example, in herbaceous plant communities, either warmer or wetter conditions often lead to increased biomass or height (24,25), which leads to increased competition for light, which, in turn, determines which species are able to persist in the community. In this example, biomass or height serves as a proxy for the magnitude and mode of competitive interactions that determine community responses such as species composition or diversity.…”

Non-linear responses of net ecosystem productivity to gradient warming in a paddy field in Northeast China

“…For example, Welker et al (2004) found an increasing NEP after warming by conducting a warming experiment in a High Arctic tundra, which increased the air temperature approximately 1-1.5 • C. Ganjurjav et al (2015) found that warming in an alpine meadow on the central Qinghai-Tibetan Plateau prompted NEP. Though some previous works found that NEP decreased with the increasing temperature (Jiang et al, 2012;Wang et al, 2019a), the decreasing NEP in previous works may have been the result of drought. During drought, the increasing temperature may stimulate decomposition and ER but may contribute little to GPP as water, which results in an NEP decrease.…”