Subtropical Region Of China Research Articles

Light Drought Stress Positively Influenced Root Morphological and Endogenous Hormones in Pinus massoniana Seedlings Inoculated with Suillus luteus

Aims An ectomycorrhizal fungus (ECMF) may enhance plant drought resistance. However, there is limited information regarding the effects of ECMFs on drought resistance in Pinus massoniana Lamb., a native species representing an afforestation pioneer tree in subtropical regions of China. Methods In this study, a pot experiment was conducted to determine the effects of ECMF Suillus luteus inoculation on the root morphology and endogenous hormones of P. massoniana, including roots, leaves, and stems, under various water treatment conditions. Four water levels (regular, light, moderate, and severe drought) and three inoculations (inoculated Suillus luteus, numbered S12 and S13, and non-ECMF-inoculated) were compared using a factorial design. Results Under drought stress, P. massoniana seedlings inoculated with S12 and S13 had significantly increased root morphology development (p < 0.05). Light drought positively influenced root development, resulting in a more than twofold increase in root length and root surface area compared to non-inoculated seedlings. Concentrations of gibberellic acid (GA), zeatin riboside (ZR), and indole-3-acetic acid (IAA) in roots, stems, and leaves of inoculated S12 and S13 plants were elevated, whereas abscisic acid (ABA) concentrations were significantly lower, compared to non-inoculated seedlings. The ABA concentrations in the roots of S12 and S13 inoculated seedlings under light drought stress were 1.5 times lower than those in non-inoculated controls. Moreover, root development was positively correlated with plant total GA, IAA, and ZR but negatively correlated with ABA. ConclusionsS. luteus can promote the root growth and development of P. massoniana seedlings, notably by regulating the balance in the concentration of endogenous hormones, thus improving the drought resistance of P. massoniana seedlings.

Metabolomics analyses provide insights into the nutritional quality profiling in 95 avocado germplasms grown in China

Avocado is widely grown in tropical and subtropical regions of China. Diverse germplasms have been generated through natural hybridization and selective breeding. Here, to screen high-quality avocado germplasms, we characterized the nutritional quality of 95 avocado germplasms grown in China based on metabolomics. The oil content of the 95 avocado germplasms was 2.18 %–16.60 % and followed a normal distribution. We further profiled nine fatty acids, 16 hydrolyzed amino acids, and eight mineral elements in avocado fruit, which varied widely among different germplasms. Correlation analysis revealed significant positive correlations between fatty acid components, as well as between amino acid components and between mineral elements. Clustering analysis and evaluation of the 95 avocado germplasms identified 14 germplasms with high nutritional quality. These findings provide a basis for evaluation of avocado fruit quality and utilization of high-quality avocado germplasms, as well as important implications for the breeding of avocado.

Four New Species of Deconica (Strophariaceae, Agaricales) from Subtropical Regions of China

Deconica is a relatively small genus, with only 90 names recorded in previous research. In this study, four new species of Deconica have been identified based on morphological and phylogenetic evidence from subtropical regions of China. This represents the first discovery of new species of Deconica in China. Morphologically, D. austrosinensis is characterized by medium-sized spores that are elliptical to elongated-ellipsoid in face view, and fusiform to sublageniform and slightly thick-walled pleurocystidia; D. furfuracea is identified by a well-developed and evanescent veil, medium-sized spores that are rhomboid to mitriform in face view, and fusiform to subclavate pleurocystidia that are rare and subacute at apex; D. fuscobrunnea is recognized by dark brown pileus, medium-sized spores that are rhomboid to mitriform in face view, an ixocutis pileipellis, lageniform cheilocystidia with a long neck and lacks pleurocystidia; D. ovispora is distinguished from other Deconica species by medium-sized spores that are ovoid in face view, an ixocutis pileipellis, lageniform cheilocystidia with a long to short neck, and lacks pleurocystidia. Their distinct taxonomic status is confirmed by the positions of the four new species in ITS + LSU phylogenetic trees. Detailed descriptions and morphological photographs of four new species are presented.

