| Soil enzymes participate in all complex biochemical processes in soil,and are the key factors affecting material turnover and nutrient release.Soil enzyme activity performance indicates soil quality status and level.In this paper,invertase,urease,catalase and alkaline phosphatase were selected as the research object to study the vertical characteristics and dynamic changes of soil enzyme activities and soil physical and chemical properties in different land use types of the typical suspended reach of the lower Yellow River,to explore the changes and differences of soil enzyme activities in the beach and low land of the Yellow River,and to reveal the relationship between soil enzyme activities and soil physical and chemical properties.The main conclusions are as follows:(1)In the profile,the soil enzyme activity in the surface layer of the typical suspended reach of the lower Yellow River was the highest,and decreased with the depth of soil layer,and the change range of soil enzyme activity in the soil layer below 40 cm was smaller.Soil enzyme activities in artificial forest,natural wetland,paddy field and irrigated land were significantly higher than those in other soil layers,while the profile changes of soil enzyme activities in bare land were small,and the differences among soil layers were not significant.(2)Soil enzyme activities were affected by land use types in the typical suspended reaches of the lower reaches of the Yellow River.The activities of catalase,invertase and urease in artificial forest,natural wetland,paddy field and irrigated land were higher than those in bare land,while alkaline phosphatase was lower than that in bare land.Soil alkaline phosphatase activity of bare land was higher than the other four types of land in all soil layers,and the difference increased with the depth of soil layer.The activities of catalase and urease in the surface soil of artificial forest and irrigated land were higher than those of natural wetland,paddy field and bare land,and the difference decreased with the depth of soil layer,and the activities of invertase in irrigated land were higher than those in other four land types.The soil enzyme activities of the low-lying land were generally higher than those of the Yellow River beach area,with the soil depth,the gap gradually decreased.The difference of soil enzyme activities between natural wetland and paddy field and the Yellow River beach area was great,and the difference of soil enzyme activities between artificial forest was the smallest.The activities of catalase,urease and alkaline phosphatase were the highest in the surface soil of paddy field,and the activities of invertase and alkaline phosphatase in the soil of artificial forest were significantly lower than those in natural wetland,paddy field and irrigated land.The soil enzyme activities were affected by land use types in the whole soil profile,and the effect was gradually weakened with the soil depth.(3)From the seasonal change,the range of catalase activity is the smallest,and the range of alkaline phosphatase activity is the largest.The change of four kinds of enzyme activity from October to April is greater than that from April to July.The variation range of soil alkaline phosphatase activity in lowland was generally higher than that in Yellow River beach,and the seasonal variation range of soil invertase activity in artificial forest and irrigated land in Yellow River beach was higher than that in lowland.The variation of soil catalase activity in the low land of the back river and the beach of the Yellow River was similar.(4)Soil physical and chemical properties affected the change of soil enzyme activity,soil enzyme activity and soil ammonium nitrogen,total nitrogen,active organic carbon and organic carbon were significantly positively correlated(P<0.05),in which total nitrogen,active organic carbon and organic carbon had the greatest direct impact on soil enzyme activity,while the indirect impact of enzyme activity was also the greatest.The soil carbon and nitrogen content of the lowland was higher than that of the Yellow River beach,so the soil enzyme activity of the lowland was higher than that of the Yellow River beach;The soil carbon and nitrogen content of farmland(paddy field and irrigated land)was higher as a whole,and its enzyme activity was also higher as a whole.In the typical suspended reach of the lower Yellow River,compared with other land use types,agricultural cultivation can improve soil carbon and nitrogen content and soil enzyme activity,and improve soil quality. |
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