Objectives Soil organic sulfur forms and arylsulphatase activities are sensitive to the changes of soil sulfur pool. We compared the soil organic sulfur forms and arylsulphatase activity characteristics of the main land use types derived from the natural karst wetland, to assess the sustainability of land use types.
Methods The study was carried out in a typical karst wetland area in Guilin City, Guangxi Zhuang Autonomous Region of China. Soil samples were taken in the natural marsh wetland (CK), and the derived paddy field, upland, orchard, breeding land and abandoned land, at depths of 0−10, 10−20, 20−30 and 30−40 cm for the analysis of organic sulfur forms and arylsulphatase activities, respectively.
Results 1) Compared with CK, soil total S stocks, the contents of ester bonded sulfur, carbon bonded sulfur and residual sulfur showed decreasing in the other five land use types. The carbon bonded sulfur, ester bonded sulfur, and residual sulfur accounted for 39.08%−63.54%, 22.91%−34.28%, and 13.55%−28.46% of the organic sulfur, respectively. The ester bonded sulfur and residual sulfur proportions in the soils under five land use types were lower than CK, and the carbon bonded sulfur proportion was higher than CK (P<0.05). 2) The soil organic and total S content in CK ranged 158.4−442.2 mg/kg and 180.2−510.8 mg/kg. The average total S in CK was 345.5 mg/kg, lower than that of the world (700 mg/kg). The average organic and total S contents in the 0−40 cm soil layers under the five land use types were all significnatly different from those of CK, and declined in the order of CK>paddy field>upland>breeding land>orchard>abandoned land. 3) The arylsulphatase activities decreased with the increasing of soil depth under all the land use types. Compared with CK, the soil arylsulphatase activities of the five land types decreased by 18.19% (paddy field), 27.48% (upland), 39.72% (orchard), 33.81% (breeding land), and 51.77% (abandoned land), respectively.
Conclusions The reclamation of natural marsh wetlands leads to the decrease of soil total and organic sulfur contents significantly (P<0.05). The average soil total sulfur content under the five land use types (98.06−222.9 mg/kg) is lower than that of soils at tilling layer in 10 provinces (299 mg/kg) in southern China. Soil organic carbon, total nitrogen, soil water content and arylsulphatase are the main factors causing the proportion change of soil organic sulfur forms. Therefore, controlling the reclamation scale of karst wetland is important for maintaining the balance of soil nutrients and ecosystem health of the Huixian karst wetland in the long run.
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