黄土丘陵区撂荒群落演替序列种根系对氮素施肥方式和水平的形态响应

采用盆栽试验,研究了黄土丘陵区撂荒群落演替序列种(即,黄土丘陵区摞荒群落演替主要阶段的优势种)根系对氮素施肥方式和水平的形态响应,对了解我国氮沉降增加背景下的群落生态效应及人为施肥干扰促进植被恢复具有较好的理论和实践意义。测试并分析了6个演替序列种在不同施氮方式(匀质和异质施氮)和水平(高、低和无氮对照)条件下植株个体生物量指标(地上及地下生物量和根冠比)、根系形态指标(根长、直径、表面积、比根长和比表面积)的变化及其差异显著性;并且利用根钻法和单样本T检验比较了异质施氮方式下施氮斑块与不施氮斑块根系形态指标的差异。结果表明:1)6种演替序列种地上、地下生物量和根冠比存在种间固有差别,施氮方式和水平整体上对三者无显著影响;施氮方式和植物种类对根冠比存在显著交互作用,说明个别种的根冠比对施氮方式响应明显,其中猪毛蒿根冠比在异质施氮方式下显著高于匀质施氮。2)6种演替序列种根系塑形指标包括比根长、比表面积和直径存在种间差别,并且施氮水平对比根长影响显著,高、低施氮水平下比根长都显著低于不施氮对照。3)狗尾草和铁杆蒿分别在异质高氮和异质低氮条件下施氮斑块根系生物量密度显著高于未施氮斑块;猪毛蒿在异质高氮条件下施氮斑块发生了更多的伸长生长,其根长、根表面积、比根长和比表面积在施氮斑块中的密度显著高于未施氮斑块;猪毛蒿和狗尾草在异质高氮条件下,以及白羊草在异质低氮条件下,其根系直径在施氮斑块显著小于未施氮斑块。从根系形态变化敏感性和施氮对促进植物生长来看,演替过程中演替序列种对施氮响应的敏感性总体上呈降低趋势,前期种对施氮响应更敏感,从施氮获利也更多,因而恢复前期进行人为干扰促进植被恢复效果也会更好。

Morphological responses of six successional plant species in old-fields of the Loess Plateau to the pattern and level of nitrogen application in a pot experiment

How successional species differentially respond to nitrogen addition is of theoretical importance to understand the plant community-level consequences of China''s accelerated nitrogen deposition amidst ongoing global climate change. Such research also has an immediate, practical significance for revegetation strategies through targeted fertilization. In this paper, a field potting experiment was carried out to test the biomass benefits and morphological responses of six successional seral species in the Loess Hilly Region of Northern Shaanxi. The factorial experimental design had two treatments: a nitrogen fertilization pattern (i.e., homogeneous vs. heterogeneous nitrogen) and nitrogen fertilization level (i.e., high, low, and zero nitrogen the control]). The plant response variables measured were individual biomass (i.e., aboveground and belowground biomass, and root-branch ratio) and several root morphological features (i.e., root length, diameter, and surface area; specific-root length; and specific-root surface area). These eight response variables were tested separately for treatment effects using three-way ANOVAs; in addition, improved root morphological features in the fertilized patches were compared to those in the non-fertilized patches using a simple t-test. The results showed that (1) the aboveground biomass, belowground biomass, and root/branch ratio differed significantly among the six successional seral species; this may reflect their species-specific differences, as they were largely not affected by nitrogen fertilizer pattern or its level of application. Nevertheless, a significant interactive effect between fertilizer pattern and species upon the root/branch ratio between was found. This implied that some plant species-for example, Artemisia scoparia in our case-had a significant response to nitrogen pattern in terms of its root-branch ratio whereas others did not. (2) The specific root length, specific surface area, and root diameter also differed significantly among the six successional seral species. The nitrogen fertilization level significantly affected the specific root length; it was lower both at high and low levels of nitrogen fertilization in comparison to the controls (unfertilized plants). (3) Under the treatment of heterogeneous fertilization at high level, the proliferation of root biomass of Setaria viridis in the fertilized patches was significantly higher than in the non-fertilized patches. Similarly, under heterogeneous fertilization at low level, the root biomass of Artemisia sacrorum was significantly higher than its counterparts growing in the non-fertilized patches. Artemisia scoparia under heterogeneous fertilization at high level, more elongation, root length root surface area, specific root length, and specific surface area in the fertilized patches were significantly higher than in the non-fertilized patches. However, the root diameters of Artemisia scoparia and Setaria viridis in the patches of heterogeneous fertilization at high level, and the diameter of Bothriochloa ischaemum in the patches of heterogeneous fertilization at low level, were all significantly lower than those in the non-fertilized patches. From the perspective of morphological responsive sensitivity and a biomass benefit from fertilization, both of these plant traits exhibited an overall tendency to decrease along succession. That is to say, the early-successional seral species tend to respond more actively, and to assimilate more nitrogen in their formation of biomass, than the late-successional species do. This implies that for the successful revegetation of infertile fields, they should be fertilized as early as possible once been abandoned.