Effect of phosphorous stress on photosynthesis rate and root physiological characteristic of cowpea seedlings

Effects of phosphorus stress on some physiological indexes of Vigna unguiculata (Linn.) Walp. were studied by hydroponic culture method. The results showed that the main root length under the no phosphorus application treatment (LP) was about 43% longger than that of the control (HP), the lateral root number increased by 33% compared with the control, and the root volume was raised, while the leaf area reduced when the culture solution had no phosphate. When there was no phosphorus supplied, the root activity and secreted acid phosphatase were increased to 2.3 and 1.7 times of those of the phosphorus application treatment, respectively. Compared with the control, both the photosynthetic rate and the transpiration rate decreased by 30%. Under the phosphorus deficiency the dry mass lowered remarkably, and the size of stomata became smaller and stomata density decreased. These results showed that the phosphorus deficiency affected the shoot dry mass accumulation and almost had no effects on accumulation of root dry mass. Phosphorus deficiency had more negative effects on shoot than on root.