How does a wetland plant respond to increasing temperature along a latitudinal gradient?

Global warming affects plant fitness through changes in functional traits and thereby ecosystem function. Wetlands are declining worldwide, and hence, ecosystem functions linked to wetlands are threatened. We use Caltha palustris “a common wetland plant” to study whether warming affects growth and reproduction differently depending on origin of source population, potentially affecting phenotypic response to local climate. We conducted a 2‐year in situ temperature manipulation experiment using clone pairs of C. palustris in four regions, along a 1300‐km latitudinal gradient of Sweden. Open‐top chambers were used to passively increase temperature, paired with controls. Growth and reproductive traits were measured from 320 plants (four regions × five sites × two treatments × eight plants) over two consecutive seasons to assess the effect of warming over time. We found that warming increased plant height, leaf area, number of leaves, and roots. High‐latitude populations responded more strongly to warming than low‐latitude populations, especially by increasing leaf area. Warming increased number of flowers in general, but only in the second year, while number of fruits increased in low‐latitude populations the first year. Prolonged warming leads to an increase in both number of leaves and flowers over time. While reproduction shows varying and regional responses to warming, impacts on plant growth, especially in high‐latitude populations, have more profound effects. Such effects could lead to changes in plant community composition with increased abundance of fast‐growing plants with larger leaves and more clones, affecting plant competition and ecological functions such as decomposition and nutrient retention. Effects of warming were highly context dependent; thus, we encourage further use of warming experiments to predict changes in growth, reproduction, and community composition across wetland types and climate gradients targeting different plant forms.     

A comparative study on carbohydrate reserves and ethanolic fermentation in the roots of two wetland and non‐wetland species after commencement of hypoxia

The problem of availability of storage carbohydrates (fructans and starch) in oxygen‐deficient roots was investigated in wetland species ( Senecio aquaticus Hill., Myosotis palustris [L.] L. Em. Rchb.) and compared with related non‐wetland species ( Senecio jacobaea L., Myosotis arvensis [L.] Hill.) with respect to ethanolic fermentation (PDC activity, ethanol production).
In response to 24 h of hypoxic treatment, the pyruvate decarboxylase (PDC) activity in roots increased 4‐fold in M. arvensis and S. jacobaea , 2‐fold in S. aquaticus and only slightly in M. palustris . The rise in PDC activity was accompanied by an increase in ethanol content in the roots. The increase in ethanolic fermentation in roots of intact plants was associated with a slight increase in fructose and glucose and in a clear rise in sucrose content during the first 24‐48 h after commencement of the hypoxic treatment. Following 24 h of hypoxia, the content of fructans started to increase significantly for the duration of the experiment (9 days) in the four species. Since starch content changed only slightly during this period, the fructan:starch ratio increased under low energy availability. In the roots of flooding‐tolerant Senecio aquaticus , the ratio shifted most clearly from 2:1 in normoxia to 9:1 in hypoxia. For the roots of the two wetland species investigated, the results indicate a stronger accumulation of carbohydrates accompanied by a lower increase in PDC activity under root hypoxia, when compared with the related non‐wetland species respectively.     

Analysis of the decrease in photosynthesis on desiccation of mosses from xeric and hydric environments

Three moss species [ Tortula ruraliformis (Besch.) Grout. Bryum pseudotriquetrum (Hedw.) Schaegr and Dicranella palustris (Dicks.) Crund. ex. E. F. Warb. ( D. squarrosa (Starke) Schp.] collected from a range of habitats differing in water availability were desiccated in controlled conditions. All species became photosynthetically inactive when dried below a water content of 100–200% dry weight. Only Tortula ruraliformis , a moss from arid sand dunes. was able to recover fully to pre-desiccated rates of photosynthetic electron transport during subsequent rehydration. The rate of recovery was influenced by irradiance during desiccation. Mosses from hydric habitats showed some resumption of photosynthetic electron transport (following rehydration) if dried in the dark. but did not do so if dried even in low light. In these circumstances the mosses showed evidence of lasting photoinhibition of photosynthesis after rehydration. The desiccation-tolerant T. ruraliformis became significantly photoinhibited only when continually exposed to high irradiance (1200 μmol m⁻² s⁻¹) in the hydrated state. If allowed to desiccate whilst exposed to high irradiance this species showed less evidence of photoinhibition after rehydration, and was not at all affected by desiccation in low irradiance. Photon flux absorption in dry moss was 50–60% less than that in hydrated moss as a result of leaf curling. However, the reduction in absorption of photosynthetically active radiation cannot account for the total loss of photosynthetic oxygen evolution and variable chlorophyll fluorescence observed in the desiccated mosses.     

