RESULTS
Elemental concentrations in G. acmenoides and G. bidwillii – All plant tissue elemental concentrations presented in this study are based on dry weight. The bulk elemental concentrations in young leaves, old leaves and twigs of the wild G.acmenoides and the dosed G. bidwillii are shown in Table 1 and 2 respectively, and that of the concentration of Mn in young, old leaves and twigs of G. bidwillii in Figure 2. The concentrations of Mn in the wild G. acmenoides were remarkable, with significantly (p <0.05) high mean value of 39 000 µg g-1 (SE ± 3540) in old leaves, compared to 24 000 µg g-1 (SE ± 410) in young leaves and 5840 µg g-1 (SE ± 2820) in twigs (Table 1). Similarly, the concentrations of Ca and Na in G. acmenoides tend to be high in old leaves (9250 ± 785 µg g-1 Ca, 710 ± 70.0 µg g-1 Na) than in young leaves (5590 ± 145 µg g-1 Ca, 660 ± 190 µg g-1 Na) and twigs (4700 ± 400 µg g-1 Ca, 170 ± 35.0 µg g-1 Na) (Table 1). The concentrations of Fe and Mg in old leaves of G. acmenoides were also high with concentrations of 75.0 µg g-1 Fe (SE ± 17.0) and 1290 µg g-1 Mg (SE ± 108) respectively compared to 840 µg g-1 Mg (SE ± 38.0) and 45 µg g-1 Fe (SE ± 0.70) in its young leaves. However, no significant difference was observed between Mg in old leaves and twigs of G.acmenoides (Table 1). Values of Al tend to be also high in old leaves (200 ± 38.0 µg g-1 Al) than young leaves (53.0 ± 0.85 µg g-1 Al) and twigs (6.0 ± 10.5 µg g-1 Al). Nonetheless, the concentration of K was high in young leaves (9380 ± 1040 µg g-1 K) than old leaves (3660 ± 160 µg g-1 K) and twigs (2710 ± 570 µg g-1 K). No significant difference (p>0.05) was observed for Ni, P and Zn in young, old leaves and twigs of G. acmenoides (Table1).
In the old leaves of G. bidwillii , the mean Mn concentrations at the T4 , T3 and T2 treatment levels were 24 400 µg g-1 (SE ± 10 700), 21 800 µg g-1 (SE ± 8850) and 14 100 µg g-1(SE ± 12 600), respectively. These are more than 2-fold the Mn hyperaccumulation threshold at the T4 and T3 treatment levels and greater than 1-fold the Mn hyperaccumulation threshold at theT2 treatment level (Fig. 2 and Table 2). The old leaves ofG. bidwillii at the control (T1 ) also contained up to 10 900 µg g-1 Mn (mean 5490 µg g-1). In the young leaves, however, Mn concentration at the T4 andT3 treatment levels were 17 100 µg g-1 (SE ± 8440) and 12 600 µg g-1 (SE ± 11 000) respectively which are more than 1-fold the Mn hyperaccumulation threshold (Fig. 2 and Table 2). On the other hand, the T2 treatment level contained 8300 µg g-1 (SE ± 4270) which is almost around double the T1 value (4600 µg g-1) in young leaves (Fig. 2 and Table 2). In the twigs, the highest treatment level (T4 ) contained 17 400 µg g-1 (SE ± 6690) Mn which is more than 1.5-fold the Mn hyperaccumulation threshold than that observed at the T3 (5000 ± 1150 µg g-1), T2 (4300 ± 1220 µg g-1) and the T1 (2900 ± 1300 µg g-1) treatment levels (Fig. 2 and Table 2).
Unlike G. acmenoides , the concentration of Ca in the dosedG. bidwillii was high in the young leaves with concentrations of 9400 µg g-1 (SE ± 2280) at T1 , 5700 µg g-1 (SE ± 1820) at T2 , 12 400 µg g-1 (SE ± 2790) at T3 and 11 200 µg g-1 (SE ± 4000) at T4 treatment level compared to that in the old leaves (Table 2). The twigs on the other hand, contained high amounts of Ca at the T1 , T2 andT4 treatment levels than in young and old leaves with mean values of 17 100 µg g-1 (SE ± 1580), 11 100 µg g-1 (SE ± 2970) and 11 700 µg g-1(SE ± 3780) respectively (Table 2) except at the T3 treatment level where the concentration of Ca was high in young leaves than in old leaves and twigs. The concentration of Al in old leaves of G. bidwillii tend to be high at the T3 and T4 treatment levels with concentrations of 9000 µg g-1 (SE ± 5400) and 10 700 µg g-1 (SE ± 5370) respectively compared to that in the young leaves and twigs (Table 2). The concentration of K at the T1 (22100 ± 2960 µg g-1 K) treatment level in young leaves was significantly (p <0.05) higher than those observed at the other treatment levels (T2 ,T3 , T4 ) in old leaves and twigs. However, Mg tend to be high at the T1 (4790 ± 1900 µg g-1 Mg) treatment level in old leaves compared to those observed at the other treatment levels (T2 , T3 , T4 ) in young leaves and twigs (Table 2). Whereas no significant difference was observed between the concentration of Na at the T1 and T2treatment levels of young and old leaves, the concentration of Na at theT4 treatment level in twigs (1100 ± 840 µg g-1 Na) was significantly (p <0.05) higher compared to that in young leaves (440 ± 260 µg g-1 Na) and old leaves (630 ± 140 µg g-1 Na) (Table 2). The values for Fe and Zn were low at all treatment levels compared to other elements in young, old leaves and twigs (Table 2). Nonetheless, the concentration of P was below the limit of detection (<6.00 µg g-1) in young, old leaves and twigs at all treatment levels, and this could probably be due to the low P demand in the experimental G. bidwillii (Table 2).
Soil chemical properties – The soil pH of the wild G. acmenoides was low (pH = 4.20) compared to that of G. bidwilliipot soils (pH 5.27–5.95) (Table 3). Extractable Mn values for DTPA and Sr(NO3)2 increased with the dose levels, as expected. Variability in Mn values for DTPA and Sr(NO3)2 can be explained by the strong binding of Mn2+ to the organic matter of the potting mix thereby making it less available.
µXRF elemental mapping of wild G.acmenoides and G. bidwillii – Manganese in the wildG . acmenoides collected from the Mn-enriched substrate in Amamoor has strong enrichment throughout the leaf blade and petiole of young and old leaves, while veins and midrib have relatively lower concentrations (Figs. 3 and 4). Calcium and K are strongly enriched in the veins and midrib, and with high concentrations of Ca in the stem and petiole and low K in the leaf margins of young and old leaves (Fig. 3). In G. bidwillii , the distribution of Mn is high at the apex and lamina but low in the midrib, margin and veins (Fig. 4). However, K tends to be concentrated at the tip/margin, midrib, and petiole and veins whereas Ca is high in the midrib, margin and veins but low in the leaf lamina (Fig. 4).