Vegetation Characteristics Of Grassland And Its Responses To Water Condition Of Pailugou Watershed In Qilian Mountains

The Qilian Mountains is located in the northern margin of the Qinghai TibetPlateau, in the northeast of Qinghai province and western border of Gansu Province,is one of the most important mountains in China, it is fold block mountain. Because ofthe geographical location is special, it is formed a compound ecological system inQilian Mountainous. In the compound ecological system, comprising a plurality offorest ecosystem, grassland, desert, glacier and snow capped mountains. Vegetationlush, complex structure, community types and natural forest dominated in the areas,which provided favorable conditions for these studies of relationship betweenvegetation and moisture conditions. As an important part of vegetation, grasslandcan regulate the climate, keep soil moisture, reduce soil erosion and improve theecological balance of the ecological environment, and is also the pillar of animalhusbandry in the economy. Qilian Mountains are the water source of Heihe, ShiyangRiver and Shule River, and Hexi oasis, research on grassland vegetation in QilianMountains, not only has important environmental significance, also has the profoundsocial and economic significance. Therefore, in this study, grassland of different slopeat2700m as the research object, investigation and determination on the grasslandvegetation characteristics (biomass, coverage and herb height) and moistureconditions (precipitation, soil moisture, grassland evapotranspiration) in2011, thispaper studies the relationship between vegetation and moisture conditions ofgrassland, and water balance on the sunny slope of grassland. In order to reveal theoutlet characteristics of grassland vegetation and water consumption rule in Pailugouwatershed, provide scientific basis for forest vegetation restoration and reconstruction.The main conclusions of this study are as follows:(1) Moisture characteristic1) The seasonal changes of precipitation is obvious in Pailugou watershed ofQilian Mountains, has obvious wet and dry season. In2011the total rainfall is343.4mm, precipitation in growth season (May to September) is302.3mm, accountingfor88.03%of the annual precipitation; precipitation in non growing season is41.1mm,accounting for11.97%of the annual precipitation.2) Seasonal varies of soil water content are consistent in different slopes ofgrassland, and the soil water content of shady slope is larger than the sunny slope. Inthe growing season from May to September, average soil water content of sunnyupper slope, middle slope, lower slope were15.01%,14.41%,15.39%; the averagesoil water content of shady upper slope, middle slope, lower slope were24.15%,31.59%,29.33%. Soil water content has small fluctuation during the early and late ofgrowing season, has big fluctuation during the middle of growing season, Thedifferent soil water content in different periods may caused by the different ofprecipitation, rainfall intensity and vegetation growth. The changes of surface soilwater content is larger than below the surface, and in another word, below the surfacesoil water content is relatively stable, and the soil water content was decreased withthe increase of soil depth. 3) The seasonal dynamic patterns of grassland evapotranspiration both in sunnyand shady slope showed a single peak type, reaching a peak in July or August. Thegrassland evapotranspiration changed according to the following rule: bare landevapotranspiration> grassland evapotranspiration,and grassland evapotranspiration atshady slope> grassland evapotranspiration at sunny slope. the grassevapotranspiration was mainly consumed at soil evaporation; grassland rainfall mostconsumed by grassland evapotranspiration.(4) The impact factors of grasslandevapotranspiration are precipitation, air temperature,air relative humidity, windspeed, soil water content and solar radiation. The precipitation and air temperaturehas a significant linear relationship with grassland evapotranspiration (R2=0.861).(2) The characteristics of grassland vegetation1) Whether it is in sunny or shady slope, herb height of July higher than June. Atthe same time, different slope position has different vegetation height in the samemonth, which may caused by the different constitute of plant in different slopeposition and precipitation. Compared by the growth of vegetation height in thedifferent slope, the average height in shady slope herbs were7.0cm and10.9cm inJune and July, while the average growth height in sunny herb are respectively5.2cmand9.5cm in June and July, the shady slope herbaceous growth height> sunny slopeherbaceous growth height.With the increase of temperature and precipitation, thecoverage of herbaceous reached100%in July in sunny slope and shady slope.2) The seasonal changes of aboveground biomass of herbaceous in growingseason of2011showed a maximum in July, the plant growth mainly concentratedbefore mid July, then it is stopped in August. Underground biomass in sunny andshady herbs has a marked decline in August and September. The growing season in2011, average herbaceous biomass of sunny slope is1601.89g/m2, among them,aboveground biomass is168.42g/m2, underground biomass is1433.47g/m2; averageherbaceous biomass of shady slope is2058.14g/m2, among them, abovegroundbiomass is276.90g/m2, underground biomass is1781.24g/m2. From the herb rootshoot ratio, underground biomass was significantly greater than that of abovegroundbiomass, underground biomass of sunny slope was about6.74times to theaboveground biomass, underground biomass of shady slope was approximately6.22times to the aboveground biomass.(3)The relationship between vegetation and moisture conditions of grassland1) With the increase of precipitation, herbaceous aboveground biomass firstlydecreased and then increased in sunny slope, underground biomass showed agradually increasing trend. Herbaceous aboveground and underground biomass withincreasing precipitation showed a U tendency in shady slope. The correlationcoefficients of performance of herbs biomass and precipitation: aboveground biomassin sunny slope (R2=0.991), underground biomass in sunny slope (R2=0.918),aboveground biomass in shady slope (R2=0.870), underground biomass in shadyslope(R2=0.755), correlation coefficient of different slope herbaceous biomass andprecipitation were aboveground biomass bigger than underground biomass, showedthat effects of precipitation to aboveground biomass larger than the undergroundbiomass. 2) Quantitative research on herbaceous biomass and soil moisture content inQilian Mountains showed that, with the increase of soil water content, herbaboveground biomass is reduced at first and then increased in sunny slope(R2=0.887);. With the increase of soil water content, underground biomass isincreasing in sunny slope, there is a positive correlation (R2=0.760); with the increaseof soil water content, herb aboveground biomass is increased in shady slope(R2=0.643); With the increase of soil water content, underground biomass isincreasing at first and then reduced in shady slope (R2=0.690). The impact of soilwater content on different slope to herbaceous biomass has different degree, it is thecomprehensive effect of environmental factors.3)Study on the relationship between evapotranspiration and herbaceous biomassat2700m in Pailugou watershed showed that, with the increase of evapotranspiration,herbaceous aboveground biomass is first increase and then decrease in sunnyslope(R2=0.779);with the increase of evapotranspiration,herbaceous undergroundbiomass is decreases first and then increases in sunny slope, they have significantcorrelation (P=0.037, R2=0.999). With the increase of evapotranspiration, herbaceousaboveground biomass is reduced in shady slope (R2=0.436); With the increase ofevapotranspiration, underground biomass is also reduced in shady slope (R2=0.899).(4) A preliminary study on the water balance of grasslandThe precipitation of growth seasons in2011is297.4mm, grasslandevapotranspiration is is302.4mm,which is the maximum water output in grassland;secondly,0-40cm soil water content variation is always positive, showed that the soilwater content is supplied, soil water content total variation is218.6mm; most of thebalancing item of grassland was negative, negative value indicates that the layer getwater vertical input or lateral added adjacent soil. The water balance of growingseason is negative in2011, is not conducive to the growth and development plant.