Leaf Physiology Research Articles

Impact of soil moisture stress during the silk emergence and grain-filling in maize.

Suboptimal soil moisture during the growing season often limits maize growth and yield. However, the growth stage-specific responses of maize to soil moisture regimes have not been thoroughly investigated. This study investigated the response of maize to five different soil moisture regimes, that are, 0.25, 0.20, 0.15, 0.10, and 0.05 m3 m-3 volumetric water content (VWC), during flowering and grain-filling stages. Sub-optimal soil moisture at the flowering and grain-filling stages reduced ear leaf stomatal conductance by 73 and 64%, respectively. An increase in stress severity caused significant reductions in ear leaf chlorophyll content and greenness-associated vegetation indices across growth stages. Fourteen days of soil moisture stress during flowering delayed silk emergence, reduced silk length (19%), and silk fresh weight (34%). Furthermore, sub-optimal soil moisture caused a significant reduction in both kernel number (53%) and weight (54%). Soil moisture stress at the flowering had a direct impact on kernel number and an indirect effect on kernel weight. During grain-filling, disruption of ear leaf physiology resulted in a 34% decrease in kernel weight and a 43% decrease in kernel number. Unlike grain-filling, treatments at the flowering significantly reduced kernel starch (3%) and increased protein by 29%. These findings suggest that developing reproductive stage stress-tolerant hybrids with improved resilience to soil moisture stress could help reduce the yield gap between irrigated and rainfed maize.

Phenotypic plasticity in leaf traits in response to experimental precipitation increase: Wettability, foliar water uptake and gas exchange

AbstractWater availability is one of the factors affecting plant growth and development, especially in arid and semiarid environments. Changes in precipitation due climate change alter water availability to plants impacting on plant physiology. Numerous studies have focused on plant response to reduced precipitation and less on the effects of increased precipitation. The main objective of this study was to evaluate biophysical and physiological leaf traits in response to experimental water addition in four dominant shrubs and one grass species in a Patagonian steppe, during the dry season. The experiment consisted of two treatments: control and water addition, increasing the average annual rainfall by 25% during 6 years. We measured leaf wettability, water status, transpiration, photosynthesis, stomatal conductance, water use efficiency and foliar water uptake (FWU). In addition, we determined the phenotypic plasticity index of these evaluated traits. We expected lower FWU and higher transpiration and photosynthesis rates due changes in leaf surface properties under water addition treatment. All study species responded significantly to treatment with higher loss of water per transpiration and lower FWU. Also, all species increased photosynthesis rate and water use efficiency (WUE). However, water potential and leaf wettability did not change with higher precipitation. Thus, higher phenotypic plasticity was observed in functional than in morphological traits. Since functional traits were more sensitive than leaf surface traits, plants may quickly take advantage when environmental conditions tend to be more favourable to growth. Our findings suggest that plants of Patagonian steppe have adaptive ability to respond to environmental changes through plastic responses.

Rhizosphere-inhabiting fungi isolated from native plants of the atacama desert affect leaf traits of ‘chardonnay’ grapevines (Vitis vinifera L.).

Studying new alternatives for promoting plant growth is crucial to face a changing climate. This study aimed to determine the beneficial effect of fungal strains isolated from the rhizospheric soil of two native plants from the Atacama Desert on physiological leaf traits of inoculated ‘Chardonnay’ grapevines. Rhizosphere fungi were isolated from Baccharis scandens and Solanum chilense and tested in vitro for plant growth-promoting traits, including indole acetic acid, phosphate solubilization, siderophore production, and polyamine production. Aspergillus niger, Microdochium bolleyi, and Westerdikeya centenaria were isolated, showing plant growth-promoting attributes and high salt tolerance in almost all tested isolates. Then, the fungi were stabilized and co-inoculated in pot-grown ‘Chardonnay’ plants (Vitis vinifera L.) growing in outdoor conditions to evaluate gas exchange variables, chlorophylls (as SPAD value), water potential, proline and sugar content, and lipid peroxidation in leaves. Inoculation of the fungal strains significantly increased the photosynthesis rate, which was associated with higher mesophyll conductance and SPAD values. The co-inoculation also induced an enhanced protective condition for oxidative damage. Increased carbon assimilation resulted in higher soluble sugars and intrinsic water use efficiency in leaves without altering the water status of treated plants. Our results demonstrated the beneficial effects of co-inoculating rhizosphere-inhabiting fungi isolated from native plants from the Atacama Desert on physiological traits of ‘Chardonnay’ grapevines.

