Degree Type

Dissertation

Date of Award

1996

Degree Name

Doctor of Philosophy

Department

Botany

First Advisor

Arnold van der Valk

Abstract

Life history characteristics of two floating-leaved species, Nymphoides cristata (Roxb.) O. Kuntze and N. indica (L.) O. Kuntze, were investigated. The purpose of the study was to determine why N. cristata is common in wetlands with an annual drawdown, and N. indica in permanently inundated wetlands. Life history characteristics were studied in the field and along a water gradient in a concrete tank. In a second study, 20 monsoonal wetlands were sampled for their seed banks and vegetation. These studies were conducted at the Keoladeo National Park, Bharatpur, India;N. cristata is favored under drawdown conditions because of greater survival of its seedlings and its ability to regenerate from root fragments following flooding. N. cristata seedlings at the 1- and 2-leaf stage showed no mortality to a water depth of 140 cm, while those of N. indica had 20 to 100% mortality at water depths between 70 and 140 cm. In the field, 7% of N. cristata seedlings survived flooding versus 2% of N. indica seedlings. Adult plants of N. cristata regenerated from root fragments after a drawdown (29%), while no plants of N. indica regenerated from root fragments;N. indica is favored under permanently inundated conditions because its response to herbivory, rate of clonal growth and growth responses allow it to persist and to colonize unoccupied space. On a per plant basis, vegetative reproduction was four time greater for N. indica than for N. cristata. Biomass allocation to leaves (42-46% vs 27-31%) and growth responses, including relative growth rate (0.0-31.4 vs 0.6-17.1 mg g-1 day-1), net assimilation rate (-1.4-2.3 vs -2.3-1.1 g m-2 day-1), leaf area ratio (8.5-10.8 vs 7.6-13.3 m2 kg-1) and leaf weight ratio (0.43-0.47 vs 0.28-0.29 g g-1) were greater for N. indica than N. cristata, respectively;Seasonal composition of plant communities in monsoonal wetlands is regulated by a seed bank that is small (822 to 4,467 seed m-2) but species rich (7 to 15 species m-2). Seed bank size and species richness were independent of wetland area and potential water depth. Under normal monsoonal precipitation, four vegetation phases, deep-water monsoonal, shallow-water monsoonal, cool season and hot season, consisting of different plant guilds were identified.

DOI

https://doi.org/10.31274/rtd-180813-10261

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Daniel Harry Mason

Language

en

Proquest ID

AAI9626055

File Format

application/pdf

File Size

105 pages

Share

COinS