Population differentiation and dynamics of five pioneer species of Gaultheria from the secondary forests in subtropical China.

BACKGROUND: The influence of native secondary succession associated with anthropogenic disturbance on the biodiversity of the forests in subtropical China remains uncertain. In particular, the evolutionary response of small understory shrubs, particularly pioneer species inhabiting continuously disturbed habitats, to topographic heterogeneity and climate change is poorly understood. This study aimed to address this knowledge gap by focusing on the Gaultheria crenulata group, a clade of small pioneer shrubs in subtropical China. RESULTS: We examined the genetic structure and demographic history of all five species of the G. crenulata group with two maternally inherited chloroplast DNA (cpDNA) fragments and two biparentally inherited low-copy nuclear genes (LCG) over 89 natural populations. We found that the genetic differentiation of this group was influenced by the geomorphological boundary between different regions of China in association with Quaternary climatic events. Despite low overall genetic diversity, we observed an isolation-by-distance (IBD) pattern at a regional scale, rather than isolation-by-environment (IBE), which was attributed to ongoing human disturbance in the region. CONCLUSION: Our findings suggest that the genetic structure of the G. crenulata group reflects the interplay of geological topography, historical climates, and anthropogenic disturbance during the Pliocene-Pleistocene-Holocene periods in subtropical China. The observed IBD pattern, particularly prominent in western China, highlights the role of limited dispersal and gene flow, possibly influenced by physical barriers or decreased connectivity over geographic distance. Furthermore, the east-to-west trend of gene flow, potentially facilitated by the East Asian monsoon system, underscores the complex interplay of biotic and abiotic factors shaping the genetic dynamics of pioneer species in subtropical China's secondary forests. These findings can be used to assess the impact of environmental changes on the adaptation and persistence of biodiversity in subtropical forest ecosystems.

Phylogeographic patterns match the floristic subdivisions: The diversification history of a widespread herb in subtropical China.

BACKGROUND AND AIMS: Subtropical China is dominated by evergreen broad-leaved forests (EBLFs) and is acknowledged as a critical region for its high floristic richness and endemism. Understanding of evolutionary mechanisms of such global biodiversity hotspots comes almost exclusively from long-lived tree species. Herbaceous plants represent critical biodiversity components in forests, however, the diversification history of understory herbs in subtropical EBLFs remain poorly understood. Here, we investigated the phylogeographic patterns and demographic history of Oreocharis auricula, a widespread perennial herb endemic to the EBLFs of subtropical China. METHODS: Both cpDNA sequences and single-copy nuclear genes were used to investigate the genetic variation among 657 individuals from 68 populations. Evidences from molecular dating, demographic history construction, and species distribution modeling were also combined to infer the phylogeography and evolutionary history of O. auricula. KEY RESULTS: Strong phylogeographic signals have been congruently observed using nuclear and plastid DNA markers, with the diversification patterns generally consistent with the recognized floristic subdivisions of subtropical China. Notably, we revealed an important phylogeographic barrier along the Nanling mountain range, which is also around a climatic transition at 24-26°N latitude in subtropical China, separating the south monsoon subtropical EBLFs from the mid-subtropical EBLFs. Demographic expansion and significant niche divergence were detected among the extant lineages, which may have diverged during the early Pleistocene. CONCLUSIONS: The inherent characteristics of understory herbs with limited dispersal and short generation time intensify the genetic divergence response of O. auricula to abiotic forces, contributing to the profound phylogeographic imprints of mountains and climate in such herbaceous flora. To further substantiate the generality of the identified patterns, it is paramount to extend phylogeographic investigations to other understory herbaceous taxa in subtropical China. These results have expanded our understanding of the diversification processes of subtropical forests in China.

Molecular phylogeography and species distribution modelling evidence of 'oceanic' adaptation for Actinidia eriantha with a refugium along the oceanic-continental gradient in a biodiversity hotspot.

