Gas exchange acclimation to elevated CO2 in upper-sunlit and lower-shaded canopy leaves in relation to nitrogen acquisition and partitioning in wheat grown in field chambers

Growth at elevated CO₂ often decreases photosynthetic capacity (acclimation) and leaf N concentrations. Lower-shaded canopy leaves may undergo both CO₂ and shade acclimation. The relationship of acclimatory responses of flag and lower-shaded canopy leaves of wheat (Triticum aestivum L.) to the N content, and possible factors affecting N gain and distribution within the plant were investigated in a wheat crop growing in field chambers set at ambient (360 μmol mol⁻¹) and elevated (700 μmol mol⁻¹) CO₂, and with two amounts of N fertilizer (none and 70 kg ha⁻¹ applied on 30 April). Photosynthesis, stomatal conductance and transpiration at a common measurement CO₂, chlorophyll and Rubisco levels of upper-sunlit (flag) and lower-shaded canopy leaves were significantly lower in elevated relative to ambient CO₂-grown plants. Both whole shoot N and leaf N per unit area decreased at elevated CO₂, and leaf N declined with canopy position. Acclimatory responses to elevated CO₂ were enhanced in N-deficient plants. With N supply, the acclimatory responses were less pronounced in lower canopy leaves relative to the flag leaf. Additional N did not increase the fraction of shoot N allocated to the flag and penultimate leaves. The decrease in photosynthetic capacity in both upper-sunlit and lower-shaded leaves in elevated CO₂ was associated with a decrease in N contents in above-ground organs and with lower N partitioning to leaves. A single relationship of N per unit leaf area to the transpiration rate accounted for a significant fraction of the variation among sun-lit and shaded leaves, growth CO₂ level and N supply. We conclude that reduced stomatal conductance and transpiration can decrease plant N, leading to acclimation to CO₂ enrichment.     

Temperature dependence of growth,development, and photosynthesis in maize under elevated CO2

Global atmospheric carbon dioxide concentrations (C_a) are rising. As a consequence, recent climate models have projected that global surface air temperature may increase 1.4–5.8 °C with the doubling of C_a by the end of the century. Because, changes in C_a and temperature are likely to occur concomitantly, it is important to evaluate how the temperature dependence of key physiological processes are affected by rising C_a in major crop plants including maize (Zea mays L.), a globally important grain crop with C₄ photosynthetic pathway. We investigated the temperature responses of photosynthesis, growth, and development of maize plants grown at five temperature regimes ranging from 19/13 to 38.5/32.5 °C under current (370 μmol mol⁻¹) and doubled (750 μmol mol⁻¹) C_a throughout the vegetative stages using sunlit controlled environmental chambers in order to test if the temperature dependence of these processes was altered by elevated C_a. Leaf and canopy photosynthetic rates, C₄ enzyme activities, leaf appearance rates, above ground biomass accumulation and leaf area were measured. We then applied temperature response functions (e.g., Arrhenius and Beta distribution models) to fit the measured data in order to provide parameter estimates of the temperature dependence for modeling photosynthesis and development at current and elevated C_a in maize. Biomass, leaf area, leaf appearance rate, and photosynthesis measured at growth C_a was not changed in response to CO₂ enrichment. Carboxylation efficiency and the activities of C₄ enzymes were reduced with CO₂ enrichment indicating possible photosynthetic acclimation of the C₄ cycle. All measured parameters responded to growth temperatures. Leaf appearance rate and leaf photosynthesis showed curvilinear response with optimal temperatures near 32 and 34 °C, respectively. Total above ground biomass and leaf area were negatively correlated with growth temperature. The dependence of leaf appearance rate, biomass, leaf area, leaf and canopy photosynthesis, and C₄ enzyme activities on growth temperatures was comparable between current and elevated C_a. The results of this study suggest that the temperature effects on growth, development, and photosynthesis may remain unchanged in elevated C_a compared with current C_a in maize.     

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.     

