Physiological And Growth Responses Of Quercus Aquifolioides To Elevational Gradient In Different Seasons

Elevation is one of the most complex environmental factors in alpine ecosystem.It affects e.g.temperature,light,moisture and soil nutrient availability,which may further affect plant growth and physiology.Furemore,effects of evevation on plant growth and physiology may depend on seasons.We took a common evergreen broad leaved tree,Quercus aquifolioides,as our target speices to explore effects of elevation on plant growth,morphology,and physiology.Along the elevational gradient of the Balang Mountain,we took samples at 2843,2978,3159,3327,3441 and 3589 m a.s.l on the sunny slope.At each elevation,we randomly selected 6 trees of Q.aquifolioides,took samples of 2-year old leaves,2-year old shoots,stems(>4-year old shoots)and fine roots(diameter<3 mm)in summer and winter,and then measured the growth and physiological indexes of different organs.Height and diameter of Q.aquifolioides decreased with increasing elevation.During the growing season,leaf mass per area and S13C increased with increasing elevation,suggesting that the target species has a higher water-use efficiency and resource utilization ability.In summer,the concentration of NSC(non-sturctural carbohydrates)in leaves increased with elevation,and the concentration of NSC in other organs was not lower at high elevation than at lower elevations,suggesting that the carbon supply at the high elevation is sufficient for plant growth in the growing season.The concentration of NSC in fine roots decreased with elevation in winter,but the total concentration of NSC in the whole plants showed no significant difference between the two sampling seasons,suggesting that NSC may transfer in different organs.During the entire growing season,NSC in leaves may have gradually transfered to other organs,which can guarantee the plant survival in the dormant season(winter).The plant tended to invest more in starch,storing in the organs in summer.In winter,NSC would transfer to soluble sugar to resist low temperature,which can guarantee the plant survival during the dormant season and restore growth in the next year.Soil available N increased with elevation,but soil available P decreased.Total N did not show a clear pattern along the elevational gradient,but the total P decreased with increasing elevation in all organs,and had a strong positive correlation with soil available P.N:P in different organs linearly increased with elevation in summer,and also had an increasing tendency in winter,suggesting that P is an important limiting element for plant growth and physiology in higher elevation.The results suggest that elevation restricts the growth of Q.aquifolioide,but the concentration of NSC is sufficient for plant growth during the growing season.Short supply of P is likely an important reason to limit the distribution of Q.aquifolioides in study area.