The Functional Traits And Their Diversities Of Tropical Forest Plants On Hainan Island, China

Plant functional traits are the features(morphological,physiological, phenological) that influence survival, growth,reproduction and fitness of a plant. Plant functional diversity is the value and range of the functional traits.Studies on the functional traits have increasingly been a new approach in community ecology in recent years, which can contribute to understanding community assembly and maintenance mechanism of species diversity. By analyzing plant functional traits and their diversities,we can understand the relationships between organisms and their abiotic environment,which is the basis for further exploring the changing of ecosytem functions and related ecosytem sevices.Tropical forests are the terrestrial ecosystems with complex structures and harboring the most abundant species.They play important roles in the regional and global biodiversity conservation and ecological functioning. The species rich and structural complex tropical forests are regarded as the most ideal place for exploring the maintenance mechanisms of biodiversity. Hainan Island is a region with the largest area of natural tropical forests in China. It has the unique and varied tropical vegetation types, in which rich array of tropical flora thrives.Understanding the spatial and temporal variations of plant functional traits and their diversities not only has theoretical implications in community ecology but also has important practical values in biodiversity consevation and ecological restoration on Hainan IslandIn this thesis,researches are done from three aspects. Firstly, a plant functional traits data base of the main woody species of Hainan Island was constructed,based on referring to the already exsted plant trait poolsand on combining with the field investigations of more than 10 years by our research group.The range and value of each functional traits and their variations with taxon(family and genera) levels. Furthermore, based on the field investigations of communities and measurements of fuctional traits and environmental factors across the six typical old-growth forest types in the Bawangling Nature Reserve on the Hainan Island, The variations of community struture, species diversity and community–level plant functional traits with vegetation types and environmental factorswere analyzed. Finally, the functional diversity and phylogenetic diversity indices were calculated based on plant functional traits.And the relationships btetween these indices and the environmental factors across the six old-growth forest vegetation types were examined.The main results are as as follows: 1. Statistics on 10 functional traits of 2281 woody plant species on the Hainnan Island showed that,: The species richness of tree growth-form plays a predominantrole, followed by the shrub and linas, phnerophytes predoniate life forms tropical woody plants. Broad-leaved species are significantly richer than of theconiferous species;leaves are predominantly leathery and papery; C3 species are significantly richer than the C4 and CAM species; Berries and nuts are predonminant in fruit types; Animal disperal mode playsthe most important role, thesecond is the wind disperal mode, and water disperal mode are the fewest; Species with no thorns are significantly richer than those of non-thorn species;andbuttress only exists in tall tree species.The dsitibutions of plants with different functional traits are probablly consistent with the habitat conditionds on the Hainan Island.2. The comparison of community struture and diversity featuresacross the six forest vegetation types(TDMRF means tropical deciduous monsoon rain forest; TCF means tropical coniferous forest; TLRF means tropical lowland rain forest; TMRF means tropical montane rain forest; TMEF means tropical montane everygreen forest; TMDF means tropical montane dwarf forest). Species richness and stem abundance dsitributions along the size classes were characterized by the "reverse-J" type curves. The individual-based rarefaction and species rank-abundance curves showed that the species richness were the highest in the TMRF and TLRF, the TDMRF and TCF were the second in richness, and the TMEF and TMDF had the lowest.The the species abundances of TDMRF,TCF and TLRF had significantcorrelations with soil p H, air temperature and soil available nitrogen. And those for the TMRF,TMEF and TMDF had significant correlations with canopy openness, soil organic matter and soil available phosphorus.3. Based on measurement and analysis on 9 environmental factors across the six old-growth forest vegetation types,We can see that different vegetation types were associated with habitats characterized by certain combinations of environmental factors. The TDMRF is characterized by high air temperature, soil organic matter and soil p H, but low total phosphorus, available phosphorus, canopy openness and soil water content habitat; the TCF is associated with high air temperature, canopy openness, and soil p H, but low soil water content and soil nutrients. The TLRF has low soil water content, canopy openness, and soil nutrients(especially P), and has moderate air temperature and soil p H; the TMRF is associated with high soil water content and moderate canopy openness, soil nutrients and soil p H. The two vegetation types at the highest elevations(TMEF and TMDF) have high canopy openness, soil phosphorus(both TP and AP), and soil organic matter, low soil nitrogen(both TN and AN) and air temperature, and moderate soil water content.4. Five plant functional traits across the six forest vegtation types were measured and their relationships with the environmental factors were analyzed at community level. CWM_SLA is the highest in the TDMRF. CWM_CC has the highest values in the TMRF and TLRF. CWM_LNC is the lowest in the TMDF and has significant differences with each of the other five vegetation types. CWM_LPC is the highest in the TDMRF while the TLRF has the lowest. CWM_WD has relative high values in the TDMRF, TMRF and TMEF. Changes in plant fuctional traits at community-level and theie environmental correlations across the forest vegetation types are analysed. In the TDMRF, CWM_SLA is positively correlated with soil water content but negatively correlated with available nitrogen and canopy openness; CWM_CC is positively correlated with available nitrogen but negatively correlated with canopy openness; CWM_WD is positively correlated with available nitrogen. In the TCF, CWM_CC is positively correlated with canopy openness and available nitrogen. In the TLRF, CWM_SLA, CWM_LNC and CWM_LPC are all positively correlated with available phosphorus. In the TMRF, CWM_SLA and CWM_LPC are positively correlated with total phosphorus, while CWM_CC is positively correlated with canopy openness. In the TMEF, CWM_SLA and CWM_LNC are positively correlated with total phosphorus and soil organic matter. CWM_LPC is positively correlated with soil organic matter but negatively correlated with p H. In the TMDF, CWM_SLA is positively correlated with total nitrogen and total phosphorus. CWM_LNC is positively correlated with total nitrogen, CWM_LPC is positively correlated with soil water content but negatively correlated with p H.5. Functional and phylogenetic diversity indices were calculated on basis of the plant functional traits across the six old-growth forest vegetation types. Both FRic and FEve are positively correlated with species richness across the six old-growth forest vegetation types. The FDiv is the highest in the TDMRF. The FDis also is the highest in the TDMRF. Changes in functional diversities and their environmental correlations across the forest vegetation types are analysed. In the TDMRF, the FRic is negatively correlated with canopy openness and total phosphorus, the FEve is positively correlated with soil water content and FDiv is negatively correlated with total phosphorus. In the TCF, the FRic is negatively correlated with total phosphorus and FDiv is positively correlated with soil water content but negatively correlated with soil organic content. In the TLRF, the FEve is positively correlated with available nitrogen and FDiv is positively correlated with total phosphorus but negatively correlated with soil mater content. In the TMRF, both FRic and FDis is positively correlated with total phosphorus. In the TMEF, the FEve is positively correlated with total phosphorus but negatively correlated with soil p H and the FDis is negatively correlated with soil p H. In the TMDF, both the FRic and the FDis are positively correlated with total phosphorus but negatively correlated with soil organic matter, respectively.6. Based on 3 phylogenetic diversity indices and 9 environmental factors across the six old-growth forest vegetation types. Phylogenetic structure all showed the clustering trend, indicating that the effect of environmental filtering across the six old-growth forest vegetation types were predominant. The phylogenetic diversity(PD) first incresed and then decreased along with the elevational gradient. Changes in phylogenetic structures indice and their environmental correlations across the forest vegetation types are analysed.Phylogenetic diversity indicesare affected by different environmental factors in the TDMRF,TMEF and TMDF, the key environmental factors are canopy openness, soil water content, soil pH and available nitrogen.