Soil Water Storing And Holding Capacity And Regulation Under Different Restored Vegetations In Loess Hilly Region

The main task of ecological construction on the Loess Plateau is vegetation restoration,and the soil water here is the limiting factor for vegetation restoration.This study on the basis of predecessors' work and ours,in view of the Loess Plateau ecological construction demand and the leading issues of ecology and environmental science research,and taking restoration vegetations in the Loess Plateau as the research object,through the methods of combining the field experiment and indoor analysis expansion,to study the dynamics and distribution of soil water storage(SWS)during vegetation restoration,clarified the spatial distribution of soil water and the affecting factors,the relationship between soil water and carbon,soil water storage and stoichiometrical characteristics,explored the inter-annual variation of soil water and evaluated the soil water holding capacity and availability during the vegetation restoration.The main results are as follows:(1)Long-term vegetation restoration had significant effect on the SWS from grassland to forest.The SWS significantly decreased with vegetation restoration.The SWC associated with the SWS in the 0-500 cm soil depth significantly decreased at the early stage of restoration(0-50 a)and tended to decrease slightly at the later stage of forest(50-150 a).The SWC was lower in the upper soils than in the lower soils at the different restoration stages,as well as the SWS,however,the SWS in 200-300 cm soil layer was higher than other layers at all the restoration stages.And the BD,soil porosity and soil particle composition were better along with the vegetation restoration.(2)The soil water reservoir and carbon pool were significantly influenced by the long-term vegetation restoration from grassland to forest.The SWS in the different soil layers gradually decreased along with the vegetation restoration and increased with the soil depth(0-200 cm)at each restoration stage.However,the soil organic carbon storage(SOCS)increased gradually along with vegetation restoration and tended to decrease along with the increase in soil depth;it was highest in the topsoil(0-20 cm).In addition,the soil depth at which the SWS intensely varied and at which the SOCS tended to be stable moved downward and upward,respectively,with the vegetation succession.The correlation between SWS and SOCS was significant(P<0.05)in the long-term restoration and gradually weakened with the increase in the soil depth and vegetation restoration stages.Clay,silt,sand,total porosity(TP),inactive porosity(IP),aeration porosity(AP)and capillary porosity(CP)were the important factors influencing the coupling interaction of SWS and SOCS at the grass restoration stages(< 50 a),and BD influenced this interaction at the shrub and early forest restoration stages(<130 a).The effect of soil's physical factors on the interaction of SWS and SOCS gradually weakened during the vegetation restoration succession.(3)Long-term vegetation restoration had significant effects on the SWS and stoichiometrical characteristics of areas transitioning from grassland to forest.The SWS significantly decreased with vegetation restoration,whereas the C:P ratio,N:P ratio,TN and TP clearly increased.Only the grassland SWC tended to be stable in the soil layer below 80 cm.With increasing soil depth in the 0-60 cm soil layer in each restoration stage,the SWS increased gradually,whereas the SOC,C:P ratio,N:P ratio,TN and TP decreased significantly before stabilizing in the soil layer below 60 cm.The SWS exhibited significant relationships with SWC,SOC,TN and TP;thus,SOC,TN and TP are the key chemical factors affecting SWS.(4)Different land use types showed the various soil water characteristics from grassland to shrub land to forestland.The soil water holding capacity(SWHC)indicated by the soil water characteristic parameter A deriving from the soil water characteristic curves was the strongest at the forestland,the medium at the shrub land and the weakest at the grassland.And the soil water availability(SWA)at different land use types showed the same trend with SWHC.From grassland to forestland,the soil physical properties were ameliorated to some extent in the 0-50 cm soil layers.Soil texture,porosity and BD were the key factors affecting the SWHC and availability.(5)For all three land uses(grassland,shrub land and forestland)being considered,vegetation types had a significant effect on the SWS.In the 0-500 cm soil layer,SWS in grassland and shrub land was significantly higher in August 2014 than in August 2005,but the opposite was true in the forestland.In the same year,SWS in the grassland was the highest,followed by the shrub land,and the lowest value occurred in the forestland.In the grassland,the SWC increased with the soil depth until 50 cm,while in the shrub land,the SWC increased first and decreased later,where the inflection point occurred at the 260 cm and 200 cm soil depths in August 2005 and August 2014,respectively.In the forestland,the SWC varied intensely in the soil layer above 360 cm.In addition,SWS and SWC showed a highly significant and positive relationship in the 0-60 cm soil layer(P<0.01)(Table 2);SWC and total porosity showed a significant and positive relationship in the 0-20 cm soil layer(P<0.05);SWS and BD showed a significant and positive relationship(P<0.05)in the 0-60 cm soil layer;SWS and TN showed highly significant and negative relationship(P<0.01);and TN and SWC showed a significant and negative relationship(P<0.05).