Tall Fescue Research Articles

Connectivity of Photosynthesis and Respiration with the Content of Chlorophyll Pigments in Plants of Reed Fescue Festuca arundinacea Schreb. under the Impact of Alkanes and Aromatic Hydrocarbons

Connectivity of Photosynthesis and Respiration with the Content of Chlorophyll Pigments in Plants of Reed Fescue Festuca arundinacea Schreb. under the Impact of Alkanes and Aromatic Hydrocarbons

178 Tag Your It: Use of Wearable Biometric and Remote Sensing Technology to Monitor Animal Growth, Performance, and Efficiency in Extensively Managed Landscapes

Abstract Energy budgets in grazing cattle are notoriously difficult to study given complex environmental and physiological interactions between plants and animals, each operating according to individual grazing budgets. However, these synergistic energy pathways can be modeled using a series of mechanistic relationships describing forage resource distribution and animal behavior, each which can be observed with high levels of accuracy and precision using biometric sensors and remote sensing technology. The objective of this study is to demonstrate the coordination of data inputs into a coherent framework utilizing biometric and remote sensing technology. Crossbred steers (n = 10) were fitted with GPS and video tracking collars (Vectronic) and accelerometers (Wildbytes technologies), then managed for 286 days as part of a broader research grazing ecology project on pasture (~11.54 hectare) comprised of bermudagrass (Cynodon dactylon) and tall fescue (Festuca arundinacea) and equipped with an automated walk-over-weigh (TruTest) scale system. Distribution of forage quality was sampled monthly with a ½ m2 quadrat using a 20 x 20-meter grid (n = 297) and remotely assessed via an unmanned aerial vehicle (Matrice 100) mounted hyperspectral camera (MicaSense) at 8 cm resolution. Animal behavior was predicted utilizing a trained randomforest prediction algorithm, and linked to geo-location and forage quality at the spatial-temporal scale in Program R. We then constructed animal ethogram, distribution of forage quality, and spatial-temporal distribution of animal behavior across the grazing landscape for a test period. We found steers allocated the greatest proportion of time to grazing and resting behaviors, 30 and 60% respectively, with the remainder dedicated to ruminating and walking behaviors. A diurnal, circadian rhythm in animal behavior demonstrates that steers grazed between 0900 and 1000 in the morning, and again between 1300 and 2000 in the evening, while resting behavior dominated the hours between 0300 and 0900, with a slight increase in grazing behavior noted at 0600, or approximately sunrise. Animal behavior linked forage availability showed steers selectively grazed areas with higher NDVI signatures, while seeking sources of water and cover to practice resting behavior. Given the need to develop robust models predicting forage intake and energy in grazing animals to improve sustainability and environmental metrics, animal tracking and biometric technologies offer a vital solution to improving management of extensively managed grazing livestock.

PSV-20 The Effect of Bacillus Spp. Supplementation on Performance and Immune Function of Heifers Grazing Tall Fescue Pastures

Abstract Probiotics are purported to improve gastrointestinal tract health across a variety of species. Thus, we evaluated the effects of supplementing a blend of Bacillus spp. on performance and immune function in immature beef cattle. Crossbred heifers (n = 192) were stratified by initial body weight (196 ± 15.4 kg) and randomly assigned to 1 of 24 pastures (1.8 ha each) of Kentucky 31 tall fescue. Heifers were offered 2.84 kg daily of a commodity feed blend and the supplement contained either no probiotic (CON) or of Bacillus spp. (BAC). Bacillus spp. was offered at 3 grams per head per day. Heifers were weighed on consecutive days on d 0 and 1, along with d 84 and 85 to establish initial and final body weight. Interim weights were taken every 28 d. A humoral response to chicken egg albumin (OVA) was established following a subcutaneous injection with OVA. To assess heifers’ immune responses, plasma was taken from two heifers per pasture on d 1, 15, 29, 43, and 57. Plasma samples were measured for the presence of anti-OVA IgG, proinflammatory cytokines, anti-inflammatory cytokines, and chemokines. There were no trt*day interactions (P ≥ 0.30) for plasma response variables. Concentrations of pro-inflammatory cytokines IL-1α and IFN-γ decreased (P ≤ 0.01) in heifers supplemented with BAC. The anti-inflammatory cytokine IL-1 F5 decreased (P = 0.02) with BAC supplementation. Chemokines MIG and MIP-1β also decreased (P ≤ 0.03) with BAC supplementation. Heifers fed BAC tended to display (P = 0.09) greater titers of anti-OVA IgG than the control. Body weight and average daily gain did not differ (P ≥ 0.53) throughout the experiment. Under the conditions of this experiment, heifers supplemented with Bacillus spp. demonstrated modulated immune responses.

