休眠前期玉兰树干液流的变化及其对环境因子的响应

2011年9月26日-11月5日,利用热平衡技术连续测算了引种北京4年的红花玉兰[抗寒型(HK)和非抗寒型(HF)]、黄玉兰(HY)和二乔玉兰(EQ)的树干液流,结合同步观测的环境因子数据,分析休眠前玉兰的树干液流和综合环境因子的变化,以及在0.5h尺度和日尺度下液流对各环境因子的响应.结果表明:休眠前,玉兰的树干液流呈明显的逐日下降趋势.影响玉兰树干液流的7个环境因子可分为气象因子(MI)和土壤因子(SI)两类.树干液流与MI具有同步的单峰节律性变化规律,与SI呈同步降低趋势.MI和SI对树干液流的共同影响程度为69.8％ ～73.2％.0.5 h尺度和日尺度下,玉兰树干液流与总辐射(Rs)、空气水汽压亏缺(D)、相对湿度(RH)、气温(Ta)和风速(w)极显著相关；在0.5h尺度下与土壤温度(Ts)和土壤含水量(SWC)的相关性不显著,在日尺度下与Ts、SWC和昼长(Z)极显著相关,相关系数在0.8左右.日尺度下进入各回归模型的环境因子有Rs、Z和D,而0.5h尺度下除SWC和Ts外其余环境因子均进入模型,且日尺度逐步回归决定系数(0.92 ～0.96)大于0.5h尺度(0.77 ～0.87)(除HF外).除HF外,其余玉兰的液流变化规律与各单一环境因子间的相关程度一致,这与HF无法正常越冬而其余玉兰在北京顺利越冬的实际情况相一致.

Dynamic change of Yulania sap flow before dormancy in response to environmental factors

From September 26 to November 5,2011,the sap flow of Yulania wufengensis trees including cold-resistance type(HK) and non cold-resistance type(HF),Y.’Sunspire’(HY),and Yulania × soulangeana(EQ) which were introduced into Beijing four years before was monitored by Flow-32 stem heat balance sensor,and,in combining with the environmental factors monitored synchronically,the changes of the sap flow before dormancy and the environmental factors were analyzed,with the responses of the sap flow to the environmental factors investigated at the scales of 0.5 h and 1 day.The sap flow of the Yulanias trees before dormancy displayed an obvious trend of declining day by day.The environmental factors affecting the sap flow could be divided into two categories,i.e.,meteorological index(MI) and soil index(SI).The sap flow of the Yulanias trees had a synchronous variation rhythm with MI,and declined in parallel to SI.The combined effect of MI and SI on the diurnal changes of the sap flow was 69%-73%.At both 0.5 h and 1 day scales,the sap flow showed significantly correlations with total radiation(Rs),air vapor pressure deficit(D),air relative humidity(RH),air temperature(Ta),and wind speed(w).The sap flow showed no significant correlations with soil temperature(Ts) and soil water content(SWC) at 0.5 h scale,but had significant correlations with Ts,SWC,and day length(Z) at 1 day scale(the correlation efficient was about 0.8).Only Rs,Z,and D were included into the model at 1 day scale,but almost all environmental factors(except SWC and Ts) were included in the model at 0.5 h scale.Except for HF type,the regression coefficients of the model for the Yulanias trees at 1 day scale(0.92-0.96) were larger than those at 0.5 h scale(0.77-0.87),and the correlations between the dynamic changes of sap flow and the environmental factor were consistent,which was in accord with the fact that the HF could not overwinter in Beijing but the others could.