Dinghushan Biosphere Reserve Research Articles

Changes in Water Utilization Characteristics of Trees in Forests across a Successional Gradient in Southern China

Elucidating the water utilization strategy of trees during forest succession is a prerequisite for predicting the direction of forest succession. However, the water utilization characteristics of trees in forests across a successional gradient remain unclear. Here, we utilized the hydrogen and oxygen stable isotopes combined with the Bayesian mixed model (MixSIAR) to analyze the water utilization of dominant trees (Pinus massoniana, Castanea henryi, and Schima superba) in forests along a successional gradient in the Dinghushan Biosphere Reserve of China. Furthermore, we determined the primary factor affecting the water utilization of various trees based on variation partitioning analysis and a random forest model. Our results illustrated that in the early-successional forest, the water utilization ratios from shallow soil layers by P. massoniana were significantly lower than that in the mid-successional forest (51.3%–61.7% vs. 75.3%–81.4%), while its water utilization ratios from deep soil layers exhibited the opposite pattern (26.1%–30.1% vs. 9.0%–15.0%). Similarly, the ratios of water utilization from shallow soil layers by C. henryi (18.9%–29.5% vs. 32.4%–45.9%) and S. superba (10.0%–25.7% vs. 29.2%–66.4%) in the mid-successional forest were relatively lower than in the late-successional forest, whereas their water utilization ratios from deep soil layers showed the contrary tendency. Moreover, our results demonstrated that the diverse water utilization of each tree in different successional forests was mainly attributed to their distinct plant properties. Our findings highlight the increased percentage of water utilization of trees from shallow soil layers with forest succession, providing new insights for predicting the direction of forest succession under changing environments.

Terrirubrum flagellatum gen. nov., sp. nov. of Terrirubraceae fam. nov. and Lichenibacterium dinghuense sp. nov. from forest soil and proposal of Rhodoblastaceae fam. nov.

Two Gram-negative, aerobic, rod-shaped bacterial strains, 7MK25T and 6Y81T, were isolated from forest soil of Dinghushan Biosphere Reserve, Guangdong Province, PR China. Based on the results of 16S rRNA gene sequence analysis, strain 7MK25T showed the highest similarity (93.6 %) to Methyloferula stellata AR4T, followed by Bosea thiooxidans DSM 9653T (93.3 %). Strain 6Y81T had the highest similarity of 97.9 % to Lichenibacterium minor RmlP026T, followed by Lichenibacterium ramalinae RmlP001T (97.2 %). Phylogenomic analysis using the UBCG and PhyloPhlAn methods consistently showed that strain 7MK25T formed a sister clade to Boseaceae, while strain 6Y81T formed an independent clade within the genus Lichenibacterium, both in the order Hyphomicrobiales. The digital DNA-DNA hybridization and average nucleotide identity values between strains 7MK25T, 6Y81T and their close relatives were in the ranges of 19.1-29.9 % and 72.5-85.5 %, respectively. The major fatty acids of 7MK25T were summed feature 8 (C18 : 1 ω7c/C18 : 1 ω6c), C19 : 0 cyclo ω8c, C16 : 0 and C17 : 0 cyclo, while those of 6Y81T were summed feature 8 (C18 : 1 ω7c/C18 : 1 ω6c), C16 : 0 and C16 : 0 3-OH. Strains 7MK25T and 6Y81T took diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylcholine as their dominant polar lipids, and Q-10 as their major respiratory quinone. On the basis of phenotypic and phylogenetic data, strain 7MK25T is proposed to represent a novel species of a novel genus with name Terrirubrum flagellatum gen. nov., sp. nov., within a novel family Terrirubraceae fam. nov., with 7MK25T (=KCTC 62738T=GDMCC 1.1452T) as its type strain. Strain 6Y81T represents a novel species in the genus Lichenibacterium, for which the name Lichenibacterium dinghuense sp. nov. (type strain 6Y81T=KACC 21 727T=GDMCC 1.2176T) is proposed. Rhodoblastaceae fam. nov. with Rhodoblastus as the type genus is also proposed to solve the non-monophylectic problem of the family Roseiarcaceae.

