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Soil organic carbon (SOC) is a crucial medium of the global carbon cycle and is profoundly affected by multiple factors, such as climate and management practices. However, interactions between different SOC fractions and land-use change have remained largely unexplored in karst ecosystems with widespread rock outcrops. Owing to the inherent heterogeneity and divergent response of SOC to land-use change, soil samples with close depth were collected from four typical land-use types (cropland, grassland, shrubland, and forestland) in the karst rocky desertification area of China. The aim of this study was to explore the responses of SOC dynamics to land-use types and underlying mechanism. The results showed that land-use type significantly affected SOC contents and its fractions. Compared with cropland, the other three land uses increased the total organic carbon (TOC), microbial biomass carbon (MBC), and non-labile organic carbon (NLOC) contents by 6.11–129.44%, 32.58–173.73%, and 90.98–347.00%, respectively; this demonstrated that a decrease in both labile and recalcitrant carbon resulted in SOC depletion under agricultural land use. Readily oxidized organic carbon (ROC) ranged from 42 to 69%, accounting for almost half of the TOC in the 0–40-cm soil layer. Cropland soil showed significantly higher ROC:TOC ratios than other land-use types. These results indicated that long-term vegetation restoration decreased SOC activity and improved SOC stability. Greater levels of soil exchangeable calcium (ECa) and clay contents were likely responsible for higher stabilization and then accumulation of SOC after vegetation restoration. The carbon pool index (CPI) rather than the carbon pool management index (CPMI) exhibited consistent variation trend with soil TOC contents among land-use types. Thus, further study is needed to validate the CPMI in evaluating land use effects on soil quality in karst ecosystems. Our findings suggest that land-use patterns characterized by grass or forest could be an effective approach for SOC-sequestration potential and ensure the sustainable use of soil resources in the karst area. [ABSTRACT FROM AUTHOR]

Carbonate weathering by rain is considered to play an important role in the karst landform evolution. Rock outcrops (or stone teeth) are frequently visible on the earth’s surface, especially in karst landscapes, but there is no consensus on how they appeared or increased in number. This study estimated the extent of rain-induced weathering dissolution of limestone using hydro-chemical data from a karst area enjoying a subtropical monsoon climate, and proposed a mechanism of soil sinking and rock outcrops emerging, based on the assumption that the dissolved subsoil limestone is the main cause of geomorphic reworking of the karst surface topography. By calculation, the weathering dissolution rate of subsoil limestone is greater than the residue formation rate by dissolution of exposed and subsoil limestone in both forested and cleared karst surfaces, and soil sink at a rate of 0.126 mm a−1 in forested and 0.111 mm a−1 in the cleared karst, implying relative growth of exposed limestone and the spontaneity of the karst process. Besides, smaller values of subsoil dissolution rate and soil sinking rate in the cleared than in the forested demonstrate that soil sinking and rock outcrops emergence are both slower without the cover of forests, while the opposite was true for dissolution of exposed limestone, implying that deforestation may not an absolute promoting factor to karst landscape. This soil sinking model provides a new explanation for the changes in the soil–rock position relationship, which is contrasting with the traditional karst soil loss model that generally attributes rock emergence to soil slope erosion or/and underground soil leaks. [ABSTRACT FROM AUTHOR]

Yunnan of southwestern China supports an extremely rich biodiversity and various vegetation types dominated by evergreen broad-leaved forest. The floristic composition, species diversity, physiognomy and biogeography of three major types of the evergreen broad-leaved forest in Yunnan were surveyed using 1-ha plots. The three forest types are very diverse in species composition, diversity, physiognomy and biogeography, although they are commonly dominated by species of the families Fagaceae, Theaceae and Lauraceae. The lower montane evergreen broad-leaved forest (LMEB) in southern Yunnan is extremely rich in species and is characterized by a tropical physiognomy and dominated by tropical Asian species, similar to the tropical lower montane evergreen forest commonly in southeast Asia. The semi-wet evergreen broad-leaved forest (SWEB) on plateaus and the upper montane evergreen broad-leaved forest (UMEB) in central and northern Yunnan are characterized by a subtropical physiognomy and are dominated by Sino-Himalayan and Chinese endemic species, and are unique in southwestern China. The SWEB and the UMEB should be given high conservation values due to their uniqueness and abundant Chinese endemic species. Especially, the SWEB should be given the highest protection because most remnants of this forest have lost due to heavily human disturbance. [ABSTRACT FROM AUTHOR]

The mechanisms underlying soil organic carbon (C) dynamics during forest succession remain challenged because amount, quality, and composition of C inputs change with tree growth and species composition. Soils were collected from two stages (grassland and young secondary forest) of secondary succession after the clear-cut of primary old-growth forest due to land-use change, with a native old-growth forest (undisturbed for more than 200 years) as the reference. Soil samples were incubated for 170 days and the priming effects were quantified by one pulse addition of 13C-labeled glucose. 13C-PLFAs (phospholipid fatty acids) were analyzed to identify microbial functional groups utilizing glucose and to explore their accordance with SOM priming during succession. Soil C was primed much more strongly in young secondary forest than in grassland or old-growth forest. Priming resulted in large C losses (negative net C balance) in young-forest soil, whereas C stocks increased in grassland and old-growth forest (positive net C balance). Microbial composition assessed by PLFA and utilization of easily available organics (13C-PLFA) indicated that fungi were mainly responsible for priming in young-forest soil. Consequently, labile C released by litter decomposition and root exudation together with the availability of soil nutrients determines microbial functional groups that decompose soil organic matter during initial succession. These findings provide novel ecological connections between soil organic matter dynamics and C (de)stabilization with microbial functioning during forest succession and show that priming direction and intensity is important to distinguish soil C dynamics in young- and old-growth forests. [ABSTRACT FROM AUTHOR]