| Based on the field investigation and monitoring, the influences of differentdisturbances on the above-ground vegetation characteristic and the below-ground soilproperties were studied in the typical steppe of Loess region. We divided differentplots of treatments into four types: enclosure (E), enclosure plus fertilization (EF),enclosure plus burning (EB) and grazing (G), which has the same soil type,topography and hydrothermal conditions. Our results showed that:1) The dominant vegetation community type of grazing plots isAgropyron cristatum+Potentilla acaulis+Artemisia sacrorum due to long-termgrazing. The dominant vegetation community type of exclusion of grazing plots isStipa grandis+Poa sphondylodes+Medicago ruthenica due to fencing utilization.The dominant vegetation community type of fertilization plots is Carex duriuscula+Stipa bungeana+Stipa grandis. The dominant vegetation community type of burningplots is Artemisia sacrorum+Stipa bungeana+Stipa grandis.2) The total plant coverage, height and above-ground biomass of differentdisturbance manners is that EF>EB>E>G, and the community density of differentdisturbance manners is that E>EF>EB>G. Community richness index (R and Ma)showed a certain tendency within these four treatments: G>EF>EB>E, andcommunity evenness index (Jswand Ea) was in an order of E>G>EB>EF. Meanwhile,the order of diversity index (H′and D) was as follows: G>E>EB>EF, whiledominance index showed an opposite tendency.3) The soil physical properties in the four different disturbances were as follows:In the0~50cm soil layer, the soil bulk density increased with soil depth inenclosure(E), enclosure-fertilization(EF) and enclosure-burning(EB) grassland, whiledecreased in grazing(G) grassland. In the0~20cm soil layer, soil bulk density of Ggrassland was significantly higher than the other three types while EF was the lowest.In the0~50cm soil layer, the soil water content increased with soil depth in the fourtypes of disturbances and tended to be in the order of EB>EF>E>G. In the0~40cm soil layer, soil organic carbon, total nitrogen and available potassium all decreasedwith soil depth, and total phosphorus decreased with soil depth, while these variablesof EB increased at first and then decreased in the other three types. In the0~30cmsoil layer, the order of soil nutrient content tended to be EF>EB>E>G. The nutrientcontent of G in0~10cm soil layer was significantly lower than the other three typesof disturbances (P<0.01).4) The organic carbon content and density decreased with soil depth, but thedecreased amount are different among the four disturbances. In the0~50cm soil layer,the order of the soil organic carbon content was EF>EB>E>G. In the0~50cm layer,the order of soil organic carbon density was EF>EB>E>G, while enclosure-fertilizedgrassland reached the highest (14.51kg·m-2), followed by enclosure-burning grassland(13.86kg·m-2), fencing grassland (12.27kg·m-2) and grazing grassland (11.85kg·m-2).Grazing can decrease the soil organic carbon density, while fertilization and fencinghave positive effects on the soil organic carbon density.5) There was a negative correlation relationship between communityproductivity and Shanner-Winener index and Simpson index, which supported thelight and root competition hypothesis. Above-ground biomass was positively relatedto vegetation coverage, height and soil water content. Soil organic carbon content wassignificantly positive correlated with above-ground biomass and total nitrogen in the0~50cm soil layer, while it just showed positively relationship with soil water contentin0~30cm soil layer. Furthermore, the results showed that soil organic matter waspositively related (P<0.01) to total nitrogen, total phosphorus and available potassiumin all the four types of disturbances, and total nitrogen showed a positive relationshipwith total phosphorus and available potassium.6)Based on the grayness relationship analysis, our results indicated that:EF(0.9075)＞EB(0.8167)＞E(0.6305)＞G(0.5598). |
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