Atmospheric evaporative demand and water deficit on the ecophysiology of Rubber seedlings

The search for genetic materials resistant to adverse weather conditions has been a major focus in studies on species of economic interest. The objective of the present study was to assess the growth and photosynthesis of rubber seedlings clones under two conditions of atmospheric evaporative demand, characterized by fluctuations in temperature (TEMP) and vapor pressure deficit (VPD), associated to two water regimens. Hevea brasiliensis Muell. Arg (RRIM 600 and FX 3864) clones were assessed in two microclimates, at low (TEMP 21.2 ºC and VPD 0.29 Kpa) and high (TEMP 26.9 ºC and VPD 1.49 Kpa) atmospheric evaporative demand, under two water regimens: water deficit and well-watered. Water deficit 50% water availability was sufficient to reduce the net CO2 assimilation rate, leaf area and total chlorophyll of the clones studied that impacted growth in both microclimates. The effects of water deficit on growth and net carbon assimilation rate were intensified under high atmospheric evaporative demand. However, when comparing the two clones studied, RRIM 600 showed greater growth and photosynthesis without water restriction. The FX 3864 clone, despite the high CO2 assimilation values under high atmospheric demand and without water restriction, showed a reduced growth. The results of this study form an important basis for the selection of genotypes with the potential to develop in adverse climatic conditions. In this sense, the RRIM 600 genotype is recommended as a promising material that would best adapt under adverse climatic conditions.

Influence of spatial variability of soil chemical attributes on the nutritional status and growth of the rubber tree

The productive potential of the rubber tree (Hevea brasiliensis) is dependent on its genetic composition, in addition to edaphoclimatic factors and management practices. However, as soil properties are not homogenous, knowing the spatial variability of soil attributes would be important to increase productivity and reduce production costs. In this context, the objective of this study was to determine the spatial variability of chemical attributes of the soil and its influence on the nutritional status and growth of rubber tree clones. Clones FX 3864, FDR 5788, CDC 312, and RRIM 600 were planted at Jaturnaíba Farm, in the municipality of Silva Jardim, Rio de Janeiro State, Brazil. The sampling sites were distributed at a spacing of 20 × 20 m on the northern and southern sides of the relief. The chemical attributes of the soil (pH, Ca2+, Mg2+, K+, P, Al3+, H+Al, sum of bases, cation exchange capacity, and base saturation) were evaluated at a depth of 0­20 cm in the different clone plantations. Additionally, the N, P, K, Ca, and Mg content as well as trunk circumference and total plant height, were also evaluated. Geostatistics was used to determine the spatial variability of the soil and clone attributes, while Ordinary Kriging was used to draw variability maps of the variables. A difference in the distribution of the variables, which was dependent on the slope of the relief, was detected through the maps. The southern side presented better conditions as some degradation was observed on the northern side. Certain soil characteristics influenced the distribution of the attributes of the planted clones; for example, the low concentration of Ca2+ in the soil caused Ca deficiency in the FX clone on the southern slope, indicating that liming did not supply enough nutrients for this clone. Our results showed that the variability in soil attributes influenced the nutritional status and growth of the rubber tree clones, indicating that variability maps can guide the planting and management of the rubber tree, providing more efficient management.

Reconciling Rubber Expansion with Biodiversity Conservation.

Over five million hectares of tropical forest were cleared across mainland Southeast Asia and sub-Saharan Africa for rubber plantations between 2003 and 2017 [1, 2]. Millions of hectares of further clearance are predicted as rubber demand rises, which will have major consequences for biodiversity [3]. A key question is how to reconcile rubber expansion with biodiversity conservation. We assessed the feasibility of simultaneously meeting global future demand for rubber with conservation of extinction-threatened amphibians, birds, mammals, and reptiles. We compared the spatial congruence of rubber bioclimatic suitability with extinction vulnerability [4] in Africa, Asia, and New Guinea, where large-scale rubber cultivation is viable, and simulated rubber expansion under different scenarios. We found no "win-win" areas with highest rubber suitability and lowest extinction vulnerability. Projected rubber demand could be met by allowing expansion primarily in New Guinea and African Guinea. However, New Guinea has high ecosystem intactness and both regions are rich in endemics. Scenarios suggest converting only areas suitable for cultivation would cause the largest biodiversity losses, including endangered species, whereas prioritizing conservation would result in only the conversion of highly unsuitable land. Compromise scenarios that balance production with conservation could cut biodiversity losses by two-thirds, protecting most endangered species while maintaining high rubber suitability. Development of high-yielding hardy clones expands the amount of win-win areas, as well as suitable areas with high extinction risk. These trade-offs reveal that clonal research and development, strategic corporate and government land-use policies, and rigorous impact assessments are needed to prevent severe biodiversity losses from rubber development.

