Effects of Phosphorus Deficiency on Growth and Nitrogen Fixation of Soybean after Nodule Formation

Abstract

Phosphorus had a key role in soybean growth, however, it is very different to separate the role in soybean growth from that in nodule function. The research was conducted to elucidate the effects of phosphorus deficiency on growth and nitrogen fixation after nodule formation in soybean. Soybean seedlings were cultivated in nutrient solution culture with normal phosphorus concentration (30 μmol L-1), which was shifted to 0 and 4 μmol L-1 after nodule formation resulting in phosphorus deficience for soybean plants. The results showed that phosphorus deficiency negatively influenced soybean plant growth at the ninth day of phosphorus deficiency treatment and nitrogen fixation at the beginning of the treatment. The nodule number increased by 11.8%, 15.4%, and 20.0%, respectively in 0, 4, and 30 μmol L?1 phosphorus treatments at the ninth day of treatment compared with that at the third day. Leghemoglobin concentration per gram of plant and per nodule biomass increased with phosphorus concentration increase. These suggested that phosphorus deficiency affected significantly nodule development and nitrogen fixation when soybean plants formed sufficient nodule.