不同水氮处理下毛白杨碳氮磷化学计量特征

Effects of irrigation and nitrogen application on carbon, nitrogen, and phosphorus stoichiometry of Populus tomentosa

为了解灌水和施氮对毛白杨(Populus tomentosa Carrière)优良无性系休眠期各器官碳(C)、氮(N)、磷(P)化学计量特征的影响,利用毛白杨速生丰产林10年连续灌水和施氮双因素试验(通过灌水分别维持土壤含水量至田间持水量的45%、60%、75%;施氮量为0、101.6、203.2、304.8 kg/hm2,共计12个处理,每个处理3次重复)林地,选择其中的优良无性系S86为研究对象,2016年10月末待树木生长停止进入休眠期时,在每个水氮处理小区选取1株标准木并对其进行伐倒肢解处理后,测定分析毛白杨根、干、枝中的碳、氮、磷含量.结果显示:(1)毛白杨树干和枝碳、磷含量显著高于根(P <0.05);氮含量在各器官间差异显著,大小为枝>根>干. C:N在各器官间差异显著,大小为干>根>枝;C:P在各器官间差异不显著;N:P在各器官间差异显著,大小为枝>根>干.(2)灌水对各器官碳含量无显著影响,施氮显著降低根碳含量;灌水、施氮以及两者交互作用均显著影响根、干、枝氮含量,灌水和施氮显著增加各器官氮含量,并在高水高氮条件下毛白杨各器官氮含量显著增大.(3)灌水和施氮显著降低了毛白杨各器官C:N,对C:P影响不显著,显著增加N:P含量.本研究表明,灌水和施氮均促进了毛白杨各器官对氮的吸收,从而提高各器官氮含量;灌水和施氮降低了各器官C:N,促进了毛白杨生长;尽管此区为毛白杨适生区,但毛白杨速生丰产林仍受氮素限制,灌水和施氮是提高毛白杨速生丰产林生长量的重要栽培措施.(图2表6参41)

This study aims to explore the effects of irrigation and nitrogen application on the stoichiometric characteristics of carbon (C), nitrogen (N), and phosphorus (P) in various organs of Populus tomentosa Carrière during dormancy. The fast-growing, high-yield P. tomentosa clonal S86 plantation with a 10-year continuous irrigation and nitrogen application rate was selected. The soil water content was adjusted to 45%, 60%, and 75% of field capacity by irrigation and the nitrogen application was 0, 101.6, 203.2, and 304.8 kg/hm^2. There were a total of 12 treatments with three replicates. At the end of October 2016, when the tree growth entered the dormant period, a sample tree was selected from each plot and felled to sample roots, stems, and branches for the determination of C, N, and P content.(1) The content of C and P in the stems and branches of P. tomentosa was significantly higher than that in the roots (P < 0.05);the content of N differed significantly among organs and could be ranked as branch > root > stem. The C:N ratio was significantly different among organs and could be ranked as stem > root > branch;The C:P ratio was not significantly different among organs;The N:P ratio was significantly different among organs and could be ranked as branch > root > stem.(2) Irrigation had no significant effect on the C content in all organs. Nitrogen application significantly reduced the root C content;irrigation, nitrogen application, and their interaction significantly affected the N content of root, stem, and branch. Irrigation and nitrogen application significantly increased the N content of various organs, and the N content of various organs of P. tomentosa increased significantly under high water content and a high nitrogen application rate.(3) Irrigation and nitrogen application significantly reduced the C:N ratio in various organs of P. tomentosa, but had no significant effect on the C:P ratio and significantly increased the N:P ratio. Irrigation and nitrogen application promote N uptake, thereby increasing the N content of all organs. Irrigation and nitrogen application reduce the C:N ratio and increase the growth rate of P. tomentosa;although this area is suitable for P. tomentosa, fast-growing and high-yield timber plantation may still be restricted by N. Irrigation and nitrogen application are two important cultivation measures to improve the timber yield of P. tomentosa plantations.