Transpiration and normalized difference vegetation index response of seashore paspalum to soil drying

Abstract

A consistent response has been observed among many plant species in their leaf gas exchange as soils are subjected to a drying cycle; except for one case, these studies have not included turfgrass species. The current study reports the change in transpiration rate of six genotypes of seashore paspalum (Paspalum vaginatum Swartz) during soil drying when grown on either an organic soil or sand. On organic soil, the response was consistent with results with other plant species in that there was no decline in transpiration rate until the fraction of transpirable soil water (FTSW) reached the range of 0.25 to 0.31. The decline in transpiration rate when plants were grown on sand occurred in the FTSW range of 0.10 to 0.17, which was also consistent with reports for other species when grown on sand. The lower FTSW for the decline in transpiration rate on sand appears to be a result of the greater retention of water in fully wetted sand in pot experiments as compared with field conditions. Because the decline in transpiration occurred at a higher FTSW in 'SeaIsle Supreme', 'Aloha', and 'SeaIsle 1' than in 'SeaIsle 2000', this is an indication that these genotypes are water-conserving and may be better suited to water-deficit conditions. Quality changes in these grasses were monitored daily during the drying cycle by reflectance measurements of their normalized difference vegetation index (NDVI). No change in NDVI was observed for grasses grown on either soil type until the soil had become very dry and transpiration had decreased to low rates.