The Comparative Photodegradation Activities of Pentachlorophenol (PCP) and Polychlorinated Biphenyls (PCBs) Using UV Alone and TiO2-Derived Photocatalysts in Methanol Soil Washing Solution

Photochemical treatment is increasingly being applied to remedy environmental problems. TiO₂-derived catalysts are efficiently and widely used in photodegradation applications. The efficiency of various photochemical treatments, namely, the use of UV irradiation without catalyst or with TiO₂/graphene-TiO₂ photodegradation methods was determined by comparing the photodegadation of two main types of hydrophobic chlorinated aromatic pollutants, namely, pentachlorophenol (PCP) and polychlorinated biphenyls (PCBs). Results show that photodegradation in methanol solution under pure UV irradiation was more efficient than that with either one of the catalysts tested, contrary to previous results in which photodegradation rates were enhanced using TiO₂-derived catalysts. The effects of various factors, such as UV light illumination, addition of methanol to the solution, catalyst dosage, and the pH of the reaction mixture, were examined. The degradation pathway was deduced. The photochemical treatment in methanol soil washing solution did not benefit from the use of the catalysts tested. Pure UV irradiation was sufficient for the dechlorination and degradation of the PCP and PCBs.     

二氧化钛纳米颗粒对沼泽土壤反硝化和N2O排放的影响

近年来,二氧化钛纳米颗粒（TiO₂NPs）环境释放量不断增加,并通过多种途径进入湿地生态系统,不可避免地影响到湿地生态系统环境和功能。然而,关于TiO₂NPs对沼泽土壤反硝化作用和氧化亚氮（N₂O）排放的影响机及制尚不明确。选择典型沼泽土壤,通过室内培养实验研究土壤理化性质、反硝化酶活性、反硝化速率（DNR）和N₂O排放对不同剂量TiO₂NPs 0 mg/kg （CK）、10 mg/kg （A10）、100 mg/kg （A100）、1000 mg/kg （A1000）输入的响应,探讨TiO₂NPs输入对沼泽土壤反硝化作用和N₂O排放影响的内在机制。结果表明：不同剂量TiO₂NPs处理显著降低了土壤pH （P<0.05）,A10处理显著降低土壤总有机碳（TOC）含量（P<0.01）,A1000处理显著降低硝态氮（NO₃^--N）和亚硝态氮（NO₂^--N）含量（P<0.05）。TiO₂NPs处理抑制硝酸盐还原酶（NAR）活性,促进一氧化氮还原酶（NOR）和氧化亚氮还原酶（NOS）活性（P<0.01）,A1000处理先促进后抑制了亚硝酸盐还原酶（NIR）活性（P<0.05）。不同剂量TiO₂NPs处理抑制了土壤DNR,促进了N₂O排放,TiO₂NPs处理通过抑制NIR活性,降低土壤DNR,同时通过促进NOR活性,提高N₂O排放。综上,TiO₂NPs输入通过影响反硝化还原酶活性改变沼泽土壤反硝化过程,导致沼泽土壤N₂O排放增加,改变湿地氮的源、汇功能,影响全球气候变化。为TiO₂NPs输入的湿地环境风险评估研究提供理论基础。     

Study of the photodegradation of 2-chlorobenzoic acid by TiO2 and the effects of eutrophicated water on the reaction

The photodegradation of 2-chlorobenzoic acid (2-CBA) in suspensions of TiO₂ was examined under different operational parameters. The optimal condition could be obtained through the experiment, i.e. that the concentration of 2-CBA was 30 mg/L and the dosing quantity of TiO₂ was 0.01 g under UV light in the case of pH 3.5. Above reaction process was in accordance with first order kinetics model. The influence on photocatalytic degradation caused by typical anions in eutrophicated water body such as NO₃⁻ and H₂PO₄⁻ was explored in this work, which revealed that both two anions had inhibitory effect on the degradation process. In addition, alcohol was introduced into the process to identify the degradation mechanism of 2-CBA with TiO₂, and the reaction route of 2-CBA could be predicted through the analysis on the intermediate.     

