Tropical forest soils serve as substantial and persistent methane sinks.

Although tropical forest soils contributed substantially global soil methane uptake, observations on soil methane fluxes in tropical forests are still sparse, especially in Southeast Asia, leading to large uncertainty in the estimation of global soil methane uptake. Here, we conducted two-year (from Sep, 2016 to Sep, 2018) measurements of soil methane fluxes in a lowland tropical forest site in Hainan island, China. At this tropical forest site, soils were substantial methane sink, and average annual soil methane uptake was estimated at 2.00 kg CH4-C ha-1 yr-1. The seasonality of soil methane uptake showed strong methane uptake in the dry season (-1.00 nmol m-2 s-1) and almost neutral or weak soil methane uptake in the wet season (-0.24 nmol m-2 s-1). The peak soil methane uptake rate was observed as -1.43 nmol m-2 s-1 in February, 2018, the driest and coolest month during the past 24 months. Soil moisture was the dominant controller of methane fluxes, and could explain 94% seasonal variation of soil methane fluxes. Soil temperature could not enhance the explanation of seasonal variation of soil methane fluxes on the top of soil moisture. A positive relationship between soil methane uptake and soil respiration was also detected, which might indicate co-variation in activities of methanotroph and roots and/or microbes for soil heterotrophic respiration. Our study highlights that tropical forests in this region acted as a methane sink.

[Acute Toxicity and Safety Assessment of Three Typical Organic Pollutants to Two Aquatic Organisms].

Acute toxic effects of three typical organic pollutants 1 ,2,4-trichlorobenzene (1,2,4-TCB), nitrobenzene and chlorpyrifos were investigated using Tetrahymena thermophila and Limnodrilus hoffmeisteri as living test organisms under laboratory conditions. The results showed that with the increase of pollutants' concentration and the extension of time, toxicity of the three kinds of pollutants significantly enhanced, and the mortality of two kinds of aquatic organisms also had a rising trend, and an obvious dose-effect relationship. The 96 h-LC50. values of 1 ,2, 4-TCB, nitrobenzene and chlorpyrifos were 71.88, 285.76, and 5.50 mg x L(-1) for L. hoffmeisteri and 15.58, 140.22, and 14.69 mg x L(-1) for T. thermophila. These results showed that the toxicity among the three typical pollutants to T. thermophila was 1 , 2,4-TCB > chlorpyrifos > nitrobenzene. Findings were able to provide more information on water quality criteria and more data on their toxicity to indigenous aquatic organisms in China.

[Physiological Effect of Vallisneria natans Under Different Concentrations of Nitrogen, Phosphorus and Chloramphenicol].

The effects of peroxidase(POD), superoxide dismutase(SOD) activities and malondialdehyde(MDA), soluble proteins and chlorophyll in the leaves of Vallisneria natans exposed to different concentrations of nitrogen and phosphorus in the eutrophication water body and chloramphenicol after 7 days were investigated in the study. The soluble protein content increased significantly in group eutrophic water and 0.2 µg.L-1 chloramphenicol, and the concentration of protein was 2.38 times of that in group 0 µg.L-1 chloramphenicol. In group of eutrophic water and 0. 2 µg.L-1 chloramphenicol, POD activities decreased significantly to 33. 84% of that in group 0 µg.L-1 chloramphenicol. With the increasing of the joint concentration, SOD activities decreased. SOD activities in group of mesotrophic and 0. 2 µg.L-1 chloramphenicol was 28. 59% of that in group of 0 µg.L-1 chloramphenicol.

[Toxicity of three chlorophenols to protozoa Tetrahymena thermophila].

Using Tetrahymena thermophila as the indication organism, the single acute toxicity and genotoxicity induced by 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP) were determined. The results showed that the 24, 48, 72 and 96-hour EC50 values of 3 individual CPs to T. thermophila were 3.69, 3.54, 3.02, 2.34 mg x L(-1); 3.23, 2.83, 2.56, 1.97 mg x L(-1) and 0.63, 0.45, 0.34, 0.28 mg x L(-1), respectively, which revealed that the acute toxicity of CPs increased with the number of chlorine on benzene ring. Effects of water hardness on the acute toxicities of 2,4-DCP, 2,4,6-TCP and PCP to T. thermophila were evaluated. It showed that the effect of water hardness on the acute toxicities of the three CPs to T. thermophila had a certain influence, but the impact was relatively insignificant. The results in the SCGE showed that there were significant differences (P < 0.05) between the control and treatment groups at various concentrations of the three CPs. It recommended that the comet assay of T. thermophila was sensitive to the three detected CPs and could be a useful tool for screening and detecting of environmental genotoxins.

