Growth and allocation strategies of some perennial weeds of slash and burn agriculture (Jhum) in northeastern India

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Abstract
Growth and allocation patterns of dry matter and nutrients (nitrogen, phosphorus, and potassium) in four important perennial weeds, viz., Eupatorium odoratum, Grewia elastica, Imperata cylindrica, and Thysanolaena maxima, were analysed. Eupatorium odoratum, a C3 species and exclusively dependent upon the sexual mode of reproduction, had the highest values for relative growth rate and net assimilation rate. This species also showed the highest concentrations of nutrients in the leaf tissue. Eupatorium odoratum exhibited a greater allocation of its total biomass as well as nutrients to stem as compared with the other three species all of which can "sprout" (regenerate from underground organs) after fire. The reverse was true for the allocation of biomass and nutrients to the leaf component. The two rhizomatous species (I. cylindrica and T. maxima) diverted significantly greater proportions of dry matter as well as nutrients to belowground tissues compared with the two nonrhizomatous species (E. odoratum and G. elastica). The two C4 species, I. cylindrica and T. maxima, showed higher efficiency in nutrient uptake in spite of their low nutrient demand per unit dry matter production. The findings are discussed in relation to the photosynthetic and regenerative strategies of these species.