ASHS 2024 Conference

Evaluating Plasticity and Acclimation of Linked Hydraulic Traits of Different Taxa Across a Climatic Gradient in the Western U.S. - Amelia Keyser Gibson
Climate Ready Stomata: Stomata Morphology and Physiology Varies Across Western US Sites and Irrigation Deficit Treatments in Rosa and Hibiscus syriacus Cultivars - Miro Stuke
Ice Formation and Progression in Rhododendron, and a Mechanistic Hypothesis for Winter Thermonasty of Leaves - Rajeev Arora
Trade-Offs in Reproductive Traits and Buds' Freezing Survival Strategies Among Prunus Species - Camilo Villouta
Potential Genes Involved in the Adaptation of Potato to Long Term Heat Stress - Jiwan Palta
Species-specific Differences in Leaf Photosynthetic Rate when Substituting Far-red Light for PAR Photons - John Ertle
Investigating Dormancy and Germination Characteristics to Promote Restoration Success in the Northern Great Plains - Bret Lang

Increasing drought conditions and variable water availability under climate change impact plant productivity, ecosystem function and the global carbon cycle, with many species-level responses remaining unknown. Variation in response and ability to acclimate to decreased water availability differs among plant species and across biomes. This project utilized a preexisting water deficit trial of horticultural taxa across sites in the Western U.S. to assess the interactions between acclimation to climate and water availability across a growing season. Four focal taxa, Physocarpus ‘Diabolo’, P. ‘Little Devil’, Cercis canadensis and C. occidentalis shared across three locations in Washington, Oregon and Utah were measured for physiological and hydraulic traits on the leaf and stem scale in response to irrigation treatment. The cultivars of Physocarpus are popular landscape shrubs known for their distinctive purple foliage yet understudied physiologically. C. occidentalis and C. canadensis have distinct native ranges, with the former originating west of the Rocky Mountains while the latter is east coast in origin, thus their performance was compared across these western U.S. sites. Full gas exchange, specific leaf area, 13C isotope discrimination, hydraulic conductivity, stomatal conductance, ΦPSII, were analyzed and water use efficiency was calculated each taxon at each location. Impacts of site, treatment, taxa and change across the growing season were analyzed on this suite of traits. Results show distinctions in water use strategy by climatic location (p: 1e-05) and between closely related species and cultivars. Additionally, physiological measurements indicate measurable physiological plasticity across the growing season. These findings indicate the importance of setting on the ability of different plant cultivars to acclimate to water stress, taxa-level differences among horticulturally important species, and overall knowledge of plant drought response, knowledge gaps that are crucial to address in the face of anthropogenic climate change.

Stomatal morphology dictates the maximum stomatal conductance and relates to plant water use efficiency and carbon assimilation rate. Aspects of stomatal morphology, including size characteristics and density, are plastic in some taxa, can respond to environmental stressors, and are thought to be relevant in drought acclimation within an individual. The Climate Ready Landscape Plants (CRLP) trial consists of 6 sites across the Western U.S. that have installed common garden drought experiments that utilized daily ETo to implement three water deficit treatments. Stomatal conductance and stomatal images were collected from 3 cultivars of Hibiscus syriacus and 3 cultivars of Rosa spp. from 4 of these sites: Seattle, WA; Aurora, OR; Davis, CA; and Irvine, CA. Stomatal images were measured to determine stomatal density and size, which was used to calculate gsmax. Differences between stomatal traits were tested between sites and water deficit treatments using ANOVA. Correlation between gsw and gsmax were determined with regression analysis. PCA was used to determine which site characteristics and treatments primarily explain observed differences. Here we aim to test 1) Are stomatal morphological traits plastic across water deficit treatments and sites in multiple Rosa and Hibiscus syriacus varieties? 2) Does measured stomatal conductance (gsw) correlate with morphologically derived anatomical maximums (gsmax)? 3) Do site characteristics across the maritime Western US predict physiological and morphological stomatal traits? Findings reveal important ecological and horticultural considerations in plant stress response to drought and acclimation potential across an environmental and latitudinal gradient. The results can help in plant selection and categorization of species vulnerability, based on ability to manipulate stomatal characteristics in response to water deficit.

