Carbon and nitrogen supplementation to soybean through stem injection and its effect on soybean plant senescence

Abstract

Plant senescence studies have indicated that internal competition for nutrients such as carbon (C) and nitrogen (N) can be an important factor in the initiation of senescence. A greenhouse experiment was conducted to determine the effect of increased supplies of C and N on senescence of soybean (Glycine max [L.] Merr) plants. Soybean plants were injected with solutions of sucrose (150gL‐1), N (15 mM N), and distilled water from the onset of flowering until senescence using a modified stem injection technique. The average uptake rate of all solutions was 1.3 mL d‐1 per plant. The plants injected with sucrose accumulated the most biomass, followed by those injected with N and distilled water. Soybean plants injected with sucrose senesced 17 days later than the distilled water control while senescence was not delayed for plants injected with N. Injection of either N or sucrose increased the concentration and content of N in soybean plants. The results indicated that intra‐plant‐competition for reduced C plays an important role in plant senescence. Because the total amount of N injected was only 2% of the total plant N, as compared to 31 % for C, the role of intra‐plant competition for N was less clear.