Dietary chenodeoxycholic acid attenuates high-fat diet-induced growth retardation, lipid accumulation and bile acid metabolism disorder in the liver of yellow catfish Pelteobagrus fulvidraco

This experiment was conducted to investigate whether dietary chenodeoxycholic acid (CDCA) could attenuate high-fat (HF) diet-induced growth retardation, lipid accumulation and bile acid (BA) metabolism disorder in the liver of yellow catfish Pelteobagrus fulvidraco. Yellow catfish (initial weight: 4·40 (sem 0·08) g) were fed four diets: the control (105·8 g/kg lipid), HF diet (HF group, 159·6 g/kg lipid), the control supplemented with 0·9 g/kg CDCA (CDCA group) and HF diet supplemented with 0·9 g/kg CDCA (HF + CDCA group). CDCA supplemented in the HF diet significantly improved growth performance and feed utilisation of yellow catfish (P < 0·05). CDCA alleviated HF-induced increment of hepatic lipid and cholesterol contents by down-regulating the expressions of lipogenesis-related genes and proteins and up-regulating the expressions of lipololysis-related genes and proteins. Compared with the control group, CDCA group significantly reduced cholesterol level (P < 0·05). CDCA significantly inhibited BA biosynthesis and changed BA profile by activating farnesoid X receptor (P < 0·05). The contents of CDCA, taurochenodeoxycholic acid and glycochenodeoxycholic acid were significantly increased with the supplementation of CDCA (P < 0·05). HF-induced elevation of cholic acid content was significantly attenuated by the supplementation of CDCA (P < 0·05). Supplementation of CDCA in the control and HF groups could improve the liver antioxidant capacity. This study proved that CDCA could improve growth retardation, lipid accumulation and BA metabolism disorder induced by HF diet, which provided new insight into understanding the physiological functions of BA in fish.

Characterization of fifteen key genes involved in iron metabolism and their responses to dietary iron sources in yellow catfish Pelteobagrus fulvidraco

BACKGROUND

Iron is an essential metal element for organisms, whose metabolism is regulated by many genes and also dietary iron sources. However, the characterization, distribution and the responses of iron metabolism-related genes to different iron sources were not clear in fish.

METHODS

The full-length cDNA sequences of fifteen iron metabolism-relevant genes (tf, tfr1, hp, fpn1, ho1, ho2, tfr2, hjv, hepcidin, fth, ftl, ftm, irp1, irp2 and hif2α.) were obtained via 3' and 5' RACE PCR from yellow catfish, a widely distributed freshwater teleost in China and other Asian countries. Their molecular characterizations were analyzed via the bioinformatic methods. Real-time quantitative PCR was used to explore their mRNA distribution in nine tissues. Their mRNA expression responses in four tissues (heart, brain, kidney and gill) were explored in yellow catfish fed diets with five iron sources, including ferrous sulfate (FeSO4), ferrous bisglycinate (Fe-Gly), ferrous chloride (FeCl2), ferric citrate (Fe-CA) and ferric oxide nanoparticles (Fe2O3NPs).

RESULTS

Compared with mammals and other teleost, these members shared similar domains. Their mRNAs were expressed in nine tested tissues, but mRNA levels varied. Yellow catfish fed the diets containing Fe-Gly and Fe2O3NPs had higher iron contents in heart, brain, kidney and gill. Meantime, different dietary iron sources addition affected their mRNA expression differentially in brain, heart, kidney and gill. It should be pointed out that only three biological replicate tanks were used in the present feeding treatment, and more biological replicate tanks (more than five) should be emphasized in further researches.

CONCLUSION

Taken together, our study identified fifteen iron metabolism-relevant genes, explored their mRNA expression in nine tissues, and their mRNA expression in the responses to different dietary iron sources in four tissues, indicating their important regulatory function in iron metabolism and homeostasis.

Copper induces liver lipotoxicity disease by up-regulating Nrf2 expression via the activation of MTF-1 and inhibition of SP1/Fyn pathway

Excessive copper (Cu) intake leads to hepatic lipotoxicity disease, which has adverse effects on health, but the underlying mechanism is unclear. We found that Cu increased lipotoxicity by promoting Nrf2 recruitment to the ARE site in the promoters of five lipogenic genes (g6pd, 6pgd, me, icdh and pparγ). We also found that Cu affected the Nrf2 expression via different pathways: metal regulatory transcription factor 1 (MTF-1) mediated the Cu-induced Nrf2 transcriptional activation; Cu also enhanced the expression of Nrf2 by inhibiting the SP1 expression, which was achieved by inhibiting the negative regulator Fyn of Nrf2. These promoted the enrichment of Nrf2 in the nucleus and ultimately affected lipotoxicity. Thus, for the first time, we elucidated that Cu induced liver lipotoxicity disease by up-regulating Nrf2 expression via the MTF-1 activation and the inhibition of SP1/Fyn pathway. Our study elucidates the Cu-associated obesity and NAFLD for fish and possibly humans.

[Change in nitrogen availability of northern peatlands and its effect on carbon sink function]

Northern peatlands are typical nitrogen-limited ecosystems, which are sensitive to global climate change and human activities. The increases of endogenous available nitrogen caused by climate warming and exogenous nitrogen input caused by human activities changed the nitrogen availability of northern peatlands, and would affect carbon and nitrogen cycling and carbon sink function of peatland. Here, we review the influence factors of carbon accumulation rate and carbon sink function in northern peatlands. The effects of nitrogen deposition, freezing and thawing, fire and other factors on nitrogen availability of northern peatlands were reviewed. The responses of plants and soil microorganisms to changes in nitrogen availability were elaborated from carbon fixation and carbon emission processes, respectively. The research related to carbon sink function of peat ecosystems under the influence of glo-bal change was prospected, aiming to help the implementation of the 'double carbon' goal.