BACKGROUND: Refugia is considered to be critical for maintaining biodiversity; while discerning the type and pattern of refugia is pivotal for our understanding of evolutionary processes in the context of conservation. Interglacial and glacial refugia have been studied throughout subtropical China. However, studies on refugia along the oceanic-continental gradient have largely been ignored. We used a liana Actinidia eriantha, which occurs across the eastern moist evergreen broad-leaved forests of subtropical China, as a case study to test hypotheses of refugia along the oceanic-continental gradient and 'oceanic' adaptation. RESULTS: The phylogeographic pattern of A. eriantha was explored using a combination of three cpDNA markers and 38 nuclear microsatellite loci, Species distribution modelling and dispersal corridors analysis. Our data showed intermediate levels of genetic diversity [haplotype diversity (hT) = 0.498; unbiased expected heterozygosity (UHE) = 0.510] both at the species and population level. Microsatellite loci revealed five clusters largely corresponding to geographic regions. Coalescent time of cpDNA lineages was dated to the middle Pliocene (ca. 4.03 Ma). Both geographic distance and climate difference have important roles for intraspecific divergence of the species. The Zhejiang-Fujian Hilly Region was demonstrated to be a refugium along the oceanic-continental gradient of the species and fit the 'refugia in refugia' pattern. Species distribution modelling analysis indicated that Precipitation of Coldest Quarter (importance of 44%), Temperature Seasonality (29%) and Mean Temperature of Wettest Quarter (25%) contributed the most to model development. By checking the isolines in the three climate layers, we found that A. eriantha prefer higher precipitation during the coldest quarter, lower seasonal temperature difference and lower mean temperature during the wettest quarter, which correspond to 'oceanic' adaptation. Actinidia eriantha expanded to its western distribution range along the dispersal corridor repeatedly during the glacial periods. CONCLUSIONS: Overall, our results provide integrated evidence demonstrating that the Zhejiang-Fujian Hilly Region is a refugium along the oceanic-continental gradient of Actinidia eriantha in subtropical China and that speciation is attributed to 'oceanic' adaptation. This study gives a deeper understanding of the refugia in subtropical China and will contribute to the conservation and utilization of kiwifruit wild resources in the context of climate change.

Opening a door to the spatiotemporal history of plants from the tropical Indochina Peninsula to subtropical China.

The complexity of global biodiversity in the tropical Indochina Peninsula and subtropical China bioregions has fascinated biologists for decades, but little is known about the spatiotemporal patterns in these regions. Accordingly, the aims of present study were to investigate the evolutionary and distribution patterns of Engelhardia in these regions and establish a model for examining biogeographic patterns and geological events throughout the tropical Indochina Peninsula and subtropical China. The effects of geological events occurring in the area between the Indochina Peninsula and subtropical China bioregions on the two trees species (i.e., E. roxburghiana and E. fenzelii) were evaluated. A robust phylogenetic framework of 884 individuals from 79 populations was used to generate time-calibrated cytoplasmic and nuclear phylogenetic frameworks based on cpDNA, nrDNA, and nSSR data, respectively. When considered along with ancestral area reconstructions, the genetic data were also used to assess and reconstruct the species' population genetic structure and diversity. These analyses yielded important information about the (1) historical distribution relationships between the tropical and subtropical flora of China; (2) effects of the East Asian summer monsoon (EASM) on the evolutionary history of Asia's plants; and (3) importance of biogeography in conservation planning. Although cytoplasmic-nuclear discordance indicated cpDNA and nrDNA were subject to distinct evolutionary mechanisms that reflected respective evolutionary histories of the plastid and nuclear genomes of prior demographic and biogeographic events. The tropical elements of Engelhardia occupied the Indochina Peninsula during the early Eocene, whereas the subtropical elements were transformed from the tropical elements during Miocene cooling and the onset of the EASM at the Oligocene-Miocene boundary, intensified during the late Miocene and Pliocene, facilitating the transformation of Engelhardia from the tropical Indochina Peninsula to subtropical China. Demographic history provided insights into prominent planning frameworks in conservation biology, namely that subtropical China functioned as a refugium during past climate oscillations and will continue to serve in this capacity in the future.

Cytotype distribution and chloroplast phylogeography of the Actinidia chinensis complex.