土壤磷含量与有效性对N2O排放量的影响元分析

土壤氧化亚氮(N₂O)主要产生于土壤微生物参与的氮循环过程,其排放量受磷含量及有效性影响。添加磷肥有助于缓解陆地生态系统磷限制,提升土壤有效磷含量,进一步影响土壤微生物对氮的利用,同时控制N₂O排放。然而不同独立实验中N₂O对外源磷添加的响应差异较大。研究从发表的中、英文文献中收集了54份关于施用磷肥与N₂O排放量的观测结果,采用元分析方法确定添加外源磷后N₂O排放量的响应差异及潜在影响因素。结果表明：(1)外源磷添加对土壤N₂O排放量影响不显著;但在磷肥施用量> 50 kg P/hm²的室外实验中土壤N₂O排放量显著降低了32.5%;施用NaH₂PO₄的室内实验中N₂O排放量显著降低了18.4%。(2)土壤N₂O对外源磷添加响应的高变异性是磷肥施用量和土壤含水量、土壤pH、土地利用类型、磷肥种类、纬度和实验时间多种影响...     

鼎湖山针阔叶混交林凋落物CO2释放对模拟酸雨的响应

该研究2011年1月开始在鼎湖山针阔叶混交林(混交林)进行模拟酸雨实验,设置4个不同处理水平,即对照(CK)(pH为4.5左右的天然湖水)、T_1(pH=4.0)、T_2(pH=3.25)和T_3(pH=2.5)。2013年1—12月对不同酸雨强度处理下的森林凋落物CO_2释放速率进行为期1 a的连续观测,探讨酸雨对混交林凋落物C排放的影响。结果表明:凋落物CO2释放通量在对照样方为(1 507.41±155.19) g CO_2·m~(-2)·a~(-1),其中湿季和旱季分别占年通量的68.7%和31.3%。模拟酸雨抑制了森林凋落物CO_2释放,与CK相比,T_2和T_3处理下的CO_2释放通量分别显著降低15.4%和42.7%(P0.05);且这种抑制作用具有季节差异性,处理间的显著差异只出现在湿季。凋落物CO_2释放速率与土壤温度和土壤湿度分别呈显著指数相关和显著直线相关,同时,酸雨处理降低了凋落物CO_2释放的温度敏感性。混交林凋落物CO_2释放在模拟酸雨下的抑制效应与土壤累积酸化而导致的土壤微生物活性变化有关,表现为模拟酸雨作用下土壤pH值和微生物量碳显著下降。上述结果说明酸雨是影响混交林土壤碳循环的重要因子之一。     

模拟氮沉降和降雨对华西雨屏区常绿阔叶林土壤呼吸的影响

从2013年12月至2014年11月,通过野外原位试验,对华西雨屏区常绿阔叶林进行了模拟氮沉降和降雨试验,采用LI-8100土壤碳通量分析系统(LI-COR Inc.,USA)测定了对照(CK)、氮沉降(N)、减雨(R)、增雨(W)、氮沉降+减雨(NR)、氮沉降+增雨(NW)6个处理水平的土壤呼吸速率,并通过回归方程分析了温度和湿度与土壤呼吸速率间的关系。结果表明:(1)氮沉降和增雨抑制了常绿阔叶林土壤呼吸速率,减雨促进了常绿阔叶林土壤呼吸速率。(2)减雨使华西雨屏区常绿阔叶林土壤呼吸年通量增加了258 g/m~2,而模拟氮沉降和增雨使华西雨屏区常绿阔叶林土壤呼吸年通量分别减少了321g/m~2和406g/m~2。(3)减雨增加了土壤呼吸的温度敏感性,模拟氮沉降和增雨降低了土壤呼吸的温度敏感性。(4)模拟温度和湿度与土壤呼吸速率间回归方程分析表明,土壤水分对土壤呼吸速率的影响较小。(5)模拟氮沉降和增雨处理减少土壤微生物生物量碳、氮的含量,减雨处理增加了土壤微生物生物量碳、氮的含量。(6)模拟氮沉降和降雨对华西雨屏区土壤CO_2释放的影响未表现出明显的交互作用。     