Mitochondrial oxidative stress mediated Fe-induced ferroptosis via the NRF2-ARE pathway

Ferroptosis is a regulated form of cell death induced by iron (Fe)-dependent lipid peroxidation. At present, the underlying molecular mechanisms remain elusive. Herein, we hypothesized that mitochondria and the NRF2 (transcription factor nuclear factor E2-related factor 2) are potential mediators of ferroptosis, considering their well-established involvement in the oxidative stress pathway. We found that a high iron diet increased hepatic iron content and promoted glutathione (GSH) depletion, lipid peroxidation and oxidative stress. Dietary iron overload also decreased mRNA and protein expression levels of glutathione peroxidase 4 (GPX4) and cystine-glutamate antiporter (SLC7A11), and increased mRNA and protein expression of acyl-CoA synthetase long-chain family member 4 (ACSL4), which are all markers of ferroptosis. Consistent with ferroptosis, iron overload promoted lipid peroxidation and the generation of mitochondrial reactive oxygen species (ROS), and decreased the mitochondrial membrane potential (MMP). Pre-treatment with deferoxamine mesylate (DFO, an iron chelator) alleviated ROS generation and lipid peroxidation, indicating a causative link between iron overload and lipid peroxidation. Suppression of mitochondrial oxidative stress attenuated ferroptosis. Experiments with HEK293T cells revealed that Fe-induced ferroptosis involved direct inhibition of NRF2 binding to antioxidant response elements (AREs) within the promoters of the gpx4 and slc7a11 genes, which in turn induced transcriptional silencing. In conclusion, our study provided a direct link between mitochondrial oxidative stress and ferroptosis via the NRF2-ARE pathway.

Mitochondria-Dependent Oxidative Stress Mediates ZnO Nanoparticle (ZnO NP)-Induced Mitophagy and Lipotoxicity in Freshwater Teleost Fish

Due to many special characteristics, zinc oxide nanoparticles (ZnO NPs) are widely used all over the world, leading to their wide distribution in the environment. However, the toxicities and mechanisms of environmental ZnO NP-induced changes of physiological processes and metabolism remain largely unknown. Here, we found that addition of dietary ZnO NPs disturbed hepatic Zn metabolism, increased hepatic Zn and lipid accumulation, downregulated lipolysis, induced oxidative stress, and activated mitophagy; N,N,N',N'-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN, Zn²⁺ ions chelator) alleviated high ZnO NP-induced Zn and lipid accumulation, oxidative stress, and mitophagy. Mechanistically, the suppression of mitochondrial oxidative stress attenuated ZnO NP-activated mitophagy and ZnO NP-induced lipotoxicity. Taken together, our study elucidated that mitochondrial oxidative stress mediated ZnO NP-induced mitophagy and lipotoxicity; ZnO NPs could be dissociated to free Zn²⁺ ions, which partially contributed to ZnO NP-induced changes in oxidative stress, mitophagy, and lipid metabolism. Our study provides novel insights into the impacts and mechanism of ZnO NPs as harmful substances inducing lipotoxicity of aquatic organisms, and accordingly, metabolism-relevant parameters will be useful for the risk assessment of nanoparticle materials in the environment.

Effects of long-term nitrogen addition on dissolved organic matter characteristics in a temperate wetland of Northeast China

Dissolved organic matter (DOM) plays an indispensable role in ecosystem services and functions in wetlands. While most wetlands have undergone increased nitrogen (N) loading due to intensive human activities, the response of DOM characteristics to long-term N addition remains unexplored. In this study, we assessed the changes in dissolved organic carbon (DOC), NH₄⁺, NO₃^-, dissolved organic N (DON), dissolved total N (DTN), and dissolved total phosphorus (DTP) in surface water and soil pore water at 15 cm depth after 10 years of N addition at four levels (0, 60, 120, and 240 kg N hm^-2 year^-1) in a freshwater marsh of Northeast China. We also examined the effect of N addition on DOM aromaticity and humification by measuring the specific UV absorbance at 254 nm (SUVA₂₅₄), the color per C unit (C/C ratio), and the fulvic acid/humic acid ratio (E4/E6 ratio). Our results showed that N addition significantly altered DOM properties, but the direction and magnitude of these changes generally did not vary with the N addition level. During the growing season, DOC, NH₄⁺, NO₃^-, DON, and DTN concentrations in both surface water and soil pore water were increased by N addition. Accordingly, N addition increased the DOC/DTP and DTN/DTP ratios but decreased the DOC/DTN ratio in surface water and soil pore water. In addition, the SUVA₂₅₄ value and C/C ratio increased, while the E4/E6 ratio reduced after N addition in surface water and soil pore water, indicating increases in DOM aromaticity and humification. These observations suggest that long-term N addition changes DOM characteristics by causing stoichiometric imbalances and increasing recalcitrant compounds in temperate freshwater wetlands, which may then deteriorate water quality, alter microbial-mediated ecological processes, and impact downstream aquatic ecosystem structures.

