Factors affecting spatial variation of annual apparent Q₁₀ of soil respiration in two warm temperate forests.

Junwei Luan,Xueling Zhu,Jingxin Wang,Shirong Liu

doi:10.1371/journal.pone.0064167

Abstract

A range of factors has been identified that affect the temperature sensitivity (Q10 values) of the soil-to-atmosphere CO2 flux. However, the factors influencing the spatial distribution of Q10 values within warm temperate forests are poorly understood. In this study, we examined the spatial variation of Q10 values and its controlling factors in both a naturally regenerated oak forest (OF) and a pine plantation (PP). Q10 values were determined based on monthly soil respiration (RS) measurements at 35 subplots for each stand from Oct. 2008 to Oct. 2009. Large spatial variation of Q10 values was found in both OF and PP, with their respective ranges from 1.7 to 5.12 and from 2.3 to 6.21. In PP, fine root biomass (FR) (R = 0.50, P = 0.002), non-capillary porosity (NCP) (R = 0.37, P = 0.03), and the coefficients of variation of soil temperature at 5 cm depth (CV of T5) (R = −0.43, P = 0.01) well explained the spatial variance of Q10. In OF, carbon pool lability reflected by light fractionation method (LLFOC) well explained the spatial variance of Q10 (R = −0.35, P = 0.04). Regardless of forest type, LLFOC and FR correlation with the Q10 values were significant and marginally significant, respectively; suggesting a positive relationship between substrate availability and apparent Q10 values. Parameters related to gas diffusion, such as average soil water content (SWC) and NCP, negatively or positively explained the spatial variance of Q10 values. Additionally, we observed significantly higher apparent Q10 values in PP compared to OF, which might be partly attributed to the difference in soil moisture condition and diffusion ability, rather than different substrate availabilities between forests. Our results suggested that both soil chemical and physical characters contributed to the observed large Q10 value variation.

Highlights

Soils are the largest carbon pool in the terrestrial ecosystem, estimated to contain almost three times as much carbon as the atmosphere between the depths of 0–300 cm of soil [1,2]
We found that stand structure parameters (total basal area, maximum DBH for trees within 4 m of the measurement points) well explained the spatial distribution of fine root biomass [34], which indicated that the spatial pattern of fine root biomass is comparably stable, because stand structure is relatively stable for an ecosystem in a given time
High spatial variation of soil water content (SWC) was found in all measurement campaigns (Fig. 2), with the CV of SWC ranging from 10.7% to 27.2% for pine plantation (PP) and from 10.7% to 26% for oak forest (OF) (Fig. 2)

Summary

Introduction

Soils are the largest carbon pool in the terrestrial ecosystem, estimated to contain almost three times as much carbon as the atmosphere between the depths of 0–300 cm of soil [1,2]. This value is much higher if northern permafrost regions are considered [3]. The response of RS to climate change, which usually is called apparent temperature sensitivity of RS (Q10 value) and estimated based on empirical functions, is of importance in predicting possible feedbacks between the global carbon cycle and the climate system [7]. Empirical response functions are still a valid method to derive annual estimates of RS based on specific field measurements (e.g. Savage et al [10]), when it is not limited by water content and the simulation is made through interpolation rather than extrapolation [11]

Methods

Results

Discussion

Conclusion