Carbon Mineralization under Different Saline—Alkali Stress Conditions in Paddy Fields of Northeast China

Sining Wang,Jingjing Wang,Zihao Zhou,Zhaoyang Li,Yunke Qu,Zhenxue Dai,Jie Tang,Yuqing Liu

doi:10.3390/su12072921

Abstract

Soil organic carbon (SOC) mineralization (conversion of carbonaceous material to carbon dioxide) plays a central role in global carbon cycle. However, the effects of SOC mineralization under different saline–alkali stress conditions are poorly understood. In order to understand the carbon mineralization processes, four paddy fields with different saline and alkali degrees were chosen as the experimental samples and the soil CO2 emission fluxes at nine different time steps of the whole simulation experiment were observed. The physical and chemical properties of soils of four field conditions were compared for the dynamic changes of CO2 flux in the progress of paddy field cultivation simulations. The results showed that the first three fields (P1, P2, and P3) were weakly alkaline soils and the last one (P4) was strongly alkaline soil. The SOC content of each plot was significantly different and there was a near-surface enrichment, which was significantly negatively correlated with the degree of alkalization. The accumulation process of the SOC mineralization during the incubation time was consistent with the first-order kinetic model. In the initial stage of mineralization, the amount of CO2 released massively, and then the release intensity decreased rapidly. The mineralization rate decreased slowly with time and finally reached a minimum at the end of the incubation period. This study indicates that the SOC mineralization process is affected by a variety of factors. The main factors influencing SOC mineralization in the saline–alkaline soils are the exchangeable sodium percentage (ESP), followed by enzyme activities. Salinization of the soils inhibits the rate of soil carbon cycle, which has a greater impact on the carbon sequestration than on the carbon source process. The intensity and completeness of the SOC mineralization reactions increase with increasing SOC contents and decrease with increasing ESP levels.

Highlights

The process of CO2 exchange between soil and atmosphere is affected by soil conditions, environment, and land management [1]
Soil Enzyme Activities The change of the Soil organic carbon (SOC) content is affected by climate conditions and soil background nutrients in the study area
Organic carbon mainly comes from residues of plants, animals, microbial, and root exudates, and its content varies in the dynamic process of continuous decomposition and formation [38]

Summary

Introduction

The process of CO2 exchange between soil and atmosphere is affected by soil conditions, environment, and land management [1]. In the situation of global climate changes, some extreme weather conditions or natural disasters (such as rainstorms, droughts, floods, etc.) can exacerbate the formation and proportion of saline–alkali lands and increase the threat of the salinization and alkalinization of soils in arid or semi-arid areas [4,5,6] which can cause the destruction of ecological main function areas [7,8]. Land management, such as farming, fertilization, land use, and agricultural expansion is one of the main driving factors of the CO2 increase, which in turn leads to an increase in saline–alkali soil areas [2,9]. Soil salinization is becoming a major environmental threat affecting soil structures and functions [10]

Results

Discussion

Conclusion