The acidic nature of tropical soils is problematic to plants because typically innocuous forms of aluminum (Al) are solubilized into phytotoxic forms at low pH, which may cause major damage to plant roots. Removal of toxic Al may create a more hospitable environment for plants not resistant to Al-toxicity. Moreover, a decrease in Al toxicity may help facilitate natural succession in tropical soils, where Al toxicity limits plant growth. Several studies have documented the ability of certain plants to accumulate Al. However, the effect of Al-accumulating plants on Al toxicity is difficult to quantify in a field setting. We set up a greenhouse hydroponics experiment to test the effects of Hydrangea macrophylla (Hydrangeaceae), an Al-accumulating plant, on Al toxicity and to quantify Al accumulation in above- and below-ground tissues. Hydrangea cuttings were grown in 8.5L buckets with a modified Hoagland solution for 10 weeks. After week one, cuttings were exposed to 0, 10, 100 or 1000μM Al (n=10 per treatment). Cuttings harvested after weeks three, seven and ten were separated into roots and shoots, then dried, weighed, and analyzed for Al content. Solution samples were taken from each bucket at each sampling period and analyzed for Al content.
Results/Conclusions We performed repeated measures ANOVA on shoot and root biomass and shoot and root Al content. Shoot biomass increased with time (p<0.0001) but not according to Al treatment (p=0.2171; time*treatment p=0.9915). Root biomass increased with time for all treatments (p<0.0001), but not in the same manner (time*treatment p=0.0238). Root biomass in the high Al treatment increased at a slower rate than the control (0μM Al) or low Al (10μM Al) treatments. At each sampling period, there was a significant effect of solution Al concentration on shoot Al concentration (p<0.0001). Al concentration increased with time (p<0.0001) and at a faster rate in the high Al treatment (p<0.0001). There was a significant effect of solution Al concentration on root Al concentration (p<0.0001). Root Al concentration did not change over time in all treatments (time p=0.0773; time*treatment p=0.0109). Solution chemical analyses are nearly complete. Our lab is testing the facilitative properties of Al-accumulating plants on degraded landscapes in Costa Rica. Al-accumulators may be an important tool in the restoration of acid soils throughout the tropics. Quantifying the effect of Al-accumulating plants on solution Al chemistry will allow ecologists to more efficiently utilize Al-accumulating plants in restoration efforts.
