黄土丘陵区辽东栎群落优势种和主要伴生种树干液流动态特征

运用Granier热扩散探针法(TDP),于2011年5月对黄土丘陵区延安市南郊公路山辽东栎群落优势种(辽东栎)和3个伴生种(山杏、细裂槭、桃叶卫矛)树干液流进行连续测定,并同步监测气象环境因子(太阳辐射、空气温度和相对湿度)和土壤水分动态,比较分析辽东栎、山杏、细裂槭、桃叶卫矛的树干液流通量密度日变化动态及其对环境因子的响应特征。结果表明,辽东栎、山杏、细裂槭和桃叶卫矛液流通量密度日变化动态特征总体上反映了气象环境因子变化的昼夜规律性,呈单峰或双峰型曲线,但辽东栎与山杏、细裂槭、桃叶卫矛液流通量密度日变化规律存在一定的差异。辽东栎液流启动时间较早,通常在5:00左右,而山杏、细裂槭和桃叶卫矛液流启动时间均晚于辽东栎一个小时以上。辽东栎液流达到峰值的时间也较其它树种早,通常出现在9:00前后;细裂槭、桃叶卫矛和山杏液流通量密度达到峰值的时间分别在10:00、11:00和13:00前后。细裂槭和桃叶卫矛液流通量密度日变化曲线峰值较窄。除此之外,土壤水分状况对伴生种的影响程度要比优势种的大。相关分析表明,树干液流通量密度与太阳辐射和空气水汽压亏缺均呈极显著正相关。优势种与伴生种的液流动态差异可能与树木本身特性以及群落对光能的限制性再分配有关。

Characteristics of sap flow dynamics in dominant and companion trees in a natural secondary oak forest in the loess hilly region

Granier-type thermal dissipation probes were applied to continuously measure the stem sap flow dynamics in oak (Quercus liaotungensis) and three other tree species (Armeniaca sibirica, Acer stenolobum, and Euonymus bungeanus) representing the dominant and companion species, respectively, during the growing season from May to October, 2011, in a natural secondary forest near Yan''an of Shaanxi Province in the loess hilly region. Solar radiation (Rs), air temperature, and relative air humidity were monitored simultaneously. The diurnal dynamics of sap flux densities and their responses to environmental factors for the four tree species (Q. liaotungensis, A. sibirica, A. stenolobum, and E. bungeanus) were analyzed. The results showed that patterns of diurnal variation of sap flux densities in the four species were similar, with a single-or double-peak curve, generally reflecting the changes in environmental factors (e.g., Rs). However, there were some differences among the four tree species. The starting time of sap flow in Q. liaotungensis was usually around 05:00, more than 1 hour earlier than the other three species. Sap flux densities in Q. liaotungensis reached daily peaks earlier than others, usually around 09:00, whereas A. stenolobum, E. bungeanus, and A. sibirica reached their daily peaks at 10:00, 11:00, and 13:00, respectively. The companion species A. stenolobum and E. bungeanus showed a relatively narrow peak in their diurnal patterns of sap flux densities, suggesting a limitation of radiation conditions within the community. In addition, soil moisture conditions showed a more obvious effect on companion tree species than on the dominant species. Correlation analysis indicated that sap flux densities were significantly correlated with both solar radiation and vapor pressure deficit during the monitoring period. The difference in sap flux densities between dominant and companion trees may be attributed to both properties of the tree species and redistribution of radiation by canopies.