Water Holding Capacity Of Litter And Its Effect On Soil Respiration In Dominant Vegetation Communities Of Qilian Mountains

The vegetation communities of Qilian Mountains provide a natural green barrier for the sand invasion in northwest region,and also provides support guarantee for the water conservation of Qilian Mountains.The litter layer between forest plant layer and soil layer not only plays an important role in soil and water conservation and regulation of river runoff,but also affects soil respiration by regulating soil surface temperature and humidity.Therefore,the litter layer plays an important role in regulating the hydrological process and carbon cycle of Qilian Mountains.In this study,the litter layer of Picea crassifolia forest,Sabian przewalskii forest and Potentilla fruticosa shrub were selected as our study objects,and the thickness and storage were measured,and the water holding capacity and time dynamic changes of surface mulch of different vegetation communities were studied by using root drill sampling method and indoor simulated rain soaking method.At the same time,under natural rainfall conditions,by measuring the soil moisture content under the litter before and after rainfall in different places,the contribution of natural rainfall events to soil moisture under different terrain and litter conditions is studied and analyzed.Li-8100 soil carbon flux automatic measurement system was used to measure soil respiration rate under different mulches and bare soil.Results showed that:(1)The thickness and stock of litter in each vegetation community were all expressed as the semi-decomposed layer is higher than the undecomposed layer.The total thickness of litter under the three vegetation communities ranged from 1.8 to 2.9cm,and the total stock volume ranged from 20.41 to 45.31 t·hm^-2.In general,the litter volume of arbor forest was higher than that of Potentilla fruticosa shrub.The order of litter thickness and storage of litter under different covering types in the Picea crassifolia forest was shown as moss+litter layer>litter>grass+litter layer.(2)The order of largest water holding rate of litter in different vegetation communities was Potentilla fruticosa shrub(326.63%)>Picea crassifolia forest(267.82%)>Sabian przewalskii forest(175.23%).The order of effective interception rates of precipitation by litter from big to small in the order were Picea crassifolia(67.34 t·hm^-2)>Sabian przewalskii(50.70 t·hm^-2)>Potentilla fruticosa(36.07 t·hm^-2).The water-holding capacity of litter under different covering types in the Picea crassifolia forest was different(moss+litter layer>litter>grass+litter layer).(3)In the natural rainfall event,under the same rainfall adjustment,the threshold range of rainfall starting to supplement soil water was 1.4?5.62 mm under different slope conditions and litter thickness,the order of the amount of rainwater infiltration into the soil of different vegetation communities was Potentilla fruticosa shrub>Picea crassifolia forest>Sabian przewalskii forest.In the small rainfall event,the order of effective precipitation was Potentilla fruticosa shrub>Sabian przewalskii forest>Picea crassifolia forest.The results showed that the maximum rainfall threshold of the litter supplement to soil water was 1.98 mm and 3.72 mm at the slope of 13°for Sabina przewalskii forest and Picea crassifoliar forest,respectively,while the maximum rainfall threshold of the litter supplement to soil water was 5.63mm at the slope of 31°for Potentilla fruticosa shrub.(4)Moss layer and litter layer significantly increased the soil respiration flux,the order of contribution rate to soil respiration rate was the moss layer of Picea crassifolia>litter layer of Picea crassifolia>litter layer of Sabina przewalskii>litter layer of Potentilla fruticosa.Mulches could also increase or decrease the sensitivity of soil respiration rate to temperature,and the response of soil respiration rate to soil temperature at 5cm was significantly greater than that to surface temperature.(5)The daily change curves of soil respiration rate in both soils covered by litter and none in the three plots expressed all single-peak type,and the peak of the respiration rate appeared between 13:00?17:30.In July,the peak value of soil respiration rate in the soil covered by litter and moss was 0.5?2 h earlier than that in bare soil,while it was 0.5?3 h later from August to September.The sequence of monthly mean soil respiration rate in both soils covered by litter and the bare in different vegetation communities was Potentilla fruticosa>Picea crassifolia>Sabina przewalskii sample plots.The presence of litter and moss layer did not affect the seasonal change trend of soil respiration.(6)There were significant logarithmic and power functions relationship between litter water holding capacity,litter water absorption rate and soaking time.The soil respiration rate in each vegetation community was related to surface temperature,surface humidity,soil temperature at 5 cm,and volumetric water content.There was a significant exponential or power function correlation(P<0.01).