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Emission Rates, Survival, and Modeled Dispersal of Viable Pollen of Creeping Bentgrass

^a USDA-ARS National Forage Seed Production Research Center, 3450 SW Campus Way, Corvallis, OR 97331
^b USDA Forest Service Pacific Northwest Region, P.O. Box 3623, Portland, OR 97208
^c Dep. Botany and Plant Pathology, Oregon State Univ., Corvallis, OR 97331

View larger version (22K): [in this window] [in a new window]   Figure 1. Sampling array for measuring number of pollen grains in a plume emitted from a plot of creeping bentgrass. Rotary impaction samplers were mounted on poles at heights of 0.5, 1.5, 2.5, and 4.0 m. The poles were set at 22.5° intervals along a 135° arc with a radius of 10 m, downwind from the center of a 6- by 6-m plot of creeping bentgrass. Two additional poles with samplers at 0.5 and 2.5 m height were placed upwind of the plot to measure background pollen concentrations. All samplers were run simultaneously during the sampling period of 15 or 30 min. To estimate total pollen passing through the downwind sampling array during the sampling period, the plume cross-section was divided conceptually into rectangles (indicated here in dashed lines). Pollen flux through each rectangle was derived by multiplying the spore concentration measured at the appropriate sampler by air volume moving through that rectangle. Air volume was calculated from measured or interpolated wind speed at sampler height, sampling duration, and cross-sectional area of the rectangle. The pollen fluxes of all rectangles were summed to produce the total flux.

View larger version (11K): [in this window] [in a new window]   Figure 2. Survival of creeping bentgrass pollen exposed outdoors. Pollen, collected within 15 min of anther dehiscence, was immobilized on traps made of feather down. Viability was assessed as germinability on an artificial medium. Each data point is the average of seven experiments, three replicate traps per time interval per experiment. Vertical bars represent standard error of the mean. The smooth curve is best-fit exponential decline equation: Proportion surviving = 0.6e(–0.036 x min).

View larger version (24K): [in this window] [in a new window]   Figure 3. Diurnal patterns of creeping bentgrass pollen in the air 0.75 m above a commercial creeping bentgrass field, located approximately 2 km from pollen plume sampling site, for several days during anthesis. Data were collected with a Burkhard 7-d volumetric suction sampler, read as pollen grains per air volume per 2-h time interval.

View larger version (17K): [in this window] [in a new window]   Figure 4. Comparison of days for favorability to pollen dispersal. A standard diurnal pattern of pollen emission was applied to actual weather conditions on each of the days between 25 June and 9 July 2005. Simulations of dispersal and deposition were run in CALPUFF. The height of each bar is the sum of the number of pollen grains modeled to be deposited at 360 receptor sites located in a ring (one receptor per degree) with a radius of 3 km from the test plot. Complete weather data for 1 July were not available.

View larger version (25K): [in this window] [in a new window]   Figure 5. Sampling results and modeled deposition for creeping bentgrass pollen on 25 June 2005. (A) Pollen concentrations measured by rotary impaction samplers in the sampling array depicted in Fig. 1. Background pollen concentrations, measured upwind of the plot, have been subtracted. (B) CALPUFF-simulated dry deposition of pollen grains from a 2.4-ha field of creeping bentgrass, using the diurnal pattern of pollen emission rates and the weather conditions that occurred on 25 June 2005. Isopleth units are the number of viable pollen grains deposited per m2 of surface area during 24 h (2400–2400 h). (C) CALPUFF-simulated dry deposition from a 25-ha field on the same date.

View larger version (24K): [in this window] [in a new window]   Figure 6. Sampling results and modeled deposition for creeping bentgrass pollen on 8 July 2005. (A) Pollen concentrations measured by rotary impaction samplers in the sampling array depicted in Fig. 1. Background pollen concentrations, measured upwind of the plot, have been subtracted. (B) CALPUFF-simulated dry deposition of pollen grains from a 2.4-ha field of creeping bentgrass, using the diurnal pattern of pollen emission rates and the weather conditions that occurred on 8 July 2005. Isopleths units are number of viable pollen grains deposited per m2 of surface area during 24 h (2400–2400 h). (C) CALPUFF-simulated dry deposition from a 25-ha field on the same date.

View larger version (20K): [in this window] [in a new window]   Figure 7. CALPUFF modeling results for a simulation in which creeping bentgrass pollen was lifted as much as 20 m above the ground in a single event by a hypothetical 5-m diam. thermal vortex ("dust devil") occurring during weather conditions that existed on 8 July 2005. Map shows deposition in units of viable pollen grains per m2 surface area.

View larger version (22K): [in this window] [in a new window]   Figure 8. Comparison of modeled pollen deposition for two dates differing in weather conditions and pollen emission profiles, for two field sizes representing the 10th and 90th percentile sizes of creeping bentgrass seed production fields in Oregon (2.4 and 25 ha). For one of the days, simulation results from a hypothetical dust devil event are also shown. Values were derived from maps shown in Fig. 5 to 7, and represent the maximum distances for each of the indicated viable pollen deposition concentrations.