Effects of forest gap size on initial decomposition of twig litter in the subalpine forest of western Sichuan,China

林窗调控的土壤水热环境和分解者群落结构可能深刻影响凋落物分解过程, 已有的研究结果具有不确定性。为了解高海拔森林林窗面积对凋落枝分解的影响, 采用凋落物分解袋法, 于2012-2016年冬季和生长季节, 研究了川西亚高山森林255-290 m ²(FG1)、153-176 m ²(FG2)、38-46 m ²(FG3) 3种面积林窗和林下对岷江冷杉(Abies faxoniana)凋落枝质量损失的影响。结果显示: 林窗面积大小显著改变了林窗和林下的雪被厚度、温度和冻融循环频次; 雪被厚度和温度以FG1林窗最高, 林下最低; FG1、FG2、FG3林窗和林下枝条分解4年后的质量残留率分别为59.9%、59.5%、62.1%和55.3%, 分解系数k值分别为0.127、0.131、0.120和0.135, 95%分解时间分别为23.6、22.7、25.0和22.2 a; 与林下相比, 林窗显著增加了第一年和第二年生长季节的质量损失速率, 降低了第一年和第四年冬季的枝条质量损失速率; 林窗大小对质量损失速率的影响随分解时期变化差异明显, 质量损失速率在第一年和第三年冬季随林窗面积增大而增大, 在第三年生长季节随林窗面积增大而降低; 枝条质量损失的比例在第一年最高, 随林窗面积增加而增加, 且冬季高于生长季节。综上所述, 林窗环境变化深刻影响亚高山森林凋落枝分解, 但这种影响随林窗面积和分解时间有所差异。     

Patterns of leaf surface wetness for montane and subalpine plants

The frequency and duration of water on leaf surfaces have important consequences for plant growth and photosynthetic gas exchange. The objective of the present study was to compare the frequency and duration of leaf wetness under natural field conditions among species and to identify variation in structural features of leaves that may reduce surface wetness. During June–September 1992 in the central Rocky Mountains (USA), natural leaf wetting due to rain and dewfall was observed on 79 of 89 nights in open meadow habitats compared to only 29 of 89 nights in the understorey. Dew formation occurred at relative humidities that were often well below 100% because of radiational heat exchange with cold night skies and low wind speeds (< 0.5 m s^?1). A survey of 50 subalpine/montane species showed that structural characteristics associated with the occurrence and duration of leaf surface wetness differed among species and habitats. Both adaxial and abaxial surfaces accumulated moisture during rain and dewfall events. Leaf surfaces of open-meadow species were less wettable (P= 0.008), and had lower droplet retention (P= 0.015) and more stomata P= 0.017) than adjacent understorey species. Also, leaf trichomes reduced the area of leaf surface covered by moisture. Ecophysiological importance is suggested by the high frequency of leaf wetting events in open microsites, influences on growth and gas exchange, and correspondence between leaf surface wettability and habitat.     

Factors Related to the Recovery of Subalpine Woodland on Mauna Kea,Hawaii1

We measured mature tree and sapling density, tree associations, crown size, age structure, recovery from ungulate browsing, and grass cover at four study sites in two types of subalpine woodland on Mauna Kea volcano, island of Hawaii. Beginning in 1981, introduced ungulates were reduced in number to allow regeneration of Sophora chrysophylla (mamane) in habitat supporting the endangered Hawaiian finch, Loxioides bailleui (palila). We found Sophora regeneration at all four study sites, but regeneration was higher in mixed species woodland with codominant Myoporum sandwicense (naio) than in areas where Sophora dominated. Regeneration of Myoporum was uniformly very low in comparison. Invasive grass cover, which suppresses Sophora germination, was highest in mid-elevation woodland where Sophora dominated. The distribution of mature and sapling Sophora were both related to study site, reflecting previous ungulate browsing and uneven recovery due to grasses. Densities of Sophora snags were not different among any of the sites, suggesting a more even distribution in the past. Selective browsing before ungulate reduction may have favored Myoporum over Sophora, leading to high densities of mature Myoporum in codominant woodland. After ungulate reduction, however, we found no pattern of competitive inhibition by Myoporum on regeneration of Sophora. Reduction of Myoporum is not likely to enhance habitat for Loxioides as much as supplemental plantings of Sophora, glass control, and continued ungulate eradication. Mid-elevation Sophora woodland areas, where Loxioides forage and nest in high densities, would benefit the most from these management actions.     

