Leaf Senescence Is Different in Tall Fescue Induced by Salinity and Shade.

Turfgrass visual quality is one of the most important components of turf quality.  Leaf firing, a form of chlorosis, often is the most obvious symptom developed when the grass is under salinity stress.  The objective of this study was to investigate the process of leaf senescence under natural, shade, and saline conditions.  Two tall fescue varieties, previously reported as salt tolerant (Tar Heel II) and sensitive (Wolf pack), were investigated in this study.  We added NaCl and CaCl₂ to the full strength Hoagland solution to a final EC about 25 dS m^-1 to mimic saline stress.  The salt solution was applied at seven-day intervals to the sand root zones for the salinity treatment.  We used a shade material that allowed 30% passing of light to simulate accelerated aging.  Plants that received Hoagland solution only were used as control.  The two varieties were not different in relative water content (RWC), normalized vegetation index (NDVI), quantum yield of photosynthesis system II (PSII), and chlorophyll content.  The tall fescue plants under salinity stress showed a similar trend to the accelerated aging treatment in quantum yield of PSII, NDVI, and epicuticlar wax accumulation, but responded differently from the control and accelerated aging in chlorophyll content and RWC.  Electronic microscopy also demonstrated differences at subcellular levels for the senescence induced by salinity and shade.