Water Vapor Conductance Research Articles

Epicuticular wax and its effect on canopy temperature and water use of Sorghum

Epicuticular wax is thought to enable sorghum [Sorghum bicolor (L.) Moench] plants to cope with drought. Increased reflectivity of solar radiation and reduced conductance of water vapor are mechanisms responsible for aiding plants in water conservation. Increased reflectivity should lead to a decrease in canopy temperature and water use, whereas decreased conductance should lead to an increase in canopy temperature because of a decrease in evaporative cooling. It is not clear how these competing effects exert control over water use in a crop such as sorghum. To better understand the role of epicuticular waxes on the energy balance of sorghum, experiments were conducted to determine the effects of waxes on field-scale energy fluxes using near-isogenic lines of grain sorghum having different levels of epicuticular wax loading. Waxes caused an overall 2% increase in albedo, and about 86% of the reflected energy between 400 and 1100 nm was from near-infrared wavelengths. This is at variance with recent reports that suggest that waxes can substantially increase the reflectivity of sorghum. Instead, our results indicated that the amount of reflected radiant energy due to waxes was small. When water was non-limiting, waxes caused a 22% decrease in canopy conductance compared to a 2% increase in albedo on average. Consequently, at the expense of higher canopy temperatures, waxes caused a 5% reduction in latent heat flux when water was not limiting. Without rain, water became limiting to plants with lower wax load sooner than it did for plants with higher wax load. The high wax load canopy then was on average 0.4 °C cooler, had 24% greater canopy conductance and 13% greater latent heat fluxes compared to the low wax one. Results suggested that the primary mechanism through which waxes affect the energy balance of sorghum is by means of reduced conductance of water vapor.

Leaf gas exchange and stable carbon isotope composition of redbay and avocado trees in response to laurel wilt or drought stress

Symptoms of laurel wilt, a vascular plant disease caused by the fungus Raffaelea lauricola, are similar to those of drought stress. We compared physiological responses of redbay and avocado trees infected with laurel wilt to responses of trees with drought stress. Trees were either inoculated with R. lauricola, subjected to drought stress, or irrigated daily and not inoculated (non-stressed, control). Disease symptoms, net CO2 assimilation (A), stomatal conductance of water vapor (gs), substomatal CO2 concentration (Ci), intrinsic water use efficiency (WUEi), leaf chlorophyll index (LCI), the ratio variable to maximum leaf chlorophyll fluorescence (Fv/Fm), leaf nitrogen (N) concentration, and the ratio of 13C to 12C (δ13C) in leaves were determined prior to inoculation and the imposition of drought stress and when plants showed moderate to severe stress symptoms. Laurel wilt-infected and drought-stressed trees of each species had lower A and gs and higher Ci, Fv/Fm, and LCI than non-stressed trees. Redbay trees with laurel wilt had significantly higher (less negative) leaf δ13C values than non-stressed trees, whereas no significant differences were found in leaf δ13C values among avocado treatments. In avocado trees with laurel wilt, there was a negative linear correlation between δ13C values and Ci but no significant correlation between δ13C values and leaf N in the inoculated trees. Inhibition of photosynthesis in avocado and redbay infected with laurel wilt was determined to be a result of the both stomatal and biochemical factors.

The first Similifaveoloolithidae (Wormoolithus luxiensis oogen. et oosp. nov.) from the Upper Cretaceous of Jiangxi Province, China

ABSTRACT This study describes a new member of Similifaveoloolithidae from the Upper Cretaceous Zhoutian Formation of Jiangxi, China. The new ootaxon, Wormoolithus luxiensis oogen. et oosp. nov., is erected based on eggs collected from a partial clutch and represents the second oogenera of Similifaveoloolithidae. Wormoolithus shares some unique features with Similifaveoloolithus such as irregularly branched eggshell units, irregular cavities in the inner part of eggshell that are worm-like in tangential view and oblique pore canals in the outer part of the eggshell that show honeycomb-like structure in tangential view. And it is distinguished from the latter by longer polar axis and equatorial diameter and absence of compact layer. Although the clutch is not complete, the preserved parts show that the eggs are closely stacked in the nest. In addition, clay minerals that occur in pores and a high estimated water vapour conductance indicate a humid burial nest microenvironment.

