| Soil fertility is one of the most important ecological functions of soils and shows great spatial heterogeneity. Land use has considerable influence on soil fertility through affecting plant growth, development and their succession. The landscape in karst region is of high spatial heterogeneity, and has obvious dual structure, and soil is barren and discontinuous along with serious erosion, resulting in marked vulnerability. So, selecting appropriate land use is an important measure of ecological protection, recovery and reconstruction in this region. The present study aimed to reveal the main responding factors of soil fertility to land use types and impacts of land use types on soil fertility; and to screen optimal land use types in this region. Six typical land use types in this region (i.e. burning, cutting, cutting plus with root removal, enclosure, maize plantation, and pasture plantation) were selected in this research, based on dynamic monitoring in sample plot, the influence of land use types on the general characteristic and spatial heterogeneity of plant, soil moisture, soil nutrients and soil microorganisms was investigated and analysed. Main results are as follows:(1) There was an obvious difference in plant diversity and structure between complete enclosure and24years spontaneous recovery with evergreen and deciduous broad-leaved mixes forest in Karst peak cluster region. Compared with enclosure, except that planting maize and pasture caused great damage on vegetation, burning, cutting, and cutting plus with root removal significantly increased plant diversity.(2) Soil moisture had local superiority under the special drought condition in Karst region, indicated by25.38%～38.47%of soil moisture in rainy season and15.26%～18.93%even in dry season with moderate or strong variation. Spatial pattern of soil moisture under the same land use type had little variation in different seasons, among which concave distribution was observed in enclosure treatment, unimodal distribution in cutting plus with root removal, maize plantation and pasture plantation, fragment distribution in burning and cutting treatments. Spatial variation of soil moisture differed under the six land use types in different seasons, but presented moderated or strong spatial autocorrelation.(3) The pH of limestone soil developed from dolomite was up to7.83-7.98, and its content of nutrients was far greater than that in red soil and increased with reduce of human disturbance. Medium or strong spatial heterogeneity in soil nutrients was found under various land use types, for example, pH showed an inversion phenomenon; SOM, TN, TP, AN, and AP showed unimodal distribution characteristics, TK and AK showed fragemented patches. The impacts of different land use types on the spatial variation and distribution of soil nutrients varied with weak regularity.(4) Both soil microbial biomass and its population in limestone soil developed from dolomite were higher than that in red soil, but lower than that in soil parented from limestone. Properties of soil microorganisms varied in different land use types, but all of them had spatial heterogeneity and presented unimodal distribution as a whole. Moreover, spatial continuity of soil microbial biomass was better than that of soil microbial population. Poor spatial continuity was found in soils planted maize and pasture, due to heavy disturbance from human activities.(5) Soil nutrients such as SOM, TN, and AN were most significantly influenced by land use types in depressions between karst hills, followed by soil microorganisms. Interactions between soil factors varied with land use types. For example, considerable interactions existed in soil TP with MBP, TK with MBC, TN with actinomycetes in the burned area, while TN and MBC in cutting treatment, AP and MBN cutting plus root removal treatment, pH with MBC and fungus in enclosure treatment, TN and TK with MBP in maize plantation, pH with fungus and actinomycetes in pasture plantation. The six land use types in depressions between karst hills could be divided into four categories according to optimize order by cluster analysis, and enclosure and burning treatments were better than others. |
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