Patterns of plant sexual systems in subtropical evergreen broad-leaved forests in Ailao Mountains,SW China

Aims Sexual systems influence many components of the ecology and evolution of plant populations and have rarely been documented in subtropical evergreen broad-leaved forests (SEBLF). Here we report frequency distribution and ecological correlates of plant sexual systems in SEBLF at Ailao Mountains, and compare our results with that of tropical and cool temperate forests.Methods We examine the sexual systems of 703 species of woody angiosperms belonging to 103 families and 296 genera based on a comprehensive survey of SEBLF at Ailao Mountains Natural Reserve. Information of plant sexual systems and ecological traits were mainly based on published literatures and specimens as well as our field observations. The associations between plant sexual system and ecological traits were assessed with chi-square tests.Important findings Among these species, 60.2% were hermaphroditic, 15.8% were monoecious and 24.0% were dioecious. The percentage of dioecious sexual system among tree species (22.2%) in SEBLF was comparable to those of tropical tree floras, but much higher than those of temperate forests at North America. The percentage of monoecious sexual system among tree species (30.1%) in SEBLF was higher than that of tropical tree floras, but much lower than those of temperate forests at North America. Monoecy was significantly associated with the tree growth form and was relatively common in temperate genera. Dioecy was significantly associated with fleshy fruits and monoecy was significantly associated with dry fruit type in SEBLF. The high percentage of diclinous sexual systems (monoecy and dioecy) in SEBLF may be associated with the origin of the flora and the prevalence of relatively small inconspicuous flowers of the forests in the Oriental Region.     

Patterns and Ecological Correlates of Pollination Modes Among Bromeliad Communities of Andean Forests in Bolivia

Abstract: We studied the distribution of five pollination modes (ornithophily, chiropterophily, entomophily, mixed/unspecific, autogamy) among the bromeliad communities of 74 forest sites in the Bolivian Andes and adjacent lowlands. We recorded a total of 188 bromeliad species belonging to 16 genera, including 115 (61 %) ornithophilous, 14 (7 %) chiropterophilous, 45 (24 %) entomophilous, 8 (4 %) autogamous, and 6 (3 %) species with mixed pollination mode. Ornithophily was the dominant pollination mode at high elevations and in wet regions, while entomophily dominated in arid regions. Chiropterophily was most common in wet lowland regions, autogamy in arid sites, and mixed pollination in the lowlands. Pollination modes were rather evenly distributed among life-forms and ecophysiological types, with a few exceptions: terrestrial forest bromeliads, mostly belonging to unarmed, soft-leaved taxa, had a prevalence of entomophily and few ornithophilous species; large, spiny terrestrial bromeliads of Puya and Bromelioideae showed a prevalence of ornithophily; and autogamy was restricted to the neotenous subgenus Diaphoranthema of Tillandsia. The restriction of unspecific pollination modes to the lowlands is hypothesized to be related to the abundance of pollinators, eliminating the need for specialized co-evolution, or to the overall rarity of bromeliads in this environment, precluding the development of specialized relationships. The low representation of entomophilous species in small dry forest regions compared to extensive areas is assumed to be due to the seasonal influx of hummingbirds and/or bats. Overall, the frequency of individual pollination modes was related to the availability of pollinators as determined by temperatures and humidity.     

Tropical Forests of Xishuangbanna,China1

Lowland tropical forests once covered a large fraction of tropical southern China, but currently have an extent of ca 633,800 ha, mostly in Xishuangbanna of southern Yunnan. The Xishuangbanna region has a typical monsoon climate with a mean annual temperature ranging between 15.1°C and 21.7°C, and precipitation between 1200 and 2500 mm. There is a pronounced dry season between November and April with frequent occurrence of heavy fog. Rainfall during the wet season between May and October accounts for over 80 percent of total annual precipitation. Water deposition from fog accounts for over one‐third of total water input during the dry season in the forests, suggesting an important role that fog may play in pushing up the northern limit of tropical rain forest in Southeast Asia.     

Ecological Characteristics of Macroalgae in Mangrove Forests in Fujian,China

The flora and distribution of macroalgae as well as the biomass of its two dominant species were studied in mangrove forests in Fujian Province, China. There were totally 42 species belonging to 24 genera of macroalgae, in which 15 species/8 genera belonged to Cyanophyta, 7/3 to Rhodophyta, and 20/13 to Chlorophyta. The biomass of the dominant species Caloglossa leprieurii and Catenella impudica were 2.22 to 8.44 g/m2 DW and 2.69 g/m2 DW in June,and 0.15 to 0.20 g/m2 DW and 2.12 g/m2 DW in December, respectively. On the tnmk surface of the mangrove plants,macroalgae appeared vertically to be distributed from lower upwards into six belts, namely Vaucheria sp. belt, Catenella impudica belt, Caloglossa ogasawaraensis-Bostrychia mixta belt, Calogiossa leprieurii belt, Chaetomorpha macrotona-Rhizoclonium riparium belt, and Chlorococcum sp. belt.     

