荒漠结皮层藓类植物死亡对表层土壤水分蒸发和入渗的影响

Effects of moss mortality on soil water evaporation and infiltration of moss-dominated biological soil crusts

水分是荒漠植物生长最主要的限制因子,藓类结皮作为荒漠土壤表层重要覆被物,对土壤水分蒸发入渗具有重要影响。研究表明,在全球气候变化背景下,不确定的降水格局变化导致结皮层藓类植物出现集群死亡现象,但这一过程对荒漠地表土壤水分蒸发与入渗过程的影响及其机理尚不清楚。以古尔班通古特沙漠齿肋赤藓结皮为研究对象,利用便携式渗透计和蒸发仪,研究了结皮层藓类植物死亡对土壤水分蒸发与入渗的影响。结果表明,与裸沙相比,藓类结皮的存在显著抑制了水分入渗,而藓类植物死亡的结皮层抑制作用最大,其初渗速率、稳渗速率和累积入渗量分别是活藓类结皮的39.89%、85.91%及64.48%,仅为裸沙的5.96%、13.13%及20.42%。在水分蒸发初期,裸沙的水分蒸发速率明显高于活藓类结皮和藓类植物死亡的结皮层,但藓类植物死亡的结皮层维持相对稳定的蒸发速率的时间长于裸沙和活藓类结皮,这也导致最终累计蒸发量以藓类植物死亡的结皮层最高、裸沙最低。可见,荒漠生物土壤结皮中藓类植物死亡会明显减少土壤水分入渗、增大水分蒸发,进一步影响荒漠表层土壤水分格局,从而影响生物土壤结皮与维管植物的水分利用关系。

Water is the most important limiting factor for plant growth in desert.Biological soil crusts(BSCs),as important community soil-surface organisms in desert,tend to occupy interspaces between vascular plants in arid ecosystems and play an important role in soil hydrological processes,especially water evaporation and infiltration.Previous studies showed that the uncertain change of precipitation patterns has led to the mortality of the desert moss crusts.However,it is not clear whether moss mortality affects the evaporation and infiltration of the crusted topsoil water.In this study,moss crusts dominated by Syntrichia caninervis were selected to investigate the effects of moss mortality on soil water evaporation and infiltration in Gurbantunggut desert.Three different surface types were included in this paper,there were living moss crust,dead moss crust and bare sand(as control).Soil water evaporation and infiltration were measured by using Mini-Disk Infiltrometer and Evaporation meter.In order to provide a theoretical basis for further study of the impact of desert moss crusts on the hydrological processes of desert ecosystem.The results showed that moss crusts significantly inhibited water infiltration compared with bare sand,and the inhibition degree of dead moss crusts was the greatest.The initial infiltration rate,steady infiltration rate and cumulative infiltration amount of dead moss crusts were 39.89%,85.91%and 64.48%of those of living moss crusts,and were 5.96%,13.13%and 20.42%of bare sand,respectively.In the initial stage of water evaporation,the evaporation rate of bare sand was significantly higher than that of living moss and dead moss crusts,but the time for maintaining a relatively stable evaporation rate of dead moss crusts was longer than that of bare sand and living moss crusts,which also led to the highest final cumulative evaporation of dead moss crust and the lowest of bare sand.Our results indicated that moss mortality of moss-dominated BSCs could significantly reduce soil water infiltration and increase water evaporation,which would consequently affect the soil water distribution pattern and thus affect the relationship between BSCs and vascular plants water use.This study demonstrates the important effects of biological soil crusts upon soil hydrological processes.At present,it is an indisputable fact that global warming has led to the extinction of a large number of species.Therefore,it is of great importance to evaluating the ecological effects of mosses mortality in arid and semi-arid environments.The results of this paper not only can provide certain scientific basis for revealing the response mechanism of the hydrological processes of BSCs to global warming,but also can provide a theoretical basis for protecting the species diversity of desert plants and surface stability in desert.