土地利用与管理对干旱区绿洲土壤有效磷再分布的耦合影响

Soil available phosphorus is one of major limiting nutrient elements for plant productivity in arid ecosystems. In recent years, native sandy steppes have been converted extensively into plantations (i.e. Haloxylon ammodendron, Populus gansuensis and Pinus sylvestris) or farmlands with different management practices. However, little information is available about the combined effects of land use and management on soil phosphorus fractions and availability in an arid oasis. Therefore, the objective of this study is to reveal the redistribution characteristics and its driving mechanisms of soil phosphorus fractions and availability across six typical land use types, which lies in Lin-ze oasis in the middle reaches of the Heihe River Basin in the arid regions of China. Based on this objective, we are going to implement specifically the following jobs. Firstly, it is essential to survey ecologically (including vegetation coverage, irrigation amount, fertilizer input etc), and to select sampling sites across six land use types. Soil samples for this study will be collected to analyze soil pH, soil texture, soil moisture, soil organic carbon, total nitrogen, phosphatase activity, microbial biomass carbon, nitrogen and phosphorus across six land use types. Secondly, soil phosphorus composition will be determined by the modified Hedley sequential fractionation procedure and solution 31P nuclear magnetic resonance (31P-NMR) spectroscopy. Thirdly, based on all above data sets, the relative contribution of vegetation coverage, irrigation and fertilization on the redistribution of soil available phosphorus fractions is to be calculated using partial RDA method, and the influence of eco-environmental factors on soil available phosphorus fractions will be evaluated by multiple regression, path analysis and structural equation modeling. Finally, this study is i) to elucidate the horizontal and vertical distribution characteristics of soil phosphorus fractions and availability across land use types; ii) to evaluate the relative contribution of vegetation coverage, irrigation and fertilization on the redistribution of soil available phosphorus fractions from the landscape scale; iii) to assess the effects and contribution rates of main soil eco-environmental factors on soil available phosphorus fractions from the quadrat scale. These findings, taken together, will help the enrichment of phosphorus cycling theory and methods in this arid oasis ecosystem, and are also useful as a reference to which future soil phosphorus utilization and management can be compared.

土壤有效磷严重缺乏是限制干旱区绿洲生态系统功能的主要因子。近年来，人工绿洲外围大面积天然荒漠草地被转变为人工林和灌溉农田，然而，至今尚缺乏对土地利用方式和土地管理强度相互作用在不同尺度上影响绿洲土壤磷素组分及其再分布的系统研究。本项目以黑河中游的临泽绿洲6种典型土地利用类型为研究对象，通过野外样带调查、定位观测以及采用改进的Hedley磷素分级和磷的核磁共振波谱（31P-NMR）分析方法对样地土壤剖面中磷素组分（化合物）及其含量进行测定，重点研究不同土地利用方式和管理强度相互作用对土壤磷素组分特别是有效磷组分再分布的影响，在景观尺度上解析植被类型、灌溉和施肥管理对土壤有效磷组分再分布的驱动效应及机理，在样方尺度上解析主要土壤生态环境因子对土壤有效磷组分再分布的影响程度及其调控机理。研究成果有助于干旱区绿洲土壤磷素循环理论和研究方法的发展，并为人工绿洲土壤磷素的高效利用管理提供科学依据。

土壤有效磷严重缺乏是限制干旱区绿洲生态系统功能的主要因子。近年来，人工绿洲外围大面积天然荒漠草地被转变为人工林和灌溉农田，然而，至今尚缺乏对土地利用方式和土地管理强度相互作用在不同尺度上影响绿洲土壤磷素组分及其再分布的系统研究。. 目前，本项目重点研究了黑河中游荒漠绿洲区不同土地覆被下土壤养分资源（特别是磷养分资源）特征及其管理策略。结果表明：（1）不同土地覆被下土壤磷素含量分布差异特征显著，并且呈现出中等变异性甚至强变异。（2）不同土地覆被下土壤各磷素形态处于动态平衡状态，磷组分之间相互转化、影响和制约。（3）影响土壤有效性转化的主要磷素形态为Ca8-P、Ca2-P、中等活性有机磷等。（4）不同土地覆被下土壤全氮、全磷、速效氮、速效磷以及速效钾等养分含量的分异特征明显。（5）不同土地覆被下全氮养分含量和全磷养分含量总体上缺乏，速效氮养分含量、速效磷养分含量以及速效钾养分含量总体上中等。（6）梭梭土壤养分资源最丰富，湿地次之，樟子松、农田、杨树林、固定沙地以及沙丘土壤养分资源递次降低。. 可见，提高土壤养分有效性并使其达到平衡状态对于植被生长及土壤环境优化十分重要。研究成果有助于干旱区绿洲土壤养分（磷素）循环理论和研究方法的发展，并为人工绿洲土壤养分（磷素）的高效利用管理提供科学依据。