412 Awardee Talk: New Insights into Mechanisms of Serotonin Receptor-Mediated Vasoactivity and Complex Interactions with Ergot Alkaloids in Bovine Vasculature

Abstract Ergovaline (ERV), produced in toxic endophyte-infected tall fescue, causes potent vasoconstriction of bovine vasculature by interacting with serotonin (5-HT) receptors. Ergovaline acts as a partial agonist of 5-HT2A-mediated vasoconstriction. The duration of ERV exposure affects 5-HT-mediated vasoactivity of mesenteric blood vessels. If ERV and 5-HT exposure occur simultaneously, ERV can increase 5-HT-mediated vasoconstriction. If 5-HT exposure occurs after blood vessels have had prior ERV exposure, increasing levels of 5-HT can induce vasorelaxation of blood vessels. To better understand mechanisms of 5-HT-mediated vasorelaxation, lateral saphenous veins from steers (n = 5) were assessed for vasoactivity in response to increasing concentrations of selective 5-HT receptor agonists Isolated vessel segments were suspended in chambers of a multi-myograph containing 5 mL of continuously oxygenated Krebs-Henseleit buffer and equilibrated to 1 g tension for 90 min. Vessels were pre-contracted with 1×10-4 M phenylephrine and exposed to increasing concentrations of 5-HT or 5-HT receptor agonists that were selective for 5-HT1B, 5-HT2B, 5-HT4, and 5-HT7. Vasoactive response data were normalized as a percentage of the maximum contractile response induced by the phenylephrine pre-contraction. Increasing concentrations of 5-HT resulted in divergent vasoconstriction and vasorelaxation responses that were dose-dependent. Serotonin caused an 86.3% increase (P < 0.01) in relaxation activity at 1×10-7 M and 5-HT caused a 166% increase (P < 0.01) in contraction activity at 1x10-4 M. Increasing concentrations of the selective 5-HT1B agonist did not result in any vasoactive response. Increasing concentrations of agonists selective for 5-HT2B, 5-HT4, or 5-HT7 resulted in a 27.3%, 91.6%, or 43.9% (P < 0.01) increase in maximal vasorelaxation activity. Of these 5-HT receptor agonists, the selective 5-HT4 receptor agonist resulted in the lowest -log IC50 value (6.30) compared with 5-HT2B and 5-HT7 receptor agonists (4.21 and 4.66, respectively). To confirm the involvement of 5-HT4 in 5-HT-mediated vasorelaxation, blood vessels were exposed to either DMSO (control), a selective 5-HT2A antagonist (1×10-5M), or selective antagonists of 5-HT2A and 5-HT4 simultaneously for 5-min before the pre-contraction with phenylephrine and additions of 5-HT. Antagonism of the 5-HT2A receptor did not result in increased vasorelaxation activity compared with control. Antagonism of the 5-HT2A receptor and 5-HT4 receptor simultaneously inhibited vasorelaxation activity and increased (P < 0.01) the maximal contractile response occurring at 1×10-4 M by 47% compared with control. Approximately 84% of the maximal vasorelaxation activity occurring in response to 5-HT could be accounted for through 5-HT4. These data provide strong evidence that 5-HT4 is the primary receptor involved with 5-HT-mediated vasorelaxation in bovine lateral saphenous vein. More research is needed to determine if 5-HT4-mediated vasorelaxation is responsible for relaxation responses observed in blood vessels with prior ERV exposure. This will aid in the development of strategies for alleviating symptoms of sustained vasoconstriction that occur during fescue toxicosis in ruminants.

285 Duration of Ergovaline Exposure Influences Serotonin-Mediated Vasoconstriction and Vasorelaxation of Bovine Vasculature

