黄土高原半干旱草地封育后土壤碳氮矿化特征

土壤有机碳和全氮的分布与矿化是退化草地封育后土壤生态效应研究的重要内容和指标。结合野外调查和室内培养实验,研究了半干旱黄土区不同封育年限草地土壤有机碳和全氮的含量变化及其矿化特征。结果表明,封育对半干旱黄土区退化草地土壤有机碳和全氮的影响主要体现在0-40 cm土层封育超过17a后,封育年限的影响逐渐减弱。封育显著增加了土壤有机碳矿化速率和C_(min)/C_0封育对有机碳矿化速率的影响与封育年限和土层深度无关,而对C_(min)/C_0的影响则与封育年限和土层深度有关。封育显著提高了0-40 cm土层土壤氮素矿化速率,但是降低了40-80 cm土层土壤氮矿化速率,并且降低了080 cm土层N_(min)/N_0。碳氮矿化速率与有机碳和全氮之间显著相关,而与碳氮比之间的相关性较小。这些结果表明,退化草地封育后土壤碳氮元素的转化主要受土层深度、封育年限以及土壤碳氮含量的影响。     

帽儿山不同林龄落叶阔叶林土壤微生物生物量及其季节动态

土壤微生物在生态系统生物地球化学循环过程中扮演着重要角色,对于受到干扰后退化土壤的肥力恢复具有重要的意义,然而,采伐后次生林发展过程中土壤微生物生物量的动态尚不明确。在帽儿山森林生态站的落叶阔叶林中设置了一个由采伐后0年(采伐迹地)、10年、25年、56年的林分构成林龄系列样地,采用氯仿熏蒸浸提法,在生长季期间(4–10月)每月测定各林分土壤微生物生物量碳含量(C_(mic))、微生物生物量氮含量(N_(mic))、土壤可溶性有机碳含量(Cdis)、可溶性全氮含量(Ndis)、土壤含水率、温度等因子,以探索采伐干扰后不同林龄林分土壤微生物生物量的时间动态及其影响因子。结果表明:(1)不同林龄林分土壤微生物生物量生长季均值差异显著,C_(mic)表现为56年和采伐迹地显著高于25年和10年林分;N_(mic)表现为采伐迹地、56年显著高于10年林分,25年林分居中;C_(mic)/N_(mic)表现为56年、10年林分显著高于25年林分、采伐迹地。(2)采伐迹地微生物生物量季节变化格局与其他3个林龄林分的差异主要体现在生长季后期,前者表现为降低,而后者表现为升高或变化不明显;10年、25年、56年林分C_(mic)、N_(mic)季节变化格局的差异主要体现在生长季前期,变化幅度随林龄增长而降低;4个林龄林分C_(mic)/N_(mic)季节变化均表现为"W"形。(3)土壤微生物生物量的主要影响因子随林龄而变:随林龄增长,C_(mic)、N_(mic)的影响因子由土壤含水率(采伐迹地、10年生)逐渐转变为土壤可溶性养分含量(10年、25年、56年林分);采伐迹地C_(mic)/N_(mic)影响因子为土壤温度和Cdis,其他3个林龄林分则为Cdis/Ndis。这些结果说明:在采伐干扰后的次生林发展过程中,植被组成和土壤理化性质不断变化,提高了土壤微生物生物量,进而改善了土壤养分状况,显示出地上植被变化与地下微生物动态的密切联系。     

