Interspecific variability of plant stomatal response to step changes of [CO2]

The kinetics of a stomatal response to sudden increases or decreases of CO₂ concentrations ([CO₂]) was studied in 13 plant species growing in the field. Plants were well supplied with water. In each plant, gas exchange measurements were made on a fully developed leaf that was first left to achieve steady-state stomatal conductance (g_s) at 400 μmol (CO₂) mol⁻¹) and then exposed to a step change of [CO₂] (to 700 μmol mol⁻¹ in one experiment; and to 700 and back to 400 μmol mol⁻¹ in a second experiment). Porometric data were captured in intervals of 3 s until a new steady state was reached.A comparison of t_1/2, the half-time needed to achieve new g_s, indicates similar responses of stomata in grasses when compared to herbs. The stomata of C₄ plants responded in approximately 5 min, the highest closure rate was detected in Echinochloa crus-galli and Digitaria sanguinalis. Opening rates were similar to closing rates and the response as a whole was rather symmetric. In C₃ plants, the full response of stomata was much slower. Analysis revealed differences in absolute rates of g_s change between C₃ and C₄ plants. These differences can be related to the specificities of the type of photosynthetic metabolism. C₄ photosynthesis enables plants to reduce g_s, which can hasten further changes of diffusivity in response to the environmental signals. A possible coupling of C₄ metabolism to the regulation of guard cells also has to be taken into account when explaining the observed results.     

Changes in root system structure,leaf water potential and gas exchange of maize and triticale seedlings affected by soil compaction

The physiological reasons associated with differential sensitivity of C₃ and C₄ plant species to soil compaction stress are not well explained and understood. The responses of growth characteristics, changes in leaf water potential and gas exchange in maize and triticale to a different soil compaction were investigated. In the present study seedlings of triticale and maize, representative of C₃ and C₄ plants were subjected to low (L – 1.10 g cm⁻³), moderate (M – 1.34 g cm⁻³) and severe (S – 1.58 g cm⁻³) soil compaction level. Distinct differences in distribution of roots in the soil profile were observed. Plants of treatments M or S in comparison to treatment L, showed a decrease in leaf number, dry mass of stem, leaves and roots, and an increase in the shoot to root ratio. A drastic decrease in root biomass in M and S treatments in the soil profile on depth from 15 to 40 cm was observed. Any level of soil compaction did not influence the number of seminal and seminal-adventitious roots but decreased their length. The number and total length of nodal roots decreased with compaction. Changes of growth traits in M and S treatments in comparison to the L were greater for maize than for triticale and were accompanied by daily changes in water potential (ψ) and gas exchange parameters (P_N, E, g_s). Differences between M and S treatments in daily changes in ψ for maize were in most cases statistically insignificant, whereas for triticale, they were statistically significant. Differences in the responses of maize and triticale to soil compaction were found in P_N, E and g_s in particular for the measurements taken at 12:00 and 16:00. The highest correlation coefficients were obtained for the relationship between leaf water potential and stomatal conductance, both for maize and triticale, which indicates the close association between stomata behavior and changes in leaf water status.     

Leaf photosynthesis of Haberlea rhodopensis before and during drought

Haberlea rhodopensis is a homoiochlorophyllous resurrection plant that shows a low rate of leaf net CO₂ uptake (4–6 μmol m^?2 s^?1) under saturating photosynthetic photon flux densities in air (21% O₂ and about 390 ppm CO₂). However, leaf net CO₂ uptake reaches values of 17–18 μmol m^?2 s^?1 under saturating CO₂ and light. H. rhodopensis leaves have a very low mesophyll CO₂ conductance that can partly explain the low rate of leaf net CO₂ uptake in normal air. Experimental evidences suggest that mesophyll conductance is not sensitive to temperature in the 20–35 °C range. In addition, it is shown that the (1) transpiration rate of H. rhodopensis is nearly linearly related to the vapour pressure difference between the leaf and the ambient air within the interval from 0.5 kPa to 2.5 kPa at a leaf temperature of 25 °C and (2) leaf net CO₂ uptake in normal air under saturating light does not change much with leaf temperature (between 20 °C and 30 °C). At a leaf relative water content of between 90% and 30%, the decrease of leaf net CO₂ assimilation during drought can be explained by a decrease of leaf CO₂ diffusional conductance. Accordingly the non-photochemical chlorophyll fluorescence quenching decreases only at relative water contents lower than 20%, indicating that photosynthetic activity maintains a trans-thylakoidal proton gradient over a wide range of leaf water contents. Moreover, PSII photochemistry (as estimated by the Fv/Fm ratio and the thermoluminescence B band intensity) is only affected at leaf relative water contents lower than about 20%, thus confirming that primary photosynthetic reactions are resistant to drought. Interestingly, the effect of leaf desiccation on photosynthetic capacity, measured at very high ambient CO₂ molar ratios under saturating PPFD, is identical to that observed for three non-resurrection C₃ mesophytes. This demonstrates that the photosynthetic apparatus of H. rhodopensis is not more resistant to desiccation when compared to other C₃ plants. Since the leaf area decreases by more than 50% when the leaf relative water content is reduced to about 40% during drought it is supposed, following Farrant et al. [Farrant, J.M., Vander, W.C., Lofell, D.A., Bartsch, S., Whittaker, A., 2003. An investigation into the role of light during desiccation of three angiosperms resurrection plants. Plant Cell Environ. 26, 1275–1286], that H. rhodopensis leaf cells avoid mechanical stress.     

