Effect of Potato/Maize Intercropping on Photosynthetic Characteristics and Yield in Two Potato Varieties

Abstract

The intercropping of potato and maize is widely practiced in China. In the potato/maize system, competition for light is an issue as the leaves of potato and maize become different strata within the canopy. The potato/maize intercropping trials using two potato varieties including Zhongshu 5 (early-maturing variety with erect branches) and Mila (mid-late maturing variety with spread branches) with the sole cropping potato as contro1 were carried out to determine the dynamic changes of LAI, SLW, Chl a+b, Chl a/b ratio, photosynthetical active radiation (PAR), gas exchange attributes in leaves at three position levels at tuber initiation stage and tuber expanding stage and yield. The results indicated that intercropping led to decrease LAI, SLW and Chl a/b ratio and increase Chl a+b. In addition, the gradual decrease in PAR, water use efficiency (WUE), stomatal limitation (L s =1–C i /C a , C a : ambient CO 2 concentration) and the increase in net photosynthetic rate (P n ), stomatal conductance (G s ), intercellular CO 2 (C i ) and transpiration rate (T r ) were observed from tuber initiation stage to tuber expanding stage. There was a continuous significant reduction in PAR, P n , G s and T r from the upper leaves to the middle and lower leaves in all treatments, with a lower reduction under intercropping than under sole cropping. The variations in P n , G s , C i , and L s indicated the decreased photosynthetic activity in the middle and lower leaves pertaining, to both stomatal and non-stomatal mechanisms. Intercropping also declined P n in the upperleaves and elevated P n in the middle and lower leaves. Furthermore, there were higher Chl a+b in vegetative growth stage and tuber initiation stage and lower Chl a+b in tuber expanding stage and starch accumulation stage in Zhongshu 5/maize than in Mira/maize system, with the opposite changing trend for SLW. Higher LAI and Chl a/b ratio at all developmental stages, higher PAR in the upper leaves and lower PAR in the middle and lower leaves were observed, and higher P n in the middle and lower leaves in Zhongshu 5 than in Mira in intercropping systems but the similar Pn in the upper leaves. In comparison with Mira, there were lower Gs , Ci , and T r and higher WUE and L s in leaves at the same position levels in Zhongshu 5. In summary, intercropping led to substantial reduction in tuber yield at harvest time due to the change on the light environment and the photosynthetic characteristics of potato in potato/maize systems. Nonetheless, intercropping deteriorated the light environment for Zhongshu 5/maize system while improved the light environment for Mira/maize system, which led to lower LER in the former (1.24) than in the latter (1.40), showing the stronger intercropping superiority for Mira/maize system in the production.