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Submitted to: Experimental Agriculture
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/1/2014 Publication Date: 2/16/2015 Citation: Perez, D.O., Goenaga, R.J. 2015. Influence of aluminum on growth, mineral nutrition and organic acid exudation of rambutan (Nephelium lappaceum). Experimental Agriculture. doi: 10.1017/S00144779714000489. Interpretive Summary: The most productive soils of the world are already under cultivation, and those available for agricultural expansion are often strongly acid, possessing toxic levels of soil aluminum (Al). High soil Al could drastically reduce crop yields by causing a reduction in root growth, and therefore limiting exploitation of soil by roots for moisture and nutrients. Incorporation of lime to the soil is a common practice to ameliorate acidity but it is not very effective below the plough layer and often, lime is not available to farmers with limited resources. Previous studies demonstrated that rambutan is highly tolerant to acid soils however, little is known about the physiological process conferring Al tolerance to rambutan trees. The objective of this study was to determine if this tolerance is brought about organic acid exudation which may form an Al-ligand complex making Al non-toxic in the rhizosphere. A randomized complete block design experiment with six Al concentrations (0, 1.0, 2.3, 4.1, 6.7 and 10.2 mM Al) was carried out to evaluate the effect of aluminum on nutrient content, plant growth, dry matter production and Al-induced organic acid exudation in rambutan. The results of this study confirmed that this crop is highly tolerant to Al in the rhizosphere. No evidence of organic acid exudation was found in this study. Accumulation of Al in leaves, stems and roots suggests the existence of an Al-sequestration mechanism in rambutan which may involve an Al-ligand complex which translocates from roots to shoots, where it may accumulate in leaf vacuoles. This study confirms the Al tolerance of rambutan and provides useful information to Extension Agents and growers about the adaptability of this crop to acid soils. Technical Abstract: A randomized complete block design experiment with six aluminum (Al) concentrations was carried out to evaluate the effect of aluminum on nutrient content, plant growth, dry matter production and Al-induced organic acid exudation in rambutan (Nephelium lappaceum). One rambutan cultivar was grown in nutrient solution at pH 4.0 with (1.0, 2.3, 4.1, 6.7 and 10.2 mM Al) and without Al. The results of this study confirms that this crop is highly tolerant to Al in the rhizosphere as evidenced by: 1) a root tolerance index of 0.85 when plant roots are exposed to Al concentrations as high as 3.5 mM; 2) root tissue Al concentrations as high as 6800 mg/g and the plants survived; 3) number of leaves, plant height and stem diameter being little affected when plants were grown at an Al concentration in the soil solution as high as 3.5 mM; 4) although plants exhibited leaf abscission, they were able to tolerate Al concentrations in the nutrient solution as high as 10.2 mM during the experimental period. No evidence of organic acid exudation was found in this study. Accumulation of Al in leaves, stems and roots suggests the existence of an Al-sequestration mechanism in rambutan which may involve an Al-ligand complex which translocates from roots to shoots, where it may accumulate in leaf vacuoles. |