Response of ecosystem CO2 exchange to biomass productivity in a high yield grassland

We measured the biomass production and ecosystem carbon CO₂ exchange in a high yield grassland dominated by Miscanthus sinensis. The experimental grassland is managed by mowing once a year in winter every year and the harvested biomass on the ground is left to become the humus. The maximum aboveground and belowground biomasses were 1117 and 2803 g d.w. m^?2 in our grassland. Although the high potential of our grassland for biomass production led to higher carbon uptake than with other types of grassland, the large biomass contributed to a higher respired carbon loss. Biomass increase led to a linear increase in ecosystem respiration. Over the 3 years, RE₁₀ increased with increasing aboveground biomass. The potential gross primary production at a photosynthetic photon flux density of 2000 μmol m² s^?1 logarithmic increased with LAI. These responses of CO₂ exchange to biomass production suggest this grassland behaved as weak CO₂ sink or near carbon neutral (?78 and 17 g C m^?2 year^?1) in current management.     

Antagonism between elevated CO2, nighttime warming,and summer drought reduces the robustness of PSII performance to freezing events

Plant responses to warming, elevated CO₂, and changes in summer precipitation patterns involve complex interactions. In this study we aim to reveal the single factor responses and their interactive effects on photosystem II (PSII) performance during an autumn-to-winter period. The study was carried out in the CLIMAITE multifactor experiment, which includes the combined impact of elevated CO₂ (free air carbon enrichment; CO₂), warming (passive nighttime warming; T) and summer drought (rain-excluding curtains; D) in a temperate heath ecosystem. PSII performance was probed by the effective quantum yield in light, F_v′/F_m′, using the pulse amplitude methodology, and the total performance index, PI_total, which integrate changes of the chlorophyll-a fluorescence transient including the maximal quantum yield in darkness, F_v/F_m.Decreasing temperature during autumn linearly reduced PI_total, both in the wavy hair-grass, Deschampsia flexuosa, and in the evergreen dwarf shrub common heather, Calluna vulgaris, and following freezing events the PI_total and F_v′/F_m′ were reduced even more. Contrary to expected, indirect effects of the previous summer drought reduced PSII performance before freezing events, particularly in Calluna. In combinations with elevated CO₂ interactive effects with drought, D × CO₂ and warming, T × D × CO₂, were negatively skewed and caused the reduction of PSII performance in both species after occurrence of freezing events. Neither passive nighttime warming nor elevated CO₂ as single factors reduced PSII performance via incomplete cold hardening as hypothesized. Instead, the passive nighttime warming strongly increased PSII performance, especially after freezing events, and when combined with elevated CO₂ a strongly skewed positive T × CO₂ interactive effect was seen. This indicates that these plants take advantage of the longer growing season induced by the warming in elevated CO₂ until a winter frost period becomes permanent. However, if previously exposed to summer drought this positive effect reverses via interactive D × CO₂ and T × D × CO₂ effects immediately after freezing events, causing the full combination of TDCO₂ not to differ from the control.In a future warmer climate with high CO₂ and summer drought, the occurrence of freezing events thus seem highly decisive for reducing PSII performance in the autumn-to-winter period. Such a reduced robustness of PSII performance may be highly decisive for the magnitude of the late season photosynthetic carbon uptake and reduce the growing season length in these temperate heath plants.     

