Effect of light deficiency on productivity of intercrops in rubber-crop agroforestry system

The objective of current study was to reveal the effect of light deficiency on the productivity of different intercrops in an agroforestry system. Based on rubber-yam bean and rubber-peanut agroforestry systems, the light intensity, crop biomass, photosynthetic physiology, and other parameters were determined to investigate the effect of light deficiency on the productivity of different sun-like intercrops and potential influencing factors. The daily light intensity was unimodal in the intercropped area in the agroforestry system. The average light intensity accounted for 51.3%-59.0% of bare land control. Yield of the intercrops was significantly lower than the yield of monocultural treatments (P < 0.05). However, the yield of intercropped yam bean was 22.9 t·hm^-2 and reached 85.3% of the yield of monocultural yam beam, while intercropped peanut was only 39.2% that of monocultural peanut. There was no significant effect of light deficiency on ribulose-1, 5-bisphosphate carboxylase/oxygenase activity of intercropped yam bean and peanut in different sites. However, the contents of chlorophyll (especially chlorophyll b) of intercropped yam bean and peanut were significantly increased, and the content of carotenoid was significantly reduced compared to monocultural treatments (P < 0.05). Their photosynthesis rate also was decreased compared to monocultural treatments. Nevertheless, the leaf area of intercropped yam bean in the agroforestry system was higher than monocultural yam bean, while that of the intercropped peanut was significantly reduced by 59.1%-88.4% (P < 0.05). The results conclusively indicate that yam bean is more suitable than peanut as an intercrop in the rubber-based agroforestry system. Intercropped yam bean could maintain relatively higher productivity, probably due to increased photosynthesis, by increasing leaf area to capture light.