Surface conductance for evapotranspiration of tropical forests: Calculations, variations, and controls

Tropical forests are responsible for the evaporation and transpiration of large quantities of water into the atmosphere annually. Surface conductance (gs) is a poorly understood phenomenon that plays a central role in regulating this evapotranspiration. We studied the calculations, variations, and environmental factors controlling gs based on eddy flux measurements from 10 tropical forest sites that covered a wide range of water gradients across continents. We found that boundary layer conductance (gb) is comparable with aerodynamic conductance for momentum (gaM) and thus, it should not be ignored in estimations of total aerodynamic conductance for water vapor (gaV). Based on the findings, we have made some recommendations for gaM estimation both with and without measurements of turbulence. The seasonal variation of gs is low in humid sites but large in sites with a dry season. A value of 24.8 ± 13.8 mm s−1 was suggested for maximum surface conductance (gsmax) for tropical forests. Both water vapor deficit (D) and radiation (Q) play an important role in controlling gs. The model driven by both D and Q could capture the diurnal variations of gs well and could be implemented in large-scale models in future. We believe the findings of this study could contribute substantially to our understanding of tropical forest gs.

Cuticle deposition improves the biosecurity of eggs through the laying cycle and can be measured on hatching eggs without compromising embryonic development

The cuticle is part of the egg's natural defense and it can be improved by genetic selection. Prior to adoption of this measurement in breeding programs, questions that need to be addressed are whether improved cuticle deposition will result in a reduced risk of eggs becoming contaminated and whether selection for this trait will have any unintended consequences on the incubation process. Bacterial penetration experiments were carried out using eggs from a pedigree line of broiler breeders (BB) and Rhode Island Red (RIR) layers. Within the natural variation in cuticle deposition in each line, a good cuticle was shown to reduce an egg's susceptibility to penetration by Escherichia coli (BB, P = 0.023) and Salmonella typhimurium (RIR, P < 0.001). Deglycosylation of cuticle proteins had little effect on their antimicrobial activity. The effect of bird age on cuticle deposition was also examined. Shell color decreased with age as anticipated; however, we found no evidence that cuticle deposition decreases with age, at least up to 50 wk. A thicker cuticle could affect the water vapor conductance (WPC) of hatching eggs. The WPC of eggs was, therefore, measured on eggs selected from the top and tail of the cuticle distribution, this time in a Lohmann Selected Leghorn (LSL) pedigree line. Broiler breeder eggs were also tested. No evidence of a relationship between cuticle deposition and WPC was found for LSL or BB eggs. Cuticle deposition measurements require eggs to be stained. Here, we show that this has no adverse effect on embryo development at d 12 of incubation. Thus, we conclude that cuticle deposition is important in preventing bacterial penetration of eggs in genetically divergent breeds of chicken and that the measurement can be practically incorporated into breeding programs. This will contribute to improving the biosecurity of eggs by reducing vertical and horizontal transmission of potentially zoonotic and pathogenic organisms from parent to offspring.

Convergent evolution of reduced eggshell conductance in avian brood parasites.

