Light Acclimation in Citrus Leaves. II. CO2 Assimilation and Light, Water, and Nitrogen Use Efficiency

Abstract

Abstract Net CO2 assimilation (A) rates of ‘Duncan’ grapefruit (Citrus paradisi Macf.) and ‘Pineapple’ orange (C. sinensis L.) seedlings grown under 3 different photosynthetic photon flux densities (PPFD), were measured in an open gas exchange system under controlled environmental conditions. Apparent quantum yield (ø), mesophyll conductance to CO2 (Gm), leaf conductance to H2O vapor (G1), transpiration (E) and water use efficiency (WUE) also were examined. Leaves of both species grown under high PPFD (full sunlight) had the greatest maximum rates of A, but the low PPFD (90% shade) leaves had the highest ø. The WUE of low PPFD grapefruit leaves was less than that of the high PPFD leaves but increased within 2 weeks after being moved into full sunlight. Transferring seedlings from low to high PPFD decreased ø of grapefruit but not of orange leaves. Changes in A were more strongly correlated to Gm than to G1. Carbon dioxide assimilation rate was positively correlated to total leaf nitrogen content. Citrus leaf photosynthetic characteristics and resources use efficiency not only acclimate to the light regimes under which they expand and mature, but leaves are capable of acclimating to new light regimes, even after full maturation.