2000—2020年青海湖流域植被降水利用效率时空变化

Spatial and temporal characteristics of annual vegetation precipitation use efficiency in the Qinghai Lake Basin from 2000 to 2020

植被降水利用效率(PUE)是评价植被生产力对降水量时空动态响应特征的重要指标。以年净初级生产力(NPP)数据、年降水量数据为基础,利用地理信息系统(GIS)和遥感(RS)技术,计算并研究了2000—2020年青海湖流域植被降水利用效率时空分布格局及其地形效应,结合年均气温、年均地表温湿度、年生长季光合有效辐射吸收系数和年植被覆盖度等数据,探讨了PUE与各因子间的相关关系。结果表明:(1)青海湖流域单位像元(1 km^(2))PUE平均值在0.4—0.7 gC m^(-2)mm^(-1)间变化,平均为0.54 gC m^(-2)mm^(-1),且在年际间无显著变化趋势(R^(2)=0.05,P≥0.05)。在空间上,青海湖流域多年PUE平均值环湖呈现不均匀分布,除青海湖东岸外,PUE值随湖面距离增大呈减小趋势;其高值区主要集中分布在青海湖西岸和南岸的半环区;年PUE变化趋势的斜率值为-0.05—0.04 gC m^(-2)mm^(-1)a-1,其中显著变化的区域占流域面积的29.63%。(2)青海湖流域多年PUE平均值在海拔效应和坡度坡向两种不同微地形效应下表现出明显的差异。海拔每升高50 m,PUE值将减少0.02 gC m^(-2)mm^(-1);随坡度增加,PUE值呈降低趋势,平坡至险坡(>45°)的变化范围为0.3—0.61 gC m^(-2)mm^(-1);不同坡向PUE值表现为由东北坡向西南坡递减,范围为0.52—0.56 gC m^(-2)mm^(-1)。(3)在空间上,青海湖流域PUE值与地表温度、光合有效辐射吸收系数、植被覆盖度和叶面积指数相关性较为明显。沿海拔梯度,空气温度和地表温度与PUE呈极显著正相关(R^(2)=0.94,P<0.01;R^(2)=0.98,P<0.01),光合有效辐射吸收系数、植被覆盖度和叶面积指数与PUE显著正相关(R^(2)=0.89,P<0.05;R^(2)=0.90,P<0.05;R^(2)=0.86,P<0.05),地表土壤湿度与PUE无显著相关性(R^(2)=0.16,P≥0.05)。评估了青海湖流域植被降水利用效率的特征及其与各因子间的相关关系,明确了植被对降水的利用能力及其耗水特性,可为青海湖流域植被保护和国家公园建设提供理论参考。

Vegetation precipitation use efficiency(PUE)serves as a crucial indicator for evaluating the productivity of vegetation in response to spatial and temporal precipitation dynamics.Using annual net primary productivity(NPP)and precipitation,the spatial and temporal distribution of PUE and its topographic effect in the Qinghai Lake Basin from 2000 to 2020 was calculated.To examine the relationship between PUE and various factors,geographic information system(GIS)and remote sensing(RS)were utilized by combining annual mean air temperature,annual mean land surface temperature,annual mean surface soil moisture,annual fraction of absorbed photosynthetically active radiation,and annual fractional vegetation cover.The results indicated that:(1)the mean unit pixel(1 km^(2))PUE in the Qinghai Lake Basin ranged 0.4—0.7 gC m^(-2)mm^(-1),with average about 0.54 gC m^(-2)mm^(-1).Moreover,there was no marked trend in PUE across the years assessed(R^(2)=0.05,P≥0.05).The average of multi-year PUE in the Qinghai Lake Basin was distributed unevenly around Qinghai Lake,except for the eastern shore,where PUE decreased with the increasing distance from the lake.High⁃value areas were mainly concentrated in semi⁃annular areas on the western and southern shores.The slope of the annual PUE trend ranged-0.05—0.04 gC m^(-2)mm^(-1)a-1,with significant changes observed across 29.63%of the basin area.(2)The average PUE over several years was found to vary in the Qinghai Lake Basin depending on altitude and microtopography.A 50 m increase in altitudinal gradients led to a 0.02 gC m^(-2)mm^(-1)decrease in PUE.Additionally,an upward trend in slope gradients resulted in a decline of PUE,with ranged 0.3—0.61 gC m^(-2)mm^(-1)from flat slope to dangerous slope(>45°);different slope aspects also resulted from the northeast to the southwest,which ranged 0.52—0.56 gC m^(-2)mm^(-1).(3)There was spatial correlation between the PUE and land surface temperature,fraction of absorbed photosynthetically active radiation,fractional vegetation cover and leaf area index in the Qinghai Lake Basin in the last 21 years was correspondingly obvious.Along the altitudinal gradient,air temperature and land surface temperature showed highly significant positive correlations with the PUE(R^(2)=0.94,P<0.01;R^(2)=0.98,P<0.01),fraction of absorbed photosynthetically active radiation,fractional vegetation cover and leaf area index were significantly positively correlated with the PUE(R^(2)=0.89,P<0.05;R^(2)=0.90,P<0.05;R^(2)=0.86,P<0.05),and surface soil moisture had no significant correlation(R^(2)=0.16,P≥0.05).This paper examined the PUE in the Qinghai Lake Basin and the correlation with different factors.It elucidated the precipitation use capacity and water consumption characteristics of vegetation,providing theoretical support for conservation practices in the Qinghai Lake Basin and the development of the National Parks.