Influence of Human Activity Intensity on Habitat Quality in Hainan Tropical Rainforest National Park,China

Due to long-term human activity interference,the Hainan Tropical Rainforest National Park(HTRNP)of China has experienced ecological problems such as habitat fragmentation and biodiversity loss,and with the expanding scope and intensity of human activity impact,the regional ecological security is facing serious challenges.A scientific assessment of the interrelationship between human activity intensity and habitat quality in the HTRNP is a prerequisite for achieving effective management of ecological disturbances caused by human activities and can also provide scientific strategies for the sustainable development of the region.Based on the land use change data in 2000,2010,and 2020,the spatial and temporal variations and the relationship between habitat quality(HQ)and human activity intensity(HAI)in the HTRNP were explored using the integrated valuation of ecosystem services and trade-offs(InVEST)model.System dynamics and land use simulation models were also combined to conduct multi-scenario simulations of their relationships.The results showed that during 2000–2020,the habitat quality of the HTRNP improved,the intensity of human activities decreased each year,and there was a negative correlation between the two.Second,the system dynamic model could be well coupled with the land use simulation model by combining socio-economic and natural factors.The simulation scenarios of the coupling model showed that the harmonious development(HD)scenario is effective in curbing the increasing trend of human activity intensity and decreasing trend of habitat quality,with a weaker trade-off between the two compared with the baseline development(BD)and investment priority oriented(IPO)scenarios.To maintain the authenticity and integrity of the HTRNP,effective measures such as ecological corridor construction,ecological restoration,and the implementation of ecological compensation policies need to be strengthened.

A test of the mycorrhizal-associated nutrient economy framework in two types of tropical rainforests under nutrient enrichments

Shifts in tree species and their mycorrhizal associations driven by global change play key roles in biogeochemical cycles. In this paper, we proposed a framework of the mycorrhizal-associated nutrient economy(MANE), and tested it using nutrient addition experiments conducted in two tropical rainforests. We selected two tropical rainforests dominated by arbuscular mycorrhizal(AM) and ectomycorrhizal(ECM) trees, and established eighteen20 m×20 m plots in each rainforest. Six nitrogen(N) and phosphorus(P) addition treatments were randomly distributed in each rainforest with three replicates. We examined the differences in soil carbon(C) and nutrient cycling, plant and litter productivity between the two rainforests and their responses to 10-year inorganic N and P additions. We also quantified the P pools of plants, roots, litter, soil and microbes in the two rainforests. Overall,distinct MANE frameworks were applicable for tropical rainforests, in which soil C, N and P were cycled primarily in an inorganic form in the AM-dominated rainforest, whereas they were cycled in an organic form in the ECMdominated rainforest. Notably, the effects of mycorrhizal types on soil P cycling were stronger than those on C and N cycling. The intensified N and P deposition benefited the growth of AM-dominated rainforests instead of ECMdominated rainforests. Our findings underpin the key role of mycorrhizal types in regulating biogeochemical processes, and have important implications for predicting the ecological consequences of global changes.

Pollination Biology of Ficus hispida in the Tropical Rainforests of Xishuangbanna, China

Ficus hispida L. (Moraceae) is a remarkable species in the ecosystem of tropical rainforests in Xishuangbanna, China. The figs and fig_pollination wasps (Chalcidoidae: Agaonidae) are highly co_evolved mutualists that depend completely on each other for propagating descendants. Pollination of all fig species is done by fig wasps; their unique symbiotic associates, the fig wasps, cannot develop in anywhere except in the fig syconia. The present paper reports on the biology and flowering phenology of F. hispida , as well as the propagation character and pollination behavior of the fig wasps (Ceratosolen solmsi marchali Mayr) based on our observations in the rainforests of Xishuangbanna, southern Yunnan of China. F. hispida is a dioecious tree that annually blossoms and bears fruits 6-8 times, with four to five fruit_bearing peaks. The male trees produce pollen and provide fig wasps with reproductive havens, while the female trees produce fig seeds after pollination by the female wasps. Pollen of F. hispida cannot escape from the dehiscent anthers until they are disturbed by fig wasps. The female wasps open the anthers and collect pollen with their antennal scrapes, mandibles and legs, and then carry pollen to the female receptive syconia where fertilization takes place. Meanwhile, some of the female wasps lay eggs in the male receptive syconia. It takes about 3-67 min to search for the receptive syconia for pollination, and 15-23 h to enter the female receptive syconia. The number of female wasps entering a syconium has close relation with the impregnation and seed_bearing rate of female flowers, as well as the oviposition and reproduction rate of the fig wasps themselves. F. hispida is endowed with a relatively high level of seed bearing (54.1%-82.5%, average 73.8 %). The wasp oviposition rate on the male flowers is between 72.3% and 93.8% with a mean of 84.4%.

