The response of soil respiration to precipitation change is asymmetric and differs between grasslands and forests

Abstract

Intensification of the Earth's hydrological cycle amplifies the interannual variability of precipitation, which will significantly impact the terrestrial carbon (C) cycle. However, it is still unknown whether previously observed relationship between soil respiration (Rs) and precipitation remains applicable under extreme precipitation change. By analyzing the observations from a much larger dataset of field experiments (248 published papers including 151 grassland studies and 97 forest studies) across a wider range of precipitation manipulation than previous studies, we found that the relationship of Rs response with precipitation change was highly nonlinear or asymmetric, and differed significantly between grasslands and forests, between moderate and extreme precipitation changes. Response of Rs to precipitation change was negatively asymmetric (concave‐down) in grasslands, and double‐asymmetric in forests with a positive asymmetry (concave‐up) under moderate precipitation changes and a negative asymmetry (concave‐down) under extreme precipitation changes. In grasslands, the negative asymmetry in Rs response was attributed to the higher sensitivities of soil moisture, microbial and root activities to decreased precipitation (DPPT) than to increased precipitation (IPPT). In forests, the positive asymmetry was predominantly driven by the significant increase in microbial respiration under moderate IPPT, while the negative asymmetry was caused by the reductions in root biomass and respiration under extreme DPPT. The different asymmetric responses of Rs between grasslands and forests will greatly improve our ability to forecast the C cycle consequences of increased precipitation variability. Specifically, the negative asymmetry of Rs response under extreme precipitation change suggests that the soil C efflux will decrease across grasslands and forests under future precipitation regime with more wet and dry extremes.

How big is big enough? Surprising responses of a semiarid grassland to increasing deluge size

“…Similarly, there is evidence of both linear and saturating responses of soil respiration with increasing rain event size (Chen et al, 2008, 2009; Munson et al, 2010; Song et al, 2012). A greater number of studies have assessed ecosystem response to seasonal or annual precipitation totals, but have also found variable results, with ANPP, BNPP, and soil respiration exhibiting either a linear or saturating relationship with precipitation amount (Du et al, 2020; Hao et al, 2019; Hsu & Adler, 2014; Kong et al, 2013; Ru et al, 2018; Wilcox et al, 2017; Wu et al, 2018; Zhu et al, 2016). Our results are consistent with a season‐long rainfall manipulation also conducted in this semiarid grassland.…”

“…For canopy greenness, there was clearly a time lag required for plant growth to fully respond to deluges (Figure 3b), and for soil respiration, the largest events likely caused temporary anoxic conditions, reducing soil CO 2 efflux. Prior studies have shown that soil microbial (heterotrophic) respiration is limited by saturated soil conditions (Chen et al, 2009; Du et al, 2020; Yang et al, 2020), but plant root (autotrophic) respiration could also be affected (Ben‐Noah & Friedman, 2018). As the soils dried, and with more time to respond, these daily relationships became linear, and in some cases slightly convex as the smallest deluge treatment plots ceased responding.…”

“…This could result in a saturating, rather than a linear, relationship between ANPP and rain event size. In many ecosystems, this saturating response pattern manifests as “negative asymmetry,” in which ecological processes exhibit greater reductions under dry conditions than increases under equivalent wet conditions (Du et al, 2020; Hsu & Adler, 2014; Hsu et al, 2012; Wilcox et al, 2017; Yang et al, 2020). Semiarid systems have exhibited inconsistent evidence for such asymmetric responses (Felton et al, 2019; Haverd et al, 2017; Wu et al, 2018; Yang et al, 2020; Zhang et al, 2017).…”

Asymmetric responses of terrestrial C:N:P stoichiometry to precipitation change

“…Similar to previous studies (Du et al., 2020; Liu et al., 2016), we standardized the precipitation treatment levels across different studies by converting all of the manipulation levels to a percentage of the annual precipitation (ΔR%). For the studies in which the precipitation treatments were applied seasonally, the ΔR% was calculated as the changes in the amount of precipitation during the treatment period divided by its annual precipitation (Zhou et al, 2018a).…”

“…Nevertheless, such asymmetric responses to changes in precipitation tend to be variable for different ecological processes due to diverse mechanisms, such as belowground C processes, C allocations between above‐ and belowground ecosystems, as well as soil organic C, and their interactions (Luo et al., 2017). Recent evidence suggests that such an asymmetric hypothesis is appropriate for soil microbial communities (Zhou et al., 2018a) and soil respiration (Du et al., 2020). Whether the responses of C:N:P stoichiometry in plant–soil–microorganism systems to precipitation changes follow the predictions of the double asymmetry model remains unclear.…”