Physiological adaptation of Kentucky bluegrass to localized soil drying

This study was designed to investigate effects of surface soil drying (SD) on water relations, gas exchange, growth characteristics, and abscisic acid (ABA) content of leaves and roots for Kentucky bluegrass (Poa pratensis L.), and to examine whether physiological adaptation to SD is associated with hydraulic or chemical regulation. 'Award' and 'Nuglade' were subjected to three soil moisture treatments in a growth chamber: (i) well-watered control; (ii) SD (0-20 cm); and (iii) full soil profile (0-40 cm) drying (FD). Under SD, turf quality (TQ), relative water content (RWC), photosynthesis, and cell membrane stability remained the same as the controls, but stomatal conductance (g,) declined by 35 and 45%, and shoot growth rates were reduced by 50 and 40% for Award and Nu glade, respectively. Root DW decreased in 0- to 20-cm dry soil, but increased compared with controls in the 20- to 40-cm wet soil under SD. The ABA content increased by four to sixfold in roots at 0- to 20-cm drying soil and did not change in the 20- to 40-cm wet soil under SD conditions. The ABA content was also higher in leaves of SD plants. The results suggested Kentucky bluegrass adapted to localized soil drying by maintaining TQ, photosynthesis, leaf water status (WS), and root growth using water in the deeper soil profile. Decline in g, and shoot growth was independent of leaf WS, and could be hormonally controlled, which could help maintain favorable WS in leaves by reducing water loss under SD conditions.