Factors influencing small-scale distribution of 10 macrolichens in King George Island,West Antarctica

Lichens are among the main primary colonists in most terrestrial ecosystems of Antarctica, where the effects of environmental factors on spatial distribution of lichens are essential to understanding the functioning of Antarctic terrestrial ecosystems. We measured abundance of 10 frequently observed macrolichens and 15 environmental factors at a small scale （20 cm× 20 cm）, in the ice-free areas of Fildes Peninsula and Ardley Island, King George Island, West Antarctica, and assessed the effects of environmental factors on the local distribution of these lichens. Canonical correspondence analyses （CCA） show that 8 out of 15 environmental factors, belonging to 4 sets of variables, are important in spatial distribution of the 10 lichens. Variation partitioning analyses show that most of the variation in distribution of the 10 lichens is described by the spatial heterogeneity of substrate, bird influence and microclimate and topography, whereas human impact has no significant effects.     

LICHEN GROWTH RATES ON GLACIER FORELANDS IN SOUTHERN NORWAY: PRELIMINARY RESULTS FROM A 25-YEAR MONITORING PROGRAMME

A unique 25-year lichen growth monitoring programme involving 2,795 individuals of the Rhizocarpon subgenus at 47 sites on 18 glacier forelands in the Jotunheimen–Jostedalsbreen regions of southern Norway is reported. The data are used to address fundamental questions relating to direct lichenometry: spatial and temporal variability in lichen growth rates, climatic effects on lichen growth rates, lichen growth models, and implications for lichenometric dating. Mean annual (diametral) growth rate ranged from 0.43 to 0.87 mm yr⁻¹ between sites, which is attributed primarily to local habitat differences. Interannual variability in annual mean growth rate exceeded 1.0 mm yr⁻¹ at some sites. Annual mean growth rates for all sites combined varied from 0.52 to 0.81 mm yr⁻¹ and was positively correlated with annual mean temperature and winter mean temperature (both r = 0.64, p <0.005) but not with summer seasonal temperature: positive correlations with annual and winter precipitation were less strong and the correlation with summer precipitation was marginally significant (r = 0.41 p <0.10). Growth-rate models characterized by annual growth rates that remain approximately constant or increase with lichen size up to at least 120 mm tended to fit the data more closely than a parabolic model. This is tentatively attributed to a long 'linear/mature' phase in the growth cycle. Comparison with growth rates inferred from indirect lichenometry suggest that such high measured growth rates could not have been maintained over the last few centuries by the largest lichens used in southern Norway for lichenometric dating. Several hypotheses, such as the effects of competition and climate change, which might explain this paradox, are discussed.     

Two‐hourly surface change on supra‐tidal rock (Marengo,Victoria, Australia)

A traversing micro‐erosion meter was used to measure rock surface micro‐topography over 40 cm² on a supra‐tidal cliff face from early morning to late evening in late spring. From 06:00 hours to 22:00 hours the relative heights of 188 coordinates were obtained using the meter at 2‐hour intervals, resulting in a data set of 1607 readings. Monitoring shows that rock surfaces are dynamic entities, with significant rise and fall relative to the first measurement at shorter timescales than previously reported. The maximum positive rise between readings was 0·261 mm and lowering was 0·126 mm. The pattern of change did not relate as expected to environmental variables such as temperature or insolation. Rather, the surface showed greater surface change in the early morning and late afternoon. It is hypothesized that this pattern relates to the expansion and contraction of lichen thalli as moisture is absorbed during higher humidity in the morning and late afternoon. The implications of these results for weathering studies are considered. Copyright © 2006 John Wiley & Sons, Ltd.     

