Abstract
Functional response traits of four perennial grass species (Imperata cylindrica, Cenchrus ciliaris, Sporobolus diander, and Cynodon dactylon) growing on the fly ash dump and referral site having native soil were evaluated with the objective of selecting species suitable for rapid development of vegetation cover on the fly ash dumps. All the four species showed spectacular plastic responses in functional traits of plants grown on the fly ash dump and are induced by habitat and hence are adaptive. The traits associated with the root system such as root length, spread, the volume of the substratum occupied by the root system, and root biomass showed greater plasticity than the traits of the shoot system such as shoot biomass, the mean number of tillers per clump, and mean height of tillers. For instance, for all the grass species, the ratio of root/shoot biomass was higher for fly ash grown plants as compared to that of plants grown in native soil. The highest ratio was recorded for C. dactylon (5.61 ± 2.36) and I. cylindrica (5.37 ± 2.36) whereas the lowest ratio was recorded for C. ciliaris (1.87 ± 0.44). This suggests greater allocation of resources to root than to shoot by the species for space exploitative growth that enables them to acquire nutrients from nutritionally poor and unfavorable substratum like fly ash dump. Such a strategy enables species to establish and regenerate on barren areas that include fly ash dumps. The higher root length, spread, biomass, and root/shoot ratio in plants of all the species grown on fly ash as compared to plants grown on the native soil substantiate that plasticity in functional traits enabled the species to adapt to stressed habitats. The plastic responses observed are specific to the trait, specific to the species, and specific to the environment. This is evident by the quantitative differences in the responses between traits within a species, between species, and between habitats. The phenotypic plasticity induced by the fly ash altered the relationships between functional traits of the plants. This is evident by the marked differences in the r-values for different character associations between plants grown on fly ash dump and native soil. The results suggest that all the four grass species evaluated can be used for the rapid development of vegetation cover on the fly ash dumps to mitigate environmental contamination.