Differential Biomass Allocation to Above-Ground Plant Components by Two Invasive Sida Congeners in a Dry Tropical Peri-Urban Vegetation in India

Differing biomass allocation strategy could be a necessary plant-trait associated with invasive weeds in an alien environment. The present study focused on exploring differential biomass allocation pattern as an invasive plant-trait in the two pantropical invasive malvaceous weeds Sida acuta Burm f. and Sida cordifolia L. in an anthropic peri-urban vegetation in Indian dry tropics. Eighty plant individuals from each of these two congeners across their varying developmental stages were clipped off from their dominantly growing study site at the polluted bank of Kali river in Bulandshahr (28o04’ & 28o43’ N lat. and 77o08’ & 78o28’ E long.) in the national capital region of India. The plant individuals were separated into different aboveground plant components (leaf, stem-axis, branch and reproductive parts that included flowers/capsules/seeds). They were oven-dried, weighed and the mass fractions of each component estimated as its dry weight relative to total aboveground plant biomass. In the weedy and ruderal vegetation here, these two congeners with > 47 g m -2 above-ground biomass and about 25% importance value index, showed striking difference in their biomass allocation strategy. S. acuta had significantly higher leaf and branch mass fractions, reflective of its profuse branching habit and differentially higher biomass investment for photosynthetic function. In contrast, S. cordifolia had significantly larger reproductive mass fraction (for increased colonizability) and stem-axis biomass. The overall stem biomass was comparable, indicative of common perennial tendency for firm establishment in the alien environment. With increasing plant size, both the congeners showed a similar trend of decreasing leaf mass fraction and increasing mass fractions of support and reproductive structures. Biomass allocation was significantly influenced by species, growth phase (reproductive/vegetative) and ontogeny. Thus, the present study indicated a strategic differing pattern of biomass allocation to different plant components by the congeners S. acuta and S. cordifolia which could be attributed to their invasibility in dry tropical environments.