沙坡头人工固沙区的种子库动态

沙坡头人工固沙区的土壤种子库中共有４６种植物的种子,属于１７个科。其中菊科植物最多,达１１种;其次为藜科,７种;禾本科７种;豆科４种。既是现有植被组分种,其种子又存在于种子库中的,占总种数的３３．３％ 。油蒿（Ａｒｔｅｍ ｉｓｉａ ｏｒｄｏｓｉｃａ）、花棒（Ｈｅｄｙｓａｒｕｍ ｓｃｏｐａｒｉｕｍ ）和柠条（Ｃａｒａｇａｎａ ｋｏｒｓｈｉｎｓｋｉｉ）的种子产量为５４５±６７６．７３粒／ｍ ２、６．６７±１３．７４粒／ｍ ２、０．０３２±２．４３×１０－ ３粒／ｍ ２。油蒿在植株上成熟时不受虫害,而花棒、柠条的种子受害比例分别为３１．９２％ 和８３．２９％ 。在最适埋藏深度下,油蒿、柠条、花棒种子的累积发芽率分别可达７８．３％ 、８５．０％ 和６６．７％ ;萌发速度：油蒿＞ 柠条＞ 花棒。根据种子库动态分析和植被调查结果可初步预测：沙坡头人工固沙植被的演替趋向将是灌木以油蒿为主,草本以雾冰藜（Ｂａｓｓｉａ ｄａｓｙｐｈｙｌｌａ）、小画眉草（Ｅｒａｇｒｏｓｔｉｓｐｏａｅｏｉｄｅｓ）为主的群落     

Streamflow-induced variations in nitrate flux in tributaries to the Atlantic Coastal Zone

Streamflow-related variability in nutrient flux represents an important source of uncertainty in managing nutrient inputs to coastal ecosystems. Quantification of flux variability is of particular interest to coastal resource managers in adopting effective nutrient-reduction goals and monitoring progress towards these goals. We used historical records of streamflow and water-quality measurements for 104 river monitoring stations in an analysis of variability in annual and seasonal flux of nitrate to the Atlantic coastal zone. We present two measures of temporal flux variability: the coefficient of variation (CV) and the exceedence probability (EP) of 1.5 times the median flux. The magnitude of flux variations spans a very wide range and depends importantly upon the season of year and the climatic and land-use characteristics of the tributary watersheds. Year-to-year variations (CV) in annual mean flux range over two orders of magnitude, from 3–200% of the long-term mean flux, although variations more typically range from 20–40% of the long-term mean. The annual probability of exceeding the long-term median flux by more than 50% (EP) is less than 0.10 in most rivers, but is between 0.10 and 0.35 in 40% of the rivers. Year-to-year variability in seasonal mean flux commonly exceeds that in annual flux by a factor of 1.5 to 4. In western Gulf of Mexico coastal rivers, the year-to-year variablity in the seasonal mean flux is larger than in other regions, and is of a similar magnitude in all seasons. By contrast, in Atlantic coastal rivers, the winter and spring seasons, which account for about 70% of the annual flux, display the smallest relative variability in seasonal mean flux. We quantify the elasticity of nutrient flux to hypothetical changes in Streamflow (i.e., the percent increase in flux per percentage increase in mean discharge) to allow the approximation of flux variability from streamflow records and the estimation of the effects of future climatically-induced changes in Streamflow on nutrient flux. Flux elasticities are less than unity (median = 0.93%) at most stations, but vary widely from 0.05% to 1.59%. Elasticities above unity occur most frequently in the largest rivers and in rivers draining the arid portions of the western Gulf of Mexico Basin. Historical flux variability and elasticity generally increase with the extent of arid conditions and the quantity of nonurban land use in the watershed. We extend the analysis of flux variability to examine several case studies of highly unusual meteorological events capable of significantly elevating nitrate flux and degrading estuarine ecology.     