Effects of the endoparasitoid Cotesia chilonis (Hymenoptera: Braconidae) parasitism,venom, and calyx fluid on cellular and humoral immunity of its host Chilo suppressalis (Lepidoptera: Crambidae) larvae

The larval endoparasitoid Cotesia chilonis injects venom and bracoviruses into its host Chilo suppressalis during oviposition. Here we study the effects of the polydnavirus (PDV)-carrying endoparasitoid C. chilonis (Hymenoptera: Braconidae) parasitism, venom and calyx fluid on host cellular and humoral immunity, specifically hemocyte composition, cellular spreading, encapsulation and melanization. Total hemocyte counts (THCs) were higher in parasitized larvae than in unparasitized larvae in the late stages following parasitization. While both plasmatocyte and granulocyte fractions and hemocyte mortality did not differ between parasitized and unparasitized hosts, in vitro spreading behavior of hemocytes was inhibited significantly by parasitism throughout the course of parasitoid development. C. chilonis parasitism suppressed the encapsulation response and melanization in the early stages. Venom alone did not alter cellular immune responses, including effects on THCs, mortality, hemocyte composition, cell spreading and encapsulation, but venom did inhibit humoral immunity by reducing melanization within 6 h after injection. In contrast to venom, calyx fluid had a significant effect on cell spreading, encapsulation and melanization from 6 h after injection. Dose–response injection studies indicated the effects of venom and calyx fluid synergized, showing a stronger and more persistent reduction in immune system responses than the effect of either injected alone.     

Pea plant responsiveness under elevated [CO2] is conditioned by the N source (N2 fixation versus NO3− fertilization)

The main goal of this study was to test the effect of [CO₂] on C and N management in different plant organs (shoots, roots and nodules) and its implication in the responsiveness of exclusively N₂-fixing and NO₃⁻-fed plants. For this purpose, exclusively N₂-fixing and NO₃⁻-fed (10 mM) pea (Pisum sativum L.) plants were exposed to elevated [CO₂] (1000 μmol mol⁻¹ versus 360 μmol mol⁻¹ CO₂). Gas exchange analyses, together with carbohydrate, nitrogen, total soluble proteins and amino acids were determined in leaves, roots and nodules. The data obtained revealed that although exposure to elevated [CO₂] increased total dry mass (DM) in both N treatments, photosynthetic activity was down-regulated in NO₃⁻-fed plants, whereas N₂-fixing plants were capable of maintaining enhanced photosynthetic rates under elevated [CO₂]. In the case of N₂-fixing plants, the enhanced C sink strength of nodules enabled the avoidance of harmful leaf carbohydrate build up. On the other hand, in NO₃⁻-fed plants, elevated [CO₂] caused a large increase in sucrose and starch. The increase in root DM did not contribute to stimulation of C sinks in these plants. Although N₂ fixation matched plant N requirements with the consequent increase in photosynthetic rates, in NO₃⁻-fed plants, exposure to elevated [CO₂] negatively affected N assimilation with the consequent photosynthetic down-regulation.     

Comparison of Zostera marina and maerl community metabolism

The photosynthetic and repiratory metabolism of Zostera marina and maerl communities was compared, in the same area of the Bay of Brest in March–April, using benthic chambers. P–E curves for both oxygen and carbon were established for bottom irradiances between 0 and 525 μmol m⁻² s⁻¹. An exponential function was fitted to calculate daily production. Community metabolic quotients did not differ for maerl and seagrass beds. Community photosynthetic quotients were significantly higher (1.19) whereas community respiratory quotients were lower (0.70) than 1. Maerl and seagrass bed P–E curves mainly differed by the minimum saturating irradiance (E_k). Net community production was estimated to 26.8 mmol C m⁻² d⁻¹ for Z. marina meadows and 8.6 mmol C m⁻² d⁻¹ for maerl beds. The two communities can, therefore, be considered as autotrophic during the March–April period. Community respiration did not differ between Z. marina meadows and maerl beds, with an average value of 53.8 mmol C m⁻² d⁻¹ during a day. In similar environmental conditions, the production of maerl beds corresponds to approximately one third that of seagrass meadows. The maerl communities, therefore, form productive ecosystems, relevant to temperate coastal ecosystems functioning.     