Abstract Ergovaline (ERV), produced in toxic endophyte-infected tall fescue, causes potent vasoconstriction of bovine peripheral and visceral vasculature. Ergovaline acts as both an agonist and an antagonist in bovine gut blood vessels through serotonin (5-HT) receptors and it appears that the type of action could be influenced by the extent of ERV exposure. Because it was unclear how the duration of ERV exposure influences 5-HT-mediated vasoactivity, experiments were designed to evaluate how simultaneous or prior ERV exposure influenced 5-HT-mediated vasoactivity of mesenteric artery (MA) and vein (MV) segments from Holstein steers (n = 10). Isolated vessel segments were incubated in Krebs-Henseleit buffer containing 0, 0.01, or 0.1 mM ERV for 24-h befoe the 5-HT dose-response or exposed to fixed concentrations of 0, 0.01, or 0.1 mM ERV simultaneously during the 5-HT dose-response. Vessels were suspended in chambers of a multi-myograph containing 5 mL of continuously oxygenated Krebs-Henseleit buffer and equilibrated to 1 g tension for 90 min. Vessels were exposed to increasing concentrations of 5-HT (5 × 10-8 M to 1 × 10-4 M) every 15 min and contractile responses were normalized as a percentage of the maximum contractile response induced by 120 mM KCl reference addition. Two-way analysis of variance was used to separately analyze data for each vessel type and duration of exposure using the MIXED procedure of SAS for the main effects of 5-HT and ERV concentration and the 5-HT × ERV concentration interaction. When 5-HT concentration increased from 5 ′ 10-8 M to 1 ′ 10-6 M, simultaneous addition of 0.1 mM ERV increased (P < 0.01) the contractile response of MV compared with additions of 0 mM ERV and 0.01 mM ERV. At 1 ′ 10-4 M 5-HT, the simultaneous presence of 0.01 mM ERV and 0.1 mM ERV decreased (P < 0.01) the contractile response of both MA and MV compared with 0 mM ERV addition. As 5-HT concentrations increased, the contractile response increased (P < 0.01) in both MA and MV with no previous ERV exposure, but decreased in MA and MV with 24-h prior exposure to 0.01 mM ERV and 0.1 mM ERV. These data demonstrate that the duration of ERV exposure influences 5-HT-mediated vasoconstriction and likely vasorelaxation in bovine mesenteric vasculature. If ERV and 5-HT exposure occur simultaneously, ERV can act as a partial agonist of 5-HT-mediated vasoconstriction. If 5-HT exposure occurs after blood vessels have had prior ERV exposure, it appears that 5-HT may induce vasorelaxation of blood vessels. More research is needed to identify receptors and mechanisms involved with 5-HT-mediated vasoconstriction and vasorelaxation before and after exposure to ERV. This will aid in the development of strategies for alleviating symptoms of sustained vasoconstriction that occur during fescue toxicosis in ruminants.

Silicon-mediated herbivore defence in a pasture grass under reduced and Anthropocene levels of CO2.

The uptake and accumulation of silicon (Si) in grass plants play a crucial role in alleviating both biotic and abiotic stresses. Si supplementation has been reported to increase activity of defence-related antioxidant enzyme, which helps to reduce oxidative stress caused by reactive oxygen species (ROS) following herbivore attack. Atmospheric CO2 levels are known to affect Si accumulation in grasses; reduced CO2 concentrations increase Si accumulation whereas elevated CO2 concentrations often decrease Si accumulation. This can potentially affect antioxidant enzyme activity and subsequently insect herbivory, but this remains untested. We examined the effects of Si supplementation and herbivory by Helicoverpa armigera on antioxidant enzyme (catalase, CAT; superoxide dismutase, SOD; and ascorbate peroxidase, APX) activity in tall fescue grass (Festuca arundinacea) grown under CO2 concentrations of 200, 410, and 640 ppm representing reduced, ambient, and elevated CO2 levels, respectively. We also quantified foliar Si, carbon (C), and nitrogen (N) concentrations and determined how changes in enzymes and elemental chemistry affected H. armigera relative growth rates and plant consumption. Rising CO2 concentrations increased plant mass and foliar C but decreased foliar N and Si. Si supplementation enhanced APX and SOD activity under the ranging CO2 regimes. Si accumulation and antioxidant enzyme activity were at their highest level under reduced CO2 conditions and their lowest level under future levels of CO2. The latter corresponded with increased herbivore growth rates and plant consumption, suggesting that some grasses could become more susceptible to herbivory under projected CO2 conditions.

Allelopathic effects of Zelkova schneideriana Hand. Mazz root exudates on growth of rape, wheat, maize and tall fescue

Allelopathic effects of Zelkova schneideriana Hand. Mazz root exudates on growth of rape, wheat, maize and tall fescue

Connectivity of Photosynthesis and Respiration with Content of Chlorophyll Pigments in Plants of Reed Fescue <i>Festuca arundinacea</i> Schreb. Under the Impact of Alkanes and Aromatic Hydrocarbons

The association of degradation of membrane-bound chlorophyll with changes in dark respiration rates and photosynthesis in Festuca arundinacea Schreb. leaves under the influence of various concentrations of limit and aromatic hydrocarbons present in technogenic emissions was studied. 1 day after intoxication a negative correlation between the content of non-phytol forms of pigments and the rate of photosynthesis was found. Positive correlation was found between the content of: 1) phytol forms and the rate of photosynthesis; 2) non-phytol forms and respiration rate. The relationships between the processes changed after 3 days characterizing the detoxifying and adaptability of plants.