Anatomical, morphological and physiological leaf characters of black betel (Piper betle L. var. nigra) in varying natural and man-made habitats

Abstract. Kuswandi PC, Ariyanti NA, Yunus MF, Amri CNAC. 2023. Anatomical, morphological and physiological leaf characters of black betel (Piper betleL. var. nigra) in varying natural and man-made habitats. Biodiversitas 24: 3236-3244. Piper betle L. var. nigra or black betel (known as Sirih hitam in Indonesia) contains valuable secondary metabolites, such as alkaloids, flavonoids, saponins, tannins, phenols, carotenoids, steroids and terpenoids. Black betel leaf extract has been shown to have antimicrobial activity thus there is a prospect to be developed as a promising herbal plant. Nevertheless, little information is available about its development as a medicinal plant. This research studies the influence of different habitats on several characters of black betel leaves with the aim to understand the suitable environmental conditions for the optimum growth of black betel plants. We used a survey method and random sampling of black betel leaves in four locations in Java Island, Indonesia, namely Banyuwangi which represents natural habitat, and Karanganyar, Ngaglik and Pakem which represent man-made habitats. Measurements of temperature, humidity, soil moisture and light intensity were carried out at each location. Analyses of leaf area, leaf water content, total leaf chlorophyll content and flavonoid content were undertaken and statistically analyzed using SPSS software. Leaf transverse sections were also observed. The results showed that the environmental parameters differed in the four locations. Leaves samples from the natural habitat in Banyuwangi were significantly different (P<0.05) from the three man-made habitats for chlorophyll and flavonoid content. For water content, significant difference was only for Banyuwangi samples with those from Karanganyar and Pakem. For leaf area, significant difference was only found between the Banyuwangi samples and Karanganyar. Observations on the transverse cross section of midrib of black betel leaves from the four locations showed structures that are generally found in Piper betle species, namely the presence of an epidermal layer, trichomes in the abaxial part of the leaf, several layers of the hypodermis, visible vascular tissue and the presence of secretion cells. There were several differences in the leaf anatomy such as greater number of trichomes on the leaves from Karanganyar, the secretory cells that were more visible in the leaves from Ngaglik and Banyuwangi and the sclerenchymal tissue that was more visible in the leaves from Banyuwangi. Such differences are likely influenced by variations in environmental parameters thus showing that the man-made habitat in the Karanganyar location can affect leaves characters similar to black betel plant grown in its natural habitat in Banyuwangi.

Xylem function and leaf physiology in European beech saplings during and after moderate and severe drought stress

Abstract The extreme drought events in the last years caused high mortality amongst European beech (Fagus sylvatica L.) across Central Europe. Thus, knowledge of the response of beech to drought and its ability to recover its xylem and leaf functions after drought release is needed to better understand beech survival. In this study, changes in xylem function, leaf gas exchange, chlorophyll fluorescence and morphology of European beech saplings during drought and recovery phases were assessed. Beech saplings were exposed to three different watering intensities—well-watered (W), moderately drought stressed (M) and severely drought stressed (S) for 25 days, and then saplings were rewatered for 14 days. Reduced irrigation caused a drop in shoot water potential to −1.1 and −3.1 MPa in M and S saplings, respectively. Stomatal conductance in M and S saplings decreased to 15 and 5 per cent of that in W saplings, respectively, and it corresponded with a decrease in the photosynthesis rate and chlorophyll fluorescence parameters. Leaf water content and shoot functional xylem area were significantly affected by drought only in S saplings. Hence, these parameters could be used as sensitive indicators that distinguish plants at no risk of mortality from those at increasing risk under drought stress. In S saplings, some leaves also dried from the edges, leaving a green active central part. During the recovery phase, the leaf gas exchange and chlorophyll fluorescence parameters had recovered 4 days after rewatering in M saplings, whereas in S saplings, they were still lower after 2 weeks. Moreover, xylem function did not fully recover in S saplings till the end of the recovery phase. Hence, subsequent drought periods, even of lower intensity, could lead to tree mortality if tree functions have not fully recovered from the previous drought.