海南霸王岭热带山地雨林森林循环与树种多样性动态

通过对海南岛霸王岭热带山地雨林的调查 ,研究了热带山地雨林树种多样性特征随森林循环的动态变化规律。结果表明 :( 1 )热带山地雨林森林循环不同阶段斑块在森林景观中所占的面积比例分别是 :林隙阶段 ( G)占 38.5 0 % ,建立阶段 ( B)占 2 8.5 0 % ,成熟阶段 ( M)占 2 7.0 0 % ,衰退阶段 ( D)占 6 .0 0 %。 ( 2 )热带山地雨林中乔木树种的密度随森林循环的变化趋势是由 G→B→M呈现出逐渐增加的趋势 ,以成熟阶段达到最大 ,而到衰退阶段又趋于下降。灌木树种则表现出 G阶段斑块的密度最大 ,B阶段的最小 ,从 B到 M有所增加 ,到 D又稍有下降。 ( 3)热带山地雨林中不同高度级和不同径级的树木的密度在森林循环的不同阶段表现出不同的增减趋势 ,其随森林循环过程呈现出的动态变化可能与不同阶段斑块内的空间、环境及物种生物学特性有关。 ( 4 )热带山地雨林中树木的平均胸径、平均高、平均胸高断面积、平均单株材积随森林循环过程呈现出不断增加的趋势 ,其中平均胸径和平均高随森林循环的变化较为平缓 ,而平均胸高断面积和平均单株材积之变化较为陡急。 ( 5 )热带山地雨林森林循环不同阶段的物种多样性指数不同 ,其中 G和 B阶段的物种丰富度和多样性指数值较接近 ,M阶段的物种丰富度达到最大 ,D阶段则最小。     

西双版纳热带季节雨林145个树种繁殖体特征

分析了西双版纳热带季节雨林20公顷动态监测样地中145个树种的繁殖体特征。结果表明：雨季散布的种类最多（71.03%）,在雾凉季及干热季散布的种类相对较少;果实类型以核果,蒴果,浆果居多,黑色、黄色、褐色果实最为常见;动物散布的种类最多（56.55%）,其次为机械散布,独立散布,风力散布;大种子树种（种子最大长度〉10mm）较占优势（53.10%）;树种单粒种子重量从2.3×10^-5～22.29g不等,但76.55%的种子的重量集中在0.01～10g之间;干热季散布的种子平均重量显著高于雨季和雾凉季;独立散布的种子重量最大,风力散布的种子重量最小,而机械弹射的种子重量和动物散布的种子重量之间差异不显著;树种的成年个体最大胸径与种子重量之间存在显著正相关。     

Dispersal spectra,diaspore size and the importance of endozoochory in the equatorial Andean montane forests

The dispersal syndrome hypothesis states that plant diaspores show morphological features that are the results of adaptation for dispersal by a particular vector. This can enable to identify the relative importance of dispersal agents within plant communities. Nevertheless, there is still little information about seed dispersal spectra and diaspore traits related to different dispersal agents in the equatorial montane forests, despite their high biodiversity and important ecosystem services as watersheds for human communities. Due to an increase in environmental stress at high elevations a reduction in the prevalence of endozoochory, and a reduction in the size of endozoochorous diaspores in plant assemblages could be expected. We reviewed published data from 64 Andean cloud forest plots to assess the dispersal spectra, the incidence of different traits related to seed dispersal, and the distribution of dispersal syndromes within cloud forests of northern South America. We then evaluated two questions related to seed dispersal in these forests: (1) Does the number and percentage of endozoochorous species in woody plant assemblages decrease at higher elevation? and (2) Does the mean diaspore size of endozoochorously dispersed tree assemblages decrease with elevation?     

