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

Aluminium (Al) is toxic to most plants, but recent research has suggested that Al addition may stimulate growth and nutrient uptake in some species capable of accumulating high tissue Al concentrations. The physiological basis of this growth response is unknown, but it may be associated with processes linked to the regulation of carbon assimilation and partitioning by Al supply. To test alternative hypotheses for the physiological mechanism explaining this response, we examined the effects of increasing Al concentrations in the growth medium on tissue nutrient concentrations and carbon assimilation in two populations of the Al-accumulator Melastoma malabathricum. Compared to seedlings grown in a control nutrient solution containing no Al, mean rates of photosynthesis and respiration increased by 46% and 27%, respectively, total non-structural carbohydrate concentrations increased by 45%, and lignin concentration in roots decreased by 26% when seedlings were grown in a nutrient solution containing 2.0 mM Al. The concentrations of P, Ca and Mg in leaves and stems increased by 31%, 22%, and 26%, respectively, in response to an increase in nutrient solution Al concentration from 0 to 2.0 mM. Elemental concentrations in roots increased for P (114%), Mg (61%) and K (5%) in response to this increase in Al concentration in the nutrient solution. Plants derived from an inherently faster-growing population had a greater relative increase in final dry mass, net photosynthetic and respiration rates and total non-structural carbohydrate concentrations in response to higher external Al supply. We conclude that growth stimulation by Al supply is associated with increases in photosynthetic and respiration rates and enhanced production of non-structural carbohydrates that are differentially allocated to roots, as well as stimulation of nutrient uptake. These responses suggest that internal carbon assimilation is up-regulated to provide the necessary resources of non-structural carbohydrates for uptake, transport and storage of Al in Melastoma malabathricum. This physiological mechanism has only been recorded previously in one other plant species, Camellia sinensis, which last shared a common ancestor with M. malabathricum more than 120 million years ago.

: Mean square (MS), F Statistics and P values following two way analysis of variance (ANOVA) on cellulose concentrations (%) in leaves, roots and stems of fast and slow growing populations of M. malabathricum grown for 10 weeks in nutrient solutions containing 0 mM, 0.5 mM, 2.0 mM AlCl3.The significance of these values is indicated as follow: *, P < 0.05; **, P < 0.01; ***, P < 0.001.)

Fig. S1 :
Fig. S1: Boxplots of concentrations of P, K, Ca and Mg (mg g -1 ) in the stems of fast and slow Fig. S6: Boxplots of concentrations of starch in leaves, stems and roots (mg g -1 ) of slow

Table S2 :
Mean square (MS), F Statistics and P values following two way analysis of variance (ANOVA) of P, K, Ca and Mg concentrations in the stems of fast and slow growing populations of M. malabathricum seedlings grown for 10 weeks in nutrient solutions containing 0 mM,

Table S3 :
Mean square (MS), F Statistics and P values following two way analysis of variance (ANOVA) of P, K, Ca and Mg concentrations in the roots of seedlings of fast and slow growing populations of M. malabathricum grown for 10 weeks in nutrient solutions containing 0 mM,

Table S4 :
Mean square (MS), F Statistics and P values following two way analysis of variance (ANOVA) on hemicellulose concentrations (%) in

Table S6 :
Mean square (MS), F Statistics and P values following two way analysis of variance (ANOVA) on lignin concentrations (%) in leaves, roots and stems of fast and slow growing populations of M. malabathricum grown for 10 weeks in nutrient solutions containing 0 mM,

Table S7 :
Mean square (MS), F Statistics and P values following two way analysis of variance (ANOVA) on soluble sugar concentrations in leaves, stem and root of M. malabathricum seedlings of fast and slow growing populations grown for 10 weeks in nutrient solutions containing

Table S8 :
Mean square (MS), F Statistics and P values following two way analysis of variance (ANOVA) on starch concentrations in leaf, stem and root of M. malabathricum seedlings of fast and slow growing populations grown for 10 weeks in nutrient solutions containing 0 mM,

Table S9 .
Summary of principal components analysis of whole plant nutrient concentrations and physiological variables for two populations of M. malabathricum grown without Al in the nutrient solution (0 mM).The significance of these values is indicated as follow: *, P <

Table S10 .
Output from a general linear model fitting data on final dry mass for plants from two populations of M. malabathricum grown without Al addition to the nutrient solution to their scores along the first two axes of a PCA describing variation in 12 traits.

Table S11 .
Summary of principal components analysis of whole plant nutrient concentrations and physiological variables for two populations of M. malabathricum grown with Al in the nutrient solution (0.5 or 2.0 mM AlCl3).The significance of these values is indicated as

Table S12 .
Output from a general linear model fitting data on final dry mass for plants from two populations of M. malabathricum grown with Al in the nutrient solution (0.5 or 2.0 mM AlCl3) to their scores along the first two axes of a PCA describing variation in 12 traits.