Stomatal control of transpiration

Biomimetic Design of Breathable 2D Photothermal Fabric with Three-Layered Structure for Efficient Four-Plane Evaporation of Seawater

2D photothermal membranes have demonstrated numerous advantages in solar desalination due to their flexibility, scalability, and low cost. However, their practical applications are limited by the restricted evaporation area and obstructed vapor channels. A biomimetic design of the breathable 2D photothermal fabric is reported, which is composed of two carbon-nanotube-hydrogel-coated polyester (PET) fabrics separated by fiber pillars, with the upper fabric layer having a hole array as stomatal channels. This fabric shows high solar-absorption efficiency (96.1%) and decreased water-evaporation enthalpy (1664.6 kJ kg-1). The hanging fabric as a heliotropic evaporator exhibits four-plane evaporation feature and achieves a high evaporation rate of 2.6 kg m-2 h-1 under sunlight (1.0 kW m-2) illumination, better than the traditional floated model (single-plane, 1.6 kg m-2 h-1). The evaporation rate can be further enhanced to 4.2 kg m-2 h-1 upon introducing adscititious airflow (2 m s-1). Simultaneously, the heliotropic-hanging design allows the dropping of concentrated brine, avoiding solid-salt-crystallization.

Practical Considerations and Limitations of Using Leaf and Canopy Temperature Measurements as a Stomatal Conductance Proxy: Sensitivity across Environmental Conditions, Scale, and Sample Size

Stomatal conductance (gs) is a crucial component of plant physiology, as it links plant productivity and water loss through transpiration. Estimating gs indirectly through leaf temperature (Tl) measurement is common for reducing the high labor cost associated with direct gs measurement. However, the relationship between observed Tl and gs can be notably affected by local environmental conditions, canopy structure, measurement scale, sample size, and gs itself. To better understand and quantify the variation in the relationship between Tl measurements to gs, this study analyzed the sensitivity of Tl to gs using a high-resolution three-dimensional model that resolves interactions between microclimate and canopy structure. The model was used to simulate the sensitivity of Tl to gs across different environmental conditions, aggregation scales (point measurement, infrared thermometer, and thermographic image), and sample sizes. Results showed that leaf-level sensitivity of Tl to gs was highest under conditions of high net radiation flux, high vapor pressure deficit, and low boundary layer conductance. The study findings also highlighted the trade-off between measurement scale and sample size to maximize sensitivity. Smaller scale measurements (e.g., thermocouple) provided maximal sensitivity because they allow for exclusion of shaded leaves and the ground, which have low sensitivity. However, large sample sizes (up to 50 to 75) may be needed to differentiate genotypes. Larger-scale measurements (e.g., thermal camera) reduced sample size requirements but include low-sensitivity elements in the measurement. This work provides a means of estimating leaf-level sensitivity and offers quantitative guidance for balancing scale and sample size issues.

White LED Lighting Increases the Root Productivity of Panax ginseng C. A. Meyer in a Hydroponic Cultivation System of a Plant Factory

To identify effective light spectra for increasing the productivity of Panax ginseng, we conducted experiments in a controlled environment using a hydroponic cultivation system in a plant factory. We investigated the effect of single LEDs (red, blue, and yellow) and mixed LEDs (red + blue and red + blue + white). The relationships between four light spectra (red, blue, yellow, and white) and physiological responses (net photosynthetic rate, stomata conductance, transpiration rate, and intercellular CO2 partial pressure), as well as growth responses (shoot and root biomass), were analyzed using multivariate statistical analysis. Among the four physiological response variables, shoot biomass was not increased by any pathway, and root biomass was increased only by the intercellular CO2 partial pressure. Red and yellow light increased shoot biomass, whereas white light promoted an increase in the net photosynthetic rate and enhanced root biomass. In contrast, blue light was less effective than the other light spectra in increasing both shoot and root biomass. Therefore, red and yellow light are the most effective light spectra for increasing shoot biomass and white light is effective for increasing root biomass in a plant factory that uses artificial LED lighting. Furthermore, the intercellular CO2 partial pressure is an important physiological variable for increasing the root biomass of P. ginseng.

