田间条件下小麦和玉米秸秆腐解过程中微生物群落的变化——BIOLOG分析

对秸秆分解微生物演变机理的研究是调控秸秆还田、提高农田地力的理论基础。本试验基于土壤置换试验平台,利用BIOLOG方法研究在寒温带、中温带和中亚热带气候下,埋于黑土、潮土和红壤中的小麦和玉米秸秆在腐解过程中微生物对碳源利用的变化规律。试验中利用网袋法区分直接分解秸秆微生物。试验结果发现秸秆腐解微生物的碳源代谢活性(Average Well Color Development AWCD值表示)在腐解0.5 a和1 a后表现出一定的随气候变化规律,即随温度和降雨量的增加而降低。其中0.5 a为海伦(0.765±0.060)>封丘(0.737±0.165)>鹰潭(0.326±0.076),1 a为海伦(0.630±0.092)>封丘(0.319±0.096)>鹰潭(0.291±0.029),但这种趋势在腐解2 a后减弱。气候条件是影响秸秆腐解微生物碳源代谢活性的主要因素,其次是腐解时间和土壤类型。主成分分析表明在腐解0.5 a后海伦、封丘地区的微生物群落代谢特征与鹰潭差异较大,而1 a后封丘和鹰潭的微生物群落代谢特征与海伦的差异较大,腐解2 a后不同气候条件下的秸秆腐解微生物对碳源的利用趋于一致,均对含氮化合物利用较多。     

植物秸秆腐解特性与微生物群落变化的响应

采用网袋法探讨不同新鲜秸秆在农田土壤的腐解特征,结合Biolog微平板技术,对不同秸秆处理中土壤微生物群落多样性进行了研究。结果表明,随着腐解时间的增加,新鲜秸秆的残留率波动不大,秸秆的腐解速度为玉米秸秆大于大豆秸秆。整个腐解时期,不同秸秆处理中土壤微生物群落的平均颜色变化率AWCD值由高到低依次为FCN(新鲜玉米秸秆+氮)、FC(新鲜玉米秸秆)、FB(新鲜大豆秸秆),说明玉米不同秸秆处理中土壤微生物群落的密度大、稳定性好,大豆秸秆处理中土壤微生物群落相对密度小,稳定性差,3种不同秸秆处理中土壤微生物的AWCD值之间没有显著差异(P0.05),但不同秸秆类型与腐解时间的交互作用之间的差异达到极显著水平(P0.01)。3种不同秸秆处理中土壤微生物的优势种群主要以糖类和多聚物为主,在腐解中后期难分解物质逐渐累积,均表现为对芳香化合物的利用最弱。3种秸秆的腐解残留率与土壤pH、有机质、碱解氮、速效钾、土壤温度、氨基酸、多胺类的碳源利用方面影响较大,土壤含水量和秸秆含水量的高低在一定程度上影响不同秸秆的腐解残留率。     

玉米秸秆腐解规律及土壤微生物功能多样性研究

试验以玉米长期连作和玉米—小麦轮作土壤为研究对象,采用网袋法设定秸秆覆盖和深埋2个还田处理,间隔不同时间取样,分析秸秆腐解特征及土壤微生物群落功能多样性。结果表明,针对不同土壤来说,玉米—小麦轮作土壤中2种秸秆还田方式下(T1和T2),玉米秸秆腐解速率、养分(N、P和K)释放率均高于玉米长期连作土壤(CT1和CT2);不同秸秆腐解时间下,土壤微生物群落功能多样性各处理表现不同。总的来说,T1和T2处理的微生物群落平均颜色变化率、丰富度指数、优势度指数和均匀度指数均高于CT1和CT2。在玉米长期连作种植区,秸秆深埋比秸秆覆盖能更有效提高玉米秸秆腐解率和改善土壤微生物群落结构的功能多样性。     

