Freezing can increase the emissions of carbon dioxide(CO_2) and nitrous oxide(N_2O) and the release of labile carbon(C) and nitrogen(N) pools into the soil. However, there is limited knowledge about how both emissions respond differently to soil freezing and their relationships to soil properties. We evaluated the effect of intensity and duration of freezing on the emissions of CO_2 and N_2 O, net N mineralization, microbial biomass, and extractable C and N pools in soils from a mature broadleaf and Korean pine mixed forest and an adjacent secondary white birch forest in northeastern China. These soils had different contents of microbial biomass and bulk density. Intact soil cores of 0–5 cm and 5–10 cm depth sampled from the two temperate forest floors were subjected to -8, -18, and -80°C freezing treatments for a short(10 d) and long(145 d) duration, and then respectively incubated at 10°C for 21 d. Soil cores, incubated at 10°C for 21 d without a pretreatment of freezing, served as control. Emissions of N_2 O and CO_2 after thaw varied with forest type, soil depth, and freezing treatment. The difference could be induced by the soil water-filled pore space(WFPS) during incubation and availability of substrates for N_2 O and CO_2 production, which are released by freezing. A maximum N_2 O emission following thawing of frozen soils was observed at approximately 80% WFPS, whereas CO_2 emission from soils after thaw significantly increased with increasing WFPS. The soil dissolved organic C just after freezing treatment and CO_2 emission increased with increase of freezing duration, which paralleled with a decrease in soil microbial biomass C. The cumulative net N mineralization and net ammonification after freezing treatment as well as N_2 O emission were significantly affected by freezing temperature. The N_2 O emission was negatively correlated to soil p H and bulk density, but positively correlated to soil K_2SO_4-extractable NO_3^--N content and net ammonification. The CO_2 emission was positively correla
采用室内土柱培养方法,研究不同土壤湿度(55%和80%土壤充水孔隙度,WFPS)条件下外源碳(葡萄糖,6.4 g C·m^(-2))和2种形态氮(NH_4Cl和KNO_3,4.5 g N·m^(-2))的添加对温带成熟阔叶红松混交林和次生白桦林土壤冻结后融化过程中氧化亚氮(N_2O)排放量的影响。结果表明:冻结过程会激发2种林分土壤融化初期N_2O的排放。随着土壤湿度的增加,2种林分土壤大量消耗硝态氮,反硝化作用强烈,导致融化初期N_2O激发效应的强度大,持续时间长,尤其是白桦林土壤。单施葡萄糖后,2种林分土壤大量消耗铵态氮和硝态氮,进而显著促进2种林分土壤融化初期N_2O的激发排放;随着土壤湿度的增加,葡萄糖对2种林分土壤N_2O累积排放量的促进作用减弱,这可能与高湿度条件下,冻结后融化过程中土壤释放大量溶解性有机碳(DOC)有关。低湿度条件下,2种林分土壤融化过程N_2O排放是铵态氮限制性的,即硝化潜势占主要优势,尤其是白桦林土壤;高湿度条件下,白桦林土壤具有很强的反硝化潜势,并且随着葡萄糖的施加,这种反硝化潜势加强。逐步回归分析显示:2种林分土壤冻结后融化过程N_2O累积排放量受到土壤pH、WFPS及水浸提DOC含量的影响,共同解释其66%的变化,并且与土壤水浸提溶解性有机氮含量呈显著的正相关;阔叶红松混交林土壤冻结后融化过程N_2O累积排放量与微生物生物氮呈显著负相关。综上可推测,温带森林土壤融化过程中N_2O的排放主要依赖于冻结处理后的土壤pH、WFPS以及溶解性有机质释放量的变化。
采用室内土柱培养的方法,研究在不同湿度(55%和80%WFPS,土壤充水孔隙度)和不同氮素供给(NH_4Cl和KNO_3,4.5 g N/m^2)条件下,外源碳添加(葡萄糖,6.4 g C/m^2)对温带成熟阔叶红松混交林和次生白桦林土壤融化过程微生物呼吸和微生物碳的激发效应。结果表明:在整个融化培养期间,次生白桦林土壤对照CO_2累积排放量显著高于阔叶红松混交林土壤。随着土壤湿度的增加,次生白桦林土壤对照CO_2累积排放量和微生物代谢熵(q_(CO_2))显著降低,而阔叶红松混交林土壤两者显著地增加(P<0.05)。两种林分土壤由葡萄糖(Glu)引起的CO_2累积排放量(9.61—13.49 g C/m^2)显著大于实验施加的葡萄糖含碳量(6.4g C/m^2),同时由Glu引起的土壤微生物碳增量为3.65—27.18 g C/m^2,而施加Glu对土壤DOC含量影响较小。因此,这种由施加Glu引起的额外碳释放可能来源于土壤固有有机碳分解。融化培养结束时,阔叶红松混交林土壤未施氮处理由Glu引起的CO_2累积排放量在两种湿度条件下均显著大于次生白桦林土壤(P<0.001);随着湿度的增加,两种林分土壤Glu引起的CO_2累积排放量显著增大(P<0.001)。单施KNO_3显著地增加两种湿度的次生白桦林土壤Glu引起的CO_2累积排放量(P<0.01)。单施KNO_3显著地增加了两种湿度次生白桦林土壤Glu引起的微生物碳(P<0.001),单施NH_4Cl显著地增加低湿度阔叶红松混交林土壤Glu引起的微生物碳(P<0.001)。结合前期报道的未冻结实验结果,发现冻结过程显著地影响外源Glu对温带森林土壤微生物呼吸和微生物碳的刺激效应(P<0.05),并且无论冻结与否,温带森林土壤微生物呼吸和微生物碳对外源Glu的响应均与植被类型、土壤湿度、外源氮供给及其形态存在显著的相关性。