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。     

不同植茶年限土壤-微生物生物量碳氮磷化学计量特征

退耕还林(草)等生态建设工程的实施引起土壤碳(C)、氮(N)、磷(P)循环及其化学计量特征发生变化,继而对土壤微生物生物量的化学计量造成潜在影响,然而,土壤-微生物C∶N∶P化学计量的时间动态及协调关系仍不明确。本试验选取三峡库区小流域退耕地——茶园为研究对象,以玉米地为对照,探索土壤-微生物生物量C、N、P随植茶年限(<5 a、5～10 a、10～20 a、20～30 a和>30 a)的变化特征,分析其化学计量比、微生物熵(qMBC、qMBN、qMBP)、化学计量不平衡性(土壤C、N、P计量比与微生物生物量C、N、P计量比的比值)之间的关系。结果表明：随着植茶年限增加,土壤和微生物生物量C、N、P、土壤C∶N和C∶P均显著升高,而土壤N∶P整体下降,微生物生物量C∶P和N∶P呈先升后降的变化趋势,微生物生物量C∶N变化不显著。此外,茶树种植年限对土壤、微生物间的化学计量不平衡性以及微生物熵均存在显著影响,随着植茶年限增加,qMBC先降低后升高,qMBN和qMBP呈波动上升;碳氮化学计量不平衡性(C∶N_imb)和碳磷化学计量不平衡性(C∶P_i...     

大兴安岭北部天然针叶林土壤氮矿化特征

采用顶盖埋管法对大兴安岭地区天然针叶林(樟子松林、樟子松-兴安落叶松混交林和兴安落叶松林)土壤铵态氮(NH~+_4-N)、硝态氮(NO~-_3-N)、净氮矿化速率进行研究,并探索土壤理化性质与氮矿化之间的相关性,为大兴安岭地区森林生态系统土壤养分管理及森林经营提供帮助。结果表明:观测期内(5—10月)3种林型土壤无机氮变化范围为31.51—70.42 mg/kg,以NH~+_4-N形式存在为主,占比达90%以上,且与纯林相比混交林土壤无机氮含量较高。3种林型土壤净氮矿化、净氨化、净硝化速率月变化趋势呈V型,7、8月表现为负值,其他月份为正值。净氮矿化速率变化范围樟子松林为-0.54—1.28 mg kg~(-1) d~(-1)、樟子松-兴安落叶松混交林为-0.13—0.55 mg kg~(-1) d~(-1)、兴安落叶松林为-0.80—1.05 mg kg~(-1) d~(-1)。土壤净氨化过程在土壤氮矿化中占主要地位,占比达60%以上。3种林型土壤净氮矿化、净氨化及净硝化速率垂直差异显著,0—10 cm土层矿化作用明显高于10—20 cm土层(P0.05)。土壤氮矿化速率与土壤含水量、土壤有机碳含量、土壤C/N、枯落物全氮含量和枯落物C/N均存在显著相关性。不同类型的森林土壤及枯落物的质量也存在差异,进而影响土壤氮矿化特征。     

长期施肥下农田土壤-有机质-微生物的碳氮磷化学计量学特征

探讨外源养分的输入对土壤系统内碳、氮、磷化学计量特征的影响,对于深刻认识农田土壤有机碳(C)和养分循环及其相互作用过程具有重要意义。以26年的农田长期定位施肥试验为平台,分析长期不同施肥条件下土壤、有机态及微生物生物量碳、氮、磷含量及其化学计量学特征,并根据内稳性模型y=c x~(1/H)计算其化学计量内稳性指数H。结果表明:与长期撂荒处理(CK_0)相比,种植作物条件下26年化肥配施有机肥处理(MNPK和1.5MNPK)显著降低微生物生物量氮含量,但显著提高了微生物生物量磷的含量。相对于撂荒处理,即使长期配施化肥磷处理(NP、PK、NPK),其土壤有机磷降低显著。对于C∶N比而言,化肥配施有机物料处理(秸秆或有机肥)的土壤C∶N比、有机质C∶N及微生物生物量C∶N比均显著低于化肥处理(N、NP、PK和NPK)。对于C∶P比而言,相对于撂荒处理,26年施用磷肥(化肥磷或有机磷)显著降低了土壤C∶P比和微生物生物量C∶P比,而CK和偏施化肥处理(N、NP和PK)显著降低了土壤有机质C∶P比。对于土壤N∶P比而言,撂荒处理土壤N∶P比显著高于其他处理,而撂荒处理土壤有机质N∶P比显著高于CK和化肥处理,表明不施肥或化肥条件下作物种植加剧了土壤有机质中氮素的消耗。微生物生物量C∶N、C∶P、N∶P比的内稳性指数H分别为0.24、0.75、0.64,不具有内稳性特征。微生物生物量C∶N、C∶P、N∶P比分别与土壤C∶N、C∶P、N∶P比呈显著正相关关系,但与土壤有机质碳氮磷化学计量比之间无显著相关性。表明土壤碳、氮、磷元素的改变会直接导致微生物生物量碳、氮、磷化学计量比的改变,但微生物生物量碳氮磷化学计量比对土壤有机质碳氮磷化学计量比无显著影响,土壤有机质的碳氮磷计量比可能更多是受到作物和施肥等养分管理措施的影响。     