Phylogenetic relatedness, not geographic origin, shapes traits across ontogenetic stages for common native and exotic plants in subtropical China

Abstract Functional traits, which shift as a plant develops from seed to adult and may be phylogenetically conserved, are widely acknowledged to be associated with exotic species invasion. However, existing studies comparing functional traits between native and invasive species often focus on a single ontogenetic stage, yielding mixed results. It remains unclear whether the functional trait differences and their relationship with invasiveness (e.g. range size) of exotic species remain consistent across ontogenetic stages. In this study, we experimentally compared 18 traits across the seed, early growth and adult stages of 127 native and exotic species from 19 families. These species are common and often co‐occur in the subtropical region of China. We also explored the linkage between these traits, alongside their phylogenetic relatedness with native species and exotic species' range size in China. Our results show that only seed mass differed between native and exotic species. Moreover, the compositions of traits across all stages and the entire lifespan were primarily influenced by phylogenetic relatedness rather than geographic origin. Further, the range size of exotic species in China positively correlated with their mean phylogenetic distance to native species, with no association with individual functional traits or functional distinctiveness. Synthesis. Our results emphasize the importance of comparing functional traits across ontogenetic stages between native and exotic species to improve our understanding of the role of functional traits in shaping plant invasion. Our findings also underscore the pivotal role of phylogenetic relatedness in shaping plant functional traits and the distribution of exotic species in their new ranges.

Comparison of Nitrous Oxide Consumption of Paddy Soils Developed from Three Parent Materials in Subtropical China

Paddy soils developed from various parent materials are widely distributed in the subtropical region in China and have a non-negligible but unclear potential to consume nitrous oxide (N2O) due to long-term flooding. This study selected three of the most common paddy soils in subtropical China, developing from quaternary red soil (R), lake sediment sand (S), and alluvial soil (C), to study their total N2O consumption and total nitrogen (N2) production using N2-free microcosm experiments. These paddy soils were treated with N2O addition (N2O treatment) or helium (He) addition (CK treatment) and incubated under flooding and anoxic conditions. The results showed that three alluvial soils (C1, C2, and C3) consumed over 99.93% of the N2O accumulated in the soil profile, significantly higher than R and S soils (p < 0.05). And the N2 production in three C soils was also significantly higher than other soils, accounting for 81.61% of the total N2O consumption. The main soil factors affecting N2O consumption in C, S, and R soils were soil clay content (p < 0.05), soil sand content (R2 = 0.95, p < 0.001), and soil available potassium (AK) (p < 0.01), respectively. These results indicate flooding paddy soils, no matter the parent materials developed, could consume extremely large amount of N2O produced in soil profiles.

Climate change favors expansion of three Eucalyptus species in China.

Eucalyptus has become one of the most widely planted species in tropical and subtropical regions in China, with important economic, ecological, and social values. However, it is currently unclear how climate change will affect different Eucalyptus species. Therefore, it is urgent to investigate the potential distribution and dynamics of Eucalyptus under current and future climate scenarios. In this study, we analyzed the potential distribution patterns of the three main Eucalyptus species (Eucalyptus grandis, Eucalyptus urophylla, and Eucalyptus tereticornis) under current and future climatic conditions (2041-2060 and 2061-2080) using the optimized MaxEnt model, which integrates a variety of environmental data including climate, topography, soil, and human influence. We also identified the main factors affecting the potential distributions of the three main Eucalyptus species. The model indicated that E. grandis exhibited heightened sensitivity to the mean temperature of the coldest quarter (7.0-20.0 °C) and annual mean temperature (11.9-24.2 °C), whereas E. urophylla displayed heightened sensitivity to precipitation of the warmest quarter (272-1694mm) and annual precipitation (812-2624mm). Conversely, E. tereticornis demonstrated heightened sensitivity to annual mean temperature (12.7-24.5°C) and temperature seasonality (63.8-598.9). Under the current climate, E. tereticornis had the widest suitable distribution area (124.91 × 104 km²), followed by E. grandis (124.89 × 104 km²) and E. urophylla (119.81 × 104 km²). Under future climate change scenarios, the suitable ranges of E. grandis, E. urophylla and E. tereticornis will continue to expand. This study highlights the importance of climate change in Eucalyptus distribution and provides quantified potential distribution maps for three Eucalyptus species under current and future climate conditions in China. This research offers valuable scientific insights pertinent to the management and rational site selection for Eucalyptus plantations.

Chromium(VI) Adsorption and Reduction in Soils under Anoxic Conditions: The Relative Roles of Iron (oxyhr)oxides, Iron(II), Organic Matters, and Microbes.