Spatio-temporal characteristics of vegetation water use efficiency and their relationships with climatic factors in alpine and subalpine area of southwestern China

水分利用效率(WUE)是深入理解生态系统水碳循环及其耦合关系的重要指标。为了揭示气候变化背景下区域尺度不同植被类型的响应和适应特征, 对中国西南高山亚高山地区2000-2014年的9种植被类型的WUE时空特征及其影响因素进行探究。该研究基于MODIS总初级生产力(GPP)、蒸散发(ET)数据和气象数据, 估算西南高山亚高山区植被WUE, 采用趋势分析及相关分析等方法, 分析了研究区植被WUE与气温、降水及海拔的关系。主要结果: (1)西南高山亚高山区2000-2014年植被WUE多年均值为0.95 g·m^-2·mm^-1, 整体呈显著增加趋势, 增速为0.011 g·m^-2·mm^-1·a^-1; 空间上WUE呈东南高西北低的分布, 85.84%区域的WUE呈增加趋势。(2)西南高山亚高山区各植被类型WUE多年均值表现为常绿针叶林>稀树草原>常绿阔叶林>有林草原>农田>落叶阔叶林>混交林>郁闭灌丛>草地; 时间上, 各植被类型WUE均呈上升趋势。(3)西南高山亚高山区89.56%区域的WUE与气温正相关, 92.54%区域的WUE与降水量负相关; 各植被类型中, 草地WUE与气温的相关性最高, 有林草原WUE与降水量的相关性最高。(4)西南高山亚高山区典型的地带性顶极植被常绿针叶林的WUE具有较强的海拔适应性及应对气候变化的能力。     

亚高山森林林窗大小对凋落叶木质素降解的影响

木质素降解是认识高寒森林凋落物分解过程的关键环节,可能受到林窗大小及其在不同季节水热环境的影响。采用分解袋法,研究了川西亚高山森林不同面积大小林窗下红桦(Betula albo-sinensis)和岷江冷杉(Abies faxoniana)凋落叶在初冻期、深冻期、融化期、生长季节初期、生长季节中期和生长季节后期的木质素分解动态特征。研究结果表明,采样时间和林窗面积大小对两种凋落叶的木质素降解均有显著影响。经历1a分解,红桦凋落叶的木质素降解了21.53%—27.65%,而岷江冷杉凋落叶的木质素富集了7.95%—19.40%。较大林窗促进了冬季岷江冷杉凋落叶和生长季节红桦凋落叶木质素的降解,抑制了冬季红桦凋落叶木质素的降解;而生长季节岷江冷杉凋落叶木质素富集速率则为林下大林窗中林窗小林窗。逐步回归分析表明,凋落叶木质素的降解过程在冬季主要受到负积温和土壤冻融循环次数的影响(木质素结构的物理破碎),而在生长季节则主要受到平均温度和正积温的影响(木质素的生物降解)。可见,川西亚高山森林木质素降解受林窗格局变化的显著影响,且林窗大小对凋落叶木质素降解的影响与物种和分解时期有关。     

萘对川西亚高山森林土壤微生物量、丰度和磷脂脂肪酸的影响

萘作为土壤动物化学抑制剂已在土壤动物生态功能的研究中广泛使用,但其非目标效应使其应用仍存在很大的不确定性。为了解在亚高山森林土壤应用萘抑制土壤动物群落的非目标效应,以川西亚高山森林土壤为研究对象,采用微缩实验研究了土壤微生物生物量、丰度和磷脂脂肪酸对萘胁迫的短期响应。结果表明,萘处理和对照的土壤微生物生物量碳(MBC)、真菌丰度以及细菌、真菌、革兰氏阳性菌(G~+)和革兰氏阴性菌(G~-)PLFAs含量在整个培养期间表现为降低的变化趋势,二者的土壤微生物生物量碳和G~+PLFAs含量以培养52d最低,细菌、真菌和G~-PLFAs含量以培养的45d最低。萘处理和对照的微生物生物量氮(MBN)含量表现出先升高后降低的动态,微生物生物量碳氮比(MBC/MBN)则表现为相反趋势。对照的真菌/细菌PLFAs比值呈现先升高后降低的动态,以培养的17d最高,但萘处理的真菌/细菌PLFAs比值无明显变化规律;萘处理的G~+/G~-PLFAs比值表现为降低的变化趋势,对照的G~+/G~-PLFAs比值表现为先降低后升高的趋势。萘处理仅显著影响了G~+/G~-PLFAs比值,但萘处理和采样时间的交互作用显著影响MBC/MBN、细菌丰度、真菌/细菌丰度比以及细菌、真菌的PLFAs含量、真菌/细菌PLFAs比值、G~+/G~-PLFAs比值。萘作为土壤动物抑制剂对川西亚高山森林土壤微生物群落的非目标效应具有时间变异性。     

