Consistent time allocation fraction to vegetation green-up versus senescence across northern ecosystems despite recent climate change.

Extended growing season lengths under climatic warming suggest increased time for plant growth. However, research has focused on climatic impacts to the timing or duration of distinct phenological events. Comparatively little is known about impacts to the relative time allocation to distinct phenological events, for example, the proportion of time dedicated to leaf growth versus senescence. We use multiple satellite and ground-based observations to show that, despite recent climate change during 2001 to 2020, the ratio of time allocated to vegetation green-up over senescence has remained stable [1.27 (± 0.92)] across more than 83% of northern ecosystems. This stability is independent of changes in growing season lengths and is caused by widespread positive relationships among vegetation phenological events; longer vegetation green-up results in longer vegetation senescence. These empirical observations were also partly reproduced by 13 dynamic global vegetation models. Our work demonstrates an intrinsic biotic control to vegetation phenology that could explain the timing of vegetation senescence under climate change.

Organic matter distribution in the icy environments of Taylor Valley, Antarctica.

Glaciers can accumulate and release organic matter affecting the structure and function of associated terrestrial and aquatic ecosystems. We analyzed 18 ice cores collected from six locations in Taylor Valley (McMurdo Dry Valleys), Antarctica to determine the spatial abundance and quality of organic matter, and the spatial distribution of bacterial density and community structure from the terminus of the Taylor Glacier to the coast (McMurdo Sound). Our results showed that dissolved and particulate organic carbon (DOC and POC) concentrations in the ice core samples increased from the Taylor Glacier to McMurdo Sound, a pattern also shown by bacterial cell density. Fluorescence Excitation Emission Matrices Spectroscopy (EEMs) and multivariate parallel factor (PARAFAC) modeling identified one humic-like (C1) and one protein-like (C2) component in ice cores whose fluorescent intensities all increased from the Polar Plateau to the coast. The fluorescence index showed that the bioavailability of dissolved organic matter (DOM) also decreased from the Polar Plateau to the coast. Partial least squares path modeling analysis revealed that bacterial abundance was the main positive biotic factor influencing both the quantity and quality of organic matter. Marine aerosol influenced the spatial distribution of DOC more than katabatic winds in the ice cores. Certain bacterial taxa showed significant correlations with DOC and POC concentrations. Collectively, our results show the tight connectivity among organic matter spatial distribution, bacterial abundance and meteorology in the McMurdo Dry Valley ecosystem.

Correcting a major error in assessing organic carbon pollution in natural waters.

Microbial degradation of dissolved organic carbon (DOC) in aquatic environments can cause oxygen depletion, water acidification, and CO2 emissions. These problems are caused by labile DOC (LDOC) and not refractory DOC (RDOC) that resists degradation and is thus a carbon sink. For nearly a century, chemical oxygen demand (COD) has been widely used for assessment of organic pollution in aquatic systems. Here, we show through a multicountry survey and experimental studies that COD is not an appropriate proxy of microbial degradability of organic matter because it oxidizes both LDOC and RDOC, and the latter contributes up to 90% of DOC in high-latitude forested areas. Hence, COD measurements do not provide appropriate scientific information on organic pollution in natural waters and can mislead environmental policies. We propose the replacement of the COD method with an optode-based biological oxygen demand method to accurately and efficiently assess organic pollution in natural aquatic environments.

Bacteria in the lakes of the Tibetan Plateau and polar regions.

The Tibetan Plateau, also termed 'the Third Pole' harbors the largest number of high-altitude lakes in the world. Due to the presence of extreme conditions such as low temperature and oligotrophy, the lakes of the Tibetan Plateau share environmental features in common with lakes in the polar regions. However, the extent to which these environments are analogous, or indeed whether they harbor similar microbial communities or a high level of endemic species is poorly understood. Here we compared high-throughput 16S rRNA gene sequencing data from the lakes of the three different regions in order to characterize their taxonomic diversity, the community composition and biogeography. Our results showed despite the similarity in environmental conditions, the spatial distribution of the bacterial communities was distinct with only 3.1% of all operational taxonomic units (OTUs) being present in all three regions (although these OTUs did account for a considerable proportion of the total sequences, 36.4%). Sequences belonging to Burkholderiales and Actinomycetales dominated the shared OTUs across all three regions. Scale dependent distance decay patterns provided evidence of dispersal limitation. Climatic variables and dispersal limitation were apparently both important in controlling the spatial distribution of bacterial communities across regions. This work expands our understanding of the diversity and biogeography of lake bacterial communities across the Tibetan Plateau and provides insights into how they compare to those of the Antarctic and Arctic.

Heavy metals in the surface sediments of lakes on the Tibetan Plateau, China.

