黑河下游绿洲胡杨生长状况与叶生态特征

选择黑河下游额济纳绿洲为研究区,以优势物种胡杨(Populus euphratica Oliv.)为研究对象。在2009年和2010年对研究区胡杨的生长状况、叶生态特征和生境进行了调查。调查结果表明:胡杨受水分胁迫的程度增强,生长态势变差,其枯枝比由2.45%增加到81.00%,其比叶面积由11.84 m2/kg减少到5.35 m2/kg。叶气孔密度变化很大,最小值为105(个/mm2),最大值为218(个/mm2),平均值为158.4(个/mm2),随着地下水埋深的增加,叶气孔密度先减少后增加之后再显著减少(P0.05),呈三次函数关系。研究得出枯枝比能够反映胡杨分布区地下水的变化状况,是林相描述比较重要的指标,比叶面积和叶气孔密度能够指示胡杨种群环境变化。研究结果可为荒漠河岸林恢复和生态输水效应评价提供科学依据。

The growth state of Populus euphratica Oliv. and its leaf ecological characteristics in the lower reaches of Heihe River

The study was conducted in the lower reach of Heihe River, which is located in an extremely arid desert in northwest China. We pay a particular attention on Populus euphratica Oliv that adapts to continental arid climate and is a dominant component of the riparian ecosystem. Groundwater levels in the riparian ecosystem may have influences on states of plant growth. In turn, plant leaves may reflect different growth states. To reveal the growth state and leaf-related physiological responses of Populus euphratica Oliv forest to groundwater table variations, 42 sampling plots of Populus euphratica Oliv under different DG were selected to investigate the relationship between Populus euphratica Oliv and its inhabit. We investigated the ratio of died branches to total branches, the specific leaf area (SLA), and the stomatal density (SD) of Populus euphratica Oliv, and DG in 2009 and 2010. The result showed that the ratio of died branches to total branches increased continually with the increasing DG, ranging from 2.45% to 81.00%, whereas the SLA decreased with the increasing DG from 11.84 m²/kg to 5.35 m²/kg. In contrast, the SLA decreased with the increasing DG. Additionally, the SD has a complex change trend with the increasing DG. The SD first decreased, then increased, and at last decreased again with the increasing DG. The minimum of SD is 105 (pore/mm²), the maximum is 218 (pore/mm²),and the mean value is 158.40 (pore/mm²). We can draw conclusions that Populus euphratica Oliv suffers from various degrees of water stress due to changes in the DG. The ratio of died branches to total branches can obviously be used to indicate the variation of groundwater level. Populus euphratica Oliv has low productivity under severe water stress due to SLA and SD decline. Therefore it is necessary to balance water requirement between humans and nature and protect Populus euphratica Oliv from extinction in this area. SD and SLA are important parameters to measure the response of the growth state of Populus euphratica Oliv. These findings should be helpful in monitoring the growth and development of Populus euphratica Oliv forests as well as in assessing the efficiency of ecological water delivery in the study areas.