Microbial Activity and 13C/12C Ratio as Evidence of N-Hexadecane and N-Hexadecanoic Acid Biodegradation in Agricultural and Forest Soils

The dynamics of microbial degradation of exogenous contaminants, n-hexadecane and its primary microbial oxidized metabolite, n-hexadecanoic (palmitic) acid, was studied for topsoils, under agricultural management and beech forest on the basis the changes in O₂ uptake, CO₂ evolution and its associated carbon isotopic signature, the respiratory quotient (RQ) and the priming effect (PE) of substrates. Soil microbial communities in agricultural soil responded to the n-hexadecane addition more rapidly compared to those of forest soil, with lag-periods of about 23 ± 10 and 68 ± 13 hours, respectively. Insignificant difference in the lag-period duration was detected for agricultural (t_lag = 30 ± 13 h) and forest (t_lag = 30 ± 14 h) soils treated with n-hexadecanoic (palmitic) acid. These results demonstrate that the soil microbiota has different metabolic activities for using n-hexadecane as a reductive hydrocarbon and n-hexadecanoic acid as a partly oxidized hydrocarbon. The corresponding δ¹³C of respired CO₂ after the addition of the hydrocarbon contaminants to soils indicates a shift in microbial activity towards the consumption of exogenous substrates with a more complete degradation of n-hexadecane in the agricultural soil, for which some initial contents of hydrocarbons are inherent. It is supposed that the observed deviation of RQ from theoretically calculated value under microbial substrate mineralization is determined by difference in the time (Δt_i) of registration of CO₂ production and O₂ consumption. Positive priming effect (PE) of n-hexadecane and negative PE of n-hexadecanoic (palmitic) acid were detected in agricultural and forest soils. It is suggested that positive PE of n-hexadecane is conditioned by the induction of microbial enzymes that perform hydroxylation/oxygenation of stable SOM compounds mineralized by soil microbiota to CO₂. The microbial metabolism coupled with oxidative decarboxylation of n-hexadecanoic acid is considered as one of the most probable causes of the revealed negative PE value.     

Factors affecting the survival ofRhizoctonia bataticola in black soil

Summary Survival ofRhizoctonia bataticola was adversely affected at high soil moisturei.e. 60 and 80% MHC (moisture holding capacity); activity was good below 40% MHC. Half-life period was considerably reduced at 80% MHC. Variations in soil pH and addition of saltsviz Na₂SO₄, MgSO₄, CaCl₂ and NaCl did not affect the saprophytic activity of the fungus.     

青藏高原高寒草甸土壤CO2排放对模拟氮沉降的早期响应

研究大气氮沉降输入对青藏高原高寒草甸土壤-大气界面CO₂交换通量的影响,对于准确评价全球变化背景下区域碳平衡至关重要。通过构建多形态、低剂量的增氮控制试验,利用静态箱-气相色谱法测定土壤CO₂排放通量,同时测定相关土壤变量和地上生物量,分析高寒草甸土壤CO₂排放特征及其主要驱动因子。研究结果表明:低、高剂量氮输入倾向于消耗土壤水分,而中剂量氮输入有利于土壤水分的保持;施氮初期总体上增加了土壤无机氮含量,铵态氮累积效应更为显著;施氮显著增加地上生物量和土壤CO₂排放通量,铵态氮的促进效应显著高于硝态氮。另外,土壤CO₂排放通量主要受土壤温度驱动,其次为地上生物量和铵态氮储量。上述结果反映了氮沉降输入短期内可能刺激了植物生长和土壤微生物活性,加剧了土壤-大气界面CO₂排放。     

Biodegradation of p-nitrophenol by methyl parathion-degrading Ochrobactrum sp. B2