Chromium (Cr) transformation in soils mediated by iron (Fe) (oxyhr)oxides, Fe(II), organic matter (OM), and microbes is largely unexplored. Here, their coupling processes and mechanisms were investigated during anoxic incubation experiments of four Cr(VI) spiked soil samples with distinct physicochemical properties from the tropical and subtropical regions of China. It demonstrates that easily oxidizable organic carbon (EOC, 55-84%) and microbes (16-48%) drive Cr(VI) reduction in soils enriched with goethite and/or hematite, among which in dryland soils microbial sulfate reduction may also be involved. In contrast, EOC (38 ± 1%), microbes (33 ± 1%), and exchangeable and poorly crystalline Fe (oxyhr)oxide-associated Fe(II) (29 ± 3%) contribute to Cr(VI) reduction in paddy soils enriched with ferrihydrite. Additionally, exogenous Fe(II) and microbes significantly enhance Cr(VI) reduction in ferrihydrite- and goethite-rich soils, and Fe(II) greatly promotes but microbes slightly inhibit Cr passivation. Both Fe(II) and microbes, especially the latter, promote OM mineralization and result in the most substantial OM loss in ferrihydrite-rich paddy soils. During the incubation, part of the ferrihydrite converts to goethite but microbes may hinder the transformation. These results provide deep insights into the geochemical fates of redox-sensitive heavy metals mediated by the complicated effects of Fe, OM, and microbes in natural and engineered environments.

Biochar–water–soil interactions: Implications for soil desiccation cracking behavior in subtropical regions

In subtropical regions, soil desiccation cracking often exerts a significant impact on the interactions between soil water and the atmosphere, making it a subject of great interest in the fields of geotechnical and geoenvironmental engineering. Despite the growing utilization of biochar as a sustainable soil amendment, there remains a lack of in-depth understanding of biochar–water–soil interactions, as well as its impact on soil desiccation cracking behavior. To address this gap, this study investigated the influence and mechanism of woody biochar dosages and particle sizes on the cracking behavior of three typical clayey soils in subtropical regions in China, namely Pukou expansive soil (PKE), Xiashu soil (XS), and Zhongshan lateritic soil (ZSL). The quantitative analysis of crack images revealed that the use of biochar was not consistently effective in preventing soil cracking. The application of biochar reduced the crack ratio in PKE and XS by up to 24.03% and 53.89%, respectively. In contrast, ZSL exhibited a 74.57% increase in crack ratio with the addition of 10% biochar. This influence can be further enhanced by increasing the dosage and reducing the particle size of biochar. The microstructural analysis demonstrated that biochar exerts an inhibitory effect on PKE and XS primarily through direct replacement, direct barrier, and indirect physical mechanisms. Moreover, an indirect chemical effect between biochar and clay particles was proposed to explain the exacerbated cracking observed in biochar-amended ZSL. To effectively utilize biochar for soil cracking mitigation in subtropical regions, it is essential to evaluate the initial mineral composition and cation type of the soil.

Spatial variation of gully erosion determinants across subtropical regions of China

Gully erosion, with an enormous threat to global economic development and ecological security, results from the comprehensive effect of soil inherent properties and external geo-environmental factors. Previous studies on gully causative factors were mainly conducted on a specific site, case, or region, and limited systematic investigation has been performed on their spatial variation. Based on gully inventory in the seven provinces of southern China, this study investigated the spatial variation of thresholds for fifteen potential causative factors by the frequency ratio model, and analyzed the contribution of these factors to gully erosion by the Boruta algorithm. The results showed that gully density generally increased from north to south, characterized by a clustered distribution within a specific range, but the threshold of each potential factor exhibited a slight difference. Particularly, gully formation was predominantly influenced by multi-year average rainfall erosivity, multi-year average rainfall, and population density. However, the relative importance of these factors to gully erosion showed significant spatial heterogeneity. The relative importance increased from north to south for the factors of rainfall erosivity (8.25 %-13.56 %), rainfall (8.62 %-12.01 %), and slope aspect (0.35 %-1.22 %), but decreased for the factors of slope gradient (2.93 %-6.24 %), temperature (5.23 %-8.89 %), normalized difference vegetation index (NDVI) (5.25 %-7.80 %), and fraction vegetation coverage (FVC) (4.11 %-7.23 %). Overall, climatic factors exhibited an increasing contribution to gully erosion from north to south, whereas the influence of topography and vegetation coverage decreased along the same gradient. These findings will facilitate a better gully erosion control in southern China.

