Influence of floristic composition on the net primary production and dry matter turnover in a tropical grassland

Abstract

Plant biomass, net primary productivity and dry matter turnover were studied in a grassland situated in a tropical monsoonal climate at Kurukshetra, India (29°58'N, 76°51'E). Based on differences in vegetation in response to microrelief, three stands were distinguished on the study site. The stand I was dominated by Sesbania bispinosa, stand II represented mixed grasses and stand III was dominated by Desmostachya bipinnata. Floristic composition of the three stands revealed the greatest number of species on stand II (75). The study of life form classes indicated a thero-cryptophytic flora. The biomass of live shoots in all the three stands attained a maximum value in September (424-1921 g m⁻²) and below ground plant biomass in November (749-1868 g m⁻²). The annual above ground net primary production was greatest on stand I (2143 g m⁻²) and lowest on stand II (617 g m⁻²). The rate of production was highest during the rainy season (15.34 to 3.18 g m⁻² day⁻²). Below ground net production ranged from 1592 to 785 g m⁻² y⁻² and the rates were high in winter and summer seasons. Total annual net primary production was estimated to be 3141, 1403, 2493 and 2134 g m⁻² on stands I, II, III and on the grassland as a whole, respectively. The turnover of total plant biomass plus below ground biomass indicated almost a complete replacement of phytomass within the year. The system transfer functions showed greater transfer of material from total net primary production to the shoot compartment during rainy season and to the root compartment during winter and summer seasons.