ORIGINAL PAPER K. Maithani · A. Arunachalam · R.S. Tripathi H. N. Pandey Influence of leaf litter quality on N mineralization in soils of subtropical humid forest regrowths Received: 16. April 1997 K. Maithani 1 · A. Arunachalam 1 ( ✉ ) · R.S. Tripathi · H.N. Pandey Department of Botany, North-Eastern Hill University, Shillong-793022, Meghalaya, India Present address: 1 Forest Environment and Sustainable Development Unit, Faculty of Applied Science, North Eastern Regional Institute of Science and Technology, Nirjuli-791109, Arunachal Pradesh, India Tel.: 03 60-47 40 3/111 (office), 4 77 32 (residential); Fax: 03 60-4 43 07; e-mail: aa@nerist.ernet.in Biol Fertil Soils (1998) 27:44–50 © Springer-Verlag 1998 Abstract Laboratory net N mineralization as influenced by leaf litter quality of several subtropical tree species was studied in soils of forest regrowths of three different age groups. Concentrations of NH 4 + and NO 3 – in the soil gener- ally increased with age of forest regrowth. However, dur- ing incubation concentrations fluctuated markedly. In the “soil only” treatment, the cumulative N mineralization, ammonification and nitrification rates were highest in soils of the 13-year-old regrowth, followed by those of the 16- and 7-year-old regrowths. Soils from all three regrowths planted with Quercus dealbata had greater N mineraliza- tion rates than soils planted with Pinus kesiya. Overall, leaf litter of Schima khasiana showed the highest release of N, followed by leaf litter of Q. griffithii ; greatest immo- bilization of N was recorded for Rhododendron arboreum leaves and P. kesiya needles. The percentage of N accumu- lated/depleted from the leaf litter correlated positively with the initial N concentration, and correlated negatively with the lignin content and C/N ratio. Key words N mineralization · Leaf litter · Forest regrowths · Schima khasiana · Quercus dealbata Introduction Typically, 70–90% of nutrients needed annually for forest growth are derived from the decomposition of organic detri- tus (e.g. Vogt et al. 1991). Decomposition is a complex mi- crobe-fauna mediated process which is accelerated by envi- ronmental conditions that enhance faunal and microbial ac- tivity (Swift et al. 1979). Substrate quality (initial chemical composition of decomposing material) is a critical factor in determining the rate of litter decay and nutrient release (Bloomfield et al. 1993). Chemical indices of the residue quality are concentrations of C, N, P, hemicellulose, cellu- lose, lignin, polyphenols etc., and C/N and lignin/N ratios. Loss of nutrients is minimal in undisturbed forests and any deficit is balanced by inputs from various sources. This dynamic equilibrium is often disturbed by various anthropogenic activities. The resulting losses of nutrients can, however, be minimized by synchronizing the supply of nutrients with plant growth demand (Myers et al. 1994). One way of achieving this synchrony is through manipulating the quality and quantity of organic inputs on the forest floor. In order to examine this, the initial chemi- cal composition of litter from tree species growing in three different age groups of forest regrowths was determined, and their effects on N mineralization were studied under laboratory conditions. Materials and methods Study sites Soil and leaf litter samples were collected from 7-, 13- and 16-year- old forest regrowths located at high altitude (1850–1900 m asl) in Meghalaya, India (25 ° 34'N, 91 ° 56 ° E). The average annual rainfall is 2500 mm in this region and the mean maximum and minimum air temperatures are 26 °C and 14 °C, respectively. Detailed vegetation and soil analysis are summarized in Arunachalam et al. (1996 a, b) and Maithani et al. (1996). In brief, the soil of the area is lateritic (oxisol), which is slightly acidic (pH 5.12–5.26) and rich in organic matter (6.2–10.7%). The main vegetation is subtropical wet hill forest (Champion and Seth 1968) and the dominant species of the region are Quercus spp., Schima spp., Rhododendron spp. in the virgin for- ests and Pinus kesiya in the degraded ones. Soil and litter sampling and analysis Surface soil (0–10 cm) from the 7-, 13- and 16-year-old forest re- growths was collected in bulk during April 1996. The field soil was