人工油松林中不同植物叶片非结构性碳水化合物含量对氮添加的响应

全球氮沉降通过影响树木叶片的生理过程影响森林生态系统的结构与组成,但目前关于氮沉降对森林生态系统中不同植物叶片非结构性碳水化合物(NSC)含量的影响还不十分清楚.本研究选取黄土丘陵区人工油松林中油松、辽东栎、忍冬、绣线菊、黄刺玫、茜草、披针苔草7种主要高等植物,比较了3年氮添加(0、3、6、9 g N·m^-2·a^-1,分别用N₀、N₃、N₆、N₉表示)对7种植物叶片中NSC的影响.结果表明: 不同植物叶片可溶性糖、淀粉含量变异很大,二者变异最高的均为黄刺玫,最低的分别为绣线菊和披针苔草;不同植物可溶性糖、淀粉对氮添加的响应存在明显差异.N₆处理下茜草的可溶性糖和淀粉的变异高于其他物种,N₃和N₉处理下绣线菊的变异高于其他物种,可溶性糖和淀粉含量变异最小的物种在不同氮添加水平下不同.随着氮添加水平的增加,油松和披针苔草的可溶性糖含量持续升高,绣线菊持续降低,辽东栎、忍冬和黄刺玫的可溶性糖含量先降低后增加,在N₆处理达到最小,而茜草的可溶性糖含量呈现较复杂的变化趋势.氮添加对植物叶片中淀粉含量的影响表现为油松、忍冬和披针苔草的淀粉含量持续增加,绣线菊先降低后增加,在N₃处理达到最小,而黄刺玫和茜草则呈现较复杂的变化趋势,辽东栎淀粉含量变化趋势平缓.在氮添加后,土壤pH、有机碳、全氮、全磷与植物叶片NSC含量无相关关系,仅N₀和N₃水平下上述土壤理化指标会显著影响可溶性糖/淀粉.表明林地不同植物叶片中NSC含量对氮添加的响应明显不同,研究全球氮沉降或氮添加对林地生态系统的影响需要考虑不同植物,尤其不同生活型植物的不同响应.

Responses of non-structural carbohydrates content in leaves of different plant species in Pinus tabuliformis plantation to nitrogen addition.

Through its impact on plant physiological processes, global nitrogen deposition could alter the structure and composition of forest ecosystems. However, we are not clear about the effects of N deposition on leaves’ non-structural carbohydrate (NSC) content of different plants. In this study, we compared the responses of NSC contents in seven different plant species to four nitrogen addition levels (0, 3, 6, and 9 g N·m^-2·a^-1, referred to as N₀, N₃, N₆, N₉, respectively), including Pinus tabuliformis, Quercus liaotungensis, Lonicera japonica, Spiraea salicifolia, Rosa xanthina, Rubia cordifolia, and Carex lanceolata in an artificial Pinus tabuliformis forest located in the hilly area of the Loess Plateau. The contents of soluble sugar and starch varied greatly in plant species, with the highest variability in R. xanthina and the lowest in S. salicifolia and C. lanceolata. There were significant differences in the responses of soluble sugar and starch contents to nitrogen addition among different species. Under N₆ treatment, the variability of soluble sugar and starch in R. cordifolia came the first while S. salicifolia exceeded all other species under N₃ and N₉ treatments on that rating. The specific species with the lowest variability of soluble sugar and starch contents differed with nitrogen addition levels. With the increases of nitrogen addition rate, the soluble sugar content of P. tabuliformis and C. lanceolata exhibited a continuous rising trend, an opposite trend of S. salicifolia, while that of Q. liaotungensis, L. japonica, and R. xanthina decreased first and then increased, reaching its minimum at N₆ treatment. The response of R. cordifolia to nitrogen addition was complex. With respect to starch content, P. tabuliformis, L. japonica and C. lanceolata showed a continuous increase trend with nitrogen addition whereas S. salicifolia decreased first and then increased, troughing at N₃ treatment. R. xanthina and R. cordifolia responded complicatedly yet Q. liaotungensis appeared less responsive. Under N addition treatments, there was no explicit correlation between NSC content and soil physical and chemical properties including pH, organic carbon, total nitrogen and phosphorus. There was a significant influence of those soil properties on the soluble sugar/starch ratio under N₀ or N₃ treatment. Our results indicate that different species have obviously different responses of NSC to nitrogen addition. Future research concerning the impacts of global nitrogen deposition on forest ecosystems should take into account the target species, especially to pay attention to the responses of vegetation with different life forms.