黄土丘陵沟壑区刺槐混交林生态化学计量特征与碳储量

为了探讨混交林与纯林养分状况和固碳能力的差异,以黄土丘陵沟壑区刺槐(Robinia pseudoacacia)纯林、油松(Pinus tabuliformis)纯林以及刺槐+油松(Robinia pseudoacacia+Pinus tabuliformis)混交林、刺槐+山杨(Robinia pseudoacacia+Populus davidiana)混交林为对象,通过野外调查和室内分析相结合的方式,研究混交林与纯林生态系统的生态化学计量特征与碳储量。结果表明:(1)刺槐+油松混交林显著增加刺槐枝和根的C含量和叶、干的P含量及枝的C:P与N:P,并显著增加油松叶、枝和根的N含量和枝、干、根的N:P,但显著降低油松各器官的C:N,而刺槐+山杨混交林仅显著增加刺槐枝的P含量。(2)刺槐+油松混交林的土壤C含量显著高于刺槐纯林,土壤P含量显著低于油松纯林;刺槐+山杨混交林与刺槐纯林土壤P含量差异不显著。(3)总体纯林中乔木叶片与凋落物的C含量显著相关,C:N、C:P在乔叶-凋落物-土壤中均显著相关;但在总体混交林中仅有凋落物与土壤中的P含量与C:P显著相关。(4)刺槐+山杨混交林乔木层碳储量显著高于刺槐纯林,刺槐+油松混交林林下植被层与土壤层碳储量显著高于刺槐纯林。研究结果为深入了解黄土高原养分循环机制奠定基础,同时也为黄土高原人工林的经营管理提供理论依据。     

黄土高原刺槐林不同组分生态化学计量关系研究

碳、氮、磷生态化学计量比是生态系统过程和功能的重要特征。刺槐具有生长快、适应性强、耐干旱贫瘠等特点,是黄土高原区水土保持造林的主要树种,以黄土高原刺槐林为研究对象,研究其不同坡向叶片-枯落物-土壤间的碳氮磷生态化学计量学特征,并对其相关性进行分析。结果表明,在阴坡和阳坡,C∶N表现为叶片枯落物土壤,C∶P,N∶P表现为枯落物叶片土壤;叶片、枯落物、土壤C∶N、C∶P、N∶P在阴阳坡均无显著性差异(p0.05),但叶片、枯落物、土壤在两两之间均有显著性差异(p0.05)。土壤的C∶N、C∶P、N∶P均表现为0~10cm10~20cm层,但差异性不显著。不论在阴坡或阳坡,叶片与枯落物的C∶N均为正相关(p0.05);在阳坡,叶片与枯落物的N∶P相关性显著;在阴坡,枯落物与0~10cm土壤的C∶N为显著正相关(p0.05)。     

山西省油松林生态系统碳氮磷化学计量特征

为了评价山西省油松林生态系统的生态化学计量特征,以山西省油松人工幼龄林(AY)、人工中龄林(AM)、天然幼龄林(NY)和天然中龄林(NM)为研究对象,通过38块标准地实测数据,探讨了4种森林类型的化学计量特征。结果显示:1)AY,AM,NY和NM乔木叶片的C∶N∶P分别为276∶8∶1,283∶8∶1,458∶12∶1和362∶11∶1,灌木叶片的C∶N∶P分别为181∶11∶1,132∶8∶1,228∶9∶1和221∶15∶1,草本叶片的C∶N∶P分别为211∶8∶1,200∶9∶1,190∶8∶1和230∶11∶1,凋落物的C∶N∶P分别为347∶3∶1,246∶5∶1,507∶9∶1和327∶9∶1,土壤(0—100cm)的C∶N∶P分别为23∶6∶1,37∶7∶1,28∶6∶1和30∶5∶1;2)4种类型的C∶N和C∶P基本都表现为凋落物叶片土壤,凋落物和叶片的C∶N和C∶P表现为AYAM,NYNM,土壤的C∶N和C∶P则为AMAY,NMNY,而N∶P则表现为叶片凋落物土壤,在林龄上表现规律不明显,植物叶片N∶P14,存在N限制;3)4种类型植物叶片C∶P均表现为乔木叶片草本叶片灌木叶片,表明油松林生态系统中乔木叶建成效率最高,而灌木叶建成效率最低;4)4种类型土壤层随着土层厚度的增加,C∶N表现出下降规律,C∶P和N∶P规律表现不明显。研究结果表明,4种生态系统的叶片、凋落物和土壤的化学计量特征具有一致性。     

