北京城市绿化树种叶片碳同位素组成的季节变化及与土壤温湿度和气象因子的关系

Study on seasonal variation in carbon isotope composition correspond with soil temperature and humidity and weather factors for main greening tree species in Beijing

城市绿化树种是城市生态系统的重要组成部分,为了探讨城市绿化树种水分利用效率的季节变化及其影响因素,本文对北京24个城市绿化树种(包括6个常绿针叶和18个落叶阔叶树种)叶片碳同位素组成(δ13C)的季节变化以及与土壤温湿度和气象因子的相关性进行了研究。结果表明:常绿树种叶片δ13C季节间差异不显著,春、夏和秋季的平均值都接近-25.9‰,在-27.0‰～-24.5‰间变化;落叶树种叶片δ13C季节间差异极显著(p=1.97×10-7<p=0.01),除国槐外夏季各树种叶片δ13C最低,平均为-27.095‰,而春季最高,为-25.638‰,秋季居中,为-26.291‰,且种间差异极显著(p=5.05×10-6<p=0.01),最大为-23.396‰(白腊春季),最小为-28.360‰(臭椿夏季),变幅达5‰;落叶树种叶片δ13C与土壤温湿度和气象因子的相关性明显高于常绿树种,达到显著水平,表明落叶树种的叶片δ13C更易受环境的影响,而常绿树种叶片δ13C主要受自身的生物学特性决定。叶片δ13C值春季>秋季>夏季,表明绿化树种水分利用效率(WUE)也为春季>秋季>夏季。研究发现:叶片δ13C与比叶面积(SLA)呈显著的负相关(落叶p=6.195×10-8<p=0.01;常绿p=0.002<p=0.01),因此,SLA可以在生产作为叶片δ13C简易代替指标来估计WUE。

Greening tree species in urban is vital part of urban ecosystem. To study effects of seasonal variation and other variables on water use efficiency the tree species, 24 trees species （6 evergreen conifer and 18 deciduous broadleaf trees） were used to examined seasonal change in the foliar δ^13C and relationships of the δ^13C with soil temperature, humidity and the other weather variables in Beijing Botanical Garden in 2006, The results showed that the foliar δ^13C of evergreen specieshad insignificant difference, and the seasonal change wad from -27.0%v to -24.5%v, however, the foliar δ^13C these deciduous species and the seasonal change were insignificantly different （p = 5.05 ~ 10 -6 〈 P = 0.01, p = 1.97 ~ 10 -7 〈 p =0.01 ）. The largest values of the foliar δ^13C （ -23. 396%o） was found in Fraxinus Chinese in spring and the smallest values was 28. 360%v （Ailanthus altissima） in summer, the difference was 5%v. The foliar δ^13C deciduous species was significantly correlated with soil temperature, humidity and weather factors, however, the correlation was insignificant for the evergreen trees. That suggest that deciduous species is more sensitive to environmental change, but the foliar δ^13C of evergreen species is affected by their physiological traits. The foliar δ^13C was greater in spring than that in autumn, followed by summer. The results indicate WUE was greater in spring than that in autumn, followed by summer. The study also found the foliar δ^13C had a significantly negative relationship with specific leaf area（SLA）. Therefore, SLA may replace foliar δ^13C to represent WUE in practice.