四种温带森林土壤氮矿化与硝化时空格局

利用PVC管原位培养连续取样法测定了东北地区4种具有代表性的森林生态系统(硬阔叶林、蒙古栎林、红松林、落叶松林)土壤氮素矿化、硝化的时间动态及氮矿化的空间分布格局.结果表明:4种森林土壤氮素矿化存在明显的时空变异.蒙古栎和红松林土壤在6月份表现出强烈的氮矿化和硝化作用,而硬阔叶林及落叶松林7月份氮素矿化强烈.4种森林生态系统上层土壤的氮净矿(硝)化率显著高于下层土壤.4种林型土壤的硝化过程在氮矿化过程中占有重要地位,其NO-3-N在无机氮中的比例分别为:79.9%～91.1%(硬阔叶林)、50.7%～80.5%(蒙古栎林)、54.1%～92.0%(红松林)、63.7%～86.5%(落叶松林).生态系统构成决定了土壤氮素的矿化能力.阔叶林和针阔混交林生态系统矿化率大于纯针叶林生态系统.硬阔叶林、红松林、蒙古栎林、落叶松林的平均净矿化率分别为:(0.58±0.01) mg · kg-1 · d-1、(0.47±0.19) mg · kg-1 · d-1、(0.39±0.11) mg · kg-1 · d-1和(0.23±0.06) mg · kg-1 · d-1.4种林型氮素矿化作用与地下5 cm温度呈正相关,并受土壤表层 (0～10 cm)水分显著影响.土壤微生物量氮与土壤氮矿化呈显著正相关.     

原始红松林退化演替后土壤氮矿化特征变化

土壤氮矿化是氮素生物地理化学循环的重要环节,表征着土壤的供氮潜力,其变化过程会影响森林生态系统生产力。从小兴安岭典型的原始红松林及其退化形成的次生阔叶林样地采集土壤样品,采用好气室内培养法,研究在不同培养温度(4℃、12℃、20℃、28℃和36℃)和湿度(20%、40%、60%、80%和100%饱和持水量,WHC)下,2种林地土壤氮转化速率的变化。结果表明:与原始红松林相比,次生阔叶林表层土(0—20 cm)的有机质、全碳、全氮、硝态氮、碳/氮比、全磷、速效磷、速效钾、pH值均显著升高,铵态氮显著降低(P0.05)。采用方差分析结果表明:原始红松林表层土壤的净矿化速率、净硝化速率均显著低于次生阔叶林,但净氨化速率的变化则相反;培养温度和湿度及两者的交互作用均对土壤氮转化速率影响显著(P0.001)。原始红松林和次生阔叶林净矿化速率对温度和湿度变化的响应存在一定差异,最适温度和湿度分别为28℃—36℃和60%(WHC)。原始红松林土壤氮矿化温度敏感性指数(Q_(10))显著高于次生阔叶林(P0.05),均值分别为2.08和1.80,Q_(10)与基质质量指数(A)呈负相关,与土壤有机质呈极显著负相关(P0.01)。     

