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

Abstract

Background There are many studies on disentangling the responses of autotrophic (AR) and heterotrophic (HR) respiration components of soil respiration (SR) to long-term drought, but few studies have focused on the mechanisms underlying its responses. Methods To explore the impact of prolonged drought on AR and HR, we conducted the 2-year measurements on soil CO2 effluxes in the 7th and 8th year of manipulated throughfall reduction (TFR) in a warm-temperate oak forest. Results Our results showed long-term TFR decreased HR, which was positively related to bacterial richness. More importantly, some bacterial taxa such as Novosphingobium and norank Acidimicrobiia, and fungal Leptobacillium were identified as major drivers of HR. In contrast, long-term TFR increased AR due to the increased fine root biomass and production. The increased AR accompanied by decreased HR appeared to counteract each other, and subsequently resulted in the unchanged SR under the TFR. Conclusions Our study shows that HR and AR respond in the opposite directions to long-term TFR. Soil microorganisms and fine roots account for the respective mechanisms underlying the divergent responses of HR and AR to long-term TFR. This highlights the contrasting responses of AR and HR to prolonged drought should be taken into account when predicting soil CO2 effluxes under future droughts.

Effect of Changes in Throughfall on Soil Respiration in Global Forest Ecosystems: A Meta-Analysis

“…The forest type, a vital part of the stand structure, can affect the variability in the properties of aboveground litter and belowground root biomass and distribution [56,71], which could in turn affect the responses of forest soil respiration to precipitation changes [17,45,[72][73][74]. Soil CO 2 emissions in coniferous forests appear to be insensitive to increased TF (Figure 2b) compared with the control, whereas the responses of the soil CO 2 emissions to TF reduction are more negative in coniferous and mixed forests than in broadleaf forests (Figure 2a).…”

“…The SEM analysis showed that the effect sizes of fine root biomass, soil microbial biomass and dissolved organic C content (e.g., lnR roots , lnR mbc and lnR DOC ) played a substantial role in regulating annual soil CO 2 emissions under the altered TF conditions (Figure 7). The changes in soil microbial biomass C and fine root biomass upon altered precipitation would affect soil heterotrophic and autotrophic respiration [28,73,74], which is likely related to the changes in the lnR CO2 values among the experimental categories. To date, only 10 paired observation data points are available showing the responses of soil heterotrophic respiration and autotrophic res-piration to decreased precipitation in temperate (n = 7) and subtropical broadleaf forests (n = 3) [21,28,73,74,90,91].…”

“…The changes in soil microbial biomass C and fine root biomass upon altered precipitation would affect soil heterotrophic and autotrophic respiration [28,73,74], which is likely related to the changes in the lnR CO2 values among the experimental categories. To date, only 10 paired observation data points are available showing the responses of soil heterotrophic respiration and autotrophic res-piration to decreased precipitation in temperate (n = 7) and subtropical broadleaf forests (n = 3) [21,28,73,74,90,91]. On average, annual soil autotrophic respiration upon decreased precipitation was increased by 33.4% (95% CI: −24.0% to 134.1%) in temperate forests, while it was decreased by 54.0% (95% CI: −79.7% to 4.2%) in subtropical forests.…”