Ochrobactrum sp. B2, a methyl parathion-degrading bacterium, was proved to be capable of using p-nitrophenol (PNP) as carbon and energy source. The effect of factors, such as temperature, pH value, and nutrition, on the growth of Ochrobactrum sp. B2 and its ability to degrade p-nitrophenol (PNP) at a higher concentration (100 mg l⁻¹) was investigated in this study.The greatest growth of B2 was observed at a temperature of 30 °C and alkaline pH (pH 9–10). pH condition was proved to be a crucial factor affecting PNP degradation. Enhanced growth of B2 or PNP degradation was consistent with the increase of pH in the minimal medium, and acidic pH (6.0) did not support PNP degradation. Addition of glucose (0.05%, 0.1%) decreased the rate of PNP degradation even if increased cell growth occurred. Addition of supplemental inorganic nitrogen (ammonium chloride or ammonium sulphate) inhibited PNP degradation, whereas organic nitrogen (peptone, yeast extract, urea) accelerated degradation.     

In situ annual nitrogen mineralization predicted by simple soil properties and short-period field incubation

A typical method to determine nitrogen mineralization is year-round field incubation of undisturbed soil cores. As this technique is very laborious, the aim of the present study was to establish less time consuming methods to assess the annual N mineralization. Options considered were reducing the period of subsequent field incubations to less than a full year, and prediction using simple (direct) soil measurements. In situ annual N mineralization was measured in 74 semi-natural, unfertilized sites under year-round vegetation cover by sequential incubation of undisturbed soil cores during 2 full years. The sites classify into 14 very different plant community types and encompass a wide range of edaphic conditions. A high correlation with the annual N mineralization was maintained when sequential incubations were restricted to the period early March–mid August (r=0.98). Shorter periods may also be used, as long as they lie within the period early March–mid August and cover 3 months at least. The average annual N mineralization could be predicted accurately using the soil mineral nitrogen pool (N_min), moisture content and pH as the predictor variables. In a multiple regression model based on log-transformed values, the R ² was 0.835. Samples (preferably bulked) are best taken in early March, just before the start of the growing season. Higher N_min contents (moisture and pH assumed constant) indicated higher annual N mineralization rates. Higher moisture contents (at constant N_min and pH) generally indicated lower annual rates. Soil pH showed a quadratic relation (at fixed N_min and moisture) with maximum annual mineralization occurring at a pH-CaCl₂ value of 5.5–5.6. N_min appeared to be the most important predictor variable. Even within plant community types (with a reduced range of conditions), its relationship with the annual N mineralization persisted. Frequently studied factors, such as total soil N, organic matter content, C:N ratio, soluble organic N and particle size composition, only showed low and insignificant correlations, although stronger relationships have sometimes been reported. It is assumed this discrepancy is caused by the smaller range of conditions usually studied. This revised version was published online in June 2006 with corrections to the Cover Date.     

降雨量改变对常绿阔叶林干旱和湿润季节土壤呼吸的影响

通过野外原位试验,研究降雨量改变对华西雨屏区常绿阔叶林干旱和湿润季节土壤呼吸速率的影响。采用LI-8100土壤碳通量分析系统(LI-COR Inc.,USA)测定干旱和湿润季节对照(CK)、增雨10%(LA)、增雨5%(TA)、减雨10%(LR)、减雨20%(MR)、减雨50%(HR)6个处理水平的土壤呼吸速率,并通过回归方程分析温度和湿度与土壤呼吸速率间的关系。结果表明:湿润季节土壤呼吸速率高于干旱季节,HR处理对干旱季节土壤呼吸速率影响较大,而LA处理对湿润季节土壤呼吸速率的影响较大。TA和LR处理使土壤呼吸的温度敏感性增加,而HR、LA和MR处理使土壤呼吸的温度敏感性降低,干旱季节Q10值高于湿润季节。各处理湿润季节土壤微生物量碳氮含量显著高于干旱季节,HR、MR和LA处理减少土壤微生物生物量碳、氮的含量,而TA和LR处理增加土壤微生物生物量碳、氮的含量。与湿润季节相比,干旱季节土壤水分对土壤呼吸速率的影响较大;而与土壤温度相比,土壤水分对土壤呼吸速率的影响较小。在降雨量改变的背景下,华西雨屏区常绿阔叶林无论是干旱还是湿润季节,适当增雨和减雨都会促进土壤呼吸速率,而较高量的增雨和减雨会抑制土壤呼吸速率。     

