Growth and photosynthetic responses of soybean seedlings to maize shading in relay intercropping system in Southwest China

Abstract

Intercropping, a traditional and worldwide cropping practice, has been considered as a paradigm of sustainable agriculture based on complementary mechanisms among different crop species. Soybean (Glycine max) is widely relay intercropped about 60 days before maize (Zea mays) harvest in Southwest China. However, shade caused by tall maize plants may be a limiting factor for soybean growth at a seedling stage. In field research, we studied the ecophysiological responses of two widely cultivated soybean varieties [Gongqiudou494-1 (GQD) and Gongxuan 1 (GX)] to maize shading in a relay intercropping system (RI) compared with monocropped soybean plants (M). Our results showed that soybean seedlings intercropped with maize exhibited significantly downregulated net photosynthetic rate (P N ) (-38.3%), transpiration rate (-42.7%), and stomatal conductance (-55.4%) due to low available light. The insignificant changes in intercellular CO 2 concentration and the maximum efficiency of PSII photochemistry suggested that the maize shading-induced depressions in P N were probably caused by the deficiency of energy for carbon assimilation. The significantly increased total chlorophyll (Chl) content (+27.4%) and Chl b content (+52.2%), with lowered Chl a/b ratios (-20.5%) indicated soybean plants adjusted their light-harvesting efficiency under maize shading condition. Biomass and leaf area index (LAI) of seedlings under RI decreased significantly (-78.7 and -71%, respectively) in comparison with M. Correlation analysis indicated the relative reduction in biomass accumulation was caused by the decline in LAI rather than P N , it affected negatively the final yields of soybean (32.8%). Cultivar-specific responses to maize shading were observed in respects of LAI, biomass, and grain yield. It indicated that GX might be a better cultivar for relay intercropping with maize in Southwest China.

Gas exchange, photosynthetic pigments, and growth in tomato: lettuce intercropping

“…In fact, there was less P N and F v /F m in the intercropping system compared to monoculture ( Figures 3C and 5B). The results of our study corroborate those observed by Su et al (2014) and Gong et al (2015).…”

“…On the other hand, 'Vanda' exhibited lower chlorophyll contents and higher growth (DM accumulation); this shows that it is more efficient in chlorophyll content and growth ratio than 'Lucy Brown' (Figures 6E, 6F, and 8C). The results of our study for Chl b concur with those found by Su et al (2014) and Gong et al (2015), who confirmed that shading causes increased Chl b content in leaves and decreased plant biomass accumulation. Shading can also reduce biomass production and the accumulation of biomass from the secondary crop (in this case, lettuce plants) in intercropping systems (Reynolds et al, 2007;Peng et al, 2009).…”

“…In the early morning hours, the incidence of blue light from the light spectrum is not absorbed by the leaves because the light has a characteristically shorter wavelength and more energy; it is decisive in the opening movement of the stomata that does not occur at the maximum opening of stomatal pore, and therefore results in lower g s and P N . According to Su et al (2014), this condition is known as stomatal limitation of photosynthesis. These results are consistent with those found by other researchers, who evaluated the effect of shading on the growth of various crops under intercropping (E) (A and E), stomatal conductance (g S ) (B and D), and net photosynthesis (P N ) (C and F) of lettuce ('Lucy Brown', 'Vanda' 1 and 2 plants) under two cropping systems (monocropping and intercropping) and four lettuce transplanting periods (0, 7, 14, and 21 d after tomato transplanting).…”

“…In the case of intercropping, light intensity can be considered a limiting factor for plant growth because the canopy can shade the associated species (He et al, 2013;Gong et al, 2015). In low light, energy processes of plant metabolism will be reduced, such as ATP synthesis and carbohydrates, causing lower biomass production and decreased productivity (Su et al, 2014).…”

“…Studies have found that shading caused by intercropping reduces plant physiological responses, thus reduced growth and productivity (Su et al, 2014;Gong et al, 2015).…”