Circadian rhythms in Kalanchoë: effects of irradiance and temperature on gas exchange and carbon metabolism

Gas exchange in K. blossfeldiana shows a circadian rhythm in net CO₂ uptake and transpiration when measured under low and medium irradiances. The period length varies between 21.4 h at 60 W m^-2 and 24.0 h at 10 W m^-2. In bright light (80 W m^-2) or darkness there are no rhythms. High leaf temperatures result in a fast dampening of the CO₂-uptake rhythm at moderate irradiances, but low leaf temperatures can not overcome the dampening in bright light. The rhythm in CO₂ uptake is accompanied by a less pronounced and more rapidly damped rhythm in transpiration and by oscillations in malate levels with the amplitude being highly reduced. The oscillations in starch content, usually observed to oscillate inversely to the acidification in light-dark cycles, disappear after the first cycle in continuous light. The balance between starch and malate levels depends in continuous light on the irradiance applied. Leaves show high malate and low starch content at low irradiance and high starch and low malate in bright light. During the first 12 h in continuous light replacing the usual dark period, malate synthesis decreases with the increasing irradiance. Up to 50 W m^-2 starch content decreases; at higher irradiances it increases above the values usually measured at the end of the light period of the 12:12 h light-dark cycle.Abbreviations CAM Crassulacean acid metabolism - FW fresh weight - PEP phosphoenolpyruvate     

Circadian rhythms in crassulacean acid metabolism: phase relationships between gas exchange,leaf water relations and malate metabolism in Kalanchoë daigremontiana

Hypocotyls of 5-d-old etiolated soybean seedlings (Glycine max (L.) Merr. cv. Altona) were treated with (a) dithiothreitol (DTT) or one of the sulfhydryl-binding reagents N-ethylmaleimide (NEM), p-hydroxymercuribenzoate (PMB) und p-chloromercuribenzene sulfonic acid (PMBS), (b) one of the sulfhydryl reagents in combination with DTT, (c) sulfhydryl reagent subsequent to treatment with DTT, and (d) PMBS followed by DTT. Glyceollin was extracted 24 and 48 h after initiation of treatment. The order of decreasing glyceollin-eliciting activity was PMBSDTT>PMBNEM. Elicitor effectiveness of sulfhydryl reagents and their reactivity with either L-cysteine or sulfhydryl groups in soybean hypocotyls were not strictly correlated. Mixtures of sulfhydryl reagent and DTT, pretreatment of hypocotyls with DTT and subsequent application of either PMB or PMBS, as well as application of PMBS prior to DTT induced less glyceollin than sulfhydryl reagents alone. In contrast, such pretreatment did not appreciably alter glyceollin accumulation elicited by NEM. The results indicate that glyceollin synthesis can be regulated by interaction with sulfhydryl groups located mainly at the outer surface of the plasmalemma.Abbreviations DTT DL-dithiothreitol - NEM N-ethylmaleimide - PMB p-hydroxymercuribenzoate (sodium salt) - PMBS p-chloromercuribenzene sulfonic acid     

Effects of Water and Turgor Potential on Malate Efflux from Leaf Slices of Kalanchoë daigremontiana

Malate efflux from leaf cells of the Crassulacean acid metabolism plant Kalanchoë daigremontiana Hamet et Perrier was studied using leaf slices submerged in experimental solutions. Leaves were harvested at the end of the dark phase and therefore contained high malate levels. Water potentials of solutions were varied between 0 and −5 bar using mannitol (a slowly permeating solute) and ethylene glycol (a rapidly permeating solute), respectively. Mannitol solutions of water potentials down to −5 bar considerably reduced malate efflux. The slowly permeating solute mannitol reduces both water potential and turgor potential of the cells. The water potential of a mannitol solution of −5 bar is just above plasmolyzing concentration. Malate efflux in ethylene glycol at −5 bar was only slightly smaller than at 0 bar, and much higher than in mannitol at −5 bar. Tissues in rapidly permeating ethylene glycol would have turgor potentials similar to tissues in 0.1 mm CaSO₄. The results demonstrate that malate efflux depends on turgor potential rather than on water potential of the cells.     

