盐生荒漠地表水、热与CO_2输送的实验研究

Water,Heat and CO_2 Transfer over a Salinized Desert in the Arid Area

利用安装在准噶尔盆地南缘多汁盐柴类荒漠上的涡度相关系统与配套的微气象观测系统所得数据,分析了显热、潜热与CO2通量的日过程和季节变化特点及各通量间的相互关系。数据显示了一个明显违背植物水分关系一般规律的现象:当水汽(潜热) 通量明确显示土壤水分亏缺时,净光合(CO2通量) 却未受到影响。因此推测当地原生植物的根系在积盐严重的土壤上层没有发育,所以其水分状况与光合能力不受上层土壤干湿的影响,观测到的水汽通量的变化主要由土壤蒸发的变化造成的。

An eddy-covariance system and a micrometeorological station were installed at south periphery of Gurbantonggut Desert in April of 2002. Evaluation of the data showed that the measurements of sensible heat (H), latent heat (LE) and CO 2 fluxes were reliable. However, a special phenomenon was revealed from detailed analysis on the diurnal and seasonal changes of the fluxes: when LE fluxes signified a strong water shortage and hence severe water stress should have been applied on the plants, CO 2 fluxes indicated that the photosynthesis of the plant community was not affected. This was obviously against generally-accepted theory on plant-water relations. No concrete evidence available so far can explain this phenomenon, but we may speculate that local shrub plant might not benefit from the rainfall. Being a salinized desert, its upper soil layer contains high salt content. Thus shrub roots could not develop and survive at upper layer of the soil. On the contrary, roots might develop mainly at deep soil layers near the groundwater table. Therefore, whether rainfall wetted the upper soil layer or not, plant water condition was not affected, but the evapotranspiration (LE) was. The measured change of LE fluxes mainly came from evaporation of soil surface and CO 2 fluxes were mainly determined by plant photosynthesis. Since the former is mainly influenced by soil water condition near soil surface and the latter determined by soil water condition near the groundwater table, it is just reasonable that the two aspects are not correlated. Thus, the phenomena reported here occurred under the combined local climatic, botanical and soil conditions and it is not really against the principle of plant-water relations in general.