How are the Girdling-induced Alhagi sparsifolia senescence and chlorophyll fluorescence changes?

2016-02-02

Cele Oasis located in the southern edge of the Taklimakan Desert, and due to the impact of extreme drought condition, the ecological environment in Cele Oasis is very fragile. Here Alhagi sparsifolia is one of the most important species, it is not only because A. sparsifolia is the largest populations in Cele Oasis, but also because A. sparsifolia is a deep-rooted plant which gives it powerful ability of sand-fixing. In addition, A. sparsifolia is the main fodder in local which herders reserved in winter. To this end, A. sparsifolia also plays a very important role in local agricultural production. In short, A. sparsifolia is not only plays an important role in maintaining the stability of ecosystem and ecological environment in the southern edge of the Taklimakan Desert, but also is essential for the local agricultural development.

However, along with global climate change, the environment in Xinjiang is undergoing the change from lower temperature to higher temperature, and from arid to humid.

The change of climate may affect many aspects of plant growth. For instance, the changes of temperature and humidity will directly lead to the change of senescence process in plants. In addition, increased rainfall always accompanied by the frequently activity of animal and microbial. These change resulted in the increase of risk of mechanical injury in plant phloem. It is because phloem is the channel for sugar delivery in plants, and phloem sap contained a lot of sugar and other nutrient which is important to animals and microbials. To this end, when faced with global climate change, the process of plant senescence tends to be complicated. As an important stage in plant growth process and in the life cycle, senescence had an extreme effect on the plants. And the change of A. sparsifolia senescence may subsequently influence the ecological environment and agricultural economic structure in Cele.

Senescence constitutes the final stage of a plant organ and tissue development and is a subject to gene control and strict regulation. To study the leaf senescence in A. sparsifolia after the phloem was damaged. We set up an experiment at the late growing season, when A. sparsifolia entered the natural senescence period. We carried out girdling treatment on the A. sparsifolia phloem to increase the sugar content in leaves and to investigate carbohydrate-induced leaf senescence.

The results showed that after the semi-girdling and full-girdling treatment, organic matter could not exclude leaves due to the destruction of sieve tubes. This led to constantly increasing sugar contents in leaves. Girdling was shown to greatly accelerate the senescence of plants. In girdled leaves, chlorophyll (Chl) a, Chl b, carotenoids (Car), and both ratios of Chl a/b and Chl/Car were significantly reduced. On the donor side of PSII, the oxygen-evolving complex was inhibited under high concentrations of carbohydrates, which was manifested as the emergence of the K phase in fluorescence kinetic curves. On the acceptor side of PSII, the high carbohydrate content also led to the disruption of electron transport and reduced light-use efficiency, which was manifested as a reduction in numerous fluorescence parameters. We believe that the emergence and development of plant senescence was not necessarily induced by the high content of carbohydrates, because even a decrease in the carbohydrate concentration could not stop the senescence process. Although the high content of carbohydrates in plants could induce plant senescence, this kind of senescence was likely a pathological process, including degradations of physiological functions.

This study was published in Photosynthetica in December 2015.

Contact:

Prof. LI Xiangyi

State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences

E-mail: lixy@ms.xjb.ac.cn