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Despite the high sensitivity of Flux Variance Similarity (FVS) partitioning to leaf‐level water use efficiency (WUE), relatively little work has been done comparing WUE algorithms. We evaluated four intercellular CO2 concentration parameterizations (constant_ppm, constant_ratio, and linear and square root functions of vapor pressure deficit) and one optimized WUE approach using eddy covariance data for three C3 (wheat – Triticum aestivum L., canola – Brassica napus L., and soybean – Glycine max L.) and two C4 (maize – Zea mays L. and sorghum – Sorghum bicolor L. Moench) grain crops. The different data requirements of the WUE models resulted in discrepancies in the number of partitioned outputs among WUE algorithms. The transpiration:evapotranspiration (T:ET) ratios found with the five WUE algorithms varied by 6%–8% for soybean and maize, 12%–13% for wheat and canola, and 22% for sorghum. The crops producing larger variations in computed T:ET also tended to have higher estimated WUE magnitudes. The constant_ppm and constant_ratio parameterizations showed better potential to partition ET in all crops, except soybean. The linear and square root WUE models failed to produce reduced T:ET ratios during wet periods in all crops, except soybean. The optimized WUE approach has potential as a benchmark for comparing other WUE algorithms for C3 crops. The applicability of the linear and optimized WUE approaches was uncertain in C4 crops. Agreement and disagreement among the five WUE algorithms in multiple crops provide new perspectives for applying FVS partitioning to a range of biomes and climate conditions. Key Points: Flux Variance Similarity (FVS) partitioning shows high sensitivity to water use efficiency (WUE) estimates from five WUE algorithmsFive WUE algorithms yielded considerable differences in FVS algorithm performance and partitioned transpiration:evapotranspiration ratiosOptimized WUE approach showed the potential to use as a benchmark to compare with other WUE algorithms for sensitivity analysis in C3 crops [ABSTRACT FROM AUTHOR]

Grasslands in the Southern Great Plains of the United States have major ecological and economic importance, with strong climate and water cycle connections. The historic native prairie grassland has been managed differently for enhancing productivity, while consequently altering water vapor fluxes. However, little is known about the impacts of different management activities on evapotranspiration (ET) at different spatio-temporal scales. In this study, we quantified and compared ET between co-located introduced managed pasture (MP) and native prairie (NP) pasture. Additionally, we compared the Moderate Resolution Imaging Spectroradiometer (MODIS)-derived ET at four different spatial scales: 30 m (ETMOD30), 200 m (ETMOD200), 500 m (ETMOD500), and 1000 m (ETMOD1000) with eddy covariance-measured ET (ETEC). Large differences in ETEC were observed between two pastures from half-hourly to seasonal scales, with variations mainly controlled by the amount of rainfall and management activities. The results demonstrated differential responses of MP and NP in a pluvial year. The ETMOD30 showed a better agreement with ETEC than did the ETMOD200, ETMOD500, and ETMOD1000. The ETMOD200, ETMOD500, and ETMOD1000 largely underestimated ETEC, most likely due to their inability to capture the spatial heterogeneity of vegetation growth impacted by various management activities. Our results facilitate understanding of the difference in ET of MP and NP due to differences in vegetation resulting from different management activities and their differential responses to precipitation. [ABSTRACT FROM AUTHOR]

