Influence of pH and plant nutrient status on ion fluxes between tomato plants and simulated acid mists

Abstract

SUMMARYDiffusion along concentration gradients, ion exchange, active uptake, and physical damage are possible mechanisms causing fluxes of ions between plant tissues and acidified moisture on plant surfaces. The temporal patterns of ion fluxes during individual wetting events should vary in a predictable manner in relation to moisture pH, plant nutritional status, and the operational mechanism. Tomatoes {Lycopersicon esculentum Mill.) were grown hydroponically at relative nutrient addition rates (/?J of 7, 12, and 15% per day. At similar growth stages, the plants were exposed to HCl-acidified mists of pH 2-5, 4-0, or 5-6 for 4 h, or left unmisted as controls. Whole-plant throughfall was analysed for pH and ion concentrations after 15, 30, 60, 120, and 240 min. Surface chemical contamination was minimized by pre-rinsing with deionized water. Except for H+ during the first 15-30 min, all ions showed efflux for the duration of the mistings. Effluxes were low (< 150/*equiv m""^ h"^), time-invariant, and unrelated to R^ at mist pH of 4-0 and 5-6. At pH 2-5, effluxes of K+, Mg2+, NOg", and PO/-increased over time, while Ca^+ efflux increased during the first hour, then remained constant. Maximum efflux (105 to 730 /*equiv m'^ h^^) mostly occurred at pH 2-5 and R^ = 17 % d'S increasing in the order NH/ = SO/" < NOf < PO/~ < Ca^+ = Mg2+ < K+ < H+. These results suggested that although ion diffusion and ion exchange contributed to observed effluxes, an additional mechanism, temporally accumulating physical damage to cuticles and cell membranes below a threshold pH between 4 0 and 2-5, was involved. Foliar concentrations of K, Ca, and Mg did not differ significantly among treatments, but ion effluxes into pH 2-5 mists removed 1-13 % of the wholeplant element contents, with the largest removal for Ca.

Effects of Simulated Acid Rain on Growth and Yield of Cassava Manihot esculenta (Crantz)

“…This is similar to the earlier results of Liu et al (2010) and Evans (1984). Reduction was due to the removal of Mg + from the tetrapyrol ring of the chlorophyll molecules by H + (Foster, 1990) or due to increase of transpiration by acid rain (Evans et al, 1997). Recently similar results were also observed on many crops like mustard, radish, potato, bean plant Chehregani (2007) Relative growth rate and harvest index was highest at pH 2.0 and pH 3.0 compared to the control plants (Table 3) and this have been reported by a number of authors (Steinfeld et al, 1998;Ekanayake, 1994;Cock et al, 1977).…”

Relative importance of factors controlling the leaching and uptake of inorganic ions in the canopy of a spruce forest

“…There may also be critical acidity values, varying with plant species, over which physical damages to the waxes, cuticles or the underlying cells occur. In such conditions, the exchange flux of cations (Wood & Bormann 1975;Foster 1990) and anions (Evans et al 1981;Evans et al 1985;Percy & Baker 1988) could be enhanced. We noted that all the open rain H + concentration values were well below the value corresponding to the pH threshold causing visible damage to conifers (Turunen & Huttunen (1991) reviewed values of pH 2.3) and producing the strongest throughfall responses.…”

“…The pore diameter, density and affinity for specific cations is dependent on the acidity and cationic composition of the cuticle water (Sch/nherr 1976; Ertel et al 1992). The apoplast water is in contact with xylem sap and therefore there may be substantial apoplastic pools of Ca 2+ , Mg 2+ , K + , NO3, S4 -and PO-because these ions are transported in inorganic form (Foster 1990). In the case of unbalanced nutrition due to a poor nutritional environment and the atmospheric pollution, such as in the spruce trees at the site of the experiments (Hambuckers & Remacle 1991), some ions may be absorbed in excessive amounts because the ion absorption partially reflects the…”

“…In forests, the concentrations of several dissolved ions in the surface water were found to control their exchange fluxes with the canopy (Olson et al 1985;Schaeffer et al 1988;Lovett et al 1989;Foster 1990;Wilson 1992). Mecklenberg et al (1966) demonstrated that the source of Ca 2 + leached from bean plants is not derived from the cell interior.…”

“…Mecklenberg et al (1966) demonstrated that the source of Ca 2 + leached from bean plants is not derived from the cell interior. Numerous reports show that low pH water increases the rates of cation leaching and the neutralization of acidity, although sometimes it may diminish the rates of uptake (Wood & Bormann 1975;Adams & Hutchison 1984;Kelly & Strickland 1986;Paoletti et al 1989a;Paoletti et al 1989b;Schier 1987;Kaupenjohann et al 1988;Foster 1990;Muir 1990;Scherbatskoy & Tyree 1990;Turner & Tingey 1990). The cation leaching could be explained by the exchange with H + , whereas physical damage by the strong acidity to the foliar cuticle or to the underlying cells is also possible and could result in an increase in anion leaching (Percy & Baker 1988).…”