恢复年限、林下植被及季节对马尾松林土壤氮转化的影响

侵蚀红壤区植被恢复能有效防治土壤侵蚀,改善生态环境。提高侵蚀退化地土壤氮矿化潜力、增加氮有效性是改善贫瘠土壤植被生长发育的关键途径,对恢复侵蚀地生态系统具有重要意义。采用顶盖埋管培养法研究了不同恢复年限(Y0、Y16、Y34))不同芒萁处理的马尾松林土壤净氮矿化量和净氮矿化速率的季节变化特征,分析了植被恢复年限、林下植被覆盖及季节变化对土壤氮矿化的交互影响。结果表明,植被恢复能使侵蚀退化地土壤养分条件得到改善。不同恢复年限马尾松林净氮矿化最高值出现在夏秋季,而在春季为负值。植被恢复能使土壤净氮矿化量显著增加,且净氮矿化过程以氨化作用为主。净氨化速率与净矿化速率具有相似的季节变化,硝化速率随着恢复年限增加季节变化减小。林下裸露地净氮矿化量及速率低于芒萁覆盖地,且去除芒萁可以降低净氮矿化量及速率。方差分析表明,恢复年限、季节变化及其交互作用能显著影响土壤净氮矿化量及矿化速率(P0.001),而芒萁处理未能达到显著水平(P0.05)。马尾松林土壤氮转化过程季节变化明显,林分管理应按季节变化进行,林下芒萁覆盖对侵蚀退化地马尾松林土壤氮恢复具有重要作用。     

长期施肥黄土旱塬农田土壤-微生物-植物系统碳氮磷生态化学计量特征

探讨长期不同施肥制度对农田土壤、植物生态系统的碳(C)、氮(N)、磷(P)含量及其生态化学计量比的影响,可为揭示该系统能量平衡和养分循环,实现农业生态系统元素平衡及可持续发展提供参考意义。以位于黄土高原半干旱地区的长武国家黄土高原农业生态实验站长期施肥试验为研究对象,选取不施肥(CK)、单施氮肥(N)、单施磷肥(P)、施氮磷肥(NP)、单施有机肥(M)、氮肥配施有机肥(NM)、磷肥配施有机肥(PM)、氮磷肥配施有机肥(NPM)8个处理,分析了黄土旱塬典型农田土壤-微生物-植物生态系统中C、N、P含量及其生态化学计量变化规律。研究结果表明:1)长期单施有机肥和化肥配施有机肥处理可显著提高土壤和有机质C、N、P含量。2)氮、磷肥的输入显著降低了土壤和小麦C∶N、N∶P,施P显著降低了有机态C∶P和小麦C∶P;有机肥配施对微生物生物量和小麦C∶N∶P的影响更为明显。3)长期有机肥配施条件下土壤养分和小麦化学计量比存在较强的相关关系。微生物生物量碳与有机C、N、P呈显著正相关,土壤微生物生物量氮与土壤N、P总量呈显著正相关,微生物生物量磷与土壤C、N、P总量含量呈显著负相关;植株碳含量与微生物...     

