Improving and evaluating the soil cover indicator for agricultural land in Canada

A soil cover days (SCD) model has been developed by Agriculture and Agri-Food Canada for use as an agri-environmental indicator to monitor the relationship between agricultural production activities and agri-environmental quality. The SCD indicator integrates information on crops, soils, climate, and field activities to estimate the total equivalent number of days that agricultural soils are covered by crop canopy, crop residue and snow in a given year. Daily cover fractions of plant and residue for a given crop in an ecoregion are simulated using typical crop calendar and field management practices, and the equivalent number of days that soil is covered by snow in winter is derived from long term climate normals. The equivalent SCD for a spatial unit is then derived as the area-weighted sum of different crops and different management practices within the unit. This paper presents the SCD framework, details an assessment of the accuracy of the model and outlines future improvements. Annual snow days derived from 30-year climate normals as used in the model was strongly correlated (excluding mountain areas) with that derived from satellite data (R² = 0.45, n = 48), even though the remote sensing product showed significant temporal and spatial variability. Crop residue fraction estimated by the model was strongly correlated with field data collected over major crop areas and crop types (R² = 0.74, n = 55), and modelled plant cover fraction was well correlated with that derived from remote sensing data (R² = 0.57, n = 57). Large discrepancies were observed for some samples due to deviation of the actual crop calendar from that estimated using climate normals. National map showing the change in the indicator from 1981 to 2011 reveals changes in crop and residue management practices.     

Growth and development of cotton (Gossypium hirsutum L.) in response to CO2 enrichment under two different temperature regimes

An increase in atmospheric CO₂ concentration ([CO₂]) together with other climate change factors could greatly affect agricultural productivity. Understanding the impact of the change in atmospheric [CO₂] in conjunction with the ongoing global change is crucial to prepare for mitigation and any adaptation for future agricultural production. The main goal of this project was to study the time-course pattern of cotton plant growth in response to [CO₂] and temperature to investigate the hypothesis that whether response to elevated [CO₂] would change at different temperatures. An experiment was conducted in the controlled-environment chambers of the Georgia Envirotron with two different day/night temperatures levels, e.g., 25/15 °C and 35/25 °C, and three CO₂ concentrations, e.g., 400, 600 and 800 μmol l^?1. The experimental design was completely randomized with four replicates (plastic containers) per treatment. Growth analysis was conducted at bi-weekly intervals during the growing season. In addition, leaf area, leaf dry mass, root dry mass, square dry mass, boll dry mass and total above dry mass per plant were also measured at each sampling. Plant traits, including plant height, number of leaves, number of squares and number of bolls were recorded weekly. The number of days to emergence, squaring, flowering and maturity were also observed. The results showed that by increasing [CO₂] to 600 μmol l^?1 total biomass increased at both temperature levels, but a further increase of [CO₂] up to 800 μmol l^?1 increased total biomass only at the temperature of 35/25 °C. Throughout the growing season, there was no significant effect of [CO₂] levels on LAI. Increasing temperature from 25/15 °C to 35/25 °C had a positive impact on LAI across all CO₂ levels (P < 0.05). Increasing CO₂ from 400 to 600 μmol l^?1 significantly increased the number of squares by 31.4%, but a further increase to 800 μmol l^?1 caused a 6.6% decrease (non-significant) in the number of squares. The interactive effects of [CO₂] and temperature indicated that at a higher temperature, CO₂ would be more beneficial as we proceed towards the end of the growing season. However, further studies are needed to really understand the interaction between higher [CO₂] and temperature levels and cultivar characteristics.     

Plasticity of rice tiller production is related to genotypic variation in the biomass response to elevated atmospheric CO2 concentration and low temperatures during vegetative growth

Appropriate resource partitioning to either production of new tillers or growth of individual tillers is a critical factor for increasing rice biomass production and facilitating adaptation to climate change. We examined the contributions of genotypic variation to the tiller number and individual tiller growth of 24 rice cultivars in response to an elevated atmospheric CO₂ concentration [CO₂] (control + 191 μmol mol⁻¹) and a low air temperature (control minus 4.7 °C) during 56 days of vegetative growth after transplanting. For all genotypes combined, biomass increased by 27% under elevated [CO₂] and decreased by 34% at low temperature, with a significant genotype × temperature interaction. The increase caused by elevated [CO₂] resulted from increased tiller number, and the decrease caused by low temperature resulted from decreased growth of individual tillers. Despite the different overall responses to elevated [CO₂] and low temperature, most of the genotypic variation in biomass at elevated [CO₂] and low temperature was explained by the responses of tiller number rather than by individual tiller growth. The genotypes with the highest biomass response to elevated [CO₂] had a smaller reduction of biomass under low temperature. These results highlight the greater importance of genotypic variation in tiller number than in individual tiller growth in the response of biomass to environmental change.     

