Comparative differences in photosynthetic characteristics, ion balance, and nitrogen metabolism between young and old wild soybean leaves under nitrogen deficiency

It is a hot issue and an effective method in botany and agronomy to improve cultivation crops using existing wild plant resources without creating invasive plants. Wild soybean is not only a wild ancestor of cultivated soybean, but also an excellent germplasm resource to improve it. The photosynthetic characteristics, ion balance, and nitrogen (N) metabolism of young and old leaves in two wild soybean genotypes (common wild soybean: W1; barren tolerant wild soybean: W2) were analyzed under different intensities of N deficiency. The results showed that N deficiency inhibited the growth and total N content in both genotypes, but W2 was less inhibited. Under the high intensity of N deficiency, the root length in W2 was significantly longer than that in the control group (P < 0.05), which suggested that N deficiency tolerance in W2 was stronger than that in W1. W2 in young leaves maintained stable net photosynthetic rate (pN) and photosynthetic pigment content. Mg²⁺ and K⁺ were transported from old leaves to young leaves. Meanwhile, GOGAT and GDH activities were increased in W2 old leaves and GOT activity was increased in W2 young leaves. W2 young leaves maintained stable photosynthetic assimilation capability, provided energy and basic skeleton for old leaves, and stable N metabolism in old leaves could provide nitrogen metabolites for carbon metabolism in young leaves. The aim of this study was to reveal the physiological mechanisms by which wild soybean seedlings resist low nitrogen stress from the perspective of carbon and nitrogen metabolism by comparing the differences in carbon and nitrogen metabolism between common wild soybean and barren tolerant wild soybean in response to nitrogen deficiency. This study provides a theoretical foundation for the protection and utilization of wild soybean resources.¹2Nitrogen (N); common wild soybean (W1); barren tolerant wild soybean (W2); photosynthetic rate (pN); glutamate synthase (GOGAT); glutamate dehydrogenase (GDH); aspartate aminotransferase (GOT).