川西亚高山天然次生林不同演替阶段土壤-微生物生物量及其化学计量特征

开展不同恢复演替阶段天然次生林土壤-微生物生物量及其化学计量特征关系的研究,可为有效和持续管理川西亚高山次生林提供科学依据。以川西亚高山米亚罗林区20世纪60、70、80年代3种采伐迹地经自然恢复演替形成的次生林（SF60、SF70和SF80）和岷江冷杉（Abies faxoniana）原始林（PF）为研究对象,探讨了表层（0-20 cm）土壤有机碳（C_soil）、全氮（N_soil）、全磷（P_soil）含量及微生物生物量碳（C_mic）、氮（N_mic）、磷（P_mic）含量随自然恢复演替的变化特征,分析了它们的化学计量比与微生物熵（qMB）之间的相互关系。结果表明：（1）随着恢复演替年限的增加,C_soil和N_mic含量显著降低,N_soil和P_soil及C_mic和P_mic含量呈现先升后降的显著变化趋势,且3种次生林的表层土壤碳、氮、磷及其微生物生物量的含量均低于PF。（2）次生林恢复年限对土壤微生物熵C（qMBC）和P（qMBP）没有显著影响,但对土壤微生物熵N（qMBN）存在显著影响。（3）土壤-微生物化学计量不平衡性C_imb：N_imb随自然恢复演替进程呈先降后升的显著变化趋势,C_imb：P_imb呈不显著的降低趋势,N_imb：P_imb呈现显著降低趋势。冗余分析显示,N_imb：P_imb和C_mic：N_mic是影响qMB变化的主导因子,其中N_imb：P_imb解释了qMB变化的62.6%,说明土壤氮磷及其活性组分（N_mic和P_mic）含量变化可能会影响到qMB变化。综上可知,次生林近60 年的自然恢复演替引起了土壤碳氮磷含量的显著变化;天然次生林土壤-微生物生物量碳氮磷化学计量比主要受到氮磷的协同影响,且SF60土壤质量状况较差,为此,对SF60林分可适当增加氮素供给以促进其林木生长,进而提升土壤质量。     

云贵高原喀斯特坡耕地土壤微生物量 C、N、P空间分布

土壤微生物是地球生物演化进程中的先锋种类,具有重要的生态修复功能,但空间分布格局是否存在的争议很大。以云贵高原典型喀斯特坡耕地为对象,基于网格法取样,用经典统计学和地统计学综合分析了土壤微生物生物量的空间变异特征。结果表明,云贵高原喀斯特坡耕地土壤微生物生物量碳(C_mic)、磷(P_mic)以及碳氮比(C_mic/N_mic)适宜,氮(N_mic)的含量较低,变异均很大,空间自相关性明显,最佳拟合模型均为指数模型。块金值C₀较小(0.0016-0.0087),C₀/(C₀+C)均<25%(2.6%-10.2%),变程a较短(22.2-51.0 m),其强烈的空间变异主要由结构性变异引起。Kriging等值线图表明,C_mic、N_mic和C_mic/N_mic的高值区分布在坡的中上部,P_mic的高值区则在坡的中下部和坡脚。云贵高原喀斯特坡耕地土壤微生物不仅存在着小尺度的空间分布格局,而且不同土壤微生物属性的空间分布不同。     

Plant functional traits and soil microbial biomass in different vegetation zones on the Loess Plateau

Plant functional traits built the relationships between plant diversity, species composition, and physiology along with the environmental changes, thus influencing soil microbial community. As the sensitivity indicators, soil microbial biomass and plant functional traits responses soil micro-organism and plant characteristics in direct way. Ten plant functional traits of 149 species and soil microbial biomass (carbon, nitrogen, and phosphorus) were analyzed across the different vegetation types (forest, forest-steppe, and steppe) that are divided by environmental gradient (temperature and precipitation), aimed to find the correlations among them. Our results confirmed the greatest values of plant functional traits (except the leaf density and the fine root density) that were distributed in the steppe zone, mainly due to the different mean annual temperature and mean annual precipitation conditions. For different plant growth forms, the plant functional traits were significant differences among the vegetation zones. The advantages of higher rate nutrient cycling, plentiful biomass supplements, and favorite habit conditions lead to the forest-steppe zone with the highest C_mic and N_mic concentrations. The canonical correlation analysis indicated that leaf nitrogen, root nitrogen, and fine root densities were correlated with root exudate and tissue which affected the concentrations of soil organic carbon (SOC) and total nitrogen (N), consequently impacting soil microbial biomass carbon (C_mic) and soil microbial biomass nitrogen (N_mic). Soil is the medium that connects micro-organism and plant root system that influenced leaf nitrogen, root nitrogen, and fine root density of plant functional traits, the concentrations of SOC and total N that plant feedback are consequently influencing C_mic and N_mic.     

