Publications - Faculty - Recently Submitted Faculty Publications 2008

Syvertsen - Proc. Fla. State Hort. Soc.

PARTIAL ROOT ZONE DRYING WITH AND WITHOUT SALINITY AFFECTS WATER USE EFFICIENCY OF CITRUS

Ayako Kusakabe, Juan Carlos Melgar, Jill Dunlop, and J.P. Syvertsen

Abstract. A greenhouse experiment was conducted using partial root zone drying (PRD) with and without saline water on split-root ‘Swingle’ citrumelo (Citrus paradisi Macfad. × Poncirus trifoliata (L.) Raf.)  seedlings potted in an autoclaved fine sandy soil to evaluate leaf water use efficiency (WUE) and photosynthetic responses.  Each root system was  split in half and the following five treatments were applied: 1) both root halves irrigated  with 50% ETc each (100% ETc control or well-watered [WW]), 2) one half irrigated with 100% ETc while the other received no water (PRD), 3) one half irrigated with 50% ETc water plus 50 mM NaCl while the other received no water (PRS), 4) both sides irrigated with 50% ETc plus 50 mM NaCl (SS), or 5) one half irrigated with 50% ETc and  one half irrigated with 50% ETc plus 50 mM NaCl (WS). Citrus seedlings in the PRD and PRS treatments used 33 to 42% less water and grew 23 to 33% less than the WW controls. PRD and PRS plants reduced shoot growth while root growth was less affected, leading to an increase in root: shoot ratio. Roots in the PRD and PRS dry sides had higher levels of abscisic acid (ABA) in roots but not in leaves.  PRS reduced net CO2 assimilation rate (ACO2) but leaves above the PRD dry side had higherACO2 than the WW plants and leaves on the PRD wet side. PRD resulted in water savings without loss of leaf function but the mechanism that regulates stomatal closure and transpiration appeared to be independent of ABA concentrations in roots.