不同添加剂处理秸秆腐解物对红壤性质的影响

有机废弃物的资源化高效利用是目前生产实际中面临的紧迫问题。本文通过布置土壤培育试验,施用不同添加剂处理后的水稻秸秆腐解物,研究土壤养分和生物性状变化。结果显示,施用添加剂处理的水稻秸秆腐解物对红壤理化指标和生物学性质有明显影响。施用碱渣处理的秸秆腐解物能够提高土壤pH,缓解红壤酸化;施用秸秆腐解物对红壤碱解氮含量影响不明显,但可提高速效磷、速效钾含量,尤其施用FeSO4处理的秸秆腐解物效果较为显著;培养60 天时施用添加剂处理秸秆腐解物的红壤脲酶、转化酶活性达到高峰,并且均表现为添加剂处理秸秆腐解物>无添加剂处理秸秆腐解物>对照,其中施用碱渣处理的秸秆腐解物的土壤酶活性较高;施用秸秆腐解物后红壤微生物生物量碳、微生物生物量氮含量呈现先减少后增加的动态变化,培养结束时微生物生物量碳最高的为碱渣处理,较施用无添加剂处理和对照分别提高46.5% 和286.2%,而微生物生物量氮最高的则为碱渣配合FeSO4处理;与对照相比,各处理土壤微生物对碳源的利用能力增强,尤其是施用碱渣处理秸秆腐解物不仅能够显著提高微生物AWCD值,还明显提高了红壤微生物功能多样性。以上结果表明,施用碱渣处理的水稻秸秆腐解物对红壤肥力提升和生物功能提高具有明显效果。     

湿地土壤微生物碳源代谢活性对不同水分条件的动态响应 ——以鄱阳湖为例

为深入了解湿地土壤微生物群落代谢特征对不同水分条件的响应变化,本研究以鄱阳湖湿地表层土壤为研究材料,采用室内控制试验,运用Biolog技术探讨土壤微生物碳源代谢活性在不同水分条件(干燥、湿润、淹水)下连续处理132 d的变化特征。结果表明:湿润组土壤微生物代谢活性最高,其平均光密度值(AWCD)在处理的第72天分别是淹水组和干燥组的1.34倍和3.95倍;同时土壤微生物对不同碳源类型的利用能力也发生了显著的差异性变化,其中干燥组利用的主要碳源为多聚物类和碳水化合物类(占总碳源利用率的39.25%和36.53%),而淹水组对氨基酸类碳源有较高的利用能力(占总碳源利用率的36.33%)。土壤微生物碳源代谢特征在处理的第21天达到稳定状态,而土壤理化性质和土壤微生物群落结构在处理的第72天发生显著变化,同时研究发现淹水条件升高了土壤pH和铵态氮含量,降低了微生物群落多样性。由此可知,水分条件不仅会影响湿地土壤微生物总体碳源代谢活性强度,还会改变对不同碳源的相对利用能力,最终导致土壤环境发生改变。     

小麦和玉米秸秆腐解特点及对土壤中碳、氮含量的影响

通过室内模拟培养试验,揭示了不同水分条件下小麦和玉米秸秆在土壤中的腐解特点及对土壤碳、氮含量的影响。结果表明,1)水分条件对有机物质腐解的影响较大,在32 d的培养期间,相对含水量为60%(M60)时,土壤CO2释放速率始终低于含水量80%(M80)的处理。M60条件下释放的CO2-C量占秸秆腐解过程中释放碳总量的40.1%,而M80条件下达到51.5%;M60条件下,添加秸秆土壤中有机碳含量平均提高2.24 g/kg,显著高于M80条件下的1.43 g/kg。2)添加玉米秸秆的土壤,在培养期内CO2释放速率始终高于小麦秸秆处理,CO2-C累积释放量和有机碳净增量分别为408.35 mg/pot和2.12 g/kg;而小麦秸秆处理分别仅为378.94 mg/pot和1.56 g/kg,两种秸秆混合的处理介于二者之间。3)与未添加秸秆相比,土壤中添加小麦或玉米秸秆后,土壤有机碳、微生物量碳、全氮和微生物量氮含量均显著提高,且数量上总体趋势表现为:玉米秸秆两种秸秆混合小麦秸秆。可见,适宜水分条件有利于秸秆腐解过程中秸秆中碳向无机碳方向转化,而不利于向土壤有机碳方向转化;且玉米秸秆比小麦秸秆更易腐解。秸秆在土壤中腐解对补充土壤碳、氮作用很大,可改善土壤微生物生存条件,提高土壤质量。     