BACKGROUND: Plant phylogeographic studies of species in subtropical China have mainly focused on rare and endangered species, whereas few studies have been conducted on taxa with relatively wide distribution, especially polyploid species. We investigated the cytotype and haplotype distribution pattern of the Actinidia chinensis complex, a widespread geographically woody liana with variable ploidy in subtropical China comprising two varieties, with three chloroplast fragments DNA (ndhF-rpl132, rps16-trnQ and trnE-trnT). Macroevolutionary, microevolutionary and niche modeling tools were also combined to disentangle the origin and the demographic history of the species or cytotypes. RESULTS: The ploidy levels of 3338 individuals from 128 populations sampled throughout the species distribution range were estimated with flow cytometry. The widespread cytotypes were diploids followed by tetraploids and hexaploids, whereas triploids and octoploids occurred in a few populations. Thirty-one chloroplast haplotypes were detected. The genetic diversity and genetic structure were found to be high between varieties (or ploidy races) chinensis and deliciosa. Our results revealed that these two varieties inhabit significantly different climatic niche spaces. Ecological niche models (ENMs) indicate that all varieties' ranges contracted during the Last Inter Glacial (LIG), and expanded eastward or northward during the Last Glacial Maximum (LGM). CONCLUSIONS: Pliocene and Plio-Pleistocene climatic fluctuations and vicariance appear to have played key roles in shaping current population structure and historical demography in the A. chinensis complex. The polyploidization process also appears to have played an important role in the historical demography of the complex through improving their adaptability to environmental changes.

Temporal dynamics of stomatal regulation and carbon- and water-related traits for a native tree species in low subtropical China.

Stomata are pivotal in modulating water and carbon processes within plants. However, our understanding of the temporal dynamics of water- and carbon-related traits, as influenced by stomatal behavior, remains limited. Here, we explore how stomatal regulation behavior and water- and carbon-related traits vary with changing environments by examining the seasonal variations in these traits of the native tree species Schima superba in low subtropical China. In February, April, and July of 2022, a series of water- and carbon-related traits were measured in the leaves and stems. The results showed that S. superba exhibited isohydric behavior in February when the soil dried out and vapor pressure deficit (VPD) was lower but anisohydric behavior in April and July when the soil was wetter and VPD was higher. In February, NSC and their components increased, and a relatively large contribution of soluble sugars to the change in NSC was observed. In the branches and phloem, NSC and their components displayed a relatively high monthly variability, suggesting their role in maintaining carbon balance within the trees. Conversely, the NSC in the leaves demonstrated minimal monthly variability. The specific leaf area, as well as the concentration of nitrogen (N) and phosphorus (P) per unit mass in leaves and the cumulative stem water release, exhibited a decrease with a reduction in soil water potential. Interestingly, the hydraulic conductivity remained consistent throughout this process. Furthermore, the relatively low monthly growth rate observed in February could suggest a carbon sink limitation. In conclusion, the increased NSC and decreased water status of S. superba under relatively stressed soil conditions indicated a trade-off between water and carbon storage. Our findings enhance our comprehension of the dynamics and regulation of water and carbon status in forests, thereby advancing the development of plant carbon and water process models under climate change scenarios.

Quadrat soil pollen signal reflects plant important values in forests and shrublands from subtropical China.

Pollen analysis, a crucial tool in botany and ecology for examining historical biotic dynamics, has elicited debate owing to its complex link with vegetation. The challenge lies in discerning the ecological significance of pollen data. In this study, we conducted detailed quadrat surveys on Jinhua Mountain, subtropical China, analyzing topsoil pollen to determine whether pollen signals accurately reflect key ecological components in the forests and shrublands. We performed direct comparisons between pollen and plant compositions and calculated pollen percentages and plant Important Values (IVs) for each quadrat. The results indicate greater homogeneity in pollen composition across the study area compared to plant composition, particularly in the high percentage of Pinus pollen. However, distinct plant communities exhibited significantly different pollen compositions, as evidenced by the multi-response permutation test. This divergence aligns with variations in the dominant plant species across different communities. There were significant correlations between pollen percentages and plant IVs, with correlation coefficients of 0.55 (p < 0.001) at the quadrat level and 0.78 (p < 0.001) at the taxon level. These results support the utility of pollen analysis for representing ecologically significant values in subtropical Chinese forests and shrublands. Such correlations might also be extrapolated to pollen-based paleoecological studies.

