16 Soil Nitrogen Dynamics
Isabel Serrasolses, Victoria Diego and David Bonilla
16.1 Introduction
Soils are by far the largest nitrogen (N) pool in forest ecosystems, usually exceeding 85% of total ecosystem capital (Cole and Rapp 1981). Most of the soil
N is tied to organic matter and only a small percentage of the total N is available to plants through N mineralization. Aboveground, N returns to the soil
via litterfall and, after an 'Immobilization period on the forest floor, litter decomposition supplies mineral N to the soil. The forest floor contains large
pools of readily mineralizable N and is thus a major supplier of mineral N to
trees (Keeney 1980; Casals et al. 1995). The forest floor of Mediterranean forests contains similar or lower amounts of organic matter than temperate forests but higher amounts than tropical forests (Cole and Rapp 1981).
N mineralization in Mediterranean soils is usually highest in periods of
favourable temperature and water availability, thus exhibiting a marked seasonality, with most mineralization occurring in spring and autumn (Lemee
1967; Read and Mitchell 1983). Nitrification is more dependent on suitable
conditions than ammonification because nitrifier populations are very sensitive to soil moisture, ammonium supply, and drying and rewetting cycles
(Schaefer 1973; Davidson et al.I992).
Nitrate leaching is one of the major pathways for N loss in terrestrial ecosystems because nitrate is relatively mobile in soils and it is easily leached by
percolating water. The rate of leaching in a soil profIle depends on the nitrate
concentration in soil water and on the downward flux of water. Therefore N
leaching in Mediterranean ecosystems has also a marked seasonal pattern
determined by rainfall, almost coinciding with the N mineralization pattern.
In undisturbed holm oak (Quercus ilex L.) forests there is a net retention of
N on a whole catchment scale (Chap. 20), since the soils retain the N inputs
from atmospheric deposition and also retain most of the mineral N produced in the soil. Hence, N leaching should be negligible in these soils.
The aim of this chapter is to evaluate the soil N availability in the holm
oak forests of Prades and Montseny. To achieve this purpose the dynamics of
Ecological Studies, Vol. 137
Ferran Roda et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999
Isabel Serrasolses, Victoria Diego and David Bonilla
16.1 Introduction
Soils are by far the largest nitrogen (N) pool in forest ecosystems, usually exceeding 85% of total ecosystem capital (Cole and Rapp 1981). Most of the soil
N is tied to organic matter and only a small percentage of the total N is available to plants through N mineralization. Aboveground, N returns to the soil
via litterfall and, after an 'Immobilization period on the forest floor, litter decomposition supplies mineral N to the soil. The forest floor contains large
pools of readily mineralizable N and is thus a major supplier of mineral N to
trees (Keeney 1980; Casals et al. 1995). The forest floor of Mediterranean forests contains similar or lower amounts of organic matter than temperate forests but higher amounts than tropical forests (Cole and Rapp 1981).
N mineralization in Mediterranean soils is usually highest in periods of
favourable temperature and water availability, thus exhibiting a marked seasonality, with most mineralization occurring in spring and autumn (Lemee
1967; Read and Mitchell 1983). Nitrification is more dependent on suitable
conditions than ammonification because nitrifier populations are very sensitive to soil moisture, ammonium supply, and drying and rewetting cycles
(Schaefer 1973; Davidson et al.I992).
Nitrate leaching is one of the major pathways for N loss in terrestrial ecosystems because nitrate is relatively mobile in soils and it is easily leached by
percolating water. The rate of leaching in a soil profIle depends on the nitrate
concentration in soil water and on the downward flux of water. Therefore N
leaching in Mediterranean ecosystems has also a marked seasonal pattern
determined by rainfall, almost coinciding with the N mineralization pattern.
In undisturbed holm oak (Quercus ilex L.) forests there is a net retention of
N on a whole catchment scale (Chap. 20), since the soils retain the N inputs
from atmospheric deposition and also retain most of the mineral N produced in the soil. Hence, N leaching should be negligible in these soils.
The aim of this chapter is to evaluate the soil N availability in the holm
oak forests of Prades and Montseny. To achieve this purpose the dynamics of
Ecological Studies, Vol. 137
Ferran Roda et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999