不同还田量对秸秆养分释放规律及微生物功能多样性的影响

秸秆还田试验采用尼龙网袋田间埋土试验方法,设置5个秸秆还田量水平:CL1(20 g)、CL2(35 g)、CL3(60 g)、CL4(85g)、CL5(100 g),研究不同还田量下秸秆腐解特征、养分释放规律及微生物功能多样性的影响。结果表明:经过165 d秸秆腐解,各处理组中秸秆中养分释放速率表现为:TKTPTOCTN,且腐解前期快、后期慢。秸秆还田量为60 g时,秸秆累积腐解率最高,达到56.05%,且养分释放最快,而秸秆还田量为20 g腐解最慢。反映秸秆降解微生物活性的平均颜色变化率(AWCD)受秸秆还田量的影响,呈现出CL 3CL2CL4CL5CL1。对秸秆降解微生物群落功能多样性指数进行显著性分析,结果表明,Simpson指数(D)和Shannon指数(H)均为CL3最高,其中CL3的Shannon指数与其他处理差异均显著(P0.05),而各处理组的Simpson指数差异均不显著(P0.05)。     

五大连池火山群土壤微生物群落代谢多样性及影响因素研究

火山岩母质发育的土壤孕育了结构功能独特的土壤微生物群落。为评估火山生态系统土壤微生物的代谢多样性及其影响因素,选择五大连池火山群为研究对象,基于“时空替代”的研究方法,利用Biolog微平板技术,分析不同地质年代火山南北两个坡向的土壤微生物碳源代谢多样性,结合土壤理化指标进一步分析影响土壤微生物碳源代谢多样性的环境因子。结果表明：不同地质年代火山土壤微生物群落功能多样性存在显著差异。平均颜色变化率(AWCD)随培养时间延长而逐渐增加,南坡AWCD值随土壤发育时间增加而增加,北坡AWCD值无明显变化规律。土壤微生物碳源代谢的指数速率(P值)和潜力(K值)南北坡存在差异显著。主成分分析结果表明,南坡主成分1和主成分2分别能解释变量方差的80.85%和12.54%,土壤微生物的碳源代谢格局差异主要是由糖类(CH)和酯类(ES)引起的,二者共解释总变异量的64.93%;北坡主成分1和主成分2分别能解释变量方差的70.13%和19.77%,土壤微生物的碳源代谢格局差异主要是由带磷基糖类(CH.P)和酯类(ES)引起的,二者共解释总变异量的80.41%。冗余分析表明,土壤速效磷、总有机碳、铵态氮、...     

Biolog-Eco解析垦殖与自然恢复黑土微生物群落代谢功能季节变化

为动态比较土壤垦殖前后微生物群落代谢功能是否发生变化,利用Biolog-Eco技术对不同季节自然恢复(NR)和垦殖不同施肥处理[不施肥(NoF)、施化肥(CF)和化肥配施有机肥(CFM)]黑土微生物在4℃、15℃和28℃培养温度下的代谢功能多样性进行了研究。结果表明:4种处理在同一采样时期不同培养温度下,Biolog微孔板的单孔平均颜色变化率(Average Well Color Development,AWCD)值均表现为28℃>15℃>4℃,即微生物代谢活性随培养温度的升高而升高;同一采样时期样品在相同培养温度下黑土微生物对碳源的代谢能力总体呈现为NR>CFM>CF>NoF。微生物在积雪融化期和积雪覆盖期对碳源的利用能力高于植物生长季节。主成分分析(Principle Component Analysis,PCA)结果显示,不同采样时期NoF样品和其它3种处理相比微生物功能多样性差异较大;NR、CF和CFM在作物非生长季节(3月、4月和12月)的样品在PCA图中分散度小于在作物生长季节(6月)的样品。该研究结果综合表明,垦殖处理较自然恢复降低了土壤微生物群落对碳源的代谢能力,但并未改变微生物群落功能;不同季节土壤微生物功能多样性存在差异,NR、CF和CFM细菌群落在作物生长的夏季对碳源的利用能力差异最大。     

