新疆植被总初级生产力对大气水分亏缺的响应

Responses of vegetation gross primary production to vapor pressure deficit in Xinjiang

近几十年来新疆气候变化显著,“暖湿化”转型与“湿干转折”先后出现,势必对地区植被生产力、大气干旱状况以及二者间的响应关系产生影响。以植被总初级生产力(GPP)和大气水分亏缺(VPD)作为评价指标,分析了1982—2018年新疆地区植被GPP、VPD的时空分布与演变规律,并揭示了大气水分胁迫对植被GPP的影响。结果表明:(1)新疆植被GPP整体具有北高南低的分布特征,年均值为256.6 g C·m^(-2)·a^(-1),呈显著上升趋势。GPP增加趋势占植被总面积的82.00%,其中增加显著区约占42.81%,多分布于南疆绿洲和北疆山前农业区;GPP下降趋势占比较小且分布零散。(2)新疆地区VPD具有“山区低、平原/盆地高”的鲜明格局,年均值为0.66 kPa,呈不显著波动上升趋势。全疆大部地区表现出VPD显著性上升,下降趋势零星出现在昆仑山脉高海拔山区。(3)新疆植被GPP对VPD的响应“正负共存”,并具有明显空间异质性。GPP与VPD的负相关占植被区总面积的54.52%,主要出现在山前草地地带;正相关则主要分布在塔里木盆地边缘和天山北坡及其东段,以栽培作物和灌木类型为主。VPD对GPP的影响在不同植被类型间差异鲜明,而在同一植被类型内正、负响应共存。分析认为,虽然大气水分胁迫尚未成为地区植被生产力变化的主导驱动力,但在新疆干旱化急剧增加背景下,仍需加强对GPP与VPD响应关系的跟踪。

Climate change in Xinjiang,China,has been remarkable in recent decades.With a significant shift from warm-wet to warm-dry,regional vegetation productivity,atmospheric drought conditions,and the response relationship between them will inevitably be affected.Based on multisource data such as ground meteorological observations and reanalysis data,considering remote sensing products,vegetation gross primary productivity(GPP),and vapor pressure deficit(VPD)as indicators,this study analyzed the spatial-temporal distribution and evo-lution patterns of vegetation GPP and VPD in Xinjiang from 1982 to 2018,as well as the influence of VPD changes on GPP.The results are as follows:(1)The annual mean GPP in Xinjiang was higher in the northern region,espe-cially the mountains,than in the southern region.The annual mean GPP in Xinjiang was 256.6 g C·m^(-2)·a^(-1) with a significant upward trend in interannual variability(R2=0.72,P<0.01).Approximately 82.00%of the total vegeta-tion area showed an increasing trend,of which the area with significant increase accounted for 42.81%,mostly distributed in the oasis at the edge of the Tarim Basin in southern Xinjiang and agricultural areas on the north slope of Tianshan Mountains.The area with a decreasing GPP trend accounted for a small percentage,and its dis-tribution was scattered.(2)VPD showed a distinct difference of“low in the mountains and high in the basins”.A nonsignificant fluctuating upward trend was observed in the VPD,with an annual mean value of 0.66 kPa.Signifi-cant increases in VPD occurred in approximately 82.02%of the whole territory,predominantly in the Tarim and Junggar Basins.In contrast,decreasing trends occurred sporadically in the high-altitude mountainous areas of the Kunlun Mountains.(3)Overall,the response of GPP to VPD was characterized by a distinct spatial heterogeneity with positive and negative correlations.The negative correlation between GPP and VPD accounted for 54.52%of the total vegetation area,mainly in the grassland at the front edge of the mountain.While the positive correlation was mainly distributed at the edge of the Tarim Basin,the northern slope of the Tianshan Mountains and its east-ern section were dominated by cultivated crops and shrubs.Comparative analyses showed that GPP-VPD correla-tions differed significantly across vegetation types.The study proved that the change in VPD has already affected the vegetation productivity in Xinjiang.Although it has not yet become a major limiting factor,there is still a need to strengthen the tracking of the GPP and VPD response relationship to provide a scientific reference for op-timizing ecological restoration and governance.