Priming effects on labile and stable soil organic carbon decomposition: Pulse dynamics over two years.

Xiuwei Zhang,Xiaozeng Han,Peng Wang,Wantai Yu,Weixin Cheng,Ben Bond-Lamberty

doi:10.1371/journal.pone.0184978

Abstract

Soil organic carbon (SOC) is a major component in the global carbon cycle. Yet how input of plant litter may influence the loss of SOC through a phenomenon called priming effect remains highly uncertain. Most published results about the priming effect came from short-term investigations for a few weeks or at the most for a few months in duration. The priming effect has not been studied at the annual time scale. In this study for 815 days, we investigated the priming effect of added maize leaves on SOC decomposition of two soil types and two treatments (bare fallow for 23 years, and adjacent old-field, represent stable and relatively labile SOC, respectively) of SOC stabilities within each soil type, using a natural 13C-isotope method. Results showed that the variation of the priming effect through time had three distinctive phases for all soils: (1) a strong negative priming phase during the first period (≈0–90 days); (2) a pulse of positive priming phase in the middle (≈70–160 and 140–350 days for soils from Hailun and Shenyang stations, respectively); and (3) a relatively stabilized phase of priming during the last stage of the incubation (>160 days and >350 days for soils from Hailun and Shenyang stations, respectively). Because of major differences in soil properties, the two soil types produced different cumulative priming effects at the end of the experiment, a positive priming effect of 3–7% for the Mollisol and a negative priming effect of 4–8% for the Alfisol. Although soil types and measurement times modulated most of the variability of the priming effect, relative SOC stabilities also influenced the priming effect for a particular soil type and at a particular dynamic phase. The stable SOC from the bare fallow treatment tended to produce a narrower variability during the first phase of negative priming and also during the second phase of positive priming. Averaged over the entire experiment, the stable SOC (i.e., the bare fallow) was at least as responsive to priming as the relatively labile SOC (i.e., the old-field) if not more responsive. The annual time scale of our experiment allowed us to demonstrate the three distinctive phases of the priming effect. Our results highlight the importance of studying the priming effect by investigating the temporal dynamics over longer time scales.

Highlights

Global soil organic carbon (SOC) stock is largely regulated by plant input from primary production and the release of CO2 from microbial decomposition of SOC [1]
We obtained quantitative priming effects of added maize leaves on SOC decomposition under treatment factors of two soil types (Mollisol from Hailun and Alfisol from Shenyang), two treatments of SOC stabilities within each soil types, and at many different times of measurements throughout 815 days of incubation
Overall the priming effect of added maize leaves on SOC decomposition varied widely during the entire experiment

Summary

Introduction

Global soil organic carbon (SOC) stock is largely regulated by plant input from primary production and the release of CO2 from microbial decomposition of SOC [1]. The role of the priming effect in regulating soil carbon balance has recently become a focal area of research [6]. The potential impact of the priming effect on SOC dynamics is widely recognized [7], incorporating the priming effect into global carbon models remains challenging, mostly due to the large uncertainties associated with both the direction and the magnitude of measured priming effects [8,9]. A crucial research question is: does the priming effect impact the stable SOC fraction more than the labile SOC fraction?

Objectives

Methods

Results

Discussion

Conclusion