Effects of Hemlock Woolly Adelgid Control Using Imidacloprid on Leaf-Level Physiology of Eastern Hemlock

Widespread mortality of eastern hemlock (Tsuga canadensis [L.] Carr.) has been occurring due to the introduction of hemlock woolly adelgid (Adelges tsugae Annand) (HWA), threatening millions of hectares of hemlock-dominated forests in the eastern United States. HWA feeds at the base of needles and removes stored carbohydrates, which can impact leaf-level physiology, contributing to the decline of the tree. However, these physiological mechanisms in HWA-infested hemlocks are still not clearly understood. We investigated hemlock leaf physiology year-round at three forested sites with various degrees of infestation. At each site, half the trees were treated with imidacloprid (Merit® 2 F, Bayer, Kansas City, MO, USA) while the rest were left untreated. Imidacloprid is widely used to control HWA but can itself have phytotoxic effects. After one growing season, there was an increase in photosynthetic rates (7.5%, p = 0.0163) and stomatal conductance (7.1%, p = 0.0163) across sites in the trees treated with imidacloprid. After two years, the imidacloprid treatment also increased bud break from 22.5% to 88.7% at Fishburn (the most severely impacted site) and from 22.7% to 58.9% at Mountain Lake (the least impacted site), and slightly increased chlorophyll fluorescence for treated trees at Fishburn. Chemical treatment also slightly increased water use efficiency at Mountain Lake. These results suggest that HWA is causing tree mortality largely through a reduction in leaf area caused by decreasing bud break and also by a slight, but significant, reduction in leaf-level photosynthesis and stomatal conductance.

Foliar application of methyl jasmonate affects impatiens walleriana growth and leaf physiology under drought stress

ABSTRACT In this study, the effects of foliar applied methyl jasmonate (MeJA) on drought-stressed Impatiens walleriana growth and leaf physiology parameters: stomatal conductance, chlorophyll, flavonoid, anthocyanin, and nitrogen balance index (NBI), were evaluated. These parameters could serve as indicators of drought tolerance of I. walleriana, a popular horticultural plant worldwide that is very sensitive to drought. The experiment included four treatments: control, drought-stressed plants sprayed with distilled water, drought-stressed plants sprayed with 5 µM MeJA, and drought-stressed plants sprayed with 50 µM MeJA. Foliar spraying with MeJA was performed twice: seven days before and on the day of drought induction. The stressed plant groups were non-irrigated to achieve soil water contents (SWC) of 15 and 5%, while control plants were well-watered throughout the experiment (35–37% SWC). The results of this study showed that drought significantly reduced I. walleriana fresh and dry shoot weight, as well as total leaf area, but did not impact on dry matter content. The foliar application of MeJA improved growth parameters of I. walleriana, depending on the elicitor concentration and drought intensity. Stomatal conductance was slightly reduced at 5% SWC, and foliar applied MeJA at both concentrations. The flavonoid index was slightly reduced at 15 and 5% SWC when 50 µM MeJA was foliar applied, while there were no observed changes in the anthocyanin index in any treatments. The foliar application of 50 µM MeJA increased the chlorophyll index and NBI of I. walleriana at 5% SWC, indicating a contribution of the elicitor to plant drought tolerance at the physiological level.

