不同干旱土壤条件下杨树的耗水规律及水分利用效率研究

 在适宜土壤水分（70%θf）,中度干旱（55%θf）和严重干旱（40%θf）3种土壤水分条件下研究杨树（Populus simonii）的耗水特性和水分利用特征。结果表明，随着土壤含水量的下降，杨树叶水势、相对含水量(RWC)、生长速率、光合速率及单叶水分利用效率（WUE）显著下降；在适宜水分和中度干旱条件下，杨树的快速生长和干物质迅速积累时期主要集中在5～6月，严重干旱下快速生长时期和干物质积累主要集中在5月；杨树总耗水量和总生物量的大小顺序为：适宜水分＞中度干旱＞严重干旱；WUE则表现出中度干旱下最高，严重干旱下最低；杨树在适宜水分下的日、旬、月耗水量明显高于中度干旱和严重干旱处理；杨树在适宜水分、中度干旱和严重干旱条件下的最高耗水月分别在6～7月，最高旬耗水量分别在7月中旬、上旬和6下旬；在中度水分亏缺和严重水分亏缺下的最高耗水日出现的时间比适宜水分下的最高耗水日提前1～2个月以上。一天中的最大耗水高峰随着杨树生育期和土壤含水量的不同而有明显差异。研究结果表明，杨树不具备耐旱植物的特征，因此在黄土高原缺水地区不适宜大面积栽植，只能用于水分条件较好的立地条件下造林。

WATER USE EFFICIENCY AND WATER CONSUMPTION CHARACTERISTICS OF POPLAR UNDER SOIL DROUGHT CONDITIONS

We studied water consumption and water use characteristics of poplar under three different soil water regimes: adequate soil water, medium drought, and severe drought conditions, which were about 70%, 55% and 40% of field capacity. The results showed that water potential, water content, photosynthesis rate, water use efficiency of leaves, and plant growth rates decreased significantly with decreases in soil water content. At levels of adequate soil water content and medium drought, fast growth and biomass accumulation of poplar occurred during May and June, whereas this occurred during May only under severe drought conditions. Total water consumption and biomass growth were greatest under adequate soil water conditions, decreased under medium drought, and was lowest under severe drought conditions. Total water use efficiency was highest under medium drought conditions and lowest under severe drought. Patterns of water consumption on a daily rate, every 10 days, and monthly rates were different under the three soil water treatments. For all three treatments, the highest monthly water consumption occurred in July and then June. The highest water consumption over a ten-day period was in the second ten days of July, the first ten days of July, and the last ten days of June for the three treatments, respectively. The highest water consumption day of the medium and severe drought treatments occurred one or two months earlier than the adequate soil water treatment. The time of day when the greatest water consumption occurred changed throughout the life span of the poplar and under the differnt soil water treatments. From our results, we conclude that poplar does not have characteristics of drought resistance plants; hence, we do not recommend that this species is planted over a wider range in the loess plateau.