Growth and physiological responses of sago palm against aluminum stress in acidic conditions.

Sago palm (Metroxylon sagu Rottb.) grows in natural peat swamps, which are poorly drained and has high acidity and generally contain highly exchangeable Al. It is, therefore, considered to be acidand Al-resistant. In this study, the growth, physiological characteristics and nutrient concentrations in the plant tissues of sago palm grown under a hydroponic system were investigated for 4.5 months. When sago palm seedlings were cultured at pH 5.7, pH 4.5 and pH 3.6, the leaf morphogenesis, nutrient uptake and dry matter production were maintained regardless of a small decrease in the photosynthetic rate through the decrease of stomatal conductance. In the case in which seedlings were grown at pH 3.6 with different levels of AlCl3·6H2O corresponding to 0, 10, 20, 100 and 200 ppm Al, the plant length and dry matter production increased with a mild Al concentration in the growth media, such as 10 ppm Al. This result was attributed to the increase in the P and N uptake. In contrast, all the growth parameters significantly decreased under the 200 ppm Al treatment. The critical value to inhibit the growth of sago palm was considered to be around 200 ppm Al in the growth media. In addition, sago palm maintained a low Al 3+ concentration in all of the plant parts. Therefore, it could be concluded that sago palm has high resistance to Al with mechanical restriction of the excess Al based on the Al exclusion ability under the acid condition.