The Water-holding Functions Of Different Vegetation Types In The Eastern Slope Of Helan Mountains In Terms Of Litter Layers And Soil Layers And Their Influencing Factors

The water content of forests is an important aspect of ecosystem function.The study compares the variation patterns and differences in the water content function of different vegetation types in the litter layer and soil layer on the shaded and sunny slopes of a small watershed,and explores the main regulatory factors of water content function,with a view to providing a theoretical basis for the regional forest hydrological cycle and the construction of water-conserving forests.In this paper,the study area was taken as the Xiangshigou sub-basin on the eastern slope of the Helan Mountains in Ningxia,and the litter matter and soil of desert grassland,Amygdalus mongolica bushes,Ulmus glaucescens forest,Pinus tabuliformis forest,mixed forest,Picea crassifolia forest and subalpine meadow on the shaded and sunny slopes of the basin were used as the study objects.The water-holding function of the soil and litter layers,the amount of litter accumulation,the nutrients of litter and the physicochemical properties of the soil were measured indoors to analyse the differences in water-holding function between different vegetation types.Correlation and redundancy analyses were used to understand the correlation between different influencing factors and water content function,and to identify the main regulating factors of water content function.The main conclusions of this study are as follows:(1)Litter accumulation,water content,P,C/P,soil water content,total porosity,capillary porosity,non-capillary porosity,TN and TP were significantly greater on the shaded slopes than on the sunny slopes,while N/P and soil capacity were the opposite;at different stages of decomposition,litter accumulation,N and P were greatest in the decomposed layer,while litter and litter fruit were the smallest,and C content was greatest in the semi-decomposed layer and least in the decomposed layer;C/N C/N,C/P and N/P were all greatest in litter fruits,while C/N and C/P were smallest in the decomposed layer and N/P was smallest in the semi-decomposed layer;between vegetation types,litter stock,water content,N,soil water content,total porosity,capillary porosity and soil organic matter were significantly higher in the highelevation vegetation types(Picea crassifolia forest,mixed forest and Pinus tabuliformis forest)than in the low-elevation Amygdalus mongolica bushes and desert grassland.However,litter C,P,C/N,and soil bulk weight were the opposite.(2)The maximum amount of water held and effective storage of litter matter by different vegetation types on the eastern slopes of the Helan Mountains varied significantly between different decomposition stages,with a maximum of 5.19～10.72t·hm-2 and effective storage of 2.98～26.95t·hm-2,with the decomposed layer being the largest and the litter fruit the smallest.The highest and lowest vegetation types were Picea crassifolia forest and Pinus tabuliformis forest,Amygdalus mongolica bushes and desert grassland,which could absorb up to 6.62-10.59 t·hm-2 and effectively store 2.93-10.62 t·hm-2,while there was no significant difference between different slopes.The amount of water held and lost by litter showed a good logarithmic relationship with the time of immersion and water loss respectively,and the rate of water absorption and water loss by litter showed a significant power function relationship with the time of immersion and water loss.Litter accumulation was still the main limiting factor for the water content function of litter.(3)The maximum water holding and storage capacity of different vegetation types on the eastern slopes of the Helan Mountains is greater on shady than on sunny slopes;the vegetation types at higher altitudes(Picea crassifolia forest,mixed forest and Pinus tabuliformis forest)are higher than those at lower altitudes(Amygdalus mongolica bushes and desert grassland);and the physical properties of soils are the main limiting factors for the water content function of soils.(4)The water content capacity of vegetation on shaded slopes was higher in the litter layer than in the soil layer,and between different vegetation types it showed Picea crassifolia forest(0.653)>mixed forest(0.620)>subalpine meadow(0.603)>Pinus tabuliformis forest(0.508)>Ulmus glaucescens forest(0.430)>Amygdalus mongolica bushes(0.336)>desert steppe(0.066);the water content capacity of vegetation on sunny slopes The weight of the soil layer was higher than that of the withered layer,and the different vegetation types showed a mixed forest(0.777)>Picea crassifolia forest(0.745)>Pinus tabuliformis forest(0.673)>subalpine meadow(0.553)>Ulmus glaucescens forest(0.252)>desert grassland(0.107)>Amygdalus mongolica bushes(0.022);on the combined shaded and sunny slopes,the weight of the soil layer was higher than that of the withered layer.The water-holding capacity of the different vegetation types was:Picea crassifolia forest(0.773)>mixed forest(0.699)>Pinus tabuliformis forest(0.562)>subalpine meadow(0.555)>Ulmus glaucescens forest(0.342)>desert grassland(0.173)>Amygdalus mongolica bushes(0.170).The above results show that the water content capacity of the shady slopes of the eastern slope of the Helan Mountains is stronger than that of the sunny slopes,and that the water content capacity of the coniferous forests at higher elevations is stronger than that of the scrub and desert grassland at lower elevations.the soil layer was still the main regulator of the water content function,and litter accumulation and soil physical properties were the main limiting factors for the water content function of the litter and soil layers.The results of the study can provide a theoretical basis for the construction of regional forest hydrological cycles and water-conserving in this region and even in semi-arid mountain ecosystems.