Creating a virtual leaf.

When microscopy meets modelling the exciting concept of a 'virtual leaf' is born. The goal of a 'virtual leaf' is to capture complex physiology in a virtual environment, resulting in the capacity to run experiments computationally. One example of a 'virtual leaf' application is capturing 3D anatomy from volume microscopy data and estimating where water evaporates in the leaf and the proportions of apoplastic, symplastic and gas phase water transport. The same 3D anatomy could then be used to improve established 3D reaction-diffusion models, providing a better understanding of the transport of CO2 across the stomata, through the airspace and across the mesophyll cell wall. This viewpoint discusses recent progress that has been made in transitioning from a bulk leaf approach to a 3D understanding of leaf physiology, in particular, the movement of CO2 and H2O within the leaf.

Characterization of the layered SIF distribution through hyperspectral observation and SCOPE modeling for a subtropical evergreen forest

Solar-induced chlorophyll fluorescence (SIF) has been widely used as a prospective proxy of plant photosynthesis to accurately detect the response of vegetation to climate change and study terrestrial ecosystem carbon cycle. However, the challenge of estimating vegetation gross primary product (GPP) based on SIF observations remains unresolved due to the confounding effects of leaf physiology and canopy structure, especially the vertical heterogeneity of plant attributes. Radiative transfer models are ideally suited to investigate the variability in radiance signals including fluorescence, but previous studies lack vertically layered spectra to validate the model. In this study, we developed a vertically layered hyperspectral system and proposed an innovative framework for assessing vertical characteristics of SIF and improving the estimation of GPP based on SIF in a subtropical evergreen forest. The global sensitivity analysis on Soil-Canopy-Observation of Photosynthesis and Energy fluxes (SCOPE) model with vertical profiles showed that chlorophyll content (Cab), leaf inclination distribution (LIDFa), leaf area index (LAI), and senescent material (Cs) dominate the vertical variations in reflectance (Ref) and SIF. We found that the vertical characteristics of SIF were mainly impacted by these parameters of the adjacent vertical layer, except for the effects of LAI across the vertical layers on the observed understory SIFU, which were approximately equivalent. 7.8 ± 1.7% of the SIFU was transferred to the top of canopy, contributing up to 17% of the SIF observed on the top of canopy (SIFTOC) during the year. Furthermore, our findings suggest that substituting the observed SIFTOC with the total emitted SIF, particularly from the simulated overstory and understory SIF, could enhance the correlation between GPP and SIF with an increased R2 (ΔR2 = 0.09). This study highlights the importance of accounting for the contribution of the layered SIF in the quantification of the total SIF emission and can benefit the GPP estimation based on SIF signals in subtropical evergreen forests with high canopy density.

Leaf physiological responses of the citrus commercial varieties grafted onto rootstocks

The use of rootstocks provides choices to growers to increase fruit quality and yield, obtain high-density planting, avoid juvenility, and control tree size. The choice of rootstock for a citrus orchard was an important consideration. The aim of the study was to evaluate the effects of citrus rootstocks on leaf mineral composition and leaf physiology of the citrus commercial cultivars (‘Pontianak’ tangerine, ‘Pamindo’ pamelo and ‘Montaji’ lemon). For this purpose, the citrus commercial cultivars were budded onto Japansche citroen (JC) and Citrumelo rootstocks and then leaf mineral composition (total nitrogen, phosphor and kalium concentration) and leaf physiology (chlorophyll index, respiration rate, stomatal conductance and photosynthetic rate) of each scion were measured. Results showed that rootstock type had different influence on leaf mineral composition and leaf physiology in leaf of each scion. For total nitrogen, total kalium and stomatal conductance variables, rootstocks had no effect. For total phosphor variable, JC rootstock induced higher value than Citrumelo in all scion. For chlorophyll Index variable, Citrumelo induced higher value on ‘Pamindo’ and lower value on ‘Montaji’ than JC but had no effect on ‘Pontianak’ tangerine. For respiration rate and photosynthetic rate variable, Citrumelo induced higher value than JC in ‘Pamindo’ but had no effect on ‘Pontianak’ tangerine and ‘Montaji’. Therefore, ‘Pamindo’ was better to be budded on Citrumelo, ‘Montaji’ and ‘Pontianak’ tangerine were better to be budded on JC.