[Soil properties and microbial respiration activities of riparian forest wetland in the north of permafrost zone, the Great Hing'an Mountains, Northeast China]

Riparian wetlands in permafrost regions are critical regions for hydrological, ecological, and biochemical processes. We studied the soils of riparian and transition wetlands and analyzed physicochemical properties, stoichiometry, and microbial respiration activities (microbial biomass carbon, basal respiration, microbial entropy, and metabolic entropy) of the humus layer and diffe-rent soil layers. The results showed that the main differentiation of soil physical and chemical pro-perties in riparian forest wetlands was below 20 cm. Compared to the wetlands of transition zone, total carbon content, total nitrogen content, C/P and N/P decreased significantly with soil depth in riparian forest wetlands. These changes in soil stoichiometry were mainly caused by soil nitrogen content. Such a result meant that the transferring of nitrogen was relatively fast and that there was nitrogen limitation. The main differentiation of Na, Mg, K and Ca in soil occurred in the 30 cm layer of the transition zone and the 20 cm layer of the riparian forest wetlands. The correlations between soil Mg content and total C, total N, total P contents were significant. It meant that the soil Mg was an important element to riparian wetlands in the Great Hing'an Mountains. Microbial respiration activities of the humus layer in riparian forest wetlands and transition zone were higher than those in the other soil layers, indicating that the content of labile carbon fractions was high. The correlations between soil microbial respiration activities and soil properties, stoichiometry, nutrient elements were different in riparian wetland and transition zone. Soil total nitrogen contents were significantly correlated with soil microbial respiration activities in riparian wetland, indicating that soil microbial respiration activities were limited by nitrogen in riparian wetland of the Great Hing'an Mountains.

Copper (Cu) induced changes of lipid metabolism through oxidative stress-mediated autophagy and Nrf2/PPARγ pathways

Oxidative stress can induce occurrence of non-alcoholic fatty liver disease (NAFLD). Nrf2 is a central regulator of cellular oxidative stress and also participates in the control of lipid deposition and metabolism. Here, we hypothesize that oxidative stress-mediated Nrf2 activation participates in the regulation of the Cu-induced lipid deposition. We found that Cu excess activated oxidative stress and autophagy, up-regulated lipogenesis and lipid metabolism, suppressed Keap1 expression and activated Nrf2 signaling. Moreover, Cu induced lipid deposition via oxidative stress and the mitochondrial dysfunction. Oxidative stress mediated Cu-induced activation of Nrf2 and autophagy. The activation of autophagy helps to alleviate Cu-induced lipid deposition and accordingly provided a protective role against Cu-induced NAFLD. Meantime, Cu-induced oxidative stress promoted Nrf2 recruitment to the PPARγ promoter, inducing target gene transcription, and subsequent lipogenesis. Our findings, for the first time, provide direct evidences for Nrf2 function in the modulation of lipogenic metabolism via the transcriptional activation of PPARγ, and elucidate the mechanisms by which Nrf2 functions as the central regulator of lipogenic genes and highlights the significance of Nrf2 as potential therapeutic targets for oxidative stress-associated obesity and NAFLD for fish and human beings.

Transcriptional responses of four slc30a/znt family members and their roles in Zn homeostatic modulation in yellow catfish Pelteobagrus fulvidraco

The study characterized their regulatory functions of four znt members (znt1, znt2, znt6 and znt8) in Zn homeostasis in vertebrates. We found that the -1281/-1296 bp locus on the znt1 promoter, the -1/-16 bp locus on the znt2 promoter, the -825/-839 bp locus on the znt6 promoter, the -165/-180 bp locus and the -274/-292 bp STAT3 locus on the znt8 promoter were functional MTF-1 binding sites and had metal responsive element (MRE). Zn incubation increased activities of four znt promoters, which was mediated by MRE sites on znt1, znt2, znt6 and znt8 promoters and by STAT3 binding site on znt8 promoter. Moreover, Zn activated the transcription of these znts genes through MTF-1-MRE-dependent pathway. Zn incubation up-regulated the mRNA and total protein expression of ZnT1, ZnT2 and ZnT8 at both 24 h and 48 h. Overall, for the first time, this study offered novel insights for regulatory mechanism of Zn homeostasis in vertebrates.

Molecular characterization of ten zinc (Zn) transporter genes and their regulation to Zn metabolism in freshwater teleost yellow catfish Pelteobagrus fulvidraco

BACKGROUND

Zn is an essential trace element for vertebrates, and Zn uptake and transport is related with the ZIP family of Zn transporters. Meantime, Zn also influenced the expression of ZIP family members.

METHODS

We cloned and characterized the full-length cDNA sequences of ten Zn transport-relevant genes (ZIP1, ZIP3, ZIP6, ZIP7, ZIP8, ZIP9, ZIP10, ZIP11, ZIP13 and ZIP14) from yellow catfish Pelteobagrus fulvidraco, investigated their mRNA tissue expression. These ZIP mRNA expression was also assessed in the primary hepatocytes and intestinal epithelial cells of yellow catfish in response to three Zn levels (0, 30 μM and 60 μM, respectively).