Seven New Species of Entoloma Subgenus Cubospora (Entolomataceae, Agaricales) from Subtropical Regions of China.

Entoloma is a relatively large genus in Agaricales, with a rich diversity of species and a wide distribution. In this study, seven new species of Entoloma belonging to the subgenus Cubospora have been identified based on morphological and phylogenetic evidence from subtropical regions of China. Morphologically, E. excavatum is characterized by the yellow, depressed, estriate pileus and medium-sized basidiospores; E. lacticolor is recognized by the white and papillate pileus, adnexed lamellae, and presence of clamp connections; E. phlebophyllum is identified by the pink-to-maroon and estriate pileus, and lamellae with lateral veins; E. rufomarginatum differs from other cuboid-spored species by the lamellae edge which is red-brown-underlined; E. subcycneum is characterized by the white pileus and carneogriseum-type cheilocystidia; E. submurrayi is recognized by the pileus margin exceeding the lamellae, 2-layered pileipellis with hyphae of different widths, and the presence of clamp connections; E. tomentosum is identified by the tomentose pileus, heterogeneous lamella edge, and versiform cheilocystidia with brown-yellow contents. Their distinct taxonomic status is confirmed by the positions of the seven new species in both the ITS + LSU and 3-locus (LSU, tef-1α, rpb2) phylogenetic trees. Detailed descriptions, color photos, and a key to related species are presented.

Analysis of the Fungal Community Composition in Endemic Orchids with Terrestrial Habitat in Subtropical Regions.

Habenaria and Liparis are well-known orchid genera that grow in terrestrial habitats in the tropics, subtropics or temperate zones. Three species have been found in subtropical regions of China, inhabiting terrestrial to epiphytic habitats. This study focuses on three species, H. dentata (distributed in Asia), H. yachangensis, and L. gigantea. For H. yachangensis and L. gigantea, there is no information about the mycorrhizal community in these species. This study aims to conduct the fungal community screening of Chinese ground orchids from subtropical regions. We performed a comparative analysis of the fungal community among H. dentata, H. yachangensis, and L. gigantea, determining their ITS regions using NGS paired-end sequences. The results clarified the diversity and the predominance of fungal genera. Ascomycota was abundant compared to Basidiomycota or other fungi groups in all communities, with a high dominance in all populations, especially for L. gigantea. At different root spatial locations, the fungal community diversity and richness were higher in the soil than in the rhizosphere or inner root. However, the results suggest that L. gigantea has a different fungal community compared to Habenaria species. In this order, the subtropical terrestrial orchids have a different fungal network compared to the northern terrestrial orchids. Also, there is a high probability of co-existence and co-evolution of endophytic fungi in these terrestrial orchids, indicating the potential role of host plants in selecting an endophytic fungal community. Furthermore, our results highlight the need to elucidate the microbe interactions of these unique orchids for long-term purposes, such as isolating indigenous fungi for suitable inoculants for further orchid propagation, restoration, and conservation.

First Report of Alternaria alternata Causing Postharvest Fruit Rot of Indian Jujube (Ziziphus mauritiana) in China.

