Are variations in heterotrophic soil respiration related to changes in substrate availability and microbial biomass carbon in the subtropical forests?

Hui Wei,Sara Vicca,Guoliang Xiao,Xiaomei Chen,Weijun Shen,Bertrand Guenet

doi:10.1038/srep18370

Abstract

Soil temperature and moisture are widely-recognized controlling factors on heterotrophic soil respiration (Rh), although they often explain only a portion of Rh variability. How other soil physicochemical and microbial properties may contribute to Rh variability has been less studied. We conducted field measurements on Rh half-monthly and associated soil properties monthly for two years in four subtropical forests of southern China to assess influences of carbon availability and microbial properties on Rh. Rh in coniferous forest was significantly lower than that in the other three broadleaf species-dominated forests and exhibited obvious seasonal variations in the four forests (P < 0.05). Temperature was the primary factor influencing the seasonal variability of Rh while moisture was not in these humid subtropical forests. The quantity and decomposability of dissolved organic carbon (DOC) were significantly important to Rh variations, but the effect of DOC content on Rh was confounded with temperature, as revealed by partial mantel test. Microbial biomass carbon (MBC) was significantly related to Rh variations across forests during the warm season (P = 0.043). Our results suggest that DOC and MBC may be important when predicting Rh under some conditions, and highlight the complexity by mutual effects of them with environmental factors on Rh variations.

Highlights

Was often based on statistically significant relationships between soil respiration rate and primary productivity[12], photosynthates[18], or litter production[19]
Soil microbial properties including microbial biomass, community composition, and enzyme kinetics are considered important for predicting Rh and SOC storage in recent studies[25,27,28], but they are still poorly represented in terrestrial C cycling models[29]
Most of the precipitation occurred in the warm season at the four sites (Supplementary Fig. S1), soil moistures at 5 cm depth (M5) were significantly different between the warm and cool seasons in the broadleaved forest (BF) (P = 0.045) and not in the other three forests (P = 0.101 for coniferous and broadleaved forest (CF), P = 0.844 for coniferous tree species (CP), and P = 0.159 for broadleaved tree species (BP); Fig. 1d)

Summary

Introduction

Was often based on statistically significant relationships between soil respiration rate and primary productivity[12], photosynthates[18], or litter production[19]. To clarify the substrate-soil respiration relation, further studies remain needed, especially in natural ecosystems where the input of organic materials (e.g., litter and root exudates) may greatly affect the forms and amounts of substrate availability to respiration. Soil microbial properties including microbial biomass, community composition, and enzyme kinetics are considered important for predicting Rh and SOC storage in recent studies[25,27,28], but they are still poorly represented in terrestrial C cycling models[29]. This study was conducted with three objectives: the first was to observe seasonal and forest-type Rh variability in the four subtropical forests, the second to explore potential relationships between substrate availability and the Rh variations, and the third to clarify the role of microbial biomass in soil respiration processes. We aimed to provide empirical evidences for whether substrate availability and microbial biomass C should be taken into account in terrestrial C cycling models

Objectives

Methods

Results

Conclusion