RESULTS

All these genes shared the similar domains with the corresponding members in mammals. The mRNA expression of the ten ZIP genes was detected in nine-tested tissues, but variable among these tissues. Flow cytometry analysis and confocal microscopy observation indicated that intracellular free Zn²⁺ concentration in hepatocytes and intestinal epithelial cells increased with increasing Zn incubation concentration at both 24 h and 48 h. Zn incubation differentially influenced mRNA levels of ZIP transporters in the hepatocytes and intestinal epithelial cells, in a time- and cells-dependent manners. In the hepatocytes, at 24 h, compared to the control, Zn addition down-regulated mRNA levels of ZIP1, ZIP3, ZIP6, ZIP7, ZIP8, ZIP9, ZIP11 and ZIP14; however, ZIP10 mRNA levels were lower in 60 μM Zn group than those in the control and 30 μM Zn group. At 48 h, mRNA levels of ZIP1, ZIP6, ZIP7, ZIP9, ZIP10 and ZIP14 declined with increasing Zn incubation concentrations; ZIP3 mRNA levels were the lowest in 60 μM Zn group and showed no significant differences between the control and 30 μM Zn group. In the intestinal epithelial cells, at 24 h, Zn addition down-regulated mRNA levels of ZIP1, ZIP6, ZIP7, ZIP8, ZIP9, ZIP10, ZIP11, ZIP13 and ZIP14; ZIP3 mRNA levels were lower in 60 μM Zn group than those in the control and 30 μM Zn group. At 48 h, Zn addition up-regulated mRNA levels of ZIP6 and ZIP9, but down-regulated mRNA levels of ZIP8, ZIP10 and ZIP13. ZIP7, ZIP11 and ZIP14 mRNA abundances were the lowest in 60 μM Zn group and showed no significant differences between the control and 30 μM Zn group.

CONCLUSION

For the first time, our study characterized ten ZIP family members in yellow catfish, explored their mRNA tissue expression. Their regulation to Zn addition were also investigated in the hepatocytes and intestinal epithelial cells of yellow catfish. Our study revealed the mechanism of cells exposed to Zn addition and provided novel insights for the regulatory mechanism of Zn homeostasis.

Chronic nitrogen addition promotes dissolved organic carbon accumulation in a temperate freshwater wetland

Temperate wetlands have been undergoing increased nitrogen (N) inputs in the past decades, yet its influence on dissolved organic carbon (DOC) dynamics is still elusive in these ecosystems. Here, using a field multi-level N addition (0, 6, 12, and 24 g N m^-2 year^-1) experiment, we investigated the changes in aboveground plant biomass, DOC production from plant litters, DOC biodegradation, and DOC concentration in surface water and soil pore water (0-15 cm depth) following 10 years of N addition in a freshwater marsh of Northeast China. We observed that, irrespective of N addition levels, N addition caused an increase in DOC production from plant litters under both non-flooded and flooded conditions. Conversely, DOC biodegradation was inhibited by N addition in both surface water and soil pore water. Because of enhanced DOC production from plant litters and declined DOC biodegradation, N addition elevated DOC concentration in surface water and soil pore water across the growing season. In addition, long-term N addition increased aboveground plant biomass, but decreased species richness. Our results suggest that long-term N enrichment promotes DOC accumulation through the contrasting effects on litter-derived DOC production and microbial decomposition of DOC in temperate wetlands.

Long-term phosphorus addition enhances the biodegradability of dissolved organic carbon in a nitrogen-limited temperate freshwater wetland

Phosphorus (P) enrichment is expected to strongly influence dissolved organic carbon (DOC) biodegradation. However, the relationship between P availability and DOC biodegradation is largely unknown in nitrogen (N)-limited ecosystems. Here, we investigated the changes in the ratio of DOC to dissolved total nitrogen (DTN), specific UV absorbance at 254nm (SUVA₂₅₄), and DOC biodegradation in surface water and soil pore water (0-15cm depth) following eight years of multi-level P addition (0, 1.2, 4.8, and 9.6gPm^-2year^-1) in an N-limited freshwater marsh in Northeast China. We found that P addition caused an increase in DOC biodegradation in surface water and soil pore water, irrespective of the P addition levels. Compared with the control treatment, the P addition rates of 1.2, 4.8, and 9.6gPm^-2year^-1 increased DOC biodegradation by 20.7%, 15.2%, and 14.5% in surface waters, and 11.3%, 9.4%, and 12.0% in soil pore waters, respectively. The DOC biodegradation was separately negatively correlated with the DOC:DTN ratio and SUVA₂₅₄, indicating that the positive effect of P addition on DOC biodegradation was caused by the elevated N concentration and the reduced DOC aromaticity. Our findings suggest that P enrichment enhances the biodegradability of DOC through increased N availability and altered DOC chemical composition, which would accelerate DOC loss from the waters and alter ecosystem C balance in N-limited temperate wetlands.

Effect of long-term phosphorus addition on the quantity and quality of dissolved organic carbon in a freshwater wetland of Northeast China

Understanding how P enrichment alters the quantity and quality of dissolved organic carbon (DOC) is important, because of their role in regulating the C cycle. Here, we established a four-level P addition experiment (0, 1.2, 4.8, and 9.6gPm^-2year^-1) in a N-limited freshwater wetland in the Sanjiang Plain, Northeast China. The aim of this study was to examine the effects of eight years of P addition on DOC concentration, SUVA₂₅₄ (Abs²⁵⁴/DOC concentration, indicating the aromaticity of DOC), C:C ratio (Abs⁴⁰⁰/DOC concentration, indicating the proportion of colored humic substances in DOC), and E4:E6 ratio (Abs⁴⁶⁵/Abs⁶⁶⁵, indicating the molecular size of humic substances) in surface water and soil pore water (0-15cm depth) during the growing season (June through September). Our results showed similar changing trends in concentration and optical properties of DOC following eight years of P addition in the both surface water and soil pore water across the sampling dates. Generally, P addition decreased DOC concentration, SUVA₂₅₄, and C:C ratio, and increased E4:E6 ratio, irrespective of P addition levels. These altered optical properties of DOC indicated that P addition decreased the molecular weight and aromaticity of DOC, and thus increased the quality of DOC. These results suggest P enrichment substantially reduces the quantity of DOC in N-limited temperate freshwater wetlands, and imply that increased DOC quality following P addition can further provide a positive feedback to decreased DOC pool.

