Yanyou Wu

Soil-released carbon dioxide from microbial biomass carbon in the cultivated soils of karst areas of southwest China.

Abstract Soil microbial biomass and the emission of CO2 from the soil surface were measured in yellow soils (Ultisols) of the karst areas of southwest China. The soils are relatively weathered, leached and impoverished, and have a low input of plant residues. The measurements were made for a 1-year period and show a reciprocal relationship between microbial biomass and surface CO2 efflux. The highest (42.6±2.8 mg CO2-C m–2 h–1) and lowest (15.6±0.6 mg CO2-C m–2 h–1) CO2 effluxes are found in the summer and winter, respectively. The cumulative CO2 efflux is 0.24 kg CO2-C m–2 year–1. There is also a marked seasonal variation in the amount of soil microbial biomass carbon, but with the highest (644±71 μg C g–1 soil) and lowest (270±24 μg C g–1 soil) values occurring in the winter and summer, respectively. The cumulative loss of soil microbial biomass carbon in the top 10 cm of the soil was 608 μg C g–1 year–1 soil over 17 sampling times. The mean residence time of microbial biomass is estimated at 105 days, suggesting that the carbon in soil microbial biomass may act as a source of the CO2 released from soils.

Role of electricity production in the anaerobic decolorization of dye mixture by exoelectrogenic bacterium Shewanella oneidensis MR-1

This study investigated the anaerobic decolorization of the dye mixture containing methyl orange (MO) and naphthol green B (NGB) by Shewanella oneidensis MR-1. S. oneidensis MR-1 showed a strong ability to decolorize the dye mixture. MO was easier to get the electrons and inhibited the reduction of NGB, despite of its lower redox potential than NGB. The Mtr respiratory pathway played an important role in this process. Meantime, addition of extracellular electron shuttles accelerated the decolorization. Those results suggest that the decolorization capacity of S. oneidensis MR-1 is associated with the electricity production. The operating parameters, such as electron acceptors, temperature, and pH, were also investigated in this study. Thus, this work may facilitate a better understanding of the extensive nonspecific reduction capacity of exoelectrogens and is beneficial for promoting their application in bioremediation.

Photosynthetic characteristics involved in adaptability to Karst soil and alien invasion of paper mulberry (Broussonetia papyrifera (L.) Vent.) in comparison with mulberry (Morus alba L.)

Unlike mulberry (Morus alba, M.a.), paper mulberry (Broussonetia papyrifera, B.p.) can acclimate to Karst soil and incline to alien invasion. The photosynthetic parameters, diurnal changes of carbonic anhydrase, and chlorophyll fluorescence induction, and water potential were measured on sunny days (SD) and cloudy days (CD). Photosynthetic midday depression occurred in B.p. but not in M.a. The irradiance-and CO2-saturated photosynthetic rates of B.p. were significantly higher than those of M.a. There was no significant difference in water use efficiency between the two species on a SD. The maximum fluorescence, maximum quantum yield, photochemical quenching, and relative electron transport rate in the leaves of B.p. were much higher than those in M.a. The activity of carbonic anhydrase (CA) of B.p., on either an SD or a CD, was much greater than that of M.a. Higher transpiration rate (E) and net photosynthetic rate (PN) of B.p. resulted in the lack of water in mesophyll cells. Although a higher CA activity of B.p. supplied both water and CO2 for the photosynthesis of mesophyll cells, water in mesophyll cells was the factor limiting photosynthesis, and the intercellular CO2 concentration of B.p. was high and stable.