Niche-dependent microbial assembly in salt-tolerant tall fescue and its contribution to plant biomass

Tall fescue (Festuca arundinacea Schreb.) is promising for biogas production in cold climate zones and displays good performance and high biomass under moderate to severe salt stress. The plant microbiome is crucial for enhancing plant growth and boosting crop yield under salt stress. To determine the variations of microbiome composition and abundance in different plant compartments with salt-tolerant tall fescue cultivars under salt stress, this study performed 16S ribosomal RNA amplicon and internal transcribed spacer (ITS) sequencing. Moreover, the study investigated the effect of enriched bacteria on tall fescue growth and salt tolerance. The aboveground and belowground compartments shaped distinct and overlapping microbial communities, as evidenced by the fact that Proteobacteria and Ascomycota displayed various preferences in inhabiting each compartment. Salt stress drove significant changes in microbiome composition in different compartments. Interestingly, the abundance and diversity of bacteria varied more significantly than those of fungi in response to salt stress. Microbes may enhance the carbon fixation pathways in prokaryotes and flagellar assembly functions to improve the salinity tolerance of tall fescue. Moreover, the inoculation experiment revealed that Halomonas lutescens could promote plant salt tolerance and biomass accumulation. Taken together, this research presents clear insight regarding the dynamics of plant microbiome recruitment in different tall fescue compartments under salt stress and highlights the role of the microbes in regulating plant salt tolerance, thus offering huge potential for increasing the resilience of crop and bioenergy production in agriculture and industry to salt stress.

Comparative study of morphological, anatomical, cell wall compositional, and leaf elemental features of traffic‐tolerant versus traffic‐sensitive tall fescue (Festuca arundinacea)

AbstractTurfgrass traffic tolerance is essential for athletic field aesthetics and performance. Tall fescue (Festuca arundinacea Scherb.; syn. Schedonorus arundinaceus [Schreb.] Dumort., nom. cons.) is utilized on athletic fields due to its high tolerance to traffic stress. However, the physiochemical characteristics and mechanisms associated with traffic tolerance are not understood. Therefore, identifying traffic‐tolerant characteristics would be beneficial for selecting future turfgrass varieties. The objective of this study was to identify morphological, mechanical, and anatomical characteristics of traffic‐tolerant and traffic‐sensitive tall fescue varieties. Simulated traffic was applied to the 2018 National Turfgrass Evaluation Program tall fescue trial at the Iowa State Horticulture Research Station. A modified Baldree traffic simulator applied 24 simulated traffic events yearly during August and September 2019–2021. The four most traffic‐tolerant/traffic‐sensitive varieties, each, were selected based on the average final percent green cover after simulated traffic. Evaluations included leaf width and thickness, leaf angle, plant density, intercellular void space, and maximum and final resistive force of three‐point bending testing. Additionally, cell wall constituents, hemicellulose, cellulose, lignin, and concentration of three elements (nitrogen [N], calcium [Ca], potassium [K]) were quantified in the leaf. Compared to traffic‐sensitive varieties, the traffic‐tolerant group (SE5302, SE5STAR, BGR‐TF3, and PST‐5DART) exhibited wider leaves (3.53 vs. 2.73 mm), lower plant density (23.4 vs. 38.6 plants 7 cm−2), larger intercellular void space (29,532 vs. 10,051 μm2), greater maximum resistive force (0.607 vs. 0.350 N), and greater final displacement force (0.531 vs. 0.288 N). The identification of these characteristics could be used as selection criteria for traffic‐tolerant varieties of tall fescue in future.

PSVI-5 Using Red Clover Extract to Mitigate Tall Fescue Toxicosis

Abstract Tall fescue toxicosis is caused by ergot alkaloids produced by the fungus Neotyphodium coenophialum that resides within the majority of the tall fescue plants in the Southeastern and lower Midwestern US. Tall fescue (Festuca arundinacea) toxicosis is estimated to cost livestock producers over $1 billion dollars annually through reduced growth and reproductive performance. Improvements in performance by cattle grazing toxic tall fescue can have substantial economic advantages for livestock producers throughout the tall fescue region. Numerous methods to mitigate tall fescue toxicosis have been tried over the past 60+ years, but a practical solution to this problem has not been discovered to date. Forages used to dilute fescue include clovers which will not compete on much of the marginal sites that tall fescue predominates. As mentioned above, clovers have been used to dilute toxic fescue and have shown to be a good mitigation strategy if the clovers persist. Red clover extract (RCE) has shown promise in the mitigation of symptoms related to tall fescue toxicosis, but effective dosages have not yet been determined to date. Dorper ewe and wether lambs (n = 30, 34 ± 0.97 kg initial BW) were weighed and assigned randomly to one of five diets in a 2-period study. Diets consisted of a positive control of non-toxic tall fescue seed with no RCE (CONT), a negative control of toxic tall fescue seed with no RCE (E+0) and toxic tall fescue seed with RCE supplemented at 0.33 (E+33), 0.67 (E+67), and 1 (E+100) percent of the diet. Fescue seed was mixed with liquid molasses to ensure consumption, and seed, DDGS and RCE was offered at approximately 0800 and 1600 h, and bermudagrass hay was offered for ad libitum consumption. Lambs were housed in individual 1 × 1.5 m pens in an enclosed building where temperature was maintained at 27° C (80° F). The animal had an ad libitum access to water. Each period consisted of a 14-day adaptation period followed by 7 d of total fecal and urine collection. Diets were offered for ad libitum consumption during the first 12 days of each period and then held constant during the remaining 9 days. Dry matter (DM) and organic matter (OM) intake was greater (P < 0.05) from CONT than all other treatments and E+33 was greater (P < 0.05) than E+10 and E+67. Digestibility of DM and OM were greater (P < 0.05) from CONT than all other treatments. By contrast, the diets did not influence (P > 0.05) nitrogen balance, urinary nitrogen losses, fecal nitrogen losses and nitrogen retained. Overall, results demonstrated that RCE inclusion into the diet of toxic tall fescue did not significantly change growth and performance parameters in sheep.

