Abstract: To understand the effects of drought stress on N and P stoichiometry in different organs of poplar seedlings, one-year-old Populus × xiaozhuanica cv. Zhangwu seedlings were grown under suitable water level, mild, moderate and serious water stress treatments, i.e., 80%, 60%, 50% and 40% of field capacity, with water controlling method in pots. The results showed that compared with the suitable water level treatment, with the increase of drought stress time, N content firstly declined and then increased in leaves, while it firstly decreased and then had no difference with the suitable water treatment in stems, and declined in roots in the drought stress treatments. P content firstly decreased and then increased in leaves and stems, and increased in roots in the drought stress treatments. However, N/P firstly elevated and then declined in leaves and stems, and decreased in roots in drought stress treatments. There were significant correlations among roots, stems, and leaves in N or P content (P<0.05), while N content was not correlated with P content in all organs (P>0.05). N content of different organs followed the order: leaves>stems and roots, but there was no significant difference in P content among different organs. Meanwhile, the coefficients of variation for N content and N/P followed the order: roots>stems>leaves, but the coefficient of variation for P content was similar in different organs. These results indicated that with the increase of drought stress, N limitation for poplar seedlings was enhanced. The variation degree of N was smaller than that of P in leaves and stems, but the variations of N and P were similar in roots under drought stress.

Key words: bacterial community structure, high-throughput sequencing technology, soil environmental factor, redundancy analysis, degraded grassland, eastern Qilian Mountains