黄土高原不同植被带刺槐生态化学计量特征

为阐释刺槐(Robinia pseudoacacia)人工林在不同植被带下的化学计量特征,明确气候因素对其的影响,采用样地调查与实验室分析结合处理的方法对黄土高原森林带、森林草原带、草原带中刺槐人工林的叶片、枯落物及土壤进行C,N,P含量测定,分析了化学计量比,同时剖析了气候因子与各元素之间的关系。结果表明:(1)不同组分C,N,P含量差异均显著,表现为叶片枯落物土壤,各植被带内养分含量表现各异,其中森林草原带叶片与土壤养分含量处于最高水平。(2)同植被带C/P与N/P均呈现出叶片与枯落物显著高于土壤的趋势,而植被带间各组分化学计量比差异程度不同。(3)各植被带养分含量在叶片—枯落物—土壤间均具有一定的相关性,表明养分在生态系统内持续流动。(4)叶片C,N,P含量随着年均降水(MAP)和年均温度(MAT)的升高而降低,而枯落物与之表现出相反的趋势,土壤养分随年均太阳辐射量(MASR)增大而降低。研究结果为深入探索黄土高原刺槐人工林养分在空间上的耦合机制提供一定的参考依据。     

氮添加对华北落叶松叶片化学计量与养分重吸收效率的影响

为了解华北落叶松林叶片化学计量特征和养分重吸收效率与N素供应的关系,以24年生华北落叶松人工林为研究对象,设置3个水平(0,8,15 g/(m~2·a))连续6年的野外氮添加控制试验,测定氮添加后华北落叶松成熟叶片、凋落叶片和林分土壤养分含量的变化。结果表明:成熟叶片C含量在年际间差异显著(P0.05),氮添加显著增加成熟叶2016—2018年的C、N含量,降低2018年的P含量,导致2018年N/P在轻度氮添加下比对照增加20.20%,重度氮添加下增加34.43%,2018年N/P在重度氮添加下出现峰值20.50,表明氮添加在一定程度上驱动该林分生长的P养分限制;凋落叶中的C、N、P含量及化学计量在年际间和氮添加处理下均呈显著差异(P0.05),氮添加显著增加凋落叶2016—2018年的C含量、C/P和N/P,显著降低2016—2018年的P含量;2016—2018年,轻度氮添加下NRE(氮重吸收效率)和NRE/PRE(氮重吸收效率/磷重吸收效率)显著降低,氮添加下PRE(磷重吸收效率)显著增加;相关分析表明,NRE与凋落叶N含量,PRE与凋落叶P含量呈显著负相关,相关系数分别为-0.860和-0.772;氮添加显著增加土壤有效氮的含量,降低土壤pH(除2016年)和速效磷含量。氮添加导致华北山地针叶林树木生长受不同程度的P养分限制,推测氮添加驱动的林分受P限制可能与该区土壤养分初始状况有关,为全球气候变化下森林的养分管理提供参考依据。     