Application of Oil Palm Empty Bunch Ash Nanoparticle on Epidermal Cell Thickness and Chlorophyll Content of the Soybean Leaf

The utilization of oil palm empty bunch (OPEB) could be a powerful solution to manage such large volume of wastes produced from the oil palm plantation. Ash created from this waste could be used as soil ameliorant as well as additional agent for liquid fertilizer. Its form in nano size might increase the leaf absorption. Therefore, this study was aimed to investigate the effect of OPEB ash nanoparticle on epidermal cell thickness and chlorophyll content of soybean leaves. This study was carried out using completely randomized design to examine five levels of OPEB ash nanoparticle concentration, ranging from 0, 1.25, 2.5, 3.75, and 5%. Each concentration was repeated nine times. OPEB ash nanoparticle was applied firstly at 2 weeks-old plants and repeated weekly up to 5 times. Application OPEB ash nanoparticle was performed through foliar spray. The results showed that OPEB ash nanoparticle affect the soybean leaf physiology, particularly the structure and anatomy of its stomata. In addition, application of 0.125% OPEB ash nanoparticle increased the epidermal cell thickness. However, higher concentration of OPEB ash nanoparticle was found to inhibit the chlorophyll formation.

Specific Sound Frequency Improves Intrinsic Water Efficiency in Rice Leaf by Imparting Changes in Stomatal Dimensions

Various attempts have been made to increase rice production, including breeding for high-yielding and stress-tolerant varieties, a good crop management system, and increased agricultural input in rice production. Soundwave stimulation has been demonstrated to affect plant growth; thus, this method can be employed in the current rice production methods to improve yield. The study aims to determine the effects of different sound wave qualities on the general growth, physiological, and morphological of rice seedlings. Rice seeds of the MR219 variety were grown under a glasshouse condition in a nested design with five replications and were stimulated with various sound wave frequencies. Various sound wave frequencies, 380, 359, 357, 353, and 350 Hz, were obtained by placing the pot at varying distances (80, 160, 240, 320, and 400 cm, respectively) from the sound source, except control treatment. There were significant effects in some of the parameters: plant height, leaf physiology, and stomatal pore and length when treated with varying sound wave qualities. Plants can be stimulated with 380, 357, and 350 Hz soundwaves frequencies for the best photosynthetic experience. In addition, 359 Hz of sound wave stimulation resulted in high water use efficiency, which is beneficial in improving crop performance in drought conditions. Thus, it was demonstrated that the sound wave stimulation method has the potential to enhance rice performance in addition to the regular agronomic practices of rice production in farmers’ fields.

Effect of chemical regulators on the recovery of leaf physiology, dry matter accumulation and translocation, and yield-related characteristics in winter wheat following dry-hot wind