Changes in lipid composition, water relations and gas exchange in leaves of two young ‘Chemlali’ and ‘Chetoui’ olive trees in response to water stress

The comparative responses of two young olive trees (Olea europaea L. ‘Chemlali’ and ‘Chetoui’) to drought stress were investigated during 1 month. Three-month-old own-rooted plants were subjected to two irrigation treatments: WW (well watered plants that were irrigated with fresh water to maintain a soil water content close to field capacity), and WS (water stressed plants by withholding water). Leaf water potential, gas exchange and leaf lipid composition were studied. ‘Chemlali’ was able to maintain higher leaf CO₂ assimilation rate and leaf stomatal conductance throughout the drought cycle compared to ‘Chetoui’. Water stress induced a larger decrease in the total lipid content in ‘Chetoui’ than in ‘Chemlali’. Interestingly, the constitution of different lipid classes was highly altered in ‘Chetoui’. Lipid changes in Chemlali, a drought tolerant cultivar, revealed more stability of its cellular membranes to drought stress as compared to the drought susceptible olive cultivar, Chétoui. Furthermore, in comparison to the controls, drought stressed plants showed an increase in the degree of unsaturation of leaf lipids in the two olive cultivars. Moreover, the results observed in Chemlali showed that besides changes in lipids composition this cultivar may have an efficient defence strategy which can be related on antioxidative production against oxidative stress.     

Effects of Phoslock® treatment and chironomids on the exchange of nutrients between sediment and water

Effects of chironomids on sediment–water exchange of nutrients and their impact on the efficiency of Phoslock^® (a lanthanum (La) modified clay for phosphorus (P) removal in freshwater systems) were tested during a 35 days incubation experiment with sediment cores from a Danish eutrophic Lake. Four different sediment treatments with increased or natural densities of chironomids in combination with Phoslock^® were used: (1) Control + (2) Chironomids + (3) Phoslock + (4) Chironomids & Phoslock. Nutrients in the overlying water were followed during the incubation period. The treatments with Phoslock reduced P in the overlying water significantly compared to the control treatment. In addition, the chironomids significantly increased sediment nitrate uptake as well as sediment ammonium release. After the incubation period, a sequential extraction of P and La was conducted. The Phoslock treatment led to a reduction of the iron-bound P pool in the sediment and a higher HCl-extractable P pool. Also, most La was recovered in the HCl extract, indicating that P became strongly bound to La in the Phoslock matrix. Sequential extraction of pure Phoslock demonstrated that the bentonite matrix of Phoslock contained redox sensitive iron, and that ammonium might be released from Phoslock, when dispersed in water.     

Day-night changes in leaf water relations associated with the rhythm of crassulacean acid metabolism in Kalanchoë daigremontiana

A study was made of the day-night changes under controlled environmental conditions in the bulk-leaf water relations of Kalanchoë daigremontiana, a plant showing Crassulacean acid metabolism. In addition to nocturnal stomatal opening and net CO₂ uptake, the leaves of well-watered plants showed high rates of gas exchange during the whole of the second part of the light period. Measurements with the pressure chamber showed that xylem tension increased during the night and then decreased towards a minimum at about midday; a significant increase in xylem tension was also seen in the late afternoon. Cell-sap osmotic pressure paralleled leaf malate content and was maximum at dawn and minimum at dusk. The relationship between these two variables indicated that the nocturnally synthesized malate was apparently behaving as an ideal osmoticum. To estimate bulk-leaf turgor pressure, values for water potential were derived by correcting the pressurechamber readings for the osmotic pressure of the xylem sap. This itself was found to depend on the malate content of the leaves. Bulk-leaf turgor pressure changed rhythmically during the day-night cycle; turgor was low during the late afternoon and for most of the night, but increased quickly to a maximum of 0.20 MPa around midday. In water-stressed plants, where net CO₂ uptake was restricted to the dark period, there was also an increase in bulk-leaf turgor pressure at the start of the light period, but of reduced magnitude. Such changes in turgor pressure are likely to be of considerable ecological importance for the water economy of crassulacean-acid-metabolism plants growing in their natural habitats.Abbreviation and symbols CAM Crassulacean acid metabolism - P turgor pressure - osmotic pressure - water potential Dedicated to Professor Dr. H. Ziegler on the occasion of his 60th birthday     

