2000—2017年内蒙古荒漠草原植被物候变化及对净初级生产力的影响

荒漠草原分布于干旱区和半干旱区,对气候变化的响应极为敏感,但目前学术界对于荒漠草原物候与生产力变化的研究仍较为薄弱。有鉴于此,论文采用2000—2017年MODIS NDVI数据和气象数据,利用通用数量化方法提取内蒙古荒漠草原植被的生长季始期(start of season, SOS)和生长季末期(end of season, EOS);基于Carnegie-Ames-Stanford Approach (CASA)模型估算了植被净初级生产力(NPP),并分析了植被物候和净初级生产力之间的关系。研究结果表明：① 2000—2017年内蒙古荒漠草原SOS呈显著提前趋势(0.88 d/a,P<0.05),EOS不显著提前(0.13 d/a,P>0.05),生长季长度(length of season, LOS)呈显著延长趋势(0.76 d/a)。81.53%像元的SOS与2—4月平均气温呈负相关(8.21%显著相关,P<0.05),60.80%像元的SOS与4月降水量呈负相关关系(6.12%显著相关,P<0.05);65.16%像元的EOS与9月平均气温呈负相关(5.03%显著相关,P<0.05),78.61%像元的EOS 与7—9月降水量呈正相关关系(10.12%显著相关,P<0.05)。② 内蒙古荒漠草原多年平均NPP为104.71 gC/(m ²·a),有自东向西逐渐降低的区域差异;在研究时段内,春、夏季和生长季的NPP均呈不显著增加趋势,秋季NPP有不显著减少趋势;生长季降水量增加有利于生长季NPP的积累。③ 春季NPP与SOS呈不显著负相关,秋季NPP与EOS呈显著正相关。LOS的延长促进了NPP的累积,其中生长季NPP与EOS的推迟关系更为密切。研究结果揭示气候变化对内蒙古荒漠草原植被物候和生产力有显著影响,对区域生态系统管理和生态建设具有重要参考意义。

Phenological changes of desert steppe vegetation and its effect on net primary productivity in Inner Mongolia from 2000 to 2017

Desert steppe is distributed in the semiarid and arid areas and is extremely sensitive to climate change.However, limited field observations and lack of community surveys have resulted in insufficient research on the vegetation phenology and productivity of the desert steppe. Based on the normalized difference vegetation index(NDVI) data from the MODIS dataset during 2000-2017, we used a relative threshold method to extract the phenological parameters in the desert steppe of Inner Mongolia, including the start of growing season(SOS), the end of growing season(EOS), and the length of growing season(LOS). We then estimated the spatiotemporal changes in net primary productivity(NPP) of the desert steppe vegetation by the Carnegie-Ames-Stanford Approach(CASA) model. Finally, we analyzed the relationship between desert steppe productivity,phenophases, and climate variables. Our results show that: 1) during the study period, SOS advanced significantly at a rate of 0.88 d/a(P<0.05), while EOS advanced at a rate of 0.13 d/a(non-significant). The average LOS lengthened significantly by 0.76 d/a(P<0.05). The SOS was correlated negatively with mean temperature from February to April in 81.53% pixels(8.21% was significant) and negatively correlated with April precipitation in 60.80% pixels(6.12% was significant). The EOS showed a negative relationship with mean temperature in September in 65.16% pixels(5.03% was significant) but positively correlated with precipitation from July to September in 78.61% pixels(10.12% was significant). 2) The average annual NPP from 2000 to 2017 was 104.71 gC/(m^2· a) in the study area, showing regional differences with an obviously decreasing trend from east to west. Net primary productivity in spring, summer, and the growing season increased insignificantly, while NPP in autumn showed an insignificant decreasing trend. The increase of precipitation in the growing season is beneficial to the accumulation of ecosystem NPP. 3) Advance of SOS was conducive to the accumulation of spring NPP, and the delay of EOS promoted the accumulation of autumn NPP.There was a significant correlation between the LOS and NPP during the growing season(P<0.05). This study revealed the impacts of climate change on vegetation phenology and productivity of the desert steppe in Inner Mongolia, which is significant for ecosystem management and ecological construction of the region.