Combined effects of temperature and salinity on functional responses of haemocytes and survival in air of the clam Ruditapes philippinarum

The combined effects of temperature and salinity on both immune responses and survival in air of the clam, Ruditapes philippinarum, were evaluated for the first time. The animals were kept for 7 days at three differing temperature (5 °C, 15 °C, 30 °C) and salinity values (18 psu, 28 psu, 38 psu), and effects of the resulting 9 experimental conditions on total haemocyte count (THC), Neutral Red uptake (NRU), haemolymph protein concentration, and lysozyme activity in both haemocyte lysate (HL) and cell-free haemolymph (CFH) were evaluated. The survival-in-air test was also performed. Two-way ANOVA analysis revealed that temperature influenced significantly THC and NRU, whereas salinity and temperature/salinity interaction affected NRU only. Temperature and salinity did not influence significantly HL and CFH lysozyme activity, as well as haemolymph total protein content. Survival-in-air test is widely used to evaluate general stress conditions in clams. In the present study, temperature and salinity were shown to influence the resistance to air exposure of R. philippinarum. The highest LT₅₀ (air exposure time resulting in 50% mortality) value was recorded in clams kept at 18 psu and 15 °C, whereas the lowest value was observed in clams kept at 28 psu and 30 °C. Overall, results obtained demonstrated that temperature and salinity can affect some functional responses of haemocytes from R. philippinarum, and suggested a better physiological condition for animals kept at 15 °C temperature and 18 psu salinity.     

Effects of Zn2+ and niflumic acid on photosynthesis in Glycine soja and Glycine max seedlings under NaCl stress

The effects of two anion/Cl^? channel inhibitors, Zn²⁺ and niflumic acid (NA), on seedling photosynthetic and fluorescent parameters of two Glycine soja populations (salt-tolerant BB52; salt-sensitive N23227) and Glycine max cultivar (salt-tolerant Lee68) were studied and compared under salt stress. Treatments with Zn²⁺ and NA only (10, 20 μmol L^?1) were also imposed for comparisons. Results showed that, there were non-toxic and non-nutritional effects of Zn²⁺ and NA treatments alone on seed germination and seedling growth of soybeans. Under 150 mmol L^?1 NaCl for 6 d, leaf chlorophyll and carotenoid contents, net photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i), transpiration rate (Tr), and the maximum photochemical efficiency of photosystem II (PS II) (F_v/F_m) except the stomatal limitation (Ls) significantly decreased in three kinds of soybean seedlings when compared with their control plants. The NaCl stress plus additional 20 μmol L^?1 Zn showed an obvious enhancement of leaf chlorophyll and carotenoid contents, P_n, G_s, C_i and Tr, especially for the G. max cultivar Lee68, but the supplementation of 20 μmol L^?1 NA showed the reverse effects.     

Impact of in vitro CO2 enrichment and sugar deprivation on acclimatory responses of Phalaenopsis plantlets to ex vitro conditions

We assessed the effect of growth at either 400 μmol mol^?1 (ambient) or 1000 μmol mol^?1 (elevated) CO₂ and 0 g L^?1 (deprivation) or 30 g L^?1 (supplementation) sugar on morphological traits, photosynthetic attributes and intrinsic elements of the CAM pathway using the CAM orchid Phalaenopsis ‘Amaglade’. The growth of shoot (retarded) and root (induced) was differently affected by CO₂ enrichment and mixotrophic regime (+sugar). The Fv/Fm ratio was 14% more in CO₂-enriched treatment than at ambient level during in vitro growth. At elevated level of CO₂ and sugar treatment, the content of Chl(a + b), Chl a/b and Chl/Car was enhanced while carotenoid content remained unaltered. During in vitro growth, gas-exchange analysis indicated that increased uptake of CO₂ accorded with the increased rate of transpiration and unchanged stomatal conductance at elevated level of CO₂ under both photo- and mixotrophic growth condition. At elevated level of CO₂ and sugar deprivation, activities of Rubisco (26.4%) and PEPC (74.5%) was up-regulated. Among metabolites, the content of sucrose and starch was always higher under CO₂ enrichment during both in vitro and ex vitro growth. Our results indicate that plantlets grown under CO₂ enrichment developed completely viable photosynthetic apparatus ready to be efficiently transferred to ex vitro condition that has far-reaching implications in micropropagation of Phalaenopsis.     