Decomposition processes in soil of a healthy and a declining Phragmites australis stand

Decomposition processes were investigated in the soil of a declining, more eutrophic and a healthy, less eutrophic freshwater reed (Phragmites australis (Cav.) Trin. ex Steudel) stand in the littoral zone of Rožmberk fishpond, Czech Republic. Soil and pore water were sampled five times from April to October 1998. Chemical properties, CO₂ production in oxic and anoxic conditions, CH₄ production, denitrifying enzyme activity (DEA) and bacterial biomass were measured under laboratory conditions in suspensions prepared from homogenised soil samples. The more eutrophic West stand was more anaerobic than the East stand, with lower redox potential, lower pH and with a higher amount of organic acids, mainly acetic and lactic acid. Mean seasonal concentrations of total nitrogen in pore water, nitrogen of amino acids and proteins, and reducing sugars were all higher in the soil at the more eutrophic stand. Higher nutrient status and more reduced conditions at the more eutrophic stand were accompanied by (i) a limitation of aerobic microbial activities (CO₂ production in oxic conditions: 0.35 versus 0.54 μmol CO₂ cm⁻³ h⁻¹); lower DEA (4.0 versus 20.2 nmol N₂O cm⁻³ h⁻¹) and a lower proportion of bacteria that were active in aerobic conditions; (ii) by a prevalence of anaerobic over aerobic microbial processes; (iii) by a higher rate of methanogenesis (15.0 versus 11.5 nmol CH₄ cm⁻³ h⁻¹) and (iv) by an overall lower rate of microbial processes as compared to less eutrophied stand. The shift from aerobic to anaerobic microbial metabolism, and a coinciding restriction of metabolic activities at the more eutrophic stand are indicative of an elevated oxygen stress in the soil, associated with accumulation of metabolites toxic to both the micro-organisms and the reed. Possible links between eutrophication, decomposition processes in the soil and reed decline are discussed.     

Carbon mineralization of Chinese fir (Cunninghamia lanceolata) soils under different temperature and humidity conditions

Burned and unburned mineral soils (0–10 cm) from a 40-year-old Chinese fir (Cunninghamia lanceolata) forest in Nanping, Fujian, China were incubated for 90 days at different temperatures (25 °C and 35 °C) and humidity [25%, 50%, and 75% of water holding capacity (WHC)] conditions. Carbon (C) mineralization of all soils was determined using CO₂ respiration method. The results showed that CO₂ evolution rates of the burned and control soils exhibited similar temporal patterns, and similar responses to temperature and moisture. CO₂ evolution rates for all soil samples decreased with incubation time. At different humidity conditions, average rate of C mineralization and cumulative mineralized C from burned and control soils were significantly higher at 35 °C than at 25 °C. This implied that C mineralization was less sensitive to soil moisture than to temperature. In both soils at 25 °C or 35 °C, the amount of soil evolved CO₂ over the 90 days incubation increased with increasing moisture content from 25% to 75% WHC. A temperature coefficient (Q₁₀) varied with soil moisture contents. The maximum values recorded for Q₁₀ were 1.7 in control soil and 1.6 in burned soil both at 25% WHC. However, there were no significant differences in Q₁₀ values between the control and burned soils over all moisture ranges (P > 0.05). The data of cumulative C–CO₂ released from control and burned soils were fitted to two different kinetic models. The two simultaneous reactions model described mineralization better than the first-order exponential model, which reflected the heterogeneity of substrate quality. Based on these results, it is possible to conclude that temperature and moisture are important in the controls of C mineralization, and the combined effects of these variables need to be considered to understand and predict the response of CO₂ release in subtropical ecosystems to climate change.     

