Coordinated responses of leaf and nodule traits contribute to the accumulation of N in relay intercropped soybean

Abstract

Maize (Zea mays L.)–soybean (Glycine max L. Merr.) relay intercropping provides a way to enhance land productivity. However, the late-planted soybean suffers from shading by the maize. After maize harvest, how the recovery growth influences the leaf and nodule traits remains unclear. A three-year field experiment was conducted to evaluate the effects of genotypes, i.e., supernodulating (nts1007), Nandou 12 (ND12), and Guixia 3 (GX3), and crop configurations, i.e., the interspecific row spacing of 45 (I45), 60 (I60), 75 cm (I75), and sole soybean (SS), on soybean recovery growth and N fixation. The results showed that intercropping reduced the soybean total leaf area (LA) by reducing both the leaf number (LN) and unit leaflet area (LUA), and it reduced the nodule dry weight (NW) by reducing both the nodule number (NN) and nodule diameter (ND) compared with the SS. The correlation and principal component analysis (PCA) indicated a co-variability of the leaf and nodule traits in response to the genotype and crop configuration interactions. During the recovery growth stages, the compensatory growth promoted soybean growth to reduce the gaps of leaf and nodule traits between intercropping and SS. The relative growth rates of ureide (RGR_U) and nitrogen (RGR_N) accumulation were higher in intercropping than in SS. Intercropping achieved more significant sucrose and starch contents compared with SS. ND12 and GX3 showed more robust compensatory growth than nts1007 in intercropping. Although the recovery growth of relay intercropping soybean improved biomass and nitrogen accumulation, ND12 gained a more significant partial land equivalent ratio (pLER) than GX3. The I60 treatment achieved more robust compensation effects on biomass and N accumulation than the other configurations. Meanwhile, I60 showed a higher nodule sucrose content and greater shoot ureide and N accumulation than SS. Finally, intercropping ND12 with maize using an interspecific row spacing of 60 cm was optimal for both yield advantage and N accumulation.