Brood parasitism has evolved independently in several bird lineages, giving rise to strikingly similar behavioural adaptations that suggest convergent evolution. By comparison, convergence of physiological traits that optimize this breeding strategy has received much less attention, yet these species share many similar physiological traits that optimize this breeding strategy. Eggshell structure is important for embryonic development as it controls the flux of metabolic gases, such as O2, CO2 and H2O, into and out of the egg; in particular, water vapour conductance ( GH2O) is an essential process for optimal development of the embryo. Previous work has shown that common cuckoos ( Cuculus canorus) have a lower than expected eggshell GH2O compared with their hosts. Here, we sought to test whether this is a trait found in other independently evolved avian brood parasites, and therefore reflects a general adaptation to a parasitic lifestyle. We analysed GH2O for seven species of brood parasites from four unique lineages as well as for their hosts, and combined this with species from the literature. We found lower than expected GH2O among all our observed brood parasites both compared with hosts (except for brown-headed cowbirds ( Molothrus ater)) and compared with the expected rates given their phylogenetic positions. These findings suggest that a lowered GH2O may be a general adaptation for brood parasitism, perhaps helping the parasite nestling to develop greater aerobic fitness. This article is part of the theme issue 'The coevolutionary biology of brood parasitism: from mechanism to pattern'.

Losing half the conductive area hardly impacts the water status of mature trees

The water status of transpiring tree crowns depends on a hydraulic continuum from the soil matrix around roots to the sub-stomatal cavity of leaves, with a multitude of hydraulic resistances along this path. Although the stem xylem path may not be the most critical of these resistances, it had been suggested that a >50% interruption of that path by drought-stress-induced embolization (air filling) of conduits is critical for tree survival. Here we show that cutting the sapwood of mature, 35 m tall trees in half hardly affects crown water status and transpiration. Counter expectation, this first adult tree sapwood interception experiment revealed that shoot water potential in the canopy (assessed by using a 45 m canopy crane) either remained unaffected (spruce) or became less negative (beech), associated with small reductions in leaf diffusive conductance for water vapour. We conclude that the stem xylem of these trees has a large overcapacity and the tree hydraulics debate requires a critical re-visitation.

Growth and gas exchanges of red pitaya under different shading conditions

Plants with yellow cladodes are commonly present in commercial red pitaya orchards, in Ceara, mainly during the warmer seasons of the year. Therefore, this study aimed to evaluate the effect of shading on the growth and gas exchanges of red pitaya. We tested five shading levels on stock plants (full sunlight, 35, 50; 65 and 80% shading) via randomized block design (RBD), with five replications and two plants per plot. After 180 days, the following characteristics were evaluated: sum of the length of the axillary shoots, number of axillary shoots, diameter, thickness of secondary shoots, photosynthetic rate, stomatal conductance of water vapor, transpiration, internal carbon dioxide concentration, ratio of internal to external CO2 concentration, instantaneous and intrinsic water use efficiency, and instantaneous carboxylation efficiency. The plants presents large and thin cladodes, apparently blanching under 80% shading; therefore, we concluded that cultivation in full sunlight caused a negative effect on gas exchanges and growth of red pitaya.. The use of 35% shading at 180 days increased the photosynthetic rate, water use efficiency and carboxylation, with increase vegetative growth.

Effect of Vegetation on the Energy Balance and Evapotranspiration in Tallgrass Prairie: A Paired Study Using the Eddy-Covariance Method

We carried out a paired study in tallgrass prairie to evaluate the influence of vegetation on the energy exchange and evapotranspiration. Two eddy-covariance systems were installed over two adjoining sites, one of which was denuded of vegetation, with the adjacent, control site kept undisturbed. Our year-long investigation shows that, for quantifying the ground surface heat flux, the soil heat storage above the soil plates is more important than the sub-surface soil heat flux, both temporally and in magnitude. The incorporation of the soil heat storage, therefore, is indispensable for energy balance closure in areas with short vegetation. At our control site, we observed a critical threshold of 0.17 m3 m−3 in the surface (top 0.3 m) soil water content, whereby the energy partitioning is significantly affected by the presence of the photosynthetically active vegetation when the surface soil water content is higher than this critical threshold. The pattern of energy partitioning approaches that of the treated site when the surface soil water content is lower than this threshold (during drought), because of the suppression of plant physiological activities. This threshold also applies to the surface conductance for water vapour at the control site, where yearly evapotranspiration is 728 ± 3 mm (versus 547 ± 2 mm for the treated site). Thus, the soil water content and presence of active vegetation are the key determinants of energy partitioning and evapotranspiration. Any land-cover changes or vegetation-management practices that alter these two factors may change the energy and water budgets in tallgrass prairie.