Soil nitrate accumulation explains the nonlinear responses of soil CO2 and CH4 fluxes to nitrogen addition in a temperate needle-broadleaved mixed forest

The responses of soil-atmosphere carbon (C) exchange fluxes to growing atmospheric nitrogen (N) deposition are controversial, leading to large uncertainty in the estimated C sink of global forest ecosystems experiencing substantial N inputs. However, it is challenging to quantify critical load of N input for the alteration of the soil C fluxes, and what factors controlled the changes in soil CO₂ and CH₄ fluxes under N enrichment. Nine levels of urea addition experiment (0, 10, 20, 40, 60, 80, 100, 120, 140 kg N ha⁻¹ yr⁻¹) were conducted in the needle-broadleaved mixed forest in Changbai Mountain, Northeast China. Soil CO₂ and CH₄ fluxes were monitored weekly using the static chamber and gas chromatograph technique. Environmental variables (soil temperature and moisture in the 0–10 cm depth) and dissolved N (NH₄⁺-N, NO₃⁻-N, total dissolved N (TDN), and dissolved organic N (DON)) in the organic layer and the 0–10 cm mineral soil layer were simultaneously measured. High rates of N addition (≥60 kg N ha⁻¹ yr⁻¹) significantly increased soil NO₃⁻-N contents in the organic layer and the mineral layer by 120%-180% and 56.4%-84.6%, respectively. However, N application did not lead to a significant accumulation of soil NH₄⁺-N contents in the two soil layers except for a few treatments. N addition at a low rate of 10 kg N ha⁻¹ yr⁻¹ significantly stimulated, whereas high rate of N addition (140 kg N ha⁻¹ yr⁻¹) significantly inhibited soil CO₂ emission and CH₄ uptake. Significant negative relationships were observed between changes in soil CO₂ emission and CH₄ uptake and changes in soil NO₃⁻-N and moisture contents under N enrichment. These results suggest that soil nitrification and NO₃⁻-N accumulation could be important regulators of soil CO₂ emission and CH₄ uptake in the temperate needle-broadleaved mixed forest. The nonlinear responses to exogenous N inputs and the critical level of N in terms of soil C fluxes should be considered in the ecological process models and ecosystem management.     

The interactive effects of elevated carbon dioxide and water table draw-down on carbon cycling in a Welsh ombrotrophic bog

The effects of elevated atmospheric CO₂ (eCO₂) and water table draw-down on soil carbon sequestration in an ombrotrophic bog ecosystem were examined. Peat monoliths (11 cm diameter, 25 cm deep) with intact bog vegetation were exposed to ambient or elevated (ambient + 200 mg l^?1) atmospheric CO₂, combined with a natural water table (level with the peat surface) or a water table draw-down (?5 cm). Eight observations per treatment were included in the study, which was conducted over a 12 week period. Concentration of dissolved organic carbon (DOC), phenolic compounds and the fluxes of CO₂ and CH₄ were measured. The eCO₂ treatment caused an increase in the CH₄ and CO₂ fluxes and a small decrease in both the DOC and phenolic concentrations. The water table draw-down invoked decreases in phenolic and DOC concentrations, a decrease in CH₄ flux and a small increase in CO₂ flux. The combined (eCO₂ + water table draw-down) treatment caused a larger than expected CH₄ flux decrease and CO₂ flux increase and an increase in DOC concentration. Our results suggest very different effects on the system dependent on the treatment applied. The draw-down treatment principally increased oxidation of the rhizosphere resulting in increased decomposition and as such a removal of material from the dissolved carbon pool. The data also suggest labile carbon availability may be limiting the rate of decomposition and so slowing inorganic nutrient and carbon pool turn-over. The elevated CO₂ addressed the labile-carbon limitation. Under the environment of the combined treatment, these limitations were effectively removed, culminating in a destabilisation of the carbon-sequestering environment to a weaker sink (or even a source) of atmospheric carbon.     

Elevated CO2 and water-availability effect on gas exchange and nodule development in N2-fixing alfalfa plants

N₂-fixing alfalfa plants were grown in controlled conditions at different CO₂ levels (350 μmol mol^?1 versus 700 μmol mol^?1) and water-availability conditions (WW, watered at maximum pot water capacity versus WD, watered at 50% of control treatments) in order to determine the CO₂ effect (and applied at two water regimes) on plant growth and nodule activity in alfalfa plants. The CO₂ stimulatory effect (26% enhancement) on plant growth was limited to WW plants, whereas no CO₂ effect was observed in WD plants. Exposure to elevated CO₂ decreased Rubisco carboxylation capacity of plants, caused by a specific reduction in Rubisco (EC 4.1.1.39) concentration (11% in WW and 43% in WD) probably explained by an increase in the leaf carbohydrate levels. Plants grown at 700 μmol mol^?1 CO₂ maintained control photosynthetic rates (at growth conditions) by diminishing Rubisco content and by increasing nitrogen use efficiency. Interestingly, our data also suggest that reduction in shoot N demand (reflected by the TSP and especially Rubisco depletion) affected negatively nodule activity (malate dehydrogenase, EC 1.1.1.37, and glutamate-oxaloacetate transaminase, EC 2.6.1.1, activities) particularly in water-limited conditions. Furthermore, nodule DM and TSS data revealed that those nodules were not capable to overcome C sink strength limitations.     

