Variation Of Temperature Sensitivity Of Soil Respiration In Weibei Dry Farmland

Soil respiration is an important carbon flux between the terrestrial ecosystem and the atmosphere,and it plays a critical role in global carbon cycling.Temperature sensitivity of soil respiration(often expressed as Q₁₀)is regarded as an important mechanism for the possi-ble feedback between the carbon cycle in terrestrial ecosystem and the climate system.Q₁₀value was the key process in the understanding of terrestrial ecosystem carbon cycle,and its response to the climate change has dramatic effects on the feedback between terrestrial carbon cycle and global warming.The field experiment was conducted in the Wangdonggou?35°13?N,107°40?E;1220 m a.s.l?,Changwu Country,Shaanxi Province,China,where the State Key Agro-Ecological Ex-perimental Station on the Loess Plateau was located.The experiment was included 1)differ-ent crop type with winter wheat?Triticum aestivum L.?and spring maize?Zea mays L.?at two N fertilization levels(no fertilization?CK?and 160 kg N hm^–1);2)three fertilization regimes in winter wheat,no fertilization?CK?,160 kg N ha^–1?N?,and 160 kg N ha^–1 and 39 kg P ha^–1?N+P?;3)five nitrogen fertilization rates treatments,i.e.,0,45,90,135,and 180 kg N ha^-1(N₀,N₄₅,N₉₀,N₁₃₅ and N₁₈₀)with winter wheat,based on the same phosphorus fertilization rate(39 kg P ha^-1);4)the apple orchard?Malus domestica Borkh?established in 2000 and typical cropland?winter wheat?.Soil respiration rate was in situ measured using a Li-8100soil CO₂ efflux measurement system,and soil temperature and soil moisture both at 0-5 cm were also measured at the same time.To investigate effects of crop type,fertilizer regimes and land use,on soil respiration,Soil organic carbon?SOC?,Soil nitrogen?TN?,soil microbi-al biomass carbon?MBC?,soil dissolved organic carbon?DOC?,crop yield,below-and above-ground biomass,photosynthesis rate,enzyme activities,microbial community diversity,composition and abundance were measured.The objectives of the present study were to in-vestigate based on the data from in suit measured and the analyses in Lab:1)variation of soil respiration rate and its temperature sensitivity under different crop types;2)dyadic change of soil respiration rate and temperature sensitivity under different fertilization regimes;3)dif-ference of soil respiration rate and its temperature sensitivity between cropland and apple or-chard;4)variation of environmental factors,vegetation growth,microbial community struc-ture,activity and their relationship with soil respiration rate and its temperature sensitivity.Main results were as follows:1)Crop type significant influence soil respiration and Q₁₀ value?p<0.05?.Annual mean soil respiration in spring maize were 20%(1.85 vs.1.54?mol m^-2s^-1)and Q₁₀ value 36%?2.49 vs.1.83?higher than that in wheat.The grain yield(2.93 vs.8.90 t ha^-1),above-ground biomass(7.17 vs.17.0 t ha^-1)and fine root biomass(1.71 vs.2.33 t ha^-1)in maize were sig-nificantly higher than that in wheat?all p<0.05?.2)Mean annual soil respiration rate in the N treatment and N+P treatment was 18%and48%higher than that in the CK treatment,respectively;and it was increased by 26%?14%-48%?in the N+P treatment as compared with that in the N treatment.The decrease of Q₁₀0 value in the N and N+P treatments against the CK treatment was not stable for each year,ranging from 0.01 to 0.28.The maximum decrease of Q₁₀ value in the N and N+P treatments was 10%and 15%in 2014-2015,while in other years the decrease of Q₁₀0 value was numerical but not significant.Soil microbial biomass carbon?SMBC?was increased by 10%and 50%,dissolved organic carbon?DOC?was increased by 6%and 21%,and photosynthesis rate was increased ranging from 6%to 33%with N and N+P fertilization.The relative abundance of Acidobacteria,Actinobacteria and Chloroflexi were significantly higher by 32.9%-54.1%in N addition soils?N and N+P?compared to CK treatment.3)Nitrogen fertilizer significantly increased soil respiration rate,mean annual accumula-tive R_s raised by 25%-40%.In contrast to soil respiration rate,as N fertilization rates in-creased,Q₁₀ values was significant decreased at diurnal,and multiple-year scale.Diurnal Q₁₀value was halve from 3.39 in N₀ to 1.68 in N₁₈₀ during the elongating stage,multiple-year Q₁₀value from 1.49 to 1.41.Diurnal Q₁₀ value negatively related to photosynthetic rate and N content in leaf,and multiple-year Q₁₀ value positively related to soil C/N and root C/N;and varied bacteria community was also contributed the decreased Q₁₀ value,Actinobacteria was negatively and Bacteroidetes was positively related to multiple-year Q₁₀ value.4)The average annual soil respiration rate in the apple orchard was 12%greater than that in the cropland(2.01 vs.1.80?mol m^-2 s^-1),despite that the average Q₁₀0 values in the apple orchard was 15%lower than that in the cropland?ranging from 1.63 to 1.41?.As to the dif-ferences among predominant phyla,Proteobacteria was 26%higher in the apple orchard than that in the cropland,whereas Actinobacteria and Acidobacteria were 18%and 36%lower in the apple orchard.The?-glucosidase and cellobiohydrolase activity were 15%(44.92 vs.39.09 nmol h^-1 g^-1)and 22%greater(21.39 vs.17.50 nmol h^-1 g^-1)in the apple orchard than that in the cropland.Compared to the cropland,the lower Q₁₀0 values in the apple orchard re-sulted from the variations of bacterial community structure and?-glucosidase and cellobiohy-drolase activity.In addition,the lower C/N ratios in the apple orchard?6.50 vs.8.40?possibly also contributed to its lower Q₁₀ values.5)There was a significant positive correlation between soil respiration rate and root biomass,SMBC,DOC,photosynthetic rate?p<0.05?.The temperature sensitivity of soil res-piration is related to substrate quality?C/N?and bacterial community structure.The tempera-ture sensitivity of soil respiration decreased with the decrease of C/N.Proteobacteria,Actino-bacteria and Acidobacteria were the predominant phyla in soil,which affected soil respiration rate and its temperature sensitivity.Selection of land use and crop type,and chemical fertilizer applied significantly influ-enced soil respiration rate and its temperature sensitivity.we cannot ignore the effect on the carbon balance and CO₂ concentration of terrestrial ecosystems from human activities under future climate change,such as land use pattern,agricultural management,and so on.The ef-fect of human activities should also be fully considered in models of terrestrial ecosystems and climate systems,so as to correctly estimate the change of carbon and sink capacity of ter-restrial soils under future climate change.