| Global climate has rapidly warmed in the past century,with the increase in greenhouse gas concentrations being an important driving factor.The complexity of global warming is manifested in its spatial and temporal patterns.Spatially,the warming amplitude is highest in the middle and high latitudes of the northern hemisphere,with northwest China experiencing a rapid increase of 0.3℃/10a.Temporally,the period after the 1980s has seen the largest increase in warming in nearly a century.Climate warming poses great challenges to the stability and development of forest ecosystems,and has significant impacts on forest carbon sequestration,the physiological and ecological characteristics of trees,species composition,and community structure.The Qilian Mountains in northwest China,as a climate-sensitive area affected by both the East Asian monsoon and the westerlies,are extremely vulnerable to climate change.Currently,dendrochronological studies in the Qilian Mountains mainly focus on exploring the relationship between inter-annual tree-ring width,daily radial growth,and climate.However,there are significant differences in the research results between the radial growth of interannual and intra-annual.Therefore,the Qinghai Spruce(Picea crassifolia)was selected as the research object to study dendrochronology.We collected25 trees and 50 cores in the middle of the Qilian Mountains,established a standard tree-ring width chronology,and used point dendrometers to continuously monitor the radial growth of Qinghai spruce for two years to reveal the radial growth patterns of trees at inter-annual and intra-annual scales and evaluate the stability of Qinghai spruce’s response to different climate drivers.The research results deepen our understanding of the response of Qinghai spruce in the middle of the Qilian Mountains to climate,and provide a scientific basis for guiding forestry production and forest management measures in arid and semi-arid areas.The main conclusions are as follows:(1)Data from the meteorological station in Qilian Mountain indicates a significant increase in temperature(0.3°C/10a,p<0.01)on an inter-annual scale from 1953 to 2019.The period from 1953 to 1983 is classified as a temperature-stable period(0.1°C/10a,p>0.05),while the period from 1984 to 1999 is identified as a rapid warming period(0.8°C/10a,p<0.01),and the period from 2000 to 2019 is characterized as a warming hiatus period(0.2°C/10a,p>0.05).Annual total precipitation has a large fluctuation but no significant trend(0.8 mm/10a,p>0.05).Meteorological data shows that the climate in 2022 was drier than in 2021,with an increase in the annual average temperature of0.5°C,a decrease in precipitation of 41.5 mm,an increase in soil temperature of 0.1°C,and a decrease in soil moisture content of 0.03 m~3/m~3.(2)The statistical parameters of the Qinghai spruce dendrochronology indicate its high quality and rich climate information suitable for dendrochronological studies.Specifically,it has a high mean sensitivity MS(0.307),a high expressing population signal EPS of the sample population(0.984),and a first-order serial coefficient(AC1)(0.479).The annual radial growth trend of Qinghai spruce has significantly declined(-0.645 cm~2/10a,p<0.01),with the greatest decline occurring during the rapid warming period(-11.887 cm~2/10a,p<0.01).When the temperature stagnates,the decline in the tree growth trend slows(-0.744 cm~2/10a,p<0.05).(3)On an interannual scale,Qinghai spruce is jointly restricted by high temperature and water shortage.However,there are significant differences in response during different periods of climate change.Specifically,the sensitivity of tree radial growth to temperature is positively correlated and negatively correlated to precipitation,with the strongest sensitivity.During the temperature stagnant period,the response to temperature disappears,and only a significant positive correlation with precipitation is observed at the end of the previous year’s growing season.Response stability analysis indicates that with climate change,the response of trees to temperature shows a trend of first increasing and then decreasing on an interannual scale,exhibiting significant"divergent responses."However,at the end of the previous year’s growing season,there is a stable positive response to precipitation,indicating that the constraint of precipitation on tree growth is continuous and stable.(4)On an annual scale,there are differences in the phenological characteristics of the growth season between years.In 2022,compared to 2021,the start of the growth season was delayed by 8 days(April 5th and April 13th),the end date was brought forward by 2 days(August 18th and August 16th),and the total number of growth days decreased by 10 days(136 and 126 days).The daily radial growth pattern also showed significant differences,with the radial growth rate of Qinghai spruce in 2022 decreasing by 2.2μm/d compared to 2021(13.6μm/d and 11.4μm/d),and the maximum growth rate decreasing by 4.5μm/d(22.2μm/d and 17.7μm/d).The date of the maximum growth rate was delayed by 6 days(May 22nd and May 28th),and the annual growth amount decreased by 491μm(3284μm and 2793μm).(5)On an annual scale,the radial growth of Qinghai spruce is strongly limited by soil temperature and soil moisture content in the early growth season.However,there are differences in the main controlling climate factors between different years.In 2022,it was significantly restricted by extreme high temperatures,which enhanced its negative correlation with solar radiation and positive correlation with precipitation and relative humidity.In terms of response stability,the radial growth of Qinghai spruce exhibits a stable negative response to solar radiation and a stable positive response to precipitation on an annual scale.However,there are also"divergent responses"in different years.In 2021,it was significantly restricted by solar radiation and total precipitation in the mid-to-late growth season,while in 2022,the restriction was stable in the early and mid growth season. |
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