Carbon and nitrogen in forest floor and mineral soil under four forest species in the Mediterranean region

Felícia Fonseca,Tomás Figueiredo

doi:10.3232/sjss.2018.v8.n1.04

Abstract

The organic and mineral horizons of soils are of great importance in C and N storage in forest areas. However, knowledge of the effects of forest species on the stocks of these elements is still scarce, especially in Portugal. In order to contribute to this knowledge, a study was carried out in forest stands of Pinus pinaster Aiton (PP), Pinus nigra Arnold (PN), Pseudotsuga menziesii (PM) and Castanea sativa Miller (CS), installed in the 1950s in northern Portugal. Sampling areas with similar topography, lithology and climate were selected, in order to better identify hypothesized differences in C and N storage due to forest species effect. In each stand, 15 sites were selected randomly and the forest floor (organic layers) was collected in a 0.49 m2 area. The layers H, L and F of the forest floor were identified and, for L and F, their components were separated in leaves, pine cones/chestnut husks and branches. At the same sites, soil samples were also collected at 0-10 and 10-20 cm depth. At these depths, undisturbed samples were also collected for bulk density determination. The concentrations of C and N were determined in forest floor and mineral components of the soil, and converted in mass per unit area. The quantity of C storage per unit area followed the sequence PN &gt; PM &gt; CS &gt; PP, while for N the sequence was CS &gt; PM &gt; PN &gt; PP, OM and PP keeping the same relative position in the sequence in both C and N concentrations. The PM and CS species store similar amounts of C and N, and about 90% of these elements is found in the upper 20 cm of the mineral soil. In PN and PP species, the contribution of forest floor to the storage of these elements is more expressive than in the other species, but lower than 30% in all cases.

Highlights

Forest species litter production and litter quality have a recognized importance in the accumulation, type and distribution of soil organic matter formed in the topsoil horizon
The main objective of the present study was to quantify the effects of four forest species (Pinus pinaster Aiton (PP) and Castanea sativa Miller (CS), which are well represented in North Portugal; Pinus nigra Arnold (PN) and Pseudotsuga menziesii (Mirb.) Franco (PM), with lower coverage but with forestry interest) on C and N concentrations and stocks in forest floor and top mineral soil layers
The differences among species can be essentially related to the anthropogenic disturbances in PP and CS stands, pine cones production and quality of organic material constituting the forest floor (Tables 2 and 3)

Summary

Introduction

Forest species litter production and litter quality have a recognized importance in the accumulation, type and distribution of soil organic matter formed in the topsoil horizon. They determine a series of processes that influence soil properties, pedogenesis, and the productivity and sustainability of ecosystems (Oostra et al 2006; Fisher and Binkley 2012). Nature and quantity of litter have an important role in forest floor formation and energy transfer between plants and soil (Santa-Regina 2001; Shaw and Harte 2001; Marty et al 2017). The forest floor plays a crucial role in the hydrological processes and can influence considerable processes at an ecosystem level, due to their location at the interface of the atmosphere and the mineral soil (Keith et al 2010)

Objectives

Methods

Results

Discussion

Conclusion