Contrasting growth responses to aluminium addition among populations of the aluminium accumulator Melastoma malabathricum

Abstract

Aluminium (Al) hyper-accumulation is a common trait expressed by tropical woody plants growing on acidic soils. Studies on Al accumulators have suggested that Al addition may enhance plant growth rates, but the functional significance of this trait and the mechanistic basis of the growth response are uncertain. This study aimed to test the hypothesis that differential growth responses to Al among populations of an Al accumulator species are associated with variation in biomass allocation and nutrient uptake. We conducted two experiments to test differential responses to the presence of Al in the growth medium for seedlings of the Al accumulator shrub Melastoma malabathricum collected from 18 populations across Peninsular Malaysia. Total dry mass and relative growth rate of dry mass (RGR) were significantly greater for seedlings that had received Al in the growth medium than for control plants that did not receive Al, but growth declined in response to 5.0 mM Al addition. The increase in growth rate in response to Al addition was greater for a fast-growing than a slow-growing population. The increase in growth rate in response to Al addition occurred despite a reduction in dry mass allocation to leaves, at the expense of higher allocation to roots and stems, for plants grown with Al. Foliar concentrations of P, K, Mg and Ca increased in response to Al addition and the first axis of a PCA summarising foliar nutrient concentrations among populations was correlated positively with seedling relative growth rates. Some populations of the Al hyper-accumulator M. malabathricum express a physiological response to Al addition which leads to a stimulation of growth up to an optimum value of Al in the growth medium, beyond which growth declines. This was associated with enhanced nutrient concentrations in leaves, which suggests that Al accumulation functions to optimise elemental stoichiometry and growth rate.

External aluminium supply regulates photosynthesis and carbon partitioning in the Al-accumulating tropical shrub Melastoma malabathricum

“…Fruits of Melastoma malabathricum L. were collected from a total of 18 populations across Peninsular Malaysia. Experimental research on the progeny of these populations growing under uniform growing conditions showed that they displayed consistent variation in growth rates that were associated with nutritional characteristics including tissue Al concentrations [ 4 , 18 ]. For the research described in this paper we selected populations in the states of Kedah and Perlis, Peninsular Malaysia, which displayed the slowest and fastest relative growth rates, respectively, among the 18 Malaysian populations examined previously [ 4 ].…”

“…Seedlings of M . malabathricum grown in nutrient solutions showed increased relative growth rate, net assimilation rate and a shift in dry mass allocation from leaves to roots in response to an increase in Al concentration from 0 to 0.5 mM Al [ 4 , 12 ]. This combination of morphological and physiological changes provides indirect evidence that Al addition may also enhance the rates of photosynthesis in M .…”

“…In recent research we have shown that growth rates and tissue Al concentrations differ widely among different populations M . malabathricum , and that seedling growth rates are positively correlated with foliar nutrient and Al concentrations among populations [ 4 ]. If up-regulation of photosynthetic rates contributes to the positive growth response of M .…”

“…malabathricum L. (Melastomataceae) that have shown contrasting growth rates and responses to Al addition in previous research [ 4 ]. This species was chosen because it is a known Al accumulator plant and previous studies have suggested that its growth may respond positively to Al addition under certain growing conditions [ 4 , 12 , 17 , 25 ]. M .…”

Autecology of Melastoma malabathricum, an invasive species in the Way Kambas National Park, Indonesia

“…In addition, the aluminum (Al) content in the invaded location was higher than in other locations, although the difference in values was not too high. However, this condition caused M. malabathricum to grow better than the other plant species, because M. malabathricum is resistant to Al stress and had the highest Al accumulator (14.4 mg.g −1 leaves dry weight) without causing growth abnormalities (Mahmud and Burslem 2018). Al 3+ content also contributes to soil acidity.…”