A calorimetric study of plant?plant and plant?soil interactions of extracts from Ixorhea tschudiana

Abstract

The effect of the CHCl3 and MeOH extracts from aerial parts from the Northwestern Argentina endemic species Ixorhea tschudiana Fenzl. on germination of the dicot tomato and the monoct onion and on soil microbial activity was studied by calorimetric and calorespirometric experiments. The CHCl3 extract inhibited seedling growth of tomato which increased with increasing concentrations. Seeds imbibed with 250 mg dm-3 extract germinated 24 h later than control and those imbibed with 100 and 500 mg dm-3 extract. This was reflected in the calculated low specific seedling growth rate (pSGΔHB) as determined from calorespirometric experiments. On the other hand, seedlings obtained in 500 mg dm-3 extract showed shorter and thicker hairy roots than control with significantly higher pSGΔHB. Probably, the extract induces inhibition of water uptake by seedling roots. Germination was reduced 50% in onion seeds imbibed with 500 mg dm-3 CHCl3 extract which apparently is due to higher rate of imbibition during the first stages as determined for calorimetry. On the other hand, 83 and 250 mg kg-1 of the MeOH and CHCl3 extract seem to selectively inhibit the growth of certain microorganisms and to enhance the activity of soil actinomycetes. Two actinobacteria were isolated from soil treated with these concentrations of both extracts: Kocuria sp. and Kocuria rosea; this latter species is known as a keratinolytic agent and seems to degrade complex carbon compounds of the soil and those incorporated by the MeOH extract. Both Kocuria specie seem to be beneficial for the soil converting substrate into biomass and thus I. tschudiana could be used as a soil phytoremediator. © 2009 Elsevier B.V. All rights reserved.