Residual mulch-film characteristics affect heavy metal migration of different soil layers in the subtropical croplands of China.

In recent years, as the abundance of residual mulch film (RMF) in agricultural soil continues to increase, whether the adsorption capacity of its surface affects the migration of heavy metals is a topic of current interest for scholars. Herein, this study investigated the distribution of RMF abundance and metal concentration in different soil layers of 75 plastic-mulching croplands in subtropical China; meanwhile, we also explored the associations of RMF characteristics with metal concentration. The results showed that land type, film mulching amount, and film mulching time were the main factors affecting RMF abundance, distribution, and particle size composition. The highest abundance of RMF was found in the garden soils (910 n·kg-1) with more than 15 years mulching period and more than 19.5 kg hm-2 of annual mulch amount. The lowest abundance of RMF was occurred in the group of field and conservation agricultural land (237 n·kg-1). Moreover, the concentrations of metals in soil, especially Cd, Cr, Cu, and Pb, were closely related to the extent of RMF contamination in the soil environment. In the 0-10 cm and 10-20 cm soil layers, microplastic abundance exhibited a negative correlation with Cr and Cu concentrations and a positive correlation with Pb concentration. Based on the above findings, it is demonstrated that RMF significantly influences the mobility of metals in soil via adsorption processes, with potential synergistic effects between RMF and heavy metals posing a heightened risk to the soil environment.

Soil phosphorus cycling microbial functional genes of monoculture and mixed plantations of native tree species in subtropical China.

Background: Transforming coniferous plantation into broadleaved or mixed broadleaved-coniferous plantations is the tendency of forest management strategies in subtropical China. However, the effects of this conversion on soil phosphorus (P) cycling microbial functional genes are still unknown. Methods: Soil samples were collected from 0-20, 20-40, and 40-60 cm (topsoil, middle layer, and subsoil, respectively) under coniferous Pinus massoniana (PM), broadleaved Erythrophleum fordii (EF), and their mixed (PM/EF) plantation in subtropical China. Used metagenomic sequencing to examine the alterations of relative abundances and molecular ecological network structure of soil P-cycling functional genes after the conversion of plantations. Results: The composition of P-cycling genes in the topsoil of PM stand was significantly different from that of PM/EF and EF stands (p < 0.05), and total phosphorus (TP) was the main factor causing this difference. After transforming PM plantation into EF plantation, the relative abundances of P solubilization and mineralization genes significantly increased in the topsoil and middle layer with the decrease of soil TP content. The abundances of P-starvation response regulation genes also significantly increased in the subsoil (p < 0.05), which may have been influenced by soil organic carbon (SOC). The dominant genes in all soil layers under three plantations were phoR, glpP, gcd, ppk, and ppx. Transforming PM into EF plantation apparently increased gcd abundance in the topsoil (p < 0.05), with TP and NO3 --N being the main influencing factors. After transforming PM into PM/EF plantations, the molecular ecological network structure of P-cycling genes was more complex; moreover, the key genes in the network were modified with the transformation of PM plantation. Conclusion: Transforming PM into EF plantation mainly improved the phosphate solubilizing potential of microorganisms at topsoil, while transforming PM into PM/EF plantation may have enhanced structural stability of microbial P-cycling genes react to environmental changes.

Spatiotemporal dynamic of subtropical forest carbon storage and its resistance and resilience to drought in China.

