Initial effects of experimental warming on carbon exchange rates, plant growth and microbial dynamics of a lichen-rich dwarf shrub tundra in Siberia

Biological soil crusts can affect seed germination and seedling establishment. We have investigated the effect of biological soil crusts on seed water status as a potential mechanism affecting seed germination. The seed water potential of two annual grasses, one exotic Bromus tectorum L. and another native Vulpia microstachys Nutt., were analyzed after placing the seeds on bare soil, on a crust that contains various lichens and mosses (mixed crust), or on a crust dominated by the crustose lichen Diploschistes muscorum (Scop.) R. Sant. (Diploschistes crust). Seed water potential and germination were similar on the bare soil and the mixed crust, except for the initial germination of V. microstachys, which was higher on the mixed crust than on the bare soil. For the two grasses studied, seed water potential was significantly higher on the bare soil and mixed crust than on the Diploschistes crust. These differences in water potential correlated with differences in germination, which was much lower on the lichen crust. Experiments were conducted under two watering regimens. Increasing the frequency of watering amplified the differences in seed water potential and germination between the Diploschistes crust and the other two surfaces. For a particular watering regimen, the bare soil, mixed crust, and Diploschistes crust received the same amount of water, but they reached significantly different water potentials. Throughout the experiments, the water potential of the soil and mixed crust remained above −0.6 MPa, while there was a marked decline in the water potential of the Diploschistes surface to about −4 MPa. To ascertain that water was the major factor limiting germination on the Diploschistes crust, we conducted germination tests in an environment with 100% relative humidity. Under these conditions, germination on the Diploschistes crust was similar to that on the bare soil. However, the seeds that germinated on the Diploschistes crust did not penetrate this surface and approximately 60% of their root tips became necrotic. Our results indicate that the presence of D. muscorum can inhibit seedling establishment by two mechanisms: a reduction in seed water absorption and an increase in root tip mortality.     

Water-related ecosystem services in Western Siberian lowland basins—Analysing and mapping spatial and seasonal effects on regulating services based on ecohydrological modelling results

For discussing and planning sustainable land management of river basins, stakeholders need suitable information on spatio-temporal patterns of natural processes and human actions. This study shows an approach to use ecohydrological modelling results for assessing water-related ecosystem services in three lowland river basins in Western Siberia. Based on the results of the ecohydrological model SWAT (Soil and Water Assessment Tool, Arnold et al., 1998), simulated output variables were used as indicators for the two regulating services water flow regulation and erosion regulation. The model results were translated into a relative ecosystem service valuation scale, which facilitates the comparison of different ecosystem services and which serves as the base for the applied mapping approach. The ecosystem service maps show different spatial and seasonal patterns. Although the daily modelling results were aggregated to seasonal maps to generate an understandable amount of information for stakeholders, differences can be depicted: during snowmelt, low regulation can be determined, especially for water flow regulation, but a very high regulation was calculated for the vegetation period during summer and for the winter period. Erosion regulation is high in two basins during all seasons. Spatio-temporal differences were modelled only for the largest basin. The SWAT model serves as a suitable quantification method for the assessment of the selected water-related regulating services.     

Promoter polymorphisms in trefoil factor 2 and trefoil factor 3 genes and susceptibility to gastric cancer and atrophic gastritis among Chinese population

The polymorphisms in trefoil factor (TFF) gene family that protect gastrointestinal epithelium might influence individual vulnerability to gastric cancer (GC) and atrophic gastritis. We used the Sequenom MassARRAY platform to identify the genotypes of TFF2 rs3814896 and TFF3 rs9981660 polymorphisms in 478 GC patients, 652 atrophic gastritis patients, and 724 controls. For the TFF2 rs3814896 polymorphism, in the subgroup aged ≤ 50 years, we found that AG + GG genotypes were associated with a 0.746-fold decreased risk of atrophic gastritis [p = 0.023, 95% confidence interval (CI) = 0.580–0.960], a 0.626-fold decreased risk of GC (p = 0.005, 95% CI = 0.451–0.868), and a 0.663-fold decreased risk of diffuse-type GC (p = 0.034, 95% CI = 0.452–0.970) compared with the common AA genotype. For the TFF3 rs9981660 polymorphism, in the male subgroup, individuals with variant AG + AA genotype were associated with a 0.761-fold decreased risk of diffuse-type GC compared with the common GG genotype (p = 0.043, 95% CI = 0.584–0.992). Additionally, we found that in subjects aged ≤ 50 years compared with common AA genotype, TFF2 rs3814896 AG + GG genotypes were associated with increased TFF2 mRNA levels in the total gastric cancer specimens and in the diffuse-type gastric cancer specimens; and in males aged ≤ 50 years compared with common GG genotype, TFF3 rs9981660 AA + AG genotypes were associated with TFF3 mRNA levels in diffuse-type gastric cancer tissues and their corresponding non-cancerous tissues. To our knowledge, this is the first report of an association between the TFF2 rs3814896 AG + GG genotypes and decreased risks of GC, diffuse-type GC, and atrophic gastritis in younger people aged ≤ 50 years, and an association between TFF3 rs9981660 AG + AA genotype and decreased risk of diffuse-type GC in men. Moreover, we found that TFF2 rs3814896 AG + GG genotypes in people aged ≤ 50 years and TFF3 rs9981660 AG + AA genotypes in younger males with diffuse-type GC were associated with higher levels of TFF2 and TFF3 mRNA respectively.     