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.     

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.     

Diurnal exchanges of CO2 and CH4 across the water–atmosphere interface in a water chestnut meadow (Trapa natans L.)

CH₄ and CO₂ fluxes across the water–atmosphere interface were measured over a 24 h day–night cycle in a shallow oxbow lake colonized by the water chestnut (Trapa natans L.) (Lanca di Po, Northern Italy). Only exchanges mediated by macrophytes were measured, whilst gas ebullition was not considered in this study. Measurements were performed from 29 to 30 July 2005 with short incubations, when T. natans stands covered the whole basin surface with a mean dry biomass of 504 ± 91 g m⁻². Overall, the oxbow lake resulted net heterotrophic with plant and microbial respiration largely exceeding carbon fixation by photosynthesis. The water chestnut stand was a net sink of CO₂ during the day-light period (−60.5 ± 8.5 mmol m⁻² d⁻¹) but it was a net source at night (207.6 ± 6.1 mmol m⁻² d⁻¹), when the greatest CO₂ efflux rate was measured across the water surface (28.2 ± 2.4 mmol m⁻² h⁻¹). The highest CH₄ effluxes (6.6 ± 1.8 mmol m⁻² h⁻¹) were determined in the T. natans stand during day-time, whilst CH₄ emissions across the plant-free water surface were greatest at night (6.8 ± 2.1 mmol m⁻² h⁻¹). Therefore, we assumed that the water chestnut enhanced methane delivery to the atmosphere. On a daily basis, the oxbow lake was a net source to the atmosphere of both CO₂ (147.1 ± 10.8 mmol m⁻² d⁻¹) and CH₄ (116.3 ± 8.0 mmol m⁻² d⁻¹).     

Temporal and seasonal changes in greenhouse gas emissions from a constructed wetland purifying peat mining runoff waters

Constructed wetlands (CW), widely used to remove nutrients from runoff waters, transform some of the carbon and nitrogen they receive into greenhouse gases, carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), and may therefore have adverse atmospheric impacts. We studied seasonal and temporal changes in C degradation and emissions of CH₄ and N₂O of a boreal CW used to purify peat mining runoff waters 5 (in 1992) and 15 (in 2001–2002) years after construction. There was a remarkable change in the cycling of carbon in the wetland as the number of years in operation increased: the mean CH₄ emission tripled from 140 to 400 mg CH₄ m⁻² d⁻¹ and the mean CO₂ release (respiration) doubled from 7270 to 13 600 mg CO₂ m⁻² d⁻¹ in the 10-year period. The reasons for the increased C gas production were the increased plant biomass, which doubled in 10 years, and a 3 °C higher average temperature in 2002 than in 1992. The N₂O fluxes did not change during the study period: the mean emissions were 340 and 450 μg N₂O m⁻² d⁻¹ in 1992 and 2002.     

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.     

Energy balance and greenhouse gas emissions in organic and conventional avocado orchards in Mexico

There is a worldwide growing awareness of the negative impacts of the increasing fossil fuel reliance and greenhouse gas (GHG) emissions from agriculture, in particular for intensive crop systems. We analyze the energy balances and greenhouse gas emissions from export-oriented avocado orchards in Mexico. Avocado is a very important export crop and one of the main drivers of land-use change in the country. We compared 12 avocado orchards under organic and conventional management during two production cycles (2010 and 2011) in a representative region of Central Mexico. Our analysis shows no significant differences in energy consumption and GHG emissions between organic and conventional systems with 55 and 56 GJ ha⁻¹, and 3.30 t CO₂ equiv. ha⁻¹ and 3.57 t CO₂ equiv. ha⁻¹, respectively.Organic systems show three times more use of renewable energy than their conventional counterparts. However both systems depend heavily on fossil fuel inputs, machinery and N-fertilizers (synthetic or organic). Also, there is a high heterogeneity in management practices and input application within both systems, which is reflected in a large variation of their energy-related parameters. Given that avocado production is rapidly expanding in Mexico, a move toward organic production without systematically changing toward less fossil fuel dependent agricultural practices would not be sufficient to ensure a sustainable production.     

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.     