Physical drivers of phytoplankton production in the southern Benguela upwelling system

Investigations of primary production (PP) were undertaken in the southern Benguela ecosystem during two research surveys in October 2006 and May 2007. Significant differences in environmental conditions, as well as biomass and PP, were observed between October and May. During October, integrated biomass and PP were significantly higher, ranging from 20.43 to 355.01 mg m⁻², and 0.71 to 6.98 g C m⁻² d⁻¹, respectively, than in May, where the range was 47.92–141.79 mg m⁻², and 0.70–3.35 g C m⁻² d⁻¹, respectively. Distribution patterns indicated low biomass and PP in newly upwelled water along the coast, higher biomass and PP in the mid-shelf region, while lower values were observed at and beyond the shelf edge. Latitudinal variations showed consistently higher biomass and PP in the St. Helena Bay region compared to biomass and PP south of Cape Town. During both surveys, phytoplankton communities were comprised primarily of diatoms and small flagellates, with no significant differences. Phytoplankton adaptation to environmental variability was characterised by increased P_m^B and E_k under elevated temperatures and irradiance, while no clear relationships were evident for α^B. Generalised Additive Models (GAMs) showed that photosynthetic parameters were all significant predictors of photosynthesis rates (P_z), with P_m^B being the most important, accounting for 36.97% of the deviance in P_z. However, biomass levels and environmental conditions exerted a much greater influence on P_z, with irradiance explaining the largest proportion (68.24%) of the deviance. Multiple predictor GAMs revealed that 96.26% of the deviance in P_z could be explained by a model which included nitrate, chlorophyll a, and irradiance.     

大叶黄杨对土壤水分梯度胁迫的生长与生理响应

以盆栽大叶黄杨为试材,研究了大叶黄杨生长与生理指标对不同程度土壤水分胁迫的响应.结果表明:土壤水分胁迫对生长指标(苗重、苗高和地径)有明显的影响,变化表现出一致的规律性,即随胁迫程度加剧均呈现出下降趋势.干旱胁迫下生理指标的变化表现出差异性:束缚水/自由水的比值随胁迫程度加强而增大;水分饱和亏缺变化和丙二醛活性在轻、中...     

青藏高原几个主要环境因子对植物的生理效应

青藏高原作物生育期间的太阳辐射及其强度,均高于我国内地,而且短波辐射比例大,光照时间长,不仅直接影响植物的光合作用、呼吸作用等重要代谢过程,而且不同光质对高原植物植株的生长高度、根系的萌生发育、叶绿素含量以及碳水化合物、蛋白质、脂肪等贮藏物质的积累等方面都有不同的影响。昼夜温差大这一环境特点与高原作物高产之间的关系尚存争议,但对作物的品质确实具有明显的影响作用。在高海拔、低气压(低CO₂含量、低O₂含量)条件下,植物表现出光合作用光饱和点升高、光补偿点降低、适温偏低,暗呼吸速率较低等特点,因而有利于植物充分利用光能,也有利于植物体内干物质的积累,而且高海拔对植物体内不同代谢成分的形成具有不同的影响作用。虽然青藏高原的多个环境因子,如太阳强辐射、蓝紫光成分多、昼夜温差大等,对高原小麦的高产来说不可缺少,但平均气温较低导致的高原地区小麦生育期明显延长是其干物质产量和籽粒产量高于平原地区的主要原因。     

4种典型滨海植物的耐盐能力

滨海植物是海岸生态系统的重要组成部分,而绝大部分滨海植物的耐盐能力与生态适应机制尚不清楚,本研究选择马鞍藤(Ipomoea pescaprae)、小刀豆(Canavalia cathartica)、全缘冬青(Ilex integra)、大叶银边海桐(Pittosporum pentandrum)4种滨海典型植物,通过对培养基质及植株叶片施加不同浓度的盐溶液,研究其根系和叶片的耐盐能力。主要结果如下:(1)根系胁迫中,盐度10导致大叶银边海桐、全缘冬青、小刀豆的老叶变黄或产生黄褐斑,盐度20和30促使植物叶片干枯、落叶,对叶片的损害从叶柄向叶脉延伸;盐度为30的叶片盐胁迫导致少量叶片从叶尖开始干枯;(2)小刀豆、马鞍藤、全缘冬青与大叶银边海桐分别可耐受盐度为10、20、20、30的短期(49 d)根系盐胁迫,藤本植物的耐盐能力为马鞍藤>小刀豆,灌木的耐盐能力为大叶银边海桐>全缘冬青;4种植物均可耐受盐度30的叶片盐胁迫,耐盐能力为马鞍藤>全缘冬青>大叶银边海桐>小刀豆。结果表明,植物的生长状态值对植物耐盐能力的指示作用更为准确与直观;4种植物均有较强的耐盐能...