9-Butyl-3-nitro-9H-carbazole

The title compound, C16H16N2O2, is a carbazole derivative with the 3-position substituted by a nitro group and the 9-position substituted by ann-butyl group. The nitro group is inclined to the benzene ring to which it is attached by 4.4 (2)°. Then-butyl substituent has an extended conformation and lies almost normal to the plane of the carbozole ring. In the crystal, inversion-related molecules stack along theaaxis and are linkedviaoffset π–π interactions, forming columns [shortest intercentroid distance = 3.773 (1) Å].

Effects of P addition on plant C:N:P stoichiometry in an N-limited temperate wetland of Northeast China

Phosphorus (P) enrichment induced by anthropogenic activities results in modified plant nutrient status, which potentially alters the stoichiometry of carbon (C), nitrogen (N), and P in plants. However, how increased P availability changes plant C:N:P stoichiometry at different hierarchical scales is unclear in N-limited ecosystems. In this study, we conducted a four-level P addition experiment (0, 1.2, 4.8, and 9.6gPm(-)(2)year(-1)) to elucidate the effect of P enrichment on plant C:N:P stoichiometric ratios at both the species and community levels in a freshwater wetland in the Sanjiang Plain, Northeast China. We found that species- and community-level plant C:N:P stoichiometry responded consistently to six years of P addition, although there was a shift in species dominance. Phosphorus addition increased plant N and P concentrations and thus decreased C:N, C:P, and N:P ratios irrespective of the P addition levels. These similar change trends at different scales resulted from the identical responses of plant N and P concentrations in different species to P addition. Moreover, plant N concentration exhibited an increasing trend with increasing P addition levels, whereas plant C:N ratio showed a declining trend. At the community level, P addition at the rates of 1.2, 4.8, and 9.6gPm(-2)year(-1) decreased the C:N ratio by 24%, 27%, and 34%; decreased the C:P ratio by 33%, 35%, and 38%; and decreased the N:P ratio by 12%, 10%, and 6%, respectively. Our results indicate that the stoichiometric responses to P addition are scale-independent, and suggest that altered plant C:N:P stoichiometry induced by P enrichment would stimulate organic matter decomposition and accelerate nutrient cycles in N-limited temperate freshwater wetlands.

Comparison between meat quality of Hanzhong White pigs and carcass weight

A total of 48 carcasses of crossbred Hanzhong White pigs were divided into 3 groups (I, 90-99 kg; II, 100-109 kg; III, 110-119 kg) to investigate the influence of carcass weight on meat quality. The intramuscular fat content of the 3 groups increased from 1.90 to 4.90%; for meat color, Warner-Bratzler shear force, drip loss, and oxidation-type muscle fiber percentage, and muscle fiber diameter of the longissimus lumborum, the indices in group II and group III were better than those in group I (P < 0.05). The saturated fatty acid and polyunsaturated fatty acid percentages of the longissimus lumborum muscle (2.80 and 37.30%, respectively) in group II were significantly lower than those in the other 2 groups, while the monounsaturated fatty acid percentage was the highest (59.10%). In conclusion, our results suggest that a carcass weight of 100-109 kg is sufficient to produce acceptable meat quality of Hanzhong White pigs.

Responses of plant nutrient resorption to phosphorus addition in freshwater marsh of Northeast China

Anthropogenic activities have increased phosphorus (P) inputs to most aquatic and terrestrial ecosystems. However, the relationship between plant nutrient resorption and P availability is still unclear, and much less is known about the underlying mechanisms. Here, we used a multi-level P addition experiment (0, 1.2, 4.8, and 9.6 g P m⁻² year⁻¹) to assess the effect of P enrichment on nutrient resorption at plant organ, species, and community levels in a freshwater marsh of Northeast China. The response of nutrient resorption to P addition generally did not vary with addition rates. Moreover, nutrient resorption exhibited similar responses to P addition across the three hierarchical levels. Specifically, P addition decreased nitrogen (N) resorption proficiency, P resorption efficiency and proficiency, but did not impact N resorption efficiency. In addition, P resorption efficiency and proficiency were linearly related to the ratio of inorganic P to organic P and organic P fraction in mature plant organs, respectively. Our findings suggest that the allocation pattern of plant P between inorganic and organic P fractions is an underlying mechanism controlling P resorption processes, and that P enrichment could strongly influence plant-mediated biogeochemical cycles through altered nutrient resorption in the freshwater wetlands of Northeast China.

[Seasonal dynamics of soil organic carbon and active organic carbon fractions in Calamagrostis angustifolia wetlands topsoil under different water conditions]

The experiment was carried in Sanjiang Plain in the northeast of China during the growing season in 2009. Soil organic carbon (SOC), as well as the soil active organic carbon fractions in the 0-20 cm soil layer of Calamagrostis angustifolia wetland under different water conditions were on monthly observation. Based on the research and indoor analysis, the seasonal dynamics of light fractions of soil organic carbon (LFOC) and microbial biomass carbon (MBC) were analyzed. The results indicated that the SOC contents had significantly seasonal dynamics, and the hydrological circle had apparently driving effect on LFOC and MBC during the growing season, especially under the seasonal flooded condition. The freeze-thaw process reduced the SOC, LFOC, MBC contents, with the decreases of 74.53%, 80.93%, 83.09%, while both carbon contents of light and heavy fractions were reduced at the same time. The result also showed that the seasonal flooding condition increased the proportion of LFOC in topsoil, which was larger in marsh meadow (13.58%) than in wet meadow (11.96%), whilst the MBC in marsh meadow (1 397.21 mg x kg(-1)) was less than the latter (1 603.65 mg x kg(-1)), proving that the inundated environment inhibited the mineralization and decomposition of organic matter. But the microbial activity could be adaptive to the flooding condition. During the growing season the MBC soared to 1 829.21 mg x kg(-1) from 337.56 mg x kg(-1) in July, and the microbial quotient was 1.51 times higher than that in June, indicating the high microbial efficacy of soil organic matter. Meanwhile, there was a significant correlation between the contents of LFOC and SOC (r = 0.816), suggesting that higher LFOC content was favorable to the soil carbon accumulation. Moreover, in the seasonal flooded Calamagrostis angustifolia wetland the soil LFOC content was significantly correlated with MBC (r = 0.95), implying that the available carbon source had more severe restriction on the microbial activity under the flooding environment.