Ziziphus mauritiana Lam., commonly known as Indian jujube or ber, is a popular fruit crops grown in tropical and sub-tropical regions of China. It is commonly stored at 4℃, relative humidity of about 90%, combined with waxing or sealing with film bag. In January 2023, a postharvest fruit rot was observed on Indian jujube in three markets located in Nanchang city of Jiangxi province, China, with a disease incidence of 4 to 10%. Initially, brown spots appeared on the surface or base of thefruit, which gradually expanded into irregular brown lesions. Gray-white hyphae developed in the center of the lesions, and ultimately thefruitrotted. To isolate the pathogen, small pieces (5 × 5 mm) of ten infected fruits were surface-sterilized in 75% ethanol for 15 s and then 1% sodium hypochlorite for 30 s, rinsed three times in sterile water, plated onto potato dextrose agar (PDA), and incubated at 25°C for 3 days. Eight strains with similar morphological characteristics were isolated, and one representative isolate (JXAA-1) was used for morphological and molecular characterization. The colonies on PDA were initially olive green with white margins, and later turned dark olive or black with profuse sporulation. Conidia were borne singly or in a chain, brown, with 1 to 5 transverse septa and 0 to 3 longitudinal septa, obclavate to obpyriform, and measured 12.9 to 33.7 × 7.5 to 12.9 μm (n = 30). On the basis of morphological characteristics, the isolates were tentatively identified as Alternaria spp. (Simmons 2007). To confirm the identification, genomic DNA was extracted from the isolate JXAA-1 with the Fungi Genomic DNA Extraction Kit (Solarbio Biotech, China). The 18S nrDNA (SSU), 28S nrDNA (LSU), internal transcribed spacer of the rDNA (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), elongation factor 1-alpha (TEF1), Alternaria major allergen gene (Alt a 1), endopolygalacturonase (EndoPG) and an anonymous gene regions (OPA 10-2) were amplified and sequenced using primers NS1/NS4, LR7/LR0R, ITS5/ITS4, gpd1/gpd2, EF1-728F/EF1-986R, Alt-for/Alt-rev, PG3/PG2b, OPA10-2L/OPA10-2R, respectively (Woudenberg et al. 2015). The obtained DNA sequences (SSU: PP190241; LSU: PP190242; ITS: PP189927; GAPDH: PP196557; TEF1: PP196558; Alt a 1: PP196559; EndoPG: PP196560; and OPA 10-2: PP196561) showed 100% homology with those of A. alternata (GenBank accession nos. MT000349 [1020/1020 bp]; KP940477 [1312/1312 bp]; MK972909 [583/583 bp]; MN615421 [593/593 bp]; MN046379 [280/280 bp]; MN304714 [490/490 bp]; MN698284 [458/458 bp] and MH975214 [701/701 bp]). A maximum likelihood phylogenetic tree was constructed by combining all sequenced loci in IQTREE web servers. The isolate JXAA-1 clustered with Alternaria alternata (CBS 121336). The fungus associated with postharvest fruit rot on Z. mauritiana was thus identified as A. alternata. To evaluate the pathogenicity, six surface sterilized fruits were wounded by a sterile scalpel and inoculated with a 10 μl drop of spore suspension (1 × 105 conidia/ml) of isolate JXAA-1. Another six fruits were inoculated with sterilized ddH2O as control and the experiment was repeated three times. All fruits were incubated at 25°C and 80% relative humidity. After 5 days, all the wounded fruit inoculated with A. alternata showed similar symptoms to those observed previously, while the control fruits remained healthy. A. alternata was consistently reisolated from infected fruit and confirmed by morphological and molecular data, fulfilling Koch's postulates. A.alternata has previously been reported causing leaf spot and fruit rot on Chinese jujube (Ziziphus jujuba) in China (Bai et al. 2015; Li et al. 2021). But to our knowledge, this is the first report of A. alternata causing postharvest fruit rot on Indian jujube (Z. mauritiana) in China. Therefore, managers should pay more attention to postharvest fruit rot of jujube caused by A. alternata, the foam bag is put on after the membrane bag is sealed, the broken or infected fruit is picked out in time to reduce the spread of pathogenic fungus.

Decoupling of nitrogen allocation and energy partitioning in rice after flowering.

Estimation of energy partitioning at leaf scale, such as fluorescence yield (ΦF) and photochemical yield (ΦP), is crucial to tracking vegetation gross primary productivity (GPP) at global scale. Nitrogen is an important participant in the process of light capture, electron transfer, and carboxylation in vegetation photosynthesis. However, the quantitative relationship between leaf nitrogen allocation and leaf energy partitioning remains unexplored. Here, a field experiment was established to explore growth stage variations in energy partitioning and nitrogen allocation at leaf scale using active fluorescence detection and photosynthetic gas exchange method in rice in the subtropical region of China. We observed a strongly positive correlation between the investment proportion of leaf nitrogen in photosynthetic system and ΦF during the vegetative growth stage. There were significant differences in leaf energy partitioning, leaf nitrogen allocation, and the relationship between ΦF and ΦP before and after flowering. Furthermore, flowering weakened the correlation between the investment proportion of leaf nitrogen in photosynthetic system and ΦF. These findings highlight the crucial role of phenological factors in exploring seasonal photosynthetic dynamics and carbon fixation of ecosystems.

