添加木醋液对沙地土壤微生物生物量和酶活性的影响

[目的]探讨沙地添加木醋液后土壤微生物生物量和酶活性的变化,为沙地土壤生物学质量的改良提供理论依据。[方法]采用盆栽植草培养法,以添加自来水为对照,对沙地添加不同稀释倍数(200,150,100,50,20)木醋液后的土壤可溶性有机碳、氮和酚,土壤微生物生物量碳氮以及土壤酶活性进行研究。[结果]向沙土添加木醋液可以显著降低土壤pH值,显著提高土壤易氧化碳、土壤水溶性碳氮、土壤可溶性酚以及无机氮的含量。在添加木醋液稀释高于50倍范围内,随木醋液稀释倍数降低,土壤微生物生物量碳氮增加以及β-糖苷酶、碱性磷酸酶和脱氢酶活性提高。添加稀释20倍的木醋液,导致土壤微生物生物量碳氮以及β-糖苷酶、碱性磷酸酶和脱氢酶活性有所降低。在高于20的稀释倍数范围内,随着施用木醋液稀释倍数的降低,α-糖苷酶、亮氨酸氨基肽酶、酸性磷酸酶和酚氧化酶的活性有显著增加的趋势。[结论]添加不同稀释倍数的木醋液会影响沙地土壤微生物生物量和酶活性。     

长期不同种植模式对东北黑土微生物群落结构与土壤理化性质的影响

利用长期定位试验资料,评价了东北黑土增施有机肥条件下玉米连作(CMC)、玉米-大豆轮作(MSR)和大豆连作(CSC)等种植模式对土壤微生物数量与结构、土壤理化性质的影响及其相互关系。结果表明:0~40 cm土层内,土壤微生物总量呈CMCMSRCSC趋势,且差异显著(P0.05);细菌数量占微生物总量的比重呈CMCMSRCSC的趋势,而真菌和放线菌所占比重均呈CSCMSRCMC的相反趋势;CMS处理下的土壤容重最低,但土壤有机碳、全氮、有效氮、有效磷含量均显著高于其他处理;相关分析发现细菌和放线菌数量与土壤容重显著负相关,但与土壤有机碳、全氮、有效氮显著正相关,而真菌数量占微生物总量的比例则与土壤容重显著正相关,与土壤有机碳、全氮、有效氮显著负相关。综上所述,长期玉米连作结合有机肥施用,有利于改善土壤理化性状,增加土壤微生物数量,但以细菌增加为主,微生物多样性呈下降的趋势。     

有机无机肥配施对麦-稻轮作系统土壤微生物学特性的影响

采用盆栽试验研究了不同比例有机无机肥配施对连续4茬麦-稻轮作后土壤微生物学特性的影响。结果表明,与对照相比,单施化肥处理促进了土壤微生物生物量碳、氮和微生物熵的增加,提高了土壤蔗糖酶、蛋白酶、脲酶活性,降低了过氧化氢酶活性,提高了放线菌的数量,但对土壤细菌、真菌数量的影响不明显;有机无机肥配施处理的土壤微生物生物量碳、微生物生物量氮、微生物熵、土壤酶活性及3大类土壤微生物数量显著高于单施化肥及对照处理;土壤微生物生物量碳、微生物生物量氮、微生物熵和3大类微生物数量随着有机肥配施比例的提高而增加,以配施30%有机肥处理的最高;土壤酶活性综合指数以配施20%有机肥处理的最高。可见,化肥配施有机肥特别是配施中高量有机肥更有利于改善土壤微生物学特性,提高土壤生产能力。     