Effect of uniconazole and limited water on growth,water relations,and mineral nutrition of “Lalandei” Pyracantha

Pyracantha (Pyracantha coccinea M. J. Roem. Lalandei) plants were treated with uniconazole at 0.5 mg ai container^–1 as a medium drench, 150 mg ai L^–1 as a foliar spray, or left untreated. Plants from all treatments were placed under three water regimes: drought acclimated, nonacclimated and later exposed to drought, or nonstressed. Acclimated plants were conditioned by seven 4-day stress cycles (water withheld), while nonacclimated were well watered prior to a single 4-day stress cycle at the same time as the seventh drought cycle of acclimated plants. Nonstressed plants were well watered throughout the study. Nonstressed plants had higher leaf water potentials and leaf conductances than acclimated and nonacclimated plants, and transpiration rates were higher in nonacclimated than acclimated plants. Uniconazole did not affect leaf water potential, leaf conductance, or transpiration rate. Acclimated plants had smaller leaf areas and leaf, stem, and root dry weights than nonacclimated or nonstressed plants. Plants drenched with uniconazole had the lowest stem and root dry weights. Acclimated plants also contained higher N concentrations than nonacclimated or nonstressed plants, and higher P concentrations than nonacclimated plants. Uniconazole medium drench treatments increased levels of Mn and P. Calcium concentration was increased in plants receiving either medium drench or foliar applications.     

Effects of high night temperature on lipid and protein compositions in tonoplasts isolated from Ananas comosus and Kalanchoë pinnata leaves

Effects of high night temperature on the lipid and protein compositions in the tonoplasts isolated from the leaves of two Crassulacean acid metabolism (CAM) plants, Ananas comosus (pineapple) and Kalanchoë pinnata were studied. The results showed that the phospholipids/protein ratios in the tonoplasts isolated from pineapple and K. pinnata leaves decreased from 1.82 to 1.21 and 2.63 to 1.50, respectively, as the night temperature increased from 20 to 37 °C. Under high night temperature, relative amount of total unsaturated fatty acids in K. pinnata was increased by 6 %, which was mainly caused by increased C18:2 and C18:3, whereas unsaturated fatty acids, C18:2 and C18:3 in pineapple did not show significant change. The distribution patterns of tonoplast proteins in the two CAM species were different between normal and high night temperature and in K. pinnata, especially those with molecular mass ranging from 66.2 to 97.4 KDa. Compared with normal night temperature, more proteins were found in pineapple, but no difference was found in K. pinnata. Thus, above result indicated that the pineapple tonoplasts could keep higher rigidity under high night temperatures compared to the K. pinnata.     

Post-fire mortality and water relations of three congeneric shrub species under extreme water stress — a trade-off with fecundity?

Mortality and water relations of three cooccurringHakea species were studied over the first year following a wildfire in scrub-health in southwestern Australia.Hakea ruscifolia regenerated from both resprouting adults and seedlings, whereasH. smilacifolia andH. polyanthema regenerated only from seedlings. We monitored seedling and resprout survival relative to pre-fire numbers and water relations (shoot water potential, transpiration, pressure-volume parameters) in order to determine the relationship between plant mortality and water relations over the critical first summer drought. Seedlings ofH. polyanthema (few initial seedlings per parent) showed little mortality (8%), achieved through both drought avoidance (low transpiration, high predawn water potential and relative water content (RWC), substantial osmotic adjustment) and drought tolerance later in the season. Seedlings ofH. smilacifolia andH. ruscifolia (high seedling/parent ratios) showed little drought avoidance and high mortality (54–68%). The remaining seedlings spent 3–4 months in a wilted condition (up to 3.6 MPa and 45% RWC below the turgor loss point inH. ruscifolia) indicating marked drought tolerance of the survivors. In contrast to its seedlings,H. ruscifolia resprouts were successful drought avoiders and experienced no mortality. The high level of survival and drought resistance ofH. polyanthema was consistent with its large seedlings (via large seeds) and low initial fecundity. The study highlights the importance of the interaction between ecophysiology-morphology and demography in determining the recruitment strategies of plants.     

