| With the warming of the climate and the intensification of drought,the ecological stability of forest ecosystems is facing serious challenges.Quercus mongolica,as an important tree species in the broad-leaved forest of northern China,is highly sensitive to climate warming and drying,and climate change may lead to significant changes in the population of Q.mongolica in China.This study focuses on Q.mongolica as the research object.From 2019 to 2021,27 natural Q.mongolica stands were selected in Northeast China and northern Hebei,with a certain geographical interval and the principle of covering the area with the most concentrated distribution of Q.mongolica.Each stand was sampled with a 20m×20m sample plot.A total of 1240 tree cores of 721 larger Q.mongolica sample trees,700 leaves,and approximately 2000 seeds were collected,combined with meteorological data from 19 nearest meteorological stations,using research methods such as dendroclimatology and geometric morphology,the response of radial growth to drought and the morphological adaptation mechanism of leaves and seeds of Q.mongolica to drought were revealed,laying a foundation for predicting the growth trajectory of Q.mongolica forests and the dynamics of Q.mongolica population in the context of warming and drying,it had important guiding significance for the protection and management of Q.mongolica forest.The main results were as follows:(1)The radial growth of Q.mongolica was positively correlated with the Palmer Drought Index(PDSI),precipitation,and relative humidity in the middle of the growth season(June-July),while negatively correlated with the highest moderate average temperature from June to July.In the northern part of the study area,from east to west,the positive correlation between PDSI,precipitation,relative humidity,and radial growth from June to July continues to weaken;The negative correlation between the highest and lowest temperatures and radial growth was also weakening,while the correlation between the lowest temperature and radial growth had no significant trend of change.In the central region,from east to west,the positive correlation between PDSI from June to July and precipitation and radial growth was increasing,while the correlation between relative humidity and radial growth has shifted from negative to positive;The relationship between the highest temperature and radial growth had shifted from positive correlation to negative correlation;The correlation between the lowest and average temperature and radial growth was not significant.In the south,from east to west,the positive correlation between PDSI,precipitation,and relative humidity from June to July and radial growth showed an increasing trend;The negative correlation between the highest temperature and radial growth also showed an increasing trend;There was no significant trend in the negative correlation between average temperature and radial growth;There was no significant correlation between the lowest temperature and radial growth overall.(2)During the period from 1989 to 2017,16 sampling points had a negative correlation between radial growth and the highest temperature,14 sampling points had a negative correlation between radial growth and average temperature,15 sampling points had a positive correlation between radial growth and precipitation,19 sampling points had a positive correlation between radial growth and relative humidity,15 sampling points had a positive correlation between radial growth and PDSI,and the response of radial growth to the lowest temperature fluctuated more frequently on the time scale,The radial growth of only 4 sampling points remained negatively correlated with the lowest temperature,while the radial growth of 2 sampling points remained positively correlated with the lowest temperature.In the relatively arid Yanshan region in the southwest of the study area,the correlation between radial growth and the highest temperature at five sampling points shifted from a negative correlation between 1989 and 2004 to a positive correlation between 2004 and 2017.(3)When PDSI>0.5,the radial growth of Q.mongolica remained basically stable;When-2<PDSI≤0.5,the average tree ring width index showed a continuous downward trend.When the degree of drought deepens from moderate drought(-3<PDSI≤-2)to severe drought(-4<PDSI≤-3),the average tree ring width index does not significantly decrease.When a short-term drought occurs,with the decrease of PDSI,the reswastance of Q.mongolica showed a significant decrease trend(P<0.05),while the resilience increases with the increase of drought intensity(P<0.05),while the trend of elastic force change was not significant(P>0.05).