71 Effects of Late Gestational Nutrient Restriction on Calf pre-Weaning Growth, Backgrounding and Feedlot Performance, and Carcass Composition

Abstract Fall-calving Hereford-SimAngus heifers [single-sired; BW: 451 ± 28 (SD) kg; BCS: 5.4 ± 0.7] bred to a single sire were individually fed 100% (control; CON; n = 12) or 70% (nutrient restricted; NR; n = 13) of NASEM metabolizable energy and metabolizable protein requirements for maintenance, pregnancy, and growth from day 160 of gestation to calving. Post-calving, all females were fed chopped tall-fescue hay supplemented to meet lactational nutrient requirements in Calan gates to constrain diets of calves to milk only until day 147, then pen-fed in drylots until weaning at day 242 ± 3 (SD). Post-weaning, calves were fed a tall fescue hay-based backgrounding diet in the same large drylots for 53 ± 12 d, then moved to partially covered pens with GrowSafe feeding systems in 2 groups and fed a corn-based feedlot diet (formulated to be 18.3% CP, 1.21 Mcal NEg/kg, DM basis; 89% DM) for 255 ± 3 d (similar days on feed rather than carcass endpoint). Cattle were harvested in a commercial plant, and camera carcass grading was performed. Data were analyzed with maternal treatment, calving date, and calf sex (when P < 0.25) as fixed effects; feedlot group was included for feedlot and carcass measures. We previously reported that birth weight was not affected (P = 0.72), but NR decreased (P < 0.04) milk production by 15%. Calves born to NR dams had reduced ADG from birth to day 147 (P = 0.02), day 147 to weaning (P = 0.08), and birth to weaning (P = 0.003), resulting in NR calves having 13% lighter (P = 0.004) weaning weight. Backgrounding ADG was not affected (P = 0.80) by maternal treatment; thus, feedlot entry BW was 11% less (P = 0.009) in NR calves. On day 28, 56, 84, and 112 on feed, NR calves weighed less (P ≤ 0.09) than control. Final BW was not affected (P = 0.91) by maternal treatment. Feedlot ADG was greater for NR calves from day 168 to slaughter (P = 0.02) and the overall feeding period (P = 0.03), but not before day 168 on feed (P ≥ 0.22). Calves born to NR dams had less (P = 0.02) dressing percentage, but improved (P = 0.02) yield grade and backfat thickness. Hot carcass weight, ribeye area, marbling score, and KPH were not affected (P ≥ 0.26) by maternal treatment. Percent prime, yield grade ≤ 2, and yield grade ≥ 4 were not affected (P ≥ 0.29) by maternal treatment. Overall, late gestational nutrient restriction decreased growth pre-weaning but increased late finishing growth, without affecting backgrounding or early feedlot growth. These cattle had leaner carcasses after similar days on feed, suggesting that late gestational nutrient restriction altered growth patterns or body composition.