Lack of P limitation on litter decomposition: a case study from long-term addition of phosphorus and nitrogen in three subtropical forests in southern China

ABSTRACT Contrary to the widely accepted belief that elevated soil respiration after phosphorus (P) fertilization indicates P limitations for soil microorganisms in (sub)tropical forests, our previous studies have proposed that the elevated respiration results from the abiotically elevated availability of carbon (C), originating from competitive desorption from sorption sites on the surface of soil particles following P fertilization. In this study, we tested the impact of P fertilization (150 kg NaH2PO4-P ha−1 yr−1) on the decomposition of tea bags (Lipton Rooibos and Green teas) in three types of subtropical forests (primary, secondary, and planted forests) at the Dinghushan Biosphere Reserve, where previous findings reported increased soil respiration following P fertilization. If the traditional view holds true, early-stage litter decomposition should be stimulated by P fertilization, similar to the observed stimulation in soil respiration. Conversely, if this is not the case, it strongly reinforces our new hypothesis. Tea bags were employed to serve a twofold purpose: to assess the effects of P fertilization on litter decomposition within the soil, rather than on the soil surface, and to concentrate on the decomposition of early-stage litter. Our results demonstrated that P fertilization did not accelerate the decomposition of tea bags, indicating the exclusive enhancement of soil respiration without simultaneous stimulation of litter decomposition. This contradicts expectations if P were limiting microbial activity, reinforcing our hypothesis. In conclusion, our study reaffirmed the hypothesis that microbial activity in tropical forest soils is not primarily limited by P availability.

Trinickia violacea sp. nov. and Trinickia terrae sp. nov., isolated from forest soil.

Two Gram-stain negative, aerobic and rod-shaped bacterial strains, DHOD12T and 7GSK02T, were isolated from forest soil of Dinghushan Biosphere Reserve, Guangdong Province, PR China. Strain DHOD12T grew at 4-42 °C (optimum, 28-33 °C), pH 4.0-8.5 (optimum, pH 5.5-6.5) and in the presence of 0-1.5 % (w/v; optimum, 0-0.5 %)NaCl; while strain 7GSK02T grew at 12-42 °C (optimum, 28-33 °C), pH 4.0-8.5 (optimum, pH 5.0-6.0) and in the presence of 0-0.5 % (w/v; optimum, 0 %) NaCl. Strains DHOD12T and 7GSK02T had the highest 16S rRNA sequence similarities of 98.0 and 98.3 % with the same species Trinickia mobilis DHG64T, respectively, and 98.4 % between themselves. In the 16S rRNA phylogeny, they formed a clade that was sister to a major cluster consisting of all described Trinickia species. Phylogenomic analyses with the UBCG and PhyloPhlAn methods consistently showed that strains DHOD12T and 7GSK02T formed a clade with T. mobilis DHG64T that was a sister of a cluster containing the remainder of the Trinickia species. The DNA G+C contents of strains DHOD12T and 7GSK02T were 63.1 and 64.6 mol%, respectively. Digital DNA-DNA hybridization and average nucleotide identity values of strains DHOD12T, 7GSK02T and their closely related strains were in the ranges of 21.6-31.4 % and 77.1-86.9 %, respectively. These two strains had the same major respiratory quinone, ubiquinone-8, and both had C16 : 0, C17 : 0 cyclo and summed feature 8 (C18 : 1 ω7c/C18 : 1 ω6c) as their major fatty acids. Their major polar lipids were phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol. Genomic analysis indicated that the two strains could have the potential to degrade aromatic compounds like other Trinickia species. On the basis of phenotypic and phylogenetic results, strains DHOD12T and 7GSK02T represent two novel species of the genus Trinickia, for which the names Trinickia violacea sp. nov. (type strain DHOD12T=LMG 30258T=CGMCC 1.15436T) and Trinickia terrae sp. nov. (type strain 7GSK02T=CGMCC 1.15432T=KCTC 62468T) are proposed.

Paraburkholderia flagellata sp. nov. and Paraburkholderia adhaesiva sp. nov., two novel species isolated from forest soil in Dinghushan Biosphere Reserve in Guangdong, China.

Two Gram-stain-negative, aerobic, motile and short rod strains, designated 4D117T and ZD32-2T, were isolated from the forest soils. Strains 4D117T and ZD32-2T grew optimally at pH 4.0-6.5, 20-33°C and pH 4.5-7.0, 33°C, respectively, and both at 0.5% (w/v) NaCl concentration. Strains 4D117T and ZD32-2T shared the highest 16S rRNA gene sequence similarity with P. acidiphila 7Q-K02T(99.1%) and P. ferrariae NBRC 106233T (98.7%), respectively. The genome size and G + C contents of strains 4D117T and ZD32-2T were 9,002,095bp, 62.9% and 6,974,420bp, 61.7%, respectively. The dDDH and ANI values between strains 4D117T, ZD32-2T and closely related Paraburkholderia species were in the ranges of 21.9-51.6% and 82.9-94.4%, and 81.7% and 25.4% between themself, respectively. Functional genomic analysis showed both strains were capable of degrading contaminants, such as benzoate, anthranilic acid and catechol for 4D117T, and benzene and catechol for ZD32-2T, indicating that they may have potentials for soil pollutant treatment. The main polar lipids of strains 4D117T and ZD32-2T were phosphatidylglycerol, phosphatidylethanolamine and diphosphatidylglycerol. Strain 4D117T contained C16:0, C19:0 cyclo ω8c and C18:1 ω7c and/or C18:1 ω6c, while strain ZD32-2T had C16:0 and C17:0 cyclo as their major cellular fatty acids (> 10%). Based on the phenotypic characters and genomic data, strains 4D117T and ZD32-2T represent two novel species of genus Paraburkholderia, for which the names Paraburkholderia flagellata sp. nov. (type strain 4D117T = GDMCC 1.2617T = NBRC 115278T) and Paraburkholderia adhaesiva sp. nov. (type strain ZD32-2T = GDMCC 1.2622T = NBRC 115282T) are proposed.

