Variations in photosynthetic characteristics and yield of maize inpotato/maize intercropping systems

Intercropping of potato with maize has been a traditional cropping system widely practiced in the mountain regions of Southwest China. Although changes have occurred in light environment of maize due to intercropping, few reports have been analyzed the importance of competition for light and related effects on maize yield in potato/maize associations. A potato/maize intercropping field experiment with two different potato-maize row ratios was carried out to determine the dynamic changes in maize features. The features analyzed included leaf area index (LAI), special leaf weight (SLW), chlorophyll a (Chla), chlorophyll b (Chlb), total chlorophyll (Chla+Chlb) and chlorophyll a/b ratio (Chla/b) of maize at different growth stages. Also photosynthetic active radiation (PAR) and gas exchange parameters of upper and lower leaves at tasseling stage of mazie were analyzed along with yield using mono-cropped maize as the control. The respective potato-to-maize row number ratios used in the study were 2︰2 and 3︰2. The results showed a substantial drop in maize LAI at all growth stages while SLW only dropped at the early growth stages before milking under intercropping compared with monocropping. Chla, Chlb and Chla+Chlb also markedly decreased in the 3︰2 intercropping system at all growth stages while it only decreased in the 2︰2 intercropping system at seedling, jointing and silking stages. Chla/b ratio dropped at jointing stage, was subsequently enhanced at silking stage and showed no significant difference at seedling and milk stages. Compared with the 2︰2 intercropping system, the 3︰2 intercropping system had significantly lower LAI at all the growth stages except the seedling stage. Also noted were high Chla, Chlb and Chla+Chlb at all the growth stages except the milking stage, and high Chla/b ratio at silking and milking stages. SLW was not significantly different at all growth stages between 2︰2 and 3︰2 intercropping systems. Furthermore, PAR, net photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) and water use efficiency (WUE) declined in all treatments from upper to lower leaves of maize. Significantly lower Pn, Gs, Tr and high Ci were noted in lower leaves of maize under intercropped conditions than under mono-cropped conditions. No significant changes were noted between intercropped and mono-cropped treatments in terms of Pn, Gs, Tr and Ci of maize upper leaves. PAR in both upper and lower leaves was markedly higher in intercropping than in mono-cropping whereas no marked variations were noted in WUE of the leaves. In comparison with the 2︰2 intercropping system, the 3︰2 system showed substantially lower PAR, Gs and Tr in both upper and lower leaves, similar Pn in upper leaves and lower Pn in lower leaves. The variations in Pn, Gs and Ci suggested that intercropping limited photosynthetic activity in lower leaves of maize due to non-stomatal processes in the 2︰2 intercropping system. However, it enhanced these parameters in the 3︰2 intercropping system due to active stomatal processes. In conclusion, intercropping substantially decreased maize yield at harvest due to changes in photosynthetic characteristics in potato/maize systems. Nonetheless, the land equivalent ratios were 0.88 and 1.24 in the 2︰2 and 3︰2 intercropping systems, respectively. This suggested that there was no advantage in the 2︰2 intercropping system but there existed obvious advantages in the 3︰2 intercropping systems.