Response of soil CO2 efflux to water manipulation in a tallgrass prairie ecosystem

Although CO₂ efflux plays a critical role in carbon exchange between the biosphere and atmosphere, our understanding of its regulation by soil moisture is rather limited. This study was designed to examine the relationship between soil CO₂ efflux and soil moisture in a natural ecosystem by taking advantage of the historically long drought period from 29 July to 21 September 2000 in the southern Central Great Plain, USA. At the end of August when soil moisture content at the top 50 mm was reduced to less than 50 g kg^–1 gravimetrically, we applied 8 levels of water treatments (simulated to rainfall of 0, 10, 25, 50, 100, 150, 200, and 300 mm) with three replicates to 24 plots in a Tallgrass Prairie ecosystem in Central Oklahoma, USA. In order to quantify root-free soil CO₂ efflux, we applied the same 8 levels of water treatments to 24 500-mm soil columns using soil from field adjacent to the experimental plots. We characterized dynamic patterns of soil moisture and soil CO₂ efflux over the experimental period of 21 days. Both soil moisture content and CO₂ efflux showed dramatic increases immediately after the water addition, followed by a gradual decline. The time courses in response to water treatments are well described by Y=Y₀+ate^–bt, where Y is either soil moisture or CO₂ efflux, t is time, Y ₀, a, and b are coefficients. Among the 8 water treatments, the maximal soil CO₂ efflux rate occurred at the 50 mm water level in the field and 100 mm in the root-free soil 1 day after the treatment. The maximal soil CO₂ efflux gradually shifted to higher water levels as the experiment continued. We found the relationship between soil CO₂ efflux and soil moisture using the data from the 21-day experiment was highly scattered, suggesting complex mechanisms determining soil CO₂ efflux by soil moisture.     

氨基酸添加对亚热带森林红壤氮素转化的影响

为探究氨基酸氮形态对亚热带土壤氮素含量及转化的影响,选择建瓯市万木林保护区的山地红壤为对象,采用室内培养实验法,通过设计60%和90%WHC两种土壤含水量并添加不同性质氨基酸,测定了土壤中铵态氮、硝态氮、可溶性有机氮的含量和氧化亚氮的释放量,分析了可溶性有机碳、土壤p H值的大小变化及其与氮素的相互关系。结果表明:与对照处理相比,氨基酸添加显著增加了土壤NH_4~+-N含量并使土壤p H值升高,且在一定程度上解除了高含水量(90%WHC)对NH_4~+-N产生的抑制,其中甲硫氨基酸的效果最为明显。酸性、碱性、中性氨基酸对土壤NO_3~--N含量和N_2O释放影响不显著,但甲硫氨基酸可显著抑制土壤硝化从而导致NH_4~+-N的积累,并在培养前期抑制土壤N_2O产生而在培养后期促进N_2O释放,总体上促进N_2O释放。60%WHC的氨基酸添加处理较90%WHC条件下降低土壤可溶性有机氮的幅度更大。氨基酸对土壤氮素转化的影响与带电性关系较小,而可能与其分解产物密切相关。可见,不同性质氨基酸处理对森林土壤氮素含量及转化存在不同程度的影响,且甲硫氨基酸对土壤氮素转化的影响机理值得深入研究。     

Soil plus root respiration and microbial biomass following water, nitrogen, and phosphorus application at a high arctic semi desert

In order to investigate the effects of anticipated increased precipitation and changing soil nutrient levels on soil CO₂ efflux from high arctic semi desert, a field experiment was carried out in Northeast Greenland. Water, phosphorus, and nitrogen were added to plots in a fully factorial design. Soil microbial biomass carbon was analysed after one year, and respiration from soil plus roots was measured in situ throughout the third growing season after initiation of the experiment. Soil plus root respiration was enhanced by up to 47%, and the microbial biomass by 24%, by the weekly water additions, but not by nutrient additions. The direct effect of increased soil moisture on CO₂ efflux suggests that future changes of precipitation levels and patterns may strongly affect below-ground respiration in arctic semi deserts, with direction of responses depending upon amounts and frequencies of precipitation events. Morover, low CO₂ emission at low light intensities regardless of treatment suggests that the major part of the below-ground respiration originated from turnover of recently fixed C. Hence, the more recalcitrant soil organic matter C pool may not change in proportion to changes in below-ground respiration rate.     