Stem water storage and diurnal patterns of water use in tropical forest canopy trees

Stem water storage capacity and diurnal patterns of water use were studied in five canopy trees of a seasonal tropical forest in Panama. Sap flow was measured simultaneously at the top and at the base of each tree using constant energy input thermal probes inserted in the sapwood. The daily stem storage capacity was calculated by comparing the diurnal patterns of basal and crown sap flow. The amount of water withdrawn from storage and subsequently replaced daily ranged from 4 kg d^–1 in a 0·20-m-diameter individual of Cecropia longipes to 54 kg d^–1 in a 1·02-m-diameter individual of Anacardium excelsum, representing 9–15% of the total daily water loss, respectively. Ficus insipida, Luehea seemannii and Spondias mombin had intermediate diurnal water storage capacities. Trees with greater storage capacity maintained maximum rates of transpiration for a substantially longer fraction of the day than trees with smaller water storage capacity. All five trees conformed to a common linear relationship between diurnal storage capacity and basal sapwood area, suggesting that this relationship was species-independent and size-specific for trees at the study site. According to this relationship there was an increment of 10 kg of diurnal water storage capacity for every 0·1 m² increase in basal sapwood area. The diurnal withdrawal of water from, and refill of, internal stores was a dynamic process, tightly coupled to fluctuations in environmental conditions. The variations in basal and crown sap flow were more synchronized after 1100 h when internal reserves were mostly depleted. Stem water storage may partially compensate for increases in axial hydraulic resistance with tree size and thus play an important role in regulating the water status of leaves exposed to the large diurnal variations in evaporative demand that occur in the upper canopy of seasonal lowland tropical forests.     

浙西北丘陵地区次生林与杉木林土壤水溶性有机碳季节动态

为了解浙江省西北部丘陵地区森林土壤水溶性有机碳含量及动态规律,以达到成熟林状态的次生林和杉木林为对象,分别对其春、夏、秋、冬4个季节的0 ～ 10、10 ～ 20 cm土层水溶性有机碳含量进行了研究.结果表明:1)0 ～10和10 ～ 20 cm土层,次生林与杉木林水溶性有机碳含量没有显著差异;2)次生林和杉木林土壤水溶性有机碳含量季节动态基本一致,均表现为冬季＞春季＞秋季＞夏季;3)0 ～10和10 ～ 20 cm土层次生林与杉木林水溶性有机碳含量与土壤温度、降水量均呈显著负相关,与土壤湿度相关性不显著,与凋落物量呈正相关,且在0 ～10 cm土层显著.     

Food Web Structure and Basal Resource Utilization along a Tropical Island Stream Continuum, Puerto Rico

Tropical stream food webs are thought to be based primarily on terrestrial resources (leaf litter) in small forested headwater streams and algal resources in larger, wider streams. In tropical island streams, the dominant consumers are often omnivorous freshwater shrimps that consume algae, leaf litter, insects, and other shrimps. We used stable isotope analysis to examine (1) the relative importance of terrestrial and algal‐based food resources to shrimps and other consumers and determine (2) if the relative importance of these food resources changed along the stream continuum. We examined δ¹⁵N and δ¹³C signatures of leaves, algae, macrophytes, biofilm, insects, snails, fishes, and shrimps at three sites (300, 90, and 10 m elev.) along the Río Espíritu Santo, which drains the Caribbean National Forest, Puerto Rico. Isotope signatures of basal resources were distinct at all sites. Results of two‐source δ¹³C mixing models suggest that shrimps relied more on algal‐based carbon resources than terrestrially derived resources at all three sites along the continuum. This study supports other recent findings in tropical streams, demonstrating that algal‐based resources are very important to stream consumers, even in small forested headwater streams. This study also demonstrates the importance of doing assimilation‐based analysis (i.e., stable isotope or trophic basis of production) when studying food webs.     

中亚热带常绿阔叶林不同演替阶段土壤活性有机碳含量及季节动态

为探明不同演替阶段土壤碳吸存潜力,选取演替时间为15a(演替初期)、47a(演替中期)、110a(演替后期)3个中亚热带常绿阔叶林,分析了各演替阶段的土壤有机碳(SOC)含量以及土壤微生物量碳(MBC)、可溶性碳(DOC)和微生物熵(SMQ)的季节变化。结果表明:演替中、后期不同土层的土壤SOC、MBC、DOC含量和SMQ均显著高于演替初期(P<0.05);与演替中期相比,演替后期土壤MBC、DOC含量有所降低,SOC含量和SMQ无显著差异。土壤SOC、MBC和DOC含量随土层加深而显著性降低(演替初、中期DOC除外),并随演替进行逐渐向腐殖质层富集。不同演替阶段MBC、DOC和SMQ均有显著季节变化,最低值出现在秋季,最高值随演替进程由冬季逐步转向夏季。相关分析表明,不同演替阶段土壤活性有机碳含量与土壤有机碳含量极显著相关(P<0.01),且土壤活性有机碳(MBC、DOC)和SMQ对土壤碳库变化更为敏感。     

The Influence of Hunting on Antipredator Behavior in Central African Monkeys and Duikers

