| The forest soil organic carbon is the largest terrestrial carbon pool.Any changes to it may cause significant influence in atmospheric CO2 concentrations,thereby accelerating or mitigating global climate change.Due to the increasing levels of atmospheric CO2,global temperatures are predicted to rise 1.0-3.7℃ by the year 2100,with a resultant increase in soil temperatures.The priming effect describes the changes in soil organic carbon(SOC)mineralization after fresh organic matter(FOM)inputs and is a major component of the soil carbon cycle.However,no conclusion has been reached on the effect of temperature increase on soil priming effect,and the underlying mechanism remains unclear.In the present study,13C isotopic tracing was applied to investigate the effect of warming on priming effect induced by FOM of different qualities(glucose,and maize)in soils along a latitudinal gradient of temperate China(mountain brown soil from Dongling Mountain of warm temperate region,dark brown forest soil from Maoer Mountain of mid-temperate region,and brown coniferous forest soil from Daxingan Mountain of cold temperate region).Meanwhile PCR sequencing method was applied to uncover the mechanisms of priming under warming by exploring the microorganism dynamics and the interaction with soil properties.And the main findings are as follows,(1)Warming and FOM additions significantly stimulated the total respiration in soils from different latitudes.Among them,maize addition induced a higher total respiration than glucose.The addition of glucose and maize decreased the temperature sensitivity(Q10)of SOM for 1.6～10.2%(p<0.05),however there was no significant difference between these two treatments(p>0.05).Meanwhile,dark brown forest soil with the highest total C and N concentration showed the highest total respiration and Q10 among these three soils(p<0.01),which was 12%and 14%higher than mountain brown soil and brown coniferous forest soil respectively in glucose treatment,and 13%and 25%higher than them respectively in maize treatment.(2)Among all the treatments,the cumulative mineralization of maize was significantly higher than glucose(p<0.05)and was 56%～143%higher than that in glucose treated soils among all the temperatures.The mineralization of both FOM showed an initial peak in the beginning of incubation,while priming effect also showed a corresponding initial peak,but both decreased as incubation continued.The cumulative priming induced by glucose and maize both decreased significantly with warming(p<0.05),by 52%～446%among all the treatments.However,the glucose induced cumulative priming was positive,while the maize induced priming was negative.Furthermore,priming effect of different stages also showed to be temperature sensitive,among them,the cumulative early-stage priming induced by glucose in Dark brown forest soil and brown coniferous forest soil inceased with warming whereas the maize induced priming in mountain brown soil and Dark brown forest soil decreased with warming.And the late-stage priming decreased with warming in both FOM treatments.As priming decreased in FOM treated soils under warming,the temperature sensitivity of SOM decreased correspondingly.(3)The addition of FOM significantly stimulated MBC at the beginning of incubation,therefor a lot of mineral N was consumed and leading to a decrease of mineral N concentration at the beginning.The correlation between PE and mineral N concentration decreased with warming,among them,the initial priming was negatively correlated(p<0.05)with mineral N at higher temperature but positively correlated(p<0.05)at lower temperature,but the late-stage priming was positively correlated(p<0.05)with N at all temperatures.Meanwhile,during incubation,no difference was found between the correlation between priming and soil properties of glucose and maize treatments,which indicates the FOM addition of different qualities didn’t affect how soil properties participated in priming,although they induced different priming effect and soil properties.Among all the treatments,the temperature sensitivity of SOM was positively correlated with soil mineral N and DOC concentration,indicating that the soil energy and nutrient state are the key factors of soil temperature sensitivity.(4)In our study,r-strategists were the dominant microorganisms in all the soils,and they were Actinobacteriota,Proteobacteria,Acidobacteriota,Choroflexi,Verrucomicrobiota,Firmi cutes,Gemmatimonadota,Bacteroidota,Patescibacteria,Myxococcota and Methylomirabilota.The addition didn’t restructure the microbial populations,but changed the relative abundance of some populations,for example,Actinobacteria,Mortierellomycota,Basidiomycota and Ascomycota in mountain brown soil,Mortierellomycota,Ascomycota,Basidiomycota and Patescibacteria indark brown forest soil,Actinobacteria,Mortierellomycota,Basidiomycota and Chloroflexi in brown coniferous forest soil.Temperature also showed significant effects on microorganisms as Basidiomycota,Gemmatimonadetes,Actinobacteria,but the effects differed in different soils,which indicates that the influence of temperature is not independent on microorganisms but also influenced by soil properties.(5)In glucose treated soils,the microorganisms taking part in priming were mainly rstrategists,then followed by K-strategists,suggesting that the mechanism responsible for earlystage priming should be energy limited extracellular enzyme synthesis and co-metabolism.As the relative abundance of typical K-strategist Basidiomycota increased significantly with increasing incubation time,and priming effect was also significantly and positively correlated with mineral N content,which indicates the corresponding mechanism for the late-stage priming is N-mining theory.As temperature decreased,the number of K-strategists positively correlated to priming increased,and this could be the reason why priming at lower temperature was higher than higher temperature.In both the glucose treatment and control,the microorganisms positively correlated to temperature sensitivity and mineral N are all r-strategists,which suggests in higher N availability situations,the dominance of r-strategist could explain the highest temperature sensitivity in dark brown forest soils among the three sites.In conclusion,warming has a strong stimulation towards soil respiration,and the glucose addition induced intensive positive priming whereas maize induced intensive negative priming.Warming reduced priming effect through declining the participation of K-strategists in priming process.Furthermore,the decrease of priming during warming caused corresponding decrease in temperature sensitivity of SOM.This study suggests that the FOM addition would affect the magnitude and direction of priming by regulating the microorganism process. |
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