Enhanced photosynthetic capacity by perennials in the riparian zone of the Three Gorges Reservoir Area, China

摘要

The flood-dry-flood cycle in the reservoir riparian zone (RRZ) of the Three Gorges Dam has dramatically changed the ecosystem structure and riparian vegetation. Previous field investigations have shown that perennial herbaceous species are dominant in the riparian zone. However, how perennials respond to flooding disturbance remains largely unclear. Intermediate disturbance (e.g. grazing, insect pest) can enhance photosynthesis via "physiological compensation" mechanism. The aim of this study is to investigate whether perennials enhance their photosynthetic capacity during dry periods and understand the mechanisms driving this. Eight species from different families in a RRZ site and a paired Upland site were chosen. We compared 12 plant traits including photosynthesis, leaf structure and nutrients, as well as soluble sugar (indicate sink-source relationship) between the two sites. Results showed that perennials in RRZ had a significant higher area-based photosynthetic capacity (A(area)) than those in Upland. Meanwhile, stomatal conductance (G(s)), leaf nitrogen concentration (LNCa) and Stem mass ratio (SMR) were also significantly higher in RRZ than Upland individuals. However, there was no sign of an unbalanced sink-source relationship in RRZ as evidenced by no difference in soluble sugar content in roots and stems between sites. The results of this study suggest that perennials have enhanced photosynthetic capacity in RRZ mainly attributed to higher LNCa and Gs but sink strength was not enhanced. These data provide insight into the ecosystem functioning of riparian areas and could be used to improve restoration practices. (C) 2016 Elsevier B.V. All rights reserved.