施肥模式对茶树根际土壤微生物数量及酶活性的影响

施肥是提高茶树根际土壤质量及促进土壤肥力提高重要的农业措施之一。为了筛选出合理的施肥模式,采用连续3年的田间定位试验方法,研究了不施肥(CK)、全量化肥(NPK)、半量化肥+半量有机肥(NPKO)、全量有机肥(O)、全量化肥+豆科绿肥(NPKL)和半量化肥+半量有机肥+豆科绿肥(NPKOL)6种不同施肥模式对茶树根际土壤微生物数量及酶活性的影响。结果表明:(1)不同施肥模式显著提高了土壤含水量和电导率,基本表现为NPKOLNPKLONPKONPKCK,其中以NPKOL施肥模式提高最为显著,而施肥模式降低了土壤容重和总孔隙度。(2)与对照(不施肥)相比,其他几种不同施肥模式提高了茶园土壤的基本肥力状况(有机碳、全氮、全磷、全钾、有效磷、有效氮和有效钾),对全磷影响并不显著。(3)不同施肥模式细菌数目、真菌数目、放线菌数目和微生物总数目均有显著的影响:与对照(不施肥)模式相比,其他几种不同施肥模式均可在一定程度上提高茶树根际土壤细菌数目、真菌数目、放线菌数目和微生物总数目,O处理下土壤细菌数目、真菌数目、放线菌数目和微生物总数目与对照差异不显著(p0.05),其余施肥模式下均显著高于对照(p0.05)。(4)不同施肥模式增加了茶树根际土壤微生物量碳、氮和土壤酶活性。综合分析表明:NPKOL施肥模式的茶树根际产量和茶树根际营养物质累积量最大,这进一步佐证了此培肥模式能促进茶产量,值得在茶园施肥上进一步推广应用。     

长期免耕与施用有机肥对土壤微生物生物量碳、氮、磷的影响

通过设置在江苏省句容农科所的田间定位试验研究长期免耕及施用有机肥料对土壤微生物生物量碳、氮、磷的影响。结果表明 :经过 1 6年 32茬稻—麦水旱轮作后 ,表土层 ( 0～ 5cm)土壤微生物生物量碳、氮、磷含量比亚表层 ( 5～ 1 0cm)分别高 2 7.5 %、43.6%和1 1 %。与常规耕翻相比长期免耕处理表土层土壤微生物生物量碳、氮含量分别增加了2 5 .4%和 45 .4% ,而微生物生物量磷无明显变化规律 ;亚表层的土壤微生物生物量碳、氮、磷免耕与耕翻两种耕作方式间的差异不显著。尽管各施肥处理施用的氮、磷、钾数量完全相等 ,但土壤微生物生物量碳、氮、磷的含量却因肥料种类的不同而异。综合 0～ 5和 5～ 1 0cm土层 ,微生物生物量碳、磷为 :猪粪 化肥 >秸秆 化肥 >绿肥 化肥 >化肥 >不施肥 ,微生物生物量氮则为 :猪粪 化肥 >绿肥 化肥 >秸秆 化肥 >化肥 >不施肥。相关分析结果显示 ,土壤微生物生物量碳、氮与土壤有机碳、土壤全氮和土壤碱解氮之间均呈极显著的正相关 ,表明其与土壤肥力关系密切 ,可作为评价土壤肥力性状的生物学指标     

水旱轮作条件下免耕土壤微生物特性研究

通过野外调查和室内分析,研究了水旱轮作条件下,不同免耕年限土壤微生物数量和生物量的变化特点及其影响因素。结果发现:（1）旱作和水作后,免耕土壤细菌数量显著低于常规耕作。随着免耕年限延长,旱作后土壤细菌数量呈先降低再增加的趋势,免耕5～6 a时最低;而水作后,不同免耕年限间无显著差异。（2）旱作后,免耕土壤真菌和放线菌数量显著高于常规耕作,而水作后,真菌和放线菌数量较常规耕作显著降低。随着免耕年限的延长,旱作后土壤真菌数量呈先降低再增加的趋势,免耕7～8 a时最低;土壤放线菌数量在免耕5～6 a后趋于稳定。水作后,土壤真菌和放线菌数量呈显著负相关。（3）旱作和水作后,免耕土壤微生物量碳和氮显著高于常规耕作,两者呈极显著正相关,变化趋势一致。随着免耕年限延长,旱作后,土壤微生物量碳、氮呈逐渐降低的趋势;水作后,土壤微生物量碳、氮呈先增加再降低的趋势。     