Experimental removal of intraspecific competitors — effects on water relations and productivity of a desert bunchgrass,Hilaria rigida

Summary Intraspecific competition in the C₄ bunchgrass Hilaria rigida was examined on a Sonoran Desert site in southeastern California. Potential competition within monospecific stands was experimentally altered by removal of the aboveground portions of all plants within a 1.5 m radius of a monitored plant. Compared with unaltered plots, altered plots had less negative soil water potentials during periods of soil drying. Leaf blades on monitored plants of altered plots remained green longer and had greater stomatal conductances than those on monitored plants on unaltered plots. Production of new culms was twice as great on altered plots. Greater root biomass and root length were observed in altered plots, and root extension into soil areas formerly occupied by roots of neighboring plants occurred within one year after treatment. The results indicate that removal of the aboveground biomass of neighboring plants reduces the competition for limited available soil water in this desert environment.     

Effect of an Epichloë endophyte on adaptability to water stress in Festuca sinensis

As water stress, including drought and waterlogging, can severely affect plant growth, this study investigated the effects of an endophyte from the genus Epichloë on two different ecotypes of Festuca sinensis grass under five soil water conditions in a controlled greenhouse experiment. Changes in F. sinensis plants grown with (E+) and without the endophyte (E−) were evaluated as they were subjected to different water treatments (20%, 35%, 50%, 65% and 80% relative saturation moisture content, RSMC). Growth parameters such as plant height, number of tillers, blade width, stem diameter, root length, total biomass, root-shoot ratio and relative water content were determined. The results showed that drought and waterlogging significantly (P < 0.05) inhibited the growth of F. sinensis. The presence of the endophyte significantly (P < 0.05) increased plant growth and root-shoot ratio under drought and waterlogged conditions. In addition, the plant height, number of tillers, blade width, stem diameter and total biomass in seedlings of both ecotypes reached the maximum at 65% RSMC, which suggests the optimal water condition. These findings also show that moderate drought (35% and 50% RSMC) could promote root growth of grass seedlings. Therefore, endophytic infections can result in enhanced host plant resistance to drought and waterlogged conditions.     

Stigma development and receptivity of two Kalanchoë blossfeldiana cultivars

Several members of the Kalanchoë genus are popular as ornamental plants. Cross-breeding and wide hybridisation are essential to continuously introduce novel traits into cultivated plant material. This study aimed to identify the major factors related to the stigma affecting cross-pollination in the Kalanchoë blossfeldiana. Pollen tube growth after pollination of K. blossfeldiana ‘Jackie’ and ‘Reese’ was examined at different stigma developmental stages. Five distinct developmental stages were identified based on changes in morphology and activity of stigmatic peroxidase. After reciprocal pollination at the five stigma developmental stages, fluorescence microscopy was used to estimate the number of pollen tubes in situ. Both cultivars had receptive stigmas from stage I to IV, which concurred with the continuous expansion of the stigma covered with exudates. No pollen tube growth was observed at stage V for both cultivars. The number of pollen tubes was significantly higher in carpels pollinated at stage III, characterized by loose arrangement of the papillae and maximal amount of exudates, compared to all other developmental stages. Stigmas showing drying exudates and absence of peroxidase exhibited a relatively decreased number of pollen tubes in situ. No pollen tubes germinated on wilting stigmas. The arrangement of the papillae, the presence of exudates and peroxidase activity affected the number of pollen tubes in cross-pollination of K. blossfeldiana cultivars ‘Jackie’ and ‘Reese’. These results will help breeders to better select the optimal time for effective pollination. The findings may be applicable for other cultivars of K. blossfeldiana and relevant for different species of Kalanchoë.     

