Seasonal changes in soil properties,microbial biomass and enzyme activities across the soil profile in two alpine ecosystems

Microbial biomass and extracellular enzyme activities control the rate of soil organic carbon decomposition,thereby affecting soil carbon pool.However,seasonal dynamics of soil microbial properties at different depths of the soil profile remain unclear.In this study,we sampled soils in the early,middle and late growing season at different soil depths(0–100 cm)in two alpine ecosystems(meadow and shrubland)on the Tibetan Plateau.We measured plant belowground biomass,soil properties,microbial biomass and extracellular enzyme activities.We found that soil properties changed significantly with sampling time and soil depth.Specifically,most of soil properties consistently decreased with increasing soil depth,but inconsistently varied with sampling time.Moreover,root biomass and microbial biomass decreased with increasing soil depth and increased with sampling time during the growing season.However,microbial extracellular enzyme activities and their vector properties all changed with depth,but did not vary significantly with time.Taken together,these results show that soil properties,microbial biomass and extracellular enzyme activities mostly decline with increasing depth of the soil profile,and soil properties and microbial biomass are generally more variable during the growing season than extracellular enzyme activities across the soil profile in these alpine ecosystems.Further studies are needed to investigate the changes in soil microbial community composition and function at different soil depths over the growing season,which can enhance our mechanistic understanding of whole-profile soil carbon dynamics of alpine ecosystems under climate change.

Long-term(42 years)effect of thinning on soil CO_(2)emission in a mixed broadleaved-Korean pine(Pinus koraiensis)forest in Northeast China

Thinning is an important forest management practice that has great potential to influence regional soil carbon storage and dynamics.The present study measured soil respiration(RS,the efflux of CO2 emitted)and its two components(heterotrophic(RH)and autotrophic(RA)respiration)from soil 42 years after thinning in comparison to un-thinning(control).Autotrophic respiration was significantly greater in the thinning plot,approximately 44%higher compared to the control,while both RSand RHwere slightly,but not significantly,higher in the thinning plot.Higher fine root biomass might have contributed to the higher RAin the thinning plot.Both RSand RHshowed clear soil temperature-dependent seasonal patterns,whereas RAwas less responsive to changes in temperature,especially within one specific season.The annual and season-specific temperature sensitivities of RSand RHwere lower in the thinning plot,specifically during the mid-growing season.Furthermore,variations in the season-specific temperature sensitivity of RSand RHwere less intense in the thinning plot.We conclude that forest thinning can reduce the temperature sensitivity of RSand RHduring the mid-growing season and increase soil CO2 emission in the long term.