Many animals can adjust their behavioral strategies to reduce predation risk. We investigated whether rain forest monkeys and duikers alter their antipredatory behavior in response to hunting by humans in southwestern Gabon. We compared monkey and duiker responses to human observers in an area where hunting is prohibited, to those in a nearby area where hunting pressure is moderate but spatially variable. The results of our study indicate that monkeys become more secretive when hunted, commencing alarm calls only when at a certain distance (typically > 50 m) from humans. We found no difference in monkey group size between hunted and no-hunting areas. In no-hunting areas, duikers often freeze in response to approaching observers, but in hunted areas they abandon this strategy and rapidly flee from humans. Duikers also whistle more often in areas where they are hunted frequently. Our findings have at least two important implications. First, behavioral observations of monkeys and duikers may be useful in gauging local hunting intensity in African rain forests. Second, duiker densities are likely to be overestimated in hunted areas, where they more readily flee and whistle, and underestimated in no-hunting areas, where they rely on freezing behavior to avoid detection. Because behavioral adaptations to hunting vary both among species and localities, these differences should be considered when attempting to derive population-density estimates for forest wildlife.     

九龙江河口浮游植物的时空变动及主要影响因素

于2009年春（5月）、夏（8月）、秋（11月）在九龙江河口水域进行了水文、化学和生物的生态完全示范区综合外业调查,研究了九龙江河口浮游植物的种类组成、密度分布、季节变化、空间差异及主要影响因素,并结合前期资料分析了年际变动。结果表明,九龙江河口的浮游植物共记录7个门类75属134种。主体是硅藻,绿藻次之,甲藻和蓝藻较少,黄藻检出率高,裸藻和金藻零星检出。种类组成的空间差异大,绿藻在河口内区淡水水域比硅藻更占优势, 中肋骨条藻（Skeletonema costatum）、短角弯角藻（Eucampia zodiacus）、圆筛藻（Coscinodiscus spp.）、颗粒直链藻（Melosira granulata）、微小小环藻（Cyclotella. caspia）是河口区咸淡水水域及近海区的主要种类。浮球藻（Planktosphneria gelotinosa）、栅藻（Scenedesmus spp.）、盘星藻（Pediastrim spp.）、小席藻（Phormidium tenus）是河口内区淡水水域的主要种类。根据浮游植物的生态类型及其生境特征大致可分为三大类群。浮游植物密度夏季最高,平均为358.68103cells/L,密集中心的季节变化明显,密度分布由优势类群的密度分布决定。中肋骨条藻和短角弯角藻的数量庞大,导致优势种突出,多样性降低,种间分布不均匀,群落结构简单化。与史料比对,种类组成因淡水藻类的列入而更丰富,密度年际降低,中肋骨条藻仍是第一优势种,但优势度有较大降幅,优势类群有重大年际变化,细胞个体较小的种类占优。盐度和营养盐对浮游植物的分布及密度变化造成极大的时空差异,存在线性、复合线性、多项回归等复杂的相关关系。     

五种温带森林土壤微生物生物量碳氮的时空格局

土壤微生物是森林生态系统中的重要分解者,在碳和氮循环中起着重要作用,同时也是对环境变化的敏感指示者。采用氯仿熏蒸浸提法测定了我国东北地区5种温带森林土壤微生物生物量碳(Cmic)和氮(Nmic)的季节动态及其在土壤中的垂直变化。结果表明:林型之间Cmic和Nmic差异显著(P0.01)。落叶松林、红松林、蒙古栎林、杨桦林、硬阔叶林的Cmic的变化范围依次为:278937mgkg-1、2181020mgkg-1、313891mgkg-1、5101092mgkg-1、4401911mgkg-1;其Nmic的变化范围依次为:1872mgkg-1、18103mgkg-1、2495mgkg-1、43125mgkg-1、40208mgkg-1。所有林型的Cmic和Nmic均随土壤深度的增加而下降。Cmic和Nmic基本上呈现出生长季开始之前下降、生长季结束时上升、其中出现12个峰值的季节变化格局,但峰值大小和出现时间随林型和土壤层次而变。010cm土层的Cmic和Nmic季节变化较大。Cmic和Nmic与凋落叶量、土壤有机碳含量和土壤总氮含量呈显著正相关。Cmic与土壤含水量呈正相关,而与土壤温度呈负相关。不同林型凋落物数量和组成、土壤理化性质的差异是导致其土壤微生物生物量时空格局差异的主要因素。