草甸草原土壤碳/氮矿化潜力及土壤微生物水分敏感性对极端干旱的响应

土壤碳、氮矿化是生态系统养分循环的关键过程,受到水分供给的强烈影响。本研究对极端干旱处理(连续3年生长季减少66%降水)的内蒙古草甸草原野外取土,采用超低温冻干后再调节土壤水分至3%、8%、13%、18%、25%和35%6个水平进行室内培养,研究极端干旱处理后土壤碳/氮矿化潜力以及土壤微生物对水分变化的敏感性。结果表明:与对照(自然降雨)相比,极端干旱处理后,6个培养水平的平均土壤氮矿化潜力显著提高14.2%,但未显著影响土壤碳矿化潜力。极端干旱显著提高土壤微生物生物量氮和土壤可溶性有机碳26.8%和26.9%。无论是对照还是极端干旱处理,土壤氮矿化潜力、碳矿化潜力和微生物生物量碳和氮均随着土壤含水量增加而增加,而可溶性有机碳从较低水分的培养水平(3%和8%)到较高水分的培养水平(>13%)显著降低,表明底物的扩散起到重要作用。极端干旱处理显著提高了碳矿化初始脉冲强度,表明极端干旱提高了土壤微生物对水分的敏感性。极端干旱显著降低了土壤碳矿化潜力/氮矿化潜力的比值,表明长期干旱可能会降低土壤碳、氮循环过程的耦合作用。极端干旱对土壤碳矿化和氮矿化过程的影响存在差异,激发了土壤微生物对水分的敏感性,弱化了碳、氮循环过程的耦合关系,并进一步影响中国北方草甸草原生态系统的生物地球化学循环过程及草地生产力。

冻融对温带森林土壤碳、氮矿化作用的影响

秋末春初,中高纬度和高海拔地区普遍存在冻融现象。随着全球气候变暖,冻融对土壤碳/氮循环过程的影响日益受到重视。本研究以长白山地区典型阔叶红松林(Pinus koraiensis)、白桦林(Betula platyphylla)和长白山落叶松林(Larix olgensis)土壤为研究对象,采用室内模拟控制试验,研究低含水量(40%)和高含水量(过饱和)条件下,冻融循环(-10~10℃)对不同林型土壤碳/氮矿化作用的影响。结果表明,在不同含水量条件下(低含水量条件下的阔叶红松林土壤除外),冻融处理均显著降低土壤有机碳矿化速率,且土壤碳矿化速率随冻融次数的增加而显著降低。冻融与土壤水分对氮矿化存在交互影响;在低含水量条件下,冻融促进土壤氮矿化作用;但在高含水量条件下,该影响不一致。本研究表明,秋末和春初的冻融循环对长白山地区森林土壤碳、氮矿化过程有重要影响,且其影响程度很大程度上取决于冻融频率和土壤含水量。

长白山苔原带土壤碳、氮矿化对氮沉降的响应

高山苔原生态系统的土壤无机氮含量较低,对氮的缓冲性弱而易受外源氮输入的影响.本研究以长白山北坡苔原带土壤为研究对象,通过室内培养试验,以NH_4NO_3为外加氮源,设置3个施氮水平:对照(CK,0 kg·hm^(-2)),低氮(N_1,25 kg·hm^(-2)),高氮(N_2,50 kg·hm^(-2)),分析长白山苔原带土壤碳、氮矿化对氮沉降的响应.结果表明:氮添加处理对长白山苔原带土壤碳矿化速率影响不显著,但对土壤碳矿化累积矿化量影响显著,N_2抑制了土壤的碳矿化作用.培养40 d后,氮添加处理提高了土壤无机氮含量;而培养80 d后,N_2与N_1的无机氮含量差异不显著,但都明显高于CK,氮输入促进了土壤氮的矿化.培养过程中,N_1处理下的微生物生物量碳、氮高于N_2和CK处理,说明低氮输入对土壤微生物活性的促进作用更明显.在未来氮沉降增加的背景下,长白山苔原土壤碳、氮周转可能加快,提高土壤无机氮含量.土壤中无机氮含量增加,虽然可以为植物生长提供更多生长所需的氮素,但也提高了土壤氮素的流失风险.

