Seasonal variations in available N and N-mineralization in relation to fine roots in landslide damaged sites in the sal forest ecosystem of Nepal Himalaya

Abstract

Seasonal dynamics of available nitrogen and N-mineralization in relation to fine root biomass was studied in five landslide damaged (1 to 58 years old) sites in the moist tropical sal (Shorea robusta) forest ecosystem of Nepal Himalaya. Comparisons were made with an undisturbed mature sal forest site located in the same region. Concentrations of soil available-N (NH4+ and NO3-) increased with the age of site till 40-year old sites and then declined. However, the proportion of NH4+ in total available N increased distinctly with increase in the age of sites. The NH4+: NO3- ratio increased considerably from 1.15 in 1-year site to 2.4 in mature sal forest. On the other hand, the net N-mineralization rate increased consistently until 58 years of age but the proportion of nitrification rate relative to ammonification rate distinctly decreased beyond 40 years indicating the dominance of ammonification over nitrification in the older sites. Fine root biomass and N- mineralization rate both increased but available-N decreased during rainy season. On the other hand fine root biomass and N-mineralization rate both decreased and available N increased during summer season. During the summer season, fine root biomass decreased by 57 - 68% indicating a rapid turnover. High turnover of fine root at the younger sites (1 to 15 yrs old) add more organic matter for the developing vegetation. Fine root biomass was positively correlated with the concentration of available-N and N-mineralization rate. It is concluded that fine root development was facilitated by higher amounts of available-N. DOI: http://dx.doi.org/10.3126/njbs.v1i0.7478 Nepalese Journal of Biosciences 1: 114-124 (2011)