Search

Information is lacking on the precision of atmometers and empirical models used to estimate turfgrass evapotranspiration (ET). Experiments were conducted to evaluate the precision of black Bellani plates, a class A evaporation pan, and the Penman-Monteith empirical model for estimating ET of 'Mustang' tall fescue (Festuca arundinacea Schreb.), 'Meyer' zoysiagrass (Zoysia japonica Steud.), 'Prairie' buffalograss [Buchloe dactyloides (Nutt.) Engelm.], and 'Midlawn' bermudagrass [Cynodon dactylon (L.) Pers. x transvaalensis Burtt-Davy] under well-watered conditions. Tall fescue was mowed once weekly at 6.5 cm, and warm-season grasses were mowed at 4.5 cm twice weekly. Diurnal ET was measured between June and September in 1993 and 1994 using weighing lysimeters and the water balance method. Evaporation from atmometers was measured during the hour that turfgrass ET was determined, and Penman-Monteith-estimated ET was calculated for the same time period. Black Bellani plate evaporation was correlated most closely with measured turf ET (R 2 = 0.73), followed by class A pan evaporation (R 2 = 0.67), and Penman-Monteith-estimated ET (R 2 = 0.60). Ranking of grasses for mean daily ET was tall fescue (6.8 mm d -1 ) > zoysiagrass (5.6 mm d -1 ) > buffalograss (5.1 mm d -1 ) = bermudagrass (5.0 mm d -1 ). The black Bellani plate provides the most precise estimate of turfgrass ET under well-watered conditions.

This paper defines several solution properties that alter the effects of heat on isolated chloroplast thylakoid membranes. Isolated bean (Phaseolus vulgaris L.) «Oregon 1604» thylakoids in various milieus were exposed to 25 or 45 °C, and the repercussion(s) of heat were determined. Raffinose (0.4-0.5 M) wass lightly more thermostabilizing than 2 M sucrose as evidenced by an amelioration of the: (i) heat-induced decline in electron transport, (ii) heat-induced alteration in the susceptibility of thylakoid polypeptides to trypsin digestion, and (iii) heat-induced decline in the maximum fluorescence transient measured at 685 nm...

Degree-day modeling applications in turfgrass management have recently seen increased interest. The predictive capacity of any degree day model is dependent on an accurate determination of the basal growth temperatures for the species under consideration. The objective of this study was to determine basal growth temperatures and growth rate constants for eight warm season turfgrasses (five species). Sprigs from bermudagrass [Cynodon dactylon (L.) Pers. cv. Arizona Common and C. dactylon lc C. transvaalensis Burtt Davey cv. Midiron], buffalograss [Buchloe dactyloides (Nutt.) Engelm. cv. Kansas Common and Texoka], zoysiagrass (Zoysia japonica Steudel cv. Meyer), St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze cv. Raleigh and Floratam], and centipedegrass [Eremochloa ophiuroides (Munro) Hackel, cv. Common] were grown at temperatures ranging from 5 to 30°C in a controlled environment chamber under 14-h photoperiods. Chamber temperature was decreased in a step-wise fashion to the next temperature after two leaves were fully expanded. Leaf growth rates at each temperature were calculated and expressed as millimeters per day. Base temperature and growth rate constants for each turfgrass were calculated with segmented nonlinear regression analysis. Base temperatures for the eight tested cultivars ranged from 0 to 13°C. Interspecific and intraspecific differences for basal growth temperature were found, indicating that degree-day model application accuracy is dependent on proper determination of target species and cultivar basal growth temperature. Joint Contribution of Kansas Agric. Exp. Stn. Contribution No. 95-393-J and Nebraska Agric. Res. Div. Journal Series No. 11054.

Kinetic parameters of 3-(3, 4-dichlorophenyl)-1, 1-dimethyl urea (DCMU)-induced inhibition of electron transport in chloroplast thylakoids isolated from Phaseolus vulgaris L. cv. Oregon 1604 were determined from analysis of a convergent, parallel electrical circuit. Through this analogue, the apparent affinity of the purported binding site for DCMU (K1) and the relative amount of DCMU-insensitive electron transport (vmax1/vo) were obtained using a reiterative non-linear least squares curve-fitting procedure. Exposure of thylakoids to heat caused a gradual increase in K1 (or decrease in the affinity of the thylakoid for DCMU) with an apparent activation energy of 134 kJ mol−1. Tryptic susceptibility of a protein region regulating K1 also decreased gradually with exposure to 45°C, suggesting that the heat-induced increase in K1 might be due to a protein conformational change. On the other hand, thylakoid exposure to 45°C resulted in a rapid (