[Contribution of litter to soil respiration under different land-use types in Sanjiang Plain]

By the soil respiration system of Li-6400, the characteristics of soil respiration with and without litter were investigated to explore the litter's contributions to soil respiration and its correlations with the input of litter and environmental factors under different land-use types in Sanjiang Plain. Results demonstrated that the average contribution of litter to soil respiration ranged from - 0.21 to 0.64 micromol/(m2 x s) in the growing season under the four land-use types. The contribution rate showed in the following order: wetland (14%) > artificial forest (12%) > soybean field (8%) > abandoned land (- 5%). As to abandoned land, the value was negative, and the litter inhibited soil respiration. The litter' s contributions to soil respiration may depend on the balance between the decomposition of litter and its shielding effects on soil respiration. There were highly significant correlations between litter's contributions to soil respiration and soil temperature at 10cm depth except for soybean field. Moreover, the influence of rainfall associated with the input of litter, which suggested that besides decomposition litter may take part in the ecological effect of climate changes in the future.

[Growth responses of belowground modules of Carex lasiocarpa to different water regimes and water experiences]

With seedling's transplanting experiment under different water levels, this paper studied the growth responses of belowground modules of Carex lasiocarpa to various water regimes and water experiences in Sanjiang Plain. The results showed that the belowground modules of C. lasiocarpa had significantly different responses to water regimes. At thriving stage, the length of rhizome and adventitious root decreased with increasing water level, and until later growth stage, the maximal value still appeared under drought condition. However, under dry-wet alternate condition, the length of rhizome and adventitious root increased most from thriving stage to the end, indicating that stable and lower water level could improve the growth of rhizome and adventitious root. The biomass of rhizome, adventitious root, and belowground part were maximal under dry-wet alternate condition at both growth stages. For those with different water experiences, the ones undergoing alternate condition in early growth season and then drought had maximal rhizome biomass, and the others under sustained alternate condition had maximal adventitious root and belowground biomass. More biomass was distributed to rhizome in the later growth season under various water regimes. The percentage of rhizome in total biomass was significantly higher under drought condition than under other water conditions through the growth season. Besides, C. lasiocarpa grew slowly when submerged, but could recover through rhizomatic reproduction after the stress disappeared.

[Estimation of evapotranspiration from a typical marsh in Sanjiang Plain]

Eddy covariance technique was adopted in measuring the evapotranspiration (ET) from a typical marsh in Sanjiang Plain in the growth season (May to September) of 2006. After analyzing the seasonal variation of the ET, the daily ET from the marsh was estimated by using Penman-Monteith (PM) and Priestley-Taylor (PT) models, and the estimated values were tested by the measured values. The results showed that the ET from the marsh had an obvious seasonal variation, with the lowest month-average daily ET in May and the highest one in July. The average daily ET in growth season was 1.94 mm x d(-1), and the total ET was 293 mm. The daily ET estimated by PM model was significantly lower than the measured one during the early and late growth seasons. A good match was observed between PT-estimated values and measured values throughout the growth season. Considering its accuracy and simplicity, PT model was more suitable for the simulation of marsh ET.

[Influence of freshwater marsh tillage on microbial biomass and dissolved organic carbon and nitrogen]

The changes in microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) were examined in order to assess the effect of surface layer soil (0 - 10 cm) under different land-use types after freshwater marshes tillage in the Sanjiang Plain Northeast China. Land uses were Deyeuxia angustifolia freshwater marshes ((DAM), cultivated land (CL), recovery freshwater marsh (RFM), constructed woodland (CW). After DAM soil tillage, MBC, MBN, DOC and DON declined strongly in agricultural surface soil layer, decreased 63.8%-80.5% (MBC), 56.3%-67.1% (MBN), 43.1%-44.3% (DOC) and 25.2%-56.1% (DON) respectively. In contrast, these C, N fraction had significant recovered in RFM and CW surface soil, increased 36.1%-59.9% (MBC), 46.7%-65.9% (MBN), 67.0%-69.3% (DOC)and 81.2%-88.3% (DON) respectively. Cultivation and land-use affected soil MBC, MBN, DOC and DON intensely. Therefore these labile C, N fractions have the significant relative under different land-use types. However DOC was more obvious controlled than DON by the land-use types. The relative between DOC and MBC, MBN have much difference than DON, the main reason of this distinction is the diverse source in available carbon and nitrogen that taken by microbial property under different land uses.