Phenolic acid content,antioxidant and cytotoxic activities of four Kalanchoë species

Phenolic acid composition, antioxidant, and cytotoxic activities in leaves of four Kalanchoe (Crassulaceae) species were evaluated. Determination of phenolic acid contents were conducted by an optimized LC–ESI-MS/MS method. The results show that Kalanchoe daigremontiana Raym.-Hamet & H. Perrier (using ASE extraction) and Kalanchoe pinnata (Lam.) Pers. contain the highest amounts of phenolic acids, while Kalanchoe nyikae Engl. the lowest ones. Among phenolic acids ferulic, caffeic and protocatechuic acids were occurring in the highest quantities in the analysed species. The greatest amounts of ferulic and protocatechuic acids were found in K. daigremontiana and K. pinnata. Moreover, the antiradical and cytotoxic activities of Kalanchoe extracts were investigated. All tested extracts possessed antioxidant activity. The obtained IC₅₀ values (μg/mL) ranged from 49.9 μg/mL to 1410 μg/mL, indicating a large variation of the activity of the analysed extracts. Cytotoxicity assays revealed dose-dependent effects in the cells lines tested. Only K. pinnata extract showed a high cytotoxicity against the H-9 human T cell line. Other extracts (K. daigremontiana, Kalanchoe milloti, K. nyikae) showed more pronounced cytotoxicity towards J45.01 cells (human acute lymphoblastic leukaemia T cells).The present study demonstrated that Kalanchoe extracts have significant antioxidant and cytotoxic effects. This suggests that these species can be used as new sources of natural antioxidants and potential anticancer compounds.     

Effects of high irradiances on photosynthesis,growth and crassulacean acid metabolism in the epiphyteKalanchoö uniflora

Summary Kalancho? uniflora was grown in the glasshouse with and without shading. Chlorophyll content, area/FW ratio and specific leaf area were higher in leaves of shaded as compared to unshaded plants. Light saturation curves and continuous gas exchange measurements showed that the apparent quantum yield and the light-saturated photosynthetic rate were higher in shaded plants. Shaded plants had lower “mesophyll resistances” than unshaded plants, indicating that the different photosynthetic capacities reflected different contents of ribulose biphosphate carboxylase-oxygenase. Highlight treatment of plants grown in the shade resulted in a decreased photosynthetic efficiency, showing that these plants were sensitive to photoinhibition. However, dry matter production was higher in unshaded than in shaded plants. Obviously the difference in irradiance between the two growth regimes did more than offset the differences in photosynthetic efficiency. Applying additional nutrients did not alter the effects of high PFDs. The results are discussed in respect to photosynthetic performence and plant distribution in the epiphytic habitat.     

Effect of elevated CO2 on growth and crassulacean-acid-metabolism activity of Kalanchoë pinnata under tropical conditions

 Kalancho? pinnata (Lam.) Pers. (Crassulaceae), a succulent-leaved crassulacean-acid-metabolism plant, was grown in open-top chambers at ambient and elevated (two times ambient) CO₂ concentrations under natural conditions at the Smithsonian Tropical Research Institute, Republic of Panama. Nocturnal increase in titratable acidity and nocturnal carbon gain were linearly related, increased with leaf age, and were unaffected by CO₂ treatments. However, under elevated CO₂, dry matter accumulation increased by 42–51%. Thus, the increased growth at elevated CO₂ was attributable entirely to increased net CO₂ uptake during daytime in the light. Malic acid was the major organic acid accumulated overnight. Nocturnal malate accumulation exceeded nocturnal citrate accumulation by six-to eightfold at both CO₂ concentrations. Basal (predawn) starch levels were higher in leaves of plants grown at elevated CO₂ but diurnal fluctuations of starch were of similar magnitude under both ambient and elevated CO₂. In both treatments, nocturnal starch degradation accounted for between 78 and 89% of the nocturnal accumulation of malate and citrate. Glucose, fructose, and sucrose were not found to exhibit marked day-night fluctuations. Received: 4 March 1996 / Accepted: 25 May 1996     

Impacts of ocean acidification on respiratory gas exchange and acid–base balance in a marine teleost, Opsanus beta