木论喀斯特自然保护区土壤微生物生物量的空间格局

土壤微生物是森林生态系统中的重要分解者,在森林生态系统物质循环和能量转换中占有特别重要的地位。以典型喀斯特峰丛洼地为试验对象,利用经典统计学和地统计方法分析了土壤微生物量的空间变异特征。结果表明:土壤微生物量的变异程度均很大,土壤微生物量碳(Cmic)、土壤微生物量氮(Nmic)、土壤微生物量磷(Pmic)的变化范围依次为:44.29—5209.63,20.91—1894.37,0.34—77.06 mg/kg。Cmic、Nmic呈极显著的相关关系,Cmic/Nmic为4.78,明显低于其它生态系统。半变异函数分析表明,Cmic和Nmic的最佳拟合模型为高斯模型,Pmic的最佳拟合模型为球状模型,Cmic/Nmic的最佳拟合模型为指数模型。土壤微生物量的块金值/基台值均介于25%—75%之间,表现为中等空间相关性,说明其受随机因素和结构因素的综合影响。Cmic、Nmic的自相关距离约为50 m,随着滞后距离的增大,自相关函数逐渐向负方向增长,达到显著的负相关。Pmic的Moran’s I在滞后距大于70 m后反而增大,表现为正相关。Cmic/Nmic的Moran’s I较小,在-0.2—0.2之间波动。Cmic、Nmic的空间分布具有很高的相似性,呈凸型片状分布,坡中含量高且向两边递减。Pmic表现为明显不同的分布格局,其在坡中上位和洼地含量较高。Cmic/Nmic呈相反的凹形零星斑块状分布。土壤微生物存在着一定的空间格局,受干扰后其含量急剧降低,因此应加强喀斯特原生生态系统的保护。     

林地覆盖对雷竹林土壤微生物特征及其与土壤养分制约性关系的影响

为了探讨林地覆盖雷竹林退化机理,给退化雷竹林恢复提供理论参考,对不同覆盖年限(CK、1、3 a 和6 a) 雷竹林土壤微生物区系组成和生物量碳(C_mic)、氮(N_mic)、磷(P_mic)等特征因子进行了测定,并分析了其与土壤养分的制约性关系。结果表明:(1) 雷竹林土壤微生物以细菌为主,真菌次之,放线菌最少,分别占土壤微生物总量的90.11%-98.03%、1.04%-9.22%和0.67%-1.37%。随覆盖年限增加,细菌、放线菌比率呈下降趋势,真菌比率呈上升趋势;土壤微生物总数、细菌和放线菌数量及C_mic、N_mic、P_mic均呈先升高后降低的变化趋势,试验雷竹林间差异极显著,真菌数量总体呈极显著升高趋势。(2)雷竹林土壤微生物特征因子与土壤有机质(SOM)、全氮(TN)、全磷(TP)、碱解氮(Available nitrogen, AN)和pH均呈显著或极显著相关,其中,CK和覆盖1 a、3 a雷竹林土壤微生物特征因子与土壤养分主要呈正相关,与pH呈负相关,而覆盖6 a雷竹林则相反。(3)不同覆盖年限雷竹林土壤养分与土壤微生物的制约性关系存在一定的差异,CK雷竹林土壤SOM、TN、AN、速效钾(AK)和pH主要影响土壤C_mic、N_mic和细菌,覆盖1 a雷竹林土壤SOM、TN、TP和AK主要影响土壤P_mic、放线菌和细菌,覆盖3 a雷竹林土壤SOM、TN、速效磷(AP)和AN主要影响土壤N_mic、放线菌和真菌,覆盖6 a雷竹林土壤SOM、TN和pH主要影响土壤N_mic、真菌。研究表明:长期覆盖雷竹林土壤细菌、放线菌数量与比例明显降低,真菌数量与比例明显提高,土壤养分与土壤微生物的制约性作用关系会发生较为明显变化,产生土壤障害,这是覆盖雷竹林退化的主要原因之一。     