Ion‐dependent metabolic responses of Vicia faba L. to salt stress

Salt-affected farmlands are increasingly burdened by chlorides, carbonates, and sulfates of sodium, calcium, and magnesium. Intriguingly, the underlying physiological processes are studied almost always under NaCl stress. Two faba bean cultivars were subjected to low- and high-salt treatments of NaCl, Na2 SO4 , and KCl. Assimilation rate and leaf water vapor conductance were reduced to approximately 25-30% without biomass reduction after 7days salt stress, but this did not cause severe carbon shortage. The equimolar treatments of Na+ , K+ , and Cl- showed comparable accumulation patterns in leaves and roots, except for SO4 2- which did not accumulate. To gain a detailed understanding of the effects caused by the tested ion combinations, we performed nontargeted gas chromatography-mass spectrometry-based metabolite profiling. Metabolic responses to various salts were in part highly linearly correlated, but only a few metabolite responses were common to all salts and in both cultivars. At high salt concentrations, only myo-inositol, allantoin, and glycerophosphoglycerol were highly significantly increased in roots under all tested conditions. We discovered several metabolic responses that were preferentially associated with the presence of Na+ , K+ , or Cl- . For example, increases of leaf proline and decreases of leaf fumaric acid and malic acid were apparently associated with Cl- accumulation.

Physiology of rice and red rice plants in competition for nitrogen

Understanding the influence of nitrogen under the physiological behavior of rice and red rice in competition is critical to success in integrated weed management. In view of this, the objective of this work was to evaluate the physiological effects of the competition of rice and red rice submitted to different nitrogen concentrations. The experiments were conducted under greenhouse conditions in the 2011/12 crop year. The experimental design was completely randomized, with six replicates. The treatments were arranged in a factorial scheme, consisting of different combinations of the rice cultivar IRGA 424 and the red rice biotype, varying the ratios between them [intraspecific competition (100:0) and interspecific competition (50:50)]; and nitrogen doses (0, 30, 60, 90, and 120 g dm -3 ) added to the soil as urea, divided in two periods, at 15 and 53 days after emergence. The variables evalu­ated were: stomatal conductance of water vapor, photosynthetic rate, hydrogen peroxide and lipid peroxidation. The results show that, in general, when compared to intraspecific competition, interspecific competition causes greater oxidative stress and negatively interferes with photosynthesis even when plants are submitted to high (90 and 120 g dm -3 N) nitrogen doses. For red rice, in turn, it is the intraspecific competition that causes higher oxida­tive stress and loss of photosynthesis in plants under lower (0 g dm -3 N) and higher (90 and 120 g dm -3 N) nitro­gen concentrations, respectively, in relation to interspecific competition.

Glycerin as a factor for moderating quality changes in table eggs during storage

Abstract. Glycerol, a by-product of biodiesel production, is non-toxic to humans and the environment. With the current increase in the demand for fuels obtained from biomass, the amount of glycerine waste production is increasing. There are many ways to dispose this substance (in pharmaceuticals, cosmetics, and in chemical industry), but its utilization is still insufficient. Therefore, the aim of this study was to assess the possibility of limiting quality changes in table eggs during storage by coating the shells with a glycerol solution. The material used in this research consisted of 270 table chicken eggs collected on the same day. On the first day of the experiment, quality traits of 30 eggs were evaluated (initial control group). The remaining 240 eggs were divided into two equal groups: control (eggs that were not subjected to any treatment) and experimental (eggs that were coated with a 5 % aqueous solution of glycerol). The eggs were placed on transport trays and stored at 14 ∘C and 70 % humidity. Quality evaluations were carried out after 14 and 28 days of storage. The depth of the air cell, mass and specific gravity of the egg, the shell characteristics (water vapour conductance, strength, mass, thickness, and density), and the content traits (pH of the albumen and yolk, Haugh units, and colour and weight of the yolk) were evaluated. The results obtained suggest that the use of glycerine may contribute to slowing adverse changes in egg quality during storage by limiting CO2 removal from the egg content, which allows the egg to maintain albumen structure. Due to the fact that glycerine is a safe, cheap, and easy-to-apply substance, its large-scale use in poultry raw material storage seems to be a very real possibility.