96 Impacts of Postweaning Dry Matter Intake Classification on Beef Heifer Performance and Cyclicity

Abstract The objective was to evaluate the relationship of postweaning dry matter intake (DMI) classifications on performance and cyclicity in fall-born beef heifers. Heifers were classified based on DMI as either low (LoDMI; < -0.5 SD from mean), average (AvgDMI; ± 0.5 SD from mean), or high (HiDMI; > +0.5 SD from mean). Hifers (n = 147), either Angus or Hereford sired by commercial dams, were utilized in the analysis. Heifers were early weaned at 82 ± 7 days of age. Following weaning, heifers were managed in partially covered, drylot pens and fed a high-energy grain diet. At postweaning intake evaluation initiation (day 1), heifers were 170 ± 22 kg and 156 ± 7 days of age. Heifer DMI was determined over 56 days using GrowSafe system, and weights were collected every 14 days. Following the postweaning intake evaluation, heifers rotationally grazed endophyte-infected tall fescue paddocks. During the 166-day grazing period, heifers were weighed and assigned a hair shedding score monthly. Heifers returned to drylot pens on day 223 for a prebreeding feed efficiency evaluation on a high-forage diet. Foot scores were assigned on day 1 and 237. Heat detection patches were used to determine percentage of heifers cycling before synchronization. Cyclicity data were analyzed using GLIMMIX and all other response variables were analyzed using the MIXED procedure of SAS 9.4. By design, postweaning DMI differed (P < 0.01) between treatments (5.5, 6.2, and 6.9 kg/d for LoDMI, AvgDMI, and HiDMI, respectively). Average daily gain (ADG) differed (P < 0.01) during the postweaning evaluation period, with LoDMI being least, AvgDMI intermediate, and HiDMI greatest. On days 1 and 56, body weights (BW) differed (P < 0.01); LoDMI were lightest, AvgDMI were intermediate, and HiDMI were heaviest. However, gain to feed during the postweaning evaluation period was not different (P = 0.33) by DMI classification. During the grazing period, BW differed (P < 0.01) on days 84 and 141; HiDMI were heavier than LoDMI and AvgDMI. On day 113, BW differed (P < 0.01); LoDMI were lightest, AvgDMI were intermediate, and HiDMI were heaviest. However, ADG and final grazing BW did not differ (P ≤ 0.12) during the grazing period by DMI classification. Hair shredding score was greater (P ≤ 0.04) for LoDMI than HiDMI on days 56, 84, and 113. Foot scores differed (P = 0.02) on day 1; LoDMI was less than AvgDMI and HiDMI. However, they only tended (P = 0.08) to be different on day 237. Percent cycling prior to synchronization did not differ (P = 0.25) by classification. In summary, LoDMI heifers performed poorer during postweaning evaluation than HiDMI heifers. However, grazing performance and cyclicity was similar among DMI classifications.

PSI-A-3 Validation of Rising Plate Meter for Predicting Herbage Mass in Tall-Fescue Pastures

Abstract The objective was to compare herbage mass (HM) estimates using a rising plate meter (RPM) and hand-sampled total collections using a forage ring. Accurate measurement of HM can be used to budget available forage in grazing systems, particularly as grass is a dynamic resource. While accurate estimation of HM can be achieved through total forage collection obtained from clipped quadrants, this is labor-intensive and time-consuming. For optimal and informed management, grass needs to be measured quickly and reliably in relation to both accuracy and precision. An RPM can be used to estimate the HM of grasslands based on the compressed sward height (CSH). However, device reliability can be affected by the naturally large variation of dry matter (DM) within CSH, which is governed by numerous factors, such as plant growth state, season species composition, and grassland management regime. Forage samples and heights were obtained weekly from grazed paddocks, which were rotated daily, over a 10-week period from June 6 to August 2, 2022. Paddocks were predominately endophyte-infected tall fescue. Each week two paddocks were randomly selected for sampling. Across both paddocks a total of 9 hand-clipped samples were randomly collected using a 0.25 m2 forage ring. All the forage within the forage ring was collected and dried for 48 h at 55 °C to determine forage DM. A Jenquip Manual Platemeter was used to measure the CSH within the forage ring before clipping. Herbage mass was estimated using the rising plate meter equation (kg DM/hectare = rising plate meter height × 158 + 200). The data were analyzed using CORR procedure of SAS 9.4. Herbage mass measured by total ring collection and RPM were not correlated (r = 0.15; P = 0.17). When RPM and total ring collection forage mass were averaged by pasture, they tended to be correlated (r = 0.44; P = 0.07). When the outlier weeks (samples 1 ,5, 6, and 7) were removed, HM measured by the total ring collection was correlated (r = 0.41; P = 0.01) to RPM. The variability in correlations across pastures and time suggest that further work is needed to understand how variables like season, weather, and clipping procedures affect reliability of RPM to accurately predict forage mass.

Disease decreases variation in host community structure in an old-field grassland.

Disease may drive variation in host community structure by modifying the interplay of deterministic and stochastic processes that shape communities. For instance, deterministic processes like ecological selection can benefit species less impacted by disease. When communities have higher levels of disease and disease consistently selects for certain host species, this can reduce variation in host community composition. On the other hand, when host communities are less impacted by disease and selection is weaker, stochastic processes (e.g., drift, dispersal) may play a bigger role in host community structure, which can increase variation among communities. While effects of disease on host community structure have been quantified in field experiments, few have addressed the role of disease in modulating variation in structure among host communities. To address this, we conducted a field experiment spanning three years, using a tractable system: foliar fungal pathogens in an old-field grassland community dominated by the grass Lolium arundinaceum, tall fescue. We reduced foliar fungal disease burden in replicate host communities (experimental plots in intact vegetation) in three fungicide regimens that varied in the seasonal duration of fungicide treatment and included a fungicide-free control. We measured host diversity, biomass, and variation in community structure among replicate communities. Disease reduction generally decreased plant richness and increased aboveground biomass relative to communities experiencing ambient levels of disease. These changes in richness and aboveground biomass were consistent across years despite changes in structure of the plant communities over the experiment's three years. Importantly, disease reduction amplified host community variation, suggesting that disease diminished the degree to which host communities were structured by stochastic processes. These results of experimental disease reduction both highlight the potential importance of stochastic processes in plant communities and reveal the potential for disease to regulate variation in host community structure.

