Growth and stoichiometry of Pinus yunnanensis seedlings in response to shade and drought interaction

In order to investigate the growth of Pinus yunnanensis seedlings and the stoichiometric characteristics of carbon(C), nitrogen(N)and phosphorus(P)of different organs in response to shade and drought treatments and the adaptive mechanism, the growth of P. yunnanensis seedlings in shade and drought environments was measured and analyzed in a potting controlled experiment using 1-year-old P. yunnanensis seedlings as the target. The experiment was set up with two levels of 0% shade and 70% shade, and four moisture gradients of normal moisture(CK, 80%±5%), light drought(LD, 65%±5%), moderate drought(MD, 50%±5%)and severe drought(SD, 35%±5%)were set to determine the growth indexes of P. yunnanensis seedlings under shade and drought treatments, as well as the C, N, and P contents of leaf, stem, coarse root and fine root, and calculate the stoichiometric characteristics of their stoichiometric characteristics. The results were as follows:(1)Seedling height, diameter and biomass increment were the greatest under 0% shade and 70% shade conditions with LD; leaf biomass increment was significantly increased under the shade treatment(70% shade)compared with no shade treatment(0% shade)in all drought stress treatments.(2)Compared with the normal water treatment, with the increase of drought stress degree, the C content in each organ of P. yunnanensis seedlings under the shade and drought interaction did not change significantly; the N content in leaf was decreasing, the N contents in stem and coarse root were increasing, and the N content in fine root was decreasing and then increasing; the P content in leaf and coarse root was decreasing, and the P content in fine root was increasing.(3)The order of variability of each element was C<N<P; C element has the smallest variability in stem and weak variability in stem, coarse root and fine root; N element has the smallest variability in leaf; P element has the largest variability in fine root.(4)There was a general correlation among the C, N and P contents in each organ of P. yunnanensis seedlings. C content was negatively correlated between coarse root and fine root, N content were positively correlated between leaf and fine root, stem and coarse root, and coarse root and fine root, and P content was positively correlated between leaf and fine root. In summary, the growth of P. yunnanensis seedlings in drought environment is mainly limited by N element; shade slows down the growth of P. yunnanensis seedlings limited by N element. P. yunnanensis seedlings improve the habitat of seedlings by increasing the utilization efficiency of N and P, and can alleviate the damage caused by drought stress. It is recommended that appropriate shade be provided when cultivating P. yunnanensis seedlings in the forest understory in the future.