[CO2 fluxes in mire and grassland on Ruoergai plateau]

With closed chamber and GC technique, a comparative study was conducted on the CO2 fluxes in mire and grassland on Ruoergai plateau during the plant growth period in 2003-2005. The results showed that the mean value of the CO2 fluxes in the three years was 203.22 mg x m(-2) x h(-1) in mire and 323.03 mg x m(-2) x h(-1) in grassland, with the former being only about 60% of the latter. The perennially water-logging of mire limited the decomposition of plant residues, roots and organic substances, resulting in a lower CO2 flux in mire than in grassland. The seasonal changes of CO2 fluxes in mire and grassland were positively correlated with air temperature, the peak value being usually appeared in July or August, and the diurnal changes of the CO2 fluxes were also positively correlated with air temperature, the peak value being usually appeared between 11:00 and 17:00. The CO2 fluxes had a higher correlation with the soil temperature at the depth of 5 cm than at the depths of 10 cm and 15 cm.

[Comparison of nocturnal ecosystem respiration measured with eddy covariance and chamber system at two agricultural sites in Sanjiang plain]

Measurements of nocturnal ecosystem respiration were conducted in a rice paddy of Sanjiang from July to September in 2004 and in a soybean field from June to September in 2005, using eddy covariance (EC) and dark chamber-gas chromatography (DC-GC). The differences of simultaneous data measured by two methods were not significant when night turbulent mixing was well. The correlations between two methods can be improved under more large friction velocity. EC measurements were poorly correlated to night ecosystem respiration estimated by chamber models for the variability inherent to EC measurements (R2 = 0.06, 0.23 for rice and soybean, respectively). However, this correlation can be improved by aggregating measurements over longer time period (R2 = 0.16, 0.75 for rice and soybean field, respectively). In general, whatever comparison with simultaneous chamber measurements or modeled results, eddy covariance measurements were consistently lower 4% - 30% than chambers, and this bias varied with crop growing stage, which were maximum in middle and minimum in early and late growing stage.

[Niche characteristics of typical marsh wetland plant populations in Sanjiang Plain]

Based on field investigation and by using Levins formulae, the niche breadth and niche overlap of dominant plant populations in Sanjiang Plain marsh wetland were studied. The results showed that the niche breadth of test marsh wetland plants decreased in the order of Carex pseudocuraica (0.907) > C. lasiocarpa (0.864) > Glyceria spiculosa (0.855) > Deyeuxia angustifolia (0.500) = Menyanthes trifotiata (0.500) = Naumburgia thyrsiflora (0.500) = Anemone dichotoma (0.500). The niche overlaps among C. lasiocarpa, C. pseudocuraica, M. trifotiata and N. thyrsiflora, and among G. spiculosa, D. angustifolia and A. dichotom were comparatively large, indicating an intense competition among them, while the niche overlap between M. trifotiata and N. thyrsiflora, and D. angustifolia and A. dichotoma was 0, suggesting their different manner of environmental adaptation. Soil water was the dominating environmental factor of wetland plant ecological adaptability. The niche fitness of plant to environment depended on the combined effect of soil water and nutrients. The niche characteristics of marsh wetland plants could better indicate their ecological adaptability and distribution range.

[Dynamics of CO2, CH4 and N2O emission fluxes from mires during freezing and thawing season]

In the Sanjiang Plain, the freezing and thawing phase have 7 - 8 months and play important role in the greenhouse gases emission. The characters of the greenhouse gases emission during freezing and thawing season in the Sanjiang Plain were studied, using the static chamber and gas chromatogram method. The results observed show that there were obvious CH4 and CO2 emissions in winter and the CH4 emission made a relatively large contribution to the total CH4 flux from the different type mires during the winter in the Sanjiang Plain. And there were significantly CH4 and CO2 emission peak values during thawing time. The CH4 and CO2 emissions fluxes from seasonal flooded mire were larger than that from continuously flooded mire during thawing time. On the contrary, the CH4 and CO2 emissions from continuously flooded mire were larger than that from seasonal flooded mire in winter. During thawing, there was exponential relationship between CO2 fluxes and the soil temperature (5cm) (R2 = 0.912, p< 0.001). Meanwhile, CO2 fluxes was obviously correlated with the CH4 emission fluxes (R2 = 0.751, p < 0.001). The mires are N2O sink in winter and gradually become N2O source, with increasing temperature during thawing time. The characters of the greenhouse gases emission, during freezing and thawing in the Sanjiang Plain respond to the microbial activity in winter and the effects of thawing on soil carbon mineralization, nitrification and denitrification.

Cold season CH4, CO2 and N2O fluxes from freshwater marshes in northeast China

Cold season (winter and thaw) CH4, CO2 and N2O fluxes from freshwater marshes (47 degrees 35'N, 133 degrees 31'E, Northeast China) were measured, using the static chamber method. The mean CH4 and CO2 fluxes from Carex lasiocarpa (Cl) were 0.5+/-0.19 and 6.23+/-1.36 mgCm(-2)h(-1), respectively, and those from Deyeuxia angustifoli (Da) were 0.18+/-0.15 and 5.22+/-2.48 mgCm(-2)h(-1), respectively in winter. There was no significant difference between Cl and Da (p > 0.05). The contributions of winter CH4 fluxes were about 5.5% and 3% in the Cl and Da, respectively. Marshes are an important potential N2O sink in winter season in northeast China. During thaw, the CH4 and CO2 emissions rapidly increased, 4.5-6 times of winter emissions. Wetland became a source of N2O. Cold season gases flux from northern wetlands play an important role in the seasonal gas exchange.

[Longitudinal observation on the control of intestinal helminthiasis]

OBJECTIVE

To search suitable measure for rapid control intestinal helminthiasis and long-term strengthen efficacy.

METHODS

The treatment was taken in egg-positive population of intestinal helminthiasis in 1986-1988. The treatment was carried out only in the selected population in 1989-1992. No measure was taken in 1993-2000.