Trinickia mobilis sp. nov. and Trinickia acidisoli sp. nov., isolated from soil.

Two novel Gram-stain-negative, aerobic and rod-shaped bacterial strains, designated DHG64T and 4D114T, were isolated from forest soil of Dinghushan Biosphere Reserve, Guangdong Province, PR China. DHG64T grew at 12-37 °C (optimum 33 °C), pH 4.5-10.0 (optimum 6.5-7.5) and in the presence of 0-2.0 % NaCl (w/v); while 4D114T grew at 12-37 °C (optimum 20-33 °C), pH 4.0-7.0 (optimum 4.5-6.0) and in the presence of 0-1.0 % NaCl (w/v). DHG64T and 4D114T showed 97.1-98.0 and 97.5-98.4 % 16S rRNA gene sequence similarities with seven species of the genus Trinickia with validly published names, respectively. In the phylogenetic trees based on 16S rRNA gene and genome sequences, both strains formed a clade with the members of genus Trinickia but well separated from each other. The average nucleotide identity and digital DNA-DNA hybridisation values for the novel strains to all species of the genus Trinickia with validly published names were in the ranges of 80.6-85.0 and 22.4-28.0 %, respectively. DHG64T contained C16 : 0, C17 : 0 cyclo and C19 : 0 cyclo ω8c, while 4D114T had C16 : 0, C17 : 0 cyclo, C19 : 0 cyclo ω8c and summed feature 2 (iso-C16 : 1 I and/or C14 : 0 3-OH) as the major cellular fatty acids. The major polar lipids for strains DHG64T and 4D114T were phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol. The DNA G+C contents of DHG64T and 4D114T were 63.0 and 62.8 mol%, respectively. Genomic analyses indicated that DHG64T and 4D114T may have potential for various applications, such as developing drugs against certain health problems and restoring environments polluted with metal ions and/or benzoate. On the basis of the results of morphological, physiological, biochemical and phylogenetic analyses, strains DHG64T and 4D114T were classified as representing two novel species of the genus Trinickia, for which the names Trinickia mobilis sp. nov. (type strain DHG64T = KACC 21223T = GDMCC 1.1282T) and Trinickia acidisoli sp. nov. (type strain 4D114T = KCTC 82876T = GDMCC 1.2131T) are proposed.

Species of Russula subgenera Archaeae, Compactae and Brevipedum (Russulaceae, Basidiomycota) from Dinghushan Biosphere Reserve

Three novel species collected from Dinghushan Biosphere Reserve (DHSBR) in southern China, Russula cylindrica Y.Song sp. nov. and R. lacteocarpa Y.Song sp. nov. in subgenus Archaeae and R. reticulofolia Y.Song sp. nov. in subg. Compactae, are described based on morphological and molecular data. In addition, Russula leucobrunnea Y.Song nom. nov. is proposed in replacement of R. leucocarpa nom. illeg. in subg. Brevipedum, as R. leucocarpa (T.Lebel) T.Lebel had been described earlier. Differences between the three novel species and their closely related taxa were analyzed. Another two known species in subg. Brevipedum, R. callainomarginis J.F.Liang & J.Song and R. japonica Hongo were also identified among specimens from DHSBR and are described and illustrated. Phylogenetic analyses of ITS and a five-locus phylogeny (concatenated LSU, mtSSU, rpb1, rpb2 and tef1) support the recognition of these taxa.