Thalassia testudinum response to the interactive stressors hypersalinity,sulfide and hypoxia

A large-scale mesocosm (sixteen 500 L tanks) experiment was conducted to investigate the effects of hypersalinity (45–65 psu), porewater sulfide (2–6 mM) and nighttime water column hypoxia (5–3 mg L⁻¹) on the tropical seagrass Thalassia testudinum Banks ex König. We examined stressor effects on growth, shoot survival, tissue sulfur (S⁰, TS, δ³⁴S) and leaf quantum efficiencies, as well as, porewater sulfides (∑TS_pw) and mesocosm water column O₂ dynamics. Sulfide was injected into intact seagrass cores of T. testudinum exposing below-ground tissues to 2, 4, and 6 mM S²⁻, but rapid oxidation resulted in ∑TS_pw < 1.5 mM. Hypersalinity at 65 psu lowered sulfide oxidation and significantly affected plant growth rates and quantum efficiencies (F_v/F_m < 0.70). The most depleted rhizome δ³⁴S signatures were also observed at 65 psu, suggesting increased sulfide exposure. Hypoxia did not influence ∑TS_pw and plant growth, but strengthened the hypersalinity response and decreased rhizome S⁰, indicating less efficient oxidation of ∑TS_pw. Following nighttime hypoxia treatments, ecosystem level metabolism responded to salinity treatments. When O₂ levels were reduced to 5 and 4 mg L⁻¹, daytime O₂ levels recovered to approximately 6 mg L⁻¹; however, this recovery was more limited when O₂ levels were lowered to 3 mg L⁻¹. Subsequent to O₂ reductions to 3 mg O₂ L⁻¹, nighttime O₂ levels rose in the 35 and 45 psu tanks, stayed the same in the 55 psu tanks, and declined in the 65 psu tanks. Thus, hypersalinity at 65 psu affects T. testudinum's oxidizing capacity and places subtle demands on the positive O₂ balance at an ecosystem level. This O₂ demand may influence T. testudinum die-off events, particularly after periods of high temperature and salinity. We hypothesize that the interaction between hypersalinity and sulfide toxicity in T. testudinum is their synergistic effect on the critical O₂ balance of the plant.     

A show cave management: Anthropogenic CO2 in atmosphere of Výpustek Cave (Moravian Karst,Czech Republic)

Anthropogenic impact on CO₂ levels was studied in the Bear Chamber of the Výpustek Cave, a show cave in the Moravian Karst (Czech Republic), during a period of active ventilation and enhanced attendance. The study showed that the natural CO₂ levels were controlled by (i) the natural CO₂ influxes from soils/epikarst (up to ∼5.64 × 10⁻² mol s⁻¹); and, (ii) the advective CO₂ fluxes out of cave atmosphere (up to 4.66 × 10⁻² mol s⁻¹). During visitor presence, the anthropogenic CO₂ flux into the chamber reached up to ∼0.13 mol s⁻¹ and exceeded all other CO₂ fluxes. The reachable anthropogenic steady states at sufficient duration of stay (up to 2.65 × 10⁻¹ mol m⁻³) could exceed the natural CO₂ levels by factor of more than nine based on the number of visitors. Recession analysis of anthropogenic pulses showed that intervals between individual visitor groups would have to be up to ∼6 h long if the cave environment has to return to natural conditions. As such pauses between individual tours are hardly realizable, a risk analysis was conducted to find the consequences of breaking natural conditions. It showed that the condition under which dripwater becomes aggressive to calcite (i.e., the point when P_CO2 in cave atmosphere exceeds the hypothetical CO₂ concentrations in epikarst that has participated on the water formation, P_CO2(H) = 10^−1.56) is potentially reachable under extreme conditions only (enormous visitor stay period and visitor number). In case of condensed water, however, any increase in CO₂ concentration will cause an increase of water aggressiveness to calcite. Therefore, in the periods and sites of enhanced condensation, it is important to strive for preservation of natural conditions.     

