Abstract:
Objectives This study investigated the effects of different P supply levels on physiological traits and seed yield of soybean genotypes with different P efficiencies.
Methods A hydroponic experiment was carried out, using six P-efficient and six P-inefficient genotypes of soybean as test materials. Based on the Hoagland nutrient solution, the P concentration was adjusted into four levels: 0 (CK), 100, 500 and 1000 µmol/L. The photosynthetic characteristics, P/Fe ratio in soybean leaves were determined at early flowering and early podding stages. The seed weight and contents of P and Fe were measured at seed filling stage (R8). Canonical correlation analysis between photosynthetic characteristics and P/Fe ratio was carried out, and stepwise regression equation was established by seed weight per plant, then pathway analysis was performed.
Results Whether in P-efficient or inefficient genotypes, 0 µmol/L of P resulted in a dramatic increase (P < 0.01) in Fo value at early flowering stage; 100 µmol/L P supply treatment significantly improves actual photochemical efficiency of PSⅡ (ΦPSⅡ) at early flowering stage, which improved the light energy conversion rate, and under this treatment, seed weights per plant of both P-efficient and P-inefficient genotypes were higher. Compared with P 100 μmol/L treatment, both Fe concentration and Fe/P ratio of leaf at early podding stage exhibited a decreasing trend with increasing P supply level. Compared with treatment of P 100 µmol/L, the seed weight per plant of P-efficient genotypes did not increase significantly at P supply of 500 and 1000 µmol/L, but seed weight per plant of P-inefficient genotypes decreased. In addition, SPAD values at early podding attained peaks under P 100 μmol/L treatment, and the SPAD value at seed filling stage stage had a positive correlation with seed weight per plant of both P-efficient and inefficient genotypes.
Conclusions P supply level affects photosynthetic efficiency as well as P/Fe ratio in soybean leaves. Normal P supply level (100 μmol/L) could regulate the chlorophyll content at the early flowering, early podding and seed filling stage, and then regulate the metabolic process, which is beneficial to grain formation in both P-efficient and P-inefficient genotypes. High P supply does not result in substantial increase in seed weight, but may result in a negative effect on seed weight.
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