干旱对土壤剖面不同深度土壤CO2通量的影响

由于全球气候变化,预计未来我国亚热带地区干旱频率和持续时间将会增加。森林土壤CO₂的释放是陆地生态系统碳循环的重要组成部分,然而,有关不同深度土壤CO₂通量对干旱响应的理解仍相当有限。选择武夷山针叶林（Coniferous Forest,CF）和常绿阔叶林（Evergreen Broadleaved Forest,EBF）为研究对象,于2014年6月至2015年12月,采用梯度法计算10、30 cm和50 cm深度各层土壤CO₂通量,探讨模拟干旱对其影响。结果表明：CF和EBF样地土壤CO₂浓度均随土壤深度的增加而升高。CF和EBF样地对照（CK）处理10 cm深度土壤CO₂生产量分别占总CO₂生产量的53.5%和55.7%,表明土壤CO₂生产量主要来源于浅层土壤,这可能与浅层土壤有高的有机碳含量及细根生物量主要分布区有关。干旱处理使CF和EBF样地不同深度土壤CO₂通量均显著减少。在两个样地土壤CO₂通量的温度敏感性（Q₁₀）值均随着土壤深度的增加而减少。干旱处理显著减少了CF样地浅层土壤的Q₁₀值（P=0.02）,对深层土壤影响不显著（30 cm：P=0.30;50 cm：P=0.23）;而在EBF样地干旱处理显著减少了深层土壤的Q₁₀值（30 cm：P=0.02;50 cm：P=0.01）,对浅层土壤影响不显著（P=0.32）。     

Sorption of phosphorus by the iron oxide-impregnated filter paper (Pi soil test) embedded in soils

Incubation experiments were carried out to evaluate the feasibility of extracting phosphorus from soil by embedding iron oxide-impregnanted filter paper strips (P_i strips) in soils having a wide range in pH, texture, and extractable-P contents. Under flooded conditions, the amount of P extracted by the P_i strips increased with the period of submergence and embedding time of the P_i strips. Under unsaturated conditions, the P_i strips were found to extract P from soils over a wide range in moisture conditions; however, keeping the soil at moisture level between saturation and field capacity was found to result in maximal sorption of P by the strips. An embedding time of 16 h was found to be adequate.Phosphorus extracted by embedding P_i strips in soil columns for 16 h at field capacity moisture level correlated significantly with P extracted by shaking the soil with 0.01 M CaCl₂ solution and a P_i strip for 16 h in the laboratory (r=0.94^**). The P extracted by embedding P_i strips correlated best with Bray 1 P in acid soils (r=0.97^**) and with Olsen P in alkaline and calcareous soils (r=0.96^**). The results of the studies demonstrate the feasibility of developing a nondestructive method of monitoring changes in plant-available P in situ under field conditions.     

A microcosm study on bioremediation of p-nitrophenol-contaminated soil using Arthrobacter protophormiae RKJ100

