Root growth and nutrient element status of creeping bentgrass cultivars differing in heat tolerance as influenced by supraoptimal shoot and root temperatures

This study was designed to determine and compare root growth and nutritional responses of creeping bentgrass cultivars that differ in heat tolerance to differential, supraoptimal, shoot and root temperatures. Shoots and roots of 'Penncross' (heat sensitive) and 'L-93' (heat tolerant) were exposed to four air/soil temperature regimes (20/20 degrees C-control, 20/35 degrees C, 35/20 degrees C, and 35/35 degrees C) in water baths and growth chambers. Exposing roots to supraoptimal root temperature (35 degrees C) while maintaining shoots at normal temperature (20 degrees C) or particularly at 35 degrees C reduced root fresh weight, root number, and contents of nitrogen (N), phosphorus (P), and potassium (K) in shoots and roots and accelerated root death for both cultivars. High root temperature had greater detrimental effects on root growth and nutrient element accumulation than high shoot temperature for both cultivars. A low root temperature at supraoptimal shoot temperature improved root growth, reduced root mortality; and increased N, P, and K contents in shoots and roots. Among the three nutrient elements, K was the most sensitive to changes in root temperature. L-93 generally maintained higher fresh weight and number of roots and higher N, P, and K contents in shoots and roots, particularly K in roots, under high root (20/35 degrees C) or shoot/root (35/35 degrees C) temperatures. The results indicated that root growth and nutrient element accumulation, particularly of K, played an important role in creeping bentgrass tolerance to heat stress imposed on shoots by high air temperature or to roots by high soil temperatures. The enhanced root growth and nutrient element relations with a low root temperature at supraoptimal ambient temperatures could lead to the improved shoot growth in cool-season grasses observed under these conditions.