Subtropical forests are rich in vegetation and have high photosynthetic capacity. China is an important area for the distribution of subtropical forests, evergreen broadleaf forests (EBFs) and evergreen needleleaf forests (ENFs) are two typical vegetation types in subtropical China. Forest carbon storage is an important indicator for measuring the basic characteristics of forest ecosystems and is of great significance for maintaining the global carbon balance. Drought can affect forest activity and may even lead to forest death and the stability characteristics of different forest ecosystems varied after drought events. Therefore, this study used meteorological data to simulate the standardized precipitation evapotranspiration index (SPEI) and the Biome-BGC model to simulate two types of forest carbon storage to quantify the resistance and resilience of EBF and ENF to drought in the subtropical region of China. The results show that: 1) from 1952 to 2019, the interannual drought in subtropical China showed an increasing trend, with five extreme droughts recorded, of which 2011 was the most severe one; 2) the simulated average carbon storage of the EBF and ENF during 1985-2019 were 130.58 t·hm-2 and 78.49 t·hm-2, respectively. The regions with higher carbon storage of EBF were mainly concentrated in central and southeastern subtropics, where those of ENF mainly distributed in the western subtropic; 3) The median of resistance of EBF was three times higher than that of ENF, indicating the EBF have stronger resistance to extreme drought than ENF. Moreover, the resilience of two typical forest to 2011 extreme drought and the continuous drought events during 2009 - 2011 were similar. The results provided a scientific basis for the response of subtropical forests to drought, and indicating that improve stand quality or expand the plantation of EBF may enhance the resistance to drought in subtropical China, which provided certain reference for forest protection and management under the increasing frequency of drought events in the future.

Phosphorus is the key soil indicator controlling productivity in planted Masson pine forests across subtropical China.

Soil physiochemical properties are critical to understanding forest productivity and carbon (C) finance schemes in terrestrial ecosystems. However, few studies have focused on the effects of the soil physiochemical properties on the productivity in planted forests. This study was therefore conducted at 113 sampling plots located in planted Masson pine forests across subtropical China to test what and how the aboveground net primary productivity (ANPP) would be explained by the soil physiochemical properties, stand attributes, and functional traits using regression analysis and structural equation modelling (SEM). Across subtropical China, the ANPP ranged from 1.79 to 14.04 Mg ha-1 year-1 among the plots, with an average value of 6.05 Mg ha-1 year-1. The variations in ANPP were positively related to the stand density, root phosphorus (P) content and soil total P content but were negatively related to the stand age, root C:P and N:P ratios. Among these factors, the combined effects of stand density, stand age and soil total P content explained 35% of the ANPP variations. The SEM results showed the indirect effect of the soil total P content via the root P content and C:P ratio on the ANPP and indirect effects of other soil properties (e.g., pH, clay, and bulk density) via the soil total P content and root functional traits (e.g., root P, C:P, and N:P) on the ANPP. By considering all possible variables and paths, the best-fitting SEM explained only 11-13% of the ANPP variations, which suggested that other factors may be more important in determining the productivity in planted forests. Overall, this study highlights that soil total P content should be used as a key soil indicator for determining the ANPP in planted Masson pine forests across subtropical China, and suggests that the root functional traits mediate the effects of soil properties on the ANPP.

Intra-annual tree-ring δ18O and δ13C reveal a trade-off between isotopic source and humidity in moist environments.

Tree-ring intra-annual stable isotopes (δ13C and δ18O) are powerful tools for revealing plant ecophysiological responses to climatic extremes. We analyzed interannual and fine-scale intra-annual variability of tree-ring δ13C and δ18O in Chinese red pine (Pinus massoniana) from southeastern China to explore environmental drivers and potential trade-offs between the main physiological controls. We show that wet season relative humidity (May-October RH) drove interannual variability of δ18O and intra-annual variability of tree-ring δ18O. It also drove intra-annual variability of tree-ring δ13C, whereas interannual variability was mainly controlled by February-May temperature and September-October RH. Furthermore, intra-annual tree-ring δ18O variability was larger during wet years compared with dry years, whereas δ13C variability was lower during wet years compared with dry years. As a result of these differences in intra-annual variability amplitude, process-based models (we used the Roden model for δ18O and the Farquhar model for δ13C) captured the intra-annual δ18O pattern better in wet years compared with dry years, whereas intra-annual δ13C pattern was better simulated in dry years compared with wet years. This result suggests a potential asymmetric bias in process-based models in capturing the interplay of the different mechanistic processes (i.e., isotopic source and leaf-level enrichment) operating in dry versus wet years. We therefore propose an intra-annual conceptual model considering a dynamic trade-off between the isotopic source and leaf-level enrichment in different tree-ring parts to understand how climate and ecophysiological processes drive intra-annual tree-ring stable isotopic variability under humid climate conditions.