Alternation between terrestrial and aquatic plants dominated organic matter sources in the Tiaoshu wetland (south China) and its response to late Pleistocene environmental changes

Widely distributed wetlands in China play an important role in the global carbon cycle. However, the long-term response of wetland evolution and carbon storage in tropical southern China to climate change remains unclear. Here, we present a sediment core record from the Tiaoshu Wetland in the northern Leizhou Peninsula and multiple proxy indicators are investigated, with the aim of better understanding past vegetation and environmental changes. The following conclusions were drawn: (i) The organic matter deposited in the Tiaoshu Wetland was mainly derived from terrestrial C3 plants and aquatic plants growing in and/or around the catchment. The temporal variability in the relative proportions of organic matter contributed by various sources revealed paleoenvironmental changes in the study area, generally consistent with regional and global climate records. (ii) The peat formation pattern in the Tiaoshu Wetland is in contrast to some individual sites reported in subtropical China, suggesting that there may be different peat formation patterns in the tropical and subtropical regions of China, which may be closely related to specific hydrothermal conditions in different regions. In addition, by comparison with atmospheric CH4 concentrations, our results suggest potential relationships between the evolution of wetlands in tropical China and global atmospheric CH4 cycles.

Linkage between Granite Weathering and Gully Erosion in Subtropical Region

Granites, widely distributed in the Earth’s crust, undergo pedogenic processes, shaping diverse soil-mantled landscapes influenced by climatic factors in different regions. Investigating the geochemical signatures in granite weathering profiles across varying climatic conditions provides valuable insights into the intricate interplay between weathering and landscape evolution. In this study, the geochemical features, particularly major and rare earth elements, and the weathering degree of granites across temperate to subtropical regions in China were examined. The results indicated significant variations in the geochemical characteristics of granite weathering profiles, both at a pedon and regional scale (p < 0.01). With increasing hydrothermal conditions from north to south, soil pH shifted from neutral to acidic, accompanied by the leaching of major elements (K2O, Na2O, CaO, and MgO) and the enrichment of Al and Fe. The total rare earth elements (∑REEs) ranged from 75 to 352 ppm, and light rare earth elements (LREEs) from 71 to 317 ppm, exhibiting less significant variations across the study area, while heavy rare earth elements (HREEs) showed higher concentrations in the subtropical region (3 to 35 ppm). Plagioclases dominated the weathering process in temperate regions, with K-feldspar progressively increasing and, eventually, dominating from temperate to subtropic regions, resulting in a shift in clay minerals from 2:1-type in the temperate to 1:1-type in the subtropic. The chemical index of alteration (CIA) and comprehensive weathering index (W) increased from fresh rock to residual soils along the weathering profiles and from north to south across the study area, ranging from 50.72 to 97.44 and 35.11 to 70.62, respectively. The intensified granite weathering degree was significantly influenced by climatic conditions (p < 0.05), especially the multi-year average precipitation (22.4%) and relative humidity (9.1%) (p < 0.01). Gully erosion on the granite weathering mantle was concentrated in granites with a comprehensive weathering index exceeding 52.51, and the spatial variation of the granite weathering degree aligned with the spatial distribution of gully density across the study area.

Assessing the Distribution and Driving Effects of Net Primary Productivity along an Elevation Gradient in Subtropical Regions of China

Globally, forest ecosystems, especially subtropical forests, play a central role in biogeochemical cycles and climate regulation, demonstrating their irreplaceable function. The subtropical region of China, characterized by its unique forest ecosystem, complex terrain, climate heterogeneity, diverse vegetation types, and frequent human activities, underscores the importance of the in-depth study of its net primary productivity (NPP). This paper employs the eddy covariance–light use efficiency (EC-LUE) model to quantitatively estimate the gross primary productivity (GPP) of this region from 2001 to 2018, followed by an estimation of the actual net primary productivity (ANPP) using the carbon use efficiency (CUE). The results showed that over these 18 years, the annual average ANPP was 677.17 gC m−2 a−1, exhibiting an overall increasing trend, particularly in mountainous areas, reserves, and the cultivated lands of the northeastern plains, whereas a significant decrease was observed around the urban agglomerations on the southeast coast. Furthermore, the Thornthwaite memorial model was applied to calculate the potential net primary productivity (PNPP), and diverse scenarios were set to quantitatively evaluate the impact of climate change and human activities on the vegetation productivity in the study area. It was found that in areas where the ANPP increased, both human activities and climate change jointly influenced ANPP dynamics; in areas with a decreased ANPP, the impact of human activities was particularly significant. Additionally, the heterogeneous distribution of ANPP across different altitudinal gradients and the driving effects of various climatic factors were analyzed. Finally, a partial correlation analysis was used to examine the relationships between the temperature, precipitation, and ANPP. This study indicated that temperature and precipitation have a substantial impact on the growth and distribution of vegetation in the region, yet the extent of this influence shows considerable variation among different areas. This provides a robust scientific basis for further research and understanding of the carbon dynamics of subtropical forest ecosystems and their role in the global carbon cycle.