Structural and functional characterization of solute binding proteins for aromatic compounds derived from lignin: p‐Coumaric acid and related aromatic acids

Lignin comprises 15–25% of plant biomass and represents a major environmental carbon source for utilization by soil microorganisms. Access to this energy resource requires the action of fungal and bacterial enzymes to break down the lignin polymer into a complex assortment of aromatic compounds that can be transported into the cells. To improve our understanding of the utilization of lignin by microorganisms, we characterized the molecular properties of solute binding proteins of ATP‐binding cassette transporter proteins that interact with these compounds. A combination of functional screens and structural studies characterized the binding specificity of the solute binding proteins for aromatic compounds derived from lignin such as p‐coumarate, 3‐phenylpropionic acid and compounds with more complex ring substitutions. A ligand screen based on thermal stabilization identified several binding protein clusters that exhibit preferences based on the size or number of aromatic ring substituents. Multiple X‐ray crystal structures of protein–ligand complexes for these clusters identified the molecular basis of the binding specificity for the lignin‐derived aromatic compounds. The screens and structural data provide new functional assignments for these solute‐binding proteins which can be used to infer their transport specificity. This knowledge of the functional roles and molecular binding specificity of these proteins will support the identification of the specific enzymes and regulatory proteins of peripheral pathways that funnel these compounds to central metabolic pathways and will improve the predictive power of sequence‐based functional annotation methods for this family of proteins.Proteins 2013; 81:1709–1726. © 2013 Wiley Periodicals, Inc.     

Progress toward a biomimetic leaf: 4,000 h of hydrogen production by coating‐stabilized nongrowing photosynthetic Rhodopseudomonas palustris

Intact cells are the most stable form of nature's photosynthetic machinery. Coating‐immobilized microbes have the potential to revolutionize the design of photoabsorbers for conversion of sunlight into fuels. Multi‐layer adhesive polymer coatings could spatially combine photoreactive bacteria and algae (complementary biological irradiance spectra) creating high surface area, thin, flexible structures optimized for light trapping, and production of hydrogen (H₂) from water, lignin, pollutants, or waste organics. We report a model coating system which produced 2.08 ± 0.01 mmol H₂ m^?2 h^?1 for 4,000 h with nongrowing Rhodopseudomonas palustris, a purple nonsulfur photosynthetic bacterium. This adhesive, flexible, nanoporous Rps. palustris latex coating produced 8.24 ± 0.03 mol H₂ m^?2 in an argon atmosphere when supplied with acetate and light. A simple low‐pressure hydrogen production and trapping system was tested using a 100 cm² coating. Rps. palustris CGA009 was combined in a bilayer coating with a carotenoid‐less mutant of Rps. palustris (CrtI^?) deficient in peripheral light harvesting (LH2) function. Cryogenic field emission gun scanning electron microscopy (cryo‐FEG‐SEM) and high‐pressure freezing were used to visualize the microstructure of hydrated coatings. A light interaction and reactivity model was evaluated to predict optimal coating thickness for light absorption using the Kubelka‐Munk theory (KMT) of reflectance and absorptance. A two‐flux model predicted light saturation thickness with good agreement to observed H₂ evolution rate. A combined materials and modeling approach could be used for guiding cellular engineering of light trapping and reactivity to enhance overall photosynthetic efficiency per meter square of sunlight incident on photocatalysts. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

广西平果县喀斯特山地蚬木生存群落物种多样性与环境的关系

基于野外调查和室内实验数据,采取主成分分析和典型相关分析相结合的方法,分析了广西平果县喀斯特山地蚬木(Excentrodendron hsienmu)生存群落物种多样性与土壤养分和地形因子间的关系。结果表明:群落各层的物种数、Shannon-Wiener指数和Pielou均匀度指数表现为乔木层灌木层草本层。主成分分析的前3个主成分解释了总变异的78.8%,第一主成分的特征值为5.29,方差贡献率为44.0%,主要反映了土壤养分的综合信息。典型相关分析显示乔木层多样性能敏感指示土壤养分变化,与土壤全磷间呈负相关、与全氮间呈正相关;灌木层物种多样性对地形变化更为敏感,与坡位和海拔间均表现为正相关关系;土壤与地形因子间存在较为密切的耦合关系,土壤全磷与坡位间呈正相关、土壤pH与岩石裸露率间呈负相关。