p-Nitrophenol (PNP), a toxic nitroaromatic compound, can build up in soils due to extensive usage of nitrophenolic pesticides and hence needs to be removed. Arthrobacter protophormiae RKJ100, a PNP-degrading organism, was used in this work to study factors affecting its growth, and then evaluated for its capacity to degrade PNP in soil microcosms. Molasses (10%) treated with 0.1% potassium hexacyanoferrate was found to be a suitable and cheap carbon source for inoculum preparation. Induction studies showed that PNP depletion was quicker when cells were induced by pre-exposure to PNP. The efficiency of PNP degradation in soil by strain RKJ100 was seen to be dependent on pH, temperature, initial PNP concentration and inoculum size. Microcosm studies performed with varying concentrations (1.4–210 ppm) of PNP-spiked soils showed that strain RKJ100 could effectively degrade PNP over the range 1.4–140 ppm. A cell density of 2×10⁸ colony forming units/g soil was found to be suitable for PNP degradation over a temperature range of 20–40°C and at a slightly alkaline pH (7.5). Our results indicate that strain RKJ100 has potential for use in in situ bioremediation of PNP-contaminated sites. This is a model study that could be used for decontamination of sites contaminated also with other compounds.     

改变凋落物输入对川西亚高山天然次生林土壤呼吸的影响

2019年5月-10月,采用LI-8100A土壤碳通量自动测量分析仪对川西米亚罗林区20世纪60年代采伐后经自然更新恢复形成的岷江冷杉（Abies faxoniana）次生针叶林（针叶林）、红桦（Betula albo-sinensis）+青榨槭（Acer davidii）+岷江冷杉次生针阔混交林（针阔混交林）和青榨槭+红桦+陕甘花楸（Sorbus koehneana Schneid）次生阔叶林（阔叶林）的土壤呼吸及土壤温湿度因子（对照、去除凋落物和加倍凋落物）进行观测。结果显示：去除和加倍凋落物对土壤温湿度的影响不显著,且3种林型之间的土壤呼吸速率差异不显著。与对照相比,去除凋落物使针叶林、针阔混交林、阔叶林的土壤呼吸速率分别降低了17.65%、21.01%和19.83%（P<0.05）;加倍凋落物则分别增加6.76%、7.28%、8.16%（P>0.05）。3种林分土壤呼吸速率均与土壤温度极显著指数相关,与土壤湿度不相关。对照Q₁₀值变幅为2.01-3.29,去除凋落物降低了3种林型的Q₁₀值;加倍凋落物分别提高了针叶林和降低了针阔混交林和阔叶林的Q₁₀值。土壤呼吸速率仅表现在天然次生林对照处理中受到土壤pH、有机质、可溶性有机氮和草本Pielou均匀度指数的显著影响。研究结果表明,天然次生阔叶林和针阔混交林凋落物对土壤呼吸的贡献及Q₁₀值高于天然次生针叶林,说明在未来CO₂浓度及温度升高背景下,地表凋落物增加并未引起天然次生林土壤呼吸速率成倍增加,更有利于该区域天然次生林尤其是针叶林的土壤碳吸存。     

施肥对板栗林地土壤N2O通量动态变化的影响

2011年6月—2012年6月期间,在浙江省临安市典型板栗林地进行施肥对土壤N2O通量变化影响的试验研究。目的在于探明不同施肥处理下板栗林地土壤N2O通量的动态变化规律,并探讨土壤N2O通量和土壤环境因子之间的关系。试验设置4个处理:对照(不施肥)、无机肥、有机肥、有机无机混合肥。采用静态箱-气相色谱法测定了板栗林地土壤N2O通量,并测定了土壤温度、水分、水溶性有机碳(WSOC)和微生物量碳(MBC)含量。结果表明:板栗林土壤N2O通量呈显著季节性变化,最大值出现在夏季,最小值出现在冬季;而且,施肥处理显著提高土壤N2O年均通量和年累积量;在整个试验期间,无机肥、有机肥和有机无机混合肥处理下土壤N2O的排放系数分别达到0.96%、1.45%和1.29%。此外,施肥也显著增加了土壤WSOC和MBC的含量(P<0.05)。不同施肥处理条件下,土壤N2O通量与土壤5 cm处温度、WSOC含量间均呈极显著正相关(P<0.01),但与MBC含量之间的相关性不显著。土壤N2O排放与土壤含水量间除对照处理外均没有显著相关性。综上所述,施肥引起土壤WSOC含量的增加可能是施肥增加板栗林地土壤N2O排放速率的主要原因之一。