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Diffusion of CO2 from the leaf intercellular air space to the site of carboxylation (g m) is a potential trait for increasing net rates of CO2 assimilation (A net), photosynthetic efficiency, and crop productivity. Leaf anatomy plays a key role in this process; however, there are few investigations into how cell wall properties impact g m and A net. Online carbon isotope discrimination was used to determine g m and A net in Oryza sativa wild-type (WT) plants and mutants with disruptions in cell wall mixed-linkage glucan (MLG) production (CslF6 knockouts) under high- and low-light growth conditions. Cell wall thickness (T cw), surface area of chloroplast exposed to intercellular air spaces (S c), leaf dry mass per area (LMA), effective porosity, and other leaf anatomical traits were also analyzed. The g m of CslF6 mutants decreased by 83% relative to the WT, with c. 28% of the reduction in g m explained by S c. Although A net/LMA and A net/Chl partially explained differences in A net between genotypes, the change in cell wall properties influenced the diffusivity and availability of CO2. The data presented here indicate that the loss of MLG in CslF6 plants had an impact on g m and demonstrate the importance of cell wall effective porosity and liquid path length on g m.

Plant growth and water use are interrelated processes influenced by genetically controlled morphological and biochemical characteristics. Improving plant water use efficiency (WUE) to sustain growth in different environments is an important breeding objective that can improve crop yields and enhance agricultural sustainability. However, genetic improvement of WUE using traditional methods has proven difficult due to the low throughput and environmental heterogeneity of field settings. To overcome these limitations, this study utilizes a high-throughput phenotyping platform to quantify plant size and water use of an interspecific Setaria italica × Setaria viridis recombinant inbred line population at daily intervals in both well-watered and water-limited conditions. Our findings indicate that measurements of plant size and water use are correlated strongly in this system; therefore, a linear modeling approach was used to partition this relationship into predicted values of plant size given water use and deviations from this relationship at the genotype level. The resulting traits describing plant size, water use, and WUE all were heritable and responsive to soil water availability, allowing for a genetic dissection of the components of plant WUE under different watering treatments. Linkage mapping identified major loci underlying two different pleiotropic components of WUE. This study indicates that alleles controlling WUE derived from both wild and domesticated accessions can be utilized to predictably modulate trait values given a specified precipitation regime in the model C₄ genus Setaria.

Sugarcane (Saccharum spp.) represents the most valuable row crop in Louisiana. High levels of biomass production and extensive tillage have degraded portions of the state's alluvial soils used to grow sugarcane. In addition to sucrose, processing the crop generates excess bagasse each year, which can represent a disposal problem for sugar factories. However, converting the bagasse to biochar at nearby pyrolysis facilities may prove to be an economical means of improving degraded soils. The objective was to determine the impacts of low rates of biochar (<3.2 mt ha−1) on soil physical, chemical, and biological properties. Plant available nutrient levels were marginally impacted by biochar additions as the biochar exhibited a relatively low surface area and neutral pH. Bagasse‐derived biochar did not affect soil nitrate retention or leaching, and overall recovery was >86%. Biochar did not increase soil CO2 evolution, indicating its stability as a soil carbon amendment. However, adding biochar with mineral nitrogen decreased CO2 evolution, compared to biochar alone, indicating a negative priming effect. Soil moisture retention was minimally impacted by biochar. Cane yield, sucrose content, and sucrose yield were not statistically affected by applying biochar with or without starter fertilizer at planting. Overall, the results indicate that lower levels of bagasse‐derived biochar minimally impacted soil properties and crop yield; however, the biochar was stable in soil and may find utility as a carbon‐rich amendment should carbon credits prove to be an additional source of grower or land‐owner revenue. Core Ideas Biochar produced at 500°C from sugarcane bagasse had a low surface area, neutral pH, and 19%–39% fixed carbon. Biochar at 0.8 and 1.6 mt ha−1 had little effect on plant available nutrients in five soils used to grow sugarcane. Biochar at 2.9 or 5.8 mt ha−1 did not increase soil carbon mineralization, indicating its stability in soil. Biochar had minimal impacts on nitrate leaching, soil moisture properties, or sugarcane yields.

