The Effects Of Precipitation Fluctuation And Different Cultivation Models On The Photosynthetic Characteristics Of Amaranthus Retroflexus

In order to study the adapting mechanism of an invasive weed-Amaranthus retroflexus response to the precipitation fluctuations, and the competition mechanism between crops and A. retroflexus in the process of invading agro-ecosystem, the photosynthetic characteristics of A. retroflexus and G. max response to different precipitation fluctuations were studied based on the method of imitating different precipitation quantity years(normal or high precipitation) and different precipitation patterns(fomer peak model, middle peak model, double peak model and later peak mode), and compare the photosynthetic characteristics of the two species in different species competition combination(monoculture Glycine max, monoculture A.retroflexus, mixture of G. max and A.retroflexus).The results showed that seasonal precipitation fluctuations had directly effects on leaf water content(LWC) of A. retroflexus and G. max, their leaves had higher LWC with higher rainfall. Thee LWC G. max had greater fluctuation range than that of A. retroflexus. Seasonal precipitation fluctuations had more significant effects on LWC of the two species than precipitation quantity fluctuations.Seasonal precipitation fluctuations had significant effects on Pmax, Gs, E, Ci, WUE of the two plants, they had higher Pmax, Gs, E with higher precipitation, Pmax of A. retroflexus was highest at early growth stages, whereas less WUE was occurred when rainfall was high.Seasonal precipitation fluctuations affected PEPcase activity, Ru BPcase activity and the ratio of PEPcase/Ru BPcase of A. retroflexus and G. max. In the high precipitation year, at the flowering and pods formation and seed filling stages of G. max had higher Ru BPcase activity than A. retroflexus as 0.09%~45.1%. Across the whole growth period, A. retroflexu had higher PEPcase activity and the ratio of PEPcase/Ru BPcase than G. max as 8.8%~91.4% and 7.8%~89.2%, respectively. In the normal precipitation year, the greatest Ru BPcase activity in A. retroflexus and G. max appeared in July, and the greatest PEPcase activity and the ratio of PEPcase/Ru BPcase in A. retroflexus and G. max appeared in June.Seasonal precipitation fluctuations had more significant effects on the content and composition of photosynthetic pigment in A. retroflexus and G. max. At G..max seedling and flowering and pods formation stages, the effects of seasonal precipitation fluctuations on photosynthetic pigment and composition in G.. max leaves were not significant, but significantly affected at the stage of seed filling. Across the whole growth period, the influence of the seasonal precipitation fluctuations on the photosynthetic pigment content and composition in leaves of A.retroflexus were significantly, which may be related to its high phenotypic plasticity. In addition, both leaf photosynthetic pigment contents of G. max and A. retroflexus, were higher in mixed cropping than monoculture.In the normal and high precipitation years, precipitation quantity and seasonal fluctuations had significant effects on photosynthetic characteristics of A. retroflexus and G. max. Seasonal precipitation fluctuations had more significant effects on photosynthetic characteristics of plants in the normal precipitation year than in the high precipitation year. Because of plentiful precipitation in high precipitation year, seasonal precipitation fluctuations had little effects on photosynthetic characteristics. In the high precipitation year, A. retroflexus and G. max showed higher Chla、Chlb、Chls 、 Cars and Pmax in the four seasonal precipitation fluctuations than CK. In the high precipitation year, seasonal precipitation fluctuations had less effect on photosynthetic characteristics of the two species in mixed-cropping than in the normal precipitation year.Overall, A. retroflexus can successfully invade agro-ecosystems, and can quickly adapt to the water fluctuation environment may be due to its high phenotypic plasticity. At the seedling stage A. retroflexus showed high photosynthetic capacity than G. max, which may be one of the reasons why it could occupy the niche quickly. A. Retroflexus and G. max also showed time niche as well. It maybe one of the important mechanism of A.retroflexus and G. max coexist for a long time in agro-ecosystems.