不同处理采伐剩余物对营造杉木幼林土壤胞外酶活性的影响

土壤酶对森林生态系统生物化学过程有重要作用,能快速反映土壤环境(如养分含量和有效性)的变化。采伐剩余物是林地土壤养分的重要来源,其处理方式会对森林土壤的养分含量和有效性产生影响。为探讨采伐剩余物不同处理方式对杉木幼林土壤酶活性的影响,在福建省三明市格氏栲自然保护区40年生的杉木成熟林采伐迹地上对采伐剩余物进行不同处理(保留RR、火烧RB、去除R)并种植杉木幼林,通过采集0-10,10-20 cm土层土壤,对6种胞外酶活性进行研究。结果表明:(1)采伐剩余物处理4年后,相比保留处理,火烧和清除处理的土壤可溶性有机碳、可溶性有机氮、无机氮、硝态氮含量均显著下降。其中火烧处理下硝态氮下降幅度显著高于清除处理,2个土层下降幅度平均分别为88%和51%;(2)相比保留处理,火烧和清除处理土壤微生物生物量碳和微生物生物量磷含量以及6种土壤酶活性,即酸性磷酸酶、β-葡萄糖苷酶、纤维素水解酶、β-N-乙酰氨基葡萄糖苷酶、过氧化酶、酚氧化酶均明显更低,而且火烧处理两土层微生物生物量碳和微生物生物量磷含量显著低于清除处理;(3)冗余分析表明,0-10 cm土层土壤酶活性与微生物生物量磷、微生物生物量碳含量显著相关,而可溶性有机氮、硝态氮、微生物生物量碳是影响10-20 cm土层土壤酶活性变化的关键因子。保留采伐剩余物有利于提高土壤养分和酶活性,是土壤肥力维持和森林生产力提高的有效经营管理措施。     

药用植物宁夏枸杞 (Lycium barbarum L.) 土壤细菌群落演替特征

【目的】研究土层、季节和树龄对宁夏枸杞土壤细菌群落结构的影响,对揭示枸杞种植区域土壤质量变化规律具有重要意义。【方法】以宁夏枸杞之乡—宁夏回族自治区中宁县为研究区,采用高通量测序分析了不同土层、季节和树龄条件下枸杞土壤细菌生物量及细菌群落结构和丰度的变化趋势。【结果】随着枸杞树龄增加,与幼龄 (种植当年,< 1 年) 枸杞土壤相比,春季和夏季 0—20 cm 中龄 (6 年) 和老龄 (12 年) 土壤总有机碳 (total organic carbon,TOC) 及 0—40 cm 土壤总有机氮 (total organic nitrogen,TON) 含量先增加后减少;春季不同树龄 0—20 cm 土壤微生物生物量碳 (microbial biomass carbon,MBC)和微生物生物量氮(microbial biomass nitrogen,MBN)一直增加,但春季和秋季 20—40 cm 则呈相反趋势。夏季中龄植株表层土壤 MBC 最高,但 MBN 却最低。随着树龄增加,枸杞表层土壤细菌多样性普遍呈先增加后减小的趋势。枸杞土壤变形菌门 Proteobacteria、放线菌门 Actinobacteria、拟杆菌门 Bacteroidete 在细菌群落中占绝对优势。相同季节老龄土壤 Proteobacteria 相对丰度普遍高于幼龄和中龄,幼龄土壤 Planctomycetes 和绿弯菌门 Chloroflexi 丰度高于中龄和老龄。变形杆菌中黄色单胞菌 Xanthomonadales、红杆菌 Rhodobacterales 和根瘤菌 Rhizobiales 占主导地位,尤其是在秋季中龄和 3 个季节的老龄枸杞土壤。土层、季节和树龄对土壤微生物数量影响不同。【结论】随着树龄增加,宁夏枸杞表层土壤微生物生物量和细菌多样性呈先增加后降低的趋势。老龄植株土壤 Xanthomonadales 数量相对最多。土层对枸杞土壤碳分布有极显著影响,树龄主要显著影响土壤氮源和细菌群落多样性,季节对枸杞土壤碳源、微生物量碳氮均有极显著影响。     