The oceanic carbonate system is changing rapidly due to rising atmospheric CO(2), with current levels expected to rise to between 750 and 1,000?μatm by 2100, and over 1,900?μatm by year 2300. The effects of elevated CO(2) on marine calcifying organisms have been extensively studied; however, effects of imminent CO(2) levels on teleost acid-base and respiratory physiology have yet to be examined. Examination of these physiological processes, using a paired experimental design, showed that 24?h exposure to 1,000 and 1,900?μatm CO(2) resulted in a characteristic compensated respiratory acidosis response in the gulf toadfish (Opsanus beta). Time course experiments showed the onset of acidosis occurred after 15?min of exposure to 1,900 and 1,000?μatm CO(2), with full compensation by 2 and 4?h, respectively. 1,900-μatm exposure also resulted in significantly increased intracellular white muscle pH after 24?h. No effect of 1,900?μatm was observed on branchial acid flux; however, exposure to hypercapnia and HCO(3) (-) free seawater compromised compensation. This suggests branchial HCO(3) (-) uptake rather than acid extrusion is part of the compensatory response to low-level hypercapnia. Exposure to 1,900 μatm resulted in downregulation in branchial carbonic anhydrase and slc4a2 expression, as well as decreased Na(+)/K(+) ATPase activity after 24?h of exposure. Infusion of bovine carbonic anhydrase had no effect on blood acid-base status during 1,900?μatm exposures, but eliminated the respiratory impacts of 1,000 μatm CO(2). The results of the current study clearly show that predicted near-future CO(2) levels impact respiratory gas transport and acid-base balance. While the full physiological impacts of increased blood HCO(3) (-) are not known, it seems likely that chronically elevated blood HCO(3) (-) levels could compromise several physiological systems and furthermore may explain recent reports of increased otolith growth during exposure to elevated CO(2).     

Interaction of hydrolytic and phosphorolytic enzymes of starch metabolism in Kalanchoë daigremontiana

The degradation of starch by a protein fraction of Kalanchoë daigremontiana Hamet et Perrier, obtained by ammoniumsulfate precipitation (30–70%), was found to be catalyzed by -and -amylase (EC 3.2.1.1 and EC 3.2.1.2, respectively) and by starch phosphorylase (EC 2.4.1.1). The activity of these enzymes was determined by chromatographic analysis of the reaction products; separation and identification of -amylase was accomplished by heat-inactivation of -amylase and -glucosidase. When the interaction of amylolytic and phosphorolytic enzymes was comparatively studied, it was found that without inorganic phosphorus in the reaction mixture, ¹⁴C-starch was converted predominantly to maltose and glucose; supplementation with 1–10 mM orthophosphate (Pi) resulted in an increase in glucose-1-phosphate formation and a concomitant reduction of maltose production. Since the total volume of starch degradation remained approximately constant, Pi apparently inhibits -amylase (Ki about 3 mM Pi). Thus, free Pi in the cell participates in the regulation of starch catabolism, serving as a substrate for starch phosphorylase while simultaneously reducing the production of maltose. With respect to glucan synthesis, adenosinediphosphoglucose--1,4-glucosyltransferase (EC 2.4.1.22), maltose phosphorylase and maltoseglucosyltransferase were also found to be active. The last-named enzyme catalyzes an exchange between dextrins and is considered to provide primer carbohydrates for the synthesis of polyglucans.Abbreviations ADPG adenosinediphosphoglucose - G1P glucose-1-phosphate - PEG polyethylenglycol - PEP phosphoenolpyruvate - Pi orthophosphate     

Effects of the planting density on water relations and production of ‘Chemlali’ olive trees (Olea europaea L.)

Water relations are a key factor limiting olive production. In this study, effects of plating density on physiological aspects and productivity of ‘Chemlali’ olive trees were analyzed under rain-fed conditions in four planting densities (156, 100, 69 and 51 trees ha⁻¹), in an experimental olive orchard located in the center of Tunisia. Seasonal changes in leaf relative water content (RWC), leaf water potential, stomatal conductance (g _s), CO₂ assimilation rate and tree production were studied. Accompanying the changes in leaf water status, all the monitored trees reduced leaf stomatal conductance (g _s) and photosynthetic rate (A) throughout the summer drought, mirroring the increase in soil moisture deficit and vapor pressure deficit. However, the decrease in gas exchange was much more pronounced in high planting densities than in low ones. Our results confirm that the increase of tree-to-tree water competition with planting density was significant in the dry climate of Tunisia. Thus, planting density is critical when planting new olive orchards in arid regions.     

