Foliage and Litter Chemistry, Decomposition, and Nutrient Release in Pinus taeda

L Kiser,Colleen Carlson,Thomas Fox

doi:10.3390/f4030595

Abstract

Following fertilization of forest plantations, high accumulations of nutrients in the forest floor creates the need to assess rates of forest floor decomposition and nutrient release. The study site was a 25-year old experimental loblolly pine plantation in the North Carolina Sandhills Region. Soluble and insoluble N, P, carbohydrate and phenol-tannin fractions were determined in foliage and litter by extraction with trichloroacetic acid. The long-term forest floor decomposition rate and decomposition and nutrient release in an experiment simulating removal of the overstory canopy were also determined. In litter, insoluble protein-N comprised 80%–90% of total-N concentration while soluble inorganic- and organic-P comprised 50%–75% of total-P concentration explaining forest floor N accumulations. Fertilization did not increase soluble carbohydrates in litter and forest floor decomposition rates. Loblolly pine forest floor decomposing in environmental conditions simulating removal of the overstory canopy was greatly accelerated and indicated 75% mass loss and release of 80% of the N pool within one year. This could result in a loss of substantial quantities of N at harvest due to low N uptake by seedlings in the newly planted next rotation suggesting management of the forest floor at harvest is essential to conserve site N capital in these N limited systems.

Highlights

Growth of forest plantations in the southeastern U.S is often limited by the availability of nitrogen (N) and phosphorus (P) [1,2]
Nitrogen has been found to be immobilized during decomposition of the loblolly pine Oi horizon and released in only modest amounts from the Oe horizon [6]
In acidic soils across of range of textures, fertilization resulted in an accumulation of P in the mineral soil suggesting increased site P availability and a potential long-term improvement in tree growth from higher P

Summary

Introduction

Growth of forest plantations in the southeastern U.S is often limited by the availability of nitrogen (N) and phosphorus (P) [1,2]. Nitrogen has been found to be immobilized during decomposition of the loblolly pine Oi horizon and released in only modest amounts from the Oe horizon [6]. Other studies that examined loblolly pine Oi horizon decomposition and nutrient release have found immobilization of N during decomposition in closed canopy stands [7,8]. The increase in litter P following fertilization was in soluble fractions [9] which readily leached from the forest floor [10]. These studies suggest that N is slowly released from the forest floor through biotic decomposition processes while P release proceeds at a faster rate due to leaching

Results

Discussion

Conclusion