Unisexual flower, spikelet, and inflorescence development in monoecious/dioecious Bouteloua dimorpha (Poaceae, Chloridoideae)

Unisexual flowers have evolved repeatedly in the angiosperms. In Poaceae, multiple transitions from bisexual to unisexual flowers are hypothesized. There appear to be at least three distinct developmental mechanisms for unisexual flower formation as found in members of three subfamilies (Ehrhartoideae, Panicoideae, Pharoideae). In this study, unisexual flower development is described for the first time in subfamily Chloridoideae, as exemplified by Bouteloua dimorpha. Scanning electron microscopy (SEM) and anatomy were used to characterize the development of male (staminate) and female (pistillate) flowers, spikelets, and inflorescences. We found the developmental pathway for staminate flowers in B. dimorpha to be distinct from that described in the other three subfamilies, showing gynoecial arrest occurs at a different stage with possible loss of some cellular contents. However, pistillate flowers of B. dimorpha had some similarity to those described in other unisexual-flowered grasses, with filament and anther differentiation in abortive stamens. Comparing our findings with previous reports, unisexual flowers seem to have evolved independently in the four examined grass subfamilies. This analysis suggests the action of different genetic mechanisms, which are consistent with previous observations that floral unisexuality is a homoplasious condition in angiosperms.     

Altitudinal Change in LAI and Stand Leaf Biomass in Tropical Montane Forests: a Transect Study in Ecuador and a Pan-Tropical Meta-Analysis

Abstract Leaf area index (LAI) is a key parameter controlling plant productivity and biogeochemical fluxes between vegetation and the atmosphere. Tropical forests are thought to have comparably high LAIs; however, precise data are scarce and environmental controls of leaf area in tropical forests are not understood. We studied LAI and stand leaf biomass by optical and leaf mass-related approaches in five tropical montane forests along an elevational transect (1,050–3,060 m a.s.l.) in South Ecuador, and conducted a meta-analysis of LAI and leaf biomass data from tropical montane forests around the globe. Study aims were (1) to assess the applicability of indirect and direct approaches of LAI determination in tropical montane forests, (2) to analyze elevation effects on leaf area, leaf mass, SLA, and leaf lifespan, and (3) to assess the possible consequences of leaf area change with elevation for montane forest productivity. Indirect optical methods of LAI determination appeared to be less reliable in the complex canopies than direct leaf mass-related approaches based on litter trapping and a thorough analysis of leaf lifespan. LAI decreased by 40–60% between 1,000 and 3,000 m in the Ecuador transect and also in the pan-tropical data set. This decrease indicates that canopy carbon gain, that is, carbon source strength, decreases with elevation in tropical montane forests. Average SLA decreased from 88 to 61 cm² g⁻¹ whereas leaf lifespan increased from 16 to 25 mo between 1,050 and 3,060 m in the Ecuador transect. In contrast, stand leaf biomass was much less influenced by elevation. We conclude that elevation has a large influence not only on the leaf traits of trees but also on the LAI of tropical montane forests with soil N (nitrogen) supply presumably being the main controlling factor.     

西双版纳不同热带森林下土壤氮矿化和硝化作用研究

 1998年7月,用埋袋法对西双版纳热带季节雨林、崖豆藤(Mellettia leptobotrya)次生林、季节雨林内林窗和轮歇地土壤的氮矿化和硝化作用进行了研究。研究结果表明季节雨林和崖豆藤次生林的格局基本相同,氮净矿化速率分别为6.55mgN·kg-1·30d-1和6.37mgN·kg-1·30d-1,硝化速率分别为16.28mgN·kg-1·30d-1和16.38mgN·kg-1·30d-1。而林窗下和轮歇地土壤的氮净矿化速率和硝化速率均为负值,氮净矿化速率分别为–7.85mgN·kg-1·30d-1和–10.69mgN·kg-1·30d-1,硝化速率分别为–2.78N·kg-1·30d-1和–3.69mg N·kg-1·30d-1。从实验结果看,在30d的培养过程中,NH4–N消耗较多,导致硝化速率大于氮净矿化速率。     

Phosphorus Fertilization Increases the Abundance and Nitrogenase Activity of the Cyanolichen Pseudocyphellaria crocata in Hawaiian Montane Forests

Nitrogen-fixing epiphytes (especially lichens with a cyanobacterial symbiont—cyanolichens) have the potential to contribute significant amounts of nitrogen (N) to montane tropical forests, which are typically low in N—but the factors controlling the abundance and distribution of epiphytic cyanolichens are poorly understood. In long-term fertilization experiments in montane forests on a 4.l million-yr-old Oxisol on the island of Kauà'i and on a 152-yr-old lava flow on the island of Hawai'i, the epiphytic cyanolichen Pseudocyphellaria crocata increased significantly in abundance in canopies of host trees fertilized with phosphorus (P). There was no response to fertilization with N or other essential elements. Nitrogen-fixation rates were also elevated in lichens in P-fertilized plots at both sites. Phosphorus supply to host trees may be an important factor controlling N inputs to montane tropical forests by N-fixing epiphytes.     