模拟氮沉降对杉木人工林土壤可溶性有机碳和微生物量碳的影响

在杉木人工林中开展模拟氮沉降试验,设计N0(对照)、N1(60kg N/hm2.a)、N2(120kg N/hm2.a)和N3(240kg N/hm2.a)4种氮沉降水平。通过连续7年的处理后,研究外加氮源对土壤可溶性有机碳及微生物量碳的影响及与土壤酶活性的关系。相同N沉降处理下,土壤有机碳、可溶性有机碳和微生物量碳均随土层加深而降低。氮沉降对土壤有机碳具有促进作用,中-低氮沉降(N1、N2)增加幅度大,高氮沉降(N3)增加幅度小。低氮(N1)处理促进土壤微生物生物量C增加,而中、高氮(N2、N3)则抑制;各氮沉降处理土壤可溶性有机碳含量从高到低的顺序为:N3、N2>N1>N0。40-60cm土壤微生物量碳与蔗糖酶、纤维素酶呈极显著正相关关系,与淀粉酶、多酚氧化酶、过氧化物酶呈极显著负相关关系;除40-60cm土层的β-葡糖苷酶外,各层土壤可溶性有机碳与土壤蔗糖酶、纤维素酶和β-葡糖苷酶活性呈极显著正相关关系,与淀粉酶、多酚氧化酶和过氧化物酶呈极显著负相关关系。因此,氮沉降增加将会对土壤碳累积与分解过程产生较大的影响。     

保护性耕作对黑土微生物群落的影响

耕作方式通过影响土壤微生物群落而影响土壤生态系统过程。本研究以传统耕作玉米连作处理为对照,通过测定土壤微生物量碳及磷脂脂肪酸含量,分析了保护性耕作(包括免耕玉米连作和免耕大豆-玉米轮作)对黑土微生物群落的影响。结果表明,保护性耕作可显著增加土壤表层(0～5cm)全碳、全氮、水溶性有机碳、碱解氮和微生物量碳(P0.05),为微生物代谢提供了丰富的资源。同时,保护性耕作显著提高了土壤表层(0～5cm)总脂肪酸量、真菌和细菌生物量(P0.05),提高了土壤的真菌/细菌值,有利于农田土壤生态系统的稳定性。研究结果对于探讨保护性耕作的内在机制具有重要意义。     

高寒草地不同退化程度下土壤微生物及土壤酶活性变化特征

为探讨不同退化程度对高寒草地土壤微生物及土壤酶活性的影响,以青藏高原东北缘祁连山3种不同退化程度(轻度退化、中度退化、重度退化)高寒草地为研究对象,测定和分析土壤3大类微生物(细菌、真菌、放线菌)和氮素生理群(氨化细菌、好气性固氮菌、嫌气固氮菌、硝化细菌、反硝化细菌)数量、微生物量(碳、氮)及土壤酶活性(蔗糖酶、脲酶、磷酸酶、过氧化氢酶)变化特征。结果表明:(1)相同土层不同退化程度,土壤3大类微生物数量、氮素生理群、微生物量以及土壤酶活性随退化程度的加重总体呈减小的趋势,重度退化程度下各指标含量最小,中等退化程度可增加10—20cm土壤放线菌、氨化细菌及反硝化细菌数量和20—30cm土壤细菌、真菌、放线菌、好气性固氮菌、反硝化细菌数量;(2)不同土层相同退化程度,土壤3大类微生物数量、氮素生理群、微生物量以及土壤酶活性随土层深度的加深均逐渐减小。研究结果对评价草地退化程度提供了新思路,同时为高寒草地的恢复和重建提供了重要的理论依据。     

Pruned tea bushes secrete more root exudates to influence microbiological properties in soil

Pruning is adopted at 3–4 years interval as an agronomic practice during tea cultivation. It was hypothesized that biomass loss during pruning will imply stress on tea bushes. The aim of this study was to quantify changes in different parameters (labile organic carbon fractions, phosphatase activity, microbial biomass and microbial respiration) in tea rhizosphere due to pruning by collecting soil samples from the rhizosphere of ten of each pruned and un-pruned tea bushes. Hot-water extractable and dissolved organic C contents in rhizosphere soil of pruned tea were significantly (P ≤ 0.05) higher than those in the soil of un-pruned tea bushes. Analysis of phospholipid fatty acids (PLFA) revealed that the rhizosphere of pruned tea plants had higher population of Gram (+) and Gram (-) bacteria, fungi, actinomycetes and lower denitrifying bacterial population as compared to un-pruned tea plants. Activity of acid phosphatase enzyme in soil was also increased due to pruning. A separate study revealed that de-centering may induce production of up to 50% more labile organic carbon compounds by young tea as compared to un-pruned plants. Therefore, it could be concluded that pruned tea bushes secrete more root exudates to influence microbiological and biochemical properties in rhizosphere.     

