塔里木河中下游地区不同地下水位对植被的影响

THE EFFECT OF GROUNDWATER LEVEL ON VEGETATION IN THE MIDDLE AND LOWER REACHES OF THE TARIM RIVER, XINJIANG, CHINA

根据近几年塔里木河中下游地区的大量监测结果 ,分析了不同地下水位对植被的影响。结果显示 :1)在塔里木河中下游 ,地下水位与植被盖度和植物种类的回归模型分别可以表示为 :Y =15 9.32e-0 .3 14 8X,R2 =0 .8193,p <0 .0 1;Y =9.113e-0 .162 3X,R2 =0 .6 0 6 7,p <0 .0 1。 2 )地下水位对植被的影响在很大程度上是通过改变土壤含水率来实现的 ,当地下水位在 1～ 4m时 ,其回归模型为 :Y =6 4 .898e-0 .515X,R2 =0 .72 7,p <0 .0 1;当地下水位在4～ 12m时 ,Y =2 1.14 7e-0 .178X,R2 =0 .6 5 8,p<0 .0 1。当地下水位在 3.5～ 4 .0m时 ,土壤含水率出现明显变化 ,因此认为 3.5m是塔里木河中下游地区草本植被生态恢复的最低水位。 3)通过胡杨叶脯氨酸 (Pro)和脱落酸 (ABA)在不同水位条件下的含量变化 ,可以认为引起胡杨水分胁迫的地下水位出现在 5 .0m。其后随着水位的降低 ,胡杨脱落酸的积累更加明显 ,地下水位与胡杨叶脱落酸含量可以表示为 :Y =0 .70 35e0 .40 8X,R2 =0 .830 4 ,p <0 .0 1。 4 )通过塔里木河下游输水后的植被调查 ,当地下水位出现明显升高后 ,植被的地表生态响应非常明显 ,乔灌草植被在水位升高至不同水位后均出现相应的变化 ,说明以上的分析是符合实际的。

Since shallow groundwater is the main source of vegetation growth in arid zones, groundwater level is one of the important eco-environmental factors affecting natural vegetation in the middle and lower reaches of the Tarim River in Xinjiang of China. Therefore, it is important to understand the relationship between the groundwater level and the vegetation. Accordingly, 12 monitoring sections with 58 monitoring wells and 58 vegetation sample plots were selected and established. Based on several years of monitoring data, we describe the influence of different levels of groundwater level on soil moisture content, vegetation (species and coverage) and the proline (Pro) and abscisic acid (ABA) content in the leaves of Populus euphratica. Regression models on groundwater level-vegetation coverage (Y=159.32e -0.314 8X, R 2=0.819 3, p<0.01) and groundwater level-species (Y=9.113e -0.162 3X, R 2=0.606 7, p<0.01) were both significant. The effect of groundwater level on vegetation function is expressed through soil moisture content, and ground water level also was significantly related to soil moisture content by the following regression models: Y=64.898e -0.515X, R 2=0.727, p<0.01 (when the groundwater levels are between 1 to 4 m of the soil surface); and, Y=21.147e -0.178X, R 2=0.658, p<0.01 (when groundwater levels are between 4 to 12 m below the surface). The soil moisture content changes significantly when the groundwater level drops to 3.5-4.0 m below the surface, henceforth, 3.5 m is regarded as the lowest groundwater level acceptable for restoration of the natural meadow vegetation. By analyzing the changes of the Pro and ABA content in the leaves of P. euphratica, we determined that water stress develops in these populations when groundwater levels drop below 5.0 m depth and that the ABA content is a more sensitive indicator of water stress than Pro content in the leaves. This relationship is described by the following equation: ABA content=0.703 5e 0.408X, R 2=0.830 4, p<0.01. Our results indicate that ground water level is a critical ecological factor controlling the vegetation in the lower reaches of the Tarim River. Some xerophytic trees, meadows and bushes were restored by changing groundwater levels; hence, any vegetation restoration efforts in this region will need to manage ground water levels to be successful.