THE TROPICAL RAINFOREST VEGETATION IN XISHUANGBANNA

The tropical rainforest in Xishuangbanna,Yunnan Province of China,is introduced in detail in this paper.Situated at the northern margin of tropical mainland SE Asia and controlled by monsoon climate,the region has been climatically at the lower limits for tropical rainforests,however true tropical rainforests exist and develop luxuriantly in the region.The reasons for this are discussed.In general phytocoenological characteristics such as vertical stratification,life form spectrum,species riches etc.the tropical rainforest in Xishuangbanna is very similar to the typical tropical rainforest in equatorial region,but it is characterized by a clear change of physiognomy between different season.As occurred at the latitudinal and altitudinal limits of tropical rainforest,the flora of the rainforest is endowed with the nature of northern margin of tropical zone of SE Asia and is transitional toward the flora of subtropical forest of China.In recent years the region has been opened up to use in a large scale and the primary forests,eseialy rainforests,have been severely destroyed,The conserva.tion and rsercho lo the ropiranr rnforest are very ugent and have io be doneat once.

Lipid concentration and composition in xylem sap of woody angiosperms from a tropical savanna and a seasonal rainforest

Lipids may play an important role in preventing gas embolisms by coating nanobubbles in xylem sap.Few studies on xylem sap lipids have been reported for temperate plants,and it remain unclear whether sap lipids have adaptational significance in tropical plants.In this study,we quantify the lipid composition of xylem sap for angiosperm species from a tropical savanna(seven species)and a seasonal rainforest(five species)using mass spectrometry.We found that all twelve species studied contained lipids in their xylem sap,including galactolipids,phospholipids and triacylglycerol,with a total lipid concentration ranging from 0.09 to 0.26 nmol/L.There was no difference in lipid concentration or composition between plants from the two sites,and the lipid concentration was negatively related to species’open vessel volume.Furthermore,savanna species showed little variation in lipid composition between the dry and the rainy season.These results support the hypothesis that xylem sap lipids are derived from the cytoplasm of individual conduit cells,remain trapped inside individual conduits,and undergo few changes in composition over consecutive seasons.A xylem sap lipidomic data set,which includes 12 tropical tree species from this study and 11 temperate tree species from literature,revealed no phylogenetic signals in lipid composition for these species.This study fills a knowledge gap in the lipid content of xylem sap in tropical trees and provides additional support for their common distribution in xylem sap of woody angiosperms.It appears that xylem sap lipids have no adaptive significance.

Activity-density and spatial distribution of termites on a fine-scale in a tropical rainforest in Xishuangbanna,southwest China

The community composition and activity-density of termites can influence nutrient cycling and other ecological functions.However,the spatial distribution and the activity-density of termites on a fine-scale in tropical forests are still unknown.We checked the spatial distribution patterns of the feeding groups and species of termites and their co-occurrence pattern in a 1-ha(100 m×100 m)plot,and their correlatiion with the environmental factors.We used a standard protocol to collect termite assemblages and classified them into five feeding groups based on their preferrred diet:fungus growers,litter feeders,soil feeders,soil-wood feeders,and wood feeders.We measured the environmental factors:soil pH,litter mass,aboveground plant biomass,and topographic position index(TPI).Soil-wood feeders showed the highest activity-density,followed by wood feeders,fungus growers,soil feeders,and litter feeders.Soil-wood feeders and fungus growers demonstated a strong correlation while litter feeders showed weak correlations with other feeding groups.Termite feeding groups and most of the termite species displayed a positive association with the high TPI and the low soil pH patches.Our results indicated that the examined environmental factors influenced the termite community assemblages and distribution patterns on a fine-scale in tropical rainforests.

