[Response of photosynthesis and growth to weak light regime in different Adzuki bean (Vigna angularis) varieties]

In order to determine the adaptability of Adzuki beans as the interplanting crops in fruit yards, field and pot experimental treatments with full natural light and weak light (48% of full natural light) regimes were conducted to test the shade tolerance and physiological responses of three Adzuki bean varieties including Funan green Vigna angularis (FGVA), early-mature black V. angularis (EBVA) and late-mature black V. angularis (LBVA). The leaf photosynthetic characteristic parameters, photosynthetic pigment contents and the activity of RuBPCase were measured during the first bloom stage. The response of growth to weak light was likewise studied. The results showed that the photosynthetic characteristic parameters, i.e., the maximum net photosynthetic rate, light saturation point and light compensation point of the three Adzuki bean varieties under the weak light stress changed differently. The weak light stress induced the reduction of net photosynthetic rate, water use efficiency and RuBPCase activity of the three Adzuki bean varieties significantly. The contents of chlorophyll a and chlorophyll b in leaves of FGVA increased significantly, while Chl a/b and carotenoid content in the leaves decreased significantly after shading. But the other two varieties did not change obviously in photosynthetic pigments content after shading. The weak light changed the growth of the three Adzuki bean varieties, such as decreasing dry matter yield and dry matter accumulation efficiency, reducing root nodule and root-shoot ratio, debasing leaves quantity and leaf area index. The first bloom stage and maturing stage of FGVA advanced, while that of EBVA delayed under weak light. However, flowers were not strong enough to seed for LBVA under the weak light. In conclusion, according to the photosynthetic characteristics changes after shading, as well as the growth status, we concluded that the shade tolerance of the three Adzuki beans was ranked as FGVA>EBVA>LBVA.