引入草木樨对半干旱黄土高原区早期植物群落演替和土壤养分的影响

植被演替早期的优势物种是影响演替进程的重要因素。以半干旱黄土高原地区退化耕地植被的自然恢复为对照,于植被恢复的早期引入两年生豆科植物草木樨(Melilotus officinalis L.),在种植密度为11.3kg.hm-2条件下,考察了6年内引入草木樨对退化耕地植被恢复过程中植物群落演替进程的影响。结果表明,与自然恢复植被相比,草木樨的引入不仅可以提高地表植被覆盖度和加速植物群落演替进程,促使一些群落演替后期物种如冷蒿(Artemisia frigida)、阿尔泰狗哇花(Heteropappus altaicus)和短花针茅(Stipa breviflora)等在植被恢复的第3年出现,同时有利于提高植被生产力和稳定性。同自然恢复相比,试验期间引入草木樨后的植被地上平均生物量提高67.90%。同时,植被恢复早期生物多样性与土壤全氮含量呈显著正相关,而草木樨的引入有利于提高土壤全氮含量;在植被恢复初期(2003～2005)引入草木樨的土壤全氮平均含量比自然恢复高7.32%;试验期间土壤速效磷含量与物种丰富度呈显著负相关。因此,在半干旱区黄土高原退化耕地植被恢复早期阶段,两年生豆科植物草木樨的引入和磷肥的施用对于加快植被恢复有着积极作用。

Effect of Introducing Biennial Legume Species,Melilotus officinalis,on Plant Community in the Early Stage of Vegetation Succession and Soil Nutrients in the Semiarid Loess Plateau of China

During the restoration of plant cover in the degraded cropland,the existence of early successional dominant species was one of the most important factors influencing the process of vegetation succession.This experiment including two treatments:(1)natural regeneration(CT),and(2) sweetclover(Melilotus officinalis L.) planted at a density of 11.3 kg·hm-2(LT),was designed to explore the dynamic of plant community in the initial vegetation succession by introducing biennial legume species into the abandoned cropland located in the semiarid Loess Plateau of China.After 6-year-experiment,the results indicated that LT helped increase vegetation cover and accelerate the course of vegetation succession.For example,some later successional species like Artemisia frigida,Heteropappus altaicus and Stipa breviflora were showing up in LT in the third year of vegetation succession.Moreover,LT was beneficial to improve the productivity and stability of plant community.In contrast to CT,the averaged aboveground biomass of LT was higher by 67.90% across the experiment.Besides,LT helped increase the soil total nitrogen in the early stage of vegetation restoration.Compared with CT,the average soil total nitrogen in 2003～2005 was higher by 7.32% in LT.Across the experiment,the soil total nitrogen and available phosphorus were the limited factors influencing the plant community in both CT and LT.Therefore,the introduction of biennial legume specie is a better way to restore the plant community in the semiarid Loess Plateau,and the addition of phosphorus fertilizer during succession of plant community is also recommended.