Climate and land-use interactively shape butterfly diversity in tropical rainforest and savanna ecosystems of southwestern China

Human-induced habitat conversion and degradation,along with accelerating climatic change,have resulted in considerable global biodiversity loss.Nevertheless,how local ecological assemblages respond to the interplay between climate and land-use change remains poorly understood.Here,we examined the effects of climate and land-use interactions on butterfly diversity in different ecosystems of southwestern China.Specifically,we investigated variation in the alpha and beta diversities of butterflies in different landscapes along human-modified and climate gradients.We found that increasing land-use intensity not only caused a dramatic decrease in butterfly alpha diversity but also significantly simplified butterfly species composition in tropical rainforest and savanna ecosystems.These findings suggest that habitat modification by agricultural activities increases the importance of deterministic processes and leads to biotic homogenization.The land-use intensity model best explained species richness variation in the tropical rainforest,whereas the climate and land-use intensity interaction model best explained species richness variation in the savanna.These results indicate that climate modulates the effects of land-use intensity on butterfly alpha diversity in the savanna ecosystem.We also found that the response of species composition to climate varied between sites:specifically,species composition was strongly correlated with climatic distance in the tropical rainforest but not in the savanna.Taken together,our long-term butterfly monitoring data reveal that interactions between human-modified habitat change and climate change have shaped butterfly diversity in tropical rainforest and savanna.These findings also have important implications for biodiversity conservation under the current era of rapid human-induced habitat loss and climate change.

Population distribution and threats to sustainable management of selected non-timber forest products in tropical lowland rainforests of south western Nigeria

Uncontrolled harvesting of non-timber forest products （NTFPs） poses a serious risk of extermination to several of these species in Nigeria. Yet, there is a paucity of information on the distribution, population status and sustainable management of NTFPs in most of the tropical lowland rainforests. We, therefore, assessed the population, distribution and threats to sustainable management of NTFPs within the tropical lowland rainforests of Omo and Shasha Forest Reserves, south western Nigeria. Data were obtained through inventory surveys on five top priority species including： bush mango （Irvingia gabonensis （Aubry-Lecomte ex O’Rorke） Baill）, African walnut （Tetracarpidium conophorum （Mull. Arg.） Hutch. ＆ Dalziel syn. Plukenetia conophora）, chew-stick （Massularia acuminata （G. Don） Bullock）, fever bark （Annickia chlorantha Setten ＆ P.J.Maas syn. Enantia chloranta） and bush pepper （Piper guineense Schumach. ＆ Thonn.）. Purposive and stratified random sampling techniques were used for the inventory. Each forest reserve was stratified into three, viz： less disturbed natural forest （for areas that have been rested for at least ten years）, recently disturbed natural forest （for areas that have suffered one form of human perturbation or the other in the last five years）, and plantation forest （for areas carrying forest plantation）. Data were collected from eighteen 10 m × 500 m belt transects located in the above strata. The species were generally fewer in both plantation and recently disturbed natural forest than the less disturbed natural forest, suggesting that forest disturbances （habitat modification） for other uses may have an effect on the occurrence and densities of the NTFPs. Exceptions to this trend were found for P. guineense and T. conophorum, which were fairly common in both plantation and recently disturbed natural forest. Among three tree NTFP species （i.e. I. gabonensis, M. acuminata and A. chlorantha）, only I. gabonensis showed a significant difference in overall DBH size classes for both reserves （t=？2.404; df =21; p=0.026）. Three tree NTFP species in both reserves further showed differences from the regular patterns of distribution of trees. The fairly regular reverse J-shaped size class distribution observed for M. acuminata in the study sites, however, suggests a recuperating population. In general, destructive harvesting of species, logging operations, low population size, narrow distribution ranges and habitat degradation are the major threats to the population of NTFPs in the study area. The implications of our findings for sustainable management of NTFPs in the study area are discussed and recommendations are made for a feasible approach towards enhancing the status of the species.

