With global climate change, increasing greenhouse effect and deteriorating ecological environment, the frequent occurrence of extreme weather phenomena not only caused serious human impact, but also changed the global ecosystem carbon balance, especially environment and ecosystem in some specific region. Studies on ecophysiological responses of most angiosperm species to environmental stress have been reported, but little is known about dioecious plant responses to changing environment. Since significant differences on growth, survival, reproductive patterns, spatial distribution, as well as resource allocation between males and females of dioecious plant have been formed during evolutionary process, sexual different ecophysiological responses should be caused by different environmental factors. In the present study, Populus cathayana Rehd. was used as model plant to study the sex-related responses and acclimations by using the ecological, physiological and biochemical methods under photoperiod transitions, elevated CO2, temperature and soil nitrogen deposition, and to expose the sexual differences in growth, biomass allocation, photosynthesis, water use efficiency, physiological and biochemical characters and cell ultrastructures in the males and females of dioecious P. cathayana. The results are as follows:
1. Sex-related responses of males and females of P. cathayana to photoperiod transitions.
Compared with controlled photoperiod treatment, short-day photoperiod significantly decreased gas exchange rates of both male and female individualsof P. cathayana, and affected many physiological and biochemical processes, and induced males and females to exhibit obvious sexual differences in growth, gas exchange, water use efficiency, lipid peroxidation protection, antioxidant defenses enzyme system, phytohormone accumulation and ultrastructures morphology. Under short-day photoperiod environment, males exhibited significant higher net photosynthesis rate (Pn), water use efficiency (WUEi), malondialdehyde (MDA), proline (Pro) and higher peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD) activities than did females. The results showed that males exhibited greater adaptabilities to short-day photoperiod than did females. The changing of ultrastructures showed that female individuals suffered more from shortening photoperiod. Whereas under the long day photoperiod, females had higher Pn, chlorophyll a/ b ratio (Chl a/b), WUEi, anti-oxidant enzyme activities and soluble protein (SP) contents than did males. The results showed that females had better ability to adapt to long day photoperiod, and the enhancement role of longday photoperiod on plant growth of males was not significant.
2. Responses of males and females of P. cathayana to elevated CO2, temperature and nitrogen deposition separately
Compared with controlled treatment, elevated CO2, temperature and nitrogen deposition separately increased the males and females plant growth, gas exchange, biomass accumulation, and also some biological characters. The different responses between males and females were found when the environment factors were changing. Males possessed significant higher plant growth, Pn, biomass accumulation than did females under elevated CO2. Although elevated temperature was conductive to the promotion of plant growth of both males and females P. cathayana, the lipid peroxidation and any other adverse effects were emerged by significant higher POD, CAT, SOD and ascorbate peroxidase (APX), especially in the individuals of females. The soil nitrogen deposition significantly increased the plant growth, gas exchange and lipid peroxidation, whereas decreased antioxidant enzymes activities in both males and females of P. cathayana, which probably due to nutritional imbalance of the dioecious plant under nitrogen enrichment environment. By the imbalance effect of nitrogen deposition, females were more sensitive in physiological and biological characters than that of males under the same condition.
3. Responses of males and females of P. cathayana to combination effect of elevated CO2, temperature and nitrogen deposition
Compared with controlled environment, CO2 and nitrogen deposition, CO2 and temperature as well as the combination of temperature and nitrogen deposition significantly affected male and female of P. cathayana plant growth, gas exchange, water status and carbohydrate accumulation. Under the combination of elevated CO2 and nitrogen deposition, height growth (HG), leaf area (LA), total leaf number (TLN), leaf weight (LW), and starch contents were significantly increased in both males and females of P. cathayana. Males exhibited significantly higher HG, Pn and WUEi, but lower starch content than did females. Under the combination of elevated CO2 and temperature treatment, HG, basal diameter (BD), LA, Pn, carbon isotope composition (δ13C) and starch contents were significantly increased in both males and females, while males exhibited higher HG, Pn, but lower starch accumulation than did females. On the other hand, the HG, LA, TNL Pn and starch content of both males and females were increased by the combination treatment of elevated temperature and nitrogen. Males had significant higher WUEi, but lower starch content than females under elevated temperature with soil nitrogen deposition conditions. Our results showed that there are sexual different responses between males and females of P. cathayana under the changing environmental factors (photoperiod, CO2, temperature, soil nitrogen) separately. However, the responses sometimes were different or even adverse when the dioecious P. cathayana grown under the combination treatments of any other two environmental factors
Key words: Populus cathayana, dioecious plant, photoperiod adaptability, elevated CO2, elevated temperature, soil nitrogen deposition