Effect of phosphorus concentration on Cunninghamia lanceolate seedling roots and potting soil

Objective To demonstrate the morphological and physiological response of Cunninghamia lanceolate roots, and the variation of nutrient and microorganism contents in potting soil under phosphorus (P) deficiency.

Method Three treatments including P deficiency (P0), normal concentration P (P1) and high concentration P (P2) were applied to potted C. lanceolate seedlings. The temporal dynamics of root phenotype and physiology, as well as the nutrient and number of microbes of the potting soil were measured.

Result After 30 days treatment, P0 had the least accumulations of shoot and whole plant dry mass, and the highest accumulation of root dry mass and root/shoot ratio, which were 2.07 and 5.37 times of those of P1, respectively. Starting from day 15, the root P uptake rate of P0 had been the lowest while P utilization rate had been the highest. At day 30, the root P uptake and utilization rates for P0 were 43.18% and 231.59% of those for P1, respectively. Root surface area and root tip number increased with the increase of treatment time, and were 3.46 cm² and 56 respectively for P0 at day 30, significantly higher compared to P1 and P2. During the entire treatment process, acid phosphatase, SOD activities and MDA content of P0 were significantly higher compared to P1 and P2. Compared with P1 and P2 treatments, P0 had obviously higher content of soil alkali hydrolysable nitrogen, serious shortage in available P, minor differences in pH, available K and cation exchange capacity, significant increase in acid phosphatase activity, and decrease in the number of fungi.

Conclusion P deficiency(P0) treatment led to increase in root dry mass accumulation and root/shoot ratio, increase in root surface area and root tip number with the increase of stress time, decrease in P uptake rate but increase in P utilization rate, and significant increase in root acid phosphatase, SOD activities and MDA content. In addition, acid phosphatase activity of the potting soil significantly increased, alkali solution nitrogen content obviously increased, available P content was in serious shortage and fungi content was the least for P0 compared to other treatments. Therefore, P deficiency has significant effect on root growth, as well as nutrient and number of microbes of potting soil.