Dependence of Soil Respiration on Soil Temperature and Soil Moisture in Successional Forests in Southern China

The spatial and temporal variations in soil respiration and its relationship with biophysical factors In forests near the Tropic of Cancer remain highly uncertain. To contribute towards an Improvement of actual estimates, soil respiration rates, soil temperature, and soil moisture were measured In three successional subtropical forests at the Dlnghuahan Nature Reserve （DNR） In southern China from March 2003 to February 2005. The overall objective of the present study was to analyze the temporal variations of soil respiration and Its biophysical dependence in these forests. The relationships between biophysical factors and soil respiration rates were compared In successional forests to test the hypothesis that these forests responded similarly to biophysical factors. The seasonality of soil respiration coincided with the seasonal climate pattern, with high respiration rates in the hot humid season （April-September） and with low rates In the cool dry season （October-March）. Soil respiration measured at these forests showed a clear Increasing trend with the progressive succession. Annual mean （± SD） soil respiration rate In the DNR forests was （9.0 ± 4.6） Mg CO2-C/hm^2 per year, ranging from （6.1 ± 3.2） Mg CO2-C/hm^2 per year in early successional forests to （10.7 ± 4.9） Mg CO2-C/hm^2 per year in advanced successional forests. Soil respiration was correlated with both soil temperature and moisture. The T/M model, where the two biophysical variables are driving factors, accounted for 74%-82% of soil respiration variation In DNR forests. Temperature sensitivity decreased along progressive succession stages, suggesting that advanced-successional forests have a good ability to adjust to temperature. In contrast, moisture Increased with progressive succession processes. This increase is caused, in part, by abundant respirators In advanced-successional forest, where more soil moisture is needed to maintain their activities.

Two new diterpene alkaloids from the South China Sea Sponge Agelas aff. nemoechinata

Two new N-methyladenine-containing diterpenes,nemoechines F（l）and G（2）,were isolated from the South China Sea sponge Agelas aff.nemoechinata.The structures were assigned on the basis of spectroscopic date.Compound 2 showed weak activity against Jurkat cell lines with IC50 of 17.1 μmol/L

Racemic Bisindole Alkaloids: Structure, Bioactivity, and Computational Study

The new racemic and dimeric in dole alkaloids with the characteristic cyclope nta[b]indole backb one,(+)-and(-)-sp on domi ne(la/lb),were isolated from a cultured sponge Tedania anhelans.A semi-synthesis was employed to obtain la/lb and the other four stereoisomers lc-If.Their structures were determined by spectroscopic analysis,single-crystal X-ray,and quantum chemical calculations.Six stereoisomers differ in bioactivity according to their absolute con figurations.Especially,(+)-sp on domi ne(la)displayed cytotoxicity against the K562 cell line and exhibited stronger Wnt and HIF1 dual signaling inhibitory activity at 5 pmol/L than the positive control,which offers an exciting starting point for further investigations.All stereoisomers significantly promoted angiogenesis and showed moderate anti-inflammation in zebrafish.A quantum chemical calculation and deuteration experiment were applied to unveil the reacti on mechanism which guides the synthesis of the target compounds.

Tetracyclic triterpenoids isolated from semi-mangrove plant Hibiscus tiliaceus

A continuing phytochemical study on the semi-mangrove plant Hibiscus tiliaceus yielded two new tetracyclic triterpenoids （3β,24S）-19（10→9）-abeo-8α,9β,10α-eupha-5,25（26）-dien-3,24-diol （tiliacol A, 1 ）, and （3β,23Z）-19（10→9）-abeo-8α,9β,10α-tircalla-5,23-dien-3,25-diol （tiliacol B, 3）, together with one known analog （2）. Their structures were elucidated on the basis of extensive spectral analyses （MS, IR, 1D NMR and 2D NMR） and comparison with literature compounds. Compound 2 showed potent cytotoxicity against both P388 and HeLa cells with ICon values of 11.2 μmol/L and 11.5 μmol/L, resoectively.

Three new non-brominated pyrrole alkaloids from the South China Sea sponge Agelas nakamurai

Three new non-brominated pyrrole alkaloids,nakamurines A-C（1-3） were isolated from the South China Sea sponge Agelas nakamurai.Their structures were elucidated on the basis of spectroscopic data.Compound 2 showed weak antimicrobial activity against Candida albicans with MIC of 60μg/mL.