Linkages between soil organic carbon fractions and carbon-hydrolyzing enzyme activities across riparian zones in the Three Gorges of China

Jiao Feng,Weibo Wang,Junjun Wu,Dandan Zhang,Qian Zhang,Xiaoli Cheng,Qianxi Li,Qiong Chen,Fan Yang

doi:10.1038/s41598-020-65200-z

Abstract

The effect of flooding on soil enzyme activities and soil organic carbon (SOC) dynamics remains a widely debated topic. Here, we investigated spatial variations in C-hydrolyzing enzyme activities, soil C contents in different fractions [i.e. labile and recalcitrant carbon (LC and RC)] from 6 sites with four different elevations at two soil depths (0–10 cm and 10–30 cm) in riparian zones of the Three Gorges Reservoir, China. At region scales, the SOC, RC contents, and RC/SOC (RIC) generally showed decreasing tendency from the upstream to the downstream. The C-hydrolyzing enzyme activities were higher in the midstream compared to other sites, which did not correspond well with the changing trend of SOC content, but matched with the spatial variation in LC content. At ecosystem scales, the RC and RIC declined with decreased elevations, but the LC showed opposite trend. Whereas, the four C-hydrolyzing enzyme activities and the specific enzyme activities were corresponded well with the changing trend of LC content. Soil C contents and enzyme activities were generally higher in top soil than deep soil across sites and elevation zones. These results reveal that the LC is the tightest factor in regulating C-hydrolyzing enzyme activities, whereas the soil C quality (i.e. RIC) and flooding collectively drive C-hydrolyzing enzyme activities possibly by affecting decomposition rates of SOC in the riparian zones.

Highlights

The linkages between soil organic carbon (SOC) and C-hydrolyzing enzyme activities can be influenced primarily by altering vegetation types under large hydroelectric projects[2,3,18,19]
Previous studies have reported that soil hydrolytic enzyme activities are tightly related to SOC content[12,23,24], the labile C (LC) derived from fresh litter input has been generally regarded as the major source of energy for microbes producing hydrolytic enzymes[25,26]
We hypothesized that 1) the SOC contents and fraction (LC, recalcitrant C (RC), and RC/SOC) would significantly differ among sites and elevations, possibly due to changes in vegetation types induced by water flooding. 2) whether the C-hydrolyzing enzyme activities would be tightly related to soil C quality (i.e. RC/SOC) and fraction in the riparian zones

Summary

Introduction

The linkages between SOC and C-hydrolyzing enzyme activities can be influenced primarily by altering vegetation types under large hydroelectric projects[2,3,18,19]. The relationship between SOC dynamics and C-hydrolyzing enzyme activities are inconsistent in various studies, possibly due to related multiple controls, especially when soil conditions are affected by hydrologic pulsing under large hydroelectric project area. Previous studies have investigated the spatial distribution of plants[18] and soil N dynamics[4], but little is known about spatial variations in SOC fractions and enzyme activities in water level fluctuation zone in the Three Gorges Reservoir. To address this major gap, the objective of this study is to reveal the linkage between spatial variations in SOC dynamics and C-hydrolyzing enzyme activities (α-glucosidase, AG; β-glucosidase, BG; 1,4-β-cellobiosidase, CB; 1,4-β-xylosidase, XS) effected by water flooding in Three Gorges. We hypothesized that 1) the SOC contents and fraction (LC, RC, and RC/SOC) would significantly differ among sites and elevations, possibly due to changes in vegetation types induced by water flooding. 2) whether the C-hydrolyzing enzyme activities would be tightly related to soil C quality (i.e. RC/SOC) and fraction in the riparian zones

Objectives

Methods

Results

Conclusion