封育年限对岩溶植被组成和土壤肥力修复的影响

Effects of exclosure duration on vegetation composition and soil fertility restoration in karst area, Guangxi

关键词:  封育年限, 群落组成, 土壤肥力, 修复, 岩溶地区

Key words:  exclosure duration, community composition, soil fertility, restoration, karst area

摘要:

岩溶植被修复是国家重大战略需求,为揭示封育年限对岩溶植被组成和土壤肥力修复的影响,该研究以空间代替时间的方法,选择不同封育年限的草丛(封育5 a)、灌丛(15 a)、灌乔林(25 a)、次顶极乔林(35 a)和顶极乔林(55 a)作为研究对象,调查分析不同封育年限岩溶植被组成和土壤肥力的特征及其修复机制。结果表明:研究样地(18 000 m²)共有维管植物175种,隶属74科139属,不同封育年限群落科属种组成明显不同,以封育5 a的最低(6科19属20种),封育35 a的最高(48科74属88种)。随着封育期延长,乔木生活型比例显著增加,灌木为先增后减,草本急剧减少,藤本先增后减。随着进展演替,群落不同层次的优势种替代规律不同,草本层为阳性杂草→阳性禾草→中生性或阴生性蕨类植物的有序性替代; 灌木层为灌木种类被乔木幼苗幼树所替代; 而乔木层却表现为常绿种类占优势到常绿与落叶树种共优势的结构性替代。封育初期群落物种组成简单,多样性较低,土壤有机质、全氮、有效氮含量较低,进入中期(25 a),多样性升高,土壤养分含量也增高,进入后期(55 a),多样性降低,土壤养分含量也相应下降,但维持在较高水平,表现出较强的协同修复效应。冗余分析(RDA)表明,群落物种组成在封育初期受土壤容重(SBD)、毛管孔隙度(CP)、全钾(TK)、速效钾(AK)、速效磷(AP)的显著影响,而在中后期则受土壤有机质(SOM)、水分含量(MC)、非毛管孔隙度(NCP)、全氮(TN)、有效氮(AN)以及碳氮磷化学计量比的显著影响。

Abstract:

Vegetation restoration in karst area is a national strategic need. In order to reveal the effects of exclosure duration on vegetation composition and soil fertility restoration in karst area, we investigated the characteristic of vegetation composition and soil fertility, and the underlying mechanisms of restoration under different exclosure duration via space-time substitution method with tussock(exclosure for 5 a), boscage(exclosure for 15 a), shrub and arbor forests(exclosure for 25 a), sub-climax arbor forests(exclosure for 35 a), and climax arbor forests(exclosure for 55 a). The results were as follows: Vascular plants in all the plots(18 000 m²)had 175 species, belonging to 74 families and 139 genera. The composition of families, genera and species were the smallest in the initial stage of exclosure with 6 families, 19 genus and 20 species, respectively, and peaked at the stage of exclosure for 35 a with 48 families, 74 genus and 88 species, respectively. The life-form ratio significantly increased for arbor, increased initially but declined later for shrubs, sharply decreased for herbs, and increased initially but declined later and maintain stable for vines with the prolong of exclosure duration. In the herbaceous layers, the vegetation succession was sequential substitution as follows: sun weeds → sun gramineous plants → mesophily or shade ferns. In shrub layers, shrubs were substituted by arbor seedlings. A structural substitution occured in arbor layers with changing from dominating by evergreen species to co-dominating by evergreen and deciduous species. A synergy restoration effect occurred between vegetation composition and soil fertility. The simple vegetation composition and low diversity connected with low content of soil organic matter(SOM), total nitrogen and available nitrogen at the initial exclosure stage(5 a). At the middle stage of exclosure(25 a), high diversity connected with high soil fertility. While, in the later stage of exclosure(55 a), low diversity connected with relative low soil fertility although it maintained at relatively high level. The redundancy analysis indicated that the community species composition was significantly affected by soil bulk density(SBD), capillary porosity(CP), total potassium(TK),available potassium(AK)and available phosphorus(AP)in the initial exclosure period, then by soil organic matter(SOM), moisture content(MC), noncapillary porosity(NCP), total nitrogen(TN), available nitrogen(AN), and stoichiometric ratio in the later exclosure period.