黄河三角洲不同人工刺槐混交林凋落物分解特性

为研究黄河三角洲不同人工刺槐混交林凋落物分解特性,选取白蜡刺槐混交林、臭椿刺槐混交林、国槐刺槐混交林、榆树刺槐混交林4种混交林,采用凋落物袋法进行为期1年8月的凋落物分解特性研究。结果表明:4种混交林凋落物分解速率变化规律相似,前期分解较快,后期分解较慢。4种混交林凋落物分解系数介于0.55~0.74,其中臭椿刺槐混交林凋落物分解系数最高,榆树刺槐混交林最低;臭椿刺槐混交林凋落物分解周期最短为4.03a,榆树刺槐混交林最长为5.47a。4种混交林凋落物中N、P、K、木质素含量以及木质素/N差异显著(P0.05),凋落物分解速率与其N、P含量呈显著正相关关系,与K含量以及C/N呈显著负相关关系。混交林土壤pH、含水量与凋落物分解系数呈显著正相关关系;电导率、碱解氮、有效磷、速效钾含量与凋落物分解系数呈显著负相关关系,表明土壤pH、含水量升高有利于凋落物分解,而电导率、碱解氮、有效磷、速效钾含量升高则减缓凋落物分解。     

祁连山青海云杉林叶片—枯落物—土壤的碳氮磷生态化学计量特征

以祁连山排露沟流域青海云杉(Picea crassifolia)林为研究对象,研究其不同海拔梯度叶片—枯落物—土壤间的碳、氮、磷生态化学计量学特征,并对其相关性进行分析。结果表明,在不同海拔梯度上,叶片、枯落物和土壤C∶N比的变化范围分别为22.95~36.72、21.41~41.61、12.41~20.70,均值大小依次为枯落物叶片土壤,C∶P和N∶P比的变化范围分别为510.2~739.8、398.6~698.1、134.1~219.7和18.13~26.86、6.71~26.28、7.96~16.56,均值大小依次均为叶片枯落物土壤。随海拔梯度的增加,除土壤C∶N比差异性不显著外(p0.05),叶片和枯落物的碳、氮、磷化学计量比在不同海拔间的差异显著性各不相同。叶片、枯落物和土壤C∶N比两两均具有显著正相关(p0.05),叶片与枯落物及土壤与枯落物C∶P比均具有显著负相关(p0.05),叶片与土壤C∶P比及不同组分N∶P比之间相关性均不显著(p0.05)。该研究结果有助于进一步了解青海云杉林碳、氮、磷在不同组分间的相互作用规律与机制。     

子午岭林区两种天然次生林叶片C、N、P化学计量特征的季节变化

为阐明不同天然林叶片C、N、P化学计量特征及季节变化规律,了解植物对环境的适应策略,以陕西省子午岭林区桥山林场的油松和辽东栎天然次生林为研究对象,对其生长季内不同月份叶片的C、N、P含量及其计量比进行了分析。结果表明:(1)油松叶片C、N、P含量及其计量比分别为48.06%,1.15%,0.11%和42.58,473.22,11.02,辽东栎叶片C、N、P含量及其计量比分别为43.16%,2.10%,0.19%和25.47,380.18,14.49;两树种叶片各指标季节间变异系数表现为C含量最小,P含量最大。(2)两树种叶片C、N、P含量及其计量比在整个生长季内的变化规律不一致,油松叶片C含量在4—6月显著下降,之后保持平稳状态,8月后显著上升,至10月基本与4月持平;而辽东栎叶片C含量在整个生长季内变化不明显。油松叶片N含量在6月前较稳定,6—8月显著下降,随后显著上升,至10月基本与6月持平;辽东栎叶片N含量在4—6月显著下降,随后保持稳定,8月后再次显著下降,并在10月达到最低值。油松叶片P含量在8月前变化不明显,8月后显著上升,并在10月达到最高值;辽东栎叶片P含量在4月到6月显著下降,随后基本不变。两树种C∶N和C∶P的变化与N、P浓度相反;油松叶片N∶P在4—6月显著下降,6—8月显著上升,8—10月再次显著下降,辽东栎叶片N∶P在6月前显著上升并达到最高值,6—10月显著下降。(3)叶片C含量和C∶N主要受树种的影响,其他各指标受树种与月份交互作用的影响最大。(4)油松叶片C含量显著高于辽东栎,N含量显著低于辽东栎,因此,C∶N显著高于辽东栎,而辽东栎叶片的N∶P显著高于油松,但P含量和C∶P在两者之间无显著性差异。除叶片C含量外,各指标季节间变异系数均表现为油松小于辽东栎。研究结果丰富了天然林生态化学计量学的研究,同时也为黄土丘陵沟壑区的森林恢复与管理工作提供了一定的理论依据。     