夜间增温对亚高山针叶林主要树种无机氮吸收的影响

吸收营养物质是植物根系的主要生理功能。氮素吸收是植物体内氮代谢的第一步, 也是最关键的一步。为了全面地认识亚高山针叶林在全球气候变化背景下对两种主要无机氮(NH₄⁺和NO₃^-)吸收特点的变化, 该研究以川西亚高山针叶林优势树种——云杉(Picea asperata)和岷江冷杉(Abies fargesii var. faxoniana)为材料, 通过红外辐射加热器模拟增温, 利用非损伤微测技术(non-invasive micromeasurement technology)研究了这两个树种吸收NH₄⁺和NO₃^-特点的变化, 同时还探究了NH₄⁺和NO₃^- 之间的相互作用对植物吸收这两种离子的影响。研究结果显示: 在云杉根系中, NH₄⁺和NO₃^-的最大吸收速率分别发生在距离根尖最顶端17-18 mm区域和17 mm处, 而岷江冷杉对这两种离子的最大吸收速率分别发生在距离根尖顶端11 mm和11.5 mm处。增温对云杉和岷江冷杉根系吸收NH₄⁺和NO₃^-有促进作用。在增温条件下, NO₃^-能够促进云杉根系对NH₄⁺的吸收, 而NH₄⁺则抑制了其对NO₃^-的吸收。无论是否增温, 岷江冷杉对NH₄⁺的吸收都不受NO₃^-的影响, 而在增温条件下, NH₄⁺会抑制岷江冷杉对NO₃^-的吸收。     

关帝山亚高山灌丛草甸群落优势种群的生态位研究

采用定量分析方法对关帝山亚高山草甸灌丛群落中的13个主要种群进行了生态位研究。首先运用TWINSPAN把33个样方分为5个群落类型,作为5个综合资源位,用Levins、Shannon—wiener生态位宽度公式和Petraitis生态位特定重叠指数公式测定群落中主要种群生态位宽度和生态位重叠,并分析各种群生态位的生态学意义。结果表明,种群生态位宽度越大,对环境的适应能力越强,对资源的利用能力也越强;生态位重叠越大,种群间的生态相似性越大,利用资源的相似性程度越高;生态位宽的种群对生态位窄的种群可能有较高的重叠值,反之则较低。     

Microbial communities and activities in alpine and subalpine soils

Soil samples were collected along two slopes (south and north) at subalpine (1500–1900 m, under closed vegetation, up to the forest line) and alpine altitudes (2300–2530, under scattered vegetation, above the forest line) in the Grossglockner mountain area (Austrian central Alps). Soils were analyzed for a number of properties, including physical and chemical soil properties, microbial activity and microbial communities that were investigated using culture-dependent (viable heterotrophic bacteria) and culture-independent methods (phospholipid fatty acid analysis, FISH). Alpine soils were characterized by significantly ( P <0.01) colder climate conditions, i.e. lower mean annual air and soil temperatures, more frost and ice days and higher precipitation, compared with subalpine soils. Microbial activity (soil dehydrogenase activity) decreased with altitude; however, dehydrogenase activity was better adapted to cold in alpine soils compared with subalpine soils, as shown by the lower apparent optimum temperature for activity (30 vs. 37 °C) and the significantly ( P <0.01–0.001) higher relative activity in the low-temperature range. With increasing altitude, i.e. in alpine soils, a significant ( P <0.05–0.01) increase in the relative amount of culturable psychrophilic heterotrophic bacteria, in the relative amount of the fungal population and in the relative amount of Gram-negative bacteria was found, which indicates shifts in microbial community composition with altitude.     

季节性冻融期间亚高山森林凋落物的质量损失及元素释放

季节性冻融期间的凋落物分解对季节性冻土区的森林生态系统过程可能具有重要的影响,但已有的研究报道很少.因此,采用凋落物分解袋法研究了岷江冷杉 (Abies faxoniana Rehder & E. H. Wilson)林和白桦(Betula platyphylla Sukaczev)林凋落叶的分解.一个季节性冻融期间,冷杉林和白桦林凋落物的质量损失率分别为(19.4 ±2.0)%和(21.5±3.5)%,约为1a中凋落物分解的64.5%和65.6%,表明季节性冻融对亚高山森林凋落物分解影响显著.冷杉凋落物中C、N、P、K、Ca和Mg的释放率为(15.0±1.0)%、(34.1±3.6)%、(17.0±0.9)%、(22.8±5.9)%、(20.1±0.1)%和(36.3±2.1)%,白桦凋落物中C、N、P、K、Ca和Mg的释放率为(20.7±0.1)%、(29.4±3.4) %、(15.7±1.3)%、(16.8±5.1)%、(21.3±1.8)%和(20.5±2 8)%.结合叶凋落物产量可以推断,冷杉林凋落物在一个季节性冻融期间释放到土壤的N、P、K、Ca、Mg为(10.17±1.14) kg · hm-2、(0.68±0.08) kg · hm-2、(4.08±0.46) kg · hm-2、(0.46±0.05) kg · hm-2、(0.09±0.01) kg · hm-2,白桦林为(5.61±1 12) kg · hm-2、(0.34±0.07) kg · hm-2、(1.21±0.24) kg · hm-2、(0.300±0.059) kg · hm-2、(0.051±0.010) kg · hm-2,这对于春季亚高山森林植物生长具有重要的生态学意义.