Different growth and physiological responses to experimental warming of two dominant plant species Elymus nutans and Potentilla anserina in an alpine meadow of the eastern Tibetan Plateau

The effects of experimental warming on the growth and physiology of grass Elymus nutans and forb Potentilla anserina were studied by using open-top chambers (OTCs) in an alpine meadow of the eastern Tibetan Plateau. The warming treatment increased mean air and soil surface temperatures by 1.53°C and 0.50°C, respectively, but it reduced soil relative water content in the surface layer. Experimental warming enhanced the growth and gas exchange of E. nutans, while it reduced those of P. anserina. Experimental warming resulted in an increased efficiency of photosystem II (PSII) in E. nutans, while decreasing it in P. anserina; significantly stimulated non-photochemical quenching, antioxidative enzymes and non-enzymes in both species; and significantly reduced malondialdehyde content in E. nutans, while promoting it in P. anserina. The results of this study indicated that the two species showed different growth responses to experimental warming and their different physiological performances further indicated that experimental warming alleviated the negative effect of low temperature on the growth and development of E. nutans, but limited the competitive ability of P. anserina in the study region.

Effect of bicarbonate treatment on photosynthetic assimilation of inorganic carbon in two plant species of Moraceae

Excessive levels of bicarbonate adversely affect the growth and metabolism of plants. Broussonetia papyrifera (L.) Vent. and Morus alba L., belonging to family Moraceae, possess the favorable characteristics of rapid growth and adaptability to adverse environments. We examined the response of these two plant species to bicarbonate stress in terms of photosynthetic assimilation of inorganic carbon. They were exposed to 10 mM sodium bicarbonate in the culture solution for 20 days. The photosynthetic response was determined by measuring the net photosynthetic rate of the leaf, water-use efficiency, and chlorophyll fluorescence on days 10 and 20. The bicarbonate-use capacity of the plants was studied by measuring the carbonic anhydrase activity and the compositions of the stable carbon and hydrogen isotopes. The photosynthetic response to high concentration of bicarbonate varied with plant species and treatment durations. High concentrations of bicarbonate decreased the photosynthetic assimilation of inorganic carbon in the two plant species to half that in the control plants on day 10. Bicarbonate treatment did not cause any damage to the reaction centers of photosystem II in Morus alba; it, however, caused a decline in the quantum efficiency of photosystem II in B. papyrifera on day 20. Moreover, B. papyrifera had a greater bicarbonate-use capacity than M. alba because carbonic anhydrase converted bicarbonate to CO2 and H2O to a greater extent in B. papyrifera. This study showed that the effect of bicarbonate on photosynthetic carbon metabolism in plants was dual. Therefore, the concentration of bicarbonate in the soil should first be considered during afforestation and ecological restoration in karst areas.

Mechanism of the plant community succession process in the Zhenjiang Waterfront Wetland

In this study, replacement of dominant populations (Phragmites australis and Phalaris arundinacea) in the plant community succession process in the Zhenjiang Waterfront Wetland was approached from three aspects: growth, photosynthesis, and specific competitive characteristics. The productivity of Phragmites, based on intrinsic rate of increase and environmental carrying capacity of the several chosen growth indices (plant length, sheath height, and biomass), was significantly higher than that of Phalaris. Phragmites had a higher photosynthetic rate than Phalaris. However, Phalaris had a markedly lower light compensation point, which suggested that it was capable of better utilization of weak light. This possibly might account for its survival beneath Phragmites. At three different coverage gradients, the relative yield total was greater than 1, indicating a certain degree of complementary resource utilization via niche separation between both species. Significant differences in the competition ratio of both species indicated a superiority of Phragmites over Phalaris in terms of competitive capability. Thus, the Phragmites population tended to exclude the Phalaris population and became the mono-dominant population in the community succession process. For Phalaris, traits such as its better utilization of weak light, its complementary resource utilization, and a partial separation of growth period compared to Phragmites prevented complete replacement of its population to some degree. In this particular study area in the Zhenjiang Waterfront Wetland, the hydrological conditions of the river beach determined by its elevation possibly acted as the dominant regulator of the plant succession process.

Composition and activity of external carbonic anhydrase of microalgae from karst lakes in China

The species composition, the net photosynthetic O2 evolution rate and the activity of external carbonic anhydrase (CA) of microalgae from three reservoirs were studied. Carbonic anhydrase activity had a significant positive correlation with the density of Cyanobacteria in Lake Aha. Microalgaes carbonic anhydrase activity in Lakes Baihua and Hongfeng was related to the density of Chlorophyceae. The species abundances of microalgae in Lake Aha, Lake Baihua, and Lake Hongfeng were different. A relationship between carbonic anhydrase activity and net photosynthetic O2 evolution rate had also been established. Algae with external CA influenced the algal productivity. These results demonstrate the role of external CA in facilitating the availability of CO2 that limits the photosynthesis of microalgae in karst lakes in China.

