宁夏平原北部地下水埋深浅地区不同灌木的水分来源

宁夏平原北部引黄灌区地下水埋深浅是该地区土壤盐碱化的主要原因, 种植耐盐植物可以吸收利用地下水, 在降低地下水位的同时可以减少对地面灌溉的依赖。为了分析银川平原北部4种灌木对不同水源的利用特征, 于2010年生长季测定了灌溉前后20年生多枝柽柳(Tamarix ramosissima)、3年生多枝柽柳、3年生宁夏枸杞(Lycium barbarum)和3年生四翅滨藜(Atriplex canescens)木质部水及不同潜在水源稳定氧、氢同位素组成(δ¹⁸O和δD), 应用IsoSource同位素线性混合模型估算了不同灌木对不同水源的利用率。同时测定了0-200 cm土壤剖面的全盐含量、含水量和pH值以及灌溉前后光合气体交换参数。结果表明: 不同深度土壤水δ¹⁸O和δD值存在较大差异, 并呈规律性变化。土壤水δ¹⁸O和δD值随深度加深呈逐渐降低的趋势。灌溉后80 cm以上土壤水δ¹⁸O和δD值低于灌溉前。无论灌溉前还是灌溉后, 20年生多枝柽柳与3年生灌木相比具有更低的δ¹⁸O和δD值。灌溉前, 3年生多枝柽柳、宁夏枸杞和四翅滨藜主要利用表层土壤水(70.1%、52.3%和48.9%); 20年生多枝柽柳对地下水的利用率最高(21.5%)。灌溉后, 3年生多枝柽柳和宁夏枸杞对80-140 cm土壤水利用率较高(59.5%和58.8%)。20年生多枝柽柳对地下水的利用率最高(18.3%)。灌溉前, 20年生多枝柽柳净光合速率、气孔导度和蒸腾速率显著高于其他3种灌木, 灌溉后3年生四翅滨藜净光合速率最高。灌溉对3年生多枝柽柳和宁夏枸杞的净光合速率和气孔导度有显著影响。无论灌溉前还是灌溉后, 3年生四翅滨藜瞬间水分利用效率均高于其他3种灌木。研究表明, 不同灌木在不同水分条件下水分利用策略不同, 这主要与植物种类及树龄有关。灌溉前幼龄多枝柽柳凭借其对干旱较强的忍耐能力利用浅层不饱和土壤水, 灌溉后其又转而利用中层土壤水, 表现出潜水湿生植物的特征, 主要吸收利用深层土壤水分, 对灌溉反应不明显。

Water sources of shrubs grown in the northern Ningxia Plain of China characterized by shallow groundwater table

Aims Shallow groundwater table is the main cause of salinization in the northern Ningxia Plain of China. The uptake of groundwater by halophytes can lower the groundwater table and reduce the demand for irrigation. Our objective was to investigate the potential water sources (different soil profile and groundwater) of four shrubs, i.e., twenty-year-old Tamarix ramosissima and three-year-old T. ramosissima, Lycium barbarum and Atriplex canescens.
Method Stable ¹⁸O and D isotope compositions (δ¹⁸O and δD) of different potential water sources and xylem water were analyzed before and after irrigation. The IsoSource mode was used to calculate the probable contribution of different water sources to the total plant water uptake. The photosynthetic gas exchange parameters, contents of salt and water and pH in 0–200 cm soil profile were also determined.
Important findings Soil water δ¹⁸O and δD in different depths differed consistently. The soil water δ¹⁸O and δD values decreased with depth. More negative soil water δ¹⁸O and δD values were recorded after irrigation. There were significant effects of evaporation and irrigation on soil water δ¹⁸O and δD values. δ¹⁸O and δD values of twenty-year-old T. ramosissima were lower than that of the three-year-old shrubs. Before irrigation, the three-year-old T. ramosissima, L. barbarum and A. canescens mainly tapped water in the upper soil layer (70.1%, 52.3% and 48.9%); highest groundwater uptake rate (21.5%) was observed for twenty-year-old T. ramosissima. After irrigation, higher water uptake rates from 80–140 cm soil profile were recorded for three-year-old T. ramosissima (59.5%) and L. barbarum (58.8%). Highest groundwater uptake rate was found for twenty-year-old T. ramosissima (18.3%). Before irrigation, the net photosynthetic rate, stomatal conductance and transpiration rate of twenty-year-old T. ramosissima were higher than those of other shrubs. Highest net photosynthetic rate were observed for three-year-old A. canescens after irrigation. Irrigation had significant effects on net photosynthetic rate and stomatal conductance of three-year-old T. ramosissima and L. barbarum. The intrinsic water use efficiency of three-year-old A. canescens was higher than other shrubs. These results suggested that different shrubs have different water use strategies, which is presumably related to species and age of shrubs. Young T. ramosissima mainly extracted soil water from upper un-saturated profile based on its strong tolerance to drought, and it switched its water use to middle soil profile after irrigation. Mature T. ramosissima turned out to bephreatophytic with growth being heavily dependent on groundwater and deep soil water and unresponsive to irrigation.