Dry-hot wind stress causes losses in wheat productivity in major growing regions worldwide, especially winter wheat in the Huang-Huai-Hai Plain of China, and both the occurrence and severity of such events are likely to increase with global climate change. To investigate the recovery of physiological functions and yield formation using a new non-commercial chemical regulator (NCR) following dry-hot wind stress, we conducted a three-year field experiment (2018–2021) with sprayed treatments of tap water (control), monopotassium phosphate (CKP), NCR at both the jointing and flowering stages (CFS), and NCR only at the jointing stage (FSJ) or flowering stage (FSF). The leaf physiology, biomass accumulation and translocation, grain-filling process, and yield components in winter wheat were assessed. Among the single spraying treatments, the FSJ treatment was beneficial for the accumulation of dry matter before anthesis, as well as larger increases in the maximum grain-filling rate and mean grain-filling rate. The FSF treatment performed better in maintaining a high relative chlorophyll content as indicated by the SPAD value, and a low rate of excised leaf water loss in flag leaves, promoting dry matter accumulation and the contribution to grain after anthesis, prolonging the duration of grain filling, and causing the period until the maximum grain-filling rate reached earlier. The CFS treatment was better than any other treatments in relieving the effects of dry-hot wind. The exogenous NCR treatments significantly increased grain yields by 12.45–18.20% in 2018–2019, 8.89–13.82% in 2019–2020, and 8.10–9.00% in 2020–2021. The conventional measure of the CKP treatment only increased grain yield by 6.69% in 2020–2021. The CFS treatment had the greatest mitigating effect on yield loss under dry-hot wind stress, followed by the FSF and FSJ treatments, and the CKP treatment only had a minimal effect. In summary, the CFS treatment could be used as the main chemical control measure for wheat stress resistance and yield stability in areas with a high incidence of dry-hot wind. This treatment can effectively regulate green retention and the water status of leaves, promote dry matter accumulation and efficient translocation, improve the grain-filling process, and ultimately reduce yield losses.

Sodium arsenite-induced changes in the wood of esca-diseased grapevine at cytological and metabolomic levels.

In the past, most grapevine trunk diseases (GTDs) have been controlled by treatments with sodium arsenite. For obvious reasons, sodium arsenite was banned in vineyards, and consequently, the management of GTDs is difficult due to the lack of methods with similar effectiveness. Sodium arsenite is known to have a fungicide effect and to affect the leaf physiology, but its effect on the woody tissues where the GTD pathogens are present is still poorly understood. This study thus focuses on the effect of sodium arsenite in woody tissues, particularly in the interaction area between asymptomatic wood and necrotic wood resulting from the GTD pathogens' activities. Metabolomics was used to obtain a metabolite fingerprint of sodium arsenite treatment and microscopy to visualize its effects at the histo-cytological level. The main results are that sodium arsenite impacts both metabolome and structural barriers in plant wood. We reported a stimulator effect on plant secondary metabolites in the wood, which add to its fungicide effect. Moreover, the pattern of some phytotoxins is affected, suggesting the possible effect of sodium arsenite in the pathogen metabolism and/or plant detoxification process. This study brings new elements to understanding the mode of action of sodium arsenite, which is useful in developing sustainable and eco-friendly strategies to better manage GTDs.

Vertical patterns of leaf physiology and biofilm characteristics for Hydrilla verticillata in both single and mixed communities

Little is known about how community composition affects vertical patterns of leaf characteristics for submerged macrophytes in freshwater lakes. Here, after sampling Hydrilla verticillata in both single and mixed communities in shallow and deep areas in a shallow lake, we measured vertical patterns of leaf biofilm and physiology characteristics. Upper leaves of H. verticillata always had more attached abiotic biofilm matters, and all biofilm characteristics exhibited declining trends from top to bottom segments in deep areas. Moreover, the amount of attached biofilm matter in the mixed community was less than in the single community in shallow areas, but the reverse was true in deep areas. The vertical pattern of leaf physiology characteristics was obvious in the mixed community. In the shallow area, leaf pigment concentrations showed increasing trends with an increasing water depth, but the enzymatic specific activity of peroxidase (POD-ESA) was precisely the opposite. In the deep area, leaf chlorophyll concentrations were greatest in the leaves of bottom segments and lowest in top segments, while carotenoids and POD-ESA were greatest in the leaves of the middle segment-II. Light intensity and biofilm were found to play an important role in regulating the vertical patterns of photosynthetic pigments and POD-ESA. Our study highlighted the effect of community composition on the vertical pattern of leaf physiology and biofilm characteristics. HIGHLIGHTS: Biofilm characteristics always showed increasing trends with increasing water depth. Community composition changed the amount of attached biofilm matter. The vertical pattern of leaf physiology was more obvious in mixed communities. Light intensity and biofilm regulated the vertical pattern of leaf physiology.

