Effects of forest type and stand age on litterfall quality and soil N dynamics in Shikoku district, southern Japan

To evaluate the effects of forest type and stand age on forest N dynamics, we investigated the leaf-litter quality and soil N mineralization in four pairs of young and middle-aged forests in Shikoku district, southern Japan. The soil N mineralization rate determined by 28-day laboratory incubation ranges from 7.1 to 206.5 mg N kg(-1) and was differed among forest types, decreasing in the order of hardwood > Japanese cedar > Japanese red pine = Hinoki cypress. The soil N mineralization rate was strongly correlated with the lignin/N ratio in leaf-litter. Leaf-litter N concentration and lignin/N ratio were different among forest types. Middle-aged forests had lower lignin concentration in leaf-litter, and marginally higher soil N mineralization than young forests. These results suggest that during stand development, the decrease in leaf-litter lignin concentration is an important mechanism that explains larger N cycling in older forests. In contrast, N concentration in leaf-litter was considered to represent the wide variation of N cycling among forest types. During stand development N use efficiency at the leaf level increased (lower N concentration in leaf-litter), whereas water use efficiency decreased (lower delta(13)C in leaf-litter). The result suggests that there is a trade-off between NUE and WUE during stand development. However, in all eight forests, NUE and WUE were positively correlated. Japanese cedar and Hinoki cypress utilize both water and N resources more efficiently than hardwood species. Therefore, the efficient use of water and N of coniferous plantations may be related with high aboveground biomass production. (C) 2004 Elsevier B.V. All rights reserved.