Quantifying the Annual Cycle of Water Use Efficiency, Energy and CO2 Fluxes Using Micrometeorological and Physiological Techniques for a Coffee Field in Costa Rica

Coffee is one of the most commonly traded agricultural commodities globally. It is important for the livelihoods of over 25 million families worldwide, but it is also a crop sensitive to climate change, which has forced producers to implement management practices with effects on carbon balance and water use efficiency (WUE) that are not well understood due to data scarcity. From this perspective, we propose crop canopy coupling to the atmosphere (Ώ) as an index of resilience and stability. We undertook an integrated observational approach for the scaling-up of measurements along the soil–plant–atmosphere continuum at different stages of the coffee crop phenological cycle. Additionally, we develop this perspective under pronounced climatic seasonality and variability, in order to assess carbon balance, WUE, and agroecosystem resilience in a sun-grown coffee field. Further, we devised a field layout that facilitates the measurement of intrinsic, instantaneous, and actual water use efficiency and the assessment of whether coffee fields differ in canopy structure, complexity, and agronomic management and whether they are carbon sources or sinks. Partitioning soil and canopy energy balances and fluxes in a sun-grown coffee field using eco-physiological techniques at the leaf and whole plant levels (i.e., sap flow and gas exchange), as proposed here, will allow the scaling-up to whole fields in the future. Eddy covariance was used to assess real-time surface fluxes of carbon, gross primary productivity (GPP), and evapotranspiration, as well as components of the energy balance and WUE. The preliminary results support the approach used here and suggested that coffee fields are CO2 sinks throughout the year, especially during fruit development, and that the influence of seasonality drives the surface–atmosphere coupling, which is dominant prior to and during the first half of the rainy season. The estimated WUE showed consistency with independent studies in coffee crops and a marked seasonality driven by the features of the rainy season. A plan for the arborization of the coffee agroecosystem is suggested and the implications for WUE are described. Future comparison of sun- and shade-grown coffee fields and incorporation of other variables (i.e., crop coefficient-KC for different leaf area index (LAI) values) will allow us to better understand the factors controlling WUE in coffee agroecosystems.

Relationships of growth, stable carbon isotope composition and anatomical properties of leaf and xylem in seven mulberry cultivars: a hint towards drought tolerance

The fast growth of mulberry depends on high water consumption, but considerable variations in drought tolerance exist across different cultivars. Physiological and anatomical mechanisms are important to plant survival under drought. However, few research efforts have been made to reveal the relationships of these two aspects in relation to drought tolerance. In this study, growth rates, leaf functional physiology and anatomical characteristics of leaf and xylem of 1-year-old saplings of seven mulberry cultivars at a common garden were compared. Their relationships were also explored. Growth, leaf physiology and anatomy were significantly different among the tested cultivars. Foliar stable carbon isotope composition (δ¹³ C) was negatively correlated with growth rates, and closely related to several leaf and xylem anatomical traits. Particularly, leaf thickness, predicted hydraulic conductivity and vessel element length jointly contributed 77% of the variability in δ¹³ C. Cultivar Wupu had small stomata, intermediate leaf thickness, the smallest hydraulically weighted vessel diameter and highest vessel number, and higher δ¹³ C; Yunguo1 had high abaxial stomatal density, low specific leaf area, moderate hydraulic conductivity and δ¹³ C; these are beneficial features to reduce leaf water loss and drought-induced xylem embolism in arid areas. Cultivar Liaolu11 had contrasting physiological and anatomical traits compared with the previous two cultivars, suggesting that it might be sensitive to drought. Our findings indicate that growth and δ¹³ C are closely associated with both leaf and xylem anatomical characteristics in mulberry, which provides fundamental information to assist evaluation of drought tolerance in mulberry cultivars and in other woody trees.