Differences of Soil Microbial Biomass and Nitrogen Transformation under Two Forest Types in Central Germany

In order to observe the tree species effect on soil N status, soil microbial biomass C and N (C_mic, N_mic), potential N mineralization and potential nitrification (under laboratory incubation conditions, 22 °C) in different subhorizons (LOf₁, Of₂, Oh and mineral soil at 0–10 cm depth) were determined at three forest sites in central Germany. At each site, two contrasting stands (Beech, Norway spruce or Scots pine) were selected, where the initial soil conditions were similar. Three sampling dates that represented different stages of tree growth were selected: growing season - August, dormant season - November, after budbreak – April. In organic layers, C_mic-to-total C (C_t) ratios under beech and under conifer were 0.72–4.74% and 0.34–2.11%, respectively. N_mic-to-total N (N_t) ratios were 2.47–11.61% and 0.71–5.77%, respectively. Both concentrations of C_mic and N_mic were significantly affected by the stand type and sampling time. Potential N mineralization rates, ranging from 3.7 to 19.7 mg N kg⁻¹ d⁻¹, showed no clear pattern in relation to stand type. However, potential nitrification rates were mostly significantly higher under beech than under contrasting conifer. In mineral soils, concentrations of C_mic and N_mic showed a clear temporal pattern in the order: August>November>April. The average N_mic and N_mic-to-N_t were higher in soils from beech than conifer, while C_mic and C_mic-to-C_t ratios were similar between the two forest types. In organic layers, the highest values of C_mic-to-N_mic ratio and C_mic were found in November samples, especially under beech. By contrast, in mineral soils the highest value of C_mic-to-N_mic ratios were found in April samples, and at that time the C_mic concentrations were the lowest, especially under conifer. These results revealed the differences in microbial growth form and survival strategy associated with different tree species and soil layers.     

Microbial diversity of topographical gradient profiles in Fushan forest soils of Taiwan

To evaluate the microbial diversity of Fushan forest soils, the variation of soil properties, microbial populations, and soil DNA with soil depth in three sites of different altitude were analyzed. Microbial population, moisture content, total organic carbon (C_org), and total nitrogen (N_tot) decreased with increasing soil depth. The valley site had the lowest microbial populations among the three tested sites due to the low organic matter content. Bacterial population was the highest among the microbial populations. The ratios of cellulolytic microbes to the total bacteria in organic layers were high, implying their roles in the carbon cycle. The microbial biomass carbon (C_mic) and nitrogen (N_mic) contents ranged from 130.5 to 564.1 μg g⁻¹ and from 16.7 to 95.4 μg g⁻¹, respectively. The valley had the lowest C_mic and N_mic. The organic layer had the highest C_mic and N_mic and decreased with soil depth. Analysis using denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR) amplicons of 16S rDNA showed that the bacterial diversity of the three sites were very similar to each other in the major bands, and the variation was in the minor bands. However, the patterns in PCR-DGGE profile through gradient horizons were different, indicating the prevalence of specific microbes at different horizons. These results suggest that the microbial diversity in the deeper horizons is not simply the diluted analogs of the surface soils and that some microbes dominate only in the deeper horizons. Topography influenced the quantity and diversity of microbial populations.     

