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题名: 黄土高原草地群落结构沿江水梯度的变化及对人工植被恢复的响应
作者: 张钦弟1
学位类别: 博士后
答辩日期: 2017-05
授予单位: 中国科学院大学
授予地点: 北京
导师: 陈利顶 ; 卫伟
关键词: Loess Plateau, plant functional traits, plant species diversity, soil moisture, precipitation gradient, vegetation restoration
其他题名: Response of grassland community structure to precipitation gradient and afforestation in the Loess Plateau
学位专业: 生态学
英文摘要: The interaction between vegetation and soil moisture and its spatial-temporal variations at different scales in the arid and semi-arid areas is a hotspot in current studies of Ecohydrology. Soil moisture plays a critical role in many surface processes in terrestrial ecosystems. Both climate change and vegetation restoration have resulted in altered hydrothermal conditions and variation in soil moisture content which affects plant community structure and function in the Loess Plateau. Grassland is a critical component of the arid and semi-arid areas, and serves as the background /baseline of soil moisture and community structure in the Loess Plateau. The aim of this study was to explore the response of grassland community structure and soil moisture to precipitation decline and afforestation, and to identify the favored shifts in vegetation and soil moisture across a regional scale. The identification of the interactions between vegetation and soil moisture is an important issue for the ecological restoration in the Loess Plateau, and can support more effective restoration policies in arid and semi-arid regions. 52 grassland sites and 18 afforestation sites were surveyed on a southeast- northwest transect along precipitation gradient in the Loess Plateau to identify the favored shifts in vegetation and soil moisture. The plant community structure was explored by both trait-based approaches and species diversity indexes, and the soil moisture in the depth of 0-3 m was observed by gravimetric approach. Variation partitioning was used to explore the relative contribution of soil moisture, precipitation and temperature to the spatial patterns of community-weighted mean traits, and the tradeoff relationship between species diversity indexes and soil moisture along the precipitation gradient was quantified in the Loess Plateau. The soil moisture condition and understory plant species diversity were compared between afforestation and natural grassland. The major conclusions is this study are: (1) To understand how precipitation, temperature and vertical soil moisture (0-3 m) combine to regulate community structure at the regional scale, we used a functional- trait approach to quantify the relative contributions of these environmental variables to community-weighted means of individual trait and a multiple trait combination. The southeast-northwest transect represents a steep hydro-thermal gradient, and drought tolerance emerged as the dominant strategy according to community-weighted mean traits. Drought-bearers were characterized by low vegetation, narrow and small leaves, low growth rate (specific leaf area) and high dry matter accumulation (leaf dry matter content) that optimize their water use efficiency and reduce transpiration. Leaf width, specific leaf area and leaf dry matter content appeared to be strong markers of this strategy, and exhibited clear drought-induced shifts along the gradient. Community- weighted mean traits were strongly influenced by water availability and its interactions with temperature. We also found mean annual temperature contributed additional effects on functional traits, suggesting co-occurring coldness stress could strengthen the effect of drought stress on functional traits in the northwest of the Loess Plateau. Compared with mean annual precipitation (MAP) and surface soil moisture (0-0.2 m), sub-surface soil moisture (0.2 m-1.0 m) contributed the largest variation of community- weighted mean traits, highlighting the importance of sub-surface soil moisture as an environmental filtering to community functional composition in drylands. Hence, we recommend using surface soil moisture (0.2 m-1.0 m) as an agent of water availability in regional studies. Results of this study can provide scientific guidance on understanding the effects of environmental changes, especially soil desiccation, on community structure and linkages to ecosystem function in water-limited ecosystems. (2) Vertical soil moisture (0-3 m) and species diversity were selected as soil-plant system variables of grasslands, and the tradeoff relationships between them along the precipitation gradient were quantified in the Loess Plateau, China. Results showed that the vertical profiles of soil moisture revealed large variations with the precipitation gradient changing, and significant linear correlation existed between the average soil moisture of the profile and the mean annual precipitation. Hereinto, the soil moisture in the shallow layer (0-1.0 m) was affected more greatly by precipitation. The Patrick index, Shannon-Wiener index and community-based functional diversity also increased linearly along the precipitation gradient, except evenness index (P>0.05). The linear piece-wise quantile regression was applied to determine the inflection points of these tradeoffs responses to the precipitation gradient. The results demonstrate the tradeoff revealed obvious trends along the precipitation gradient. The inflection point for the species diversity-soil moisture tradeoff was detected at MAP= 350 mm. Before the turning point, constraint exerted by soil moisture on species diversity existed in the relatively arid regions, while the constraint disappears or is lessened in the relatively humid regions in this study. Consequently, tradeoffs could be an ecological indicator and tool for restoration management in the Loess Plateau. (3) Afforestation can modify the nature and transformations of understory light conditions and soil moisture, which in turn can affect plant diversity and ecosystem function. Afforestation area has grown rapidly over the last few decades in the Loess Plateau in an effort to restore vegetation and control soil erosion. However, changes in soil moisture and understory plant diversity after large-scale afforestation have rarely been quantified. In this study, we measured changes in soil moisture and understory plant diversity (Patrick index, Shannon-Wiener index and evenness index) following afforestation (Robinia pseudoacacia, Hippophae rhamnoides, Caragana korshinskii) using a paired plots method with data from 18 sites along a precipitation gradient in the Loess Plateau. The adjacent natural grassland dominated by Stipa spp. was control sites, represent initial conditions before afforestation. We found a marginally significant decline in soil moisture in depth below 1.4 m and understory plant diversity after afforestation at the regional scale. The soil moisture and plant diversity responses to afforestation vary across species. For example, significant decreases in soil moisture in depth below 1.4 m and Patrick index were found for Caragana korshinskii plantations (P < 0.05). Robinia pseudoacacia plantations only effectively decreased soil moisture compared to natural grassland in depth below 2.0 m, but had no significant effect on understory plant diversity. We also found that when MAP below 430 mm, the effects of afforestation on both deep soil moisture (1-3 m) and Patrick index tended to significantly increase, suggesting that the effects of afforestation on soil moisture and understory plant diversity also vary across different regions.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/38747
Appears in Collections:城市与区域生态国家重点实验室_学位论文

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作者单位: 1.中国科学院生态环境研究中心
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