[Acute toxicity of three typical pollutants to aquatic organisms and their water quality criteria].

Two species of microalgae Chlorella pyrenoidosa, Scenedesmus obliqnus and a red worm Chironomidae larvae were selected as test organisms in determining the acute toxicity effects of Cr (VI), 2,4,6-trichlorophenol and nitrobenzene. The results were able to provide more information on water quality criteria and more data on their toxicity to indigenous aquatic organisms in China. The 96 h-EC50 values of Cr (VI), TCP and nitrobenzene on C. pyrenoidosa were 1.34 mg x L(-1, 4.55 mg x L(-1) and 86.58 mg x L(-1), respectively, while those of S. obliqnus were 19.52 mg x L(-1), 3.71 mg x L(-1) and 74.15 mg x L(-1), respectively. The mortality of C. larvae was 15% when the concentration of Cr(VI) was increased to 1,500 mg x L(-1). The 48 h-LC50 values of TCP and nitrobenzene on C. larvae were 9.29 mg x L(-1) and 98.34 mg x L(-1), respectively. These results indicated that Cr( VI) showed higher toxicity to C. pyrenoidosa, while only moderate toxicity to S. obliqnus; TCP had higher toxicity to C. pyrenoidosa and S. oblignus; while nitrobenzene was only moderately toxic to both species of microalgae. The toxicity among the three pollutants to C. larvae was in the order of TCP > nitrobenzene > Cr (VI).

[Toxic effects of high concentrations of ammonia on Euglena gracilis].

Ammonia is among the common contaminants in aquatic environments. The present study aimed at evaluation of the toxicity of ammonia at high concentration by detecting its effects on the growth, pigment contents, antioxidant enzyme activities, and DNA damage (comet assay) of a unicellular microalga, Euglena gracilis. Ammonia restrained the growth of E. gracilis, while at higher concentrations, ammonia showed notable inhibition effect, the growth at 2 000 mg x L(-1) was restrained to 55.7% compared with that of the control; The contents of photosynthetic pigments and protein went up with increasing ammonia dosage and decreased when the ammonia concentration was above 1000 mg x L(-1); In addition, there was an obvious increase in SOD and POD activities, at higher concentration (2 000 mg x L(-1)), activities of SOD and POD increased by 30.7% and 49.4% compared with those of the control, indicating that ammonia could promote activities of antioxidant enzymes in E. gracilis; The degree of DNA damage observed in the comet assay increased with increasing ammonia concentration, which suggested that high dose of ammonia may have potential mutagenicity on E. gracilis.

[Genotoxicity effect of organic pollutants in Meiliang Bay of Taihu Lake on microalga Euglena gracilis].

Organic pollutant ingredients and content of water samples from Taihu Lake were analyzed by GC-MS. Results showed that Taihu Lake was already contaminated by the organic pollutant, and 15 kinds of targeted organic pollutants were detected. At lower concentrations (1 time), organic pollutants could not have notable effect on the growth of Euglena gracilis, but could increase the content of photosynthetic pigment. At higher concentrations (5, 10 times), organic pollutants restrained the growth of E. gracilis remarkably, and decreased the content of photosynthetic pigment. Activities of SOD and POD increased with the content of organic pollutants. It is indicated that organic pollution could induce activities of antioxidation enzymes in E. gracilis. TOM and TM for the genotoxicity assay increased and DNA damage was found. In higher concentration groups, DNA damage was serious and had an obvious dose-effect relationship. It is indicated that Meiliang bay water may have potential mutagenicity. Comet assay combined with SOD analysis was of value to genotoxic monitoring of polluted water and was a suitable biomarker for organic pollutants in water.