Optimizing row spacing can potentially improve yields when resources such as light and water are limited. Sugarcane in Louisiana is principally grown on rows spaced 1.8 m apart, but interest in planting on 2.4 m rows is increasing. In this study, we hypothesized that wider row spacing would have greater water availability. Soil moisture sensors were placed at 15, 30, and 45 cm depths in treatments: 1.8 and 2.4 m row spacings, two varieties (L 01-299 and HoCP 04-838), and two planting dates. Soil moisture was monitored in 15-min intervals from 2017 to 2020. Mean volumetric water content was slightly greater in 2.4 m than 1.8 m row spacing at 15 and 45 cm, but the biggest difference was observed when soil water content reached its lowest levels where 2.4 m rows had 1.1, 3.1, and 9.8 times more water available at 15, 30, and 45 cm, respectively, compared to 1.8 m row spacing. However, in both row spacings, plant-available water was always present in the top 45 cm, even during periods of low rainfall. Potentially, high water availability provides an opportunity to increase photosynthesis in sugarcane varieties by selecting for greater photosynthetic capacity and CO2 uptake through increasesd stomatal conductance.

Stable isotope measurements are employed extensively in plant-water relations research to investigate physiological and hydrological processes from whole plant to ecosystem scales. Stable isotopes of hydrogen and oxygen are routinely measured to identify plant source water. This application relies on the assumption that no fractionation of oxygen and hydrogen isotopes in water occurs during uptake by roots. However, a large fraction of the water taken up through roots in halophytic and xerophytic plants transverses cell membranes in the endodermis before entering the root xylem. Passage of water through this symplastic pathway has been hypothesized to cause fractionation leading to a decrease in ²H of root xylem water relative to that in the surrounding soil medium. We examined 16 woody halophytic and xerophytic plant species in controlled conditions for evidence of hydrogen isotope fractionation during uptake at the root-soil interface. Isotopic separation (Δ²H = δ²Hsoil water - δ²Hxylem water) ranging from 3[per thousand] to 9[per thousand] was observed in 12 species. A significant positive correlation between salinity tolerance and the magnitude of Δ²H was observed. Water in whole stem segments, sapwood, and roots had significantly lower δ²H values relative to soil water in Prosopis velutina Woot., the species expressing the greatest Δ²H values among the 16 species examined. Pressurized water flow through intact root systems of Artemisia tridentata Nutt. and Atriplex canescens (Pursh) Nutt. caused the δ²H values to decrease as flow rate increased. This relationship was not observed in P. velutina. Destroying the plasma membranes of root cells by excessive heat from boiling did not significantly alter the relationship between δ²H of expressed water and flow rate. In light of these results, care should be taken when using the stable isotope method to examine source-water use in halophytic and xerophytic species.

Leaf carbon and oxygen isotope ratios can potentially provide a time-integrated proxy for stomatal conductance (g s) and transpiration rate (E), and can be used to estimate transpiration efficiency (TE). In this study, we found significant relationships of bulk leaf carbon isotopic signature (δ13CBL) and bulk leaf oxygen enrichment above source water (Δ18OBL) with gas exchange and TE in the model C₄ grasses Setaria viridis and S. italica. Leaf δ13C had strong relationships with E, g s, water use, biomass, and TE. Additionally, the consistent difference in δ13CBL between well-watered and water-limited plants suggests that δ13CBL is effective in separating C₄ plants with different availability of water. Alternatively, the use of Δ18OBL as a proxy for E and TE in S. viridis and S. italica was problematic. First, the oxygen isotopic composition of source water, used to calculate leaf water enrichment (Δ18OLW), was variable with time and differed across water treatments. Second, water limitations changed leaf size and masked the relationship of Δ18OLW and Δ18OBL with E. Therefore, the data collected here suggest that δ13CBL but not Δ18OBL may be an effective proxy for TE in C₄ grasses.

Aims We studied the relationship between seasonal nutrient availability and fine root density with soil depth to determine potential nutrient uptake strategies of evergreen and deciduous woody species in an infertile, seasonally dry plant community. Methods PO 4 3− , NO 3 − , and NH 4 + were measured with soil depth and across seasons, using ion-exchange resins. Fine root density was measured seasonally by counting the first four root terminal orders (root branching from tip to base). Aboveground stem density and species composition were measured. Results N and P availability were highest in the shallow soil layer and peaked in the late wet season and not during the initial rains as was hypothesized. Substantial N and P were found at deeper soil depths during the early dry season. Fine root density was highest in the shallow soil layer and in the wet season and underwent substantial turnover from dry to wet season. Stem and root area were correlated. Conclusions Having high fine root densities in the shallow soil layer benefits P uptake more than N or water uptake. Dormancy in deciduous species decreases fine root turnover but continued nutrient uptake in the dry season by the more abundant evergreen species appears to be of greater importance.

