| Vegetation restoration has profoundly changed the characteristics of the underlying surface and soil erosion of the Loess Plateau and improved the fragile ecological environment.However,soil moisture is still the main limiting factor for ecosystem restoration in the Loess Plateau.Unreasonable artificial vegetation allocation often aggravates soil moisture consumption and causes soil moisture deficiency,which seriously hinders the sustainable development of ecosystem in this region.Therefore,it is the key to realize "water-based colonization" to study the relationship between plantation ecosystem and soil moisture.In this study,the characteristics of plantation community,soil physicochemical properties and dynamic changes of soil moisture were analyzed by the method of field investigation,location monitoring and model simulation.Hydrus-1D numerical model was used to simulate the soil moisture change process of forestland.The response of soil moisture to precipitation and plantation growth was revealed.The carrying capacity of soil moisture and vegetation in different stands was evaluated,which provided scientific basis for structure optimization and sustainable restoration in loess area.The main conclusions are as follows:(1)Broad-leaved pure forest and needle-broad mixed forest are the main vegetation types in Qiaoshan forest area.The species of broad-leaved pure forest are mainly Quercus robur and Quercus liao Dong,and the species of needle-broad mixed forest are mainly Quercus robur and Pinus oleifera,and the stand density and denseness of broad-leaved pure forest are higher than needle-broad mixed forest.The soil capacity of broad-leaved pure forests and mixed conifer forests ranged from 1.30 to 1.52 g/cm3,and the soil capacity of broad-leaved pure forests was higher than that of mixed conifer forests,and the soils of both types of forests were mainly powdered,and soil organic carbon tended to decrease with increasing depth,while other soil physical and chemical properties were not significantly different.(2)Soil moisture in both stands showed a decreasing-stabilizing-increasing trend at 0-200 cm depth,with higher soil moisture content in the 0-30 cm and deep 150-160 cm soil layers,and lower soil moisture content in the 30-150 cm soil layer.Based on the soil moisture variability coefficient of the soil profile,the vertical variation of soil moisture can be roughly divided into the rapid soil moisture variation layer,the active layer and the sub-active layer.The soil moisture variation coefficients of both stands showed an overall decreasing trend with increasing depth.The soil moisture variation coefficient of broad-leaved pure forests decreased from 30.20%to 15.52%in 0-20 cm;within the soil layer of 20-160 cm,the soil moisture variation coefficient was more stable;within the soil layer of 160-200 cm,the soil moisture variation coefficient showed a stepwise decrease.The coefficient of variation of soil moisture in mixed coniferous forests also decreased rapidly from 34.85%to 15.05%in the soil layer of 0-40 cm;in the soil layer of 40-180 cm,the coefficient of variation of soil moisture showed a stable fluctuation;in the soil layer of 180-200 cm,the coefficient of variation of soil moisture showed a decreasing trend.(3)The difference of soil moisture between pure broad-leaved forest and mixed coniferous forest was obvious in the secondary rainfall process,daily,monthly and seasonal scales.In the secondary rainfall process,the effect of medium rainfall on soil moisture was mainly in the soil layer above 60 cm;The effect of heavy rain on soil moisture is mainly in the soil layer above 90 cm.After the rainstorm event,the soil moisture of 0-160 cm soil layer is replenished.In addition,mixed coniferous and broad-leaved forests are more sensitive to rainfall than pure broad-leaved forests.The diurnal variation of soil moisture in different stands was mainly concentrated in the surface layer,and the variation was more obvious before noon than afternoon.Soil moisture was relatively stable in spring and winter.Soil moisture decreased significantly from May to August due to the enhancement of plant transpiration and soil evaporation.Soil moisture was greatly replenished from September to October,and the moisture content of subactive layer reached its peak.According to the monitoring annual scale from August 2021 to August 2022,the rainfall reached 1103.36 mm.The soil water recharge of the two stands showed that the coniferous and broadleaf mixed forest(1087.68 mm)was greater than that of broadleaf pure forest(1064.35 mm),but the water consumption of broadleaf pure forest(937.85 mm)was higher than that of conifer and broadleaf mixed forest(922.81 mm).The calculation of the annual balance of soil water balance showed that the annual added value of soil water reserves of coniferous and broadleaved mixed forest(164.87 mm)was higher than those of broadleaf pure forest(126.50 mm).(4)The Hydrus-1D model was used to simulate the dynamic variation of water content in different soil layers of the two stands.It was found that the rainfall infiltration depth and infiltration amount of the two stands increased with the increase of rainfall.The soil moisture infiltration depth reached 60 cm under moderate rain,while the soil moisture infiltration depth reached 90 cm and 160 cm under heavy rain and rainstorm respectively.At the same time,it was found that the soil moisture surplus of pure broad-leaved forest and mixed broad-leaved forest reached 114 mm and 132 mm,respectively,while the soil moisture deficit was 34 mm and 19 mm,respectively,in dry year.(5)The vegetation carrying capacity evaluation model of soil moisture was constructed,and the vegetation carrying capacity of soil moisture for broad-leaved pure forest and coniferous mixed forest in the year of abundant water was 1307 plants/hm~2 and 1319 plants/hm~2,respectively;the vegetation carrying capacity of soil moisture for broad-leaved pure forest and coniferous mixed forest in the year of dry water was 844 plants/hm~2 and 874 plants/hm~2,respectively. |
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