西双版纳勐宋热带山地雨林种子植物区系的初步研究

西双版纳勐宋的热带山地雨林是一种东南亚热带山地雨林的北缘类型,它在植物区系组成上和群落学特征上是介于热带雨林和南亚热带常绿阔叶林之间的热带山地常绿阔叶林.该区系有种子植物116科327属623种.科、属、种的分布区类型分析表明:科的分布区类型以热带和亚热带分布最多(32.8%),其次是热带到温带分布(23.3%)和典型热带分布(18.1%);属的分布区类型以热带亚洲分布最多(28.4%),其次是泛热带分布(26.8%),热带分布多于温带分布(258:55);种的分布区类型以热带亚洲分布最多(65.0%),其次是中国特有分布(26.5%),热带分布远多于温带分布(431:18).区系的热带性质显著,具有明显的印度-马来西亚植物区系特点,属于热带亚洲区系的一部分.由于特殊的地理位置,西双版纳地区是许多典型热带植物的分布北界,同时又是几种热带成分的交汇地带.     

Water Relations and CO2 Exchange of Tropical Bryophytes in a Lower Montane Rain Forest in Panama

For 6 tropical bryophytes, measurements of the diel courses in water status and net CO₂ exchange were made in a submontane tropical rain forest in Panama. In addition, the response of gas exchange to changes in photon flux density (PPFD) and thallus water content (WC) was studied under controlled conditions. Diel variation of WC was pronounced, and both low and high WC limited carbon gain considerably. Low PPFD, e.g. during rain storms, was less important in limiting CO₂ exchange. More than half of the mean diurnal carbon gain of 2.9 mg C per g thallus carbon was lost during the night as respiration. Assuming that the average 24-h carbon gain was representative for the entire year, we estimated the net annual primary productivity of the mosses and liverworts to be 45% of the initial plant carbon content.     

Seed Dynamics in Relation to Gaps in a Tropical Montane Rainforest of Hainan Island, South China： （I） Seed Rain

Seed dynamics is an important part of stand dynamics in forest ecosystems. In this paper, 26 gaps were randomly selected to study the influence of gaps on the spatial and temporal patterns of seed rains in a tropical montane rainforest of Hainan Island, South China. Three zones for each gap, including outside gap zone （Non-gap）, transitional gap zone （EG-CG）, and central gap zone （CG）, were designed, and fourseed traps （each lm x lm in size） were placed in each zone. Seed rains were collected by these traps every 10 days from June 2001 to May 2002. Seed rain varied greatly with season and generally exhibited a pattern of unimodal change during the study period： seed abundance and species richness were both greater in the wet season than in the dry season. Gaps significantly influenced the temporal patterns of both species richness and density of seed rains. Gaps had no significant influences on the spatial distribution patterns of seed rain species richness, but significantly affected the spatial distribution pattern of seed rain densities. Among the three different zones of gaps, the outside gap zone generally received more seeds inputs than the two other gap zones.     

Interannual and seasonal variations of energy and water vapor fluxes above a tropical seasonal rain forest in Xishuangbanna, SW China

The values and variation characteristics of energy components, their relationship with net radiation and the characteristics of water balance in the forest were analyzed, based on the observation data of energy fluxes, meteorological parameters and biomass in a tropical seasonal rain forest in Xishuangbanna from January 2003 to December 2004. The results show that annual net radiation was 3516.4 MJ/(m² · a) and 3516.6 MJ/(m² · a) in 2003 and 2004, respectively, of which 46% and 44% were used in latent heat flux, and 12% and 11% were lost as sensible heat flux. Annual mean canopy surface conductance was 10.3 mm/s and 10.0 mm/s in 2003 and 2004, respectively. Moreover, canopy surface conductance was lower in dry-hot seasons than in fog-cool and rainy seasons. Canopy surface conductance correlated significantly and positively with leaf area index, but negatively with water vapor pressure deficit. In general, canopy surface conductance was not affected directly by soil water content, but highly depended on soil moisture status when soil water content was below 0.15 m³/m³. Annual total evapotranspiration of this forest ecosystem in dry seasons was lower than that in rainy seasons, which was considered as one of the most important reasons that tropical seasonal rain forest could survive and flourish in Xishuangbanna at limit of water and heat.