云雾山草地植物地上部分和枯落物的碳、氮、磷生态化学计量特征

碳(C)、氮(N)、磷(P)生态化学计量比是生态系统过程和功能的重要特征。为探究云雾山天然草地30年恢复演替过程中不同封育年限植物和枯落物的全碳、全氮和全磷含量及其生态化学计量特征变化规律,以云雾山封育1、12、20、30年的天然草地为研究对象,通过典型样方调査研究了黄土高原不同封育年限植物和枯落物养分变异特征。结果表明:不同封育年限间,植物地上部分C∶N、C∶P、N∶P比变化范围分别为24.91~37.37、380.1~562.1、12.14~15.86,均值分别为32.51、473.6和14.64;枯落物C∶N、C∶P、N∶P比变化范围分别为37.18~47.11、755.5~885.9、16.41~22.31,均值分别为40.71、819.9、20.30。植物地上部分C、N、P含量间呈极显著相关(p0.01);植物地上部分P含量与C∶N、C∶P、N∶P呈极显著负相关(p0.01),与枯落物C、P、C∶P、N∶P呈极显著相关(p0.01)。云雾山植物N∶P比介于14~16之间,植物生长受氮磷共同限制,建议增加草地氮、磷肥的使用量。该研究结果有助于进一步了解云雾山草地C、N、P在不同组分间的相互作用规律与机制。     

黄土丘陵区油松人工林植物器官—凋落物—土壤化学计量特征的季节变化

为了解黄土丘陵区油松人工林植物器官—凋落物—土壤的化学计量特征随季节的变化规律，通过时空替代法、野外调查取样与室内试验的手段，以陕西省延安市安塞区纸坊沟流域中林龄油松（Pinus tabuliformis）人工林为对象，分析了4—10月油松不同器官—凋落物—土壤的碳（C）、氮（N）、磷（P）生态化学计量学特征。结果表明：（1）从4—10月，叶片C、P含量逐渐上升，在10月最高，叶片的N含量和N：P及枝的N、P含量均先减小后增大，且均在8月最低，而枝的C：N及C：P和细根的C：P、N：P均先增大后减小，且均在8月最高。土壤C、N含量、C：P、N：P先增大后减小，在8月最高。凋落物N含量、C：P和N：P均呈先降后升的趋势，在6月最低，P含量变化不显著；（2）除叶片4—6月、细根4—8月N：P>14外，其他各器官4—10月均N：P<14，该区域油松生长主要受N限制；（3）叶片与凋落物的C、N含量及C：N之间均呈显著正相关，C：N、C：P与N：P之间均呈显著正相关（p<0.05）。叶片N：P与土壤C：N呈极显著负相关（p<0.01），其他化学计量特征之间均无显著相关性。凋落物C含量与土壤P含量呈显著正相关（p<0.05）。研究结果使人工林生态化学计量学的研究更加系统性，为黄土丘陵区植被良好生长提供参考依据。     

不同人工林凋落叶混合分解速率及其C,N释放动态

对岷江上游连香树、糙皮桦、云南松和云杉4种主要人工林凋落叶进行了凋落叶混合分解试验,探讨了凋落叶混合分解过程中的残留率以及分解过程中C,N含量和C,N释放率的动态变化,为试验区最佳混交树种的选择提供理论指导.结果表明,不同凋落叶分解速率存在显著差异.糙皮桦与云杉,糙皮桦与云南松,连香树与云南松凋落叶混合后对分解过程具有明显的促进作用,连香树与云杉凋落叶的混合对分解的促进作用不明显.放置于阔叶林地的针阔混合凋落叶分解速率较之放置于针叶林地快,且针阔混交有益于凋落叶的分解.在分解过程中凋落叶C含量呈减小趋势,但其释放率反之;N含量在分解过程中,连香树、云杉、云南松凋落叶表现为增加(富集)减小(释放)趋势,糙皮桦表现为减小—增大—减小的变化趋势.针阔林地凋落叶混合后促进了针叶林地凋落叶C和N的释放.     

