Heterogeneous leaves of predominant trees species enhance decomposition and nutrient release in the riparian zone of the Three Gorges Reservoir

Zhangting Chen,Changxiao Li,Hong Song,Xuemei Chen,Zhongxun Yuan,Chaoying Wang

doi:10.1038/s41598-020-74062-4

Abstract

The leaves of riparian plants are the main source of energy and nutrients in riparian ecosystems. In order to evaluate the nutrient release of reforested trees in a riparian zone, a field litterbag experiment involving three foliar types (the leaves of either coniferous and broadleaf trees as single-leaf treatment, or a mixture of coniferous and broadleaf leaves as a heterogenous-leaf treatment) and different submergence depths [no submergence (CK), shallow submergence (SS), and deep submergence (DS)] was conducted in situ in the Three Gorges Reservoir (TGR) for one year. The results showed that, when compared to the single-leaf treatment, the heterogenous-leaf treatment exhibited greater mass loss at both SS and DS, in contrast to a greater nitrogen release rate only at DS and a greater phosphorous release rate only at SS. Overall, submergence facilitated decomposition and nutrient release, although the decomposition rate was higher in SS than in DS. The results suggested that the decomposition and nutrient release of the three foliar types may increase the potential pollution risk to the TGR water environment. Thus, we propose that the leaves of the reforested riparian stands be harvested prior to submergence to preserve the water quality of the TGR.

Highlights

The Three Gorges Dam (TGD) in the upper reaches of the Yangtze River is the largest dam in the world[1]
We found that the nutrient release rate in the heterogenous-leaf treatment varied greatly with time (Table 1), which is in accordance with previous s tudies[26,47,51]
The findings of this study show that coniferous-broadleaf leaf mixtures have a profound influence on the dynamics of decomposition

Summary

Introduction

The Three Gorges Dam (TGD) in the upper reaches of the Yangtze River is the largest dam in the world[1]. Artificial vegetation restoration is being carried out, and many monocultures and mixed coniferous–broadleaf restoration plantations are still to be reforested in the riparian zone of the TGR11–13 These reforested plantations affect the water quality and influence nutrient cycling within the TGR14,15. When the water level rises to 175 m.a.s.l. in the riparian zone, the submerged perennial trees, such as the aforementioned deciduous species, will decompose and release large amounts of nutrients, e.g., N and P, which may both directly and indirectly deteriorate the water quality in the TGR2,4,19. It is necessary to study the decomposition and nutrient release of mixed plantations in the context of an artificial hydrological regime, which can enhance our understanding of the riparian ecological environment of the TGR

Objectives

Methods

Results

Discussion

Conclusion