云南大中山种子植物区系特征分析

云南省大中山有种子植物749种,隶属于137科,396属.区系成分中,世界分布33属,占总属数的8.33%;热带分布206属,占除世界分布属以外的56.75%;温带分布148属,中国特有9属.该地区植物种类丰富,古老、孑遗植物多,优势科、优势属明显,其中樟科、壳斗科、山茶科等是该区系的表征科;种子植物区系起源古老,地理成分复杂,具有明显的亚热带特性.

Study on the Characteristics of Florescence and Pollen in Lagerstroemia speciosa

[ Objective] To study the characteristics of florescence and pollen in Lagerstroemia speciosa. [ Method ] The process of flower opening and pollen tube germination of Lagerstroemia speciosa was observed and the pollen viability was determined through in vitro germination. [ Result] Sepals of L. speciosa started to diverge at 4：30 am, at 7： 00 am petals flatten up, anther diverged, and the stigma secreted a large number of mucus, it was the best time for artificial pollination. Boric acid and sucrose had a great effect on in vitro pollen germination of L. speciosa, the combination which made highest rate of pollen germination, was sucrose 150 g/L ＋ boric acid 20 mg/L ＋ CaCI2 10 mg/L. Through the fluorescence microscope, it was known that four hours after flowering, a lot of pollen grains germinated on the stigma, six hours after flowering, lots of pollen tubes entered the style and reached to 1/4 length of the style, 12 hours after flowering, pollen tubes concentrated into a beam forward, and reached to 1/2 length of the style, 24 hours after flowering, lots of pollen tubes entered the ovary in a beam and then fertilized and produced seeds. [ Conclusion] The results provide some basis for utilizing L. speciosa to breed.

Drivers of understorey biomass:tree species identity is more important than richness in a young forest

Aims Positive biodiversity-ecosystem functioning relationships have been widely reported,predominately from grassland ecosystems.However,this does not necessarily have to apply accordingly in more complex situations such as in forests across different vertical strata.For instance,overstorey tree species richness has been shown to be associated with a lower understorey productivity.Whether or not tree species richness effects add to understorey productivity by increasing(i.e.due to habitat heterogeneity)or reducing resource availability(i.e.through increasing competition)and whether understorey productivity is indeed being governed more strongly by tree species identity are likely to change over time.Moreover,studies also suggested that richness-productivity relationships change with the environmental context.Using an experimental forest plantation with manipulated tree species richness,this study examined these temporal and environmental dynamics across strata.Methods In the context of the Biodiversity-Ecosystem Functioning project in subtropical China(BEF-China),we made use of understorey biomass samples repeatedly collected over a time period of 3 years along a tree species richness gradient.The effects of tree species richness,tree species identities and time were studied across different environmental treatments for their impact on understorey biomass.Important Findings While we found significant and consistent tree layer identity effects on understorey biomass,no such effect was encountered for tree species richness.Our results also indicate that among structural layers in forests,there might not be a single,generalizable overstorey species richness-understorey productivity relationship,and that the extent as to which overstorey-related environmental factors such as light transmittance contribute to understorey productivity change with time.Overall,we demonstrate that temporal dynamics should be considered when studying relationship among structural layers in forests.

Climatic characteristics of convective and stratiform precipitation over the Tropical and Subtropical areas as derived from TRMM PR

Climatic characteristics of convective and stratiform precipitation over the Tropical and Subtropical areas are investigated based on the measurements of Tropical Rainfall Measuring Mission's(TRMM) Precipitation Radar(PR) from 1998 to 2007.Results indicate that convective precipitation are distributed mainly over the Intertropical Convergence Zone(ITCZ),the South Pacific Convergence Zone(SPCZ),the Asian Monsoon Region,regions between the South America and the Mid-America,and the Tropical Africa where the frequencies lie between 1% and 2%.But in four seasons,total area fractions of convective precipitation frequencies less than 1% all exceed 85%.The frequencies of stratiform precipitation are much higher than those of convective precipitation,and total area fractions of stratiform precipitation frequencies >1% are over 55% during four seasons.However,frequencies of the two rain types show not only remarkable regionality,but also distinct seasonal variations.Conditional rain rates of convective precipitation range from 6 to 14 mm/h whereas those of stratiform precipitation are smaller than 4 mm/h.Meanwhile,rain tops of convective precipitation are higher than those of stratiform precipitation.The mean profiles of the two rain types show significant latitudinal dependency.And the seasonal variations of precipitation profiles are displayed mainly in the variations of rain tops.The frequencies and conditional rain rates of both rain types over ocean are higher than those over land,but rain tops are just the opposite.Moreover,the seasonal variations of both rain types over ocean are weaker than those over land because of the different stable states of underlying surfaces.