Rice Diversity Collection,Conservation and Management in Northeastern India

Rice is the principal crop of northeastern region of India, where a considerable range of diversity exists. The germplasm collection has also unfold the occurrence of large number of rice landraces in the region. Between 1985 and 2002, a total 2639 accessions of rice germplasms including their wild relatives have been collected. Most of these germplasm material have been conserved in the National Gene Bank, New Delhi following their necessary characterization and evaluation. With the establishment of the Regional Gene Bank Module with medium-term storage facilities (6–7°C with 40–45% relative humidity) at Barapani, Meghalaya, the rice germplasm conservation (ex situ) have been initiated in the region.     

紫花苜蓿、黑麦草和狼尾草对Cu、Pb复合污染土壤修复能力的研究

随着经济和社会的发展,土壤重金属污染对粮食安全及人类的身体健康构成了巨大的威胁,而目前对于土壤重金属污染的治理主要以植物修复为主。为了寻找适宜修复Cu、Pb复合污染土壤的牧草,采用盆栽试验法,将试验的植物设置9组处理:1组对照组(CK),不添加任何重金属盐;4组单一污染,即单一Cu低(Cu1,200 mg×kg-1)、高浓度(Cu2 400 mg×kg-1),单一Pb低(Pb1 300 mg×kg-1)、高浓度(Pb2 800 mg×kg-1);4组Cu、Pb复合污染(Cu1Pb1、Cu1Pb2、Cu2Pb1、Cu_2Pb_2)。通过比较紫花苜蓿(Medicago sativa)、黑麦草(Lolium perenne)、狼尾草(Pennisetum alopecuroides)的适应能力和富集特征,研究了这3种常见牧草植物对受Cu、Pb复合污染土壤的修复效果。结果表明:1)紫花苜蓿地上部和根部生物量均在Pb1处理组时最大,显著高于其他处理组;黑麦草地上部生物量在Cu1Pb1处理组最大,根部生物量在Pb1处理组最大;狼尾草地上部生物量在Cu_2Pb_2处理组最大,根部生物量在Cu2处理组最大。2)Cu单一污染下,狼尾草抗性系数最大;Pb单一污染下,紫花苜蓿抗性系数最大;Cu-Pb复合污染下,狼尾草的抗性系数较大。高浓度Cu处理组3种牧草植物的地上部生物量、根部生物量和抗性系数均呈现:狼尾草黑麦草紫花苜蓿,且狼尾草显著大于黑麦草和紫花苜蓿。3)种植3种牧草植物后,土壤重金属Cu、Pb含量均有所降低。在一定浓度下,土壤Cu-Pb重金属间会相互促进对方在牧草植物中的吸收。4)3种牧草中紫花苜蓿地上部对Cu的富集系数在Cu_2Pb_2处理组最大,达1.61;黑麦草根部对Cu的富集系数在Cu_2Pb_2处理组最大,达3.80;3种牧草地上部和根部对Pb的富集系数只在黑麦草根部的Cu1Pb1处理组时大于1,达1.46。5)黑麦草对Pb的吸收能力较强,且主要积累在根系;紫花苜蓿对Cu-Pb复合污染综合修复效果最好。紫花苜蓿和黑麦草分别在Cu-Pb复合污染和Pb单一污染土壤中对Pb的转运系数大于1,分别为2.72和2.06,反映其对土壤中的Pb具有富集潜力。综合表明,黑麦草对重金属Pb具有较强的耐性,在Pb单一污染土壤的植物修复及尾矿废弃地的植被重建中,可优先作为选择的材料;紫花苜蓿对重金属Cu、Pb均具有较强的耐性,在重金属Cu单一或Cu-Pb复合污染土壤的植物修复及尾矿废弃地的植被重建中,可优先作为选择的材料。     

