黄土高原不同发育阶段生物结皮的导水和持水特征

Effects of biological soil crusts in different developmental stages on soil water permeability and water holding capacity in the Chinese Loess Plateau

为探明黄土高原不同发育阶段生物结皮对土壤导水和持水特性的影响,以裸沙和不同发育阶段生物结皮(藻结皮、藻-藓混生结皮、藓结皮)为研究对象,分别采用定水头法和威尔科克斯法对其导水和持水特性进行了测定。结果表明,在0~10 cm土层,生物结皮显著降低了土壤饱和导水率,藻结皮、藻-藓混生结皮和藓结皮土壤的饱和导水率较裸沙分别平均下降了59.3%,62.9%和27.6%;同时,其水分入渗参数(初始入渗速率、稳定入渗速率、平均入渗速率和累积入渗量)较裸沙分别平均降低了37.7%、54.3%和18.4%,延缓了土壤水分入渗过程;此外,3种发育阶段生物结皮的田间持水量(体积含水量)较裸沙分别增加了0.97、1.10和0.70倍,退水过程(0~120 h)的平均土壤体积含水量分别增加了1.14、1.40和0.74倍。与裸沙相比,不同发育阶段的生物结皮均显著降低了土壤导水率,同时提高了土壤持水性;其中藻-藓混生结皮对土壤导水和持水性能的影响大于藻结皮和藓结皮,其主要原因可能是不同发育阶段生物结皮中非维管束植物和微生物的群落结构存在差异。综上,随着生物结皮由藻向藓的发育演替,其土壤导水性呈现先降低后增加的趋势,而土壤持水性表现为先增加后降低的变化规律。

This study was conducted to understand the effects of biocrusts(biological soil crusts)in different developmental stages on soil water permeability and water holding capacity in dryland ecosystems.We firstly selected areas with different developmental stages of biocrusts(cyanobacteria,mixture of cyanobacteria and moss,and moss),as well as the adjacent bare soil,in a watershed named Liudaogou in the northern Loess Plateau of China,as study sites.Next,the soil water permeability of the different treatments was measured by the constant pressure head method and water holding capacity by the Welcox method.Lastly,the saturated hydraulic conductivity and water infiltration parameters(including stable infiltration rate,average infiltration rate,and cumulative infiltration amount)were obtained and analyzed to determine the effects of these biocrusts on soil water permeability and water holding capacity.It was found that the saturated hydraulic conductivity of the cyanobacteria,mixture of cyanobacteria and moss,and moss biocrusts was decreased on average by 59.3%,62.9%,and 27.6%,respectively,in contrast to that of the 0-10 cm soil.Moreover,the water infiltration parameters of the cyanobacteria,mixture of cyanobacteria and moss,and moss biocrusts was decreased on average by 37.7%,54.4%and 18.4%,respectively,in comparison to the bare soil.Additionally,the biocrust developmental stage greatly influenced the soil water holding capacity.As compared with bare soil,the field capacity of the cyanobacteria,mixed cyanobacteria and moss,and moss biocrusts was increased changed on average by 0.97,1.10,and 0.70 times,respectively.Correspondingly,the average volumetric water content in a drainage test(0-120 h)was changed by 1.14,1.40,and 0.74 times,respectively.All the above results indicate that biocrusts greatly reduced surface soil water permeability and increased water holding capacity as compared with the bare soil,regardless of the different developmental stages.The biocrust comprising a mixture of cyanobacteria and moss had greater impacts on soil water conductivity and water holding capacity than the cyanobacteria biocrusts and moss biocrusts,which are possibly caused by the differences in the community structure of non-vascular plants and microbes of the biocrusts.In conclusion,the soil water permeability of biocrusts initially decreases and then increases along their developmental status from cyanobacteria to mosses in dryland ecosystems,but their soil water holding capacity increases initially and later decreases with biocrust developmental stage.