Coleman Mark D, Friend Alexander L, Kern Christel C
USDA Forest Service, Southern Research Station, P.O. Box 700, New Ellenton, SC 29801, USA.
Tree Physiol. 2004 Dec;24(12):1347-57. doi: 10.1093/treephys/24.12.1347.
We established Populus deltoides Bartr. stands differing in nitrogen (N) availability and tested if: (1) N-induced carbon (C) allocation could be explained by developmental allocation controls; and (2) N uptake per unit root mass, i.e., specific N-uptake rate, increased with N availability. Closely spaced (1 x 1 m) stands were treated with 50, 100 and 200 kg N ha(-1) year(-1) of time-release balanced fertilizer (50N, 100N and 200N) and compared with unfertilized controls (0N). Measurements were made during two complete growing seasons from May 1998 through October 1999. Repeated nondestructive measurements were carried out to determine stem height and diameter, leaf area and fine-root dynamics. In October of both years, above- and belowground biomass was harvested, including soil cores for fine-root biomass. Leaves were harvested in July 1999. Harvested tissues were analyzed for C and N content. Nondestructive stem diameter and and fine-root dynamic measurements were combined with destructive harvest data to estimate whole-tree biomass and N content at the end of the year, and to estimate specific N-uptake rates during the 1999 growing season. Shoot growth response was greater in fertilized trees than in control trees; however, the 100N and 200N treatments did not enhance growth more than the 50N treatment. Root biomass proportions decreased over time and with increasing fertilizer treatment. Fertilizer-induced changes in allocation were explained by accelerated development. Specific N-uptake rates increased during the growing season and were higher for fertilized trees than for control trees.
我们建立了氮（N）有效性不同的美洲黑杨（Populus deltoides Bartr.）林分，并检验了：（1）氮诱导的碳（C）分配是否可以用发育分配控制来解释；（2）单位根质量的氮吸收量，即比氮吸收速率，是否随氮有效性增加。对株行距紧密（1×1米）的林分施用50、100和200千克氮·公顷⁻¹·年⁻¹的缓释平衡肥料（50N、100N和200N），并与未施肥的对照（0N）进行比较。在1998年5月至1999年10月的两个完整生长季节进行测量。进行重复的非破坏性测量以确定茎高和直径、叶面积以及细根动态。在这两年的10月，收获地上和地下生物量，包括用于细根生物量的土壤芯。1999年7月收获叶片。对收获的组织进行碳和氮含量分析。将非破坏性的茎直径和细根动态测量与破坏性收获数据相结合，以估计年末整株树的生物量和氮含量，并估计1999年生长季节的比氮吸收速率。施肥树木的枝条生长响应大于对照树木；然而，100N和200N处理对生长的促进作用并不比50N处理更强。随着时间推移以及施肥处理增加，根生物量比例下降。施肥引起的分配变化可以用发育加速来解释。生长季节内比氮吸收速率增加，施肥树木的比氮吸收速率高于对照树木。
