Leaf gas exchange characteristics, biomass partitioning, and water use efficiencies of two C 4 African grasses under simulated drought

Background Few studies have evaluated the effect of drought on the morpho-physiological characteristics of African C4 grasses. We investigated how drought affects leaf gas exchange characteristics, biomass partitioning, and water use efficiencies of Enteropogon macrostachyus and Cenchrus ciliaris. Methods The grasses were grown in a controlled environment under optimum conditions, that is, 70% of the maximum water-holding capacity (WHC) for the first 40 days. Thereafter, half of the columns were maintained under optimum or drought conditions (30% of maximum WHC) for another 20 days. Results Under optimum conditions, C. ciliaris showed a significantly higher photosynthetic rate, stomatal conductance, and transpiration rate than E. macrostachyus. Drought decreased the photosynthetic rate, stomatal conductance and transpiration rate only in C. ciliaris. The net photosynthetic rate, stomatal conductance, and leaf transpiration of E. macrostachyus did not differ significantly under optimum and drought conditions. E. macrostachyus showed an increase in its water use efficiencies under drought to a greater extent than C. ciliaris. Conclusions Our results demonstrate that C. ciliaris is more sensitive to drought than E. macrostachyus. The decrease in the intercellular CO2 concentration and the increase in stomatal limitation with drought in C. ciliaris and E. macrostachyus suggest that stomatal limitation plays the dominant role in photosynthesis of the studied African C4 grasses

Spatial Distribution of Mucilage in the Rhizosphere Measured With Infrared Spectroscopy

Mucilage is receiving increasing attention because of its putative effects on plant growth, but so far no method is available to measure its spatial distribution in the rhizosphere. We tested whether the C-H signal related to mucilage fatty acids is detectable by infrared spectroscopy and if this method can be used to determine the spatial distribution of mucilage in the rhizosphere. Maize plants were grown in rhizoboxes filled with soil free of organic matter. Infrared measurements were carried out along transects perpendicular as well as axially to the root channels. The perpendicular gradients of the C-H proportions showed a decrease of C-H with increasing distance: 0.8 mm apart from the root center the C-H signals achieved a level near zero. The measured concentrations of mucilage were comparable with results obtained in previous studies, which encourages the use of infrared spectroscopy to quantitatively image mucilage in the rhizosphere

Connecting the dots between root, xylem and stomata

2 páginas.- 3 referencias.- Comunicación oral presentada en el BP2021: XXIV Reunión de la Sociedad Española de Biología de Plantas y XVII Congreso Hispano-Luso de Biología de Plantas, 7 y 8 de julio de 2021. onlineStomata are present on all land plants and are key features for vascular plant water content regulation on Earth. Their primary function, i.e., stomatal closure to control water los s under soil and atmospheric drought, is Ihought to prevent cavitation in the vascular system (Brodribb et al. 2017). However, stomata are found to close much before the xylem cavitates - i.e., the leaf water potential at which stomata close by 50% (IV gs50) is much less negative than the water potential at which the xylem loses 50% of its conductivity (lV_x50) (Martin-St Paul et al. 2017). The mechanism that would allow sto mata to close promptly to a decrease in transpiration in relation to a change in leaf water potential before the decrease in hydraulic conductance is still elusive. Our hypothesis is that the loss of root-soil hydraulic conductivity, more than xylem vulnerability to embolisms, is Ihe primary constraint on transpiration during drought (RodriguezDominguez and Brodribb 2020). Thus, sto mala would close when the water potential around the roots drops more rapidly than the increase in transpiration. We investigated whether this loss of root-soil hydraulic conductivity, probably caused due to root shrinkage and the formation of air-filled gaps, aml/or damage to fine roots, appeared to be an important constraint on transpiration during drought. We conducted physiological and imaging experiments on maize plants undergoing moderate drought. We performed highresolution imaging (micro-CT) of leaves and the root-soil interface and measured in parallel the soil and plant water potentials. Transpiration, stomatal conductance, root hydraulic conductance and soil and plant water potential were also measured during soil drying in a similar set of plants. The formation of air-filled gaps along individual maize roots was visualized and quantified, finding an agreement between the soil water potential at which roots shrank and root hydraulic conductance decreased, and the soil water potential at which sto mata c1osed. These results proved the hypothesis that the loss of contact between roots and soil, and probably other root cortex modifications, triggered stomatal c10sure and transpiration reduction.Microcomputed tomography measurements were conducted at the PSYCHE beamline at SOLEIL Synchrotron (Paris, France). C.M.R-D. was supported by a "Juan de la Cierva - Incorporación" post-doctoral fellowship (Spain) and was granted a Junior Fellowship by the University of Bayreuth Centre of Intemational Excellence "Alexander von Humboldt" for conducting this specific experiment.N

