ABSTRACT
Using the eddy covariance technique, we measured the net ecosystem CO2 exchange (NEE) and its environmental and biotic factors over a coastal wetland in the Yellow River Delta to investigate the diurnal and seasonal variation in NEE and quantify the effect of environmental and biotic factors on NEE. The results showed that the diurnal change of NEE showed a distinct U-shaped curve during the growing season, but not with substantial variation in its amplitude during the non-growing season. During the growing season, the wetland acted as a significant net sink for CO2, while it became carbon source during the non-growing season. On the scale of a whole year, the wetland functioned as a strong carbon sink of -247 g C·m-2. Daytime NEE was mainly dominated by photosynthetically active radiation (PAR). Apparent quantum yield (α) and daytime respiration of ecosystem (Reco,d) reached maximum in August, while maximum photosynthesis rate (Amax) reached its maximum in July. Nighttime NEE had an exponential relationship with air temperature (Ta). The mean value of temperature sensibility coefficient (Q10) was 2.5, and it was positively related to soil water content (SWC). During the non-growing season, NEE was negatively correlated with net radiation (Rn), but not with other environmental factors significantly. However, during the growing season NEE was significantly correlated with Rn, Ta, soil temperature at 10 cm depth (Ts 10) and leaf area index (LAI), but not with aboveground biomass (AGB). Stepwise multiple regression analysis indicated that Rn and LAI explained 52% of the variation in NEE during the growing season.
Subject(s)
Carbon Dioxide/analysis , Carbon Sequestration , Wetlands , Carbon , China , Photosynthesis , Plant Leaves , Rivers , Seasons , Soil , Temperature , WaterABSTRACT
Using the Li-8150 multichannel automatic soil CO2 efflux system, soil respiration was measured continuously over a one-year period in a coastal wetland in the Yellow River Delta, China. Environmental and biological factors were measured simultaneously, including temperature, soil water content, aboveground biomass and leaf area index. The results showed that the diurnal variation of soil respiration presented a single-peak curve, but it appeared as multiple peaks when disturbed by soil freezing and surface flooding. Soil respiration showed obvious seasonal dynamics and a single peak curve. The average annual soil respiration was 0.85 µmol CO2·m-2·s-1, and the mean soil respiration rate was 1.22 µmol CO2·m-2·s-1 during the growing season. On one-year scale, soil temperature was a major factor influencing soil respiration in the coastal wetland, which explained 87.5% of the variation in soil respiration. On the growing season scale, soil water content and leaf area index accounted for 85% of the seasonal variation of soil respiration.
Subject(s)
Seasons , Soil/chemistry , Wetlands , Biomass , Carbon Dioxide/analysis , China , Floods , Plant Leaves , Rivers , Temperature , WaterABSTRACT
Wetland can be a potential efficient sink to reduce global warming due to its higher primary productivity and lower carbon decomposition rate. While there has been a series progress on the influence mechanism of ecosystem CO2 exchange over China' s wetlands, a systematic metaanalysis of data still needs to be improved. We compiled data of ecosystem CO2 exchange of 21 typical wetland vegetation types in China from 29 papers and carried out an integrated analysis of air temperature and precipitation effects on net ecosystem CO2 exchange (NEE), ecosystem respiration (Reco), gross primary productivity (GPP), the response of NEE to PAR, and the response of Reco to temperature. The results showed that there were significant responses (P<0.05) of NEE (R2 = 50%, R2=57%), GPP (R2 = 60%, R2 = 50%) Reco (R2 = 44%, R2=50%) with increasing air temperature and enhanced precipitation on the annual scale. On the growing season scale, air temperature accounted for 50% of the spatial variation of NEE, 36% of GPP and 19% of Reco, respectively. Both NEE (R2 = 33%) and GPP (R2 =25%) were correlated positively with precipitation (P<0.05). However, the relationship between Reco and precipitation was not significant (P>0.05). Across different Chinese wetlands, both precipitation and temperature had no significant effect on apparent quantum yield (α) or ecosystem respiration in the daytime (Reco,day, P>0.05). The maximum photosynthesis rate (Amax) was remarkably correlated with precipitation (P <0.01), but not with air temperature. Besides, there was no significant correlation between basal respiration (Rref) and precipitation (P>0.05). Precipitation was negatively correlated with temperature sensitivity of Reco (Q10, P<0.05). Furthermore, temperature accounted for 35% and 46% of the variations in temperature sensitivity of Reco (Q10) and basal respiration (Rref P<0.05), respectively.
Subject(s)
Carbon Cycle , Carbon Dioxide/analysis , Rain , Temperature , Wetlands , China , Photosynthesis , SeasonsABSTRACT
The antioxidative properties of a novel curcumin analogue (2E,6E)-2,6-bis(3,5-dimethoxybenzylidene)cyclohexanone (MCH) were assessed by several in vitro models, including superoxide anion, hydroxyl radical and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging and PC12 cell protection from H2O2 damage. MCH displayed superior O2â¢- quenching abilities compared to curcumin and vitamin C. In vitro stability of MCH was also improved compared with curcumin. Exposure of PC12 cells to 150 µM H2O2 caused a decrease of antioxidant enzyme activities, glutathione (GSH) loss, an increase in malondialdehyde (MDA) level, and leakage of lactate dehydrogenase (LDH), cell apoptosis and reduction in cell viability. Pretreatment of the cells with MCH at 0.63-5.00 µM before H2O2 exposure significantly attenuated those changes in a dose-dependent manner. MCH enhanced cellular expression of transcription factor NF-E2-related factor 2 (Nrf2) at the transcriptional level. Moreover, MCH could mitigate intracellular accumulation of reactive oxygen species (ROS), the loss of mitochondrial membrane potential (MMP), and the increase of cleaved caspase-3 activity induced by H2O2. These results show that MCH protects PC12 cells from H2O2 injury by modulating endogenous antioxidant enzymes, scavenging ROS, activating the Nrf2 cytoprotective pathway and prevention of apoptosis.