陕西靖边花豹湾聚湫坝地土壤微生物群落结构 特征及其影响因子

以黄土高原天然形成的花豹湾聚湫为研究对象,系统分析了3个剖面中土壤的机械组成、有机碳(SOC)、全氮(TN)、微生物生物量碳(MBC)和微生物生物量氮(MBN),并利用磷脂脂肪酸法(PLFA)测定了土壤中细菌、真菌和放线菌的数量,重点讨论了微生物数量和群落结构与碳、氮含量及机械组成之间的相关性。结果表明:1砂粒含量沿着坝尾-坝前的方向有逐渐降低的趋势,粉砂粒和黏粒含量则有逐渐升高的趋势,在垂直方向上可划分出5个明显的沉积旋回(深度分别为0~40、50~60、70~80、100~120和240~260 cm);2聚湫坝地土壤微生物主要含有脂肪酸(15:0 iso、18:1 w9c、18:1 w7c、16:0 10-methyl),约占PLFA总量的54%,土壤微生物以细菌为主,约占65%~75%,放线菌约占15%~25%,真菌约占5%~10%;33种多样性指数的变化趋势基本一致,依次为A剖面B剖面C剖面,3个剖面的土壤微生物群落结构存在比较明显的差异,其中A剖面分化明显;4土壤微生物总量、细菌数量和真菌数量与土壤中粉粒和黏粒含量以及MBC、MBN、SOC和TN均呈显著(P0.05)或极显著(P0.01)的正相关关系;5土壤中细颗粒组分可能是影响微生物数量和群落结构的主要因子。     

Plant species traits regulate methane production in freshwater wetland soils

Ecosystem and biogeochemical responses to anthropogenic stressors are the result of complex interactions between plants and microbes. A mechanistic understanding of how plant traits influence microbial processes is needed in order to predict the ecosystem-level effects of natural or anthropogenic change. This is particularly true in wetland ecosystems, where plants alter the availability of both electron donors (e.g., organic carbon) and electron acceptors (e.g., oxygen and ferric iron), thereby regulating the total amount of anaerobic respiration and the production of methane, a highly potent greenhouse gas. In this study, we examined how plant traits associated with plant inputs of carbon (photosynthesis and biomass) and oxygen (root porosity and ferric iron on roots) to mineral soils relate to microbial competition for organic carbon and, ultimately, methane production. Plant productivity was positively correlated with microbial respiration and negatively correlated to methane production. Root porosity was relatively constant across plant species, but belowground biomass, total biomass, and the concentration of oxidized (ferric) iron on roots varied significantly between species. As a result the size of the total root oxidized iron pool varied considerably across plant species, scaling with plant productivity. Large pools of oxidized iron were related to high CO₂:CH₄ ratios during microbial respiration, indicating that as plant productivity and biomass increased, microbes used non-methanogenic respiration pathways, most likely including the reduction of iron oxides. Taken together these results suggest that increased oxygen input from plants with greater biomass can offset any potential stimulation of methanogenic microbes from additional carbon inputs. Because the species composition of plant communities influences both electron donor and acceptor availability in wetland soils, changes in plant species as a consequence of anthropogenic disturbance have the potential to trigger profound effects on microbial processes, including changes in anaerobic decomposition rates and the proportion of mineralized carbon emitted as the greenhouse gas methane.     

