Turfgrasses have varying tolerance to waterlogging conditions. The objective of this study was to identify important root traits and physiological responses to waterlogging stress in seashore paspalum (Paspalum vaginatum) and bermudagrass (Cynodon sp.). After being exposed to waterlogging conditions for 28 days, turf quality, leaf photosynthesis, transpiration rate, stomatal conductance (g S), and root fresh weight were significantly decreased in bermudagrass, and root lipid peroxidation was significantly increased. However, seashore paspalum was found to be more tolerant to waterlogging conditions and changes in turf quality, photosynthesis, or lipid peroxidation were not seen. The waterlogging treatments increased specific root length (SRL), surface area, and volume and decreased root respiration and diameter to a greater extent in seashore paspalum compared with bermudagrass. Under waterlogging conditions, root aerenchyma formation was found in both seashore paspalum and bermudagrass, but to a greater extent in seashore paspalum. Both grasses exhibited significant increases in root water-soluble carbohydrate (WSC) but to a lesser extent in seashore paspalum than in bermudagrass. Shoot WSC remained unchanged in seashore paspalum but was significantly increased in bermudagrass. These results indicate greater root morphological changes such as root volume, SRL, and root porosity, as well as lower root respiration may be important contributors to waterlogging tolerance for seashore paspalum.
Bo Xiao and David Jespersen
Zai Q. Yang, Yong X. Li, Xiao P. Xue, Chuan R. Huang and Bo Zhang
Wind tunnel tests were conducted in an NH-2-type wind tunnel to investigate the wind pressure coefficients and their distribution on the surfaces of a single-span plastic greenhouse and a solar greenhouse. Wind pressures at numerous points on the surfaces of the greenhouse models were simultaneously measured for various wind directions. The critical wind speeds, at which damage occurred on the surfaces of single-span plastic greenhouses and solar greenhouses, were derived. To clearly describe the wind pressure distribution on various surface zones of the greenhouses, the end surface and top surface of the plastic greenhouse and the transparent surface of the solar greenhouse were divided into nine zones, which were denoted as Zone I to Zone IX. The results were as follows: 1) At wind direction angles of 0° and 45°, the end surface of the single-span plastic greenhouse was on the windward side, and the maximum positive wind pressure coefficient was near 1. At wind direction angles of 90° and 180°, the entire end surface of the single-span plastic greenhouse was on the leeward side, and the maximum negative wind pressure coefficient was near −1. The maximum positive wind pressure on the end surface of the single-span plastic greenhouse appeared in Zone IV at a wind direction angle of 15°, whereas the maximum negative pressure appeared in Zone VIII at a wind direction angle of 105°. 2) Most of the wind pressure coefficients on the top surface of the plastic greenhouse were negative. The maximum positive and negative wind pressure coefficient on the top surface of the plastic greenhouse occurred in Zones I and II, respectively, at a wind direction angle of 60°. 3) At a wind direction angle of 0°, the distribution of wind pressure coefficient contours was steady in the middle and lower zones of the transparent surface of the solar greenhouse, and the wind pressure coefficients were positive. At a wind direction angle of 90°, the wind pressure coefficients were negative on the transparent surface of the solar greenhouse. A maximum positive wind pressure coefficient was attained at a wind direction angle of 30° in Zone IX, whereas the maximum suction force occurred in Zone VII at a wind direction angle of 135°. 4) The minimum critical wind speeds required to impair the single-span plastic greenhouse and solar greenhouse were 14.5 and 18.9 m·s−1, respectively.