Carbon flux variation and associated biomass energy storage economic value implications in the Dinghushan Biosphere Reserve

Subtropical forests are a major carbon (C) storage pool and are therefore rich in biomass energy reservoirs. However, there have been no studies that quantify the C storage economic value, especially in the region of the Dinghushan Biosphere Reserve. This study is the first attempt to apply the eddy covariance technique to measure biomass energy storage and the associated economic value and demonstrates that CO2 flux measurement is a viable method for quantifying the ecosystem biomass energy storage. CO2 flux and micro-meteorological data were collected and analyzed to calculate the daily C sequestration and establish their inter-relationship. In addition, we used the C price estimates of Guangdong Province in China to determine the capital value of the C sequestered. The measured average annual precipitation was 1459.4 mm, the average temperature was 22.9 °C and the highest photosynthetic photon flux density (PPFD) was 334.92 μmol m−2s−1. CO2 flux and biomass energy storage varied seasonally. Photosynthetic photon flux density (PPFD) was highly correlated with gross primary production (GPP) (r2 = 0.99, p < 0.0001). Soil temperature was correlated with net ecosystem exchange (NEE) (r2 = 0.84, p < 0.0001). There was a positive correlation (r2 = 0.49, p < 0.0001) between soil moisture and NEE. The Dinghushan Biosphere Reserve sequestered an average of 5300 tCy−1 equivalent to RMB 3.3 million (USD 530,000). We conclude that economically, the Dinghushan Biosphere Reserve is highly significant to China's Guangdong Province because of its rich biomass energy reserves via C sequestration and our findings will stimulate the formulation of more aggressive conservation policies that will inevitably lead to better management of the reserve.

Seasonal Water Uptake Patterns of Different Plant Functional Types in the Monsoon Evergreen Broad-Leaved Forest of Southern China

The precipitation changes induced by climate warming have substantially increased extreme precipitation and seasonal drought events. Different plant functional types (PFTs) could exert an important role in resisting extreme climate. However, the patterns of plant water uptake in different PFTs remain uncertain, especially under different magnitudes of rainfall events. Here, we employed a stable hydrogen isotope (δD) to determine the water sources of different PFTs, including Castanopsis chinensis in the canopy layer, Schima superba in the canopy sublayer, Psychotria asiatica in the shrub layer, and Blechnum orientale on the forest floor in the monsoon evergreen broad-leaved forest in Dinghushan Biosphere Reserve, China. We further used a two-end linear mixing model to explore the water utilization among different PFTs. Our results revealed that precipitation and soil water before rainfall were the water sources of different PFTs. Furthermore, the proportions of precipitation utilized by S. superba in the canopy sublayer under light and moderate rainfalls were 6.9%–59.4% and 30.5%–66.3%, respectively, which were significantly higher than those of other species in both the dry and wet seasons. After heavy rainfall, the proportion of precipitation utilized by S. superba was the lowest (4.7%–26.5%), while B. orientale had the highest proportion of precipitation utilization (31.6%–91.5%), whether in the dry or wet season. These findings imply that different PFTs would compete with one another for water uptake. Especially under climate warming, the uneven distribution of precipitation would intensify the water competition among species, ultimately resulting in the plant community structure becoming much more unstable than before.

Seasonal droughts drive up carbon gain in a subtropical forest

AbstractThe study aimed to show that droughts are increasing in frequency and intensity in the Dinghushan Biosphere Reserve and to illustrate the effects of seasonal droughts on carbon gain in a subtropical forest. This is in response to the threat posed by increased droughts due to global climate change. We used four drought indices to accurately determine periods of drought and periods of increased precipitation. Thereafter, the measured eddy flux and soil moisture content data collected from 2003 to 2014 were compared between the droughts and wet periods to determine drought impacts on the ecosystem carbon gain. Drought accounted for about 20% of the 12-year study period, with the highest drought events and severity occurring between 2012 and 2013. The average annual precipitation and air temperature during the study period were 1404.57 ± 43.2 mm and 22.65 ± 0.1 °C, respectively, showing a decrease of 523 mm in precipitation and an increase of 2.55 °C in temperature, compared with the 30-year records (1990–2020). Contrary to most published data for most forest ecosystems globally, Dinghushan Biosphere Reserve recorded significant carbon gain during 60% of the drought period.

Species of Russula subgenus Heterophyllidiae (Russulaceae, Basidiomycota) from Dinghushan Biosphere Reserve

Two new species of subgenus Heterophyllidiae subsection Cyanoxanthinae, Russula fusiformata Y.Song sp. nov. and R. purpureorosea Y.Song sp. nov., collected from the Dinghushan Biosphere Reserve (DHSBR), are described based on both morphology and a phylogenetic analysis of the internal transcribed spacer (ITS), further increasing Heterophyllidiae species diversity in the area. Differences between the two new species and related taxa are analyzed. The other 17 reported species of Russula subgenus Heterophyllidiae that have been collected from DHSBR during mushroom explorations since 2014 are also summarized. The dominant species and the ecological distribution of all 19 species are briefly discussed, and most species are presented in macrofungal plates.