Evergreen leaves of Rhododendron species inhabiting temperate/montane climates are typically exposed to both high radiation and freezing temperatures during winter when photosynthetic biochemistry is severely inhibited. This could lead to accumulation of excess energy (radiation) in photosynthetic reaction centers causing photoinhibition or photooxidative damage. Cold-induced ‘thermonasty’, i. e. lamina rolling and petiole curling/drooping, can reduce the amount of leaf area exposed to solar radiation and has been associated with photoprotection in overwintering rhododendrons. The present study was conducted on natural, mature plantings of a cold-hardy and large-leaved thermonastic North American species (R. maximum) during winter freezes. Infrared thermography was used to determine initial sites of ice formation, patterns of ice propagation, and dynamics of the freezing process in leaves to understand the temporal and mechanistic relationship between freezing and thermonasty. Results indicated extracellular freezing in leaves always preceded the initiation or intensification of thermonasty. Ice initially formed in the vascular tissue of the midrib and then propagated into other portions of the vascular system/venation. Ice was never observed to initiate or propagate into palisade, spongy mesophyll, or epidermal tissues. These observations, together with the leaf- and petiole-histology, and a simulation of the rolling effect of dehydrated leaves using a cellulose-based, paper-bilayer system, suggest that thermonasty occurs due to anisotropic contraction of cell wall cellulose fibers of adaxial versus abaxial surface as the cells lose water to ice present in vascular tissues.

The adaptation of perennial species to winter freezing temperatures is crucial for their reproductive success and has led to the evolution of diverse survival strategies to mitigate freezing damage. Bud survival is essential for species reproduction and fruit production, as buds carry the dormant flower primordia that will bloom in the next growing season. We studied two freezing survival mechanisms: deep supercooling (DS) and extraorgan freezing (EOF). Deep supercooling involves physical or structural changes that prevent ice nucleation in florets and meristems by sequestering small amounts of water. When the critical nucleating temperature for this sequestered water is reached, ice propagation is rapid, and cellular damage is lethal. Extraorgan freezing causes a gradual dehydration of inner bud tissues, driven by the vapor pressure deficit from extracellular ice formed in bud scales. Despite existing knowledge, the survival benefits of species undergoing deep supercooling, considered a limited strategy compared to extraorgan or extracellular freezing, remain unclear. Similarly, how adaptation to freezing impacts reproductive traits in woody species is not well understood. We focused on the Prunus genus for its dual survival strategies and productive and ornamental value. This study, conducted on six Prunus species at the Arnold Arboretum in Boston, MA, spanned three developmental stages: leaf drop in fall, dormancy in winter, and pre-bud swell in spring. Data encompassed phenology, vascular tissue development, flower primordia size, differential thermal analysis, controlled freezing tests, and characteristics of flowers, fruits, and seeds. Results indicated that DS Prunus species delay vascular tissue development and grow larger flower primordia from fall compared to EOF species. Conversely, EOF species bloom later, producing more and smaller flowers and fruits in a shorter time than DS species. In summary, in the Prunus genus, DS species appear to trade a lower temperature threshold for pre-forming fewer, larger flower primordia per bud, enabling earlier blooming and more efficient use of the growing season to develop larger fruits in contrast to EOF species.

Heat stress is one of the most significant uncontrollable abiotic factors that affect potato plant growth, development, and tuber yield. While short-term acute heat stress experiments have produced considerable insights into the effects of heat stress on potato, there is a lack of information on the mechanisms involved in heat stress adaptation. Our recent studies demonstrate that under prolonged heat stress (35/25°C, day/night, for 3 weeks), newly developed leaves can maintain health and adapt to heat stress by modifying anatomy and physiology. Whereas, the leaves developed prior to heat stress (20/15 °C, day/night) on the same plant suffer (chloroses, senescence) from heat stress. We compared the gene expression in the youngest, fully expanded terminal leaflets developed under control and heat stress in two genotypes, Solanum tuberosum L. ‘Atlantic’ (ATL) and Solanum microdontum Bitter (MCD). As expected, several heat shock proteins (HSP) genes were upregulated in both genotypes. In addition, several desaturase genes were downregulated suggesting an increase in the saturation of membrane lipids may provide membrane integrity under heat stress. Our parallel physiological and anatomical studies have shown that adaptation to heat stress involves increase in stomatal density, lowering of leaf temperature via increased transpiration and maintenance of photosynthesis. Consistent with these results we found significantly regulated genes involved in ABA biosynthesis, photosynthesis, cell growth, expansion and patterning. These data offer insight into potential genes involved in heat tolerance in potato that may be useful in breeding for heat-tolerant potato varieties.

