Soil Microbial Respiration Rate And Its Influencing Factors Along A North-south Forest Transect In Eastern China

Soil organic matter is one of the most important carbon(C)pools in terrestrial ecosystems,and future warming from climate change will likely alter soil C storage via temperature effects on microbial respiration.In this study,we collected forest soils from eight locations along a 3,700 km North—South transect in eastern China(NSTEC).For eight weeks these soils were incubated under a periodically changing temperature range of 6-30°C while frequently measuring soil microbial respiration rate(Rs;each sample about every 20 minutes).This experimental design allowed us to investigate Rs and the temperature sensitivity of Rs(Q10)along the NSTEC.Besides,precipitation is a critical factor triggering soil biogeochemical processes in arid and semi-arid regions.In this study,we selected soils from two temperate forests—a mature natural forest and a degraded secondary forest-in a semi-arid region.We investigated the pulse effects of simulated precipitation(to reach 55%soil water-holding capacity)on the soil microbial respiration rate(Rs).We performed high-intensity measurements(at 5-min intervals for 48 h)to determine the maximum value of Rs(Rs-max),the time to reach Rs-max(TRs-max),and the duration of the pulse effect(from the start to the end of 1/2Rs-max).Both Rs at 20?(R20)and Q10 significantly increased(logarithmically)with increasing latitude along the NSTEC suggesting that the sensitivity of soil microbial respiration to changing temperatures is higher in forest soils from locations with lower temperature.Our findings from an incubation experiment provide support for the hypothesis that temperature sensitivity of soil microbial respiration increases with biochemical recalcitrance(C quality-temperature hypothesis)across forest soils on a large spatial scale.Furthermore,microbial properties primarily controlled the observed patterns of R20,whereas both substrate and microbial properties collectively controlled the observed patterns of Q10.These findings advance our understanding of the driving factors(microbial vs.substrate properties)of R20 and Q10 as well as the general relationships between temperature sensitivity of soil microbial respiration and environmental factors.The responses of Rs to simulated precipitation were rapid and strong.Rs-max was significantly higher in degraded secondary forest(18.69?g C g soil-1 h-1)than in mature natural forest(7.9 4?g C g soil-1 h-1).In contrast,the duration of the pulse effect and TRS-max were significantly lower in degraded secondary forest than in mature natural forest.Furthermore,the accumulative microbial respiration per gram of soil(ARS-soil)did not differ significantly between degraded secondary forest and mature natural forest,but the accumulative microbial respiration per gram of soil organic C(ARS-soc)was significantly higher in degraded secondary forest than in mature natural forest.Soil microbial biomass,soil nutrient,and litter nitrogen content were strongly correlated with the duration of the pulse effect and TRS-max.Soil physical structure,pH,and litter nitrogen content were strongly correlated with Rs-max and ARS-soc.Our results indicate that the responses of soil microbial respiration to simulated precipitation are rapid and strong and that the microbe respiration rate per gram C is able assess precisely the precipitation pulse of different soil samples as well as the effects of changing precipitation patterns on soil C content under various scenarios of global climate change.