Net Primary Productivity and Budget of Nitrogen and Phosphorus in the Herbaceous Layer of a Tropical Dry Deciduous Forest in Rajasthan in Northwest India

Abstract

The net primary productivity and budget of total nitrogen and available phosphorus in the herbaceous layer was studied in a tropical
dry deciduous thorn forest in Rajasthan state of north-western India. The average net primary productivity of the herbaceous layer
was 242 g m-2yr-1, it was the highest (257 g m-2 yr-1) at the top and the lowest (218 g m-2 yr-1) at the middle of the hill slope. Out of
the herbaceous species present in the study site, 29 species contributed more than 1 g m-2 biomass with the highest contribution by
Brachiaria ramosa (54%) and Achyranthes aspera (44%). The herbs allocated about 10 and 90% of total biomass to roots and above-ground
parts, respectively. The highest content of nitrogen in the soil, biomass, and litter was 181, 3.4, and 1.7 g m-2, respectively, during the
rainy season in July. A similar pattern was observed for phosphorus. The annual uptake of nitrogen and phosphorus by vegetation was
3.84 g m-2 and 0.76 g m-2 ; 19 and 16%, respectively, return to the soil through litterfall. Before the litterfall occurred, the nitrogen, a vital
element was translocated into below-ground parts. This is a strong strategy for the conservation of nitrogen. Phosphorus, however, did
not show such a trend. This interesting observation of the study strongly indicated that a sufficient amount of nutrients are retained in
the litter during the dry summer period.