The dinoflagellate Akashiwo sanguinea will benefit from future climate change: The interactive effects of ocean acidification,warming and high irradiance on photophysiology and hemolytic activity

Due to global climate change, marine phytoplankton will likely experience low pH (ocean acidification), high temperatures and high irradiance in the future. Here, this work report the results of a batch culture experiment conducted to study the interactive effects of elevated CO₂, increased temperature and high irradiance on the harmful dinoflagellate Akashiwo sanguinea, isolated at Dongtou Island, Eastern China Sea. The A. sanguinea cells were acclimated in high CO₂ condition for about three months before testing the responses of cells to a full factorial matrix experimentation during a 7-day period. This study measured the variation in physiological parameters and hemolytic activity in 8 treatments, representing full factorial combinations of 2 levels each of exposure to CO₂ (400 and 1000 μatm), temperature (20 and 28 °C) and irradiance (50 and 200 μmol photons m⁻² s⁻¹). Sustained growth of A. sanguinea occurred in all treatments, but high CO₂ (HC) stimulated faster growth than low CO₂ (LC). The pigments (chlorophyll a and carotenoid) decreased in all HC treatments. The quantum yield (F_v/F_m) declined slightly in all high-temperature (HT) treatments. High irradiance (HL) induced the accumulation of ultraviolet-absorbing compounds (UV_abc) irrespective of temperature and CO₂. The hemolytic activity in the LC treatments, however, declined when exposed to HT and HL, but HC alleviated the adverse effects of HT and HL on hemolytic activity. All HC and HL conditions and the combinations of high temperature*high light (HTHL) and high CO₂*high temperature*high light (HCHTHL) positively affected the growth in comparison to the low CO₂*low temperature*low light (LCLTLL) treatment. High temperature (HT), high light (HL) and a combination of HT*HL, however, negatively impacted hemolytic activity. CO₂ was the main factor that affected the growth and hemolytic activity. There were no significant interactive effects of CO₂*temperature*irradiance on growth, pigment, F_v/F_m or hemolytic activity, but there were effects on P_m, α, and E_k. If these results are extrapolated to the natural environment, it can be hypothesized that A. sanguinea cells will benefit from the combination of ocean acidification, warming, and high irradiance that are likely to occur under future climate change. It is assumed that faster growth and higher hemolytic activity and UV_abc of this species will occur under future conditions compared with those the current CO₂ (400 μatm) and temperature (20 °C) conditions.     

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.     

Exposures to elevated CO2, elevated temperature and enhanced UV-B radiation modify activities of polyphenol oxidase and guaiacol peroxidase and concentrations of chlorophylls,polyamines and soluble proteins in the leaves of Betula pendula seedlings

The activity of polyphenol oxidase (PPO) and guaiacol peroxidase (POD) and the concentrations of chlorophylls, free polyamines and soluble proteins were determined from the leaves of six genotypes of silver birch (Betula pendula Roth) seedlings exposed to short-term elevated carbon dioxide (CO₂), temperature (T), ultraviolet-B irradiation (UV-B, 280-315 nm) and their combinations. Results showed that the activity of PPO in the leaves was low but increased by elevated CO₂ and elevated T. The POD activity varied between the genotypes due to an interactive effect of CO₂ × UV-B. The soluble proteins were clearly decreased by elevated CO₂, but the level of response varied among the genotypes. The concentrations of chl a and total chlorophylls were lower in the leaves treated with elevated CO₂ than in leaves grown at ambient CO₂. An interactive effect of CO₂ × UV-B on the chl a/b ratio was found. Elevated T increased chl b concentration and decreased chl a/b ratio. Temperature treatments also caused variation in the concentrations of chl a, chl b and total chlorophylls among the genotypes. Polyamine analyses showed that the concentrations of putrescine were increased and spermine decreased in leaves treated with elevated T. However, the change in putrescine by elevated T was clearer at ambient CO₂ than in eCO₂ environment (significant effect of T × CO₂). In conclusion, the defensive enzymes, photosynthetic pigments, soluble proteins and growth-regulating polyamines in silver birch leaves were not susceptible to enhanced UV-B radiation. In contrast, all the variables responded to elevated T and/or elevated CO₂, reflecting the enhancive effects of climate change conditions not only on leaf productivity, but also on leaf turn-over rate. Most of these climate-driven changes were not regulated by UV-B radiation.     

