A computational model of the cereal leaves hydraulics

Environmental factors and plant architectonics significantly determine its water regime, namely, the water content and its movement through the tissues forced by the difference in water potentials, turgor pressure in cells, etc. In turn, the cumulative water regime affects the functioning and growth of cells, photosynthesis, and, as a result, the plant’s growth. The leaf contributes to the formation of the water regime and characterizes the contour of the plant’s adaptive system. Nevertheless, the data on the contribution of leaves to the total resistance to water transport in the plant and the structure of the hydraulic resistance of the leaf itself is still contradictory. This paper presents the formulation and justification of the monocots leaf hydraulics model based on Darcy’s law. The model was tested in computational experiments in the Comsol 4.3b package on idealized geometric models of leaf blades. Simulations showed the dependence of water potential distribution in xylem vessels and leaf mesophyll on the permeability of these tissues and on microclimatic parameters around the leaf. The adequacy of the model parameters selected as a result of testing is discussed.

The Effect of Age and Drought on the Recovery of Midday Leaf Hydraulics and Physiological Traits in Oat (Avena nuda)

The leaf hydraulic behavior has a significant role on species survival because plants often encounter drought. The effect of age and drought on the leaf water potential (ѰL), leaf hydraulic conductance (KL), stomatal density (SD) and size (SS), evapotranspiration (E), net photosynthetic rate (Pn) stomatal conductance (gs) and their post drought recovery in naked oat is not understood. This study investigated these facts in two naked oat cultivars, Yanmai (Ym) and Dingyou7 (Dy7). The plants were grown in pots and kept well-watered (WW) for the first ~30 days after sowing (DAS) after that for Experiment 1) the plants were kept in a rainout shelter; in a growth room and kept WW throughout. Experiment 2) the plants were grown at 40% drought to determine the effect of drought on the SD and SS. Experiment 3) the plants were grown in 40% field water capacity (FC) for ~25 days then, they were recovered from drought stress and ѰL, KL, SS, SD, E, Pn, and gs were determined. Under the drought, Ym lost KL whereas; Dy7 could maintain KL and higher midday ѰL and lower SD than Ym. The cultivar Dy7 showed maximum recovery of KL, ѰL, Pn, gs and E than Ym upon re-watering. The loss and recovery of KL, ѰL, Pn, E, gs and SD is controlled genetically in naked oat cultivars in combination with the environmental factors and the cultivar Dy7 has potential to enhance drought resistance in crops plants by genetic crop breeding. © 2021 Friends Science Publishers

Seasonal coordination of leaf hydraulics and gas exchange in a wintergreen fern

Wintergreen fern Polystichum acrostichoides has fronds that are photosynthetically active year-round, despite diurnal and seasonal changes in soil moisture, air temperature and light availability. This species can fix much of its annual carbon during periods when the deciduous canopy is open. Yet, remaining photosynthetically active year-round requires the maintenance of photosynthetic and hydraulic systems that are vulnerable to freeze–thaw cycles. We aimed to determine the anatomical and physiological strategies P. acrostichoides uses to maintain positive carbon gain, and the coordination between the hydraulic and photosynthetic systems. We found that the first night below 0 °C led to 25 % loss of conductivity (PLC) in stipes, suggesting that winter-induced embolism occurred. Maximum photosynthetic rate and chlorophyll fluorescence declined during winter but recovered by spring, despite PLC remaining high; the remaining hydraulic capacity was sufficient to supply the leaves with water. The onset of colder temperatures coincided with the development of a necrotic hinge zone at the stipe base, allowing fronds to overwinter lying prostrate and maintain a favourable leaf temperature. Our conductivity data show that the hinge zone did not affect leaf hydraulics because of the flexibility of the vasculature. Collectively, these strategies help P. acrostichoides to survive in northeastern forests.

