A New Scheme for Predicting Leaf Onset in Summer-Green Vegetation in the Northern Hemisphere

A modified thermal time model(MTM) was developed to reproduce the leaf onset for summer-green vegetation in the Northern Hemisphere. The model adopts the basic concept of a thermal time model(TM) in that leaf onset is primarily triggered by growing degree days(GDD). Based on global phenology data derived from satellite observations, a new parameterization for the critical model parameter Tb(i.e., baseline temperature for GDD calculation) has been introduced, and the spatial distribution of Tb was calculated. Simulations of leaf onset during 1982–2000 in the range 30–90°N showed a significant improvement of MTM over the standard TM model with constant Tb. The mean error and mean absolute error of the climatological simulation were 1.11 and 6.8 days, respectively, and 90% of the model error(5th and 95 th percentiles) was between-12.4 and 13.7 days.     

两种人工湿地条件下芦苇与芦竹生理生态特性研究

通过对芦苇（Phragmites australis）和芦竹（Arundo donax）在模拟表面流湿地和潜流湿地条件下的生长特性比较,发现在两种人工湿地生长的两种植物叶片水势基本一致。对于植株相对生长率,叶片叶绿素含量、光合速率、蒸腾速率、气孔导度等指标,芦苇各项指标在两种人工湿地间的差异不显著;芦竹在潜流湿地中的生长特性明显优于表面流湿地,二者间差异极显著（n=3,P〈0．01）。根系的生长状况与叶片水势情况表明水分供需并不是影响植物生理差异的因素;叶片叶绿素含量与光合作用的正相关表现说明叶绿素是影响两种湿地类型上植物生理特性差异的主要因素;芦苇、芦竹在两种人工湿地间的生理生态差异说明芦苇能适应两种湿地生境,而芦竹更适合种植在潜流人工湿地。     

如何利用化石植物定量研究古海拔？

古海拔问题是当前古植物学与古环境研究领域中的难点之一,属于化石植物生物学与地球科学和环境科学相互交叉、相互渗透的前沿性研究。定量研究古海拔的变化对阐述诸如青藏高原抬升历史等重大科学问题具有十分重要的意义。应用生物学的思想和方法,利用化石植物研究地质历史时期古海拔的变化是当前研究的一个热点。化石植物既是研究地质历史时期植被演替的直接证据,又是研究古海拔变化的珍贵材料。本文简述了利用化石植物定量研究古海拔的3类主要方法,即最近亲缘种分析、共存因子分析和叶相分析的基本原理和实际应用,侧重分析中国地区（如西藏南部南木林盆地）古海拔的研究进展和存在问题,并结合近年来的研究实践展望了将来的工作。     

基于多角度遥感的植被指数与叶面积指数的线性关系研究

以辐射传输方程PROSAIL为基础,模拟不同观测天顶角和不同叶面积指数(LAI)下的植被冠层光谱。利用模拟的冠层光谱构建3种常用的植被指数,并分析不同观测天顶角下叶面积指数变化对3种植被指数的影响。结果表明,MSR能较好解决由于LAI变化而引起的饱和现象。观测天顶角为-30°时,3种植被指数与叶面积指数的线性关系较30°和0°时好。     

秋茄落叶分解失重过程的季节变化和滩面差异

秋茄红树林不同季节落叶分解失重速率研究表明:落叶的干重损失速率是夏>秋>春>冬。就失重过程而言,最高的失重速率和季节间最明显的分解速率差异都出现于分解初期,淋溶作用很可能是引起这一分解特征的重要原因。落叶在林地滩面外滩(中潮带).中滩和内滩(高潮蒂)分解28d时的失重率分别为53.4%、44.8%和48.9%,即外滩>内滩>中滩。中潮带比高潮带具有较高的潮浸频度和滩面潮湿度,使得落叶在中潮带的分解快于高潮带。     

Isoprenoids of Okinawan mangroves as lipid input into estuarine ecosystem

Isoprenoids in the nonsaponifiable lipids (NSL) fraction of Okinawan mangroves were analyzed with special reference to their importance as lipid input into estuarine ecosystems. Triterpenoids and phytosterols comprised the major proportion of NSL. Identifications of the triterpenoids and phytosterols in NSL fraction were based on the interpretation of ¹³C-NMR and GC-MS spectra. The triterpenoids and phytosterols mainly comprised 11 and 6 compounds, respectively. The major components were lupeol, β-amyrin and taraxerol for triterpenoids, and β-sitosterol and stigmasterol for phytosterols. The diversity in the terpenoid composition was noted in both leaves and roots of mangrove species, implying the chemotaxonomic utility of terpenoids. Terpenoid compositions of the root are not always similar to that of leaf, suggesting that terpenoids in the root are produced by biosynthesis in situ, not by translocation of the synthate from the leaf. Terpenoids existed in greater proportion in the outer parts of the root. These data are likely to contribute to estimating the lipid input from mangrove trees adjacent to estuarine sediments and the ocean.     