毛竹林土壤有机碳及微生物量碳特征研究

通过对湖南会同林区集约经营毛竹林地土壤有机碳和微生物量碳进行测定,结果表明,毛竹林地土壤(0-60 cm)有机碳和微生物量碳含量平均值分别为1.727%和551.84 mg/kg,不同土壤层次有机碳和微生物量碳含量差异极显著,其中,0-20 cm土层有机碳含量平均值为2.607%,分别是20-40 cm和40-60 cm土层有机碳含量的1.67倍和2.57倍;0-20 cm土层的微生物量碳占土壤总微生物量碳的58.9%,分别是20-40 cm和40-60 cm土层的2.69倍和3.08倍。不同季节间土壤微生物量碳有明显变化规律,即土壤微生物量碳含量1-7月份呈上升的趋势,7月达到最大值,8-12月份呈逐渐下降趋势;不同季节间有机碳含量差异不显著。毛竹林地土壤表层土壤微生物量熵为1.118 6%,与40-60 cm土壤层相当,略高于20-40 cm土壤层,说明毛竹林不同土壤层次有机碳积累强度相当。     

生物发酵肥对温室黄瓜土壤微生物组成的影响

以大棚黄瓜根区土壤为研究对象,测定了不同施肥方式下温室黄瓜地土壤微生物3大类群和主要功能群组成及土壤微生物量碳(microbial biomass carbon,MBC),研究了温室中不同施肥方式对黄瓜根区土壤微生物组成及土壤MBC(土壤微生物生物量碳)的影响,探讨了微生物发酵有机肥对土壤肥力的影响。结果表明,土壤中细菌、真菌、放线菌数量由高到低的顺序依次为:发酵肥>发酵肥+50%化肥>常规施肥>普通有机肥>CK;土壤微生物综合指标Shannon-Wiener指数以生物发酵肥最高;氨化细菌、固氮菌及纤维素分解菌数量以生物发酵肥最高,硝化细菌数量以发酵肥+50%化肥处理最高;生物发酵肥和发酵肥+50%化肥两处理的MBC均显著高于常规施肥。施用微生物发酵有机肥可显著增加土壤微生物数量及微生物的群落多样性,并有助于提高土壤综合肥力。     

Linking microbial community structure and allocation of plant-derived carbon in an organic agricultural soil using 13CO2 pulse-chase labelling combined with 13C-PLFA profiling

We conducted a ¹³CO₂ pulse-chase labelling experiment in a drained boreal organic (peat) soil cultivated with perennial crop, reed canary grass (RCG; Phalaris arundinacea) to study the flow of carbon from plants to soil microbes. Both limed and unlimed soils were studied, since liming is a common agricultural practice for acidic organic soils. Soil samples taken within three months after the labelling and three times in the following year were used for the δ¹³C analysis of microbial phospholipid fatty acids (PLFAs), root sugars and root lipids. We estimated the contribution of carbon from root exudates to microbial PLFA synthesis. The flow of carbon from plants to microbes was fast as the label allocation in PLFAs had a peak 1–3 days after labelling. The results showed that fungi were important in the incorporation of fresh, plant-derived carbon, including root sugars. None of the main microbial PLFA biomarker groups (fungi, Gram-positive bacteria, Gram-negative bacteria, arbuscular mycorrhizal fungi) was completely lacking label over the measurement period. One year after the labelling, when the labelled carbon was widely distributed into plant biomass and soil, bacterial biomarkers increased their share of the label allocation. Liming had a minor effect on the label allocation rate into PLFAs. The mixing model approach used to calculate the root exudate contribution to microbial biomass resulted in a highly conservative estimate of utilization of this important C-source (0–6.5%, with highest incorporation into fungi). In summary, the results of this study provide new information about the role of various microbial groups in the turnover of plant-derived, fresh carbon in boreal organic soil.     

