In this paper, a pot experiment was used to test the response of reactive oxygen scavenging enzymes (SOD, CAT, POD,APX) and membrane damage (MDA) of nine co-existing species under three water deficit levels (severe, moderate and mild water deficits, corresponding to 45%-50%, 60%-65% and 75%-80% of field water capacity, respectively) in three months of growing season, to understand the subsequent community level effect from the perspective of eco-physiological mechanism of vegetation succession.The nine species routinely coexist in middle secondary successional stages in Loess Hilly Region.They are Artemisia scoparia, Cleistogenes chinensis, Oxytropis glabra, Agropyron cristatum, Cleistogenes songorica, Artemisia sacrorum, Lespedeza davurica, Artemisia giraldii and Bothriochloa ischaemum.The results showed that: (1) treatments of species, growing season and water deficit all had significant effects on SOD, CAT, POD, APX activities and MDA content.(2) For species treatment, SOD activity of L.davurica, CAT activity of B.ischaemum, POD activity of C.chinensis, CAT, POD and APX activities of O.glabra were relatively high, whereas MDA content of L.davurica was comparatively low.SOD, CAT and POD activities declined from August, and MDA content in leaves was observed fell in October.That implied that the above indexes in leaves were ordinarily higher in quick growth month.The activities of SOD and APX responded positively to water deficit, i.e., their values under severe water deficit were higher in comparison with the ones under moderate and mild water deficits;and no such significantly positive responses were observed for the activities of POD and CAT.This meant that SOD and APX activities took more active and positive role for water stress tolerance.(3) The relative high SOD activity and low MDA content in L.davurica and high APX activity of O.glabra showed that they could tolerate water deficit well, subsequently when soil moisture declined, their fitness and abundance might go rise.(4) The activities of SOD and APX of the nine co-existing species were positively correlated with their successional niche positions, i.e., species dominated in late successional stage had better drought tolerant traits.This really act in local community succession accompanied by soil drying in Loess Hilly Region wherein, e.g., species of L.davurica and O.glabra that behaved well in water deficit condition, dominate in later successional stage.%通过盆栽试验,以9种黄土丘陵区撂荒演替中期群落共存种(猪毛蒿、中华隐子草、小花棘豆、冰草、无芒隐子草、铁杆蒿、达乌里胡枝子、茭蒿和白羊草)为研究对象,测定其生长季中(8~10月)重度和中度干旱胁迫及适宜水分条件下(分别为45%~50%、60%~65%和75%~80%的田间持水量)活性氧清除酶(SOD、CAT、POD、APX)活性以及MDA含量的变化,分析土壤干旱程度、植物和生长季三因素对上述各生理指标的影响,研究群落共存种对土壤水分变化的响应,揭示水分变化后群落共存种的群体效应和植被演替的植物生理生态机制.结果表明:(1)9种群落共存种的SOD、CAT、POD、APX活性以及MDA含量存在显著的种间差异,生长季中(8~10月)以及不同水分条件下也存在显著差异.(2)达乌里胡枝子SOD活性、白羊草CAT活性、中华隐子草POD活性以及小花棘豆的CAT、POD和APX活性均相对较高,而且达乌里胡枝子的MDA含量较低;生长季中(8~10月)9种群落共存种的SOD、CAT和POD活性逐月下降且MDA含量进入10月后也有所下降,说明生长旺季耐旱性指标的生理活性较高;与POD和CAT活性相比,9种群落共存种的SOD和APX活性在重度干旱胁迫下显著提高,显示SOD和APX活性对于干旱胁迫具有较好的响应能力.(3)达乌里胡枝子和小花棘豆具有较高的SOD、APX活性和较低的MDA含量,说明达乌里胡枝子和小花棘豆的耐旱性相对较强,在土壤水分较低时,其在群落中的相对多度可能会有所上升.(4)9种群落共存种在演替序列上以前期种的SOD和APX活性相对较低,而演替后期种相对较高,表明演替后期的植物较为耐旱.
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