黄顶菊(Flaveria bidentis)入侵对土壤微生物功能多样性的影响

外来植物入侵对土壤生物多样性的影响已成为生态学领域的研究热点之一。运用Biolog技术和氯仿熏蒸浸提法研究了黄顶菊入侵对土壤微生物群落功能多样性及土壤微生物量的影响。结果表明,黄顶菊入侵后土壤微生物代谢活性显著升高;土壤微生物群落平均吸光值(AWCD)的变化趋势为:入侵地根际土(RPS)入侵地根围土(BS)未入侵地(CK),且差异显著;而CK的功能多样性指数(H)高于BS,RPS亦高于BS,差异均显著(P0.05)。主成分分析结果表明,黄顶菊入侵使土壤微生物群落的碳源利用方式和代谢功能发生改变。对不同碳源利用的分析结果表明,糖类、氨基酸类、羧酸类和聚合物为土壤微生物利用的主要碳源。入侵样地BS和RPS的微生物量碳分别比CK高27.05%、121.52%;BS和RPS的微生物量氮分别比CK高37.40%、79.80%。相关性分析表明,AWCD与微生物量碳和微生物量氮均呈极显著正相关(P0.01)。由此可知,黄顶菊入侵增强了入侵地土壤微生物代谢活性,降低了土壤微生物群落的功能多样性,增加了土壤微生物量碳、氮水平。     

温度和秸秆质量调节与秸秆分解相关的微生物磷脂脂肪酸（PLFA）组成

Variations in temperature and moisture play an important role in soil organic matter (SOM) decomposition. However, relationships between changes in microbial community composition induced by increasing temperature and SOM decomposition are still unclear. The present study was conducted to investigate the effects of temperature and moisture levels on soil respiration and microbial communities involved in straw decomposition and elucidate the impact of microbial communities on straw mass loss. A 120-d litterbag experiment was conducted using wheat and maize straw at three levels of soil moisture (40%, 70%, and 90% of water-holding capacity) and temperature (15, 25, and 35°C). The microbial communities were then assessed by phospholipid fatty acid (PLFA) analysis. With the exception of fungal PLFAs in maize straw at day 120, the PLFAs indicative of Gram-negative bacteria and fungi decreased with increasing temperatures. Temperature and straw C/N ratio significantly affected the microbial PLFA composition at the early stage, while soil microbial biomass carbon (C) had a stronger effect than straw C/N ratio at the later stage. Soil moisture levels exhibited no significant effect on microbial PLFA composition. Total PLFAs significantly influenced straw mass loss at the early stage of decomposition, but not at the later stage. In addition, the ratio of Gram-negative and Gram-positive bacterial PLFAs was negatively correlated with the straw mass loss. These results indicated that shifts in microbial PLFA composition induced by temperature, straw quality, and microbial C sources could lead to changes in straw decomposition.     

Does history matter? Temperature effects on soil microbial biomass and community structure based on the phospholipid fatty acid (PLFA) analysis

Background, aim, and scope

Temperature is an important environmental factor regulating soil microbial biomass, activity, and community. Soils from different climatic regions may have very different dominant soil microbes, which are acclimated to the local conditions like temperature. Changing soil temperature especially warming has been shown to increase the mortality rate of soil microbes. However, little is known about the responses of soil microbes coming from different climatic regions to different incubation temperatures. The objective of this study was to examine the temperature effects on microbial biomass and community of soils collected from cold, intermediate, and hot natural sites.

Materials and methods

Soils were collected from northern (Heilongjiang province), central (Jiangsu province), and southern (Guangxi province) China, these soils having very different temperature histories. The Heilongjiang soil was from the coldest region with a mean annual temperature of 1.2°C, the Jiangsu soil was intermediate with a mean annual temperature of 15.7°C, and Guangxi soil was from the hottest area, with a mean annual temperature of 21.2°C. These three soils were incubated at 4°C, 15°C, 25°C, and 35°C for up to 56 days. Phospholipid fatty acid (PLFA) analyses were conducted on days 0, 3, 7, 14, 28, and 56 to track the dynamics of soil microbes.

Results

Soil microbial biomass indexed by total phospholipid fatty acid concentration decreased with increasing incubation temperature, with that of the Heilongjiang soil decreasing most. At the end of incubation, the biomass at 35°C in the Heilongjiang, Jiangsu, and Guangxi soils had declined to 65%, 72%, and 96% of the initial biomass, respectively. The PLFA patterns shifted with increasing temperatures in all the soils, especially at 35°C; the change was biggest in the Heilongjiang soil.