Phosynthetically active radiation (PAR; 400 – 700 nm) is widely acknowledged as essential for photosynthesis in plants. However, recent research has revealed the significant contribution of far-red photons (FR; 700 – 750 nm) to photosynthetic processes, particularly when present alongside PAR. While previous studies have primarily focused on whole-plant gas exchange, limited research exists on leaf-level replication of these findings. In this preliminary study, we investigated leaf gas exchange in five field-grown crop species using A/Ci curves. We exposed the leaves to equal proportions of blue, green, and red light at a photon flux density of 1000 µmol·m-2·s-1 and replaced varying percentages (0%, 15%, or 30%) of these photons with FR. Our hypothesis, based on previous whole-plant studies, was that all species would exhibit similar photosynthetic rates (Pn) across different FR treatments. Contrary to our hypothesis, we observed species- and cultivar-specific variations in leaf-level Pn with FR treatments. For instance, strawberry and green leaf lettuce exhibited decreased Pn with increasing FR, while apple and Swiss chard showed increased Pn. Red leaf lettuce maintained consistent Pn levels. Despite these differences, the overall trends across CO2 concentrations remained consistent regardless of FR levels. Considering that direct sunlight naturally contains FR equivalent to approximately 18% of PAR, and our crops were grown in open-field conditions, our findings suggest a species-specific capacity to utilize FR in photosynthesis. These findings are preliminary, but data is being collected to examine species responses throughout a full growing season.

In wildlands, such as the prairies of the Northern Great Plains, environmental degradation has created the need for ecological restoration of native plants on the landscape. These ecological restorations require native seed. However, many seed-based restoration efforts fail in that they do not produce the desired vegetation. Lack of species-specific information on germination characteristics and dormancy of native seed could be contributing to these failures. Therefore, restoration practitioners and other users of native seed need germination and dormancy information for native species to improve outcomes. Our objectives in this study were to examine germination characteristics and seed treatments that best promote germination in plant species native to the Northern Great Plains and define dormancy classes for each of our study species. To meet these objectives and promote success in seed-based restoration, we conducted a germination experiment for 15 high-priority native forbs. Seeds were treated with four pretreatments (scarification, smoke, fertilizer, and a control), three stratification lengths (2, 4, and 8 weeks), and different temperature regimes. We examined the influence of each factor to determine the means of breaking dormancy and best planting practices. Our data indicated that a scarification treatment before planting Gaillardia aristata increased germination by over 19%. This data suggests that while the majority of our G. aristata seeds are non-dormant, a percentage are physiologically dormant. Our data also shows that Penstemon albidus is strongly influenced by temperature conditions, and the species requires a period of cold stratification to increase overall germination. This information will be used to develop best planting practices for government agencies and aid seed producers and distributors by offering seed storage and planting instructions matching the phenology of native plant species. This rigorous germination experiment can also be used as a model for other priority species and can be adapted to different ecoregions.

Multiple Modeling Approaches Reveal Temperature Dependent Germination Traits of Vegetable Varieties - Miro Stuke
Identifying Pollinators Present on Flowers of the Pawpaw Cultivars 'Sunflower' and 'Susquehanna' - Subas Thapa Magar
Characteristics of the Secondary Walls of Xylem of the Tomatoes Cultivated Under Water Deficit - Marcio Mesquita
Molecular Assessment of Heat Sensitivity in Broccoli Flowering - Thomas Bjorkman
Morpho-physiological Response of Plectranthus amboinicus under Flooding and Drought Stress - Samuel Asiedu
Effects of Paclobutrazol, Progressive-raising Temperature and Spike-truncated Treatments on Phalaenopsis Join Grace ‘TH288-4’ - Yi Chien Lu