Influence of arbuscular mycorrhizal fungi and salinity on growth,biomass, and mineral nutrition of<Emphasis Type="Italic"> Acacia auriculiformis</Emphasis>

The effect of salinity on the efficacy of two arbuscular mycorrhizal fungi, Glomus fasciculatum and G. macrocarpum, alone and in combination was investigated on growth, development and nutrition of Acacia auriculiformis. Plants were grown under different salinity levels imposed by 0.3, 0.5 and 1.0 S m^-1 solutions of 1 M NaCl. Both mycorrhizal fungi protected the host plant against the detrimental effect of salinity. The extent of AM response on growth as well as root colonization varied with fungal species, and with the level of salinity. Maximum root colonization and spore production was observed with combined inoculation, which resulted in greater plant growth at all salinity levels. AM fungal inoculated plants showed significantly higher root and shoot weights. Greater nutrient acquisition, changes in root morphology, and electrical conductivity of soil in response to AM colonization was observed, and may be possible mechanisms to protect plants from salt stress.     

Yield and N assimilation of winter wheat (Triticum aestivum L., var. Norstar) inoculated with rhizobacteria

The effects of bacterial inoculants on the growth of winter wheat were studied in a growth chamber. Azospirillum brasilense, Azotobacter chroococcum, Bacillus polymyxa, Enterobacter cloacae, or a mixture of the four rhizobacteria were the inoculants tested. Inoculation effects on yield, yield components, and N-derived from fertilizer (Ndff) were assessed. The response of plants inoculated with individual bacteria was inconsistent and varied with treatment. At the first harvest (58 days after planting-DAP) plants inoculated with the mixture exhibited increases in plant dry weight, total-N and Ndff. At the second harvest (105 DAP), plants inoculated with A. brasilense and the mixture exhibited increases in shoot biomass, whereas at maturity (170 DAP), the inoculated plants showed no differences in total-N or shoot dry matter yield, as compared to the uninoculated controls. Inoculation with A. brasilense, however, increased the Ndff in the shoots, and B. polymyxa tended to enhance grain yield. Practical use of these rhizobacteria as inoculants for winter wheat may have limited value until such time as we better understand factors which influence rhizosphere competence of bacterial inoculants.     

Trees on farms and their contribution to soil fertility parameters in Badessa, eastern Ethiopia

Surface (0–15 cm) and subsurface (30–45 cm) soil samples from under canopy, edge of canopy and away from canopy of isolated Cordia africana Lam. and Croton macrostachyus Del. trees and their leaves were examined to investigate leaf nutrient content, root biomass and the contribution of trees on farms to soil fertility parameters in Badessa area, eastern Ethiopia. Leaves of C. macrostachyus had 20% higher P and 25% lower K contents than those of C. africana. The studied species had comparable leaf N content. Both species produced shallow lateral roots that extended beyond the canopy zone. Typically, higher fine root biomass was observed in the surface soils than the subsurface soils. Both species did not affect soil organic C, pH and cation exchange capacity. Surface and subsurface soils under tree canopies had 22–26 and 12–17% higher N, respectively, than the corresponding soils away from tree canopies. Surface soil available P under tree canopies was 34–50% higher than the corresponding soil away from canopies. Available P content of subsurface soil was improved only under C. africana canopy. The available P of surface soil under C. macrostachyus canopy was more than double that for C. africana. Trees of both species increased underneath surface and subsurface exchangeable K by 18–46% compared with the corresponding controls. In conclusion, C. macrostachyus and C. africana trees on farms keep soil nutrient high via protection against leaching, translocation of nutrients from deeper to the surface layer and accumulation of litter, which create a temporary nutrient pool in the surface soils under their canopies.     