(4)Under mild drought intensity(-2<PDSI≤-1),there was no significant change in reswastance,resilience,and resilience as the drought perswasted(P>0.05).Under moderate drought intensity(-3<PDSI≤-2),there was no significant change in reswastance as drought perswasted;After more than 2 years of continuous drought,the resilience of Q.mongolica was significantly lower than that after 1 year of drought(P<0.05),while the resilience of Q.mongolica was significantly lower than that after 1 year and 2 years of drought(P<0.05).Under severe drought intensity(-4<PDSI≤-3),as the drought continues,the reswastance still does not show significant changes(P>0.05);After more than 2 years of continuous drought,the resilience of Q.mongolica was significantly lower than that after 1 and 2 years of drought(P<0.01),and the resilience of Q.mongolica was also significantly lower than that after 1 and 2 years of drought(P<0.01).(5)During short-term mild drought,Q.mongolica basically recovered to its pre drought growth level in the first and second years after drought;During short-term moderate and short-term severe drought,the growth level of Q.mongolica was higher in the first year after drought than before,but it basically returned to the growth level before drought in the second year.During moderate drought,the growth performance of Q.mongolica was basically conswastent with that during short-term mild drought;The performance of moderate and severe drought in the medium term was highly similar to that of short-term moderate and severe drought,respectively.During long-term mild drought,the growth performance of Q.mongolica was basically conswastent with that of short-term mild drought and mid-term mild drought.During long-term moderate drought,the growth level of Q.mongolica in the second year after drought was higher than that in the first year after drought,but lower than that before drought.During long-term severe drought,the trend of growth level changes in Q.mongolica was similar to that during long-term moderate drought,but the overall growth level was lower compared to that during longterm moderate drought.(6)The leaf area,leaf perimeter,leaf width and specific leaf area of Q.mongolica were significantly positively correlated with annual precipitation and aridity index(P<0.01);Leaf length was positively correlated with annual precipitation and aridity index(P<0.05);The ratio of leaf length to width was negatively correlated with annual precipitation and aridity index(P<0.01);There was a significant negative correlation between leaf circumference and annual average temperature(P<0.05).In addition,both specific leaf area and leaf width showed a significant positive correlation with longitude(P<0.05);There was a highly significant positive correlation between leaf circumference and longitude(P<0.01);There was a highly significant negative correlation between leaf aspect ratio and longitude(P<0.01);Except for a significant positive correlation between altitude and leaf aspect ratio(P<0.05).(7)With the decrease of aridity index,H1/H2 and S1/S increased significantly(P<0.05),L2/L1 and α Significantly reduced(P<0.05),and with the deepening of drought,the sharpness of the lower part of the leaf morphology significantly increased.With the decrease of aridity index,the light capture efficiency of leaves increased significantly(P<0.05).At the same time,with the decrease of aridity index,the reciprocal of leaf vein density significantly decreased(P<0.05),that was,with the deepening of drought,the leaf vein density of Q.mongolica leaves significantly increased.(8)The length and width of Q.mongolica seeds significantly increased with the increase of 100 seed weight(P<0.05),while the length to width ratio of seeds showed no significant change trend with the increase of 100 seed weight(P>0.05).The seed length,width and 100 seed weight were significantly positively correlated with annual precipitation and aridity index(P<0.01).The coefficient of variation of width was significantly positively correlated with annual precipitation and aridity index(P<0.05),but the coefficient of variation of length,length width ratio and length width ratio were not significantly correlated with annual precipitation and aridity index(P>0.05).In addition,the coefficient of variation of seed length,width,and 100 grain weight were significantly positively correlated with longitude(P<0.05).In summary,the radial growth and morphological variation of Q.mongolica are closely related to drought.The deepening of regional climate warming and drying in the future may to some extent affect the growth rate and morphological variation of Q.mongolica,thereby affecting the growth,reproduction,renewal,and distribution of Q.mongolica population.Therefore,the results of this study not only contribute to understanding the response and adaptation mechanisms of Q.mongolica to climate change,but also help predict the growth trajectory of Q.mongolica forest and the expansion dynamics of Q.mongolica population under the background of warming and drying.It has important guiding significance for the management and management of Q.mongolica forest. |
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