Genome-wide identification of MAPK family in papaya (Carica papaya) and their involvement in fruit postharvest ripening

BackgroundPapaya (Carica papaya) is an economically important fruit cultivated in the tropical and subtropical regions of China. However, the rapid softening rate after postharvest leads to a short shelf-life and considerable economic losses. Accordingly, understanding the mechanisms underlying fruit postharvest softening will be a reasonable way to maintain fruit quality and extend its shelf-life.ResultsMitogen-activated protein kinases (MAPKs) are conserved and play essential roles in response to biotic and abiotic stresses. However, the MAPK family remain poorly studied in papaya. Here, a total of nine putative CpMAPK members were identified within papaya genome, and a comprehensive genome-wide characterization of the CpMAPKs was performed, including evolutionary relationships, conserved domains, gene structures, chromosomal locations, cis-regulatory elements and expression profiles in response to phytohormone and antioxidant organic compound treatments during fruit postharvest ripening. Our findings showed that nearly all CpMAPKs harbored the conserved P-loop, C-loop and activation loop domains. Phylogenetic analysis showed that CpMAPK members could be categorized into four groups (A-D), with the members within the same groups displaying high similarity in protein domains and intron–exon organizations. Moreover, a number of cis-acting elements related to hormone signaling, circadian rhythm, or low-temperature stresses were identified in the promoters of CpMAPKs. Notably, gene expression profiles demonstrated that CpMAPKs exhibited various responses to 2-chloroethylphosphonic acid (ethephon), 1-methylcyclopropene (1-MCP) and the combined ascorbic acid (AsA) and chitosan (CTS) treatments during papaya postharvest ripening. Among them, both CpMAPK9 and CpMAPK20 displayed significant induction in papaya flesh by ethephon treatment, and were pronounced inhibition after AsA and CTS treatments at 16 d compared to those of natural ripening control, suggesting that they potentially involve in fruit postharvest ripening through ethylene signaling pathway or modulating cell wall metabolism.ConclusionThis study will provide some valuable insights into future functional characterization of CpMAPKs, and hold great potential for further understanding the molecular mechanisms underlying papaya fruit postharvest ripening.

Co-expression network analysis reveals PbTGA4 and PbAPRR2 as core transcription factors of drought response in an important timber species Phoebe bournei.

Phoebe bournei is one of the main afforestation tree species in subtropical regions of China and is famous for its timber. Its distribution and growth are significantly impaired by water conditions. Thus, it is essential to understand the mechanism of the stress response in P. bournei. Here, we analyzed the phenotypic changes and transcriptomic rearrangement in the leaves and roots of P. bournei seedlings grown for 0 h, 1 h, 24 h, and 72 h under simulated drought conditions (10% PEG 6000). The results showed that drought stress inhibited plant photosynthesis and increased oxidoreductase activity and abscisic acid (ABA) accumulation. Spatio-temporal transcriptomic analysis identified 2836 and 3704 differentially expressed genes (DEGs) in leaves and roots, respectively. The responsive genes in different organs presented various expression profiles at different times. Gene co-expression network analysis identified two core transcription factors, TGA4 and APRR2, from two modules that showed a strong positive correlation with ABA accumulation. Our study investigated the different responses of aboveground and belowground organs of P. bournei to drought stress and provides critical information for improving the drought resistance of this timber species.

First Report of Nigrospora hainanensis Causing Leaf Blight on Brachiaria Griseb in China.