Observational study of the physical and chemical characteristics of the winter radiation fog in the tropical rainforest in Xishuangbanna, China

We conducted a three-month field experiment focusing on the physical and chemical characteristics of fog in a tropical rainforest in Xishuangbanna,Southwest China,in the winter of 2019.In general,the fog would form at midnight and persist because of the increased long-wave radiative cooling combined with the high relative humidity,gentle breeze,and a relatively low aerosol number concentration in the forest;the fog would dissipate before noon due to the increasing turbulence near the surface.This diurnal cycle is typical for radiation fog.The microphysical fog properties included a relatively low number concentration of the fog droplet,large droplet size,high liquid water content,narrow droplet number-size distribution,and high supersaturation.The chemical properties showed that the fog water was slightly alkaline with low electrical conductivity,whereas the highest proportions of anions and cations therein were Cl^(−)and Ca^(2+),respectively;the chemical components were enriched in small fog droplets.In addition,we indirectly calculated the fog supersaturation according to theκ-Köhler theory.We found that condensation broadens the droplet number-size distribution at relatively low supersaturation,which is positively correlated with the fog-droplet number concentration and negatively correlated with the droplet mean-volume diameter;this affects the key microphysical processes of fog.

Responses of soil CH_(4) fluxes to nitrogen addition in two tropical montane rainforests in southern China

Background:Atmospheric nitrogen(N)deposition is projected to increase in the next few decades,which may have a marked impact on soil-atmosphere CH_(4) fluxes.However,the impacts of increased atmospheric N depositions on soil CH_(4) flux in tropical rainforests are still poorly understood.From January 2015 to December 2018,a field experiment was conducted in a primary tropical montane rainforest(PTMR)and a secondary tropical montane rainforest(STMR)in southern China to quantify the impact of N additions at four levels(N0:0 kg N⋅ha^(-1)⋅year^(-1);N25:25 kg N⋅ha^(-1)⋅year^(-1);N50:50 kg N⋅ha^(-1)⋅year^(-1);N100:100 kg N⋅ha^(-1)⋅year^(-1)on soil CH_(4) flux.Results:Four years of measurements showed clear seasonal variations in CH_(4) flux in all treatment plots for both forest types(PTMR and STMR),with lower rates of soil CH_(4) uptake during the wet season and higher rates of soil CH_(4) uptake during the dry season.Soil CH_(4) uptake rates were significantly and negatively correlated with both soil temperature and soil moisture for both forest types.Annual CH_(4) uptake for the N0 plots from the PTMR and STMR soils were2.20 and1.98 kg N⋅ha^(-1)⋅year^(-1),respectively.At the PTMR site,mean CH_(4) uptake compared with the N0 treatment was reduced by 19%,29%,and 36%for the N25,N50,and N100 treatments,respectively.At the STMR site,mean CH_(4) uptake compared with the N0 treatment was reduced by 15%,18%,and 38%for the N25,N50,and N100 treatments,respectively.High level N addition had a stronger inhibitory impact on soil CH_(4) uptake than did the low level N addition.Conclusion:Our data suggest that soil CH_(4) uptake in tropical rainforests is sensitive to N deposition.If atmospheric N deposition continues to increase in the future,the soil CH_(4) sink strength of tropical rainforests may weaken further.

Phyllosphere eukaryotic microalgal communities in rainforests:Drivers and diversity

Phyllosphere algae are common in tropical rainforests,forming visible biofilms or spots on plant leaf surfaces.However,knowledge of phyllosphere algal diversity and the environmental factors that drive that diversity is limited.The aim of this study is to identify the environmental factors that drive phyllosphere algal community composition and diversity in rainforests.For this purpose,we used single molecule real-time sequencing of full-length 18S rDNA to characterize the composition of phyllosphere microalgal communities growing on four host tree species(Ficus tikoua,Caryota mitis,Arenga pinnata,and Musa acuminata) common to three types of forest over four months at the Xishuangbanna Tropical Botanical Garden,Yunnan Province,China.Environmental 18S rDNA sequences revealed that the green algae orders Watanabeales and Trentepohliales were dominant in almost all algal communities and that phyllosphere algal species richness and biomass were lower in planted forest than in primeval and reserve rainforest.In addition,algal community composition differed significantly between planted forest and primeval rainforest.We also found that algal communities were affected by soluble reactive phosphorous,total nitrogen,and ammonium contents.Our findings indicate that algal community structure is significantly related to forest type and host tree species.Furthermore,this study is the first to identify environmental factors that affect phyllosphere algal communities,significantly contributing to future taxonomic research,especially for the green algae orders Watanabeales and Trentepohliales.This research also serves as an important reference for molecular diversity analysis of algae in other specific habitats,such as epiphytic algae and soil algae.