Crop seed germination is a critical factor in food production. Germination traits vary between different vegetables and between cultivars of the same vegetable. Traits such as germination proportion and the rate and uniformity of germination also contribute to the success of vegetable cultivars to regional temperature averages and regimes. Temperature is a major abiotic factor in seed germination, and selection of seed varieties suited for local temperatures is important to successful crop establishment. Here we aim to model the germination traits of several Korean and North American vegetable cultivars in relationship to temperature. We hypothesize that a model based on time and temperature will represent germination traits across multiple cultivars and species of vegetable. Additionally, we hypothesize that predicted germination traits will be similar within species but will vary between cultivars of the same species based on the regional temperature norms. Eleven vegetable cultivars including two corn, four radish, two pepper, and three onion, were germinated in growth chambers set at 5°C intervals between 5 and 40°C with a 12 hour photoperiod. Germination, defined by radicle emergence equal to the length of the seed, was monitored and recorded daily. Two modeling approaches were used. 1) A time to event model using the drcSeedGerm package in R was used to determine maximum germination proportion (Pmax), germination rate at 50% germination (GR50), and uniformity. 2) A 12-parameter compartmental temperature and time model was implemented, parameterized, and validated in the Cropbox modeling framework. Results show differing temperature responses in germination traits. Additionally, high uniformity was observed in most varieties within the optimal temperature range. The optimal temperature for germination was broad for the vegetable cultivars tested here, with a rapid decrease in Pmax at high and low temperature extremes, except in onions, which showed high Pmax even at 5°C, and a gradual decline above 25°C. All cultivars showed decreased Pmax at 40°C. A time to event model was able to predict germination traits in several crop species. The compartmental model was better equipped to handle heat induced seed degradation but was less parsimonious for determining germination probability and germination rate related parameters. Modeling crop germination traits can provide important context for selecting appropriate cultivars for local climates. A thermal time to event model and a compartmental model both provide potential frameworks for modeling germination traits of diverse vegetable species.

Pawpaw (Asimina Triloba) is a temperate species of tropical Annonaceae plant family native to the United States. They are small to medium-sized deciduous trees that bear unique and flavorful fruit. Pawpaw fruits are used in various culinary products such as jam, bread, ice cream, cookies, and even to produce brandy. Additionally, they contain antioxidants and acetogenins, which are currently being researched for their potential in cancer treatment. Fruit sets may be limited in some cultivars due to pawpaw flowers being protogynous and self-incompatible, blooming at various stages of development from late March to April. Consequently, the role of insects in pollination is crucial for increasing fruit production. To address this gap in research, this study aims to identify the different insect orders that visit both flowering and non-flowering branches of two distinct pawpaw cultivars (Sunflower and Susquehanna), along with their respective abundances. Ten trees from each pawpaw cultivar were selected to investigate the various pollinator types. In a completely randomized design, 40 wire cage traps with tangle trap adhesive were placed on both the flowering and non-flowering branches of each chosen cultivar. After 18 days of the flowering period, the traps were collected, and the insects captured were identified by order and counted. The data were analyzed using R software (R 4.3.2) and subjected to a one-way ANOVA with flower and non-flower of each cultivar, a two-way ANOVA, Least Significant Difference (LSD) means separation, with flowers and cultivars as the treatments. In 2023, ‘Sunflower’ had significantly more Dipterans and total insects (p-value: 0.3373 NS and 0.3740 NS). In comparison, ‘Susquehanna’ had significantly more Coleopterans (p-value: 0.40525 NS), and in ‘Susquehanna’, coleopterans had significantly more in the flower-branch (p-value: 0.0255*) for 2023. Additionally, data for 2024 will also be reported and will include additional data on insects observed inside the female receptive and matured male flowers from each cultivar.