Brachiaria Griseb is an important gramineous forage grown in tropical regions, and also a main grass species uses to restore grasslands in tropical and subtropical regions of China. In August 2022, symptoms of leaf blight were observed on nearly 30% of the Brachiaria forage grass in the base of the Chinese Academy of Tropical Agricultural Sciences, Hainan, China. Symptomatic leaves initially exhibited small, reddish-brown, round or oval spots on their tips, subsequently expanding in size along the leaf margin, and gradually becoming wilted and dry. Twenty leaves showing typical symptoms were randomly collected and pieces (5×5 mm) from the junction of diseased and healthy region were cut, sterilized with 75% alcohol for 30 s, followed by 5% sodium hypochlorite for 30 s. Rinsed three times with sterile water and dried with sterile filter paper. Leaf pieces were placed on potato dextrose agar (PDA) and incubated at 28℃. The colonies were white on the surface and gray on the reverse side. The conidiogenous cells were monoblastic, hyaline, globose or ampulliform, and 6 to 8.7(13.1) ×5 to 7.2 (9) m (n=200). Conidia is single celled, smooth, black, spherical, or ellipsoidal, and (11)13 to 16.5 × (8.2) 10.3 to16.1 m (n=100). Setae were not observed. The morphological characteristics of the isolates were consistent with Nigrospora species. A representative isolate (LNH-5) was selected for genomic DNA extraction. Sequences of the transcribed spacer region of rDNA (ITS), partial translation elongation factor (TEF1), and beta-tubulin fragment (TUB) were amplified using primer pairs ITS1/ITS4(White et al. 1990), EF-728F and EF-986R (Carbone et al. 1999) and Bt2a and Bt2b (Glass et al. 1995), respectively. The sequences of ITS (OQ473493), TEF1 (OQ506059) and TUB gene (OQ506055) were submitted to GenBank. They were 99 to 100% identical to the Nigrospora hainanensis ITS(OM283581.1)(538 out of 519 bp),TEF1(YK019415.1)(274 out of 276 bp),and TUB (OK086377.1)(405 out of 405 bp) sequences. The phylogenetic maximum likelihood analysis using the combined ITS, TEF1 and TUB sequences indicated that the isolate was part of the N. hainanensis clade (100% bootstrap value) that also contained the type isolate LC6979 of this species. Pathogenicity was tested on 15 healthy Brachiaria plants. Fungal conidia were harvested by flooding two-week-old single conidial cultures with sterile water, centrifuging, and adjusting the concentration to 107 spores/mL. Then 10 μL of conidial suspension was dropped onto the surfaces of leaves wounded with a sterile needle. Sterile distilled water was used for control treatment. The test was repeated three times. After inoculation, the plants were kept at 90~100% relative humidity at 25 to 28°C in a greenhouse for two weeks, and monitored daily for lesion development. Seven days post inoculation, all the inoculated leaves presented symptoms similar to those observed under natural conditions, while the control leaves showed no symptoms. The fungus was re-isolated from the diseased tissues by the single spore isolation method (Choi et al. 1999) to complete Koch's postulates. This pathogen has been reported on sugarcane in China (Raza et al., 2019; Zheng et al., 2022). To our knowledge, this is the first report of N. hainanensis causing leaf blight on Brachiaria plants in China.

A new dinoflagellate Gonyaulax pospelovana with resting cysts resembling Spiniferites delicatus and its biogeography and ecology revealed by DNA metabarcoding

ABSTRACT Extant species of the dinoflagellate genus Gonyaulax are capable of producing resting cysts morphologically similar to different cyst-based genera, and their cyst-theca relationships are far from resolved. Here we have carried out germination experiments on several living cysts that resemble Spiniferites delicatus from the subtropical regions of China and Mexico. Both cyst and theca morphology were examined by light and scanning electron microscopy. A new species, Gonyaulax pospelovana, is described, characterized by a cingulum displacement and an overhang of twice its width, and two short antapical spines. The cysts of G. pospelovana had a granular surface and gonal processes with petaloid tips. Maximum likelihood and Bayesian inference analyses based on LSU and SSU rRNA gene sequences revealed that strains identified as G. pospelovana were monophyletic, forming a sister clade to Gonyaulax ellegaardiae and several presumable strains of Gonyaulax spinifera. One Chinese strain and two Mexican strains of G. pospelovana were examined for yessotoxin production using LC-MS/MS, but were not found to produce a detectable amount of toxins. Metabarcoding targeting the 18S V4 rRNA gene was performed on monthly collected samples in Xiamen Bay, China. A ZOTU (zero-radius operational taxonomic units) was detected that was consistent with G. pospelovana. Its maximum abundance was recorded in summer. Additionally, an OTU was identified as G. pospelovana from the Tara Oceans metabarcoding data, which occurred in the Indian and Pacific oceans at temperatures ranging from 28°C to 31°C, suggesting that it is a warm water species.