Characteristics of typhoon disturbed gaps in an old-growth tropical montane rainforest in Hainan Island, China

Disturbances that create gaps can shape the structure and function of forests. However, such disturbance regimes in Asian tropical montane rainforests remain largely unquantified. Least studied are typhoon disturbances that are attributable to climate change. We investigated gap characteristics in terms of size, age, and gap-maker to quantify the gap disturbance regimes in an intact old-growth tropical montane rainforest on Hainan Island, China. The intensity of typhoons has increased since 1949, and typhoon winds blow mostly (45.5%) from the northeast corner of Hainan Island, resulting in a higher frequency of gaps in the northeast. A total of 221 gap-makers (trees that fell to create canopy gaps) and 53 gaps were observed in a 3.16 ha old-growth rainforest. Most canopy gaps (85%) were < 200 m(2). The average size of canopy gaps was smaller in the rainforest than in other tropical forests, while the average size of expanded gaps was similar to those in other tropical forests. The maximum age of gaps was 23.5 years indicating that gaps had more rapid turnover than other parts of tropical forests. The frequency distribution of gap-makers followed a lognormal distribution with a distinctive peak at three gap-makers, which was different from the inverse J-shaped curve typical of other tropical forests. Gaps were recorded mainly on slopes between 20A degrees and 35A degrees and wood density of gap-makers was between 0.6 and 0.7 g cm(-3). Our results suggest that small-scale disturbance was the dominant agent of gap formation in this old-growth rainforest that is subject to increasing typhoon disturbances.

Buttress trees in a 20-hectare tropical dipterocarp rainforest in Xishuangbanna, SW China

Aims buttresses are prevalent and are important to many ecological processes in tropical rainforests but are overlooked in many rainforest studies.based on a buttress survey in a 20-hectare plot,this study aims to answer the following questions:(i)is buttress forming a fixed species characteristic?(ii)is there any phylogenetic signal for buttress forming across a broad taxonomic scale?(iii)is buttress form-ing an inherent feature or simply induced by environmental factors,and how is this relevant to the size of the tree?Methods We surveyed buttresses for all 95940 trees with diameter at breast height(DbH)≥10 mm in a 20-ha tropical dipterocarp rainforest in Xishuangbanna,sW China.The occurrence of buttresses was compared across different taxa and across different tree-size classes.a phylogenetic analysis was conducted among buttressed and non-buttressed species in order to understand the evolutionary background of buttress formation.Important Findings This preliminary study showed that buttress trees are very abundant(making up 32%of trees with≥100 mm DbH)in this 20-ha tropical rainforest situated at the northern edge of the tropics.Fifty-one percent of the 468 tree species in the plot had stems that produced buttresses.large trees were more likely to develop buttresses than smaller ones.We found that although buttress formation is not a fixed species characteristic,there is a strong phylogenetic signal for buttress formation in larger species.

Genetic diversity of Mansonia altissima A. Chev. under different regimes of human impact in the Akure Forest Reserve,Nigeria

Mansonia altissima is an important West African timber tree species. For the purpose of examining the effect of human impact on its genetic diversity, genetic diversity and spatial genetic structure of the species under different regimes of human impact were investigated in the Akure Forest Reserve, Nigeria, using 504 amplified fragment length polymorphism （AFLP） markers. The results indicate a very low genetic diversity in M. altissima within the forest reserve （He = 0.045; PPL = 16.75%; Br = 1.162）. The highest genetic diversity was observed in the primary forest （H e= 0.062; PPL - 21.00%; Br = 1.204）, with the lowest genetic diversity in the isolated forest patch （He = 0.032; PPL = 9.00%; B r= 1.089）. A significant and pronounced spatial genetic structure was found in the logged forest and in the isolated forest patch. In contrast, the primary forest exhibited very weak spatial genetic structuring. As expected, no spatial genetic structure was found in the planted stands of M. altissima. From a conservation point of view, our results suggest that genetic diversity ofM. altissima is at risk in the forest reserve. The scale of human impact in the study area could pose a serious threat to the maintenance of genetic diversity of the species. These results would offer practical applications in the conservation of other tropical tree species.