Physiological impacts of beech leaf disease across a gradient of symptom severity among understory American beech

Beech leaf disease (BLD) damage is associated with the parasitic nematode Litylenchus crenatae ssp. mccannii. Foliar symptoms manifest as darkened or chlorotic galls in the interveinal portions in the leaf, which become leathery and crinkled under high severity of infection. Though nearly a decade has passed since the discovery of this disease, little is known regarding the impact of BLD on leaf function and physiology. This study assesses the variation in leaf gas exchange and physiological leaf traits among asymptomatic and BLD-infected leaves across a gradient of symptom severity within a natural forested stand in central Connecticut, USA. Leaves with BLD symptoms are found to have significantly reduced carbon assimilation and instantaneous water use efficiency, with increased levels of stomatal conductance as symptom severity progresses. Leaf response to light manipulation is also affected, with an increase in dark respiration and the light compensation point among banded and crinkled leaves. Additionally, BLD symptoms are found to have a significant influence on leaf water content, specific leaf area, and leaf nitrogen content. Relationships between gas exchange and these leaf traits yield linear correlations that are used to infer functional relationships impacted by the disease.

Differences in leaf gas exchange strategies explain Quercus rubra and Liriodendron tulipifera intrinsic water use efficiency responses to air pollution and climate change.

Trees continuously regulate leaf physiology to acquire CO2 while simultaneously avoiding excessive water loss. The balance between these two processes, or water use efficiency (WUE), is fundamentally important to understanding changes in carbon uptake and transpiration from the leaf to the globe under environmental change. While increasing atmospheric CO2 (iCO2 ) is known to increase tree intrinsic water use efficiency (iWUE), less clear are the additional impacts of climate and acidic air pollution and how they vary by tree species. Here, we couple annually resolved long-term records of tree-ring carbon isotope signatures with leaf physiological measurements of Quercus rubra (Quru) and Liriodendron tulipifera (Litu) at four study locations spanning nearly 100 km in the eastern United States to reconstruct historical iWUE, net photosynthesis (Anet ), and stomatal conductance to water (gs ) since 1940. We first show 16%-25% increases in tree iWUE since the mid-20th century, primarily driven by iCO2 , but also document the individual and interactive effects of nitrogen (NOx ) and sulfur (SO2 ) air pollution overwhelming climate. We find evidence for Quru leaf gas exchange being less tightly regulated than Litu through an analysis of isotope-derived leaf internal CO2 (Ci ), particularly in wetter, recent years. Modeled estimates of seasonally integrated Anet and gs revealed a 43%-50% stimulation of Anet was responsible for increasing iWUE in both tree species throughout 79%-86% of the chronologies with reductions in gs attributable to the remaining 14%-21%, building upon a growing body of literature documenting stimulated Anet overwhelming reductions in gs as a primary mechanism of increasing iWUE of trees. Finally, our results underscore the importance of considering air pollution, which remains a major environmental issue in many areas of the world, alongside climate in the interpretation of leaf physiology derived from tree rings.

Thermal acclimation of leaf respiration is consistent in tropical and subtropical populations of two mangrove species.

