油松、栓皮栎树干液流速率比较

应用TDP(ThermalDissipationProbe)技术对油松和栓皮栎树干液流进行了初步研究,经过野外近1a的实地定位观测,研究结果显示:栓皮栎月平均树干液流速率在整个生长期都较油松的月平均树干液流速率要高。前者大约是后者的5~10倍。栓皮栎在土壤干旱时期能够在白天产生明显的树干液流。在土壤干旱时期油松白天不产生树干液流而在晚上产生明显树干液流。在土壤相对湿润时期,油松和栓皮栎树干液流速率的波形与太阳总辐射的波形变化一致,但不同的是油松的树干液流速率波形呈明显的单峰状,而栓皮栎树干液流速率波形呈明显的多峰状。在土壤相对湿润时期太阳总辐射很低时能对油松树干液流速率产生明显的降低作用,而对栓皮栎树干液流则没有明显影响。在土壤干旱时期,油松和栓皮栎树干液流速率的峰值分别大约为0.0001cm/s和0.0006cm/s左右;在土壤水分充足时期,油松和栓皮栎树干液流速率的峰值分别大约相等约为0.0015cm/s左右,分别是油松和栓皮栎在干旱日期的液流速率峰值的10倍和2.5倍。

Study of the rate of stem sap flow in Pinus tabulaeformis and Quercus variabilis by using the TDP method

This study assessed the sap flow velocity of pine (Pinus tabulaeformis) and oak (Quercus variabilis) using Thermal Dissipation Probe (TDP), one of methods (others incliding the injection of dyes, radioactive tracers, heat pulse, water balance and nuclear magnetic resonance imaging) to estimate sap flow velocity. Then, the trans-evaporation of the stand and related factors were estimated based on the sap flow velocity. The study site was in the Experimental Station of Beijing Forestry University (about 800 ha), which locates on the north end of Taihang mountain, and closes to the east end of Yanshan mountain in Beijing. Longitude is 116(28'E and latitude is 39(54'N. The original vegetation was temperate mixed conifer-deciduous broad leaf forest with the pine and oak forest as the main forest type. The sampled plot was a 31 year old uniform mixed conifer-deciduous broad leaf forest. The crown density was 0.8 while the tree density was 1433 trees/hm~2 with a stand composition of 70% of pine and 30% of oak. In average, the diameters at breast height (DBH) were 11.4 cm and 20.6 cm, the heights (H) were 8.9 m and 12.8 m, and crown widths were 2 to 3 m and 3 to 4 m with the density of 1051 trees/ha and 382 trees/ha for the pine trees and oak trees respectively. The edge of the plot (30 m2) was trenched to the hard rock with asphalt felt buried to prevent soil water horizontal exchange from nearby. In the plot, one mean pine tree (H=9 m, DBH=11.3 cm) and one mean oak tree (H=13 m, DBH=21.2 cm) were selected for the study. A pair of TDP-50 probes connected with a data logger was inserted into the stem of each tree at a height of 1.5 m to monitor the sap flow velocity using the Stem Flow System (ICT Corporation, Australia) for about one year.The monthly average of sap flow velocity in oak stems was five to ten times higher than that in pine stems. In the dry season there was still sap flow in oak stems during daytime, but no in pine stems. However, remarkable sap flow did happen in pine stems during nighttime. The sap flow velocity in pine and oak stems were about 0.0001 cm/s and 0.0006 cm/s respectively. In the wet season, the patterns of sap flow velocity in stems of both pine and oak followed the patterns of the total solar radiation, but mono-peak found in pine while multi-peak in oak. Low total solar radiation decreased the sap flow velocity in pine stems, but did not affect it in oak stems. The sap velocities in the stems of both pine and oak were about 0.0015 cm/s, which were about 10 and 2.5 times higher than the sap flow velocities in stems of pine and oak in dry season respectively.