Temperature and substrate availability regulate soil respiration in the tropical mountain rainforests,Hainan Island,China

Aims Tropical forest plays a key role in global C cycle;however,there are few studies on the C budget in the tropical rainforests in Asia.This study aims to(i)reveal the seasonal patterns of total soil respiration(R_(T)),litter respiration(R_(L))and soil respiration without surface organic litter(R_(NL))in the primary and secondary Asian tropical mountain rainforests and(ii)quantify the effects of soil temperature,soil moisture and substrate availability on soil respiration.Methods The seasonal dynamics of soil CO_(2) efflux was measured by an automatic chamber system(Li-8100),within the primary and secondary tropical mountain rainforests located at the Jianfengling National Reserve in Hainan Island,China.The litter removal treatment was used to assess the contribution of litter to belowground CO_(2) production.Important Findings The annual R_(T) was higher in the primary forest(16.73±0.87 Mg C ha−1)than in the secondary forest(15.10±0.26 Mg C ha−1).The rates of R_(T),R_(NL) and R_(L) were all significantly higher in the hot and wet season(May–October)than those in the cool and dry season(November–April).Soil temperature at 5cm depth could explain 55–61%of the seasonal variation in R_(T),and the temperature sensitivity index(Q_(10))ranked by R_(L)(Q_(10)=3.39)>R_(T)(2.17)>R_(NL)(1.76)in the primary forest and by R_(L)(4.31)>R_(T)(1.86)>R_(NL)(1.58)in the secondary forest.The contribution of R_(L) to R_(T) was 22–23%,while litter input and R_(T) had 1 month time lag.In addition,the seasonal variation of R_(T) was mainly determined by soil temperature and substrate availability.Our findings suggested that global warming and increased substrate availability are likely to cause considerable losses of soil C in the tropical forests.

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

Spatial and temporal patterns of seed bank dynamics in relation to gaps in an old growth tropical montane rainforest of Hainan Island, South China, were studied over two consecutive years. From June 2001 to June 2003, soil seed bank sampling blocks were taken near each of the four sides of each seed trap and immediately put into a nursery for observation of seedling emergence dynamics in four seasons （each experiment in each season）. The abundances of seedlings that emerged from seed banks showed the trend of vine functional group （VFG） 〉 shrub functional group （SFG） 〉 tree functional group （TFG） 〉 herb functional group （HFG）, but the trend in species richness of seedlings that emerged from the soil seed banks was TFG 〉 VFG 〉 SFG 〉 HFG. The abundances of seedlings that emerged from seed banks in the three gap zones showed no significant differences, but significant differences did exist for the species richness. The time of sampling or seasons of experiments had significant influences on both the species richness and seedling abundances. The seedling emergence processes of each experiment all revealed the unimodal patterns. Few emergences occurred 1 year after each experiment. Compared with those under closed canopies, the recruitment rates from seed to seedlings and from seedlings to saplings In gaps were higher, but the mortality rates from saplings to big trees were also higher in the gaps.

Synergetic effects of photo-oxidation and biodegradation on failure behavior of polyester coating in tropical rain forest atmosphere

This work aimed to study the comprehensive effects of photo-oxidation and biodegradation on different failure stages of polyester coatings,which were exposed to the tropical rainforest atmosphere.The surface morphology,aging products,local aging characteristics and electrochemical behavior of the coatings were characterized with scanning electron microscope(SEM),fourier transform infrared spectroscopy(FTIR),electrochemical impedance spectroscopy(EIS)and high-resolution dispersive Raman microscope.The results showed that the surface of coatings became rougher and fungal hyphae distributed more densely on surface with the increasing of exposure time.From the aspect of polymer structure,the ultraviolet radiation destroyed the main chain of polyester through the photo-oxidation process,resulting in the breakage of aliphatic ester bonds and the formation of esters.Further,the metabolites of fungi can promote the hydrolysis of oligomers produced by the photo-oxidation.In a short,the photo-oxidation could facilitate the biodegradation of the coating.With the synergistic effect of UV photo-oxidation and fungal biodegradation,a rapid diffusion tunnel between the coating surface and the metal substrate was established at the pore defects of the coating,which finally accelerated the corrosion failure process of the coating.The main corrosion products includeα-Fe_(2)O_(3),ZnO and Zn_(5)(OH)_(6)(CO_(3))_(2).

