Soil fungi and fine root biomass mediate drought‐induced reductions in soil respiration

Abstract

1. Climate change has increased the frequency and intensity of droughts, with potential impacts on carbon (C) release from soil (i.e. soil respiration, Rs). Although numerous studies have investigated drought-induced changes in Rs, how roots and the soil microbial community regulate responses of Rs to drought remains unclear. 2. We conducted a 4-year field experiment (2014-2017) with three treatments (i.e. 70% rainfall reduction, control and ambient) in a subtropical forest to examine effects of drought on Rs and its components [i.e. autotrophic (Ra) and heterotrophic respiration (Rh)] and explore the mechanisms underlying these effects. 3. Drought significantly decreased Rs by 17% averaged over the 4 years, but it had no significant effect in the first experimental year. The decrease in Rs was mediated by soil fungi and fine root biomass. Fine root biomass was correlated negatively with Ra and Rs under drought, but positively in the control treatment. Furthermore, drought treatments increased physiological stress in the bacterial community. Structural equation model (SEM) analysis suggested that under drought conditions, microclimate affected Rs via its impact on fine root biomass and fungal biomass. 4. Our results highlight the complex interactions between microclimate, roots and soil microbes in regulating Rs under drought in subtropical forest ecosystems. Incorporating these interactions into land surface models may improve predictions of climate change impacts on forest ecosystems. K E Y W O R D S C-climate feedback, CO 2 emission, drought, fine root biomass, fungi community, physiological stress, structural equation model 1 | INTRODUC TI ON Earth system models predict that global hydrological cycles will intensify in the next decades (IPCC, 2013), thereby altering the frequency and intensity of precipitation around the world (IPCC, 2013). Consequently, several regions will experience increased droughts, which threaten the biodiversity and stability of terrestrial ecosystems and alter ecosystem structure and function | 2635 Functional Ecology ZHOU et al.

Different mechanisms underlying divergent responses of autotrophic and heterotrophic respiration to long-term throughfall reduction in a warm-temperate oak forest

“…According to the optimal partitioning theory (Bloom et al, 1985), plants should allocate more C to root growth from aboveground parts to reduce water limitation (Fuchslueger et al, 2014). However, many eld throughfall exclusion experiments of forests have shown that ne root biomass did not always support this theory, including increase (Zhou et al, 2020), decrease (Moser et al, 2014), or little change during the rst four years in this study (Lu et al, 2017), indicating that the responses of ne root to water de cit depends on intensity and duration of drought. In our system, we argued that mature trees increased belowground C allocation to adapt to the long-term drought, resulting in the higher AR.…”

“…It has been shown that drought reduced AR, and thus SR, but had no effect on HR in a dry temperate forest (Hinko-Najera et al, 2015). Another study in a subtropical forest found drought decreased both AR and HR, and hence SR (Zhou et al, 2020). A previous study in a warmtemperate oak forest also suggested that drought increased AR but not HR, and therefore SR at a small scale (e.g., 4 m × 4 m roof) throughfall reduction (Liu et al, 2016).…”

Different mechanisms underlying divergent responses of autotrophic and heterotrophic respiration to long-term throughfall reduction in a warm-temperate oak forest

“…According to the optimal partitioning theory (Bloom et al 1985), plants should allocate more C to root growth from aboveground parts to reduce water limitation (Fuchslueger et al 2014). However, many field throughfall exclusion experiments of forests have shown that fine root biomass did not always support this theory, including increase (Zhou et al 2020), decrease (Moser et al 2014), or little change during the first 4 years in this study (Lu et al 2017), indicating that the responses of fine root to water deficit depends on intensity and duration of drought. In our system, we argued that mature trees increased belowground C allocation to adapt to the longterm drought, resulting in the higher AR.…”

“…Another study in a subtropical forest found that drought decreased both AR and HR, resulting in 17% reduction in SR (Zhou et al 2020). However, a previous study in a warm-temperate oak forest suggested that drought increased SR by 26.7% at a small scale (e.g., 4 m × 4 m roof) throughfall reduction, which was mainly attributed to the increase in AR (Liu et al 2016).…”

Roots With Larger Specific Root Length and C: N Ratio Sustain More Complex Nematode Community

“…Nevertheless, numerous studies have shown that greater plant biomass does not always lead to increases in the biomass or abundance of soil micro-organisms. Neutral and negative results have also been reported (Li et al 2021;Zhou et al 2020).…”