How the interactions between atmospheric and soil drought affect the functionality of plant hydraulics

ISSN:0140-7791ISSN:1365-304

Root hydraulic phenotypes impacting water uptake in drying soils

Soil drying is a limiting factor for crop production worldwide. Yet, it is not clear how soil drying impacts water uptake across different soils, species, and root phenotypes. Here we ask (1) what root phenotypes improve the water use from drying soils? and (2) what root hydraulic properties impact water flow across the soil-plant continuum? The main objective is to propose a hydraulic framework to investigate the interplay between soil and root hydraulic properties on water uptake. We collected highly resolved data on transpiration, leaf and soil water potential across 11 crops and 10 contrasting soil textures. In drying soils, the drop in water potential at the soil-root interface resulted in a rapid decrease in soil hydraulic conductance, especially at higher transpiration rates. The analysis reveals that water uptake was limited by soil within a wide range of soil water potential (-6 to -1000 kPa), depending on both soil textures and root hydraulic phenotypes. We propose that a root phenotype with low root hydraulic conductance, long roots and/or long and dense root hairs postpones soil limitation in drying soils. The consequence of these root phenotypes on crop water use is discussed.ISSN:0140-7791ISSN:1365-304

Leaf gas exchange characteristics, biomass partitioning, and water use efficiencies of two C4 African grasses under simulated drought

Background: Few studies have evaluated the effect of drought on the morpho-physiological characteristics of African C4 grasses. We investigated how drought affects leaf gas exchange characteristics, biomass partitioning, and water use efficiencies of Enteropogon macrostachyus and Cenchrus ciliaris. Methods: The grasses were grown in a controlled environment under optimum conditions, that is, 70% of the maximum water-holding capacity (WHC) for the first 40 days. Thereafter, half of the columns were maintained under optimum or drought conditions (30% of maximum WHC) for another 20 days. Results: Under optimum conditions, C. ciliaris showed a significantly higher photosynthetic rate, stomatal conductance, and transpiration rate than E. macrostachyus. Drought decreased the photosynthetic rate, stomatal conductance and transpiration rate only in C. ciliaris. The net photosynthetic rate, stomatal conductance, and leaf transpiration of E. macrostachyus did not differ significantly under optimum and drought conditions. E. macrostachyus showed an increase in its water use efficiencies under drought to a greater extent than C. ciliaris. Conclusions: Our results demonstrate that C. ciliaris is more sensitive to drought than E. macrostachyus. The decrease in the intercellular CO2 concentration and the increase in stomatal limitation with drought in C. ciliaris and E. macrostachyus suggest that stomatal limitation plays the dominant role in photosynthesis of the studied African C4 grasses.ISSN:2097-051XISSN:2770-174

Engineering Rhizosphere Hydraulics: Pathways to Improve Plant Adaptation to Drought

