| Qilian Mountain is an important ecological barrier in the northwest China,while Qinghai Spruce is the main arbor species of forest ecosystem in the middle section of Qilian Mountain,which has important strategic significance for maintaining the ecological security of Qilian Mountain.Accurately analyzing the bio-temperature and physiological responses of forests to climate change at the catchment scale is the key to studying the impact of global change on ecosystems,and is the key to evaluate the cycle of nutrients,water,energy,and carbon in the forest ecosystem under current environmental changes.The in-depth research and accurate analysis of the relationship between forest phenology and physiological indices of trees and climate can provide scientific basis for accurately describing the structure,function and ecological and hydrological processes of forests,and also provide theoretical guidance for sustainable management of water conservation forests.Phenology is an indicator that forest responses to environmental changes,and the radial growth is the focus of tree-ring climatological research,leaf area index(LAI)is an important input parameter to simulate the carbon and water cycle in forest ecosystem,stem flow is a key factor to interpret the transpiration of forest.The study of the relationship between them and the environment is an important task of forest ecology under climate changes.In this paper,four physiological growth parameters of phenology,different radial growth,canopy LAI and different dominance sap flow of the leaf expansion and cone matures of Qinghai Spruce were monitored for two consecutive years(2015~2016),their dynamic changes were analyzed,and their relationship with air temperature,precipitation,soil temperature,and soil water content was studied.The results showed that:(1)The average temperature in 2016 at an elevation of 2700 m in the research area was 0.37°C higher than that in 2015,the spruce leaf expansion started 3 days earlier in 2016 than 2015,the cone ripening period of Qinghai Spruce was 2 days ahead in 2016 than 2015.The increase of accumulated temperature is the reason for the increase of phenological duration,when it reaches a certain value,the phenology change of Qinghai spruce will occur.There was a significant positive correlation(p<0.01)between the duration of Qinghai Spruce leaf expansion stage and the precipitation in the previous month.Both the leaf expansion stage and cone mature period were significantly affected by the precipitation in the previous month.The precipitation has a certain degree of lagging effect on the phenology of the Qinghai Spruce leaf expansion stage and cone mature period.The duration of Qinghai Spruce leaf expansion stage had significant positive correlation(p<0.01)with the soil temperature when the leaf expansion stage began,that was,the duration of leaf phenology duration was extended during the increase in soil temperature.The duration of cone mature period had significant negative correlation(p<0.01)with the soil temperature when the cone mature period began,that was,the duration of cone mature period was shortened during the increase in soil temperature.Both the phenology of Qinghai Spruce leaf expansion stage and cone mature period were significantly affected by the soil water content in the previous month.The impact of the soil water content on Qinghai Spruce leaf expansion stage and cone mature period had a certain degree of hysteresis.(2)The daily radial growth and annual radial growth of Qinghai Spruce were proportional to diameter class,large trees had the largest cumulative radial growth,and smallest tress had the smallest one.Radial growth of Qinghai Spruce in different diameter classes was less affected by air temperature but positively correlated with precipitation,and the correlation coefficient was small.The soil temperature had a significant effect on radial growth of Qinghai Spruce(p<0.05).The correlation analysis showed that,the soil temperature in 0-20 cm soil layers had a general effect on the radial growth of young and mid-trees,but had a significant effect on radial growth of large trees(p<0.05);the soil temperature in 20-80 cm soil layers had a great significant influence on the radial growth of large trees(p<0.01),and had a significant effect on the radial growth of young and mid-trees(p<0.05).The radial growth of Qinghai Spruce was positively correlated with the soil water content in the 10-20 cm soil layers,but the correlation coefficient was very small,which was significantly positively correlated with the soil water content in the 40-60 cm soil layers(p<0.05),and great significantly positively correlated with the soil water content in the 60-80 cm soil layers(p<0.01).The radial growth of young and large trees was great significantly correlated with the weighted average soil water content(p<0.01),and the radial growth of mid-trees was significantly correlated with the weighted average soil watercontent(p<0.05).The results of multiple regression analysis showed that,the hydrothermal factors commonly affecting the radial growth of the Qinghai Spruce were the soil temperature in 40-60 cm soil layers,60-80 cm soil layers,and the soil water content of 0~10cm soil layers.(3)The seasonal variation of Qinghai Spruce LAI showed a single-peak curve which rose first,reached a maximum and stayed relatively stable,and then fell again.The peak of the curve appeared around mid-July,and the LAI was between 2.33 and 4.18.The leaf index of Qinghai Spruce in different months was positively correlated with air temperature,and the precipitation.The LAI in July and August was positively correlated with air temperature(p<0.05).The Qinghai Spruce LAI in July and August was significantly correlated with soil temperature in each soil layers,and the Qinghai Spruce LAI in May and June was significantly correlated with soil temperature in 20-80 cm soil layers.Overall,the Qinghai Spruce LAI was positively correlated with the soil water content,but was slightly different in different months.The multiple regression analysis showed that,the stepwise multiple regression models fit the relationship between LAI and air temperature,precipitation,soil temperature and soil water content of Qinghai Spruce well.In general,the coefficients and the overall model have passed the test and had statistical significances,moreover,the main hydrothermal factors affecting the LAI in different months were different.(4)The monthly average sap flow density of Qinghai Spruce with different dominance degrees was ranked as: dominant wood> subdominant wood> medium wood> pressed wood.The sap flow density of dominant wood was great significant positively correlated with air temperature(p<0.01),the sap flow density of subdominant wood and medium wood was significant positively correlated with air temperature(p<0.05),and the sap flow density of pressed wood was positively correlated with air temperature.The sap flow density of Qinghai Spruce with different dominance degrees was positively correlated with soil water content,and the correlation coefficient was smaller.Among,the soil water content in 0-10 cm soil layers was significantly correlated with the sap flow density(p<0.05).The results of multiple regression analysis showed that,the hydrothermal factors commonly affecting the sap flow density of Qinghai Spruce were air temperature,soil temperature in 0-10 cm soil layers,soil water content in 10-20 cm soil layers,and soil water content in 20-40 cm soil layers. |
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