Discussion

History does have effects on soil microbes responding to environmental stress. Soil microbial biomass and PLFA profiles shifted least in the Guangxi soil with the hottest temperature history and most in the Heilongjiang soil with the coldest temperature, indicating that the distribution of free-living microorganisms is influenced by climatic factors. The majority of soil microorganisms coming from the hot regions are more adapted to high temperature (35°C) compared to those from the cold area. There are some regular changes of PLFA profiles when increasing incubation temperature to 35°C. However, the effect of incubation temperature on soil microbial community structure was inconclusive. As PLFA profile community structure is the phenotypic community structure. Genotype experiments are required to be done in future studies for the better understanding of soil microbes in different climate regions with concerning temperature variation.

Conclusions

With the increasing incubation temperature, soil microbial biomass and PLFA profiles shifted most in the soil with the coldest temperature history and least in the soil with the hottest temperature. History does matter in determining soil microbial dynamics when facing thermal stress.     

Permafrost microbial community traits and functional diversity indicate low activity at in situ thaw temperatures

Previously-frozen stores of organic carbon (C) are now subject to decomposition due to a warming Arctic climate and associated permafrost thaw; however, estimates of the amount of greenhouse gases (GHG) that may be released are not well constrained. Knowing more about the functions of the extant permafrost microbial community will inform this knowledge gap. The exploration of microbial functional traits may be useful to elucidate the relationship between microbial diversity and ecosystem function. We characterized the community traits and functional diversity of the bacterial and Archaeal component of the microbial community from three depths of permafrost, as well as the organic and mineral horizons of the seasonally-thawed active layer, by assessing ‘substrate-use richness,’ ‘substrate preference,’ ‘growth rate,’ ‘and substrate specific growth rate.’ We measured the microbial community response to 31 substrates with an EcoPlate (Biolog, Inc.) assay at three incubation temperatures (1, 10, and 20 °C) using a kinetic approach, and modeled the microbial response to each substrate with a modified logistic growth function. We hypothesized that the permafrost communities would be selected for high functional potential and activity at cold temperatures. Rather, we found that the permafrost community did not have a higher functional diversity or activity at 1 °C than the organic active layer soils. In addition, permafrost communities increased their growth rates with increasing temperature, indicating that the highest incubation temperature (20 °C) was below their temperature optimum for growth. As predicted, the permafrost communities did exhibit temperature dependent substrate preferences. Thus, permafrost microbial communities did not appear to be selected for higher metabolism and the ability to use a broad suite of substrates at low temperatures, which suggests that they may have limited function immediately following thaw when temperatures are near 0 °C. However, changes in community composition or additional permafrost warming will increase the functional capabilities of permafrost microbes to decompose the C stored in those soils.     

Variations of SOC and MBC observed in an incubated brown loam soil managed under different tillage systems for 12 years

To assess changes in organic carbon pools, an incubation experiment was conducted under different temperatures and field moisture capacity (FMC) on a brown loam soil from three tillage practices used for 12 years: no‐till (NT), subsoiling (ST) and conventional tillage (CT). Total microbial respiration was measured for incubated soil with and without the input of straw. Results indicated that soil organic carbon (SOC) and microbial biomass carbon (MBC) under ST, NT and CT was higher in soil with straw input than that without, while the microbial quotient (MQ or MBC: SOC) and metabolic quotient (qCO₂) content under CT followed the opposite trend. Lower temperature, lower moisture and with straw input contributed to the increases in SOC concentration, especially under NT and ST systems. The SOC concentrations under ST, with temperatures of 30 and 35°C after incubation at 55% FMC, were greater than those under CT by 28.4% and 30.6%, respectively. The increase in MBC was highest at 35°C for 55%, 65% and 75% FMC; in soil under ST, MBC was greater than that under CT by 199.3%, 50.7% and 23.8%, respectively. At 30°C, the lower qCO₂ was obtained in soil incubated under NT and ST. The highest MQ among three tillage practices was measured under ST at 55% FMC, NT at 65% FMC and CT at 75% FMC with straw input. These data indicate the benefits of enhancing the MQ; the low FMC was beneficial to ST treatment. Under higher temperature and drought stress conditions, the adaptive capacity of ST and NT is better than that of CT.     

