黑河下游土壤水盐对生态输水的响应及其与植被生长的关系

Abstract

生态输水作为一项改善黑河下游生态环境的人工输水工程,研究土壤水盐与地表植被对输水的响应对于下游植被的恢复与重建具有重要的理论和实践意义。以2001年和2010年野外土壤和植物样方调查资料为基础,探讨了黑河下游土壤水盐对生态输水的响应及其与植被生长的关系,结果表明:(1)输水后不同深度土壤含水率的增加幅度依次为:胡杨林＞柽柳林＞草地;(2)不同群落土壤含盐量的增加幅度依次为:苦豆子＞柽柳＞梭梭＞胡杨;同时,土壤盐分主要以HCO₃^-和Na⁺为主的轻度盐化土向以SO₄^2-、Cl^-及Ca²⁺等为主的中度和强度盐化土转化;(3)以胡杨为例,土壤含水率小于6%时,密度和冠幅与土壤含水率呈正相关,但大于6%时,冠幅和密度分别介于40-70 m²和0.5-5株/100m²之间;同样,土壤水溶性盐含量小于1%时,密度和冠幅与土壤含水率呈正相关,但大于1%时,密度在0.5-5株/100m²之间,造成上述结果的原因更多是群落的一种"自然稀疏"现象。;The Heihe River is the second longest inland river in China. The eco-environmental problems of the oasis in the lower reaches of Heihe River have markedly deteriorated over the past several decades because of the comprehensive effects of a number of factors. These factors include the continuous decrease in the discharge water of the Heihe River, human and animal population growth, increase of socio-economic activities, and climate warming. Water deliveries have been conducted by the Heihe River Bureau since 2000 to address the existing eco-environmental problems. Several scientific and realistic issues concerning this significant artificial water delivery project include the response process and mechanism of the eco-environment involving vegetation restoration and reconstruction brought about by water deliveries in the lower reaches of Heihe River. The responses of soil water and salinity variation to water deliveries were presented based on the investigation of soil and plant plots in 2001 and 2010. This paper aimed to evaluate the variance in the soil moisture and soil-soluble salt content before and after water deliveries in the lower reaches of Heihe River. The relationship between soil moisture, as well as soil-soluble salt content, and vegetation growth variables was also determined. <br> The results indicated that the soil moisture content (SMC) increased at different depths after water deliveries in Heihe River. The rate of increase varied with the different types of communities and could be arranged in the following order:<em> Populus euphratica</em>＞<em>Tamarix chinensis</em>＞Herbal. Moreover, the soil-soluble salt content (SSC) increased after water deliveries at different depths because of the strong evaporation effects. The rate of increase could be arranged in following the order: <em>Sophora alopecuroides</em>＞<em>T. chinensis</em>＞<em>Haloxylon ammodendron</em>＞<em>P. euphratica</em>. In addition, it could be found in the conversion of soil salinity type from slightly saline soil dominated by HCO₃^- and Na⁺ to medium and intense saline soil mainly dominated by SO₄^2-, Cl^- and Ca²⁺. The average density and crown, with <em>P. euphratica</em> community as an example, increased with increasing SMC of less than 6%, in which these values ranged from 40 m² to 70 m² and 0.5 plants per 100 m² to 5 plants per 100 m² at an SMC of more than 6%, respectively. Similarly, the average density ranged from 0.5 plants per 100 m² to 5 plants per 100 m² with an SSC of more than 6%. However, the average crown did not decrease with an SSC of more than 6%. Therefore, we conclude that the self thinning process of the <em>P. euphratica</em> community, rather than the salt, caused stress to the plant growth.