Haemolymph constituents and osmolality as functions of moult stage,body weight,and feeding status in marron,Cherax cainii () and yabbies,Cherax destructor (Clark, 1936)

The study investigates the change in osmolality and haemolymph constituents in marron Cherax cainii and yabbies Cherax destructor associated with moult stages, body weights and their feeding status. A total of 582 haemolymph samples from 5 moult stages (postmoult-AB, intermoult-C, and premoult stages – D₀, D₁, D₂), two body weight classes (2–15 g and 61–75 g) and nutritional status were used for analysis of osmolality, protein, glucose, and ionic concentrations of potassium and chloride following the standard biochemical procedures. The haemolymph protein, glucose, potassium and chloride levels were highest at intermoult and early premoult stages, and lowest at postmoult in both crayfish species. Except protein, no significant differences were seen in analyzed parameters between various weight classes and two species. Haemolymph osmolality, protein and glucose were significantly higher in fed crayfish, whereas no variations in haemolymph potassium and chloride concentrations were observed between the fed and unfed crayfish. Maximum osmolality was recorded at 7–8 h after feeding in both crayfish species. The results showed that the biochemical changes in the haemolymph of marron and yabbies are related to moult stages, body weight and feeding and thus can be used as tools for determining suitable diets.     

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.     

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.     

Biosynthesis of ethyl caproate and other short ethyl esters catalyzed by cutinase in organic solvent

The main objective of this work was to study the enzymatic synthesis of short chain ethyl esters, a group of relevant aroma molecules, by Fusarium solani pisi cutinase in an organic solvent media (iso-octane), and to assess the influence of different parameters on the reaction yield.Cutinase displayed high initial esterification rates in iso-octane, which amounted to 1.15 μmol min⁻¹ mg⁻¹ for ethyl butyrate (C₄ acid chain) and 1.06 μmol min⁻¹ mg⁻¹ for ethyl valerate (C₅ acid chain). High product yields, 84% for ethyl butyrate and 96% for ethyl valerate, were observed after 6 h of reaction, for an initial equimolar concentration of substrates (0.1 M).The highest product yield (97%) was observed for ethyl caproate (C₆) synthesis, a compound which is a part of natural apple and pineapple flavour, for an alcohol:acid molar ratio of 2 (0.2 M ethanol concentration).Cutinase affinity for short chain length carboxylic acids (C₄–C₆) in ester synthesis in iso-octane confirmed previous observations in reversed micellar system.     

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.     

Internal conductance to CO2 transfer of adult Fagus sylvatica: Variation between sun and shade leaves and due to free-air ozone fumigation

Two separate objectives were considered in this study. We examined (1) internal conductance to CO₂ (g_i) and photosynthetic limitations in sun and shade leaves of 60-year-old Fagus sylvatica, and (2) whether free-air ozone fumigation affects g_i and photosynthetic limitations. g_i and photosynthetic limitations were estimated in situ from simultaneous measurements of gas exchange and chlorophyll fluorescence on attached sun and shade leaves of F. sylvatica. Trees were exposed to ambient air (1× O₃) and air with twice the ambient ozone concentration (2× O₃) in a free-air ozone canopy fumigation system in southern Germany (Kranzberg Forest). g_i varied between 0.12 and 0.24 mol m⁻² s⁻¹ and decreased CO₂ concentrations from intercellular spaces (C_i) to chloroplastic (C_c) by approximately 55 μmol mol⁻¹. The maximum rate of carboxylation (V_cmax) was 22–39% lower when calculated on a C_i basis compared with a C_c basis. g_i was approximately twice as large in sun leaves compared to shade leaves. Relationships among net photosynthesis, stomatal conductance and g_i were very similar in sun and shade leaves. This proportional scaling meant that neither C_i nor C_c varied between sun and shade leaves. Rates of net photosynthesis and stomatal conductance were about 25% lower in the 2× O₃ treatment compared with 1× O₃, while V_cmax was unaffected. There was no evidence that g_i was affected by ozone.     