The morphological characteristics of the xylem elements influence water ascent in the plants. Few models determine the physical process of water movement in the vascular system of plants based on the hydraulic architecture. This study aims to determine the anatomical characteristics of the xylem and potential hydraulic conductivity at different positions along of tomatoes (Solanum lycopersicum; Solanaceae). The xylem vessels characteristics were examined in four internodes using three segments in each internode. The analogy between Ohm’s law and Hagen-Poiseuille was used to determine the hydraulic conductivities. A successive decrease in the mean vessel diameters from the bottom to the top stem was observed, with a significant difference between successive decrease in the mean vessel diameters from the bottom to the top stem was observed, with a significant between different percentages of height. The variation of the hydraulic conductivity along the useful length of tomato allowed a better application of the Hagen-Poiseuille equation.

Exploring the Effects of Irrigation Water Salinity on Physiology and Growth of Papaya (Carica papaya) in a Calcareous Soil - Ana Vargas
Physiological, Biochemical, and Morphological Responses of Achachairu (Garcinia humilis) to Soil Salinity, Flooding, and Exogenous Applications of 24-epibrassinolide - Federico Sanchez
Plant Physiological and Root Anatomical Responses of Two Novel Olive Cultivars (‘Oliana’ and ‘Lecciana’) Under Salinity - Khalid Hussain
Continuous monitoring of tree water status using microtensiometers for irrigation management in olive - Paula Guzman-Delgado
The Carbon Cost of Phosphorus Deficiency in Southern Highbush Blueberry - Marlon Retana-Cordero
Intra- and Inter-Annual Changes in Soil Health with Native Plant Monocultures - Bret Lang

In many tropical fruit production areas, including southern Florida, a rise in ocean levels resulting from climate change is anticipated to lead to greater inland intrusion of saltwater, thereby increasing salinity of the soil and/or irrigation water. Thus, knowing the salinity level of the soil or irrigation water that negatively impacts tropical fruit crops, including papaya, is important to alleviate salinity-induced damage to these crops. A study was conducted to evaluate physiological and growth responses of two papaya (Carica papaya L.) cultivars grown commercially in Florida (‘Red Lady’ and ‘Exp15’) to different irrigation salinity levels. Papaya seedlings were transplanted into 11.4-liter pots with Krome very gravelly loam soil; a calcareous soil collected from the papaya production area in south Florida. Each plant was manually irrigated three times per week with 1 liter of deionized water containing different concentrations artificial sea salt (Instant Ocean®) to obtain 4 salinity levels based on electrical conductivity (EC) of the irrigation water i.e., 0 (control), 3, 6, and 9 dS/m. Plants performance under different salinity levels was evaluated by determining net CO2 assimilation (A), stomatal conductance (gs), transpiration (E), the leaf chlorophyll index (LCI), and the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm) on a weekly basis throughout the study. Normalized difference vegetation Index (NDVI) values derived from multispectral images were also collected weekly. After seven weeks, plants were harvested and leaf relative water content (RWC), leaf water potential, leaf area, and leaf, stem, and root dry weights were determined for all plants. Five weeks after treatments were initiated, for both cultivars, plants in the 6 and 9 dS/m treatments had lower A, E, gs, LCI, and Fv/Fm than plants in the other treatments. At the end of the experiment, plants in the 3, 6, and 9 dS/m treatments had significantly lower A, E, gs, LCI, Fv/Fm, leaf water potential, leaf area, and leaf, stem, and root dry weights than plants in the other treatments. Also at the end of the experiment, ‘Exp15’ plants in the 9 dS/m treatment had lower NDVI values than plants in the other treatments, whereas there was no difference in NDVI among treatments for ‘Red Lady’. There was no significant effect of salinity treatment on RWC. The findings suggest that 'Red Lady' and ‘Exp15’ papaya plants are unable to withstand salinity levels of 3 dS/m or higher in the calcareous agricultural soil of southern Florida.