Spatial and temporal variability of surface water repellency in sandy loam soils of NW Spain under Pinus pinaster and Eucalyptus globulus plantations

This work was undertaken for two main purposes. One was to examine spatial and temporal variability in surface water repellency under field conditions in sandy loam forest soils of NW Spain, and its relationship to weather and soil moisture conditions. The other purpose was to get further inside in the dynamics of soil water repellency by studying a wetting–drying cycle under controlled laboratory conditions. Both for the field and laboratory study, water repellency was determined using the Water Drop Penetration Time test. Soil water repellency under field conditions was found to exhibit a seasonal pattern, i.e. it peaked during the summer and was absent between November and May. The time required for repellency to become re‐established during the spring was shorter under eucalyptus than under pine. Spatial variability peaked at an early stage of soil drying and was minimal during the wet period when soils were hydrophilic as well as at the end of the summer, when repellency was strongest. Spatial and temporal variability in water repellency was found to be negatively correlated with soil moisture and, to a lesser extent, with antecedent rainfall. The moisture range of the so‐called transition zone (below which the soil is hydrophobic and also above which it is hydrophobic) differed for the pine (21–50%) and eucalyptus plantations (17–36%). The lower and upper bounds of the transition zone agreed well with the soil moisture contents at the permanent wilting point and at field capacity, respectively. The laboratory results with samples in the wetting phase confirmed those of the field tests. Water repellency increased slightly during the drying phase, but not so much as in the field. Copyright © 2011 John Wiley & Sons, Ltd.     

Rainfall interception in a lower montane forest in Ecuador: effects of canopy properties

Rainfall interception in forests is influenced by properties of the canopy that tend to vary over small distances. Our objectives were: (i) to determine the variables needed to model the interception loss of the canopy of a lower montane forest in south Ecuador, i.e. the storage capacity of the leaves S and of the trunks and branches S_t, and the fractions of direct throughfall p and stemflow p_t; (ii) to assess the influence of canopy density and epiphyte coverage of trees on the interception of rainfall and subsequent evaporation losses. The study site was located on the eastern slope of the eastern cordillera in the south Ecuadorian Andes at 1900–2000 m above sea level. We monitored incident rainfall, throughfall, and stemflow between April 1998 and April 2001. In 2001, the leaf area index (LAI), inferred from light transmission, and epiphyte coverage was determined. The mean annual incident rainfall at three gauging stations ranged between 2319 and 2561 mm. The mean annual interception loss at five study transects in the forest varied between 591 and 1321 mm, i.e. between 25 and 52% of the incident rainfall. Mean S was estimated at 1·91 mm for relatively dry weeks with a regression model and at 2·46 mm for all weeks with the analytical Gash model; the respective estimates of mean S_t were 0·04 mm and 0·09 mm, of mean p were 0·42 and 0·63, and of mean p_t were 0·003 and 0·012. The LAI ranged from 5·19 to 9·32. Epiphytes, mostly bryophytes, covered up to 80% of the trunk and branch surfaces. The fraction of direct throughfall p and the LAI correlated significantly with interception loss (Pearson's correlation coefficient r = −0·77 and 0·35 respectively, n = 40). Bryophyte and lichen coverage tended to decrease S_t and vascular epiphytes tended to increase it, although there was no significant correlation between epiphyte coverage and interception loss. Our results demonstrate that canopy density influences interception loss but only explains part of the total variation in interception loss. Copyright © 2004 John Wiley & Sons, Ltd.     

Seasonal variability of leaf litter removal by crabs in a Kandelia candel mangrove forest in Jiulongjiang Estuary, China

The seasonal variability of leaf litter removal by crabs was observed from May 2006 to April 2007 in a Kandelia candel mangrove forest in Jiulongjiang Estuary, China. Daily average quantities of leaf fall ranged 0.85–3.86 gDW m⁻² d⁻¹, with high values in May, August, October and November. The whole-year's leaf fall was 6.48 t ha⁻¹ yr⁻¹ (1.81 gDW m⁻² d⁻¹). The standing stock of leaf litter on the forest floor was 7.78 gDW m⁻² averaged from the whole year's data, with the lowest value in December (1.23 gDW m⁻²) and the highest in April (16.18 gDW m⁻²). Annually averaged removal (consumption on mangrove floor + burial in burrows) rate of leaf litter by crabs was 0.59 gDW m⁻² d⁻¹. High seasonal variability was observed in the removal rates of leaf litter by crabs. Removal rates in the winter months (December, January and February) were 0.07–0.09 gDW m⁻² d⁻¹, much lower than those in other months with values of 0.59–1.18 gDW m⁻² d⁻¹. Annually averaged percentage of leaf fall removed by crabs was 33%, with the highest values in September (reached 76%) and the lowest values in winter months. Of leaf litter removed by crabs, a large proportion was buried by crabs, and only 12% was consumed by crabs on the forest floor. Leaf litter removal rate, consumption rate on the forest floor, percentages of leaf fall and standing stock removed on the forest floor were significantly positively correlated with air temperature, indicating that leaf removal ability by crabs was higher in warm months than in cold months.