Life histories of two desert species of the bulbous genus Bellevalia

Summary Annual biomass increment and biomass partitioning to leaves, roots and reproduction, and biomass storage in the below-ground bulb was measured in plants of two species of the geophytic genus Bellevalia grown outdoors at three levels of soil moisture. The differences between the species were in accordance with the hypothesis that plants of more arid environments should rely more on internal reserves than plants of more productive environments. In Bellevalia desertorum, a shallow rooted species of the most arid habitats in the Central Negev, leaf and root development during outgrowth at the beginning of winter was rather variable, and followed soil moisture availability to a certain degree. A small portion of its biomass budget was committed to seed production, which varied little among the irrigation regimes. The rest of the biomass was stored in the bulb. The amount of biomass devoted annually to reproduction was mainly determined by the amount of reserves already present in the bulb. In contrast, in B. eigii, which grows in the more productive wadis with its bulb at a depth of 15 to 30 cm, leaf and root growth was not only determined by water availability, but also by initial bulb mass. This resulted in a greater potential relative growth rate than in B. desertorum, but also in a greater risk of accumulating less biomass than it spent in root and leaf construction under poor soil moisture conditions. In this species, reproductive biomass and seed yield were proportional to current biomass gain and, in contrast to B. desertorum, independent of initial bulb mass, provided that the bulb was large enough to initiate flowering.     

Effect of low water potential on photosynthesis in intact lichens and their liberated algal components

Earlier experiments (T.D. Brock 1975, Planta124, 13–23) addressed the question whether the fungus of the lichen thallus might enable the algal component to function when moisture stress is such that the algal component would be unable to function under free-living conditions. It was concluded that the liberated phycobiont in ground lichen thalli could not photosynthesize at water potentials as low as those at which the same alga could when it was present within the thallus. However, our experience with lichen photosynthesis has not substantiated this finding. Using instrumentation developed since the mid-1970's to measure photosynthesis and control humidity, we repeated Brock's experiments. When applying “matric” water stress (equilibrium with air of constant relative humidity) we were unable to confirm the earlier results for three lichen species including one of the species,Letharia vulpina, had also been used by Brock. We found no difference between the effects of low water potential on intact lichens and their liberated algal components (ground thallus material and isolated algae) and no indication that the fungal component of the lichen symbiosis protects the phycobiont from the adverse effects of desiccation once equilibrium conditions are reached. The photosynthetic apparatus of the phycobiont alone proved to be highly adapted to water stress as it possesses not only the capability of functioning under extremely low degrees of hydration but also of becoming reactivated solely by water vapor uptake.     

Differing substomatal and chloroplastic CO2 concentrations in water-stressed wheat

Gas exchanges of wheat (Triticum aestivum L. cv. Courtot) shoots were measured before and during a water stress. While photosynthesis, transpiration and dark respiration decreased because of the stress, photorespiration increased initially, up to a maximum of 50% above its initial value. The CO₂ concentration in the intercellular space was calculated from gas-diffusion resistances, and remained approximately constant before and during the stress. On the other hand, the CO₂ concentration in the chloroplast, in the vicinity of Ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco), was evaluated from the ratio of CO₂ to O₂ uptake, using the known kinetic constants of the oxygenation and carboxylation reactions which compete for Rubisco. In the well-watered plants, the calculated chloroplastic concentration was slightly smaller than the substomatal concentration. During water stress, this concentration decreased while the substomatal CO₂ concentration remained constant. Hypotheses to explain this difference between substomatal and chloroplastic CO₂ concentrations are discussed.     

The effect of incubation media on the water exchange of snapping turtle (Chelydra serpentina) eggs and hatchlings