Acclimation of peanut (Arachis hypogaea L.) leaf photosynthesis to elevated growth CO2 and temperature

Peanut (Arachis hypogaea L. cv. Florunner) was grown from seed sowing to plant maturity under two daytime CO₂ concentrations ([CO₂]) of 360 μmol mol⁻¹ (ambient) and 720 μmol mol⁻¹ (elevated) and at two temperatures of 1.5 and 6.0 °C above ambient temperature. The objectives were to characterize peanut leaf photosynthesis responses to long-term elevated growth [CO₂] and temperature, and to assess whether elevated [CO₂] regulated peanut leaf photosynthetic capacity, in terms of activity and protein content of ribulose bisphosphate carboxylase-oxygenase (Rubisco), Rubisco photosynthetic efficiency, and carbohydrate metabolism. At both growth temperatures, leaves of plants grown under elevated [CO₂] had higher midday photosynthetic CO₂ exchange rate (CER), lower transpiration and stomatal conductance and higher water-use efficiency, compared to those of plants grown at ambient [CO₂]. Both activity and protein content of Rubisco, expressed on a leaf area basis, were reduced at elevated growth [CO₂]. Declines in Rubisco under elevated growth [CO₂] were 27–30% for initial activity, 5–12% for total activity, and 9–20% for protein content. Although Rubisco protein content and activity were down-regulated by elevated [CO₂], Rubisco photosynthetic efficiency, the ratio of midday light-saturated CER to Rubisco initial or total activity, of the elevated-[CO₂] plants was 1.3- to 1.9-fold greater than that of the ambient-[CO₂] plants at both growth temperatures. Leaf soluble sugars and starch of plants grown at elevated [CO₂] were 1.3- and 2-fold higher, respectively, than those of plants grown at ambient [CO₂]. Under elevated [CO₂], leaf soluble sugars and starch, however, were not affected by high growth temperature. In contrast, high temperature reduced leaf soluble sugars and starch of the ambient-[CO₂] plants. Activity of sucrose-P synthase, but not adenosine 5′-diphosphoglucose pyrophosphorylase, was up-regulated under elevated growth [CO₂]. Thus, in the absence of other environmental stresses, peanut leaf photosynthesis would perform well under rising atmospheric [CO₂] and temperature as predicted for this century.     

Interplay between thermal and immune ecology: effect of environmental temperature on insect immune response and energetic costs after an immune challenge

Although the study of thermoregulation in insects has shown that infected animals tend to prefer higher temperatures than healthy individuals, the immune response and energetic consequences of this preference remain unknown. We examined the effect of environmental temperature and the energetic costs associated to the activation of the immune response of Tenebrio molitor larvae following a lipopolysaccharide (LPS) challenge. We measured the effect of temperature on immune parameters including phenoloxidase (PO) activity and antibacterial responses. Further as proximal and distal costs of the immune response we determined the standard metabolic rate (SMR) and the loss of body mass (m_b), respectively. Immune response was stronger at 30 °C than was at 10 or 20 °C. While SMR at 10 and 20 °C did not differ between immune treatments, at 30 °C SMR of LPS-treated larvae was almost 25–60% higher than SMR of PBS-treated and naïve larvae. In addition, the loss in m_b was 1.9 and 4.2 times higher in LPS-treated larvae than in PBS-treated and naïve controls. The immune responses exhibited a positive correlation with temperature and both, SMR and m_b change, were sensitive to environmental temperature. These data suggest a significant effect of environmental temperature on the immune response and on the energetic costs of immunity.     

Interactive effects of elevated temperature and CO2 levels on metabolism and oxidative stress in two common marine bivalves (Crassostrea virginica and Mercenaria mercenaria)

Marine bivalves such as the hard shell clams Mercenaria mercenaria and eastern oysters Crassostrea virginica are affected by multiple stressors, including fluctuations in temperature and CO₂ levels in estuaries, and these stresses are expected to be exacerbated by ongoing global climate change. Hypercapnia (elevated CO₂ levels) and temperature stress can affect survival, growth and development of marine bivalves, but the cellular mechanisms of these effects are not yet fully understood. In this study, we investigated whether oxidative stress is implicated in cellular responses to elevated temperature and CO₂ levels in marine bivalves. We measured the whole-organism standard metabolic rate (SMR), total antioxidant capacity (TAOC), and levels of oxidative stress biomarkers in the muscle tissues of clams and oysters exposed to different temperatures (22 and 27 °C) and CO₂ levels (the present day conditions of ~ 400 ppm CO₂ and 800 ppm CO₂ predicted by a consensus business-as-usual IPCC emission scenario for the year 2100). SMR was significantly higher and the antioxidant capacity was lower in oysters than in clams. Aerobic metabolism was largely temperature-independent in these two species in the studied temperature range (22–27 °C). However, the combined exposure to elevated temperature and hypercapnia led to elevated SMR in clams indicating elevated costs of basal maintenance. No persistent oxidative stress signal (measured by the levels of protein carbonyls, and protein conjugates with malondialdehyde and 4-hydroxynonenal) was observed during the long-term exposure to moderate warming (+ 5 °C) and hypercapnia (~ 800 ppm CO₂). This indicates that long-term exposure to moderately elevated CO₂ and temperature minimally affects the cellular redox status in these bivalve species and that the earlier observed negative physiological effects of elevated CO₂ and temperature must be explained by other cellular mechanisms.     

