The effect of salinity on growth and nutrition of Leucospermum cordifolium

Abstract

SummaryThere is little information available on the tolerance of L. cordifolium to salinity. Irrigation with salt-enriched water, the main salts added being NaCl and CaCl2 (2:1), was used to study the effect of Na+ and Cl± concentration on the yield of fresh and dry matter of L. cordifolium. Five water salinity levels (0.4, 1.5, 2.5, 4.2 and 8.2 dS m±1) were imposed on a mixture of peat and volcanic ash (1:1 in volume) in pots. Soil, roots and foliar nutrients, visual rating of foliar salt lesions, and yield of fresh and dry weight of the plants were determined. Soil EC (ECe) and the levels of Na+ and Cl± in the soil accurately re¯ected the applied treatments since noticeable increases were observed as soil salinity increased. No accumulative effect was detected with the Na+ and Cl± ions in the root system throughout the duration of the experiment. Root K+ tended to decrease as the salinity of the treatments increased because of the negative effect of soil Ca2+ and Na+ on the absorption of K+. The concentration of Na+ and Cl± was much greater in the leaves than in the roots. An increase was observed in the foliar concentration of these ions as the salinity of the treatments increased, and therefore L cordifolium cannot be considered to be an ``excluder'' of Na+ and Cl±. A decrease in the yield of fresh and dry weight from the October sampling onwards was observed at concentrations in leaves above 1,039 mmol kg±1 of Na+ and 873 mmol kg±1 of Cl±. The lowest aerial-part production of fresh and dry material observed in the samplings corresponded to the highest Na+ and Cl± concentrations in the leaves. In October, nearing termination of the experimental work, yield thresholds for fresh and dry weight, expressed as electrical conductivity of irrigation water (ECi) and saturated soil extract (ECe) were 1.7 and 1.5 dS m±1 (ECi) and 3.7 and 1.9 dS m±1 (ECe), respectively. At that stage, vegetative growth was reduced 11.0% for fresh weight and 7.1% for dry weight for each increase in ECe beyond the threshold values. L. cordifolium was moderately sensitive to salinity.