The mechanism(s) involved in the photoprotection of PSII at elevated CO2 in nodulated alfalfa plants

In a previous study, we found that enhanced CO₂ subjected to nodulated alfalfa plants grown at different temperatures (ambient and ambient + 4 °C) and water availability regimes could protect PSII from photodamage. The main objective of this study was to determine the mechanism(s) involved in the photoprotection of PSII at elevated CO₂ levels in this plant. Elevated CO₂ reduced carboxylation capacity-induced photosynthetic acclimation and reduced enzymatic and/or nonenzymatic antioxidant activities, suggesting that changes in electron flow did not cause any photooxidative damage (which was also confirmed by H₂O₂ and lipid peroxidation analyses). Enhanced nonphotochemical quenching and xanthophyll cycle pigments revealed that plants grown at 700 μmol mol⁻¹ CO₂ compensated for the reduction in energy sink with a larger capacity for nonphotochemical dissipation of excitation energy as heat, i.e., modulating the status of the VAZ components. Elevated CO₂ induced the de-epoxidation of violaxanthin to zeaxanthin, facilitating thermal dissipation and protecting the photosynthetic apparatus against the deleterious effect of excess excitation energy.     

The mechanism(s) involved in the photoprotection of PSII at elevated CO2 in nodulated alfalfa plants

In a previous study, we found that enhanced CO₂ subjected to nodulated alfalfa plants grown at different temperatures (ambient and ambient + 4 °C) and water availability regimes could protect PSII from photodamage. The main objective of this study was to determine the mechanism(s) involved in the photoprotection of PSII at elevated CO₂ levels in this plant. Elevated CO₂ reduced carboxylation capacity-induced photosynthetic acclimation and reduced enzymatic and/or nonenzymatic antioxidant activities, suggesting that changes in electron flow did not cause any photooxidative damage (which was also confirmed by H₂O₂ and lipid peroxidation analyses). Enhanced nonphotochemical quenching and xanthophyll cycle pigments revealed that plants grown at 700 μmol mol^?1 CO₂ compensated for the reduction in energy sink with a larger capacity for nonphotochemical dissipation of excitation energy as heat, i.e., modulating the status of the VAZ components. Elevated CO₂ induced the de-epoxidation of violaxanthin to zeaxanthin, facilitating thermal dissipation and protecting the photosynthetic apparatus against the deleterious effect of excess excitation energy.     

Effects of gradual versus step increases in carbon dioxide on Plantago photosynthesis and growth in a microcosm study

This study investigated the effects of a gradual versus step increases in carbon dioxide (CO₂) on plant photosynthesis and growth at two nitrogen (N) levels. Plantago lanceolata were grown for 80 days and then treated with the ambient CO₂ (as the control), gradual CO₂ increase and step CO₂ increase as well as low and high N additions for 70 days. While [CO₂] were kept at constant 350 and 700 μmol mol⁻¹ for the ambient and step CO₂ treatments, respectively, [CO₂] in the gradual CO₂ treatment was raised by 5 μmol mol⁻¹ day⁻¹, beginning at 350 μmol mol⁻¹ and reaching 700 μmol mol⁻¹ by the end of experiment. The step CO₂ treatment immediately resulted in an approximate 50% increase in leaf photosynthetic carbon fixation at both the low and high N additions, leading to a 20–24% decrease in leaf N concentration. The CO₂-induced nitrogen stress, in return, resulted in partial photosynthetic downregulation since the third week at the low N level and the fourth week at the high N level after treatments. In comparison, the gradual CO₂ treatment induced a gradual increase in photosynthetic carbon fixation, leading to less reduction in leaf N concentration. In comparison to the ambient CO₂, both the gradual and step CO₂ increases resulted in decreases in specific leaf area, leaf N concentration but an increase in plant biomass. Responses of plant shoot:root ratio to CO₂ treatments varied with N supply. It decreased with low N supply and increased with high N supply under the gradual and step CO₂ treatments relative to that under the ambient CO₂. Degrees of those changes in physiological and growth parameters were usually larger under the step than the gradual CO₂ treatments, largely due to different photosynthetic C influxes under the two CO₂ treatments.     

Tillage effects on carbon footprint and ecosystem services of climate regulation in a winter wheat–summer maize cropping system of the North China Plain