Differentiation in Leaf Physiological Traits Related to Shade and Drought Tolerance Underlies Contrasting Adaptations of Two Cyclobalanopsis (Fagaceae) Species at the Seedling Stage

Adaptation and acclimation of tree seedlings to different combinations of light and water conditions can determine the species-specific patterns of distribution along environmental gradients and the underlying physiological mechanisms are fundamental to the understanding of such patterns. Seedlings of two Cyclobalanopsis species naturally occurring in southwest China, with distinct distribution and regeneration characteristics, were grown under 100%, 50% and 4% sunlight conditions and traits related to shade and drought tolerance were studied. Particularly, we investigated whether leaf hydraulics, photosynthetic traits and their functional coordination play an important role in determining seedling environmental adaptation and acclimation of the two species. Seedlings of C. helferiana showed characteristics adapted to high irradiance while C. rex had traits adapted to partially shaded environments. Cyclobalanopsis helferiana had significantly higher maximum net photosynthetic rate (Amax), light compensation point and light saturation point than C. rex and the contrasts were particularly large when they were grown under full sunlight. Cyclobalanopsis helferiana showed the highest Amax when grown under 100% sunlight, while C. rex exhibited the highest Amax at 50% sunlight. Similarly, under full sunlight conditions C. helferiana showed significantly higher leaf hydraulic conductance (Kleaf) than C. rex, i.e., 13.37 vs. 7.09 mmol m−2 s−1 MPa−1 (p < 0.01). The correlation between Kleaf and Amax followed a unified positive correlation across different light treatments of both species. Moreover, leaves of C. helferiana showed greater resistance to drought-induced hydraulic dysfunction and to desiccation than C. rex. The contrasts in functional traits between the two Cyclobalanopsis species are consistent with the hypothesis that there is a trade-off between shade tolerance and drought tolerance. Findings of the present study contribute to a deeper understanding of mechanisms of divergence between closely related (congeneric) species with respect to key ecophysiology associated with natural regeneration.

Leaf hydraulic conductance is linked to leaf symmetry in bifacial, amphistomatic leaves of sunflower

The hydraulic implications of stomatal positioning across leaf surfaces and the impact on internal water flow through amphistomatic leaves are not currently well understood. Amphistomaty potentially provides hydraulic efficiencies if the majority of hydraulic resistance in the leaf exists outside the xylem in the mesophyll. Such a scenario would mean that the same xylem network could equally supply a hypostomatic or amphistomatic leaf. Here we examine leaves of Helianthus annuus to determine whether amphistomaty in this species is associated with higher hydraulic efficiency compared with hypostomatic leaves. We identified asymmetry in the positioning of minor veins which were significantly closer to the abaxial than the adaxial leaf surface, combined with lower Kleaf when transpiration was driven through the adaxial rather than the abaxial surface. We also identified a degree of coordination in stomatal behaviour driven by leaf hydraulics, where the hydraulic conditions experienced by an individual leaf surface affected the stomatal behaviour on the opposite surface. We found no advantage to amphistomaty based on efficiencies in construction costs of the venous system, represented by vein density:stomatal density, only limited hydraulic independence between leaf surfaces. These results suggest that amphistomaty does not substantially increase whole-leaf hydraulic efficiency.

Effects of major vein blockage and aquaporin inhibition on leaf hydraulics and stomatal conductance

The density and architecture of leaf veins determine the network and efficiency of water transport within laminae and resultant leaf gas exchange and vary widely among plant species. Leaf hydraulic conductance ( K leaf ) can be regulated by vein architecture in conjunction with the water channel protein aquaporin. However, our understanding of how leaf veins and aquaporins affect leaf hydraulics and stomatal conductance ( g s ) remains poor. By inducing blockage of the major veins and inhibition of aquaporin activity using HgCl 2 , we examined the effects of major veins and aquaporins on K leaf and g s in species with different venation types. A vine species, with thick first-order veins and low vein density, displayed a rapidly declined g s with high leaf water potential in response to vein blockage and a greatly reduced K leaf and g s in response to aquaporin inhibition, suggesting that leaf aquaporins are involved in isohydric/anisohydric stomatal behaviour. Across species, the decline in K leaf and g s due to aquaporin inhibition increased linearly with decreasing major vein density, possibly indicating that a trade-off function between vein architecture (apoplastic pathway) and aquaporin activity (cell-to-cell pathway) affects leaf hydraulics.