Identification and evaluation of suitable reference genes for gene expression analysis in rubber tree leaf.

Gene expression profiles are increasingly applied to investigate molecular mechanism for which, normalization with suitable reference genes is critical. Previously we have reported several suitable reference genes for laticifer samples from rubber tree, however, little is known in leaf. The main objective of this current study was to identify some stable expression reference genes at various developmental stages of leaf, as well as during abiotic (high and low temperature extremes) and biotic stresses (pathogen stress). Gene expression profilings identified the ubiquitin-proteasome system as excellent potential as reference genes for rubber tree leaf. Among a total of 30 tested genes investigated, 24 new candidate (including 11 genes involved in the ubiquitin-proteasome system), 4 previously identified and 2 specific genes, were further evaluated using quantitative real-time PCR. Our results indicated that the new candidate genes had better expression stability comparing with others. For instance, an ubiquitin conjugating enzyme (RG0099) and three ubiquitin-protein ligases (RG0928, RG2190 and RG0118) expressed stably in all samples, and were confirmed to be suitable reference genes for rubber tree leaf under four different conditions. Finally, we suggest that using more than one reference gene may be appropriate in gene expression studies when employing different software to normalize gene expression data. Our findings have significant implications for the reliability of data obtained from genomics studies in rubber tree and perhaps in other species.

Exploration of stem endophytic communities revealed developmental stage as one of the drivers of fungal endophytic community assemblages in two Amazonian hardwood genera.

Many aspects of the dynamics of tropical fungal endophyte communities are poorly known, including the influence of host taxonomy, host life stage, host defence, and host geographical distance on community assembly and composition. Recent fungal endophyte research has focused on Hevea brasiliensis due to its global importance as the main source of natural rubber. However, almost no data exist on the fungal community harboured within other Hevea species or its sister genus Micrandra. In this study, we expanded sampling to include four additional Hevea spp. and two Micrandra spp., as well as two host developmental stages. Through culture-dependent and -independent (metagenomic) approaches, a total of 381 seedlings and 144 adults distributed across three remote areas within the Peruvian Amazon were sampled. Results from both sampling methodologies indicate that host developmental stage had a greater influence in community assemblage than host taxonomy or locality. Based on FunGuild ecological guild assignments, saprotrophic and mycotrophic endophytes were more frequent in adults, while plant pathogens were dominant in seedlings. Trichoderma was the most abundant genus recovered from adult trees while Diaporthe prevailed in seedlings. Potential explanations for that disparity of abundance are discussed in relation to plant physiological traits and community ecology hypotheses.

Impact of biochar application dose on soil microbial communities associated with rubber trees in North East Thailand.

Biochar is a potential tool to mitigate climate change by enhancing C sequestration in soils, but its use as a soil amendment to improve soil fertility and crop yields is still a contentious subject. In North East (NE) Thailand, biochar has been promoted to restore soil fertility in rubber tree plantations. Despite this, there is scarce information on the impact of biochar application on the soil biota, particularly on microbial communities associated with rubber trees. The effects of increasing doses of biochar on microbial communities were investigated in a rubber tree plantation in NE Thailand, 28 months after application. Biochar application resulted in increases of soil pH and nutrient contents and also had an impact on both bacterial and fungal communities. Changes in microbial composition and structure were observed although fungal communities were more markedly affected than bacterial communities. The nature and magnitude of the observed changes were strongly related to soil properties (pH, soil moisture and P content), while biochar dose (5, 10 or 20 tons/ha) effect was not significant. Our results highlight the need for additional research for a better understanding of the impact of biochar application on soil microbial communities and further cascading effects on ecosystem functions.

Tropical forest conversion to rubber plantation in southwest China results in lower fungal beta diversity and reduced network complexity.