RESULTS

(1) The prevalence rate of hookworm, Ascaris and Trichuris decreased to 3.2%, 37.3% and 3.5% respectively after administration of albendazole twice a year for 3 years. (2) The prevalence rate of hookworm continued to decrease to 0.5% after treatment on selected population. (3) The prevalence rate and the intensity of hookworm has been less than 1% and 10/LPG for 8 years. No hookworm larvae had been isolated from the soil.

CONCLUSION

The hookworm transmission was effectively controlled in the study site.

The effect of cobalt-60 irradiation on the infectivity of Toxoplasma gondii

Toxoplasma gondii cysts in the tissues of experimentally infected mice and pigs were irradiated with cobalt-60 at various doses and used to infect mice and kittens. Loss of parasite infectivity was confirmed following irradiation whereas control animals inoculated with non-irradiated infected tissues became infected. Experiments were repeated to calculate the minimal effective dose (MED) of irradiation to eradicate parasite infectivity. The MED for the Chinese NT strain and the American ME-49 and TS-2 strains of T. gondii cysts in mouse and pig tissues was approximately 0.6 kGy. The infectivity for mice of NT strain bradyzoites irradiated at a dose of 0.45 kGy was reduced 10,000-fold. Such irradiation may be valuable in practical operations to control T. gondii in pork products.

Effect of cobalt-60 irradiation on the infectivity of Paragonimus westermani metacercariae

A study was made to observe the effect of cobalt-60 irradiation on the viability of Paragonimus westermani metacercariae in Sinopotamon chekiangense crabs. The crabs were collected in mountain regions of the Zhejiang Province of China in which paragonimiasis is endemic. Adult cats and albino mice were infected with metacercariae irradiated at different doses. Dissection of the host animals was conducted 90 or 30 days, respectively, after infection for recovery of lung flukes. Anti-metacercariae antibody in infected mice was measured by enzyme-linked immunosorbent assay (ELISA). Results showed that metacercariae were unable to grow into adult worms in cats after exposure to gamma irradiation at a dose of 0.10 kGray. However, a small number of metacercariae exposed to a dose of 2.0 kGray excysted and survived in 1 mouse for 30 days. No worm was recovered from mice when the metacercariae were irradiated at a dose of 2.5 kGray. Seropositive results by ELISA were obtained when the mice were infected with metacercariae irradiated at doses ranging from 2.0 to 3.5 kGray.

Studies on the use of cobalt-60 gamma irradiation to control infectivity of Clonorchis sinensis metacercariae

The purpose of the present study was to observe the survival and development of Clonorchis sinensis metacercariae in their final hosts after Cobalt-60 gamma irradiation of isolated metacercariae or the parasite in fish. Guinea pigs or albino rats were orally infected with irradiated metacercariae by gavage. Bioassay, fecal examination for ova, and necropsy of infected animals, were the methods used for the estimation of minimum effective dose of gamma irradiation to control infectivity of the metacercariae. Results showed that the minimum effective irradiation dose for isolated metacercariae was 0.05 kGy. The LD50 of the irradiation dose for metacercariae in fish was 0.05 kGy, and the minimum effective dose was 0.15 kGy. No significant difference in radiation susceptibility to Co-60 gamma irradiation was found among C. sinensis metacercariae in fishes collected at different localities in northern, middle or southern parts of China. The present finding suggests that irradiation of fish by 0.15 kGy could control infectivity of C. Sinensis metacercariae and thus be adopted as a control measure in preventing infections.

Studies on the control of hookworm and other soil-transmitted helminthiases in farmers in Zhejiang Province, China

Different periodic selective chemotherapeutic schemes were used to control hookworm and other soil-transmitted helminthiases in eight villages in five counties in Zhejiang Province, China, 1985-1988. The results showed that the prevalence rates of hookworm, ascariasis, and trichuriasis decreased from 35.0-74.4%, 47.0-.76% and 22.9-47.5% to 3.2-15.8%, 9.9-47.8%, and 3.5-31.2%, respectively, using pyrantel pamoate (10 mg/kg for 1-2 days) or albendazole (400 mg for 1-2 days, once or twice a year for 2-3 years). The eggs per gram of feces of hookworm and Trichuris trichiura also dropped markedly after control. Moreover, the mean hemoglobin levels of sampled populations increased after several treatments. The authors recommend periodic selective chemotherapy as the main method to control soil-transmitted helminthiases, especially hookworm infections.

Studies on the use of cobalt-60 irradiation to control infectivity of Toxoplasma gondii cysts

Mouse brains harboring the Chinese NT strain of Toxoplasma gondii cysts were homogenized with normal saline and irradiated with cobalt-60 gamma rays at various doses. The homogenate was introduced intraperitoneally into NIH mice or per os into kittens. Loss of infectivity was confirmed according to the following criteria: no cyst found in mouse brain impression smears on the 50th day after inoculation; no oocyst found in feces of kittens 3-15 days after inoculation; subinoculation in mice and a negative IHA test. All bioassays, parasitological examinations and serological tests in the control group gave positive results. Activity of radioactive source: 10 KCi; uniform dosage: 1238 rad/min; dose range of irradiation: 0.1-1.0 KGy. Minimal effective dose of gamma rays to control infectivity of T. gondii cysts was 0.55 KGy. Infectivity of bradyzoites irradiated with gamma rays at a dose of 0.45 KGy decreased by 10,000 times. Minimal effective dose of gamma rays to control infectivity of American ME-49 and Ts-2 strain, is slightly higher (0.6KGy) than that of NT strain. These studies present useful data for practical use of cobalt-60 to control infectivity of T. gondii in meat products.