Inappropriate farm practices can increase greenhouse gases (GHGs) emissions and reduce soil organic carbon (SOC) sequestration, thereby increasing carbon footprints (CFs), jeopardizing ecosystem services, and affecting climate change. Therefore, the objectives of this study were to assess the effects of different tillage systems on CFs, GHGs emissions, and ecosystem service (ES) values of climate regulation and to identify climate-resilient tillage practices for a winter wheat (Triticum aestivum L.)-summer maize (Zea mays L.) cropping system in the North China Plain (NCP). The experiment was established in 2008 involving no-till with residue retention (NT), rotary tillage with residue incorporation (RT), sub-soiling with residue incorporation (ST), and plow tillage with residue incorporation (PT). The results showed that GHGs emissions from agricultural inputs were 6432.3–6527.3 kg CO₂-eq ha⁻¹ yr⁻¹ during the entire growing season, respectively. The GHGs emission from chemical fertilizers and irrigation accounted for >80% of that from agricultural inputs during the entire growing season. The GHGs emission from agricultural inputs were >2.3 times larger in winter wheat than that in the summer maize season. The CFs at yield-scale during the entire growing season were 0.431, 0.425, 0.427, and 0.427 without and 0.286, 0.364, 0.360, and 0.334 kg CO₂-eq kg⁻¹ yr⁻¹ with SOC sequestration under NT, RT, ST, and PT, respectively. Regardless of SOC sequestration, the CFs of winter wheat was larger than that of summer maize. Agricultural inputs and SOC change contributed mainly to the component of CFs of winter wheat and summer maize. The ES value of climate regulation under NT was ¥159.2, 515.6, and 478.1 ha⁻¹ yr⁻¹ higher than that under RT, ST, and PT during the entire growing season. Therefore, NT could be a preferred “Climate-resilient” technology for lowering CFs and enhancing ecosystem services of climate regulation for the winter wheat–summer maize system in the NCP.     

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.     

Regulating effects of climate,net primary productivity,and nitrogen on carbon sequestration rates in temperate wetlands,Northeast China

Temperate wetlands in the Northern Hemisphere have high long-term carbon sequestration rates, and play critical roles in mitigating regional and global atmospheric CO₂ increases at the century timescale. We measured soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) from 11 typical freshwater wetlands (Heilongjiang Province) and one saline wetland (Jilin Province) in Northeast China, and estimated carbon sequestration rates using ²¹⁰Pb and ¹³⁷Cs dating technology. Effects of climate, net primary productivity, and nutrient availability on carbon sequestration rates (R_carbon) were also evaluated. Chronological results showed that surface soil within the 0–40 cm depth formed during the past 70–205 years. Soil accretion rates ranged from 2.20 to 5.83 mm yr⁻¹, with an average of 3.84 ± 1.25 mm yr⁻¹ (mean ± SD). R_carbon ranged from 61.60 to 318.5 gC m⁻² yr⁻¹ and was significantly different among wetland types. Average R_carbon was 202.7 gC m⁻² yr⁻¹ in the freshwater wetlands and 61.6 gC m⁻² yr⁻¹ in the saline marsh. About 1.04 × 10⁸ tons of carbon was estimated to be captured by temperate wetland soils annually in Heilongjiang Province (in the scope of 45.381–51.085°N, 125.132–132.324°E). Correlation analysis showed little impact of net primary productivity (NPP) and soil nutrient contents on R_carbon, whereas climate, specifically the combined dynamics of temperature and precipitation, was the predominant factor affecting R_carbon. The negative relationship observed between R_carbon and annual mean temperature (T) indicates that warming in Northeast China could reduce R_carbon. Significant positive relationships were observed between annual precipitation (P), the hydrothermal coefficient (defined as P/AT, where AT was accumulative temperature ≥10 °C), and R_carbon, indicating that a cold, humid climate would enhance R_carbon. Current climate change in Northeast China, characterized by warming and drought, may form positive feedbacks with R_carbon in temperate wetlands and accelerate carbon loss from wetland soils.     

Growth of the fungus Paecilomyces lilacinus with n-hexadecane in submerged and solid-state cultures and recovery of hydrophobin proteins

The filamentous fungus Paecilomyces lilacinus was grown on n-hexadecane in submerged (SmC) and solid-state (SSC) cultures. The maximum CO₂ production rate in SmC (V_max = 11.7 mg CO₂ L_g⁻¹ day⁻¹) was three times lower than in SSC (V_max = 40.4 mg CO₂ L_g⁻¹ day⁻¹). The P. lilacinus hydrophobin (PLHYD) yield from the SSC was 1.3 mg PLHYD g protein⁻¹, but in SmC, this protein was not detected. The PLHYD showed a critical micelle concentration of 0.45 mg mL⁻¹. In addition, the PLHYD modified the hydrophobicity of Teflon from 130.1 ± 2° to 47 ± 2°, forming porous structures with some filaments <1 μm and globular aggregates <0.25 μm diameter. The interfacial studies of this PLHYD could be the basis for the use of the protein to modify surfaces and to stabilize compounds in emulsions.