Despite the extensive, ongoing conversion of tropical forests to rubber plantation, the effects of this land-use change on soil fungal community diversity and composition are still poorly known. We compared a network of sites of tropical forest in southern Yunnan, China, with a network of rubber plantation sites originally derived from this forest. Soil DNA was amplified for ITS2 and sequenced using Illumina MiSeq. We found that there was a major shift in community composition across all phyla, including a large reduction in ectomycorrhizal fungi likely related to the absence of hosts. Conversion from forest to rubber plantation had no effect on total fungal α-diversity, but rubber plantation had lower ß-diversity, resulting in lower overall gamma diversity. Networks based on co-occurrence of operational taxonomic unit in each land-use type showed that network complexity decreased with land-use change from forest to rubber plantation. Further investigation of soil functionality is needed to investigate whether this lower network complexity is related to reduced soil ecosystem resilience.

Tropical forest conversion to rubber plantation affects soil micro- & mesofaunal community & diversity.

Tropical rainforests play important roles in carbon sequestration and are hot spots for biodiversity. Tropical forests are being replaced by rubber (Hevea brasiliensis) plantations, causing widespread concern of a crash in biodiversity. Such changes in aboveground vegetation might have stronger impacts on belowground biodiversity. We studied tropical rainforest fragments and derived rubber plantations at a network of sites in Xishuangbanna, China, hypothesizing a major decrease in diversity with conversion to plantations. We used metabarcoding of the 18S rRNA gene and recovered 2313 OTUs, with a total of 449 OTUs shared between the two land-use types. The most abundant phyla detected were Annelida (66.4% reads) followed by arthropods (15.5% reads) and nematodes (8.9% reads). Of these, only annelids were significantly more abundant in rubber plantation. Taken together, α- and ß-diversity were significantly higher in forest than rubber plantation. Soil pH and spatial distance explained a significant portion of the variability in phylogenetic community structure for both land-use types. Community assembly was primarily influenced by stochastic processes. Overall it appears that forest replacement by rubber plantation results in an overall loss and extensive replacement of soil micro- and mesofaunal biodiversity, which should be regarded as an additional aspect of the impact of forest conversion.

Asymmetric birth and death of type I and type II MADS-box gene subfamilies in the rubber tree facilitating laticifer development.

The rubber tree (Hevea brasiliensis Muell. Arg.) is a rubber producing crop and contains specialized laticifers. MADS-box genes are a family of transcription factor genes that regulate plant development, especially floral organ and gametophyte development. 97 MADS-box genes were identified in the rubber tree through transcriptomes and genome mining. 93.8% of the genes were mapped onto the genome scaffolds in correspondence to the coverage (93.8%) of current version of sequenced genome. Phylogenetic analysis indicates that type II MADS-box genes have been more actively duplicated than their orthologous genes in Arabidopsis and rice, so that most (70, 72.2%) of the MADS-box genes in the rubber tree belong to type II subfamily. This is a high percentage compared to those in Arabidopsis (43.7%) and rice (56.8%). Moreover, 69 out of 70 type II genes in the rubber tree are transcribed, and they are mostly predominantly expressed in flowers, but some genes are predominantly expressed in laticifers, suggesting their roles in both flower and laticifer development. The number of type I genes in the rubber tree is only 27 (27.8%), a much smaller number compared to their orthologous genes in Arabidopsis (56.3%) and rice (43.2%). At the same time, most of the type I genes (55.6%, 15) in the rubber tree are silent and are probably pseudogenes. The high birth rate and low death rate of type II genes and low birth rate and high death rate of type I genes may corresponds to special developmental requirements in the rubber tree, e.g. the development of laticifer system for biosynthesis of cis-polyisoprene, the rubber. Moreover, atypical MIKC* factors (e.g. HbMADS1 in S-clade, and HbMADS20 in P-clade) are identified. These genes are diverged to typical MIKC* genes in sequences and facilitate functions required in laticifer development and rubber biosynthesis, which is not necessary in Arabidopsis and rice.

Differences in Distribution of Potassium-Solubilizing Bacteria in Forest and Plantation Soils in Myanmar.