Paracidobacterium acidisoli gen. nov., sp. nov. and Alloacidobacterium dinghuense gen. nov., sp. nov., two acidobacteria isolated from forest soil, and reclassification of Acidobacterium ailaaui and Acidipila dinghuensis as Pseudacidobacterium ailaaui gen. nov., comb. nov. and Silvibacterium dinghuense comb. nov.

Two aerobic and obligately acidophilic bacteria, designated 4G-K13T and 4Y35T, were isolated from the forest soil sampled at Dinghushan Biosphere Reserve, Guangdong Province, PR China. These two strains were Gram-stain-negative, non-motile and short rods that multiplied by binary division. Strains 4G-K13T and 4Y35T had the highest 16S rRNA gene sequence similarity of 97.0 and 97.2 % to Silvibacterium bohemicum DSM 103733T and Acidisarcina polymorpha SBC82T, respectively. Phylogenetic trees based on the 16S rRNA gene and whole genome sequences showed consistently that these two strains formed a major clade with members of the genera Acidipila, Acidisarcina, Silvibacterium and Acidobacterium in the family Acidobacteriaceae, but each occupied an unique position. In both the UBCG and the PhyloPhlAn phylogenomic trees, strains 4G-K13T and 4Y35T congruently formed a highly supported subclade with Acidobacterium capsulatum DSM 11244T and Acidobacterium ailaaui DSM 27394T, respectively. The major fatty acids (>5 %) of strain 4G-K13T were iso-C15 : 0, iso-C17 : 0, summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c) and summed feature 9 (iso-C17 : 1 ω9c and/or C16 : 0 10-methyl), while that of strain 4Y35T were C16 : 0, C18 : 1 ω9c, iso-C15 : 0, summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c) and summed feature 9 (iso-C17 : 1 ω9c and/or C16 : 0 10-methyl). Strain 4G-K13T contained phosphatidylethanolamine, four unidentified phospholipids, four glycolipids, two unidentified aminolipids and two unknown lipids, while strain 4Y35T had phosphatidylethanolamine, three unidentified phospholipids, two glycolipids, five unidentified aminolipids and one unknown polar lipid. The DNA G+C contents of 4G-K13T and 4Y35T were 60.5 and 55.8 mol%, respectively. Based on all these phylogenetic, physiological and chemotaxonomic data, we suggest that strains 4G-K13T and 4Y35T represent two novel species of two novel genera in the family Acidobacteriaceae, for which the names Paracidobacterium acidisoli gen. nov., sp. nov. (type strain: 4G-K13T=GDMCC 1.1195T=NBRC 113249T) and Alloacidobacterium dinghuense gen. nov., sp. nov. (type strain: 4Y35T=KACC 21728T=NBRC 114261T) are proposed. We also propose to reclassify Acidobacterium ailaaui and Acidipila dinghuensis as Pseudacidobacterium ailaaui gen. nov., comb. nov. and Silvibacterium dinghuense comb. nov., respectively, based mainly on the results of phylogenomic analysis.

An Interannual Comparative Study on Ecosystem Carbon Exchange Characteristics in the Dinghushan Biosphere Reserve, a Dominant Subtropical Evergreen Forest Ecosystem.

Compared with other forest systems, research interest in the potential for a stronger ecosystem carbon sequestration of evergreen forests throughout subtropical China has greatly increased. The eddy covariance technique is widely employed to determine accurate forest-atmosphere carbon dioxide (CO2) flux, which is subsequently used to determine forest ecosystem carbon exchange characteristics. The Dinghushan Biosphere Reserve, a subtropical monsoon evergreen broad-leaved forest, is a suitable study area due to its warm and humid climate (compared with other regions within the same latitude), consequently playing a role in the carbon cycle in the region. For this study, we hypothesized that the forest land in this region generally acts as a carbon sink, and that its carbon sequestration capacity increases over time despite the influence of climatic factors. Here, we compared net CO2 flux data derived from the eddy covariance technique over an 8-year study window. Additionally, we ascertained the effects of various environmental factors on net CO2 flux, while also using the Michaelis–Menten model and a physiologically based process model to track and report on ecosystem carbon exchange characteristics. We observed seasonal trends in daily ecosystem flux, indicative of sensitivity to climatic factors, such as air temperature, precipitation, and sunlight. The carbon sequestration capacity of the region exhibited seasonal variability, increasing from October to March (−264 g C m−2 year−1, i.e., 48.4%) while weakening from April to September (−150 g C m−2 year−1, i.e., 40.4%) on average. The net ecosystem exchange (NEE) rate varied from −518 to −211 g C m−2 year−1; ecosystem respiration (Re) varied from 1,142 to 899 g C m−2 year−1; and gross primary production (GPP) varied from 1,552 to 1,254 g C m−2 year−1. This study found that even though the Dinghushan Biosphere Reserve generally acts as a carbon sink, its carbon sequestration capacity did not increase significantly throughout the study period. The techniques (models) used in this study are suitable for application in other ecosystems globally, which can aid in their management and conservation. Finally, the Dinghushan Biosphere Reserve is both an exemplary and a model forest system useful in exploring CO2 absorption and sequestration from the atmosphere.