Silicon and Epichloë‐endophyte defences in a model temperate grass diminish feeding efficiency and immunity of an insect folivore

Abstract Plants deploy diverse anti‐herbivore defences which reduce feeding and performance of herbivores. Temperate grasses use silicon (Si) accumulation and Epichloë‐endophytes for physical and chemical (i.e. endophytic‐alkaloids) defence against insect herbivores. Recent studies suggest that Epichloë‐endophytes increase Si accumulation in their host grass. It is unknown, however, how this affects Si‐deposition on the leaf surface, their impacts on insect herbivore feeding efficiency and their immunity to potential infection/parasitism. To address this knowledge gap, we grew tall fescue (Festuca arundinacea) hydroponically with and without Si, in the absence or presence of the novel AR584 Epichloë‐strain. We exposed plants to Helicoverpa armigera (Lepidoptera: Noctuidae) in both in situ (intact leaves) and ex situ (excised leaves) feeding trials and determined the effects of Si and endophyte defences on herbivore feeding efficiency, growth rates and immunity against potential infection/parasitism. Endophytic plants supplied with Si showed 110% and 143% increases in leaf silica density and leaf Si concentrations, respectively, when exposed to herbivory, compared to non‐endophytic plants that were herbivore‐free. Despite the endophyte‐mediated increases in Si concentrations, H. armigera was only affected by Si supply; growth rates decreased by 87% and most feeding efficiency indices decreased by at least 30%. Si supply also increased mandibular wear by 16%, which was negatively correlated with H. armigera growth rates. Cellular and humoral immunity of H. armigera were negatively affected by both Si and endophytes. Endophytic‐loline alkaloid concentrations were unaffected by Si supply or herbivory, whereas herbivory increased peramine concentrations by 290%. To our knowledge, this is the first report of Si defences and Epichloë‐endophyte derived alkaloids compromising insect immunity via reduced melanisation response. Using tall fescue and H. armigera, our study suggests that deploying both physical (i.e. Si accumulation) and chemical (i.e. endophytic‐alkaloids) defences acting against multiple insect herbivore traits, including feeding efficiency, growth and immunity, may be a successful defence strategy in temperate grasses. This multi‐faceted defence may be particularly difficult for insect herbivores to overcome. Read the free Plain Language Summary for this article on the Journal blog.

Monitoring leaf area index of the sown mixture pasture through UAV multispectral image and texture characteristics

Leaf area index (LAI) is an important phenotypic trait closely related to photosynthesis, respiration, and water utilization. In recent years, unmanned aerial vehicles (UAVs) multispectral capabilities enable the acquisition of spectral information from visible light to near infrared, facilitating vegetation growth monitoring. This study aims to explore the methodology of combining vegetation indices, color indices, texture information, and ecological factors based on UAV multispectral images to enhance the accuracy of the sown mixture pasture LAI estimation. A field experiment involving 13 mixed sowing combinations of alfalfa (Medicago sativa L.), tall fescue (Festuca elata Keng ex E. Alexeev) and plantain (Plantaga lanceolata L.) was conducted out. Multiple linear regression, Bagging algorithm, support vector machine (SVM), random forest algorithm (RF), KNN algorithm, and back propagation neural network (BP) were used to construct the LAI prediction model. The results showed that combining vegetation index (VI) + color index (CI) + normalized difference texture index (NDTI), and ecological factors (EF) could enhance the accuracy of LAI estimation. The sensitive characteristic combinations for alfalfa, tall fescue, and plantain were found to be NDRE (Normalized difference red-edge index) + NGBDI (Normalized green–blue difference index) + (B) MEA-(G) HOM (Blue band Mean - Green band Homogeneity) + DTR (Daily temperature difference), MSR (Modified simple ratio) + NGRDI (Normalized green–red difference index) + (G) COR-(R) VAR (Green band Correlation – Red band Variance) + DTR (Daily temperature difference)), and MSR (Modified simple ratio) + ExG (Excess green) + (G) SEM-(G) MEA (Green band Second-order moment – Green band Mean) + DTR (Daily temperature difference), respectively. RF exhibited superior prediction capability, further enhancing the accuracy of forage LAI prediction. The alfalfa, tall fescue, and plantain obtained coefficient of determination (R2) of 0.83, 0.79 and 0.79, root mean squared error (RMSE) of 0.50, 0.58 and 0.70, and mean absolute error (MAE) of 0.36, 0.45 and 0.55, respectively. These findings provide valuable insights for the estimation of leaf area index of the sown mixture pasture through UAV multispectral images and texture characteristics.