Factors that control Typha marsh evapotranspiration

There is continuing debate about the controls on wetland evapotranspiration (E_t) and whether marshes are profligate water users. We used eddy covariance to measure the CO₂ exchange and E_t by a California Tule marsh in 2003. The marsh was dominated by Typha and Scirpus, and there was a large amount of standing litter that acted as a mulch. Canopy development was broadly related to air temperature, with rapid growth in May and senescence in October. E_t was a few tenths of a mm d⁻¹ in winter, and 3–4 mm d⁻¹ in summer. The midsummer Bowen ratio was ∼1, and the annual E_t was 49 cm. The peak rate of E_t was lower than has been reported for marshes based on lysimeter studies, somewhat lower than has been reported for marshes based on micrometeorological studies, and equivalent to, or somewhat lower than, has been reported for upland grassland. The midsummer water use efficiency was 0.0025 mol CO₂ mol⁻¹ H₂O, and the δ¹³C of foliage was −27.1‰, which are both typical for productive C₃ ecosystems. Transpiration accounted for 80% of total E_t. Evaporation from water standing beneath the canopy and mulch layer was only a minor component of the marsh's hydrological budget. The low rate of evaporation from standing water was a result of cool water temperatures, which remained within a few degrees of the nocturnal minimum on most days. We believe the mulch layer acted in a way analogous to an electrical diode that allowed the upward loss of heat from the water to the atmosphere at night, and shut off the flux of heat from the atmosphere to the water during daytime, resulting in cool subcanopy water and low rates of evaporation. Our observations are inconsistent with the hypothesis that Tule marshes are inefficient water users, or that their rates of transpiration and CO₂ uptake are unusual compared to upland ecosystems.     

Effects of controlled irrigation on water potential,nitrogen uptake and biomass production in Dalbergia sissoo seedlings

Biomass production, pattern of nodulation, nutrient uptake, net photosynthetic rate (P_n), leaf temperature (T_leaf), leaf nitrate reductase (NR) activity and free proline of Dalbergia sissoo seedlings planted in containers with 120 kg soil were studied under different water stress levels to assess the productive potential of the species in dry areas. Seedlings were irrigated at 20 mm (W₁), 14 mm (W₂), 10 mm (W₃), 8 mm (W₄) throughout the experimental period to maintain the respective treatment up to the lowest soil water content of 7.43%, 5.64%, 4.30% and 3.23%, respectively. There was a treatment (W₅) in which seedling were irrigated once to −0.03 MPa and left without re-irrigation. Decreased irrigation level resulted in lowering of leaf water potential (LWP), net photosynthetic rate (P_n), total number of root nodules and nodule dry mass and nitrogen uptake in the seedling. P_n, leaf nitrate reductase (NR) activity and seedling biomass were highest in W₁ indicating a positive relations of NR activity with CO₂ assimilation and biomass production. The decrease in P_n, leaf NR activity and LWP was sharp at W₃ onwards. Monthly changes in the values of P_n, T_leaf and NR activity indicate environmental effect on these physiological variables. Proline was detected only in the seedlings of W₃, W₄ and W₅ treatments after February and was highest in the seedlings of W₅ treatment. The study suggests that severe water deficit adversely affect physiological and biochemical processes that resulted in reduced growth, nutrient uptake and biomass productivity in D. sissoo seedlings. Re-irrigation above W₃ level is recommended for this species.     

Effect of CO2 on growth and toxicity of Alexandrium tamarense from the East China Sea,a major producer of paralytic shellfish toxins

