Variations and Indications of δ13CSOC and δ15NSON in Soil Profiles in Karst Critical Zone Observatory (CZO), Southwest China

Man Liu,Guilin Han,Zhaoliang Song,Qian Zhang

doi:10.3390/su11072144

Abstract

Soil carbon and nitrogen storage and stabilization are the key to solving the problems of mitigation of global warming and maintaining of crop productivity. In this study, the contents of soil organic carbon (SOC) and soil organic nitrogen (SON) and their stable isotope compositions (δ13CSOC and δ15NSON) in soil profiles were determined in two agricultural lands (including a farmland and an abandoned farmland) and four non-agricultural lands (including two shrub-grass lands and two shrub lands) in the karst critical zone observatory (CZO), Southwest China. The contents of SOC and SON were used for research on the effects of land use on SOC and SON storage, and the change of δ13CSOC and δ15NSON values in soil profiles were used to indicate SOC and SON stabilization. The results showed that agricultural activities reduced SOC and SON storage in the whole soil layers of farmland compared to non-agricultural lands, and farmland abandonment slightly increased SOC and SON storage. Crop rotation between peanut (C3) and corn (C4) affected the δ13CSOC in surface soils of agricultural lands (−21.6‰), which were intermediate between shrub lands (−22.7‰) and shrub-grass lands (−19.6‰). 15N-depleted SON in surface soils in farmland compared to those soil in other lands possibly associated with synthetic N fertilizer application. In soil layers below 30 cm depth the δ13CSOC deceased with depth, while the δ15NSON displayed irregular fluctuation. The change in δ13CSOC and δ15NSON through soil profiles in karst soils were more intensive than those in semiarid grassland soils indicating the less stabilization of SOC and SON in karst soils.

Highlights

Global population growth in the 21st century leads to an increasing pressure on agricultural productivity, such as food and fiber [1]
Since the vertical change of δ13CSOC with soil, depth is widely used for the indication of the rate of soil organic matter (SOM) decomposition [19]; the research of variation of δ13CSOC in soil profile is beneficial for more accurate interpretation of δ13CSOC as an indicator of C sources based on further understanding the 13C fractionation in SOM decomposition process
In the karst critical zone observatory (CZO) which is located in Puding county, Southwest China, we investigate the karst soil production and erosion processes, and the integrated geophysical–geochemical–ecological responses to anthropogenic perturbations and global climate change [26]

Summary

Introduction

Global population growth in the 21st century leads to an increasing pressure on agricultural productivity, such as food and fiber [1]. Previous studies have reported that agricultural activities, such as application of organic and inorganic fertilizers, irrigation, fallow, and intercultivation, affect SOC and SON storage, greenhouse gas emissions, loss of inorganic N, and soil structure [3,4,5,6,7]. These agricultural activities cause different kinds of feedback on SOC and SON dynamic due to the differences in climate, topography, and soil parent material in some studies [8,9,10]. Since the vertical change of δ13CSOC with soil, depth is widely used for the indication of the rate of SOM decomposition [19]; the research of variation of δ13CSOC in soil profile is beneficial for more accurate interpretation of δ13CSOC as an indicator of C sources based on further understanding the 13C fractionation in SOM decomposition process

Objectives

Methods

Results

Discussion

Conclusion