Diffusion of CO 2 from the leaf intercellular air space to the site of carboxylation ( g m ) is a potential trait for increasing net rates of CO 2 assimilation ( A net ), photosynthetic efficiency, and crop productivity. Leaf anatomy plays a key role in this process; however, there are few investigations into how cell wall properties impact g m and A net . Online carbon isotope discrimination was used to determine g m and A net in Oryza sativa wild‐type ( WT ) plants and mutants with disruptions in cell wall mixed‐linkage glucan ( MLG ) production ( CslF6 knockouts) under high‐ and low‐light growth conditions. Cell wall thickness ( T cw ), surface area of chloroplast exposed to intercellular air spaces ( S c ), leaf dry mass per area ( LMA ), effective porosity, and other leaf anatomical traits were also analyzed. The g m of CslF6 mutants decreased by 83% relative to the WT , with c . 28% of the reduction in g m explained by S c . Although A net / LMA and A net /Chl partially explained differences in A net between genotypes, the change in cell wall properties influenced the diffusivity and availability of CO 2 . The data presented here indicate that the loss of MLG in CslF6 plants had an impact on g m and demonstrate the importance of cell wall effective porosity and liquid path length on g m .

Water is the most important resource in plant growth and is a major limiting factor in sugarcane productivity worldwide. Improving water use efficiency (WUE) can increase sugarcane productivity relative to available water resources by increasing photosynthetic capacity relative to transpiration and stomatal conductance instead of decreasing stomatal conductance. Leaf carbon stable isotopic composition (δ 13 C leaf ) can serve as a proxy for intrinsic WUE (WUE i ) because WUE i and δ 13 C leaf are theoretically related through the link between intracellular and ambient CO 2 concentrations ( C i / C a ) and leaf CO 2 discrimination (Δ 13 C leaf ). In this study we surveyed 55 sugarcane genotypes for WUE i , leaf WUE (WUE leaf ), C i / C a , and δ 13 C leaf by gas exchange measurements and stable isotope analysis. We hypothesized that significant genotypic variation was found in WUE i , WUE leaf , and δ 13 C leaf within the sugarcane population in Louisiana. We also hypothesized that both WUE i and δ 13 C leaf and Δ 13 C leaf and C i / C a were correlated and that δ 13 C leaf could be used as a proxy for WUE i in sugarcane. Here WUE i and WUE leaf had a genetic effect and were controlled mostly by water loss (stomatal conductance or transpiration). WUE i , WUE leaf , C i / C a , and δ 13 C leaf were correlated, but δ 13 C leaf was not correlated with the component traits of WUE i (photosynthetic rate and stomatal conductance). δ 13 C leaf shows promise as a proxy for WUE i to at least be able to select the tails of the distribution, but the relationship between WUE i and δ 13 C leaf may not be sufficiently strong to select WUE at a finer scale.

Plant growth and water use are interrelated processes influenced by genetically controlled morphological and biochemical characteristics. Improving plant water use efficiency (WUE) to sustain growth in different environments is an important breeding objective that can improve crop yields and enhance agricultural sustainability. However, genetic improvement of WUE using traditional methods has proven difficult due to the low throughput and environmental heterogeneity of field settings. To overcome these limitations, this study utilizes a high-throughput phenotyping platform to quantify plant size and water use of an interspecific × recombinant inbred line population at daily intervals in both well-watered and water-limited conditions. Our findings indicate that measurements of plant size and water use are correlated strongly in this system; therefore, a linear modeling approach was used to partition this relationship into predicted values of plant size given water use and deviations from this relationship at the genotype level. The resulting traits describing plant size, water use, and WUE all were heritable and responsive to soil water availability, allowing for a genetic dissection of the components of plant WUE under different watering treatments. Linkage mapping identified major loci underlying two different pleiotropic components of WUE. This study indicates that alleles controlling WUE derived from both wild and domesticated accessions can be utilized to predictably modulate trait values given a specified precipitation regime in the model C genus .