Effects of vegetation succession and dry-wet seasonality on soil-litter-microbe stoichiometric characteristics in karst region of southwest China

【Objective】 This study aimed to investigate effects of vegetation succession and dry-wet seasonality on soil-litter-microbe stoichiometric characteristics， deepen the understanding of the processes of soil nutrient cycling in the karst region of southwest China， to provide scientific references for nutrient resources management and vegetation restoration in the area.【Method】 Ecosystems at shrub-grass community stage （SG）， shrub-tree transition stage （ST）， and evergreen-deciduous broad-leaved mixed forest stage （MF） in typical karst regions in Guilin of Guangxi were taken as research subjects. Soil and litter samples were collected respectively in wet and dry seasons to measure soil basic physicochemical properties， as well as the carbon （C）， nitrogen （N）， and phosphorus （P） contents in biomasses of soil， litter， and microbes. Their stoichiometric characteristics were then calculated to analyze patterns and correlations between vegetation succession and seasonality.【Result】 Whether in the dry or wet seasons， soil pH as well as the contents of dissolved nitrogen （DN） and nitrate nitrogen （NO₃^--N） increased with vegetation succession， while ammonium nitrogen （NH₄⁺-N） showed an overall decreasing trend with vegetation succession. In the dry and wet seasons with vegetation succession， soil total carbon （TC） increased by 44.8% and 23.9%， total nitrogen （TN） increased by 43.9% and 31.2%， respectively； while total phosphorus （TP） initially decreased and then increased. Soil TC and TN contents were extremely significantly higher in the dry season than in the wet season （P<0.01， the same below）， while no significant difference of soil TP was found between the two seasons （P>0.05， the same below）. In the dry and wet seasons， no significant difference was found in soil carbon-nitrogen ratio （C∶N） at different vegetation succession stages， but the carbon-phosphorus ratio （C∶P） and nitrogen-phosphorus ratio （N∶P） increased with vegetation succession； C∶N of litter significantly decreased by 37.8% with vegetation succession in the wet season， while C∶P and N∶P increased initially and then decreased， with their values extremely significantly higher in the dry season than those in the wet season. The carbon-phosphorus ratio of soil microbial biomass （MBC∶MBP） and nitrogen-phosphorus ratio of soil microbial biomass （MBN∶MBP） initially decreased and then increased with vegetation succession in the wet season. In the dry season， the MBC∶MBP at MF stage was significantly higher than that at SG and ST stages， while no significant difference was found in MBN∶MBP among vegetation succession stages. Correlation analysis indicated that with vegetation succession， the regulatory role of microbes on stoichiometric characteristics of soil and litter C， N， and P gradually weakened， while the regulatory role of litter initially increased and then decreased. Litter C∶N and N∶P， soil pH， water content， and DN were the main factors regulating stoichiometric characteristics of soil C， N， and P.【Conclusion】 Stoichiometric characteristics of C， N， and P in soil-litter-microbe of the karst region of southwest China show significant differences during vegetation succession， with notable variations of seasonality. Vegetation succession can facilitate the accumulation of soil nutrients， but in late vegetation succession， pronounced P deficiency is detrimental to plant growth and vegetation succession.