In recent decades, the frequency and intensity of harmful algal blooms (HABs), as well as a profusion of toxic phytoplankton species, have significantly increased in coastal regions of China. Researchers attribute this to environmental changes such as rising atmospheric CO₂ levels. Such addition of carbon into the ocean ecosystem can lead to increased growth, enhanced metabolism, and altered toxicity of toxic phytoplankton communities resulting in serious human health concerns. In this study, the effects of elevated partial pressure of CO₂ (pCO₂) on the growth and toxicity of a strain of Alexandrium tamarense (ATDH) widespread in the East and South China Seas were investigated. Results of these studies showed a higher specific growth rate (0.31 ± 0.05 day⁻¹) when exposed to 1000 μatm CO₂, (experimental), with a corresponding density of (2.02 ± 0.19) × 10⁷ cells L⁻¹, that was significantly larger than cells under 395 μatm CO₂₍control). These data also revealed that elevated pCO₂ primarily affected the photosynthetic properties of cells in the exponential growth phase. Interestingly, measurement of the total toxin content per cell was reduced by half under elevated CO₂ conditions. The following individual toxins were measured in this study: C1, C2, GTX1, GTX2, GTX3, GTX4, GTX5, STX, dcGTX2, dcGTX3, and dcSTX. Cells grown in 1000 μatm CO₂ showed an overall decrease in the cellular concentrations of C1, C2, GTX2, GTX3, GTX5, STX, dcGTX2, dcGTX3, and dcSTX, but an increase in GTX1 and GTX4. Total cellular toxicity per cell was measured revealing an increase of nearly 60% toxicity in the presence of elevated CO₂ compared to controls. This unusual result was attributed to a significant increase in the cellular concentrations of the more toxic derivatives, GTX1 and GTX4.Taken together; these findings indicate that the A. tamarense strain ATDH isolated from the East China Sea significantly increased in growth and cellular toxicity under elevated pCO₂ levels. These data may provide vital information regarding future HABs and the corresponding harmful effects as a result of increasing atmospheric CO₂.     

Stimuli responsive polymorphism of C12NO/DOPE/DNA complexes: Effect of pH,temperature and composition

N,N-dimethyldodecylamine-N-oxide (C₁₂NO) is a surfactant that may exist either in a neutral or cationic protonated form depending on the pH of aqueous solutions. Using small angle X-ray diffraction (SAXD) we observe the rich structural polymorphism of pH responsive complexes prepared due to DNA interaction with C₁₂NO/dioleoylphosphatidylethanolamine (DOPE) vesicles and discuss it in view of utilizing the surfactant for the gene delivery vector of a pH sensitive system. In neutral solutions, the DNA uptake is low, and a lamellar L_α phase formed by C₁₂NO/DOPE is prevailing in the complexes at 0.2 ≤ C₁₂NO/DOPE < 0.6 mol/mol. A maximum of ~ 30% of the total DNA volume in the sample is bound in a condensed lamellar phase L_α^C at C₁₂NO/DOPE = 1 mol/mol and pH 7.2. In acidic conditions, a condensed inverted hexagonal phase H_II^C was observed at C₁₂NO/DOPE = 0.2 mol/mol. Commensurate lattice parameters, a_HC ≈ d_LC, were detected at 0.3 ≤ C₁₂NO/DOPE ≤ 0.4 mol/mol and pH = 4.9–6.4 suggesting that L_α^C and H_II^C phases were epitaxially related. While at the same composition but pH ~ 7, the mixture forms a cubic phase (Pn3m) when the complexes were heated to 80 °C and cooled down to 20 °C. Finally, a large portion of the surfactant (C₁₂NO/DOPE > 0.5) stabilizes the L_α^C phase in C₁₂NO/DOPE/DNA complexes and the distance between DNA strands (d_DNA) is modulated by the pH value. Both the composition and pH affect the DNA binding in the complexes reaching up to ~ 95% of the DNA total amount at acidic conditions.     

Kinetic and anion inhibition studies of a β-carbonic anhydrase (FbiCA 1) from the C4 plant Flaveria bidentis

Several β-carbonic anhydrases (CAs, EC 4.2.1.1) are present in all land plants examined thus far. Here we report the first detailed biochemical characterization of one such isoform, FbiCA 1, from the C₄ plant Flaveria bidentis, which was cloned, purified and characterized as recombinant protein. FbiCA 1 has an interesting CO₂ hydrase catalytic activity (k_cat of 1.2 × 10⁵ and k_cat/K_m of 7.5 × 10⁶ M^?1 × s^?1) and was moderately inhibited by most simple/complex inorganic anions. Potent FbiCA 1 inhibitors were also detected, such as trithiocarbonate, diethyldithiocarbamate, sulfamide, sulfamic acid, phenylboronic acid and phenylarsonic acid (K_Is in the range of 4–60 μM). Such inhibitors may be used as tools to better understand the role of various β-CA isoforms in photosynthesis.     