Effects of Nitrogen Treatments on Organic Carbon Mineralization of Citrus Orchard Soil

[Objective] This study aimed to investigate the effect of soil organic carbon mineralization at different temperature on the amount of nitrogen application, in order to provide references for the establishment of carbon circulation model for orchard eco-system. [Method] The effects of nitrogen treatments on soil organic carbon mineralization of citrus orchard soil were investigated under 10, 20, 30 ℃ by laboratory simulated experiment. [Result] The mineralization rate decreased quickly at the be- ginning of the experiment but remained stable at the late period under three temper- ature treatments. The amounts of CO2 ranged from 1 328.25-2 219.42 mg/kg under three temperature condition, and the amount of soil organic carbon mineralization of 100 mg/kg （N4） treatment was the greatest, while that of CK was the lowest. High level nitrogen treatment （N4 and N3） were significant higher than the lower level nitro- gen treatment （N2 and N1）. The soil organic carbon mineralization rate increased with the temperature from 10 to 30℃. The dependence of soil carbon mineralization to temperature （Q10） was different under different nitrogen treatments that the Qlo value of N2 treatment was the lowest while that of the N4 treatment was the greatest. The soil organic carbon mineralization in Citrus orange orchard soil was affected significantly by high level nitrogen treatment, but with no significance under lower nitrogen treatment. [Conclusion] The dependence of soil carbon mineralization to temperature （Q10） increased with the increasing nitrogen input. The combination of nitrogen with temperature may increase the CO2 emission from Citrus orchard soil.

Catalytic oxidation of diesel soot particulates over Ag/LaCoO_3 perovskite oxides in air and NO_x

Ag/LaCoO3 perovskite catalysts for soot combustion were prepared by the impregnation method.The structure and physicochemical properties of the catalysts were characterized using X-ray diffraction,N2 adsorption-desorption,H2 temperature-programmed reduction,soot temperatureprogrammed reduction,and X-ray photoelectron spectroscopy.The catalytic activity of the catalysts for soot oxidation was tested by temperature-programmed oxidation in air and in a NOx atmosphere.Metallic Ag particles were the main Ag species.Part of the Ag migrated from the surface to the lattice of the LaCoO3 perovskite,to form La（1-x）AgxCoO3.This increased the amount of oxygen vacancies in the perovskite structure during thermal treatment.Compared with unmodified LaCoO3,the maximum soot oxidation rate temperature（Tp） decreased by 50-70 ℃ in air when LaCoO3 was partially modified by Ag,depending on the thermal treatment temperature.The Tp of the Ag/LaCoO3catalyst calcined at 400℃ in a NOx atmosphere decreased to about 140℃,compared with that of LaCoO3.Ag particles and oxygen vacancies in the catalysts contributed to their high catalytic activity for soot oxidation.The stable catalytic activity of the Ag/LaCoO3 catalyst calcined at 700℃ in a NOx atmosphere was related to its stable structure.

Relationship Between Soil Microbial Biomass C and N and Mineralizable Nitrogen in Some Arable Soils on Loess Plateau

The chloroform fumigation-incubation method was used to measure the soil microbial biomass C (SMBC)and N (SMBN) in 16 loessial soils sampled from Ausai, Yongshou and Yangling in Shaanxi Province. The SMBC contents in the soils ranged from 75.9 to 301.0 μg Cg-1 with an average of 206.1 μg C g-1, accounting for 1.36%～6.24% of the total soil organic C with an average of 3.07%, and the SMBN contents from 0.51 to 68.40 μg N g-1 with an average of 29.4 μg N g-1, accounting for 0.20%～5.65% of the total N in the soils with an average of 3.36%. A close relationship was found between SMBC and SMBN, and they both were positively correlated with total organic C, total N, NaOH hydrolizable N and mineralizable N. These results confirmed that soil microbial biomass had a comparative role in nutrient cycles of soils.

Effect of Simulated Acid Rain on Potential Carbon and Nitrogen Mineralization in Forest Soils

Acid rain is a serious environmental problem worldwide. In this study, a pot experiment using forest soils planted with the seedlings of four woody species was performed with weekly treatments of pH 4.40, 4.00, 3.52, and 3.05 simulated acid rain (SAR) for 42 months compared to a control of pH 5.00 lake water. The cumulative amounts of C and N mineralization in the five treated soils were determined after incubation at 25 ℃ for 65 d to examine the effects of SAR treatments. For all five treatments, cumulative CO2-C production ranged from 20.24 to 27.81 mg kg-1 dry soil, net production of available N from 17.37 to 48.95 mg kg-1 dry soil, and net production of NO-3 -N from 9.09 to 46.23 mg kg-1 dry soil. SAR treatments generally enhanced the emission of CO2-C from the soils; however, SAR with pH 3.05 inhibited the emission. SAR treatments decreased the net production of available N and NO3-N. The cumulative CH4 and N2O productions from the soils increased with increasing amount of simulated acid rain. The cumulative CO2-C production and the net production of available N of the soil under Acmena acuminatissima were significantly higher (P ≤ 0.05) than those under Schima superba and Cryptocarya concinna. The mineralization of soil organic C was related to the contents of soil organic C and N, but was not related to soil pH. However, the overall effect of acid rain on the storage of soil organic matter and the cycling of important nutrients depended on the amount of acid deposition and the types of forests.