Comparison of photosynthetic activity of Orychophragmus violaceus and oil-seed rape

Orychophragmus violaceus, Brassica campestris cv. Chuanyou No.8, and Brassica juncea cv. Luzhousileng diurnal changes of net photosynthetic rate (PN) and activities of carbonic anhydrase (CA) of leaves were studied. One uni-modal curve occurred at the diurnal changes of PN in O. violaceus, but bimodal curves were found in B. campestris and B. juncea. Thus photosynthetic midday depression was not found in O. violaceus but in both Brassica species. Midday depression of PN in O. violaceus was not related to high temperature or low humidity at midday but to the activity of CA.

Effect of Phosphorus Deficiency on Photosynthetic Inorganic Carbon Assimilation of Three Climber Plant Species

BackgroundP deficiency in karst areas significantly influenced leaf photosynthesis and carbon metabolisms in plants which were bad for plant growth. Meanwhile, fertilizer application would cause lots of environmental problems. Therefore planning and developing P deficiency-resistant plants in karst areas are important to prevent shortage of P resources and reduce the environmental impacts of P supplementation.ResultsThis study examined the photosynthetic response of three climber plant species, namely, Pharbitis nil (Linn.) Choisy, Lonicera pampaninii Levl, and Parthenocissus tricuspidata (Sieb.et Zucc.) Planch to phosphorus (P) deficiency stress. The plants were exposed to P deficiency stress at three treatments of 0.125 mM, 0.031 mM, and 0 mM for 30 d; 0.250 mM P was used as the control. Photosynthetic responses were determined by measurement of leaf photosynthesis, chlorophyll fluorescence, carbonic anhydrase activity, and stable carbon isotope ratios. Pharbitis nil showed high CA activity, more negative δ13C values and could maintain long-term stable photosynthetic capacity. Lonicera pampaninii also showed high CA activity but positive δ13C values compared to Pharbitis nil, and its photosynthetic capacity decreased as P deficiency stress increased. Parthenocissus tricuspidata had a low photosynthesis and positive δ13C values compared to Pharbitis nil, it could grow normally even under 0 mM P.ConclusionsPharbitis nil was tolerant to long-term, severe P deficiency stress, a finding that is attributed to its stable PSII and regulation of carbonic anhydrase. Lonicera pampaninii showed a poor adaptability to short-term P deficiency, but exhibited long-term tolerance under 0.125 mM P concentration. Parthenocissus tricuspidata was tolerant to long-term P deficiency stress, may exhibit a stomatal limitation. Besides, P deficiency stress had little effect on the way of inorganic carbon utilization of the three climber plants. Different adaptation mechanisms to P deficiency stress should be considered for the selection of species when developing P deficiency-resistant plants.

An Electrochemical Approach Coupled with Sb Microelectrode to Determine the Activities of Carbonic Anhydrase in the Plant Leaves

The electrochemical approach coupled with Sb microelectrode was developed to determine the carbonic anhydrase activity in a wide range. The sensing response of the microelectrode had a good linear relationship between potential and pH value in barbital buffer. The temperature would not affect the linear relationship. During the determination, the open-circuit potential method was taken to monitor the whole course of the reversible conversion catalyzed by carbonic anhydrase, and then the initial part of uniform velocity from the reaction curve was chosen to calculate the reaction velocity (the time to change one unit of pH). This technique, in comparison with the conventional method was used to determine the activities of bovine red blood cells carbonic anhydrase, foliar carbonic anhydrase and extracellular carbonic anhydrase in some plants. The result showed that the electrochemical approach coupled with Sb microelectrode would obtain more credible, accurate data than the conventional method.