Fossil eggs associated with a neoceratopsian (Mosaiceratops azumai) from the Upper Cretaceous Xiaguan Formation, Henan Province, China

The close association of osteological remains and fossil eggs sometimes leads to misinterpretations, particularly in the absence of adequate taphonomic data. A clutch of 15 fossil eggs from the Upper Cretaceous Xiaguan Formation, Henan Province, China occurs in close association to a partial skeleton of the neoceratopsian, Mosaiceratops azumai. Two centimeters of sediment separate several eggs on the edge of the clutch from the rostrum of the skull. However, preservation of aragonite crystals in the eggshell allows assignment of the eggs to a turtle. Physical characteristics of the bones and eggs suggest the specimen was prepared upside-down. We estimate an egg mass of 89.3 g and calculate water vapor conductance (GH2O) as 288 mgH2Oday−1 Torr−1. Using a formula that correlates egg size (53 × 58 mm) and carapace length, we estimate the carapace of the turtle that produced the clutch as 1.5 m. This egg size exceeds that of all previously reported fossil turtle eggs.

Characterization of stomata on floral organs and scapes of cut ‘Real’ gerberas and their involvement in postharvest water loss

Stomata present on leaves are the main channels for water vapor exchange between the plant and atmosphere, and contribute to water loss of cut flowers. Although cut gerberas (Gerbera jamesonii Bolus) are commonly composed of a terminal composite floral head and a scape, and have no leaves, they are also prone to severe water deficits, presumably resulting from water loss exceeding water uptake. We have investigated the distribution and characteristics of stomata of cut ‘Real’ gerberas, and their response to light and abscisic acid (ABA) treatments, to increase understanding of their functionality in postharvest water loss. Stomata were widely distributed on various parts of floral organs and the scape in cut gerberas, including the lower epidermis of the ray floret petals, trans florets, disc florets, lower epidermis of sepals, and the uppermost and middle parts of scape surfaces. The highest stomatal density was observed on the lower epidermis of sepals. Cut gerberas had the largest stomata on the middle scape surface and the smallest on the surface of the uppermost scape. Nonetheless, the lower epidermis of sepals had the highest relative stomatal area, which was higher than that of the other parts. Additionally, the lower sepal epidermis had the highest maximum stomatal conductance of water vapor (gwmax), and which was higher than that of the lower and upper leaf epidermis. The opening of stomata on various parts of cut gerberas differed in their response to light, and the highest percentage of open stomata and largest aperture were found in the stomata on the lower epidermis of sepals. Changes in water loss in cut gerberas exhibited a distinct circadian rhythm over a four-day vase period with an alternating 12-h light/dark cycle. In the lower epidermis of sepals, ABA painting treatment significantly inhibited stomatal opening and reduced water loss in cut gerberas over a 6 h light period. These findings imply the critical involvement of stomata on the lower epidermis of sepals in water loss of cut gerberas, and improve our understanding of the mechanism underlying their water deficit symptoms.