Johnson grass (Sorghum halepense (L.) Pers.) is rapidly spreading throughout the continental United States (U.S.). Thus, determining magnitudes and seasonal dynamics of carbon dioxide (CO 2 ) and water vapor (H 2 O) fluxes in Johnson grass is crucial to understand regional changes in hydrology and carbon balance. Using eddy covariance (EC), CO 2 and H 2 O fluxes were measured from June 2017 to October 2019 over a rainfed Johnson grass field in central Oklahoma. Hay was harvested from late May to early July each year, with biomass yield ~7.5 t ha -1 . Weekly averaged daily integrated net ecosystem CO 2 exchange (NEE), gross primary production (GPP), and evapotranspiration (ET) reached -8.28 ± 0.76 g C m -2 , 20.02 ± 1.62 g C m -2 , and 5.42 ± 0.26 mm, respectively. Ecosystem water use efficiency (EWUE) and ecosystem light use efficiency (ELUE) ranged from 3.22 to 3.93 g C mm -1 ET and 0.34 to 0.41 g C mol -1 PAR (photosynthetically active radiation), respectively, during peak growths. Based on aggregated fluxes for each month over the three years (2017-2019), cumulative annual NEE was -434 ± 112 g C m -2 , indicating a carbon gain by the Johnson grass field. Cumulative annual ET (858 ± 72 mm) was ~86% of the average annual rainfall (996 ± 100 mm). Results showed Johnson grass could be a carbon sink from May to September in the U.S. Southern Great Plains. Both NEE and ET did not decline up to air temperature (T a ) of ~33 °C and vapor pressure deficit (VPD) of ~2 kPa, suggesting optimum T a of ≥33 °C and VPD of ≥2 kPa for the fluxes. Results indicated that Johnson grass might be well suited for dryland production in the region. Additionally, these findings provide initial baseline information on CO 2 fluxes and ET for Johnson grass relative to other forage species in the region., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Published by Elsevier B.V.)

Eddy covariance (EC) systems provide integrated fluxes within their footprint areas. Spatial heterogeneity of up-scaled areas and spatio-temporal mismatches between EC footprint and remote sensing pixels jeopardize the performance of most satellite-based models. To examine the impact of spatial resolution of satellite products on up-scaling of fluxes, we compared the relationships between measured eddy fluxes and enhanced vegetation index (EVI) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) at 500 and 250 m spatial resolutions, Visible Infrared Imaging Radiometer Suite (VIIRS) at 500 m spatial resolution, and Landsat at 30 m spatial resolution but integrated at the paddock-scale. The experiment was conducted over a grazed native tallgrass prairie pasture, which was divided into nine paddocks for rotational grazing. The EVI data from all satellites showed consistency in detecting vegetation phenology. Seasonality of EC-measured fluxes corresponded well with remotely-sensed vegetation phenology. Approximately 80% of contribution to eddy fluxes came from within 80 m upwind distance of the 2.7 m tall EC tower. As a result, the major contributing area for the measured fluxes was mostly limited to the paddock containing the EC tower. Different timings and duration of grazing caused some heterogeneity among paddocks within the pasture. The EVI of different spatial scales showed strong relationships with CO 2 fluxes. However, Landsat-derived EVI integrated for the paddock containing the EC tower showed substantially stronger relationships with CO 2 fluxes than did MODIS and VIIRS-derived EVI integrated for multiple paddocks, most likely due to similar spatial resolutions of remote sensing and EC observations. Results illustrate that satellite products of fine-scale spatial resolution that are comparable to EC footprints can help improve the performance of satellite-based models for modeling or up-scaling of eddy fluxes, especially in heterogeneous ecosystems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Published by Elsevier B.V.)

There is little information available on the species dynamics of eimerian parasites in grazing cattle in the central Appalachian region of the United States. Therefore, the objective of this study was to describe the level of infection and species dynamics of Eimeria spp. in grazing beef cattle of various age groups over the course of a year in the central Appalachian region. Rectal fecal samples were collected from male and female calves (n=72) monthly from May through October 2005, heifers only (n=36) monthly from November 2005 to April 2006, and cows (n=72) in May, July, and September, 2005. Eimeria spp. oocysts were seen in 399 of 414 (96%) fecal samples collected from the calves from May through October. Fecal oocysts counts (FOC) in the calves were lower (P<0.05) in May than all other months and no significant differences were detected from June through September. Eimeria spp. oocysts were detected in 198 of 213 (92%) of fecal samples collected from the 36 replacement heifers monthly from November to April and monthly mean FOC did not differ during this time period. The prevalence of oocyst shedding increased to 100% in calves in September and remained near 100% in the replacement heifers during the sampling period. Eimeria spp. oocysts were also detected in 150 of 200 (75%) samples collected in May, July, and September from the cows and mean FOC did not differ significantly over the sampling period. Eimeria spp. composition was dominated by Eimeria bovis in fecal samples collected from calves, replacement heifers and cows. Mixed Eimeria spp. infections were, however, common in all groups and 13 Eimeria spp. oocysts were identified throughout the sampling period., (Copyright © 2014 Elsevier B.V. All rights reserved.)