Cluster root production and P utilization of macadamia seedling under different P treatments

Cluster root production of macadamia seedling and its P utilization under six P treatments were evaluated in this study. For plants grown in 0.2~3.2 mol·L^-1 P, the amount of cluster root, plant dry biomass and dry biomass ratio of cluster root to root system exhibit a downward trend. For the plants in 0.2~1.6 mol·L^-1 P, acid phosphatase activity (APA) of non-cluster root exhibit an increasing trend ― a direct reverse of cluster root plants. Average APA of cluster root is 72.86% higher than that of non-cluster root. Also leaf P concentration is higher than roots and stems. Root, stem and leaf P concentration in 0.2 mol·L^-1 P is much higher than in other treatments. Compared with treatment without P, P supply at 0.2~0.4 mol·L^-1 inhibits non-cluster root APA, enhances production of cluster roots, plant dry biomass, dry biomass ratio of cluster root to root system, and cluster root APA. It also increases root, stem and leaf P concentration, subsequently improving P concentration of plants. In 0~1.6 mol·L^-1 P, there are significant or very significant positive correlations between cluster root production and plant dry biomass, biomass ratio of cluster root to root system, and P concentrations of stem, root and plant. The significance of positive correlations between cluster root production and APA, and leaf P concentration exceeds 90%.