Recent studies have drawn attention to the role of mucilage in shaping rhizosphere hydraulic properties and regulating root water uptake. During drying, mucilage keeps the rhizosphere wet and conductive, but on drying it turns hydrophobic, limiting root water uptake. In this study, we introduce the concept of , defined as additives that (i) rewet the rhizosphere and (ii) reduce mucilage swelling, thereby reducing the rhizosphere conductivity. We tested whether selected surfactants behaved as rhizoligands. We used neutron radiography to monitor water redistribution in the rhizosphere of lupine ( L. cv. Feodora) and maize ( L.) irrigated with water and rhizoligands. In a parallel experiment, we tested the effect of rhizoligands on the transpiration rate of lupine and maize subjected to repeated drying and wetting cycles. We also measured the effect of rhizoligands on the maximum swelling of mucilage and the saturated hydraulic conductivity of soil mixed with various mucilage concentrations. Rhizoligand treatment quickly and uniformly rewetted the rhizosphere of maize and lupine. Interestingly, rhizoligands also reduced transpiration during drying–wetting cycles. Our hypothesis is that the reduction in transpiration was triggered by the interaction between rhizoligand and mucilage exuded by roots. This hypothesis is supported by the fact that rhizoligand reduced the maximum swelling of mucilage, increased its viscosity, and decreased the hydraulic conductivity of soil–mucilage mixtures. The reduced conductivity of the rhizosphere induced a moderate stress to the plants, reducing transpiration. Rhizoligands increase the rhizosphere wetting kinetics and decrease the maximum swelling of mucilage. As a consequence, root rehydration following irrigation is faster, a larger volume of water is available to the plant, and this water is used more slowly. This slower water consumption would allow the plant to stay turgid during a prolonged drying period. We propose that by managing the hydraulic properties of the rhizosphere, we can improve plants’ adaptation to drought

Hydraulic conductivity of soil-grown lupine and maize unbranched roots and maize root-shoot junctions

Improving or maintaining crop productivity under conditions of long term change of soil water availability and atmosphere demand for water is one the big challenges of this century. It requires a deep understanding of crop water acquisition properties, i.e. root system architecture and root hydraulic properties among other char- acteristics of the soil-plant-atmosphere continuum. A root pressure probe technique was used to measure the root hydraulic conductances of seven-week old maize and lupine plants grown in sandy soil. Unbranched root seg- ments were excised in lateral, seminal, crown and brace roots of maize, and in lateral roots of lupine. Their total hydraulic conductance was quantified under steady-state hydrostatic gradient for progressively shorter seg- ments. Furthermore, the axial conductance of proximal root regions removed at each step of root shortening was measured as well. Analytical solutions of the water flow equations in unbranched roots developed recently and relating root total conductance profiles to axial and radial conductivities were used to retrieve the root radial hydraulic conductivity profile along each root type, and quantify its uncertainty. Interestingly, the optimized root radial conductivities and measured axial conductances displayed significant differences across root types and species. However, the measured root total conductances did not differ significantly. As compared to mea- surements reported in the literature, our axial and radial conductivities concentrate in the lower range of her- baceous species hydraulic properties. In a final experiment, the hydraulic conductances of root junctions to maize stem were observed to highly depend on root type. Surprisingly maize brace root junctions were an order of magnitude more conductive than the other crown and seminal roots, suggesting potential regulation me- chanism for root water uptake location and a potential role of the maize brace roots for water uptake more important than reported in the literature

Field scale plant water relation of maize (Zea mays) under drought – impact of root hairs and soil texture

Background and aims Impact of drought on crop growth depends on soil and root hydraulic properties that determine the access of plant roots to soil water. Root hairs may increase the accessible water pool but their effect depends on soil hydraulic properties and adaptions of root systems to drought. These adaptions are difficult to investigate in pot experiments that focus on juvenile plants. Methods A wild-type and its root hairless mutant maize (Zea mays) were grown in the field in loam and sand substrates during two growing seasons with a large precipitation deficit. A comprehensive dataset of soil and plant properties and monitored variables were collected and interpreted using simulations with a mechanistic root water uptake model. Results Total crop water use was similar in both soils and for both genotypes whereas shoot biomass was larger for the wild type than for the hairless mutant and did not differ between soils. Total final root length was larger in sand than in loam but did not differ between genotypes. Simulations showed that root systems of both genotypes and in both soils extracted all plant available soil water, which was similar for sand and loam, at a potential rate. Leaf water potentials were overestimated by the model, especially for the hairless mutant in sand substrate because the water potential drop in the rhizosphere was not considered. Conclusions A direct effect of root hairs on water uptake was not observed but root hairs might influence leaf water potential dependent growth