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1. chinaXiv:201811.00111 [pdf]

Microbial adaptation to long-term N supply prevents large responses in N dynamics and N losses of a subtropical forest

Han, Xiaodge; Shen, Weijun; Zhang, Jinbo; Muller, Christoph
Subjects: Biology >> Biochemistry

Atmospherically-deposited nitrogen (N) can stimulate complex soil N metabolisms and accumulations over time. Whether long-term (decadal) N deposition effects on soil N transformations and functional microbes differ from the short-term (annual) effects have rarely been assessed. Here we conducted a laboratory 15N tracing study with soil samples from a short-term (one year) N addition site and a long-term (12 years) site in a subtropical forest. The effects of simulated N deposition on soil N2O emissions, N transformation rates and microbial nitrifying and denitrifying genes were determined. Our results showed that: (1) long-term N addition did not change soil N2O fluxes significantly in comparison to the short-term N addition. Denitrification, heterotrophic nitrification and autotrophic nitrification contributed 53%, 23% and 18% to total N2O emissions, respectively. (2) Autotrophic nitrification was the dominant N transformation process, except for the high-N treatment at the long-term site. The magnitude of soil N transformation rates was significantly different among N addition treatments but not between short- and long-term N addition sites. However, long-term N addition changed the responses of specific N transformation rates to N addition markedly, especially for the rates of nitrification, organic N mineralization to NH4+, NO3- immobilization and dissimilatory NO3- reduction to NH4+ (DNRA). (3) Responses of ammonia oxidizing archaea and bacteria (AOA and AOB) were stronger than denitrifying N2O-producers (nirK) and denitrifying N2O-reducers (nosZ) at the long-term site compared to the short-term site. (4) The close correlations among N2O flux, functional genes and soil properties observed at the short-term site was weakened at the long-term site, posing a decreased risk for N losses in the acid subtropical forest soils. There is evidence for an adaptation of functional microbial communities to the prevailing soil conditions and in response to long-term natural and anthropogenic N depositions.

submitted time 2018-11-22 Hits630Downloads295 Comment 0

2. chinaXiv:201803.00577 [pdf]

Effects of tetracyclines on bone: an ambiguous question needs to be clarified

wenxiang cheng
Subjects: Biology >> Biochemistry

Tetracyclines have been widely used in bone histomorphometry to label new bone formation and apposition rate. However, most studies of tetracyclines have also shown their strong inhibitory action on osteoclasts and their effects on osteoblast activities as well. To even obtain the in-depth understanding on this issue, we have reviewed related studies in “Pubmed” by searching the keywords “tetracyclines and osteoclast”, “tetracyclines and osteoblast”, which retrieved 115 and 159 related documents, respectively. Among these papers, some described the application of tetracyclines as fluorescent marker in bone histomorphometry, while others discussed their role in protection of bone metabolism partly through inhibiting osteoclastogenesis or bone resorption and through enhancing osteogenesis. Based on the above mentioned, it seems that tetracyclines used as bone labeling markers may affect the results of bone histomorphometry to some extent. To even confirm the effect of tetracyclines on bone cells (osteoblast, osteoclast) and in vivo bone remodeling, related research work has been performed in our research team which indicated quite different results in vivo and in vitro. Therefore, the influence of tetracyclines on bone may differ in terms of different conditions which need to be further elucidated as well.

submitted time 2018-03-15 Hits660Downloads309 Comment 0

3. chinaXiv:201705.00892 [pdf]

Bioactive Pentacyclic Triterpenoids from the Leaves of Cleistocalyx operculatus

Wang, Chen; Wu, Ping; Tian, Shuai; Xue, Jinghua; Xu, Liangxiong; Li, Hanxiang; Wei, Xiaoyi
Subjects: Biology >> Biochemistry

Thirteen new pentacyclic triterpenoids, cleistocalyxic acids AK (1, 2, 4, 5, and 713) and cleistocalyxolides A (3) and B (6), and fifteen known analogues (1428), based on taraxastane, oleanane, ursane, multiflorane, and lupane skeletons, were isolated from the leaves of Cleistocalyx operculatus. The structures of 113 were elucidated by analysis of their spectroscopic data and ECD/TDDFT computations. Cleistocalyxolide A (3), presumed to be derived from the known taraxastane-type compound 14, has a rare rearranged triterpenoid backbone. Cleistocalyxic acid B (2) displayed cytotoxicity against HepG2, NCI-N87, and MCF-7 cancer cell lines with IC50 values ranging from 3.2 to 6.5 M and cleistocalyxic acid D (5) was active against HepG2 and NCI-N87 cells with the values around 5.0 M. The non-cytotoxic cleistocalyxic acid E (7) inhibited production of IL-6 by 68.1% and TNF- by 53.7% in LPS-induced RAW 264.7 macrophages at the concentration of 2 M.

submitted time 2017-05-19 Hits1354Downloads581 Comment 0

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