封育和水平沟生态恢复措施对宁夏黄土丘陵区典型草原土壤生物学特性的影响

研究禁牧封育和水平沟生态恢复措施下黄土丘陵区典型草原土壤生物学特性变化,以期为该区草地生态建设提供依据。采用空间梯度代替时间梯度的方法,在宁夏黄土丘陵区典型草原,选取未封育(放牧)、封育3~15a、水平沟整地后1~15a的土壤,分析0—10,10—20,20—30,30—40cm土壤微生物数量、微生物生物量碳、量氮和土壤酶活性的变化特征及其相关性。结果表明:(1)试验区土壤微生物类群以放线菌为主,达到86.18%~94.43%,数量表现为放线菌细菌真菌,土壤微生物总数、细菌和放线菌数、微生物生物量碳、量氮含量,脲酶、蛋白酶、磷酸酶、蔗糖酶活性随着草地封育年限增加呈上升变化,但水平沟措施下随着整地年限延长呈上升—下降—上升的趋势,2种措施下土壤过氧化氢酶活性变化趋势与其他指标相反,真菌数在封育6a和水平沟6a较低,分别为11.33,4.67cfu/g;(2)各处理下,0—40cm土壤微生物和酶活性整体呈现上层土壤高于下层土壤,土壤微生物、酶活性与有机碳等主要养分含量相关性显著(p0.05);(3)相近恢复年限下,土壤微生物数量、微生物生物量碳、微生物生物量氮以及酶活性总体为封育草地高于水平沟(p0.05);研究认为,禁牧封育较水平沟措施更有利于黄土丘陵区典型草原土壤微生物和酶活性的增加。     

Organic matter dynamics in a temperate forest soil following enhanced drying

Climate models predict an increase in global surface temperature and a change in precipitation intensity during this century. For Europe, extended drought periods followed by heavy rainfall are expected. The consequences for soil organic matter (SOM) dynamics are poorly understood. In this study, we investigated the effect of changing soil moisture regime on SOM quality under field conditions. For this purpose, a throughfall exclusion (TE) experiment was conducted in the summers 2006 and 2007 on a Haplic Podzol under a 140 years old Norway spruce stand using a roof installation followed by re-wetting compared to non-manipulated control plots. Total organic carbon, lignin (stable carbon pool), plant and microbial sugars (labile carbon pool) and microbial biomass (phospholipid fatty acids) were determined before, during and after the experiment in the L, O, A and B horizons. No significant treatment effects could be observed for SOM quantity. Amounts of lignin and soil microbial biomass were also not affected by the moisture regime but structure of soil microbial community. In the L and organic layers, gram + bacteria and actinomycetes were reduced during water stress, while gram- bacteria, fungi and protozoa increased during drought. Warmer and drier weather led to a dominance of fungi while a cooler and moister regime favoured bacteria, at least in the L horizon. An increasing PLFA (cy17:0 + cy19:0)/(16:1ω7c + 18:1ω7c) ratio in the O layer and A horizon suggests that the microbes suffered from water stress in these horizons. This agrees with a decreasing contribution of microbial sugars to SOM with decreasing water content in the O and A horizons. Although the original plant material exhibited increasing plant sugar content with increasing dryness, the contribution of the plant sugars to total soil organic carbon (SOC) generally decreased with decreasing water content. Physical-chemical changes of soil structure can theoretically change the sugar extractability from soils and/or chemical changes of sugars structure can probably affect the analysis. Therefore, chemical alteration and stabilization could be responsible for sugar decrease in soil with increasing dryness explaining the contrast compared to the original plant material.     

Above- and belowground carbon inputs affect seasonal variations of soil microbial biomass in a subtropical monsoon forest of southwest China

Soil microbial activity drives carbon and nutrient cycling in terrestrial ecosystems. Soil microbial biomass is commonly limited by environmental factors and soil carbon availability. We employed plant litter removal, root trenching and stem-girdling treatments to examine the effects of environmental factors, above- and belowground carbon inputs on soil microbial C in a subtropical monsoon forest in southwest China. During the experimental period from July 2006 through April 2007, 2 years after initiation of the treatments, microbial biomass C in the humus layer did not vary with seasonal changes in soil temperature or water content. Mineral soil microbial C decreased throughout the experimental period and varied with soil temperature and water content. Litter removal reduced mineral soil microbial C by 19.0% in the ungirdled plots, but only 4.0% in girdled plots. Root trenching, stem girdling and their interactions influenced microbial C in humus layer. Neither root trenching nor girdling significantly influenced mineral soil microbial C. Mineral soil microbial C correlated with following-month plant litterfall in control plots, but these correlations were not observed in root-trenching plots or girdling plots. Our results suggest that belowground carbon retranslocated from shoots and present in soil organic matter, rather than aboveground fresh plant litter inputs, determines seasonal fluctuation of mineral soil microbial biomass.