Response To Climate Change Of Vessel Features And Radial Growth Of Four Hardwood Species From Temperate Forests Of Northeast China

Tree growth-climate relationships are critical for accurately assessing the impacts of climate change on forest ecosystems,predicting forest productivity and vegetation dynamics,and revealing tree adaptation strategies to climate change.It can change over time,space,and species.The existing studies on tree growth-climate relationships are mainly for coniferous species or in small-and medium-scales.The spatial-temporal variation in growth-climate relationship of angiosperms and its driving mechanisms are few,especially in the large scale.Under the background of global change,we carried out a dendroclimatological study using both macroscopic(radial growth)and microscopic(vessel traits)growth data of four main broad-leaved tree species(Fraxinus mandshurica,Phellodendron amurense,Quercus mongolica and Juglans mandshurica)in temperate broad-leaved Korean pine(Pinus koraiensis Sieb.et Zucc.)forest of northeast China,to reveal the spatiotemporal variation and driving mechanism of growth-climate relationships at large scales of angiosperms in the temperate forest.The main results are as follows:Quercus mongolica is the most obvious species with the characteristic of ring-porous wood and only 1-2 rows of large vessels,followed by Fraxinus mandshurica and Phellodendron amurense.The three ring-porous wood with a large hydraulic diameter(Dh)and average vessel area(MVA)and few number of vessels(N),while the semi-ring porous wood-Juglans mandshurica is the opposite.At the saplings(0-10a)stage,vessels in three ring-porous wood were more but small,and the distribution is closer to the semi-ring porous wood.It indicated that the saplings are different from the adult trees in the drought-resistance strategy caused by the balance between survival and growth.Ring width(RWL)of Juglans mandshurica is significantly higher than other species,while the Quercus mongolica is the smallest.The vessel density(VD)of Fraxinus mandshurica conduit was significantly higher than that of the other three species.The total vessel area(TVA)of Quercus mongolica was only 1/2 of that of other species.The differences in anatomical structure of the four species could reflect the differences in ecological habits between species.The RWL and N of each tree species slight decreased with the increase of cambial age.The Dh and MVA increased rapidly with cambial age at the young stage(25?45a)untill reaching a "shifting point".After that,the trend is obviously slowed or disappeared,which may be related to the rate of height growth.VD also shows an increasing trend with cambial age,but the "shifting point" is absent or inconspicuous.There is no obvious changes in TVA with cambial age.The existence of"shifting point" in the age-trend of vessel features makes it possible to evade the risk of detrending.The RWL of four species,Fraxinus mandshurica and Quercus mongolica,were negatively correlated with VD and positively correlated with other vessel features(especially N).The number density of vessel is generally negatively correlated with vesesel size,which is the trade-off between hydraulic efficiency and safety.RWL and TVA of the four tree species are mainly determined by N,not MVA.The effect of N on RWL is mainly by direct impact,and the indirect influence through TVA and VD pathway is weak.There is a "south-high and north-low" pattern in ring width and main vessel features(except VD)of the four tree species in general,which is the adaptation to climate at sampling sites and also a manifestation of tree habit,tree age,tree height or height-growth rate.In general,the spatial variations of vessels in four broad-leaved clearly indicate the plasticity of the xylem hydraulic structure and the trade-off between the main function of vessels with tree age or site environment.Temperature is the main climatic factor limiting the radial growth of four tree species and the effect of precipitation on tree growth is weak.The mean(T)and minimum(Tmin)temperature(especially Tmin)can promote the radial growth of the four tree species,and Fraxinus mandshurica and Juglans mandshurica are the highest and weakest.The correlation between RWL of the four tree species and water(precipitation,average relative humidity and SPEI)generally showed a trend from positive to negative from north to south,with large differences among seasons and indicators.The between RWL of the four tree species positive correlated with temperature(especially Tmin).The positive correlations between RWL in Phellodendron amurense and Quercus mongolica were mainly concentrated in the south,and the correlations between temperature and RWL in the northern sites was not significant.The RWL of the northern sites negatively correlated with summer temperature,indicating that the drought stress in the north was more obvious.The RWL of Fraxinus mandshurica has a positive correlation with the T and Tmin in almost all sites;the significant correlation with maximum temperature(Tmax)is mainly concentrated in the north(especially in autumn),which may be related to the length of growing season.The spatial variation of RWL of Juglans mandshurica and temperature(strong positive correlation in the north)seems to be different from Phellodendron amurense and Quercus mongolica,which is the embodiment of the difference in water use strategies related to wood properties.The too strong(Fraxinus mandshurica)or too weak(Juglans mandshurica)correlation can mask the spatial variability,which could be the reason for no obvious temperature-related spatial variability.The occurrence of spatial variability in tree growth-climate relationship varies with season,climatic factors and species.The change of climate limiting factors caused by latitude and longitude,altitude or small topography of sampling points is the main reason for the spatial variation of growth-climate relationship in broad-leaved trees.Large-scale climate oscillation may be its external drive in the region.After rapid(1970-80s)warming,the correlation between temperature and the relationship between the ring porous wood species was changed from an insignificant negative or positive correlation to a significant positive correlation,while the semi-ring porous(Juglans mandshurica)changed from significant positive correlation to significant negative correlation.The correlation between growth of Fraxinus mandshurica and Phellodendron amurense and water was generally changed from insignificant negative or positive correlation to significant positive correlation.For Quercus mongolica and Juglans mandshurica,the restriction of water in the southern region is negatively converted to negative,while the northern region is converted from a negative correlation to a significant positive correlation.The temporal variation in growth-climate relationships diminishes as the warming rate slows.The temporal variation in tree growth-climate relationships of broadleaf tree may be related to drought stress caused by warming.Temperature is the main climatic factor limiting the vessel features of four broad-leaved tree species in temperate forests.Vessel features are positively correlated with T and Tmin,but not with Tmax.Vessel characteristics of four broad-leaved trees were positively correlated with water in early growing season,but negatively correlated with water in other seasons.There are seasonal differences in correlation relationships between the vessel features of four tree species and temperature/precipitation,which may be related to difference in wood properties and phenology of trees.The correlation between climatic factors and vessel characteristics of four broad-leaved trees showed the same spatial variation with tree-ring width,that is,the correlation with water decreased from north to south,while the positive effect of temperature increased,indicating that drought stress was more severe in the northern sites.For Quercus mongolica and Juglans mandshurica,the correlation between RWL,N,TVA and climatic factors is often contrary to that of VD,Dh and MVA.The relationship and climatic representativeness of these features vary with tree species and seasons.The positive effect of temperature on the tree growth(vessel features)in the south is stronger,while the positive effect in the north is weakened or negative,which confirms the macro tree growth-climatic relationship to a certain extent.