中国温带草地物候对气候变化的响应及其对总初级生产力的贡献

Response of temperate grassland phenology to climate change and its contribution to gross primary productivity in China

气候变暖引起的植物物候变化影响了陆地生态系统功能和碳循环。目前研究着重关注温带和热带森林物候变化趋势、驱动因素,关于干旱半干旱地区草地物候变化及其对生态系统总初级生产力(gross primary productivity, GPP)影响仍知之甚少。因此,开展草地植物物候与生产力之间的关系研究对预测草地生态系统响应未来气候变化和区域碳循环至关重要。基于1982—2015年气象资料和GIMMS NDVI3g数据,分析了中国温带草原植被返青期(start of the growing season, SGS)和枯黄期(end of the growing season, EGS)变化及其对气候的响应,并借助一阶差分法量化物候对GPP动态变化的贡献。结果表明:(1)季前1—2个月的夜间温度增温会显著提前SGS,而当月至季前2个月的白天温度对SGS有着微弱的促进作用;季前3个月的累积降水对SGS提前作用最为强烈,累积太阳辐射在各个时期对SGS影响相对较弱。(2)不同季前时间尺度昼夜温度对草地EGS均表现出相反的作用,短期累积降水对EGS起到显著延迟的区域范围最大,太阳辐射随着季前时间的增加对草地枯黄期的延迟作用逐渐转变为提前作用。(3)EGS对草地GPP年际变化趋势的相对贡献率强于返青期。研究结果有助于深化陆地生态系统与气候变化、碳循环之间相互作用的认识,为草地适应未来气候变化和生态建设提供科学依据。

Warming-induced shifts in vegetation phenology affect ecosystem functions and the hydrological cycle.However,research has so far focuses on the trends and driving factors of phenological changes in temperate and tropical forests,while little is known about changes in grassland phenology in arid and semi-arid regions and their effects on gross primary productivity(GPP)of ecosystems.Therefore,an in-depth study of plant phenology and its relationship with productivity in grasslands under a warming context is essential to predict the response of grassland ecosystems to future climate change and the regional carbon cycle.Based on the meteorological data and GIMMS NDVI data from 1982—2015,this paper analyzed the changes in the start of the growing season(SGS)and end of the growing season(EGS)of temperate grassland vegetation in China and their responses to climate change.We also quantified the contribution of plant phenology to the dynamic change of GPP with the help of first-order difference method.The results showed that(1)in general,the increasing in nighttime temperature(Tmin)in the 1—2 month preseason phase significantly advanced SGS,however,the daytime temperature(Tmax)from the current month to first two months before the SGS had a weak effect to advance the SGS.Additionally,cumulative precipitation in the first three months before the SGS had the strongest effects on the advancement of SGS.Cumulative solar radiation was found to have a relatively weak effect on SGS in all preseason periods.(2)In terms of the EGS,the results showed that different preseason time scales of diurnal temperature showed an opposite effect on the EGS in temperate grassland,and higher nighttime temperatures would delay the onset of EGS.Short-term cumulative precipitation had a significant effect on the delay of the EGS and reached its strongest in the first 2 months of the season.The delayed effect of cumulative solar radiation on the EGS gradually changed to an advancement effect with the increase of preseason scale.(3)Based on the results of the relationship between phenology and GPP,both SGS and EGS contributed positively to the inter-annual variation of GPP in grassland across the region,and the relative contribution of EGS was stronger than that of the SGS.The results of the study help deepen the understanding of the interactions between terrestrial ecosystems and climate change and carbon cycle,and provide scientific basis for grassland adaptation to future climate change and ecological construction.