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

Abstract

Maize (Zea mays L.)-soybean (Glycerine Max L. Merr.) relay intercropping provides a way to enhance land productivity. However, the late-planted soybean suffers from maize shade. After maize harvest, how the recovery growth influences the leaf and nodule traits are still 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. Results showed that intercropping declining soybean total leaf area (LA) by reducing both the leaf number (LA) and leaf unit area (LUA) and reducing nodule dry weight (NW) by decreasing both the nodule number (NN) and nodule diameter (ND) compared with the SS. The correlation and principal component analysis (PCA) indicated a covariability of the leaf and nodule traits in response to the genotypes and crop configuration interactions. During the recovery growth stages, the compensatory growth promoted soybean growth to shrink the gap of leaf and nodule traits between intercropping and SS. The relative growth rate of ureide (RGR_U) and nitrogen (RGR_N) accumulation was higher in intercropping than in SS. The intercropping obtained more significant sucrose and starch contents compared with SS. ND12 and GX3 showed more robust compensation growth than nts1007 in intercropping. Although the recovery growth of relay intercropping soybean improved biomass and nitrogen accumulation, the ND12 gained a more significant partial land equivalent ratio (pLER) than the GX3. The I60 treatment achieves a more robust compensation effect on biomass and N accumulation than the other configurations. Meanwhile, the I60 obtained a higher nodule sucrose content and a greater shoot ureide and N accumulation than SS. Finally, intercropping ND12 with maize by practicing an interspecific row spacing of 60 cm was optimal for yield advantage and N accumulation.