Comparison of the Photosynthetic Capacity of Phragmites australis in Five Habitats in Saline‒Alkaline Wetlands.

Peng Qi,Subang An,Xingtu Liu,Kun Zhang,Xiaoyu Li,Bolong Wen

doi:10.3390/plants9101317

Abstract

Water shortages have an important impact on the photosynthetic capacity of Phragmites australis. However, this impact has not been adequately studied from the perspective of photosynthesis. An in-depth study of the photosynthetic process can help in better understanding the impact of water shortages on the photosynthetic capacity of P. australis, especially on the microscale. The aim of this study is to explore the photosynthetic adaptation strategies to environmental changes in saline‒alkaline wetlands. The light response curves and CO2 response curves of P. australis in five habitats (hygrophilous, xerophytic, psammophytic, abandoned farmland, paddy field drainage) in saline‒alkaline wetlands were measured at different stages of their life history, and we used a nonrectangular hyperbolic model to fit the data. It was concluded that P. australis utilized coping strategies that differed between the growing and breeding seasons. P. australis in abandoned farmland during the growing season had the highest apparent quantum efficiency (AQE) and photosynthetic utilization efficiency for weak light because of the dark environment. The dark respiration rate of P. australis in the drainage area of paddy fields was the lowest, and it had the highest values for photorespiration rate, maximum photosynthetic rate (Pmax), photosynthetic capacity (Pa), biomass, maximum carboxylation rate (Vcmax), and maximum electron transfer rate (Jmax). The light insensitivity of P. australis increased with the transition from growing to breeding season, and the dark respiration rate also showed a downward trend. Moreover, Vcmax and Jmax would decline when Pmax and Pa showed a declining trend, and vice versa. In other words, Vcmax and Jmax could explain changes in the photosynthetic capacity to some extent. These findings contribute to providing insights that Vcmax and Jmax can directly reflect the variation in photosynthetic capacity of P. australis under water shortages in saline‒alkaline wetlands and in other parts of world where there are problems with similarly harmful environmental conditions.

Highlights

Vegetation is a fundamental part of wetlands, so it is important to study the photosynthetic response mechanisms of vegetation for wetland protection [1,2]
This study was the first attempt to compare the response of P. australis to environmental changes from the perspective of the photosynthetic process
The findings indicate that with the transition from the growing season to the breeding season, P. australis showed decreased photosynthetic sensitivity, the rate of dark respiration showed a downward trend, and plants were more conducive to the accumulation of biomass

Summary

Introduction

Vegetation is a fundamental part of wetlands, so it is important to study the photosynthetic response mechanisms of vegetation for wetland protection [1,2]. The results showed that P. australis was the most tolerant plant because flooding resulted in an increase in the stomatal conductance of P. australis, and anaerobic enzymes in the rhizosphere improved its tolerance; in addition, the high photosynthetic rate (Pa) contributed to biomass accumulation and CO2 fixation during this period [9]. P. australis is more tolerant to short-term flooding than to high salinity [10] because these variables affect chemical oxygen demand (COD) and other indicators in water. Some plants can improve their tolerance to a high-salinity and heavy metal environment by secreting protective enzymes such as superoxide dismutase (SOD), but this only applies under low-salinity conditions; under high salinity, the ability of plants to produce SOD will decrease or even disappear, inhibiting plant growth due to reduced protection against heavy metal toxicity [12]. The decrease in Pa under low-salinity stress is related to stomatal closure, but after exceeding the concentration threshold, stomatal closure is no longer the main reason for the decrease in Pa [13]

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