Summary The effect of two different incubation media, sand and vermiculite, on the water exchange of eggs and the mass of hatchlings of snapping turtles (Chelydra serpentina) was assessed. The eggs were incubated fully buried in either sand or vermiculite at 30 °C and egg mass was measured periodically throughout incubation. The wet and dry masses of each hatchling and its residual yolk were measured at the end of incubation. The media had similar water potentials () but their thermal conductivities differed 2.8-fold. The eggs experienced a net water gain during incubation. The rates of water uptake between treatments were not statistically different throught the first 36 days of incubation but were statistically different thereafter, with eggs incubating in sand taking up water at about twice the rate of eggs incubating in vermiculite. Hatchling masses were similar to both media but hatchling water contents were significantly different. Hatchlings incubated in sand had lower water contents than hatchlings incubated in vermiculite even though the eggs in sand took up more water. Hatchling mass was correlated with egg water exchange for eggs incubated in vermiculite but not for eggs incubated in sand. The difference in egg water exchange in the two media appears to be attributable to differences in the thermal conductivity of the media. The presence of such a thermal effect supports the hypothesis that the eggs exchanged water with the media as water vapor. Egg water exchange was limited by the shell and shell membranes and not by the media. The shell and shell membranes appear to present an effective barrier to water uptake.Abbreviations M _{H 2 O} water flux (cm³·day^-1) - L _p hydraulic conductivity (cm·day^-1·kPa^-1) - A shell area (cm²) - A _p pore area (cm²) - l shell thickness (cm) - r pore radius (cm) - viscosity (kPa·day) - P _{EH 2 O} egg water potential (kPa) - P _{AH 2 O} medium water potential (kPa) - G _{H 2 O} water vapor conductance (cm³·day^-1·kPa^-1) - D _{H 2 O} diffusion coefficient (cm²·day^-1) - R gas constant (cm³·kPa·K^-1·cm^-3) - T temperature (K) - P _{EH 2 O} egg water vapor pressure (kPa) - P _{AH 2 O} medium water vapor pressure (kPa) - d egg diameter - K soil hydraulic conductivity (cm²·day^-1·kPa^-1) - DHM hatchling dry mass - WHM hatchiling wet mass - WU water uptake - IM initial egg mass     

The mechanism of photosynthetic water oxidation

Photosynthetie water oxidation is unique to plants and cyanobacteria, it occurs in thylakoid membranes. The components associated with this process include: a reaction center polypeptide, having a molecular weight (Mr) of 47–50 kilodaltons (kDa), containing a reaction center chlorophyll a labeled as P680, a plastoquinol(?)-electron donor Z, a primary electron acceptor pheophytin, and a quinone electron acceptor Q_A; three ‘extrinsic’ polypeptides having Mr of approximately 17 kDa, 23 kDa, and 33 kDa; and, in all likelihood, an approximately 34 kDa ‘intrinsic’ polypeptide associated with manganese (Mn) atoms. In addition, chloride and calcium ions appear to be essential components for water oxidation. Photons, absorbed by the so-called photosystem II, provide the necessary energy for the chemical oxidation-reduction at P680; the oxidized P680 (P680⁺), then, oxidizes Z, which then oxidizes the water-manganese system contained, perhaps, in a protein matrix. The oxidation of water, leading to O₂ evolution and H⁺ release, requires four such independent acts, i.e., there is a charge accumulating device (the so-called S-states). In this minireview, we have presented our current understanding of the reaction center P680, the chemical nature of Z, a possible working model for water oxidation, and the possible roles of manganese atoms, chloride ions, and the various polypeptides, mentioned above. A comparison with cytochrome c oxidase, which is involved in the opposite process of the reduction of O₂ to H₂O, is stressed. This minireview is a prelude to the several minireviews, scheduled to be published in the forthcoming issues of Photosynthesis Research, including those on photosystem II (by H.J. van Gorkom); polypeptides of the O₂-evolving system (by D.F. Ghanotakis and C.F. Yocum); and the role of chloride in O₂ evolution (by S. Izawa).     

Ultrasonic absorption studies of protein-buffer interactions

The acoustic absorption of protein solutions in the presence of phosphate and other buffering ions has been studied in the physiological pH range. Buffers containing hydroxyl residues as titratable groups cause a pronounced increase of protein sound absorption, which is attributed to relaxation processes of proton transfer reactions between buffer ions and accessible imidazole and -amino groups of the protein surface. Amino group based buffers like Good's buffers do not induce additional sound absorption. Measurement of the ultrasonic absorption as a function of pH and of buffer concentration, and corresponding parameter fitting of the equation describing proton transfer relaxation processes has been used to evaluate equilibrium parameters. For the imidazole group of the amino acid histidine a pK value of 6.22 and for the imidazole group of the protein lysozyme a pK value of 5.71 have been determined. In hemoglobin the ligand-linked pK changes have been monitored by recording ultrasonic titration curves.     

Water droplets in intercellular spaces of barley leaves examined by low-temperature scanning electron microscopy

Low-temperature scanning electron microscopy was used to examine fracture faces in leaf blades taken from well-watered or drought-stressed barley (Hordeum vulgare L. cv. Mazurka) seedlings. The leaf blades were freeze-fixed while hydrated and were examined with or without gold-coating. There were droplets (with a smooth surface at the resolution achieved) on the surface of cell walls in leaf blades (0.91 g^-1 water content) from well-watered seedlings grown in an environment of 67% relative humidity. These were mainly on the vascular bundle sheath, the guard and subsidiary cells, and on some mesophyll cells around the substomatal cavity and between the stoma and vascular bundle. The droplets occurred, more abundantly, in the same places in seedlings from 100% relative humidity. They occurred on a few guard cells from wilting leaf blades (0.81 g·g^-1 water content) and were absent from severely drought-stressed leaf blades (0.15 g·g^-1 water content). The droplets sublimed at the same moment as both water which was in leaf cells and water which was allowed to condense (after freeze-fixation) on the wall surface. It is suggested that the droplets are aqueous. Their possible origin and importance is discussed.