干旱对中亚草地总初级生产力时滞和累积效应的影响评估

Assessment of time⁃lag and cumulative effects of drought on gross primary productivity of grassland in Central Asia from 1982 to 2018

随着全球气候变化加剧,干旱对草原生态系统碳循环的影响更加复杂。作为全球陆地生态系统碳通量的最大组成部分,总初级生产力(GPP)对整个陆地碳循环具有深远影响,因此,探讨干旱对草地GPP的影响,对于理解区域碳循环机制,维护草地生态系统稳定发展具有重要意义。以中亚为研究区,基于NIRv-GPP和SPEI base v.2.7数据集,利用Theil-Sen Median斜率估计结合Mann-Kendall显著性检验、M-K突变检验和相关分析方法,探究1982—2018年干旱对草地GPP的时滞和累积效应。结果表明:(1)中亚地区草地GPP年平均值随时间变化整体上呈下降趋势,标准化降水蒸散指数(SPEI)年平均值呈降低趋势;(2)干旱对中亚绝大多数草地(95.6%)产生了时滞效应,滞后时间尺度集中在2—3个月;随着干旱状况的加重,滞后时间变长,滞后效应对草地GPP影响减弱;(3)中亚绝大多数草地(95.8%)对干旱存在累积响应,累积时间尺度以4、5、10月为主;随着干旱状况的加重,累积时间变短,累积效应对草地GPP影响增强;(4)通过对比研究时滞效应和累积效应发现:中亚超过四分之三(76.84%)的草地区域,干旱对草地GPP的时滞效应大于累积效应。研究结果可为理解气候变化背景下中亚生态环境动态变化特征及区域碳循环机制提供参考。

The Central Asia is located in the hinterland of Eurasia,with scarce rainfall and uneven distribution of water resources.It is the largest arid zone in the temperate and warm temperate zones of the Northern Hemisphere.The vegetation types in the Central Asia are mainly woodland,grassland and cultivated land,among which grassland occupies absolute superiority in land use types.As one of the most important components of the terrestrial ecosystem,grassland is the means of production and management object of animal husbandry,which plays a key role in maintaining the global carbon cycle,regional ecological security and social stability.With the intensification of global climate change,the effects of drought on the carbon cycle of grassland ecosystems become more complex.As the largest component of global terrestrial ecosystem carbon flux,gross primary productivity(GPP)has profound impact on the overall terrestrial carbon cycle.Therefore,it is of great significance to explore the effects of drought on grassland GPP for understanding the mechanism of regional carbon cycling and maintaining the stable development of grassland ecosystem.This paper takes Central Asia as the research area,and based on NIRv-GPP and SPEI base v.2.7 dataset,uses Theil-Sen Median slope estimation combined with Mann-Kendall significance test,M-K mutation test,and correlation analysis methods to explore the time-lag and cumulative effects of drought on grassland GPP from 1982 to 2018.The results showed that:(1)the annual average GPP and the annual average standardized precipitation evapotranspiration index(SPEI)of grassland in the Central Asia showed a downward trend over time.(2)Drought had a time-lag effect on most grassland(95.6%)in the Central Asia,and the lag time scale was concentrated in 2—3 months.With the aggravation of drought conditions,the lag time became longer,and the effect of lag effect on grassland GPP was weakened.(3)Most grassland(95.8%)in the Central Asia showed cumulative response to drought,and the cumulative time scale was mainly in April,May and October.With the aggravation of drought,the cumulative time became shorter,and the cumulative effect on grassland GPP became stronger.(4)Through comparative study of time-lag effect and cumulative effect,it was found that the time-lag effect of drought on grassland GPP was greater than the cumulative effect in more than three quarters(76.84%)of grassland areas in the Central Asia.The results can provide reference for understanding the dynamic change characteristics of ecological environment and the mechanism of regional carbon cycle in the Central Asia under the background of climate change.