Modeling aerobic decomposition of rice straw during the off-rice season in an Andisol paddy soil in a cold temperate region of Japan: Effects of soil temperature and moisture

Submerged rice paddies are a major source of methane (CH₄) which is the second most important greenhouse gas after carbon dioxide (CO₂). Accelerating rice straw decomposition during the off-rice season could help to reduce CH₄ emission from rice paddies during the single rice-growth season in cold temperate regions. For understanding how both temperature and moisture can affect the rate of rice straw decomposition during the off-rice season in the cold temperate region of Tohoku district, Japan, a modeling incubation experiment was carried out in the laboratory. Bulk soil and soil mixed with 2% of δ¹³C-labeled rice straw with a full factorial combination of four temperature levels (?5 to 5, 5, 15, 25°C) and two moisture levels (60% and 100% WFPS) were incubated for 24 weeks. The daily change from ?5 to 5°C was used to model the freezing–thawing cycles occurring during the winter season. The rates of rice straw decomposition were calculated by (i) CO₂ production; (ii) change in the soil organic carbon (SOC) content; and (iii) change in the δ¹³C value of SOC. The results indicated that both temperature and moisture affected the rate of rice straw decomposition during the 24-week aerobic incubation period. Rates of rice straw decomposition increased not only with high temperature, but also with high moisture conditions. The rates of rice straw decomposition were more accurately calculated by CO₂ production compared to those calculated by the change in the SOC content, or in its δ¹³C value. Under high moisture at 100% WFPS condition, the rates of rice straw decomposition were 14.0, 22.2, 33.5 and 46.2% at ?5 to 5, 5, 15 and 25°C temperature treatments, respectively. While under low moisture at 60% WFPS condition, these rates were 12.7, 18.3, 31.2 and 38.4%, respectively. The Q₁₀ of rice straw decomposition was higher between ?5 to 5 and 5°C than that between 5 and 15°C and that between 15 and 25°C. Daily freezing–thawing cycles (from ?5 to 5°C) did not stimulate rice straw decomposition compared with low temperature at 5°C. This study implies that to reduce CH₄ emission from rice paddies during the single rice-growth season in the cold temperate regions, enhancing rice straw decomposition during the high temperature period is very important.     

多氯联苯污染土壤的微生物生态效应研究

以多氯联苯（Polychlorinated biphenyls,PCBs）自然污染的农田土壤为材料,分析土壤中微生物区系组成、生物量C、N、土壤基础呼吸以及微生物群落功能多样性的变化。研究结果表明,在以4-氯、5-氯同系物为主的PCBs污染土壤中,污染程度对土壤细菌、放线菌的数量影响不明显,而真菌的数量除与土壤污染程度有关,可能还受到土壤pH等性状的影响;土壤微生物C、N与土壤基础呼吸随污染程度的加剧呈下降趋势,但微生物C／N基本没有变化;Biolog分析显示,土壤微生物代谢剖面（AWCD）及Simpson指数在污染程度相差较大的两组土壤样品中差异均达到了显著性水平,表明PCBs污染引起了土壤微生物群落功能多样性下降,降低了微生物对不同单一碳源底物的利用能力。     

A litter-slurry technique elucidates the key role of enzyme production and microbial dynamics in temperature sensitivity of organic matter decomposition

The rate at which organic matter decomposes generally increases with temperature, unless it is physico-chemically protected from enzymatic depolymerization. The temperature sensitivity of decomposition should increase with decreasing reaction rates, corresponding to increasing activation energy of the decomposing compounds. One approach to testing this carbon-quality temperature hypothesis is to study the effect of temperature on leaf litter decomposition, because fresh surface litter is unprotected. However, other factors such as humidity co-vary with temperature, and biological processes such as enzyme production and microbial population growth may also be thermally sensitive. We developed a litter slurry approach to isolate the effect of temperature and litter quality on decomposition. We found that pine litter decomposed faster than oak litter, consistent with a lower C:N and lignin:N ratio. During the first 14 days of decomposition, there was no difference in decomposition rate for litter incubated at 25 °C compared to 35 °C. Lower potential enzyme activity at 35 °C suggested that enzyme production was suppressed at 35 °C compared to 25 °C, resulting in similar in situ enzyme activities at the two temperatures. After 14 days, enzyme pools were similar between the two incubation temperatures, which resulted in faster decomposition at the warmer temperature, consistent with enzyme kinetic theory. At Day 14, the decomposition rate of the high quality pine litter was more temperature sensitive than the decomposition rate of the lower quality oak litter, suggesting that the quality of soluble pool rather than bulk chemistry determined the temperature sensitivity during this stage. After 28 days of incubation, oak litter decomposition was more temperature sensitive than pine litter, consistent with the carbon temperature-quality hypothesis. The litter slurry approach revealed that biological responses to temperature can affect the apparent temperature sensitivity of decomposition, and highlight a need for further research into microbial responses to temperature.     