Hydraulic Balance of a Eucalyptus urophylla Plantation in Response to Periodic Drought in Low Subtropical China

A clear understanding of hydraulic regulation in cultivated plants is crucial for addressing challenges to forest water cycling due to climate changes in low subtropical China. Experiments were conducted to determine the hydrologic balance of a Eucalyptus urophylla plantation in response to periodic drought. Trees displayed lower stomatal conductance (G_S) and leaf water potentials (Ψ_L) during the dry periods. A decrease of 22.4% was found for the maximum reference G_S (G_S at D = 1 kPa; G_Sref-max). Accordingly, specific hydraulic conductivity (k_s) decreased by 45.3 - 65.6% from the wet to the dry season, depending on the tree size. Fairly stable leaf stomatal conductance (g_s) with decreasing Ψ_L (Ψ_L < -1.6 MPa) contributed to the high water-use efficiency (WUE) of this Eucalyptus species. Additionally, the lower stomatal sensitivity (-m = 0.53) in the dry season might also be responsible for the high WUE, since we found an anisohydric behavior that was associated with photosynthetically active radiation (Q₀). Larger trees were found to use water more efficiently than small trees, due to the higher sensitivity of k_s to decreasing Ψ_L. This was also verified by the decreasing leaf carbon isotope discrimination (Δ¹³C) with increasing tree diameter. However, further studies are needed to determine the universality of these results for other Eucalyptus species in this region.

Pore size regulates operating stomatal conductance, while stomatal densities drive the partitioning of conductance between leaf sides

BACKGROUND AND AIMS

Leaf gas exchange is influenced by stomatal size, density, distribution between the leaf adaxial and abaxial sides, as well as by pore dimensions. This study aims to quantify which of these traits mainly underlie genetic differences in operating stomatal conductance (gs) and addresses possible links between anatomical traits and regulation of pore width.

METHODS

Stomatal responsiveness to desiccation, gs-related anatomical traits of each leaf side and estimated gs (based on these traits) were determined for 54 introgression lines (ILs) generated by introgressing segments of Solanum pennelli into the S. lycopersicum 'M82'. A quantitative trait locus (QTL) analysis for stomatal traits was also performed.

KEY RESULTS

A wide genetic variation in stomatal responsiveness to desiccation was observed, a large part of which was explained by stomatal length. Operating gs ranged over a factor of five between ILs. The pore area per stomatal area varied 8-fold among ILs (2-16 %), and was the main determinant of differences in operating gs between ILs. Operating gs was primarily positioned on the abaxial surface (60-83 %), due to higher abaxial stomatal density and, secondarily, to larger abaxial pore area. An analysis revealed 64 QTLs for stomatal traits in the ILs, most of which were in the direction of S. pennellii.

CONCLUSIONS

The data indicate that operating and maximum gs of non-stressed leaves maintained under stable conditions deviate considerably (by 45-91 %), because stomatal size inadequately reflects operating pore area (R(2) = 0·46). Furthermore, it was found that variation between ILs in both stomatal sensitivity to desiccation and operating gs is associated with features of individual stoma. In contrast, genotypic variation in gs partitioning depends on the distribution of stomata between the leaf adaxial and abaxial epidermis.

Water-use advantage for lianas over trees in tropical seasonal forests

Lianas exhibit peak abundance in tropical forests with strong seasonal droughts, the eco-physiological mechanisms associated with lianas coping with water deficits are poorly understood. We examined soil water partitioning, sap flow, and canopy eco-physiological properties for 99 individuals of 15 liana and 34 co-occurring tree species in three tropical forests that differed in soil water availability. In the dry season, lianas used a higher proportion of deep soil water in the karst forest (KF; an area with severe seasonal soil water deficit (SSWD)) and in the tropical seasonal forest (TSF, moderate SSWD), permitting them to maintain a comparable leaf water status than trees in the TSF or a better status than trees in the KF. Lianas exhibited strong stomatal control to maximize carbon fixation while minimizing dry season water loss. During the dry period, lianas significantly decreased water consumption in the TSF and the KF. Additionally, lianas had a much higher maximum photosynthetic rates and sap flux density in the wet season and a lower proportional decline in photosynthesis in the dry season compared with those of trees. Our results indicated that access to deep soil water and strong physiological adjustments in the dry season together with active wet-season photosynthesis may explain the high abundance of lianas in seasonally dry forests.

