Nutrient storage and turnover in organic layers under tropical montane rain forest in Ecuador

Abstract

Summary In tropical montane forests nutrients released from the organic layers of the soil can supply a large part of the vegetation's requirements. We have examined concentrations, storage, and turnover times of nutrients in the organic layer and the fluxes of nutrients by the fall of small litter (leaves, seeds, flowers, small twigs, and plant debris that passed an opening of 0.3 m × 0.3 m) in such a forest in Ecuador. The times taken for litter to turn over were estimated by relating nutrient storage in the organic layer to rate of litterfall and by incubating samples in the laboratory. The organic layer had a thickness of 2–43 cm, a mass of 30–713 t ha−1, and a nutrient storage of 0.87–21 t N, 0.03–0.70 t P, 0.12–2.5 t K, 0.09–3.2 t Ca, and 0.07–1.0 t Mg ha−1. The pH (in H2O) ranged between 3.1 and 7.4 and was correlated with the concentrations of Ca and Mg (r= 0.83 and 0.84, respectively). The quantity of small litter (8.5–9.7 t year−1) and mean concentrations of nutrients in litter (19–22 g N, 0.9–1.6 g P, 6.1–9.1 g K, 12–18 g Ca, and 3.5–5.8 g Mg kg−1) were larger than in many other tropical montane forests. The mean turnover times of elements in the organic layer increased in the order, Mg (7.0 years) < Ca (7.9) < K (8.5) < P (11) < N (14) < S (15) when calculated as the quotient of storage in the organic layer to flux by litterfall; they were < 12 years for N, P, and S in the incubation experiment. Under optimum conditions in the laboratory, the mineralization of S was just as large as the S deposition by litterfall. In weakly acid soils Mn and Zn and in strongly acid soils Ca added in a nutrient solution were immobilized during incubation. Thus, lack of S, Mn, Zn, and Ca might limit plant growth on some soils.

Variability of indices of macronutrient availability in soils at different spatial scales along an elevation transect in tropical moist forests (NE Ecuador)

“…The pools of salt-exchangeable Ca, Mg and K in the organic layers increased with elevation due to both a large increase in organic layer depth and also higher Ca ex , Mg ex and K ex concentrations at higher elevations in the organic material. In the organic layers, much more Ca, K and Mg was bound to cation exchangers on a mass basis than in the mineral soil which underlines the importance of the organic layers not only for N and P supply, but also with respect to the supply of basic (non-hydrolyzing) cations (see also Kaufmann et al 1998;Wilcke et al 2002;Wilcke et al 2008). In contrast, significant altitudinal trends in the abundance of salt-exchangeable cations in the mineral soil did not exist (except for slightly smaller Mg ex concentrations at 1500 and 2000 m).…”

Stable N isotope composition of nitrate reflects N transformations during the passage of water through a montane rain forest in Ecuador

“…All mineral soils had a loamy skeletal texture and pH values between 4 and 5. Typical for soils in the research area is a thick organic layer consisting of Oi, Oe and Oa horizons, where most of the plant-available nutrients are concentrated (Wilcke et al 2002). The thickness of the organic layer varied between 0.11 and 0.24 m. According to Bruijnzeel and Hamilton (2000) the forest can be classified as a tropical Lower Montane Forest, characterized by a high abundance of epiphytes and bryophytes.…”

“…However, there are also indications that other elements including P, base metals and even trace elements limit or co-limit plant growth in the tropical montane forest (Wilcke et al 2002;Boy et al 2008a). Nitrogen deposition is expected to increase in the tropics in the near future (Galloway et al 2004).…”

The tropical mountain forest

“…The soil types of the study sites are alumic acrisol at 1000 m, gley cambisol at 2000 m, and podzol at 3000 m (Soethe et al 2006). The organic soil layer is thick and increases with elevation, the pH ranges between 3.0 and 5.5 (Wilcke et al 2002) and is decreasing with elevation (Soethe et al 2006). The bedrock consists mainly of weakly metamorphosed Paleozoic schists and sandstones with some quartz veins.…”