Influence of temperature and salinity variations on an aquatic bug population in a tropical pond

Variation in sex ratio of Diplonychus indicus, living in a permanent pond in southern India, was studied in relation to seasonal variations in temperature and salinity. Males proved to be less susceptible to changes in these parameters. Protein content and survival of the insect were studied in relation to fluctuations of environmental conditions.     

茂兰喀斯特森林林隙幼苗出现的时空格局

通过4次对茂兰自然保护区喀斯特森林林隙内种子的天然萌发情况进行观测,分析了林隙内幼苗的萌发数量、存活率及幼苗出现的时空分布格局。结果发现：林隙中大多数萌发的幼苗存活率均较高,平均存活率达50%以上,林隙的形成,不但提高了喀斯特森林树种的萌发率,也提高了幼苗的存活率。林隙中心、近中心、林隙边缘各区域幼苗的密度存在显著的空间差异,山拐枣（Poliothyrsis sinensis）、多脉榆（Ulmus castaneifolia）等树种在林隙中心幼苗密度最大,圆果化香（Platycarya longipes）、翅荚香槐（Cladrastis platycarpa）、圆叶乌桕（Sapium rotundifolium）、掌叶木（Handeliodendron bodinieri）、黄连木（Pistacia chinen-sis）和云贵鹅耳枥（Carpinus pubescens）等树种在林隙近中心幼苗密度最大,而樟叶槭（Acercinnamomifolium）、球核荚蒾（Viburnumpropinquum）、小叶青冈（Cyclobalanopsis myrsinaefolia）、轮叶木姜子（Litsea verticillata）等则在林隙边缘光照较弱的地方生长良好。幼苗出现的时间分布特征明显,整个观察期幼苗都持续萌发,但大多数树种幼苗出现在第2观测期（3月）,幼苗出现数目从第2次到后面的几次观察期显著下降。林隙3个区域幼苗出现不是同步的,林隙中心的幼苗出现最快,与其它两个部位相比,林隙边缘的幼苗出现有滞后现象。研究结果表明林隙中心的环境条件有利于种子萌发,但林隙近中心却更利于幼苗存活。     

Patterns, determinants and models of woody plant diversity in China

What determines large-scale patterns of species richness remains one of the most controversial issues in ecology. Using the distribution maps of 11 405 woody species in China, we compared the effects of habitat heterogeneity, human activities and different aspects of climate, particularly environmental energy, water-energy dynamics and winter frost, and explored how biogeographic affinities (tropical versus temperate) influence richness-climate relationships. We found that the species richness of trees, shrubs, lianas and all woody plants strongly correlated with each other, and more strongly correlated with the species richness of tropical affinity than with that of temperate affinity. The mean temperature of the coldest quarter was the strongest predictor of species richness, and its explanatory power for species richness was significantly higher for tropical affinity than for temperate affinity. These results suggest that the patterns of woody species richness mainly result from the increasing intensity of frost filtering for tropical species from the equator/lowlands towards the poles/highlands, and hence support the freezing-tolerance hypothesis. A model based on these results was developed, which explained 76-85% of species richness variation in China, and reasonably predicted the species richness of woody plants in North America and the Northern Hemisphere.     

Thermal tolerance,net CO2 exchange and growth of a tropical tree species, Ficus insipida, cultivated at elevated daytime and nighttime temperatures

Global warming and associated increases in the frequency and amplitude of extreme weather events, such as heat waves, may adversely affect tropical rainforest plants via significantly increased tissue temperatures. In this study, the response to two temperature regimes was assessed in seedlings of the neotropical pioneer tree species, Ficus insipida. Plants were cultivated in growth chambers at strongly elevated daytime temperature (39 °C), combined with either close to natural (22 °C) or elevated (32 °C) nighttime temperatures. Under both growth regimes, the critical temperature for irreversible leaf damage, determined by changes in chlorophyll a fluorescence, was approximately 51 °C. This is comparable to values found in F. insipida growing under natural ambient conditions and indicates a limited potential for heat tolerance acclimation of this tropical forest tree species. Yet, under high nighttime temperature, growth was strongly enhanced, accompanied by increased rates of net photosynthetic CO₂ uptake and diminished temperature dependence of leaf-level dark respiration, consistent with thermal acclimation of these key physiological parameters.