Long-term effects of temperature on carbon mineralisation processes

The long-term effects of temperature on soil C mineralisation were investigated in two experiments using ¹⁴C labelled wheat straw incubated in organic soils from five coniferous forests located in different climate zones of Western Europe. In the first experiment, samples were incubated in the laboratory at 4, 10, 16, 23 or 30°C, with constant moisture, and the loss of ¹⁴C was monitored for 550 days. Double negative exponential functions fitted to the ¹⁴C loss data at different temperatures were used to define the relative proportions of labile and recalcitrant components in the original straw. The estimated proportions of these constituents were related to incubation temperatures with the amount of C reflecting the labile fraction increasing with increasing temperature. In the second experiment samples mixed with the labelled straw were incubated at 4, 16 or 30°C until the same percentage of ¹⁴C loss was reached. The samples were then incubated again at a common temperature for 30 days and CO₂ production was measured to assess the lability of the remaining material. For all the soils, the amount of readily decomposed material was higher in samples conditioned at 4° than at 30°C. It was concluded that in addition to temperature controlling rates of C mineralisation in soil it also affects the processes of decomposition so that material produced at higher temperatures was more recalcitrant than at lower temperatures.     

控制条件下水肥耦合对黄泥田还田秸秆腐解及土壤碳转化的影响

【目的】研究秸秆还田后不同水温和肥剂管理措施下土壤碳素转化特征。【方法】以华中双季稻区低产水稻土黄泥田为供试材料,模拟早稻和晚稻秸秆还田的田间环境,在实验室控制条件下,开展了两种温度环境中(15℃、35℃)不同水分(40%和100%最大田间持水量,即40%WHC、100%WHC)、配施氮肥类型(尿素、猪粪即U、M)、以及促腐菌剂添加对秸秆腐解效果及其过程中土壤碳素转化影响的研究。对水稻秸秆腐解过程中土壤CO2释放量、以及土壤可溶性有机碳(DOC)和总有机碳(TOC)含量在105天培养周期内变化特征进行动态监测分析。【结果】两种温度环境中整个培养周期内,各处理的CO2释放速率和释放总量通常表现为100%WHC-M100%WHC-U40%WHC-M40%WHC-U,即猪粪优于尿素的规律,而不论配施何种氮肥都存在100%WHC40%WHC(P0.01)的现象,同时40%WHC条件下辅施菌剂可显著提升CO2释放量;与此相反,两种温度环境下DOC含量都表现为40%WHC-M40%WHC-U100%WHC-M100%WHC-U(后两者差异小),即40%WHC条件下DOC含量显著高于100%WHC(P0.05),且配施猪粪处理优于配施尿素处理,但这两种氮肥处理间差异随培养时间延长而减小;以CO2-C释放量计算0 7 d、0 28 d、0 105 d内物料分解率,结果表明,35℃时100%WHC-U的处理中物料分解最快,15℃时40%WHC-M的处理中物料分解最慢。与之对应,105 d内TOC含量和净增量则在35℃时100%WHC-U的处理中最小(P0.01),而在15℃时40%WHC-M的处理中最大(P0.01);TOC的净增量和净损失量在相同温度条件下,尤其试验前期不同水分(P0.01)、氮素(P0.05)间均存在显著差异,且促腐菌剂添加普遍减小TOC含量;培养周期内所有处理的CO2释放速率与DOC含量间存在显著相关(P0.05)。【结论】水分状况对碳素的转化存在极大影响,其次是氮肥类型,且氮肥的影响作用随秸秆还田时间的延长而减弱;高湿条件更利于促进秸秆腐解,但导致土壤DOC含量较低,TOC的固持量也较少,而配施猪粪则可促进土壤DOC含量的提升及TOC的固持;促腐菌剂添加可促进秸秆腐解,但由于40%WHC条件下显著激发了CO2的释放而不利于土壤固碳。因此在华中低产黄泥田双季轮作稻区,早稻还田时由于气温高周期短,建议保持100%WHC、辅施适量尿素、并配合添加秸秆腐解菌剂,侧重秸秆快腐;而晚稻还田时气温低周期长,建议保持40%WHC并辅施缓效猪粪,侧重土壤固碳。