Potassium (K) has been recognized as an essential element in intensive agricultural production systems, and deficiency of K usually results in a decrease in crop yields. The utilization of potassium-solubilizing bacteria (KSB) to increase the soluble K content in soil has been regarded as a desirable pathway to increase plant yields. Following the inoculation of KSB in the soil, potassium can be released (in the form of K⁺) and consumed by plants. This study aims to investigate and compare the distribution characteristics of potassium-solubilizing bacteria between forest and plantation soils in Myanmar. In this study, 14 KSB strains were isolated from rhizosphere samples collected from forest soil, as well as fertilized rubber tree rhizosphere soil and fertilized bare soil from a plantation. Broadleaf forests with high levels of canopy cover mainly comprised the forest environment, and rubber trees were planted in the plantation environment. The Chao and abundance-based coverage estimator (ACE) indices showed that the microbial abundance of the plantation soil was higher than that of the forest soil. According to the Illumina MiSeq sequencing analysis results, the Shannon index of the forest soil was lower while the Simpson index was higher, which demonstrated that the microbial diversity of the forest soil was higher than that of the plantation soil. Potassium-solubilizing test results showed that the strains E, I, M, and N were the most effective KSB under liquid cultivation conditions. Additionally, KSB only accounted for less than 5.47% of the total bacteria detected in either of the sample types, and the distribution of dominant KSB varied with the soil samples. As another result, the abundance of Pseudomonas spp. in S1 was higher than in S2 and S3, indicating a negative impact on the growth of Pseudomonas in the fertilized rubber tree rhizosphere soil. The significance of our research is that it proves that the increasing use of KSB for restoring soil is a good way to reduce the use of chemical fertilizers, which could further provide a relatively stable environment for plant growth.

Rubber and plantain intercropping: Effects of different planting densities on soil characteristics.

Two field experiments were conducted at Ellembelle and Jomoro districts in the Western region of Ghana where rubber cultivation is a predominant farming activity. The objective of the study was to assess the effect of rubber and plantain intercropping systems on selected soil properties. The experiment was arranged in a randomized complete block design (RCBD) with 3 replications. The treatments were the sole crop rubber (R), sole crop plantain (P) and three intercrop systems comprising an additive series of plantain: one row of plantain to one row of rubber (PR), two rows of plantain to one row of rubber (PPR) and three rows of plantain to one row of rubber (PPPR). Generally, agroforestry systems improved the soil hydraulic properties considerably, with the highest cumulative infiltration rates of 5.16 and 8.68 cm/min observed under the PPPR systems at the Ellembelle and Jomoro sites, respectively. Microbial biomass C (Cmic), N (Nmic) and P (Pmic) was significantly improved (P < 0.05) under the agroforestry than the monocrop systems. The Cmic, Nmic and Pmic values were highest under the PPPR system at both Ellembelle (Cmic, = 139.9 mg/kg; Nmic = 36.26 mg/kg and Pmic = 87.6 mg/kg) and Jomoro (Cmic = 78.7 mg/kg; Nmic = 80.3 mg/kg and Pmic = 3.45 mg/kg) sites.

Responses of rubber leaf phenology to climatic variations in Southwest China.

The phenology of rubber trees (Hevea brasiliensis) could be influenced by meteorological factors and exhibits significant changes under different geoclimates. In the sub-optimal environment in Xishuangbanna, rubber trees undergo lengthy periods of defoliation and refoliation. The timing of refoliation from budburst to leaf aging could be affected by powdery mildew disease (Oidium heveae), which negatively impacts seed and latex production. Rubber trees are most susceptible to powdery mildew disease at the copper and leaf changing stages. Understanding and predicting leaf phenology of rubber trees are helpful to develop effective means of controlling the disease. This research investigated the effect of several meteorological factors on different leaf phenological stages in a sub-optimal environment for rubber cultivation in Jinghong, Yunnan in Southwest China. Partial least square regression was used to quantify the relationship between meteorological factors and recorded rubber phenologies from 2003 to 2011. Minimum temperature in December was found to be the critical factor for the leaf phenology development of rubber trees. Comparing the delayed effects of minimum temperature, the maximum temperature, diurnal temperature range, and sunshine hours were found to advancing leaf phenologies. A comparatively lower minimum temperature in December would facilitate the advancing of leaf phenologies of rubber trees. Higher levels of precipitation in February delayed the light green and the entire process of leaf aging. Delayed leaf phenology was found to be related to severe rubber powdery mildew disease. These results were used to build predictive models that could be applied to early warning systems of rubber powdery mildew disease.

Evaluation of key meteorological determinants of wintering and flowering patterns of five rubber clones in Xishuangbanna, Yunnan, China.

