生长季白桦树干液流密度的特征

Characters of Sap Flow Density for Birch during Growing Season

应用热扩散技术测定了帽儿山不同径级白桦样木生长季的树干液流,并初步分析和对比了优势木、中等木和被压木树干液流密度的特征及季节变化趋势。结果表明,白桦树干液流密度变化具有明显的昼夜节律性,一般呈单峰曲线;白桦优势木液流密度明显大于中等木和被压木,中等木和被压木液流密度值非常接近;不同天气条件下液流密度日变化规律大不相同,阴雨天液流密度值较小且变化曲线十分不规则,波动性较大,甚至出现多峰曲线。生长季,优势木、中等木和被压木日液流通量最大值均出现在6月初至7月中旬,分别为2623.97、1744.50、1689.82L.m-2.d-1;优势木日液流通量最小值出现在7月下旬至8月初,中等木和被压木日液流通量最小值均出现在生长季末期。随季节的推移,生长季各月份液流密度均值基本逐渐减小,白桦优势木6、7月份液流密度平均值较大,8月份和9月份液流密度均值较接近,10月份明显减小;中等木液流密度平均值7月份最大,6、8、9月份液流密度均值较接近,10月份液流密度波动微弱;被压木最大值出现在6月份,7、8、9月份液流密度月均值变化不大。

Sap flow density （SFD） of Betula platyphylla sampling trees in different diameter classes was measured by TDP system during growing season, and its character and seasonal trend of dominant tree, medium tree and suppressed tree were analyzed and compared. Results show that SFD of B. platyphylla has obvious daily rhythmicity and usually shows regular singlet curve. SFD of dominant tree is markedly higher than that of medium tree and suppressed tree, and SFD of medium tree and suppressed tree is closely approximated. The diurnal changes of sap flow density of birch dominant tree, medium tree and suppressed tree under different weather con-litions are different markedly, and SFD will be lower and its changing curve is completely irregular and fluctuant, or even displaying a polymodal curve during rainy and cloudy days. The maximum values of diurnal sap flow flux of dominant tree, medium tree and suppressed tree are 2 623.97, 1 744.50 and 1 689. 82 L·m^-2·d^-1, respectively, which occurs from early June to mid-July. The minimum of diurnal sap flow flux for dominant tree occurs from the last ten-day of July to early August, and that for medium tree and suppressed tree occurs at late growing season. The averages of SFD in different months decrease gradually with the prolonging of growing season. The average SFD of dominant tree is maximal in June and July, is approximated in August and September, and decrease obviously in October. The average SFD of medium tree in＇July is the highest and is approximated in June, August and September, and the minimum is in October. The average SFD of suppressed tree in June is the highest and changes slightly in July, August and September, and the minimum is also in October.