Seasonal and species variation in raffinose, short‐chain fructan, and long‐chain fructan accumulation in tall fescue (Festuca arundinacea Schreb.) and timothy (Phleum pratense L.) grown in Central Kentucky

AbstractFructans in cool‐season grasses may have some negative effects on equine health. However, they may have positive effects on ruminant performance, and fructans of different lengths appear to be metabolized differently in the rumen. Hence, seasonal variation in fructan concentrations may impact equine and ruminant performance. Long‐chain fructan with degree of polymerization (DP) > 8, short‐chain fructan (DP 4 to 8), raffinose, and three fructan trisaccharides were profiled and quantified in timothy (Phleum pratense L.) cultivar ‘Clair’ and tall fescue (Festuca arundinacea Schreb.) cultivar ‘Cajun II’ harvested in April, June, August, and October of two consecutive years in central Kentucky. Harvest year influenced concentrations of long‐chain fructan (p = .0017). Harvest date influenced species differences in raffinose (p = .0035), which was most abundant in timothy in June, and in 1‐kestose and neokestose (p < .0001), which were most abundant in tall fescue in April. Harvest date influenced species differences in short‐ and long‐chain fructan (p < .0001). Tall fescue had two‐ to three‐fold more short‐chain fructan than timothy in April, August, and October. Timothy had two‐ to five‐fold more long‐chain fructan than tall fescue in April, June, and October. Species choice and weather patterns may have contributed to relatively low concentrations of all the carbohydrates measured in this study. Fermentation or feeding studies could help to determine if the concentrations present could affect equine health or ruminant performance.

Does a decade of soil organic fertilization promote copper and zinc phytoavailability? Evidence from a laboratory biotest with field-collected soil samples

Despite chronic contamination, long-term organic fertilization tends to decrease copper (Cu) and zinc (Zn) availability in agricultural soils. Root activities of crop plants can also induce substantial changes in rhizosphere chemistry and consequently in the Cu and Zn availability in the rhizosphere. The balance between these two drivers and the overall effect of organic fertilization on Cu and Zn bioavailability to plants (i.e., phytoavailability) remains a matter of debate. We assessed the effect of a decade of agronomically realistic organic fertilization on Cu and Zn availability in the rhizosphere and their phytoavailability. Using a laboratory biotest, Festuca arundinacea was exposed to 34 soil samples collected from three agricultural field trials that had received no, mineral, or organic fertilization for a decade. Dissolved organic matter (DOM) properties (i.e., concentration, aromaticity, and binding properties toward Cu), pH, and Cu and Zn availability (i.e., total dissolved concentration and free ionic activity) were determined in the rhizosphere solutions. Cu and Zn phytoavailability was measured as the plant uptake flux. Contrary to bulk soils, organic fertilization induced very few changes in the chemistry and Cu and Zn availability in the rhizosphere solutions compared to no and mineral fertilization. Consistently, Cu and Zn phytoavailability did not increase with organic fertilization, but it was mostly driven by soil properties rather than by fertilization. Despite increasing soil Cu and Zn contamination, a decade of soil organic fertilization did not increase Cu and Zn phytoavailability, presumably due to the root-mediated levelling of Cu and Zn availability in the rhizosphere.

Convergence points of optimal herbage accumulation and intake rate by sheep grazing tall fescue

AbstractPasture management oriented towards sustainable intensification and stability of yield must consider the ideal balance between the mass of leaves removed by grazing and the mass left as residual. The former supports high animal production and the later supports an optimum soil–plant carbon balance. This study aimed to evaluate the optimal herbage level from both plant and animal perspectives, through the adjustment of instantaneous herbage accumulation rate as estimated by the Gompertz curve model and short‐term intake rate of sheep. Weekly tall fescue (Schedonorus arundinaceus) herbage accumulation was measured during seven growth periods with initiation dates in October, November and December 2015, and March, April, August and September 2016 and with the initiation dates arranged in a randomized complete block design with four replicates. Total herbage mass, leaf lamina mass, pseudo‐stem + sheath mass, senescent mass, and sward surface height were measured each week. The results demonstrated that a pre‐grazing sward surface height of 22.3 cm of tall fescue promoted the maximum short‐term intake rate of sheep and the optimum herbage accumulation rate in the spring and autumn periods. In general, the convergent point occurred after the maximum instantaneous leaf lamina accumulation rate and before the maximum instantaneous accumulation rate of pseudo‐stem + sheath and senescent material. We suggest the existence of a convergent point in which both primary and secondary production of pastoral ecosystems could be fostered.