Comparison of dendroclimatic relationships using multiple tree-ring indicators (tree-ring width and δ 13C) from Masson pine.

This study addressed the effects of climate drivers on the tree-ring width (TRW) parameters (total ring width (TR), earlywood width (EW) and latewood width (LW)) and the total ring δ 13C series of different wood components (whole wood, α-cellulose and holocelluose) from Masson pine in subtropical China. Pairwise correlation coefficients between three ring width parameters were statistically significant. EW and LW did not reveal much stronger climate sensitivity rather than TR. This indicated that the use of intra-annual ring width has little benefit in extracting more climate information. The mean δ 13C series of the three components of the total ring had the strongest climate response to the July-September relative humidity (r = -0.792 (whole wood), -0.758 (holocellulose) and -0.769 (α-cellulose)). There are no significant differences in the dendroclimatic relationships of the δ 13C series of different wood components. Through both stationary temporal and spatial-statistical perspectives, the moisture drivers (summer/autumn) had a significant impact on three ring width parameters and three components of Masson pine. Overall, the radial growth and the δ 13C series showed different responses to the same climate drivers during the same period. Moreover, the R-squared values of the strongest climate-proxy correlation coefficients were smaller than 50% for TRW. Consequently, the δ 13C series of Masson pine may be a more representative climate proxy than TRW parameters for dendroclimatology in subtropical China.

Population dynamics linked to glacial cycles in Cercis chuniana F. P. Metcalf (Fabaceae) endemic to the montane regions of subtropical China.

The mountains of subtropical China are an excellent system for investigating the processes driving the geographical distribution of biodiversity and radiation of plant populations in response to Pleistocene climate fluctuations. How the major mountain ranges in subtropical China have affected the evolution of plant species in the subtropical evergreen broadleaved forest is an issue with long-term concern. Here, we focused on Cercis chuniana, a woody species endemic to the southern mountain ranges in subtropical China, to elucidate its population dynamics. We used genotyping by sequencing (GBS) to investigate the spatial pattern of genetic variation among 11 populations. Geographical isolation was detected between the populations located in adjacent mountain ranges, thought to function as geographical barriers due to their complex physiography. Bayesian time estimation revealed that population divergence occurred in the middle Pleistocene, when populations in the Nanling Mts. separated from those to the east. The orientation and physiography of the mountain ranges of subtropical China appear to have contributed to the geographical pattern of genetic variation between the eastern and western populations of C. chuniana. Complex physiography plus long-term stable ecological conditions across glacial cycles facilitated the demographic expansion in the Nanling Mts., from which contemporary migration began. The Nanling Mts. are thus considered as a suitable area for preserving population diversity and large population sizes of C. chuniana compared with other regions. As inferred by ecological niche modeling and coalescent simulations, secondary contact occurred during the warm Lushan-Tali Interglacial period, with intensified East Asia summer monsoon and continuous habitat available for occupation. Our data support the strong influence of both climatic history and topographic characteristics on the high regional phytodiversity of the subtropical evergreen broadleaved forest in subtropical China.

Spatial Genetic Structure and Demographic History of the Dominant Forest Oak Quercus fabri Hance in Subtropical China.

Oak trees (Quercus L.) are important models for estimating abiotic impacts on the population structure and demography of long life span tree species. In this study, we generated genetic data for 17 nuclear microsatellite loci in 29 natural populations of Quercus fabri to estimate the population genetic structure. We also integrated approximate Bayesian computation (ABC) and ecological niche analysis to infer the population differentiation processes and demographic history of this oak species. The genetic analyses indicated two genetic clusters across the 29 populations collected, where most approximately corresponded to the intraspecific differentiation among populations from western and eastern China, whereas admixed populations were mainly found in central mountains of China. The best model obtained from hierarchical ABC simulations suggested that the initial intraspecific divergence of Q. fabri potentially occurred during the late Pliocene (ca. 3.99 Ma) to form the two genetic clusters, and the admixed population group might have been generated by genetic admixture of the two differentiated groups at ca. 53.76 ka. Ecological analyses demonstrated clear differentiation among the Q. fabri population structures, and association estimations also indicated significant correlations between geography and climate with the genetic variation in this oak species. Our results suggest abiotic influences, including past climatic changes and ecological factors, might have affected the genetic differentiation and demographic history of Q. fabri in subtropical China.

