黄土高原自然植被演替过程中的植物特征与土壤元素动态

在3～149年的时间尺度上,对黄土高原植被次生演替过程中植物特征和土壤养分元素动态进行了研究.结果表明:1) 随着演替时间尺度的延伸,土壤全C、全N含量呈增加趋势,而土壤全K、全Na和土壤pH值呈下降趋势,土壤全P变化趋势不明显;此外,表层(0～10 cm)土壤CaO 含量在演替系列上呈下降趋势,深层(20～30 cm,40～50 cm)则呈增加趋势.演替过程对几种土壤化学元素含量影响的程度随着土壤深度的增加而减弱.2)植物群落物种丰富度在演替的中间阶段最高.3) 在演替的早期阶段,植物群落优势种往往具有稳定的土壤种子库、CR-生活对策和S-繁殖对策,在贫瘠的土壤上具有较强的竞争能力,且具有较强的水平扩展能力和克隆繁殖能力,C-生活对策、在土壤全N含量较高的生境中具有较强竞争能力的多年生植物,在演替中后期占据群落的优势地位.此外,在所涉及的植物特征中,多年生生活史,C-、CR-、SC-、SR-、S-生活对策,以及R-、W-、Bs-、VBs- 和V-繁殖对策等特征在非优势物种中出现的频率较高.4) C-、 SC-生活对策, 克隆能力, 多年生生活史, 水平扩展能力, 种子的动物传播方式,秋季开花,荚果、坚果等特征出现的比例在一定程度上与土壤全C、全N 和全K含量正相关; 而 S-、SR-、R-、CR-生活对策,一、二年生生活史, 种子繁殖, S-繁殖对策,以及胞果、蒴果等特征的比例与土壤全Na、CaO含量和土壤pH正相关.5)在演替过程中出现的植物均属草本植物生活型,因此,草原可能是黄土高原上受制于大尺度环境条件(显域生境)下的优势植被类型(特别是降雨量不超过550 mm的地区).

Plant Traits and Soil Chemical Variables During a Secondary Vegetation Succession in Abandoned Fields on the Loess Plateau

Species dynamics in terms of both plant biological traits, ecological strategies and species richness as well as soil chemical variables during a secondary succession in abandoned fields on the Loess Plateau along a temporal sere from 3 a to 149 a were studied. The results indicated that (1) Soil total C and N increased while soil pH， total K and Na decreased with years since abandonment. No noticeable trend was found in the case of soil P along the successional sere. On the other hand, total CaO of the surface layer (0-10 cm) decreased, but that of the two deeper layers (20-30 cm, 40-50 cm) increased with years since abandonment. Soil C, N, K and P decreased, while Na, CaO and soil pH increased with increasing soil depth. (2) Species richness peaked at both mid stage of the successional sere and the intermediate portion of soil chemical variables gradient. (3) An ideal dominant species in the early successional stage were annuals with stable seed pool, CR life strategy, S regeneration strategy, and strong competitive ability on relatively poor soil, while perennials capable of intensive lateral spread and colonal ability, requiring high nutrient supply, and having C life strategy would be the dominant species in the subsequent stages. Plant traits, such as perennial life history, C , CR , SC , SR , S and R life strategies, W , S , Bs VBs and V regeneration strategies, were over represented throughout the whole sere among the other species. (4) Some traits, such as C, SC life strategies, ability of clonality, perennial life history, well developed lateral spread ability, V and VBs regeneration strategies, seed animal dispersal mode, flowering time of autumn, fruit types of legumen and nut, were more or less correlated with increased soil total C, N and K, while S , SR , R , CR life strategies, annual , biannual life history, non clonal ability, S regeneration strategy, poor lateral spread ability, and fruit types of utricle, capsule were associated with increased soil total Na, CaO and pH. The results suggested that steppes should be the dominant native vegetation coinciding with the large scaled eco climatic conditions on the Loess Plateau.