Heavy metal contamination has affected many regions in the world, particularly the developing countries of Asia. We investigated 8 heavy metals (Cu, Zn, Cd, Pb, Cr, Co, Ni, and As) in the surface sediments of 18 lakes on the Tibetan Plateau. It was found that the distributions of the heavy metals showed no clear spatial pattern on the plateau. The results indicated that the mean concentrations of these metals in the sediment samples diminished as follows: Cr > As > Zn > Ni > Pb > Cu > Co > Cd. The results of geoaccumulation index (I geo) and potential ecological risk factor (E ir ) assessments showed that the sediments were moderately polluted by Cd and As, which posed much higher risks than the other metals. The values of the potential ecological risk index (RI) showed that lake Bieruoze Co has been severely polluted by heavy metals. Principal component analysis, hierarchical cluster analysis, and Pearson correlation analysis results indicated that the 8 heavy metals in the lake surface sediments of the Tibetan Plateau could be classified into four groups. Group 1 included Cu, Zn, Pb, Co, and Ni which were mainly derived from both natural and traffic sources. Group 2 included Cd which mainly originated from anthropogenic sources like alloying, electroplating, and dyeing industries and was transported to the Tibetan Plateau by atmospheric circulation. Group 3 included Cr and it might mainly generate from parent rocks of watersheds. The last Group (As) was mainly from manufacturing, living, and the striking deterioration of atmospheric environment of the West, Central Asia, and South Asia.

Erythrobacter arachoides sp. nov., isolated from ice core.

A Gram-stain-negative, rod-shaped bacterial strain, designed RC4-10-4T, belonging to the genus Erythrobacter, was isolated from the East Rongbuk Glacier on the Tibetan Plateau. Strain RC4-10-4T grew optimally at pH 7.0, at 25 °C and in the presence of 2 % (w/v) NaCl. Summed feature 3 (C16 : 1 ω6c and/or iso-C15 : 0 2-OH), summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c) and C16 : 0 were the major fatty acids. The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, sphingoglycolipid and phosphatidylcholine. Carotenoid was detected in the cells. The DNA G+C content of the novel strain was 66.4 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain RC4-10-4T formed a distinct phylogenetic lineage within the cluster comprising Erythrobacter strains. Similarities between the 16S rRNA gene sequences of strain RC4-10-4T and the closely related strains Erythrobacter luteus KCTC 42179T, Erythrobacter gangjinensis KCTC 22330T, Erythrobacter odishensis KCTC 23981T and Erythrobacter atlanticuls KCTC 42697T were 98.0, 97.6, 97.5 and 97.2 %. The DNA-DNA hybridization values were 37.6, 15.4, 29.8 and 35.8 %, respectively. Based on the phenotypic and phylogenetic characteristics, strain RC4-10-4T represents a novel species of the genus Erythrobacter, for which the name Erythrobacter arachoides sp. nov. is proposed, with the type strain RC4-10-4T (=CGMCC 1.15507T=JCM 31277T).

Description of Conyzicola nivalis sp. nov., isolated from glacial snow, and emended description of the genus Conyzicola and Conyzicola lurida.

A cold-tolerant, translucent, yellow-pigmented, Gram-stain-positive, non-motile, rod-shaped bacteria was isolated from snow of the Zadang Glacier on the Tibetan Plateau, PR China. 16S rRNA gene sequence similarity analysis indicated that the isolate was closely related to Conyzicola lurida KCTC 29231T and Leifsonia psychrotolerans DSM 22824T at a level of 97.72 and 97.49 %, respectively. Other close relatives had a 16S rRNA gene sequence similarity of less than 97 %. The major cell-wall amino acid was 2,4-diaminobutyric acid. The cell-wall sugars were rhamnose, ribose, glucose, galactose and mannose. The major menaquinones were MK-9, MK-10 and MK-11. The major polar lipids were diphosphatidylglycerol and phosphatidylglycerol. The predominant fatty acids were anteiso-C15 : 0 and iso-C16 : 0. In DNA-DNA hybridization tests, strain ZD5-4T shared 43.6 and 34.2 % relatedness with C. lurida KCTC 29231T and L. psychrotolerans DSM 22824T, respectively. Based on phenotypic and chemotaxonomic characteristics, strain ZD5-4T was considered to represent a novel species of the genus Conyzicola, for which the name Conyzicola nivalis sp. nov. is proposed. The type strain is ZD5-4T (=JCM 30076T=CGMCC 1.12813T). Emended descriptions of the genus Conyzicola and Conyzicola lurida are also provided.

Aureimonas glaciei sp. nov., isolated from an ice core.

A bacterial strain, B5-2T, was isolated from an ice core drilled from Muztagh Glacier, China. Strain B5-2T was a Gram-stain-negative, short rod-shaped, motile by polar flagella, aerobic bacterium. The major fatty acids of strain B5-2T were summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and iso-C13 : 0. The G+C content of the DNA from strain B5-2T was 69.3 mol%. The predominant isoprenoid quinone of strain B5-2T was Q-10. The major polar lipids were phosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidyldimethylethanolamine, phosphatidylcholine, an unidentified phospholipid and sulfoquinovosyldiacylglycerol. Comparative 16S rRNA gene sequence analysis revealed that the novel strain B5-2T shared highest similarity (96.7 %) with Aureimonas altamirensis S21BT. On the basis of the results of this polyphasic study, strain B5-2T represents a novel species of the genus Aureimonas, for which the name Aureimonas glaciei sp. nov. is proposed. The type strain is B5-2T (=CGMCC 1.15493T=KCTC 52395T).