Response of the insect immune system to three different immune challenges

Insects rely on an innate immune system to effectively respond to pathogenic challenges. Most studies on the insect immune system describe changes in only one or two immune parameters following a single immune challenge. In addition, a variety of insect models, often at different developmental stages, have been used, making it difficult to compare results across studies. In this study, we used adult male Acheta domesticus crickets to characterize the response of the insect innate immune system to three different immune challenges: injection of bacterial lipopolysaccharides (LPS); injection of live Serratia marcescens bacteria; or insertion of a nylon filament into the abdomen. For each challenge, we measured and compared hemolymph phenoloxidase (PO) and lysozyme-like enzyme activities; the number of circulating hemocytes; and the nodulation responses of challenged and un-challenged crickets. We found that injection of an LD₅₀ dose of LPS from Escherichia coli elicited a more rapid response than an LD₅₀ dose of LPS from S. marcescens. LPS injection could cause a rapid decrease 2 hpi, followed by an increase by 7 dpi, in the number of circulating hemocytes. In contrast, injection of live S. marcescens produced a rapid increase and then decrease in hemocyte number. This was followed by an increase in the number of hemocytes at 7 dpi, similar to that observed following LPS injection. Both LPS and live bacteria decreased hemolymph PO activity, but the timing of this effect was dependent on the challenge. Live bacteria, but not LPS, induced an increase in lysozyme-like activity in the hemolymph. Insertion of a nylon filament induced a decrease in hemolymph PO activity 2 h after insertion of the filament, but had no effect on hemocyte number or lytic activity. Our results indicate that the innate immune system’s response to each type of challenge can vary greatly in both magnitude and timing, so it is important to assess multiple parameters at multiple time points in order to obtain a comprehensive view of such responses.     

Seasonal variations in photosynthetic irradiance response curves of macrophytes from a Mediterranean coastal lagoon

The main photosynthesis and respiration parameters (dark respiration rate, light saturated production rate, saturation irradiance, photosynthetic efficiency) were measured on a total of 23 macrophytes of the Thau lagoon (2 Phanerogams, 5 Chlorophyceae, 10 Rhodophyceae and 6 Phaeophyceae). Those measurements were performed in vitro under controlled conditions, close to the natural ones, and at several seasons. Concomitantly, measurements of pigment concentrations, carbon, phosphorous and nitrogen contents in tissues were performed. Seasonal intra-specific variability of photosynthetic parameters was found very high, enlightening an important acclimatation capacity. The highest photosynthetic capacities were found for Chlorophyceae (e.g. Monostroma obscurum thalli at 17 °C, 982 μmol O₂ g⁻¹ dw h⁻¹ and 9.1 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹, respectively for light saturated net production rate and photosynthetic efficiency) and Phanerogams (e.g. Nanozostera noltii leaves at 25 °C, 583 μmol O₂ g⁻¹ dw h⁻¹ and 2.6 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹ respectively for light saturated net production rate and photosynthetic efficiency). As expected, species with a high surface/volume ratio were found to be more productive than coarsely branched thalli and thick blades shaped species. Contrary to R_d (ranging 6.7–794 μmol O₂ g⁻¹ dw h⁻¹, respectively for Rytiphlaea tinctoria at 7 °C and for Dasya sessilis at 25 °C) for which a positive relationship with water temperature was found whatever the species studied, the evolution of P/I curves with temperature exhibited different responses amongst the species. The results allowed to show summer nitrogen limitation for some species (Gracilaria bursa-pastoris and Ulva spp.) and to propose temperature preferences based on the photosynthetic parameters for some others (N. noltii, Zostera marina, Chaetomorpha linum).