In situ glacial survival maintains high genetic diversity of Mussaenda kwangtungensis on continental islands in subtropical China.

Generally, island populations are predicted to have less genetic variation than their mainland relatives. However, a growing number of studies have nevertheless reported exceptions, indicating that the relationships were impacted by several factors, for example, historical processes. In the present study, we chose a group of subtropical islands located in South China as the study system, which are quite younger and much closer to the mainland than most of the previous studied island systems, to test the hypothesis that in situ glacial survival contributes to high levels of genetic diversity in island populations. We conducted a comparison of genetic variation between 12 island and 11 nearby mainland populations of Mussaenda kwangtungensis using eleven nuclear microsatellite and three chloroplast markers, evaluated effects of the island area and distance to mainland on genetic diversity of island populations, and simulated the potential distribution over the past by ecological niche modeling, together with the genetic data to detect the role of islands during the glacial periods. The island populations displayed comparable levels of genetic diversity and differentiation with mainland populations, overall high levels of unique polymorphisms, and the greatest values of specific within-population genetic diversity. No significant correlation was detected between genetic diversity of island populations and distance to mainland, as well as area of islands, except that allelic richness was significantly positively correlated with the area of islands. Nuclear microsatellites revealed two main clusters, largely corresponding to islands and inland populations, which divergence dated to a time of island formation by ABC analysis. Ecological niche modeling predicted a highly climatic suitability on islands during the last glacial maximum (LGM). Our results suggest that the islands have acted as refugia during the LGM and highlight the role of in situ glacial survival in maintaining high levels of genetic diversity of M. kwangtungensis in continental islands of subtropical China.

Seroprevalence and Risk Factors of Toxoplasma gondii Infection in Growth Stages of Pigs in Hunan Province, Subtropical China.

Toxoplasma gondii infection is prevalent in humans and animals worldwide. In the present study, a total of 612 serum samples were examined using indirect hemagglutination test (IHAT) for T. gondii infection. Antibodies to T. gondii were detected in 49 (8.0%, confidence interval [95% CI]: 5.9-10.2) serum samples (IHA titer ≥1:16). The T. gondii seroprevalence ranged from 4.4% (95% CI: 0-10.5) to 14.3% (95% CI: 0-40.2) among different regions in Hunan province of subtropical China. The highest seroprevalence was found in breeding sows (18.8%). The T. gondii seroprevalence was higher in winter (18.3%, 95% CI: 8.5-28.1) and spring (10.9%, 95% CI: 5.7-16.1) than in summer (6.4%, 95% CI: 2.8-10.1) and autumn (4.9%, 95% CI: 2.2-7.7), and the differences were statistically significant excepting summer. In addition, developmental stage and season were identified as risk factors for T. gondii infection. Our findings revealed the seroprevalence of T. gondii in growth stages of pigs in the Hunan province of subtropical China, indicating that it may cause public health and economic problems. To our knowledge, this is the first report of the comprehensive survey of T. gondii seroprevalence in pigs in the Hunan province of subtropical China.

New insight into the phylogeographic pattern of Liriodendron chinense (Magnoliaceae) revealed by chloroplast DNA: east-west lineage split and genetic mixture within western subtropical China.

