Spring Phenological Changes And Temperature Sensitivity Of Woody Plants In China During The Last 50 Years

Global warming has become an indisputable fact,and the impact on terrestrial ecosystems is gradually emerging.Plant phenology,as one of the most intuitive indicators of response to climate change,has become one of the hot topics in ecological research.The timing of leafout and flowering has changed significantly compared to the past few decades.Meanwhile,leaf-out and flowering have evolved to occur in a predetermined order.The change in the time interval between these two events will affect the survival and development of plants.Most studies on phenological responses to climate change have focused on the timing of individual events.It is not clear whether woody plants respond similarly to leaf-out and flowering in the direction and magnitude of change,nor is it clear what drives the change in their time intervals.Based on the observation data of surface phenophases and meteorological stations from1963 to 2014,the interannual variation trend,temperature sensitivity and time interval of growth phenophases(leaf-out period)and reproductive phenophases(flowering period)of 183 major tree species in 35 regions of China were studied,and the underlying mechanism and influencing factors were explored.The main research results are as follows:(1)Trend of interannual changes in spring phenology of woody plantsIn the past fifty years,the leaf-out and flowering of woody plants in China have mainly shown an early trend.76.3% of plants showed an early flowering trend,with 43.3% showing a significant early flowering(P<0.05);66.2% of plants showed an early trend in leaf-out,with36.7% showing a significant advance(P<0.05).From the perspective of change amplitude,the average annual advance is 0.5 days and 0.55 days.Among plants that leaf-out first,67.4% show an early trend in leaf-out,with an average annual advance of 0.53 days.76.3% of plants showed an early flowering trend,with an average of 0.58 days early per year;Among plants that flowering first,62.4% show an early trend in leaf-out,with an average annual advance of 0.42 days;76.0% of plants show an early flowering trend,with an average of 0.42 days early per year.In different climatic zones,more than 50% of woody plants exhibit an early trend in leafout,with an average annual increase of 0.07-0.46 days.More than 65% of woody plants exhibit an early trend in flowering,with an average annual increase of 0.09-0.44 days.Among different growth types of plants,more than 60% show an early trend in leaf-out,with an average annual increase of 0.10 days.More than 70% of trees show an early trend in flowering,with an average annual increase of 0.14-0.18 days.(2)Comparison of temperature sensitivity differences in woody plantsAmong plants that leaf-out first,25.9% of them have a higher sensitivity to flowering temperature than those that expand their leaves;Among flowering first,31.6% of plants have a higher sensitivity to flowering temperature than those that expand their leaves.Overall,woody plants are more sensitive to flowering temperature than leaf-out.From north to south,the response of plant spring phenology to temperature changes is becoming increasingly strong,manifested as a gradual increase in temperature sensitivity of plant spring phenology.The change in temperature sensitivity of plant leaf-out is as follows: for every 1 ℃ increase in temperature,the spring plant leaf expansion period is advanced by 3.02～6.24 days;The initial flowering period of plants in spring is advanced by 2.94～7.09 days.In addition,among different growth types of plants,the response of plant flowering to temperature changes is higher than that of leaf-out.(3)Trend of time interval changes between two spring phenotypes of woody plantsAmong the plants with leaf-out first,56.8% showed a trend of shortening the time interval between leaf-out and flowering,with an average annual shortening of 0.11 days;Among plants that flowering first,54.4% of plants show an extended trend in the time interval between leafout and flowering,with an average annual extension of 0.14 days.In general,in the past fifty years,the leaf-out and flowering of woody plants in China have mainly shown an early trend,flowering was more responsive to temperature changes than leaf-out,which resulted in a shorter time interval between leaf-out and flowering in plants that were first to flower later.In plants that flowering first,the time interval between leaf-out and flowering was longer.Changes in time intervals can have profound ecological consequences affecting species fitness,intraspecific/interspecific interactions and ecosystem stability.