Dyella telluris sp. nov. and Dyella acidiphila sp. nov., isolated from forest soil of Dinghushan Biosphere Reserve, China.

Cells of bacterial strains G9T and 7MK23T, isolated from forest soil samples collected from the Dinghushan Biosphere Reserve, Guangdong Province, PR China, were Gram-stain-negative, aerobic and rod-shaped. Strain G9T was motile with single polar flagellum and grew at 12-37 °C (optimum, 28 °C), pH 4.5-8.0 (optimum, pH 6.0-7.5) and in the presence of 0-3.5 % NaCl (optimum, 1.5%, w/v); while strain 7MK23T was non-motile and grew at 12-42 °C (optimum, 28-33 °C), pH 2.5-8.5 (optimum, pH 4.5-6.5) and NaCl levels of 0-1.0 % (optimum, 0-0.5 %, w/v). Phylogenetic analysis based on 16S rRNA gene sequences revealed that both isolates fell within the cluster of the genus Dyella. The closely related species (with a 16S rRNA gene sequence similarity >98.65%) of strain G9T were Dyella terrae JS14-6T (99.0 %), D. kyungheensis THG-B117T (98.8 %) and D. amyloliquefaciens DHC06T (98.7 %) while that of strain 7MK23T were D. mobilis DHON07T (99.2 %) and D. flava DHOC52T (99.1 %), but the average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strains G9T, 7MK23T and the closely related Dyella species listed above were in the ranges of 77.5-83.8 % and 22.0-27.0 %, much lower than the species demarcation lines of 95.5 and 70 %, respectively. Phylogenomic analyses using UBCG and Phylophlan also supported that these two strains represent two novel species of Dyella. The major fatty acids of strain G9T were iso-C15 : 0, iso-C17 : 1 ω9c and iso-C17 : 0 while that of strain 7MK23T were iso-C15 : 0 and anteiso-C15 : 0. Ubiquinone-8 was the only respiratory quinone detected in both strains. The polar lipids of strain G9T consisted of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, and several unknown phospholipids, aminophospholipids, aminolipids and lipid while strain 7MK23T contained phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylmethylethanolamine and several unknown phospholipids and aminophospholipids. The DNA G+C contents of strains G9T and 7MK23T were 64.7 and 63.4 mol%, respectively. On the basis of 16S rRNA gene sequence phylogenetic and phylogenomic analyses as well as phenotypic data obtained, we propose that strains G9T and 7MK23T represent two novel species of the genus Dyella, for which the names Dyella telluris sp. nov. (type strain G9T=KACC 21725T=GDMCC 1.2132T) and Dyella acidiphila sp. nov. (type strain 7MK23T=KCTC 62739T=GDMCC 1.1446T) are proposed.

Chitinophaga silvatica sp. nov., isolated from forest soil, and reclassification of Chitinophaga extrema as a later heterotypic synonym of Chitinophaga solisilvae.

A novel bacterial strain, designated K2CV101002-2T, was isolated from forest soil collected at Dinghushan Biosphere Reserve, Guangdong Province, PR China. Phylogenetic analyses based on 16S rRNA gene sequences showed that it belonged to the genus Chitinophaga and was most closely related to Chitinophaga terrae KP01T (99.0 %), followed by Chitinophaga extrema Mgbs1T (98.3 %) and Chitinophaga solisilvae O9T (98.1 %). The draft genome sequence was 6.8 Mb long with a relative low G+C content of 39.8 mol%. The average nucleotide identity and digital DNA-DNA hybridization values between the novel strain and closely related type strains were 71.4‒76.2 % and 18.4‒19.6 %, respectively. Meanwhile the corresponding values between C. extrema Mgbs1T and C. solisilvae O9T were 98.6 and 88.1 %, respectively. The novel strain contained iso-C15:0, C16:1 ω5c and iso-C17:0 3-OH as the major fatty acids and MK-7 as the predominant respiratory quinone. The polyphasic study clearly supported that strain K2CV101002-2T represents a new species of the genus Chitinophaga, for which the name Chtinophaga silvatica sp. nov. (type strain K2CV101002-2T=GDMCC 1.1288T=JCM 32696T) is proposed. In addition, Chitinophaga extrema Goh et al. 2020 should be taken as a later heterotypic synonym of Chitinophaga solisilvae Ping et al. 2020.