Ecophysiological and metabolic response patterns to drought under controlled condition in open-pollinated maternal families from a Fagus sylvatica L. population

The genetic variability within a plant species or population determines the extent to which drought impacts plant function at different levels of biological organization. By disentangling the extent to which drought tolerance is genetically determined within a population, we can get insights of the adaptive capacity of species to cope with climate change at the local scale. We compared the ecophysiological and leaf metabolic responses of different maternal families from a single population of the water-stress-sensitive species, Fagus sylvatica L, to an imposed drought in a controlled experiment. Nitrogen metabolism was modified by water stress, and some proteinogenic amino acids such as: proline (PRO), valine (VAL) and aspartic acid (ASP), as well as the non-proteinogenic amino-acid γ-aminobutyric (GABA), accumulated in response to drought. Gas exchange was depressed with increasing water deficit (i.e. a decrease in predawn water potential – Ψpd) in all families, with significant differences among maternal families for net photosynthesis (Anet) and stomatal conductance of water vapour (gwv). However increasing stomatal limitation of Anet did not reduce the pool of non-structural carbohydrates (NSC). In fact, under water stress NSCs, including both mono- and disaccharides, accumulated as leaf Ψpd decreased; with the most striking effect of water stress being an increase in the trisaccharide raffinose (RAF) in all the maternal families. Leaf secondary metabolites were also affected differently by water stress among the maternal families. Overall, there were differential changes among our maternal families in various leaf metabolites, in seedlings under both the well-watered and water-stressed treatments. This result supports the hypothesis that there is a high degree of intra-population variability in the response to drought at different levels of biological organization in beech, i.e. ranging from ecophysiological to metabolic responses. This intra-population genetic variability is fundamental for adaptation of the species to drier environments at its trailing range edge in a context of climate change.

Water vapor conductance: a technique using eggshell fragments and relations with other parameters of eggshell

ABSTRACT The objective of this study was to evaluate a technique for quantifying eggshell conductance using shell fragments from hatched eggs. Additional objectives were to calculate the correlation between eggshell conductance, porosity, and thickness and correlate these parameters with incubation data. The study design was fully randomized in a 3 × 3 factorial scheme (three egg regions – large end, equator, and narrow end – and three ages of broiler breeders – 29, 35, and 59 weeks). A total of [...]

An Attempt to Partition Stomatal and Non-stomatal Ozone Deposition Parts on a Short Grassland

To evaluate the damaging effect of tropospheric ozone on vegetation, it is important to evaluate the stomatal uptake of ozone. Although the stomatal flux is a dominant pathway of ozone deposition onto vegetated surfaces, non-stomatal uptake mechanisms such as soil and cuticular deposition also play a vital role, especially when the leaf area index $${LAI}< 4$$ . In this study, we partitioned the canopy conductance into stomatal and non-stomatal components. To calculate the stomatal conductance of water vapour for sparse vegetation, we firstly partitioned the latent heat flux into effects of transpiration and evaporation using the Shuttleworth–Wallace (SW) model. We then derived the stomatal conductance of ozone using the Penman–Monteith (PM) theory based on the similarity to water vapour conductance. The non-stomatal conductance was calculated by subtracting the stomatal conductance from the canopy conductance derived from directly-measured fluxes. Our results show that for short vegetation (LAI $$=$$ 0.25) dry deposition of ozone was dominated by the non-stomatal flux, which exceeded the stomatal flux even during the daytime. At night the stomatal uptake of ozone was found to be negligibly small. In the case of vegetation with $${LAI}\approx 1$$ , the daytime stomatal and non-stomatal fluxes were of the same order of magnitude. These results emphasize that non-stomatal processes must be considered even in the case of well-developed vegetation where cuticular uptake is comparable in magnitude with stomatal uptake, and especially in the case of vegetated surfaces with $${LAI}< 4$$ where soil uptake also has a role in ozone deposition.