Polymorphobacter glacialis sp. nov., isolated from ice core.

A Gram-stain-negative, non-spore-forming, rod-shaped bacterium, B555-2T, was isolated from an ice core drilled from Muztagh Glacier on the Tibetan Plateau, China. According to phylogenetic analysis with 16S rRNA gene sequences, the novel strain was most closely related to Polymorphobacter fuscus D40PT and Polymorphobacter multimanifer 262-7T with 98.4 and 96.9 % similarity, respectively. It grew optimally at pH 7 and 15 °C with 0.6 % NaCl (m/v). Carotenoid was detected from the cells. Major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, sphingoglycolipid, phophatidylmonomethy lethanolamine, phophatidylcholine. The major fatty acids were summed feature 3 (C16 : 1ω7c and/or iso-C15 : 0 2-OH) (42.8 %), summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) (28.8 %), C14 : 0 2-OH (10.1 %) and C16 : 0 (8.2 %). The predominant ubiquinone was Q-10. The DNA G+C content was 62.1 mol%. In DNA-DNA hybridization tests, strain B555-2T shared 21.9 and 18.6 % DNA-DNA relatedness with P. fuscus D40PT and P.multimanifer 262-7T, respectively. Accordingly, strain B555-2T represents a novel species in the genus Polymorphobacter, for which the name Polymorphobacter glacialis sp. nov. is proposed. The type strain is B555-2T (=CGMCC 1.15519T=KCTC 52396T).

Massilia psychrophila sp. nov., isolated from an ice core.

A Gram-stain-negative, aerobic, rod-shaped, motile bacterium, strain B1555-1T, was isolated from an ice core drilled from Ulugh Muztagh Glacier, China. The optimum growth temperature of strain B1555-1T was 15 °C and optimum pH was 7. The major fatty acids of strain B1555-1T were summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c), C16 : 0 and summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c). The predominant respiratory quinone was Q-8. The major polar lipids were phosphatidylethanolamine and phosphatidylglycerol. The DNA G+C content of strain B1555-1T was 66.0 mol%. In 16S rRNA gene sequence comparisons, strain B1555-1T was affiliated to the genus Massilia and shared 98.30 and 97.13 % similarity with Massilia eurypsychrophila B528-3T and Massilia niabensis 5420S-26T, respectively. The results of DNA-DNA hybridization revealed that strain B1555-1T showed 49.8 % relatedness with M. eurypsychrophila B528-3T and 38.5 % with M. niabensis 5420S-26T. Based on the genotypic and phenotypic evidence presented in this study, strain B1555-1T represents a novel species of the genus Massilia, for which the name Massilia psychrophila sp. nov. is proposed. The type strain is B1555-1T (=CGMCC 1.15196T=JCM 30813T).

[Characteristics and Risk Assessment of Heavy Metals in Core Sediments from Lakes of Tibet].

To explore the source of heavy metals in lake sediments and their hazard to environment on Tibetan Plateau, China, heavy metal (Cu, Zn, Cd, Pb, Cr, Co, Ni and As) levels in surface sediments of 18 lakes were investigated. Inductively Coupled Plasma Mass Spectrometry (ICP-MS, X-7 series) was used to determine the contents of heavy metals and the concentrations of carbon and nitrogen in sediment samples were analyzed by element analyzer (Vario Max CN, Elementar, Germany). The average concentrations for Cu, Zn, Cd, Pb, Cr, Co, Ni and As were 24.61 mg x kg(-1), 70.14 mg x kg(-1), 0.26 mg x kg(-1), 25.43 mg x kg(-1), 74.12 mg x kg(-1), 7.93 mg x kg(-1), 33.85 mg x kg(-1), 77.69 mg x kg(-1). It was found that heavy-metal concentrations in Tibet sediments were higher than those in Antarctic, but lower than those in the regions affected by anthropogenic activities. The contents of Cu, Zn, Pb, Cr and Co in the samples were lower than the background values of Tibet. Correlation analysis and principal components analysis (PCA) were used to analyze the origins of heavy metals. The result showed that Cu, Zn, Cd, Pb, Co, Ni and As came from soil in drainage basin and atmospheric deposition. Cr was mainly affected by human activities. Assessment on ecological risk of heavy metals was carried out using Hakanson's method and cluster analysis (CA). Assessment on ecological risk indicated that Pumoyum Co, Longmo Co and Bangong Co were at low risks, Bieruoze Co was at high ecological risk level and the other lakes were at different risk levels.