Controls of evapotranspiration and CO2 fluxes from scots pine by surface conductance and abiotic factors

Evapotranspiration (E) and CO2 flux (Fc ) in the growing season of an unusual dry year were measured continuously over a Scots pine forest in eastern Finland, by eddy covariance techniques. The aims were to gain an understanding of their biological and environmental control processes. As a result, there were obvious diurnal and seasonal changes in E, Fc , surface conductance (gc ), and decoupling coefficient (Ω), showing similar trends to those in radiation (PAR) and vapour pressure deficit (δ). The maximum mean daily values (24-h average) for E, Fc , gc , and Ω were 1.78 mmol m(-2) s(-1), -11.18 µmol m(-2) s(-1), 6.27 mm s(-1), and 0.31, respectively, with seasonal averages of 0.71 mmol m(-2) s(-1), -4.61 µmol m(-2) s(-1), 3.3 mm s(-1), and 0.16. E and Fc were controlled by combined biological and environmental variables. There was curvilinear dependence of E on gc and Fc on gc . Among the environmental variables, PAR was the most important factor having a positive linear relationship to E and curvilinear relationship to Fc , while vapour pressure deficit was the most important environmental factor affecting gc . Water use efficiency was slightly higher in the dry season, with mean monthly values ranging from 6.67 to 7.48 μmol CO2 (mmol H2O)(-1) and a seasonal average of 7.06 μmol CO2 (μmol H2O)(-1). Low Ω and its close positive relationship with gc indicate that evapotranspiration was sensitive to surface conductance. Mid summer drought reduced surface conductance and decoupling coefficient, suggesting a more biotic control of evapotranspiration and a physiological acclimation to dry air. Surface conductance remained low and constant under dry condition, supporting that a constant value of surface constant can be used for modelling transpiration under drought condition.

Comparison of photosynthetic components of wheat genotypes under rain-fed and irrigated conditions

The major environmental factor limiting the range of adaptation for wheat is drought. Fourteen wheat genotypes (Triticum aestivum L.) were grown under two environments (irrigated and rain fed) to determine physiological and photosynthetic responses to drought. Combined analysis of variance of the data showed that the environment was a significant source of variation for leaf chlorophyll content (LCC), stomatal conductance (g(s)) and grain yield (GY). Wheat genotypes differed significantly for LCC, g(s) and GY. All the measured traits under water-stress conditions except maximum photochemical efficiency of PSII (F(v)/F(m)) were lower than those under nonstress conditions. Mean GY in rain-fed conditions was 11.26% lower than that in irrigated conditions. The genotypes number 13 (Marvdasht) and 8 (M-81-13) exhibited the highest GY per unit area in both irrigation and rain-fed conditions. It was concluded that the higher LCC and g(s) under drought-stress conditions could possibly be the proper criteria for screening the drought-tolerant wheat genotypes under field conditions.

Ecophysiological analysis of two arctic sedges under reduced root temperatures

Shoot physiological activity in arctic vascular plants may be controlled by low soil temperatures. While leaves may be exposed to moderate temperatures during the growing season, root temperatures often remain near freezing. In this study, two tundra sedges, Eriophorum vaginatum and Carex bigellowii, were subjected to reduced soil temperatures, and photosynthetic parameters (light saturated photosynthesis A(max), variable to maximal fluorescence and F(v)/F(m) stomatal conductance) and abscisic acid concentrations were determined. Stomatal conductance and A(max) for both E. vaginatum and C. bigellowii strongly decreased with declining soil temperatures. Decreasing soil temperature, however, impacted F(v)/F(m) to a much lesser degree. Root and leaf ABA concentrations increased with decreasing root temperature. These observations support the contention that soil temperature is a significant photosynthetic driving factor in arctic sedges exposed to variable root and shoot temperatures. Because these two species comprise approximately 30% of the vascular ground cover of wet tussock tundra, the soil temperature responses of these sedges potentially scale up to significant effects on ecosystem carbon exchange.