Achachairu (Garcinia humilis (Vahl) C.D. Adams) is a slow-growing tropical fruit tree indigenous to the Amazonian forests in Bolivia. Each tree can produce over 15,000 fruit (400 kg/tree) harvested from cultivated and wild trees. It has significant horticultural potential because the fruit is considered delicious by many people who have tasted it. Thus, its commercial cultivation has extended to Brazil, Mexico, and Australia. The responses and tolerance of this species to abiotic stresses and the use of chemical priming to mitigate stress have never been reported. The study investigated the physiological, biochemical, and morphological responses to flooding and salinity, and the priming with 24-epibrassinolide (EB) to increase flooding and salinity tolerance of G. humilis. Three-year-old achachairu seedlings were used in several sequential experiments, including applying flooding, salinity, and EB priming in different combinations and durations. Physiological variables including leaf gas exchange [net CO2 assimilation (A), stomatal conductance of H2O (gs), and intercellular CO2 concentration (Ci)], leaf chlorophyll index (LCI), and the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm) were measured. Leaf and root nutrient concentrations, antioxidant responses, reactive oxygen species (ROS), and lipid peroxidation (MDA) were also measured. Results showed that G. humilis is very tolerant of prolonged flooding of up to 30 d, medium levels of salinity of up to 6 dSm-1, and the combined effect of flooding and salinity. Tolerance to these stresses was exhibited by physiological, biochemical, and morphological responses, consistent with tolerance traits, such as maintaining basal levels of photosynthesis, ion homeostasis, and nutrient balances, robust antioxidant responses to counter ROS increases, and limited lipid peroxidation, all of which may help limit physiological damage. Application of 1.0 mg L-1 EB as a foliar and root-drench before flooding or salinity treatments increased the levels of tolerance of G. humilis to salinity and flooding, most likely by reinforcing antioxidant responses which helped decrease ROS and lipid peroxidation.

Soil salinity poses a significant challenge in agriculture, disrupting the normal functioning of plants by reducing water and nutrient uptake. Olive trees (Olea europaea), common in Mediterranean regions, exhibit moderate to high tolerance to salinity, varying by cultivar. Interest in cultivating olive trees is growing in Florida’s coastal areas, characterized by poorly drained soil and low-quality groundwater, leading to salt accumulation in the root zone. The high salinity levels in these areas present a significant challenge for crop cultivation. Therefore, introducing new salt-tolerant cultivars is necessary to mitigate salinity stress. This study aimed to evaluate the plant physiological and root anatomical responses of two novel olive cultivars - ‘Oliana’ and ‘Lecciana’ - to salinity stress, assessing their salt tolerance. Eight-month-old plants were grown in pots using a sand medium under greenhouse conditions and treated with varying salt concentrations (0 mM, 50 mM, and 100 mM). The experiment followed a completely randomized design with three replications, each consisting of nine plants. Plants were irrigated at weekly intervals with half-strength Hoagland solution to meet their nutrient requirements. Height and trunk diameter were measured at four different time points (0, 15, 30, and 45 days). At the end of the trial, plants were destructively sampled for biomass, nutrient content, and root anatomical measurements at the latter three time points. Significant differences were observed in height, trunk diameter, and nutrient contents between the control and NaCl treatments. These findings serve as a baseline for the commercial development of salt-tolerant olive cultivars.

Water scarcity is challenging agricultural production, demanding more precise and efficient irrigation management. Plant-based continuous monitoring has emerged as a promising approach for detecting water stress progression and optimizing irrigation. However, its practical implementation is hindered by the complex interpretation of the sensors’ outputs and plant physiological status relationships. Plant water potential is among the most robust water status indicators and is widely used for irrigation management. Nevertheless, its measurement is time-consuming and requires skilled personnel, making it difficult to have frequent assessments. In this study, we explored the potential of using continuous water potential sensing to quantify olive water status and its response to irrigation. Specifically, we compared continuous and discrete tree-level measurements of water status using microtensiometers and the pressure chamber, respectively. The microtensiometers proved effective in capturing tree water status dynamics, enabling a prompt assessment of the impact of irrigation practices. Preliminary analyses show a good linear correlation between midday trunk and stem water potential values obtained with microtensiometers and the pressure chamber, with the former being less than 0.5 MPa lower, a difference that could be attributed to the specific measurement of each technique. Importantly, having continuous data allows the extrapolation of several water status parameters which can provide key information in addition to the single timepoint midday values. Overall, this study suggests microtensiometers can be a useful tool to optimize water application in olive orchards.

