Stratification of carbon fractions and carbon management index in deep soil affected by the Grain-to-Green Program in China.

Fazhu Zhao,Yongzhong Feng,Xinhui Han,Gaihe Yang,Guangxin Ren,Raffaella Balestrini

doi:10.1371/journal.pone.0099657

Abstract

Conversion of slope cropland to perennial vegetation has a significant impact on soil organic carbon (SOC) stock in A horizon. However, the impact on SOC and its fraction stratification is still poorly understood in deep soil in Loess Hilly Region (LHR) of China. Samples were collected from three typical conversion lands, Robinia psendoacacia (RP), Caragana Korshinskii Kom (CK), and abandoned land (AB), which have been converted from slope croplands (SC) for 30 years in LHR. Contents of SOC, total nitrogen (TN), particulate organic carbon (POC), and labile organic carbon (LOC), and their stratification ratios (SR) and carbon management indexes (CMI) were determined on soil profiles from 0 to 200 cm. Results showed that the SOC, TN, POC and LOC stocks of RP were significantly higher than that of SC in soil layers of 0–10, 10–40, 40–100 and 100–200 cm (P<0.05). Soil layer of 100–200 cm accounted for 27.38–36.62%, 25.10–32.91%, 21.59–31.69% and 21.08–26.83% to SOC, TN, POC and LOC stocks in lands of RP, CK and AB. SR values were >2.0 in most cases of RP, CK and AB. Moreover, CMI values of RP, CK, and AB increased by 11.61–61.53% in soil layer of 100–200 cm compared with SC. Significant positive correlations between SOC stocks and CMI or SR values of both surface soil and deep soil layers indicated that they were suitable indicators for soil quality and carbon changes evaluation. The Grain-to-Green Program (GTGP) had strong influence on improving quantity and activity of SOC pool through all soil layers of converted lands, and deep soil organic carbon should be considered in C cycle induced by GTGP. It was concluded that converting slope croplands to RP forestlands was the most efficient way for sequestering C in LHR soils.

Highlights

Soil organic carbon (SOC) is a dynamic component of the terrestrial system, with internal changes in both vertical and horizontal directions and external exchanges between the atmosphere and the biosphere [1]
In all land use types, contents of SOC, total nitrogen (TN), particulate organic carbon (POC) and labile organic carbon (LOC) in top soil (0–10 cm) were 3.26–7.86 g.kg21, 0.39–0.72 g.kg21, 0.65–1.31 g.kg21 and 0.76–1.07 g.kg21, respectively, which were significantly higher than other soil layers (P,0.05)
We found that SOC, TN, POC and LOC stocks of Robinia psendoacacia (RP), Caragana Korshinskii Kom (CK), and abandoned land (AB) were higher than slope croplands (SC) for different soil profiles, especially in depths of 40–100 cm and 100–200 cm (Fig. 4 and 5)

Summary

Introduction

Soil organic carbon (SOC) is a dynamic component of the terrestrial system, with internal changes in both vertical and horizontal directions and external exchanges between the atmosphere and the biosphere [1]. SOC storage is estimated at approximately 1500 Pg globally, which is about two and three times the size of carbon pools in the atmosphere and vegetation, respectively [2]. Since carbon uptake and storage is tightly linked to the nitrogen (N) cycle, it is important to understand how N pools and fluxes are affected by land use change [3]. More than 50% of the total SOC is stored in the subsoil [4]. Considering the potential role of SOC in atmospheric CO2 sink, it is important to understand what leads to sequestration of large amounts of SOC in the subsoil or even in deep soil. The SOC contents in deep soil layers are not fully understood in LHR of China to date

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