The architecture of termite mounds: a result of a trade-off between thermoregulation and gas exchange?

We examined the influence of gas exchange on the architectureof termitemounds. In Comoé National Park(Côted'Ivoire), Macrotermesbellicosus builds, as an adaptation toambient temperature conditions,differently shaped mounds inthe shrub savanna and the gallery forest.Previous studies suggestedthat there might be a constraint that limits thedegree of thermalinsulation of the interior (i.e., nest) of the mounds inenvironmentswith relatively low ambient temperatures. This factor causes,inproximate terms, suboptimal low nest temperatures and ultimatelyleads toreduced reproductive success in the gallery forest.In this study, we examinedwhether the necessity for gas exchangemight constrain mound architecture. Wemeasured CO₂ concentrationsin the air channels of mounds indifferent habitats and undermanipulated temperature regimes. During both thedry and therainy season we found higher CO₂ concentrations inmounds ofthe gallery forest than in mounds of the savanna. Additionalmeasurementsin forest mounds, architecturally resembling those of the savannadueto an experimental increase in ambient temperatures, revealedlowerCO₂ concentrations than unmanipulated mounds in this habitat.Generally,concentrations were higher during the rainy season comparedto thedry season and lower during day than during night. Summarizingthese resultswe present a model that illustrates this trade-offbetween thermoregulationand gas exchange under different temperatureregimes. Both factors togetherresult in different mound architecturesunder different environmentaltemperatures and may finally limitthe distribution of this species.     

Effects of inbreeding and environmental stress on fitness – using Drosophila buzzatii as a model organism

Wild endangered populations can suffer fromadverse effects on fitness due to inbreedingand environmental stress. Often, both geneticand environmental stress factors may be presentin populations at the same time. Thereforeknowledge on the potential interactions betweenthese factors is important for the conservationof wild populations. When measuring fitness(e.g. survival and reproductive potential) ofindividuals in the laboratory, and in nature,inbreeding by environment interactions are nowbeing reported more often. The increased focuson environmental dependency of inbreedingdepression will therefore enable conservationbiologists to include this knowledge in themanagement of endangered populations in thewild. In this study, the effects ofenvironmental stress and inbreeding on fitnessare estimated in a laboratory population ofDrosophila buzzatii. Random- or full-sibmating were used to generate independentreplicate lines of four different inbreedinglevels (F = 0, F = 0.25, F = 0.50, F = 0.672)in four different environments. Theenvironments were thermal and dimethoate stressseparately and in combination, as well as anon-stressful control environment. Twoexperiments were carried out to measureproductivity (a multiplicative measure offecundity and viability) using a full factorialdesign. In the first experiment, productivitywas estimated for all lines and inbreedinglevels in the environment in which flies wereinbred and reared for several generations. Inthe second experiment, productivity of thelines reared in the control environment wastested in all four environments and for allinbreeding levels. Our results show asignificant effect of inbreeding andenvironmental stress on productivity in bothexperiments and the effect increased when flieswere exposed to novel environmental conditions.Productivity was not affected by theinteraction between inbreeding andenvironmental stress when flies were tested inthe environments in which they were reared,whereas there was a tendency towards a stressby inbreeding interaction when flies wereexposed to novel environments. The variance andthe coefficient of variation in productivitywere each affected by environmental stress andinbreeding, indicating that environmentalconditions as well as genetic background areimportant for variation in productivity.However, the two measures of variation oftenshowed opposite trends. The results obtained inthis study indicate that the environmentalconditions under which inbreeding occurs areimportant. This is relevant for the maintenanceand management of populations in captivity andin relation to reintroduction of endangeredspecies in nature.