BACKGROUND: Subtropical China is a global center of biodiversity and one of the most important refugia worldwide. Mountains play an important role in conserving the genetic resources of species. Liriodendron chinense is a Tertiary relict tree largely endemic to subtropical China. In this study, we aimed to achieve a better understanding of the phylogeographical pattern of L. chinense and to explore the role of mountains in the conservation of L. chinense genetic resources. METHODS: Three chloroplast regions (psbJ-petA, rpl32-ndhF, and trnK5'-matK) were sequenced in 40 populations of L. chinense for phylogeographical analyses. Relationships among chloroplast DNA (cpDNA) haplotypes were determined using median-joining networks, and genetic structure was examined by spatial analysis of molecular variance (SAMOVA). The ancestral area of the species was reconstructed using the Bayesian binary Markov Chain Monte Carlo (BBM) method according to its geographic distribution and a maximum parsimony (MP) tree based on Bayesian methods. RESULTS: Obvious phylogeographic structure was found in L. chinense. SAMOVA revealed seven groups matching the major landscape features of the L. chinense distribution area. The haplotype network showed three clades distributed in the eastern, southwestern, and northwestern regions. Separate northern and southern refugia were found in the Wu Mountains and Yungui Plateau, with genetic admixture in the Dalou Mountains and Wuling Mountains. BBM revealed a more ancient origin of L. chinense in the eastern region, with a west-east split most likely having occurred during the Mindel glacial stage. DISCUSSION: The clear geographical distributions of haplotypes suggested multiple mountainous refugia of L. chinense. The east-west lineage split was most likely a process of gradual genetic isolation and allopatric lineage divergence when the Nanling corridor was frequently occupied by evergreen or coniferous forest during Late Quaternary oscillations. Hotspots of haplotype diversity in the Dalou Mountains and Wuling Mountains likely benefited from gene flow from the Wu Mountains and Yungui Plateau. Collectively, these results indicate that mountain regions should be the main units for conserving and collecting genetic resources of L. chinense and other similar species in subtropical China.

Evolutionary Hotspots of Seed Plants in Subtropical China: A Comparison With Species Diversity Hotspots of Woody Seed Plants.

Genetic diversity is a fundamental level of biodiversity. However, it is frequently neglected in conservation prioritization because intraspecific genetic diversity is difficult to measure at large scales. In this study, we synthesized population genetic or phylogeographic datasets of 33 seed plants in subtropical China into multi-species genetic landscapes. The genetic landscapes identified 18 evolutionary hotspots with high within-population genetic diversity (WGD), and among-population genetic diversity (AGD), or both. The western subtropical China is rich in AGD (possessing four major AGD hotspots), deserving a high conservation priority. We found that WGD was positively correlated with longitude, with most WGD hotspots locating in east subtropical China. The results showed that the locations of 12 of 18 evolutionary hotspots corresponded approximately to those of previously identified species diversity (SD) hotspots, however, a positive and significant correlation existed only between AGD and SD, not between WGD and SD. Therefore, spatial patterns of species richness in plants in subtropical China cannot generally be used as surrogate for their intraspecific diversity. This study identified multi-species evolutionary hotspots and correlated multi-species genetic diversity with SD across subtropical China for the first time, providing profound implications for the conservation of biodiversity in this important ecoregion.

Phosphorus uptake in four tree species under nitrogen addition in subtropical China.

Atmospheric N deposition is a serious problem in subtropical China where N is present in large amounts but P is deficient. Several studies hypothesized that N2 fixers can overcome phosphorus limitation by trading fixed N2 for soil phosphorus. In order to know whether N2 fixers could invest fixed N2 in extracellular phosphatase production and could stimulate arbuscular mycorrhizal fungi (AMF) to acquire soil P in N-rich subtropical China, an open-air greenhouse experiment was carried out. Two N2 fixers (Acacia mangium and Ormosia pinnata) and two non-N2 fixers (Schima superba and Pinus massoniana) were exposed to three levels of N addition: 5.6 kg ha-1 a-1 (ambient N), 15.6 kg ha-1 a-1 (middle N), and 20.6 kg ha-1 a-1 (high N). We found that the capacity of plants to acquire soil P in N-rich subtropical China is species specific. The higher P uptake rates were found for N2 fixers than non-N2 fixers under N addition, which were related to the greater soil APA and higher AMF (p < 0.01) in the soil of N2 fixers. However, with time, high N addition decreased more significant quantities of soil microbial phospholipid fatty acids (PLFAs) in the soil of N2 fixers than that of non-N2 fixers (p < 0.05). We conclude that N2 fixers have higher P uptake capacity than non-N2 fixers under ambient N deposition in subtropical China. However, continuing N deposition in the future might affect P uptake ability of N2 fixers as high N addition would decrease soil microbial PLFAs of N2 fixers.