Distinct storage mechanisms of soil organic carbon in coniferous forest and evergreen broadleaf forest in tropical China

The impact of human activities on soil carbon (C) storage in tropical forests has aroused wide concern during the past decades, because these ecosystems play a key role in ameliorating global climate change. However, there remain uncertainties about how land-use history alters soil organic carbon (SOC) stability and storage in different forests. In this study, we measured the C content and mass distributions of soil aggregates, density fractions, mineral-bound C and microbial biomass C in the organic horizon, 0-10 cm and 10-20 cm soil layers in coniferous forest and evergreen broadleaf forest at Dinghushan Biosphere Reserve in tropical China. The broadleaf forest had larger SOC stocks than the coniferous forest, but the proportion of SOC stored in different density fractions at 0-10 cm soils was similar between forest types, while a greater proportion of SOC was stored in microaggregates in the coniferous forest. Most of the SOC was held as light fraction C in the organic horizon in the coniferous forest, whereas the concentrations of mineral-bound C were higher in the broadleaf forest. These findings indicate clear differences in the protection of SOC between broadleaf and coniferous forests growing on the same soil type. We propose that historic conversion of broadleaf forest to coniferous forest has reduced soil C sequestration capacity by altering the diversity and quality of plant inputs to the soil, which in turn affected macroaggregate formation, soil chemical properties and microbial biomass. Our results thus demonstrate that changes in forest tree species composition could have long-lasting effects on soil structure and carbon storage, providing crucial evidence for policy decisions on forest carbon sink management.

Mycorrhizal fungi and phosphatase involvement in rhizosphere phosphorus transformations improves plant nutrition during subtropical forest succession

Phosphorus (P) availability is a limiting factor for plant growth in tropical and subtropical regions, but many tropical and subtropical forests maintain high levels of productivity and biodiversity under P-limited conditions, which is why P limitation and plant community biomass increase simultaneously during succession in subtropical forests. Biologically-mediated P transformations in the rhizosphere are expected to increase P acquisition by plants during forest succession in tropical and subtropical regions. In this study, we collected leaf and rhizosphere samples from the dominant tree species in three successional forests (early, middle, and late) at the Dinghushan Biosphere Reserve, Southern China, and measured the leaf P concentrations and biological properties of the rhizosphere: microbial biomass P (MBP), P fractions, acid phosphatase activity, and the biomasses of arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (EMF). We found that the leaf N:P ratio increased but the rhizosphere microbial biomass N:P ratio decreased from the early- to late-successional stages, indicating more plant P limitation and less microbial P limitation during forest succession. The decreased proportion of occluded P in the rhizosphere was negatively related to the increasing AMF biomass, and the increased proportions of labile organic P (Po) and moderately labile Po were positively associated with increasing AMF biomass but negatively related to the acid phosphatase activity that increased during forest succession. We propose a mechanism for P availability in subtropical successional forests based on AMF processes that increase the transformation of occluded P to labile and moderately labile Po forms, followed by acid phosphatase activity that converts these hydrolysable Po forms into inorganic P. Transformation of occluded P and Po fractions in the rhizosphere to plant-available P will satisfy the increasing P demand of plants during forest succession, thus maintaining the high productivity and biodiversity of P-limited tropical and subtropical forests.

Three Novel Species of Russula Pers. Subg. Compactae (Fr.) Bon from Dinghushan Biosphere Reserve in Southern China

Three novel species of Russula Pers. subg. Compactae (Fr.) Bon from southern China are described with morphological evidence and phylogenetic analyses based on ITS and the concatenated partial LSU, mtSSU, rpb1, rpb2 and tef1 gene sequences. All three species possess sparse and broad lamellae. Russula latolamellata Y.Song & L.H.Qiu, sp. nov., is characterized by its cracking, black-tan pileus, scarlet-turning context on bruising and absence of pileocystidia and caulocystidia. Russula nigrocarpa S.Y.Zhou, Y.Song & L.H.Qiu, sp. nov., can be distinguished by its off-white lamellae, small basidiospores, hymenial cystidia and pileocystidia of various forms, often with forked apices and by its gelatinous pileipellis. Russula ochrobrunnea S.Y.Zhou, Y.Song & L.H.Qiu, sp. nov., is characterized by its cracking, grayish brown pileus with striate margin, light-brown lamellae whose edges turn dark-brown when mature, small basidiospores and slightly flexuous ormoniliform hymenial cystidia. Their detailed morphological features and phylogenetic positions are discussed and compared among closely related species.

Pararobbsia silviterrae gen. nov., sp. nov., isolated from forest soil and reclassification of Burkholderia alpina as Pararobbsia alpina comb. nov.

