Responses of PSⅡ chlorophyll fluorescence under Cd stress and characteristics of Cd accumulation in Thalia dealbata and rice mono-and inter-cropping systems

【Objective】 An experiment was conducted to ascertain the effects of Cd stress on the PSⅡ chlorophyll fluorescence parameters in leaves of Thalia dealbata and rice in both the intercropping and mono-cropping systems as well as the uptake and accumulation characteristics of Cd by T. dealbata and rice. 【Method】 The chlorophyll fluorescence parameters in the leaves under different treatments were measured with PAM-2100 Chlorophyll Fluorometer. The contents of Cd in the samples from different treatments were determined using Graphite Furnace Atomic Absorption Spectrometry after wet ashing with HNO₃-HClO₄.【Result and conclusion】The F_v/F_{mYII, qP and rETR of the rice decreased with the elevated Cd content in the soil while the qN, NPQ and YNPQ of the rice showed an opposite trend, indicating that the PSⅡ photosynthetic activity was inhibited under Cd stress, while the proportion of the heat dissipation increased to alleviate the photoinhibition of PSⅡ under the condition of excessive light interception. The YNO of the rice increased in a high level of Cd content, which indicated that the higher level of Cd stress induced damage to PSⅡ reaction centres, and the quantum yield of non-regulated energy dissipation increased to a higher level under conditions of excessive light energy. The decrease of Fv/FmYII, qP and rETR in T. dealbata were much lower than those in rice with the same level of Cd stress. With a higher level of Cd stress, the YNPQ)in T. dealbata increased significantly while the variation of YNO) in T. dealbata was not obvious, which suggested that the regulatory energy dissipation mechanism played a major role in the protection of photosynthetic apparatus in Cd stress. At the same level of Cd content in soil, the sequence of Cd content was root > stem > leaf in the rice and stem > root and leaf in T. dealbata. The Cd contents in the root, stem and leaf of rice in the intercropping system were, respectively, lower than those in the monoculture system. The amount of Cd uptake by T. dealbata was significantly higher than that of rice with the same level of Cd treatment. All these results suggested that the photosystem II reaction center of T. dealbata had a higher tolerance to the Cd stress, and the Cd content of rice in intercropping system could be reduced.}