Interactions between climate, beaver activity, and pond occupancy by the cold-adapted mink frog in New York State, USA

Mink frogs (Rana septentrionalis) are cold-adapted, climate-sensitive amphibians occurring above the 43rd parallel in North America. We conducted repeated night call surveys at 46 ponds near the southern edge of the species’ range to collect presence/absence data and used information-theoretic models to relate pond occupancy to historical climate and habitat factors. Mink frog occurrence was strongly and positively influenced by pond size (>1.5 ha) and the presence of beavers (Castor canadensis). Presence of calling mink frogs decreased sharply at sites with historical mean July air temperatures >19.5 °C. Our results suggest that predicted changes in temperature over the next century might reduce the range of mink frogs in New York, yet we hypothesize that any such reductions could be mitigated by generation of suitable breeding habitat associated with future expansion of beaver populations.     

Growth of Lumbricus terrestris and Aporrectodea caliginosa in an acid forest soil, and their effects on enchytraeid populations and soil properties

A laboratory experiment was carried out to test the hypothesis that the earthworms Lumbricus terrestris and Aporrectodea caliginosa are able to maintain their populations and reproduce in the acid forest soil of a deciduous forest where no lumbricids were found in the field. The experiment was conducted in 45-l containers in which layers of mineral subsoil, humus and organic topsoil collected from the site were established. Both species survived and at least L. terrestris reproduced during the 60 weeks’ incubation. Burrows and middens of L. terrestris were recorded and quantities of litter were consumed. The presence of lumbricids increased the organic matter content of humus, reduced the acidity of the topsoil and humus layers, and suppressed the population of the enchytraeid Cognettia sphagnetorum. A dense population of Enchytraeus albidus was found in L. terrestris middens. It is concluded that edaphic factors do not explain the absence of earthworms, but isolation from cultural landscapes and lack of opportunity to colonize the site from the surroundings is the decisive factor.     

Factors related to the distribution and prevalence of the fungal pathogen Batrachochytrium dendrobatidis in Rana cascadae and other amphibians in the Klamath Mountains

The fungal pathogen Batrachochytrium dendrobatidis (Bd), which causes the disease chytridiomycosis, has been associated with declines and extinctions of montane amphibians worldwide. To gain insight into factors affecting its distribution and prevalence we focus on the amphibian community of the Klamath Mountains in northwest California. The Cascades frog (Rana cascadae), one of the most common amphibians in these mountains, experienced increased mortality as a result of Bd exposure in laboratory trials and has experienced recent, dramatic declines in other parts of California. We surveyed 112 sites in the Klamaths, all of which supported R. cascadae between 1999 and 2002, for amphibians and Bd to (1) determine the distribution of Bd, (2) evaluate changes in the distribution of R. cascadae, and (3) assess associations between potential biotic and abiotic drivers and Bd infection. Bd was widely distributed in the Klamath Mountains – we detected the pathogen at 64% of sites. R. cascadae was found at 79% of sites, and was often infected with Bd. These results suggest that Bd has not caused dramatic declines in R. cascadae in the Klamaths in recent years. Subadult R. cascadae had a higher Bd prevalence than other R. cascadae life stages (subadults: 36%, adults: 25%, metamorphs: 4%, larvae: 1%), and while the probability of infection decreased over the season for adults, it did not for subadults, suggesting that subadults may be more vulnerable to chytridiomycosis than other R. cascadae life stages. Bd prevalence in R. cascadae was highest early in the season at high-elevation sites, which may indicate that populations inhabiting high elevation sites may have a greater risk of being affected by chytridiomycosis. Three other common amphibian species also tested positive for Bd: Pacific chorus frog (Pseudacris regilla), western toad (Anaxyrus boreas), and rough-skinned newt (Taricha granulosa).