Tolerance of citrus rootstocks to poor water quality is improved by root zone aeration via selective uptake of ions, higher photosynthesis and carbon storage

Abstract

The effects of root zone aeration and irrigation water quality (WQ) were studied in two rootstocks with contrasting tolerances to abiotic stress. We hypothesized that the main influence of TWW is that of its salinity (especially Na and K and their ratios), that the organic load and its BOD have a marginal influence and that aeration facilitates selectivity of roots and/or leaves and therefore improves plant performance. The factorial experiment included root zone aeration, fresh water (FW), TWW, and fresh water with a salt concentration similar to TWW (FW + NaCl). One year old unworked rootstocks of sensitive Citrus volkameriana (Volka) and tolerant X639 (Cleopatra mandarin X Poncirus trifoliata) were treated for 4 months, followed by 2 months of recovery. Measurements included ionic and water relations, photosynthetic parameters, growth, morphology, tissue specific membrane properties, and sugar and starch contents. Volka was highly sensitive to WQ and aeration while X639 was influenced much less. During the first two months aeration increased Volka leaf photosynthesis and gas exchange by 15%, water and potassium (K) uptake by 20%, carbon storage by 15% and biomass by 20%; which compensated for the negative effects of poor WQ. Changes in distribution of K and Na ions hint at the mechanisms for the aeration influence on tolerance to poor WQ. Results indicate that aeration enhanced K transport from the roots to leaves and reduced Na concentrations in the roots of the sensitive rootstock. These, as well as changes in the wide range of leaf and root parameters measured, are discussed with relation to their implications for our understanding of plant response and tolerance to low WQ in poorly drained soils.