Long-term trends in leaf level gas exchange mirror tree-ring derived intrinsic water-use efficiency of Pinus cembra at treeline during the last century

The ability of treeline conifers in the Central European Alps to cope with recent climate warming and increasing CO2 concentration is still poorly understood. We determined basal area increment (BAI) and tree ring stable carbon isotope ratios (δ13C) of Pinus cembra trees from 1925 through 2013. Stable isotope ratios and BAI were compared with leaf level gas exchange measurements carried out in situ between 1934 and 2012, and thus, provided new insights into long-term trends of tree-ring derived intrinsic water-use efficiency (iWUE). Mature P. cembra trees at treeline responded to increasing Ca and air temperature with a parallel increase in maximum net CO2 uptake rate at ambient CO2 (Amax) and tree-ring-derived intercellular CO2 partial pressure (Ci). Amax tripled and was positively correlated to BAI and Ci. The latter increased in parallel with ambient CO2 concentration and stomatal conductance. In contrast to the instantaneous gas exchange parameters, δ13C derived iWUE informs about the long-term changes in the carbon water relations. These data showed three changes in the iWUE chronosequences, which could be identified with different long term gas exchange patterns: (1) from stomatal controlled functioning from 1925 to 1981, to a situation where (2) both net CO2 fixation (A) and leaf conductance for water vapour (gw), responded to the environment from 1982 to 1997, and (3) back to a stomata controlled pattern over iWUE from 1998 onwards. This temporal pattern was also mirrored in leaf level gas exchange assessments, suggesting a parallel increase of A and gw of P. cembra at treeline during the last nine decades.

What Does the Eggshell Cuticle Do? A Functional Comparison of Avian Eggshell Cuticles.

The avian eggshell is a highly ordered structure with several layers (mammillae, palisades, and vertical crystal layer) composed of calcium carbonate (∼96%) and minerals within an organic matrix. The cuticle is a noncalcified layer that covers the eggshells of most bird species. Eggshells are multifunctional structures that have evolved in response to diverse embryonic requirements and challenges, including protection from microbial infection, nest flooding, and exposure to solar radiation. However, experimental evidence for these functions across diverse taxa is currently limited. Here we investigated the effects of nanosphere cuticles on (1) bacterial attachment and transshell penetration, (2) eggshell wettability, (3) water vapor conductance, and (4) regulation of ultraviolet (UV) reflectance in seven ground-nesting bird species. We found considerable interspecific variation in ultrastructure and chemical composition of cuticles. Experimental removal of the cuticle confirmed that all nanospheres were highly effective at decreasing attachment of bacteria to shell surfaces and at preventing bacterial penetration. Cuticles also greatly decreased the amount of UV reflected by eggshells. In species with particularly small nanospheres, gas exchange was reduced by the presence of cuticle. Our results support the hypothesis that microbes and solar UV radiation can cause strong selection on bird eggs but also show that we need a greater understanding about the effects of specific nesting conditions (e.g., hydric and gaseous milieu) on embryo well-being and eggshell structure variation.

Technical note: An experimental set-up to measure latent and sensible heat fluxes from (artificial) plant leaves

Abstract. Leaf transpiration and energy exchange are coupled processes that operate at small scales yet exert a significant influence on the terrestrial hydrological cycle and climate. Surprisingly, experimental capabilities required to quantify the energy–transpiration coupling at the leaf scale are lacking, challenging our ability to test basic questions of importance for resolving large-scale processes. The present study describes an experimental set-up for the simultaneous observation of transpiration rates and all leaf energy balance components under controlled conditions, using an insulated closed loop miniature wind tunnel and artificial leaves with pre-defined and constant diffusive conductance for water vapour. A range of tests documents the above capabilities of the experimental set-up and points to potential improvements. The tests reveal a conceptual flaw in the assumption that leaf temperature can be characterized by a single value, suggesting that even for thin, planar leaves, a temperature gradient between the irradiated and shaded or transpiring and non-transpiring leaf side can lead to bias when using observed leaf temperatures and fluxes to deduce effective conductances to sensible heat or water vapour transfer. However, comparison of experimental results with an explicit leaf energy balance model revealed only minor effects on simulated leaf energy exchange rates by the neglect of cross-sectional leaf temperature gradients, lending experimental support to our current understanding of leaf gas and energy exchange processes.