蚂蚁筑巢对西双版纳热带森林土壤有机氮矿化的影响

蚂蚁作为生态系统工程师能够调节土壤微生物及理化环境,进而对热带森林土壤有机氮矿化速率及其时间动态产生显著影响。以西双版纳白背桐热带森林群落为研究对象,采用室内需氧培养法测定土壤有机氮矿化速率,比较蚁巢和非蚁巢土壤有机氮矿化速率的时间动态,揭示蚂蚁筑巢活动引起土壤无机氮库、微生物生物量碳及化学性质改变对有机氮矿化速率时间动态的影响。结果表明：（1）蚂蚁筑巢显著影响土壤有机氮矿化速率（P<0.01）,相较于非蚁巢,蚁巢土壤有机氮矿化速率提高了261%;（2）土壤有机氮矿化速率随月份推移呈明显的单峰型变化趋势,即6月最大（蚁巢1.22 mg kg^-1 d^-1、非蚁巢0.41 mg kg^-1 d^-1）,12月最小（蚁巢0.82 mg kg^-1 d^-1、非蚁巢0.18 mg kg^-1 d^-1）;（3）两因素方差分析表明,不同月份及不同处理对土壤有机氮矿化速率、NH₄-N及NO₃-N产生显著影响（P<0.05）,但对NO₃-N的交互作用不显著;（4）蚂蚁筑巢显著提高了无机氮库（NH₄-N与NO₃-N）、微生物生物量碳、有机质、水解氮、全氮及易氧化有机碳等土壤养分含量,而降低了土壤pH值;（5）回归分析表明,铵态氮和硝态氮对土壤有机氮矿化速率产生显著影响,分别解释87.89%、61.84%的有机氮矿化速率变化;（6）主成份分析表明NH₄-N、微生物生物量碳及有机质是影响有机氮矿化速率时间动态的主要因素,而全氮、NO₃-N、易氧化有机碳、水解氮及pH对土壤有机氮矿化速率的影响次之,且pH与土壤有机氮矿化速率呈显著负相关。总之,蚂蚁筑巢活动主要通过影响土壤NH₄-N、微生物生物量碳及有机质的状况,进而调控西双版纳热带森林土壤有机氮矿化速率的时间动态。研究结果将有助于进一步提高对土壤氮矿化生物调控机制的认识。     

Soil Amendment with <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis> CHA0: Lasting Effects on Soil Biological Properties in Soils Low in Microbial Biomass and Activity

Pseudomonas fluorescens strains are used in agriculture as plant growth-promoting rhizobacteria (PGPR). Nontarget effects of released organisms should be analyzed prior to their large-scale use, and methods should be available to sensitively detect possible changes in the environments the organism is released to. According to ecological theory, microbial communities with a greater diversity should be less susceptible to disturbance by invading organisms. Based on this principle, we laid out a pot experiment with field-derived soils different in their microbial biomass and activity due to long-term management on similar parent geological material (loess). We investigated the survival of P. fluorescens CHA0 that carried a resistance toward rifampicine and the duration of potential changes of the soil microflora caused by the inoculation with the bacterium at the sowing date of spring wheat. Soil microbial biomass (C _mic, N _mic) basal soil respiration (BR), qCO₂, dehydrogenase activity (DHA), bacterial plate counts, mycorrhiza root colonization, and community level substrate utilization were analyzed after 18 and 60 days. At the initial stage, soils were clearly different with respect to most of the parameters measured, and a time-dependent effect between the first and the second set point were attributable to wheat growth and the influence of roots. The effect of the inoculum was small and merely transient, though significant long-term changes were found in soils with a relatively low level of microbial biomass. Community level substrate utilization as an indicator of changes in microbial community structure was mainly changed by the growth of wheat, while other experimental factors were negligible. The sensitivity of the applied methods to distinguish the experimental soils was in decreasing order N _mic, DHA, C _mic, and qCO₂. Besides the selective enumeration of P. fluorescens CHA0 rif⁺, which was only found in amended soils, methods to distinguish the inoculum effect were DHA, C _mic, and the ratio of C _mic to N _mic. The sampling time was most sensitively indicated by N _mic, DHA, C _mic, and qCO₂. Our data support the hypothesis—based on ecosystem theory—that a rich microflora is buffering changes due to invading species. In other words, a soil-derived bacterium was more effective in a relatively poor soil than in soils that are rich in microorganisms.