Phosphorus (P) deficiency in plants causes detrimental effects on their growth and development, as P is a key macronutrient used in various physiological, biochemical and cell signaling processes. Research has shown that P-deficient plants exhibit several symptoms such as changes in leaf coloration, root morphology, and plant growth. However, many of those studies ignore gas exchange parameters. In this research, we studied the connection between P-deficiency and carbon (C) gain and loss in southern highbush blueberry (SHB, Vaccinium corymbosum interspecific hybrids) young plants to estimate the C cost of P-deficiency. The experiment was conducted using a hydroponic system where three-month old plants of ‘Farthing’ and ‘Keecrisp’ varieties grew in individual 2-L reservoirs filled with continuously-aerated complete nutrient solution containing 15 mg/L P during a 35-day acclimation period. After the acclimation period, plants were separated into two groups and continued to grow for 56 more days (treatment period). One group ( P) was grown in the complete nutrient solution, while the second group (-P) was grown in a P-free nutrient solution (0 mg/L P). We designed and tested a whole-plant gas exchange system that utilizes two infrared gas analyzers (CIRAS-3 and CIRAS-4) to simultaneously measure root system respiration and whole-plant C assimilation. Additionally, we measured root C exudation, fresh and dry mass accumulation, and P concentration and content. We induced P-deficiency as -P plants of both varieties had mature and young leaf P concentration below 0.12% (reference deficiency level). P plants had higher P concentration after treatment period. -P ‘Farthing’ plants had 89% less daily C assimilation than P plants, while no differences were observed in ‘Keecrisp’. Daily root respiration and C exudation, considered as ways of C loss, were, 3.5 and 2.9 times higher in -P than in P plants of ‘Farthing’. Similarly, -P ‘Keecrisp’ plants had 3.8 and 2.5 times more daily root respiration and C exudation compared to those under P. Ultimately, P deficiency caused a 136% reduction in daily C gain of ‘Farthing’ plants, while there were no differences between treatments in ‘Keecrisp’ plants. Our findings suggest that responses to P deficiency in SHB are genotype-specific, and that C budget and distribution in the plant play an important role in the responses to P-deficiency.

The interactions between plants and their soil environment influence overall soil system health. Soil provides plants with the structural support, water, nutrients, and microbial interactions they need for creating biomass and for reproduction. Conventional agriculture practices degrade soil; however, small plots of native plants within agricultural settings have been shown to provide disproportionally large benefits to both ecological and agricultural landscapes. In other words, even small plots of native plants can improve soil health. Although small plots of mixed native plant species improve soil health, they offer little in the way of income opportunities for producers through seed collection and sales. However, plots of native monocultures may offer producers an opportunity to harvest and sell seeds, taking advantage of the increasing demands of the native seed market while also increasing soil health. Therefore, this study's objective is to quantify the effects of small native plant monocultures on soil health and compare them to soil health from conventional crop plots. We investigated biological indicators of soil health such as organic matter, organic carbon, and microbial communities as well as abiotic indicators like nutrient composition. We hypothesize that, compared to crop plots, native monoculture plots will have more microbial diversity and higher amounts of soil nutrients. We tested our hypothesis by comparing soil health characteristics from plots containing five established native monocultures: Dalea candida, Agastache nepetoides, Glycyrrhiza lepidota, Liatris ligulistylis, and Tradescantia occidentalis; and one crop plot planted with a corn and soybean rotation. During the second and third season of growth, monthly soil samples were taken, and soil indicator values were compared using Tukey’s HSD post hoc tests after performing an analysis of variance (ANOVA). Results suggest that native plant species influenced soil health differently than crop rotations after three seasons of growth. Compared to crop plots, soil samples from two species of native plants, Agastache nepetoides and Tradescantia occidentalis, had higher fungi-to-bacteria ratios (p = 0.0160 and p < 0.0001, respectively), and higher amounts of saprophyte biomass (p = 0.0040 and p = 0.0484, respectively). Soils from the Agastache nepetoides plots also had higher amounts of Pre18 cyclo fatty acids (p = 0.0022) and potassium (p = 0.0159). These two species of native plants show potential for improving soil health after three years of establishment. Adding these two native monocultures to marginal production land may add soil health benefits during early establishment periods while providing a marketable crop for producers.