我国东部北亚热带植物群落季相的时空变化

Spatiotemporal variation of plant community aspections in the north-subtropical zone of eastern China

研究我国东部亚热带植物群落物候与气候变化的关系,对于揭示东部季风区生态系统对气候变化响应的整体特征和空间分异,具有重要的科学意义。利用物候累积频率拟合法对盐城、武汉、合肥、屯溪1982—1996年的植物群落季相阶段进行划分,并分析了季相阶段的时空变化及其与气温的统计关系。结果表明:(1)各站多年平均变绿期、旺盛光合期和休眠期初日均有随海拔升高而推迟的倾向,而多年平均季相阶段长度的空间分异特征不明显。休眠期初日随海拔升高而推迟的事实表明,树木秋季叶变色和落叶除受到气温的影响外,还可能与光照和霜等其它环境因素有关,从而使得海拔升高对秋季物候期提早的影响有所削弱,其生态机制有待进一步研究。(2)各站变绿期初日以提前为主,长度以延长为主;旺盛光合期和凋落期初日均以提前为主,长度延长与缩短参半;休眠期初日提前与推迟参半,长度以缩短为主。(3)各站变绿期和旺盛光合期初日与前期平均气温多呈显著负相关,而凋落期和休眠期初日与前期平均气温相关不显著。利用最佳时段气温-物候回归模型重建的1982—2006年季相阶段初日的时间序列显示,盐城、武汉和屯溪的变绿期初日呈显著提前的趋势,盐城、合肥和武汉旺盛光合期初日也呈显著提前的趋势。在2002—2006年期间,各站变绿期和旺盛光合期初日均表现出明显推迟的倾向,与各地该时段前期平均气温呈下降的倾向一致。(4)从北亚热带各站到温带北部的哈尔滨,平均每向北1个纬度,多年平均变绿期和旺盛光合期初日分别显著推迟2.7—4.0 d和1.8—2.8 d,而长度则多呈不显著缩短的趋势;凋落期初日提前不显著,但长度显著缩短1.8—2.6 d;休眠期初日显著提前2.9—3.3 d,且长度显著延长5.8—7.0 d。总体上看,上述观测事实符合植物物候空间变化的一般规律,即在生长季节前半段,低纬地区的植物物候早于高纬地区;在生长季节后半段,高纬地区的植物物候早于低纬地区。

Studying relationships between plant community phenology and climate change in subtropical zone of eastern China is crucial for revealing integral characteristics and spatial differences of ecosystem responses to climate change in the Eastern Monsoonal Region.The authors used simulating method of phenological cumulative frequency to identify aspection stages of the plant community at Yancheng,Wuhan,Hefei and Tunxi during the period 1982—1996,and analyze their spatiotemporal variation and statistical relationship with air temperature.At individual stations,annual mean onset dates of greenup,active photosynthesis and dormancy stages display a delayed tendency with increased altitudes but annual mean durations of the aspection stages do not indicate obvious spatial differentiation.The delayed tendency in the dormancy onset date with increased altitudes indicates that autumn leaf coloration and leaf fall dates of trees may also correlate to other environmental factors except air temperature,such as light and frost,which may reduce the effect of altitude increase to autumn phenophase advancement.Further studies may focus on ecological mechanisms of the above result.During the study period,the greenup onset date and duration mostly advanced and lengthened;the active photosynthesis and senescence onset dates dominantly advanced but the durations of both stages were prolonged and shortened at two stations,respectively;the dormancy onset date advanced and was delayed at two stations,respectively,but the dormancy duration was mostly shortened.Furthermore,the greenup and active photosynthesis onset dates correlate negatively with preceding mean temperatures at all stations,whereas the senescence and dormancy onset dates correlate nonsignificantly with preceding mean temperatures.Based on the time series of onset dates of the aspection stages from 1982 to 2006 reconstructed by the optimum air temperature-phenology regression equations,the greenup onset dates significantly advanced at Yancheng,Wuhan and Tunxi,and the active photosynthesis onset dates also significantly advanced at Yancheng,Hefei and Wuhan.It is worth noting that the greenup and active photosynthesis onset dates at the above stations represent an obviously delayed tendency during 2002 and 2006,which is consistent with a decreased tendency in preceding mean air temperature during the same period at the stations.From the 4 stations of the north-subtropical zone to Harbin in the north of the temperate zone,the annual mean onset dates of greenup and active photosynthesis stages show a significant delay at a rate of 2.7—4.0 days and 1.8—2.8 days per latitudinal degree northwards,respectively,but the durations of the both stages display mostly a nonsignificant shortening;the annual mean onset date and duration of senescence stage represent a nonsignificant advancement but a significant shortening at a rate of 1.8—2.6 days per latitudinal degree northwards,respectively;the annual mean onset date and duration of dormancy stage indicate a significant advancement at a rate of 2.9—3.3 days and a significant lengthening at a rate of 5.8—7.0 days per latitudinal degree northwards.Generally speaking,the above observation is consistent with the common rules in spatial variation of plant phenology,namely,plant phenophases appear earlier in lower latitudes than in higher latitudes during the first half period of the growing season,whereas plant phenophases occur earlier in higher latitudes than in lower latitudes during the latter half period of the growing season.