Effect of Potassium and C/N Ratios on Conversion of NH_4^+ in Soils

Two soils, one consisting of 1:1 clay minerals at pH 4.5 and the other containing 2:1 clay minerals at pH 7.0, were used to estimate the conversion of added NH+4 under different C/N ratios (glucose as the C source) and the addition of potassium. Under lower C/N ratios (0:1 and 5:1), a large part of the added NH4+ in the acid soil was held in the forms of either exchangeable or water soluble NH4+ for a relatively long time and under higher C/N ratio (50:1), a large amount of the added NH4+ was directly immobilized by microorganisms. In the second soil containing appreciable 2:1 type clay minerals a large part of the added NH+4 at first quickly entered the interlayer of the minerals under both lower and higher C/N ratios. In second condition, however, owing to microbial assimilation stimulated by glucose the newly fixed NH4+c ould be completely released in further incubation because of a large concentration gradient between external NH4+ and fixed NH4+ in the mineral interlayer caused by heterotrophic microorganisms, which imply the fixed NH4+ to be available to plants. The results also showed that if a large amount of K+ with carbon source together was added to soil, the higher K+ concentration of soil solution could impede the release of fixed NH4+ , even if there was a lot of carbon source.

Temperature dependence of carbon mineralization and nitrous oxide emission in a temperate forest ecosystem

The measurement of CO2 and N2O effiux from forest soils is of great importance in evaluating the role of forests as sequestering agents of atmospheric CO2 and nitrogen. To quantify the effect of site on temperature dependence of net C-mineralization and N2O-N emissions, three adjacent forest floors under beech, Norway spruce and mixed species stands were investigated at Soiling forest, Germany, by an incubation experiment for three months. The investigated net C-mineralization and N2O-N emissions from all forest floors exhibited an exponential increase with respect to temperature elevation. The temperature coefficient function （Q10 value）, was fitted to flux rates to describe the temperature sensitivity of forest floors on temperature in the range of 1-20℃. Comparing the fitted curves for temperature sensitivity of the forest floors in relation to net carbon mineralization and nitrous oxide emission rates revealed a strong positive correlation across all sites. For the whole data set of all stands, a Q10 value of 1.73-2.10 for net C-mineralization and 2.81-3.58 for N2O-N emissions per measured unit was found to describe the temperature dependency of net C-mineralization and N20-N efflux at experimental site. The absence of clear differences between beech and spruce in mono and mixed species cultures on temperature dependencies of net C-mineralization and N2O-N emission rates indicated that the flux rates were not affected by species-specific differences of litter quality.

Correlation Between CO_2 Efflux and Net Nitrogen Mineralization and Its Response to External C or N Supply in an Alpine Meadow Soil

In nutrient-limited alpine meadows,nitrogen(N) mineralization is prior to soil microbial immobilization;therefore,increased mineral N supply would be most likely immobilized by soil microbes due to nutrient shortage in alpine soils.In addition,low temperature in alpine meadows might be one of the primary factors limiting soil organic matter decomposition and thus N mineralization.A laboratory incubation experiment was performed using an alpine meadow soil from the Tibetan Plateau.Two levels of NH4NO3(N) or glucose(C) were added,with a blank without addition of C or N as the control,before incubation at 5,15,or 25 ℃ for 28 d.CO2 efflux was measured during the 28-d incubation,and the mineral N was measured at the beginning and end of the incubation,in order to test two hypotheses:1) net N mineralization is negatively correlated with CO2 efflux for the control and 2) the external labile N or C supply will shift the negative correlation to positive.The results showed a negative correlation between CO2 efflux and net N immobilization in the control.External inorganic N supply did not change the negative correlation.The external labile C supply shifted the linear correlation from negative to positive under the low C addition level.However,under the high C level,no correlation was found.These suggested that the correlation of CO2 efflux to net N mineralization strongly depend on soil labile C and C:N ratio regardless of temperatures.Further research should focus on the effects of the types and the amount of litter components on interactions of C and N during soil organic matter decomposition.