Response of Somatal Characteristics and its Plasticity to Different Light Intensities in Leaves of Seven Tropical Woody Seedlings

Stomatal characteristics and its plasticity were surveyed in leaves of four canopy species, Shoreachinensis, Pometia tomentosa, Anthocephalus chinensis, Calophyllun polyanthum and three middle-layerspecies, Barringtonia pendula, Garcinia hanburyi, Horsfieldia tetratepala, acclimated to different lightconditions for more than one year. All plants stomata are distributed on the abaxial of leaves. Pometiatomentosa and Barringtonia pendula have higher stomatal density and the guard cell length of Anthocephaluschinensis and Calophyllun polyanthum were much greater than others. Stomatal density and stomatal index(ratio of stomatal numbers to epidermal cell number) were increased with growth irradiance increased, whilenumbers of stomata per leaf were higher in the low than the high relative PFD, and stomatal conductance ofleaves was the highest in the 50% of full light except for Anthocephalus chinensis. The relative PFD has littleeffects on the guard cell length of all seven plants. We have also found a significant negative correlationbetween stomatal density and leaf area, but the stomatal conductance was not significantly positive with thestomatal conductance. The analysis of phenotypic plasticity of stomatal characteristics showed: plasticityindex for stomatal index and numbers of stomatal per leaf were similar for canopy and middle-layer species,while the plasticity index of stomatal density and stomatal conductance were significantly greater for canopyspecies than middle-layer species. The high plasticity of canopy species was consistent with the hypothesisthat specialization in a more favorable environment increases plasticity.

Growth and phenotypic plasticity of two tropical tree species under low light availability

Aims Screening tree species in tropical rainforest according to their shade tolerance is important to efficiently manage the native trees of economic significance in secondary forest enrichment regimes.The objective of this study was to determine the whole-plant light compensation point(WPLCP)and compare the phenotypic plasticity in relation to growth and carbon allocation of Cariniana legalis and Gallesia integrifolia seedlings under low light availability.Methods Seedlings were cultivated for 77 days under conditions of five photosynthetically active radiation(PAR)(0.02,1.1,2.3,4.5 and 5.9 mol photons m^(−2)day^(−1))in three replicates.Growth and carbon allocation variables were determined.Important Findings Growth rates of C.legalis were higher and lower than those of G.integrifolia under 1.1 and 5.9 mol photons m^(−2)day^(−1),respectively.The WPLCP differed significantly between the two species.In accordance with the criteria of the shade tolerance classification for these two tropical tree species,our results showed that C.legalis had lower WPLCP and phenotypic plasticity in terms of higher growth rates and greater shade tolerance than G.integrifolia.From a practical point of view,we demonstrated that the differential linkage between growth and changing PAR between the two species can become a useful tool for comparing and selecting tree species in forest enrichment projects.

Microhabitat heterogeneity associated with Vanilla spp.and its influences on the microbial community of leaf litter and soil

The impact of forest microhabitats on physiochemical properties of the soil and that of microbial communities on tropical soils remain poorly understood.To elucidate the effect of tropical forest stand on leaf litter and soil microbial communities,we studied enzyme activities,microbial biomass,and diversity in three distinct microhabitats in terms of plant richness,diameter at breast height(DBH),and physiochemical properties of soil and litter,each associated with a different Vanilla sp.In the soil,positive correlations were found between electrical conductivity(EC)and total organic carbon(TOC)with phosphatase activity,and between nitrogen(N)and water-soluble carbon(WSC)content with urease activity(UA).In the litter,the water content was positively correlated with bacterial and fungal biomass,and N and WSC contents were positively correlated with fungal biomass.Positive correlations were found between plant richness and UA in the soil,plant richness and fungal biomass in the soil and litter,and DBH and fungal biomass in the litter.Amplicon sequencing revealed differences between microhabitats in the relative abundance of some fungal and bacterial taxa and in the bacterial community composition of both litter and soil.Bacterial richness and diversity were different between microhabitats,and,in litter samples,they were negatively correlated with DBH and plant richness,respectively.By contrast,none of the soil and litter physiochemical properties were significantly correlated with microbial diversity.Our results show that significant shifts in enzyme activity,microbial biomass,and diversity in the microhabitats were driven by key abiotic and biotic factors depending on the soil or litter sample type.