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UV-B Biodosimetry in Turfgrass Canopies

^a Dep. of Plant Pathology, Univ. of Nebraska, Lincoln, NE 68583-0722
^b Dep. of Plant Pathology, Univ. of Nebraska, Lincoln, NE 68583-0722
^c Dep. of Plant Pathology, Univ. of Nebraska, Lincoln, NE 68583-0722
^d Dep. of Soil, Water and Climate, Univ. of Minnesota, St. Paul, MN 55108
^e School of Natural Resource Sciences, Univ. of Nebraska, Lincoln, NE 68583-0728
^f School of Natural Resource Sciences, Univ. of Nebraska, Lincoln, NE 68583-0728
^g Dept of Agronomy and Horticulture, Univ. of Nebraska, Lincoln, NE 68583-0724

View larger version (32K): [in a new window]   Fig. 1. Relationship between survival (S) of E. coli strain CSRO6 after sunlight exposure in dosimeter packets differing in age and solar UV-B dose (D) measured with a YES broadband radiometer. For packets 3 d old or less, n = 103; for packets over 3 d old, n = 128. Data were collected over 8 d in 1997.

View larger version (25K): [in a new window]   Fig. 2. (A) Temperatures measured with thermocouples in three dosimeter packets placed above or in a tall fescue canopy; and (B) relationship of survival (S) of E. coli strain CSRO6 in dosimeter packets on chilled agar or on wooden sticks to UV-B dose (D) measured with a YES broad-band radiometer during full sunlight exposure. All measurements were made on DOY 183, 1997. In (A), packets were mounted on wooden sticks. At ‘0’ time (1107 h CST), packet 1 was placed above the canopy while Packets 2 and 3 were placed on the soil surface. At time ‘a’, the positions were interchanged. At time ‘b’ all of the packets were transferred to an ice chest. In (B), exposure began at 1200 h CST and sets of packets were removed from sunlight at 5-min intervals.

View larger version (24K): [in a new window]   Fig. 3. Survival (S) of E. coli strain CSRO6 in dosimeter packets following exposure to various wavebands in relation to UV-B dose (D) measured with a YES broad-band radiometer. Packets were exposed to sunlight for up to 40 min while covered with foil (No light), a filter that blocked UV-B and UV-C (+UV-A/no UV-B), a band-pass filter that transmitted UV-B and UV-A but blocked visible wavelengths (+UV-A/+UV-B), or no covering (Full sunlight). The experiment was conducted on DOY 163, 1997. n = 3 at each dose.

View larger version (24K): [in a new window]   Fig. 4. UV-B transmittance measured by biodosimeter packets (bio) and a Vital radiometer (rad) at soil level in eight tall fescue canopies: (A) correlation between the methods; (B) relationship of transmittance values to leaf area index (LAI) in each canopy. In A and B, each value is a mean of 20 measurements taken along a 1-m-long track at 5-cm intervals. In A, error bars denote standard deviation. In B, vertical bars indicate the range of measurements, and data are offset on the X scale for clarity.

View larger version (14K): [in a new window]   Fig. 5. UV-B transmittance (T) measured with biodosimeter packets at the base of tall fescue canopies as a function of leaf area index (LAI). Each value (n = 68) is a mean of two measurements.

View larger version (21K): [in a new window]   Fig. 6. Relative UV-B transmittance (T) detected by biodosimeter packets on surfaces of vertical simulated grass blades placed at various heights (H) in a tall fescue canopy of 18 cm height. T was determined relative to UV-B irradiance measured horizontally above the canopy by a YES broad-band radiometer. Each value is a mean of six measurements made in each of 2 d. Error bars denote standard deviation.