All rubber tree clones (Hevea brasiliensis) exhibit regular annual wintering characterized by senescence and abscission of leaves. After 3-4 weeks, this is followed by the onset of new leaves. It is likely that the timing of leaf onset affects the susceptibility of rubber trees to rubber powdery mildew disease, as this predominantly infests young leaves. However, little information is available on the phenological behavior of different rubber clones, or how meteorological factors affect such behavior. We assessed the wintering and flowering patterns of five rubber clones in Xishuangbanna, southwest China, based on observations made from 1978 to 2011, and evaluated how these patterns responded to different meteorological factors. Partial least squares regression was used to analyze the timing of defoliation, refoliation, and flowering. Our results showed that the two clones RRIM 600 and GT1 defoliated during the last week of December and refoliated in the last week of January, and clones Yunyan 277-5, Yunyan 34-4, and PR 107 defoliated during the first week of January and refoliated in the second week of February. The number of hours of sunshine during both the rainy season and the cold dry period in the dry season were important determinants of phenological changes in the rubber trees. Similarly, higher temperatures tended to delay the onset of defoliation and refoliation, and were a triggering factor for the onset of flowering. These results may help rubber cultivators to schedule appropriate disease control measures, as well as to design hybridization programs aiming at the production of clones which are resistant to foliar disease.

Introduction of a leguminous shrub to a rubber plantation changed the soil carbon and nitrogen fractions and ameliorated soil environments.

The conversion of monoculture rubber (Hevea brasiliensis) plantations into rubber-based agroforestry systems has become a common trend in forestry management in the past few decades. Rubber-Flemingia macrophylla (a leguminous shrub) systems are popular in southwestern China's Xishuangbanna region. The biogeochemical cycles of soil carbon and nitrogen in forests are mainly affected by their fractions. This study investigated the effect of introducing Flemingia macrophylla to rubber plantations of different ages on soil carbon and nitrogen fractions. The experimental treatments included R1 (young rubber plantation), RF1 (young rubber-Flemingia macrophylla system), R2 (mature rubber plantation) and RF2 (mature rubber-Flemingia macrophylla system). The results showed that the introduction of Flemingia macrophylla to rubber plantations of different ages significantly changed soil carbon and nitrogen fractions, improved soil labile organic carbon and nitrogen contents, and ameliorated soil environments. The average soil microbial biomass organic carbon, nitrogen and nitrate-nitrogen in the 0-10 cm soil layer during the experimental period was 38.9%, 55.5%, and 214.7% higher in RF1 than R1, respectively, and 22.1%, 22.2%, and 652.2% higher in RF2 than R2, respectively. Therefore, Flemingia macrophylla can be used as an alternative interplanted tree species within rubber plantations in similar environments of southeastern Asia.

Seasonal changes in the diversity and composition of the litter fauna in native forests and rubber plantations.

The litter layer of tropical forests supports a significant fraction of total arthropod diversity and decomposition of this layer is the main pathway by which nutrients are returned to the soil and CO2 to the atmosphere. Conversion of tropical forests to agriculture is the main threat to biodiversity and ecosystem services, and understanding effects on the litter layer is important for understanding and mitigating these impacts. We used high through-put DNA sequencing of the mitochondrial cytochrome c oxidase subunit I (COI) gene to assess seasonal changes in the diversity and composition of the litter fauna at five matched pairs of native forests and rubber plantations in tropical SW China every month for a year, and measured the environmental factors expected to drive intra-annual variation. Forests and rubber had very different arthropod assemblages throughout the year, with forests more species-rich than rubber in all months except February. Very high rates of intra-annual turnover in species composition in both forests and rubber were associated with seasonality in environmental variables, with the influence of particular variables differing among taxa. Tropical arthropods are very sensitive to seasonality and sampling at only one time of the year captures only a subset of the total community.

Morpho-anatomical, physiological and biochemical changes in rubber tree seeds.

The physical, physiological and biochemical changes during the development until the dispersal of rubber tree seeds were evaluated with the purpose of estimating the point at physiological maturity. A total of 30 plants were selected at different points in a commercial planting area and had their flowers marked during the anthesis and every 15 days after marking. Fruits and seeds were collected for analysis of moisture content, dry matter, diameter and length. Details of the anatomy ultra-structure of the seeds were evaluated. The seed emergence, emergency speed index, heat resistant proteins and oxidative stress enzymes were examined. It was observed that fruits reached maximum size at 120 days after anthesis and seeds at 150 days. The seeds acquired germination capacity after 150 days. At 175 days, they presented the highest percentage of dry matter and lowest moisture, in addition to a higher percentage of germination and vigor. Therefore, it was possible to conclude that the physiological maturity of the rubber tree seeds occurs at 175 days after anthesis, and coincides with its maximum physiological quality. At 175 and 180 days post-anthesis, there is a greater expression of heat resistant proteins as well as low molecular weight and greater oxidative stress enzyme activity.