Populations from different climates often show unique growth responses to temperature, reflecting temperature adaptation. Yet, whether populations from different climates differ in physiological temperature acclimation remains unclear. Here, we test whether populations from differing thermal environments exhibit different growth responses to temperature and differences in temperature acclimation of leaf respiration. We grew tropical and subtropical populations of two mangrove species (Avicennia germinans, Rhizophora mangle) under ambient and experimentally warmed conditions in common garden at the species' northern range limit. We quantified growth and temperature responses of leaf respiration (R) at seven timepoints over ~10 months. Warming increased productivity of tropical populations more than subtropical populations, reflecting a higher temperature optimum for growth. In both species, R measured at 25 °C declined as seasonal temperatures increased, demonstrating thermal acclimation. Contrary to our expectations, acclimation of R was consistent across populations and temperature treatments. However, populations differed in adjusting the temperature sensitivity of R (Q10) to seasonal temperatures. Following a freeze event, tropical Avicennia showed greater freeze damage than subtropical Avicennia while both Rhizophora populations appeared equally susceptible. We found evidence of temperature adaptation at the whole-plant scale but little evidence for population differences in thermal acclimation of leaf physiology. Studies that examine potential costs and benefits of thermal acclimation in an evolutionary context may provide new insights into limits of thermal acclimation.

The impact of wounding and postharvest storage conditions on retention of soluble protein in sugar beet leaves.

Sugar beet leaves can be a viable and economically interesting source of high-quality protein for the food industry. We investigated how storage conditions and leaf wounding at harvest affect the content and quality of the soluble protein. After collection, leaves were either stored intact or shredded to mimic wounding induced by commercial leaf harvesters. Leaf material was stored in small volumes at different temperatures to assess leaf physiology or in larger volumes to assess temperature development at different locations in the bins. Protein degradation was more pronounced at higher storage temperatures. Wounding accelerated the degradation of soluble protein at all temperatures. Both wounding and storage at higher temperatures greatly stimulated respiration activity and heat production. At temperatures below 5°C, ribulose-1,5-biphosphate carboxylase oxygenase (RuBisCO) in intact leaves was preserved for up to 3weeks. At temperatures of 30-40°C, RuBisCO degradation occurred within 48h. Degradation was more pronounced in shredded leaves. In 0.8-m3 storage bins at ambient temperature, core temperatures rapidly increased, up to 25°C in intact leaves and up to 45°C in shredded leaves within 2-3 days. Immediate storage at 5°C greatly suppressed the temperature increase in intact but not in shredded leaves. The indirect effect of excessive wounding, that is, heat production, is discussed as the pivotal factor responsible for increased degradation of protein. For optimal retention of soluble protein levels and quality in harvested sugar beet leaves, it is advised to minimize wounding and to store the material at temperatures around -5°C. PRACTICAL APPLICATION: To preserve the soluble protein content and quality for at least 3weeks, sugar beet leaves should be harvested with minimal wounding and stored at temperatures between 1 and 5°C. When aiming to store minimally wounded leaves in larger volumes, it must be ensured that the product temperature in the core of the biomass meets the temperature criterium or the cooling strategy must be adjusted. The principles of minimal wounding and low temperature storage are transferable to other leafy crops that are harvested for food protein.

Kinetic factors of physiology and the dynamic light environment influence the economic landscape of short-term hydraulic risk.

Optimality-based models of stomatal conductance unify biophysical and evolutionary constraints and can improve predictions of land-atmosphere carbon and water exchange. Recent models incorporate hydraulic constraints by penalizing excessive stomatal opening in relation to hydraulic damage caused by low water potentials. We used simulation models to test whether penalties based solely on vulnerability curves adequately represent the optimality hypothesis, given that they exclude the effects of kinetic factors on stomatal behavior and integrated carbon balance. To quantify the effects of nonsteady-state phenomena on the landscape of short-term hydraulic risk, we simulated diurnal dynamics of leaf physiology for 10 000 patches of leaf in a canopy and used a ray-tracing model, Helios, to simulate realistic variation in sunfleck dynamics. Our simulations demonstrated that kinetic parameters of leaf physiology and sunfleck properties influence the economic landscape of short-term hydraulic risk, as characterized by the effect of stomatal strategy (gauged by the water potential causing a 50% hydraulic penalty) on both aggregated carbon gain and the aggregated carbon cost of short-term hydraulic risk. Hydraulic penalties in optimization models should be generalized to allow their parameters to account for kinetic factors, in addition to parameters of hydraulic vulnerability.