毛乌素沙地生物土壤结皮对油蒿水分吸收的影响模拟

Biocrust effects on root water uptake of shrubs in the Mu Us Desert

植物可利用水分是决定沙生灌木生长的主要因子,生物土壤结皮(简称生物结皮)在降雨期影响降水入渗,而在干旱期改变土壤蒸发,从而影响土壤水分分布,最终可能影响灌木水分吸收。然而,关于不同降水条件下生物结皮对灌木水分吸收和水分胁迫的影响机制认识不清。以油蒿为研究对象,基于试验数据和1990—2019年气象数据,采用数学模拟,定量研究了毛乌素沙地不同降水条件下生物结皮对土壤水分分布和油蒿水分吸收的影响,评价干旱期生物结皮对油蒿水分胁迫的影响。结果表明:与无结皮处理相比,生物结皮处理的土壤蒸发降低了5.1%;生物结皮改善了干旱期的土壤水分条件;生物结皮降低了植物水分胁迫的比例,平均降低比例为8.1%;生物结皮提高了植物水分吸收,平均增加比例为12.8%;生物结皮和对照植物水分吸收的比值随季节降水量的增加而降低,均值为1.13。综上,生物结皮的出现并未消极地影响沙生灌木的水分吸收。研究结果有助于理解生物结皮与灌木的共生或竞争关系。

The available water of plants is the main factor determining the growth of desert shrubs.The presence of biocrusts alters infiltration during rainfall event and changes soil evaporation during the drying period,and thus they could affect soil water distribution and local plant water uptake(PWU).However,the roles of biocrusts in PWU and plant water stress have not yet been quantified.The effects of biocrusts on soil water distribution and root water stress and uptake by plants(Artemisia ordosica)were determined based on experimental data,the simulated data derived from a physically based two⁃dimensional model,and recorded meteorological data during 1990–2019 from Yanchi site in the Mu Us Desert,China.Our results showed that(1)in comparison to the uncrusted soil,biocrusts decreased soil evaporation by 5.1%.(2)Biocrusts improved soil moisture during the drying period.(3)Biocrusts reduced the water stress fraction of the season,and the reduction percentage was 8.1%.(4)Biocrusts increased PWU by 12.8%when compared to the uncrusted soil.(5)The PWU ratio decreased with the increasing seasonal rainfall amount,with the mean value of 1.13.According to these results,we concluded that biocrusts did not negatively affect root water uptake of shrubs in drylands.Our findings about the influence of biocrusts on PWU have important implications for understanding of the symbiotic or competitive relationship between biocrusts and shrubs in dryland ecosystems.