Nonomuraea rhizosphaerae sp. nov., an actinomycete isolated from the rhizosphere soil of a rubber tree (Hevea brasiliensis Muell. Arg).

A novel actinomycete, designated strain NEAU-mq18T, was isolated from the rhizosphere soil of a rubber tree (Hevea brasiliensis Muell. Arg) collected from Xianglu Mountain in Heilongjiang Province, northeast China, and subjected to a polyphasic taxonomic study. The 16S rRNA gene sequence analysis showed that the isolate belongs to the genus Nonomuraea with high sequence similarity to Nonomuraea guangzhouensis NEAU-ZJ3T (98.5%). Phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain clusters phylogenetically with N. guangzhouensis NEAU-ZJ3T and Nonomuraea glycinis NEAU-BB2C19T. Moreover, key chemotaxonomic properties including the major menaquinones, fatty acid composition and phospholipid profile also confirmed the affiliation of the strain to the genus Nonomuraea. However, some physiological, morphological and biochemical properties, and low DNA-DNA relatedness values, enabled the strain to be differentiated from closely related species of the genus Nonomuraea. Thus, strain NEAU-mq18T is concluded to represent a novel species of the genus Nonomuraea, for which the name Nonomuraea rhizosphaerae sp. nov. is proposed. The type strain is NEAU-mq18T (=CGMCC 4.7431T=DSM 105761T).

Age alters uptake pattern of organic and inorganic nitrogen by rubber trees.

Several studies have explored plant nutrient acquisition during ecosystem succession, but it remains unclear how age affects nitrogen (N) acquisition by the same tree species. Clarifying the age effect will be beneficial to fertilization management through improving N-use efficiency and reducing the risk of environmental pollution due to NO3- leaching. To clarify the effect of age on N uptake, rubber (Hevea brasiliensis (Willd. ex A. Juss.) Muell. Arg.) plantations of five ages (7, 16, 24, 32 and 49 years) were selected in Xishuangbanna of southern China for brief 15N exposures of intact roots using field hydroponic experiments. 15N-labeled NH4+, NO3- or glycine were applied in this study. All targeted rubber trees uptake rates followed an order of NH4+ > glycine > NO3-. As age increased, NH4+ uptake increased first and then decreased sharply, partly consistent with the pattern of soil NH4+ concentrations. Uptake of glycine decreased first and then increased gradually, while no significant change of NO3- uptake rates existed with increasing age. Overall, rubber trees with ages from 7 to 49 years all showed a preference for NH4+ uptake. Young rubber trees (7 and 16 years) had higher NH4+ and lower glycine preferences than older trees (24, 32 and 49 years). Mycorrhizal colonization rates of rubber trees were higher in intermediately aged plantations (16, 24 and 32 years) than in plantations aged 7 and 49 years. A positive relationship was observed between arbuscular mycorrhizal colonization rates and NO3- preference. The results from this study demonstrate that rubber trees do not change their preference for NH4+ but strongly decreased their reliance on it with age. These findings indicate that the shift of N uptake patterns with age should be taken into account for rubber fertilization management to improve N-use efficiency and reduce the risk of environmental pollution during rubber production.

Seasonal changes impact soil bacterial communities in a rubber plantation on Hainan Island, China.

Rubber plantations have expanded rapidly over the past 20 years in tropical Asia and their impacts on regional ecosystems have garnered much concern. While much attention has been given to the negative impacts on aboveground diversity and function, the belowground bacterial soil community has received much less attention. Here, we investigated the community composition and diversity of soil bacteria of rubber plantations on Hainan Island in south China. The goals of the study were to describe changes in bacterial compositions and diversity across seasons. We found that seasonality defined by differences in rainfall amount strongly influenced bacterial communities. At both the Phylum and Family levels, we found significant differences in the total number of taxa, as well as the composition of the community as a function of season. Diversity of soil samples in the dry-rainy season was highest of three seasons, suggesting that bacterial structure was more sensitive in alternate periods of season. Diversity in the rainy season was substantial lower than in dry season. Results from a redundancy analysis showed that seasonal changes explained the largest part (31.9%) of the total variance of bacterial community composition. In conclusion, seasonal change had the greatest influence on bacterial communities, which overshadowed the effects of soil nutrient as well as other factors, and controls the bacterial communities in soils of RP in tropical region of Hainan.