Partitioning of latent heat flux at a northern peatland

The partitioning of latent heat flux (Q_E) to vascular plant and moss surface components was assessed for a Sphagnum-dominated bog with a hummock–hollow surface having a sparse canopy of low shrubs. Results from porometry and eddy covariance measurements of Q_E showed evaporation from the moss surface ranged from greater than 50% of total Q_E early in the growing season to less than 20% after a dry period toward the end of the growing season. Both soil moisture and vapour pressure deficit (D_a) affected this partitioning with drier moss and peat, lower water table, and smaller D_a all reducing moss Q_E. Daily maximum moss Q_E ranged from greater than 200 W m⁻² early in the growing season to less than 100 W m⁻² during a dry period. In contrast, vascular contribution to total Q_E increased over the season from a daily maximum of about 150 W m⁻² to 250 W m⁻² due to increase in leaf area by leaf replacement and emergence and to drying of the moss surface. Porometry results showed average daily maximum conductance from bog shrubs was near 8 mm s⁻¹. These conductance values were smaller than those reported for vascular plants from more nutrient-rich wetlands. The effect of increases in D_a on vascular Q_E were moderated by decreases in stomatal conductance. At constant available energy, vascular leaf conductance was reduced by as much as 2 mm s⁻¹ and moss surface conductance was enhanced by up to 3 mm s⁻¹ by large D_a. Considering vascular and non-vascular water transport characteristics and frequency of water table position and given the observed variations of Q_E partitioning with water table location and moss and peat water content, it is suggested that modelling efforts focus on how dry hummocks and wet hollows each contribute to Q_E, especially as related to D_a and soil moisture dynamics.     

Temperature response of C4 species big bluestem (Andropogon gerardii) is modified by growing carbon dioxide concentration

Climate change factors interact to modify plant growth and development. The objective of this study was to evaluate the response to temperature of big bluestem (Andropogon gerardii Vitman) development, growth, reproduction and biomass partitioning under low and high carbon dioxide concentrations ([CO₂]) grown in controlled environmental conditions. Ten sunlit soil–plant–atmosphere-research (SPAR) chambers were used to study the effects of two [CO₂] of low (360 μL L⁻¹) and high (720 μL L⁻¹), and five different day/night temperatures of 20/12, 25/17, 30/22, 35/27 and 40/32 °C. Big bluestem cv. Bonelli seeds were sown in pure, fine sand, in 11 rows at equal spacing and after emergence were thinned to 10 plants per row. At maturity, individual plants were harvested and divided into leaves, stems, panicles and roots. Biomass decreased either above or below the optimum temperature of 30/22 °C. The effect of high [CO₂] on biomass accumulation (12–30% increase) was visible at less than optimum temperature (30/22 °C) and absent at two high temperatures. With increase in temperature, irrespective of the [CO₂], biomass partitioned to leaves increased (35%) where as that to stems decreased (33%). Panicle weight was 6–7% of biomass at 25/17 °C and fell to 1.6% at 40/32 °C. The biomass partitioned to roots, across the temperatures, was constant for plants grown at low [CO₂] but decreased by 7% for those grown at high [CO₂]_. The decrease in panicle/seed production at two high temperatures (>30/22 °C) might reduce this species population and dominance in tallgrass prairies. The temperature response functions at different [CO₂] will be useful to improve the predictive capabilities of dynamic global vegetation models in simulating dynamics of rangelands, where big bluestem is the dominant species.     

Tropical epiphytes in a CO2-rich atmosphere

We tested the effect on epiphyte growth of a doubling of pre-industrial CO₂ concentration (280 vs. 560 ppm) combined with two light (three fold) and two nutrition (ten fold) treatments under close to natural humid conditions in daylight growth cabinets over 6 months. Across co-treatments and six species, elevated CO₂ increased relative growth rates by only 6% (p = 0.03). Although the three C3 species, on average, grew 60% faster than the three CAM species, the two groups did not significantly differ in their CO₂ response. The two Orchidaceae, Bulbophyllum (CAM) and Oncidium (C3) showed no CO₂ response, and three out of four Bromeliaceae showed a positive one: Aechmea (CAM, +32% p = 0.08), Catopsis (C3, +11% p = 0.01) and Vriesea (C3, +4% p = 0.02). In contrast, the representative of the species-rich genus Tillandsia (CAM), which grew very well under experimental conditions, showed no stimulation. On average, high light increased growth by 21% and high nutrients by 10%. Interactions between CO₂, light and nutrient treatments (low vs. high) were inconsistent across species. CO₂ responsive taxa such as Catopsis, could accelerate tropical forest dynamics and increase branch breakage, but overall, the responses to doubling CO₂ of these epiphytes was relatively small and the responses were taxa specific.