A novel Gram-stain-negative, aerobic, non-spore-forming, non-motile and rod-shaped bacterial strain, DHC34T, was isolated from forest soil of Dinghushan Biosphere Reserve, Guangdong Province, China (112° 31' E 23° 10' N). It grew optimally on R2A medium at 28 °C, at pH 6.0-7.0 and in the presence of 0-1 % (w/v) NaCl. Strain DHC34T was closely related to Burkholderia alpina LMG 28138T (98.5 % 16S rRNA gene sequence similarity). 16S rRNA gene sequence analysis showed that strain DHC34T formed a clade with B. alpina LMG 28138T, which is next to but branched deeply with Robbsia andropogonis ICMP 2807T. The phylogenetic relationships among these three strains were also supported with the phylogram based on concatenated partial gyrB, recA and trpB gene sequences. The phylogenomic tree generated with the UBCG tool showed that strains DHC34T and R. andropogonis ICMP 2807T were in a different clade. The DNA-DNA relatedness values between strain DHC34T and B. alpina LMG 28138T and R. andropogonis ICMP 2807T were much lower than 70 %. Strain DHC34T contained ubiquinone 8 as the major respiratory quinone. Its major fatty acids were C16 : 0, C17 : 0 cyclo and C19 : 0 cyclo ω8c. The DNA G+C content of strain DHC34T was 64.2 mol%. The major polar lipids were phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol, three unidentified aminophospholipids, four unidentified phospholipids, one unidentified aminolipid and a polar lipid. The phenotypic, phylogenetic, genotypic and chemotaxonomic data showed that strain DHC34T represents a novel species of a new genus in the family Burkholderiaceae, for which the name Pararobbsia silviterrae gen. nov., sp. nov. is proposed. The type strain of Pararobbsia silviterrae is DHC34T (=KCTC 42628T=LMG 28845T). On the basis of the current data, Burkholderia alpina is renamed as Pararobbsia alpina comb. nov.

Paraburkholderia pallida sp. nov. and Paraburkholderia silviterrae sp. nov., isolated from forest soil.

Two Gram-stain-negative, aerobic, motile, white-pigmented and rod-shaped bacterial strains, 7MH5T and 4 M-K11T, were isolated from forest soil of Dinghushan Biosphere Reserve, Guangdong Province, PR China. Strain 7MH5T grew at 4-37 °C (optimum, 28-33 °C), pH 3.5-9.0 (pH 4.0-5.5) and in the presence of 0-3 % (w/v) NaCl (0-1.5 w/v); while strain 4 M-K11T grew at 4-42 °C (20-33 °C), pH 3.5-8.5 (pH 4.5-6.0) and in the presence of 0-2.5 % (w/v) NaCl (0-1.5 w/v). Strains 7MH5T and 4 M-K11T have the highest 16S rRNA gene sequence similarities of 98.6 and 98.7 % to Paraburkholderia peleae PP52-1T, and 98.4 % between themselves. In the 16S rRNA gene sequence phylogram, strains 4 M-K11T and Paraburkholderia ferrariae NBRC 106233T formed a clade while 7MH5T were relatively distinct from other Paraburkholderia species. Based on the UBCG phylogenomic analysis, strains 7MH5T and 4 M-K11T formed a clade with Paraburkholderia oxyphila NBRC 105797T and Paraburkholderia sacchari LMG 19450T in the genus of Paraburkholderia. The DNA G+C contents of strains 7MH5T and 4 M-K11T were 64.2 and 64.3 %, respectively. Digital DNA-DNA hybridization and the average nucleotide identity values of strains 7MH5T, 4 M-K11T and closely related strains were in the ranges of 25.2-63.6 % and 81.0-95.5 %, respectively. The two strains had the same major respiratory quinone: ubiquinone-8. Strain 7MH5T had C16 : 0, C17 : 0cyclo, C19 : 0cyclo ω8c and summed feature 8 (C18 : 1 ω7c/C18 : 1 ω6c) as its major fatty acids, while strain 4 M-K11T had major fatty acids of C16 : 0, C17 : 0cyclo and summed feature 2 (iso-C16 : 1 I/C14 : 0-3OH). The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol. On the basis of phenotypic and phylogenetic analyses based on both 16S rRNA gene and whole genome sequences, as well as chemotaxonomic data, strains 7MH5T and 4 M-K11T represent two novel species of the genus Paraburkholderia, for which the names Paraburkholderia pallida sp. nov. (type strain 7MH5T=GDMCC 1.1450T=KACC 19962T) and Paraburkholderia silviterrae sp. nov. (type strain 4 M-K11T=GDMCC 1.1284T=CGMCC 1.15450T=KACC 19961T=LMG 29217T) are proposed.