By using packed soil-core incubation experiments,we have studied stimulating effects of addition of external carbon(C)(glucose,6.4 g Cm^(-2))on heterotrophic respiration and microbial biomass C of a mature broadleaf and Korean pine mixed forest(BKPF)and an adjacent white birch forest(WBF)soil under different wetting intensities(55%and 80%WFPS,water-filled pore space)and nitrogen(N)supply(NH_4C1 and KNO_3,4.5 g Nm^(-2))conditions.The results showed that for the control,the cumulative carbon dioxide(CO_2)flux from WBF soil during the 15-day incubation ranged from 5.44 to 5.82 g CO_2-Cm^(-2),which was significantly larger than that from BKPF soil(2.86 to 3.36 g CO_2-Cm^(-2)).With increasing wetting intensity,the cumulative CO_2 flux from the control was decreased for the WBF soil,whereas an increase in the CO_2 flux was observed in the BKPF soil(P<0.05).The addition of NH_4C1 or KNO_3 alone significantly reduced the cumulative CO_2 fluxes by 9.2%-21.6%from the two soils,especially from WBF soil at low wetting intensity.The addition of glucose alone significantly increased soil heterotrophic respiration,microbial biomass C(MBC),and microbial metabolic quotient.The glucose-induced cumulative CO_2 fluxes and soil MBC during the incubation ranged from 8.7 to 11.7 g CO_2-Cm^(-2)and from 7.4 to 23.9 g Cm^(-2),which are larger than the dose of added C.Hence,the addition of external carbon can increase the decomposition of soil native organic C.The glucose-induced average and maximum rates of CO_2 fluxes during the incubation were significantly influenced by wetting intensity(WI)and vegetation type(VT),and by WI×VT,NH_4Cl×VT and WI×VT×NH_4Cl(P<0.05).The addition of NH_4C1,instead of KNO_3 significantly decreased the glucose-induced MBC of WBF soil(P<0.05),whereas adding NH_4C1 and KNO_3 both significantly increased the glucose-induced MBC of BKPF soil at high moisture(P<0.05).According to the differences in soil labile C pools,MBC and CO_2 fluxes in the presence and absence of glucose,it can be concluded that the stimul
采用室内土柱培养的方法,研究了温带成熟阔叶红松混交林和次生白桦林土壤在不同的湿度（55%和80%WFPS,土壤充水孔隙率）和不同的氮素供应（NH4Cl和KNO3,4.5 g N m-2）条件下外源碳添加（葡萄糖,6.4 g C m-2）对森林土壤异养呼吸和微生物碳的激发效应.结果表明：培养期间次生白桦林土壤对照处理CO2累积排放量（5.44～5.82 g CO2-C m-2）显著高于阔叶红松混交林对照处理（2.86～3.36 g CO2-C m-2）.随着湿度的增加,次生白桦林土壤对照处理CO2累积排放量显著降低,而阔叶红松混交林土壤对照处理却显著增加（P〈0.05）.单施NH4Cl或KNO3处理培养期内两种林分土壤CO2累积排放量降低9.2%～21.6%（P〈0.05）,低湿度次生白桦林土壤降低最大.单施葡萄糖显著提高两种林分土壤异养呼吸、微生物碳量和微生物代谢熵.培养期间施加葡萄糖所增加的土壤CO2累积排放量（8.7～11.7 g C m-2）和土壤微生物量（7.4～23.9 g C m-2）显著大于施加的葡萄糖含碳量（6.4 g C m-2）,这可能是由土壤固有有机碳分解释放引起的.培养期间由葡萄糖引起的土壤CO2排放速率和最大排放速率不仅受到湿度及其与林分交互影响（P〈0.001）,还受到铵态氮与林分交互影响（P〈0.001）和林分、湿度和铵态氮三者交互影响（P〈0.05）.施加铵态氮显著抑制了次生白桦林土壤由葡萄糖引起的微生物碳,而施加硝态氮却无显著效应.施加两种形态的氮均显著促进高湿度阔叶红松混交林土壤由葡萄糖引起的微生物碳（P〈0.05）.经过量化由葡萄糖引起的土壤活性碳库、微生物碳及CO2排放量,发现葡萄糖对温带森林土壤异养呼吸和微生物碳的刺激效应与植被类型、湿度、外源氮供给及其形态显著相关。
