Dissolved and colloidal phosphorus fluxes in forest ecosystems—an almost blind spot in ecosystem research

Abstract

Understanding and quantification of phosphorus (P) fluxes are key requirements for predictions of future forest ecosystems changes as well as for transferring lessons learned from natural ecosystems to croplands and plantations. This review summarizes and evaluates the recent knowledge on mechanisms, magnitude, and relevance by which dissolved and colloidal inorganic and organic P forms can be translocated within or exported from forest ecosystems. Attention is paid to hydrological pathways of P losses at the soil profile and landscape scales, and the subsequent influence of P on aquatic ecosystems. New (unpublished) data from the German Priority Program 1685 ''Ecosystem Nutrition: Forest Strategies for limited Phosphorus Resources'' were added to provide up-to-date flux-based information. Nitrogen (N) additions increase the release of water-transportable P forms. Most P found in percolates and pore waters belongs to the so-called dissolved organic P (DOP) fractions, rich in orthophosphate-monoesters and also containing some orthophosphate-diesters. Total solution P concentrations range from ca. 1 to 400 μg P L -1 , with large variations among forest stands. Recent sophisticated analyses revealed that large portions of the DOP in forest stream water can comprise natural nanoparticles and fine colloids which under extreme conditions may account for 40-100% of the P losses. Their translocation within preferential flow passes may be rapid, mediated by storm events. The potential total P loss through leaching into subsoils and with streams was found to be less than 50 mg P m -2 a -1 , suggesting effects on ecosystems at centennial to millennium scale. All current data are based on selected snapshots only. Quantitative measurements of P fluxes in temperate forest systems are nearly absent in the literature, probably due to main research focus on the C and N cycles. Therefore, we lack complete ecosystem-based assessments of dissolved and colloidal P fluxes within and from temperate forest systems. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. Forest phosphorus cycle during ecosystem developmentForests are complex biogeochemical systems in which nutrient cycles readily change and become re-adjusted upon interactions with biotic and abiotic controls over diurnal, annual, decadal, centennial, and longer timescales (Hedin et al., 2003). Phosphorus (P) is an essential element for all living organisms. Modern agriculture avoids P limitation of primary production by continuous application of fertilizers, while forest ecosystems have developed efficient strategies for adapting to low P supply (Elser et al., 2007;Ilg et al., 2009;Rennenberg and Schmidt, 2010;Hinsinger et al., 2011). Increasing production of forests biomass in response to high atmospheric nitrogen (N) input and climate c...

Soil phosphorus supply controls P nutrition strategies of beech forest ecosystems in Central Europe

“…Some of the relevant P fluxes are hard to quantify (Bol et al 2016) and not yet available at the study sites. However, the different P nutrition strategies can modify the studied P characteristics of the ecosystems as well as other ecosystem properties.…”

The influence of soil properties and nutrients on conifer forest growth in Sweden, and the first steps in developing a nutrient availability metric

“…At low pH, P is bound to Fe and Al oxides, while at high pH, P is typically unavailable because of complex formation with Ca. P availability is thus maximal at intermediate pH (Chapin et al, 2002;Bol et al, 2016), while enhanced leaching of base cations occurs in acidic soils, thus lowering the amount of total 55 exchangeable bases (TEB = cation equivalent of summed K, Ca, Mg and Na - IIASA and FAO, 2012). Hence, unlike temperature or precipitation, nutrient availability cannot be assessed by measuring one single parameter.…”

Quantification of Phosphorus Exports from a Small Forested Headwater-Catchment in the Eastern Ore Mountains, Germany

“…The highest concentrations were measured during events in summer and fall after long dry periods with little or no precipitation. The increased concentration of TP-P during the summer and fall seasons indicates that during dry periods P accumulates in the soil, which then is flushed by precipitation water during rain events [6]. Recent studies have demonstrated that dry and rewetting cycles, which occur more often during summer and fall seasons, increase the export of P from the organic layers and upper mineral horizons [26].…”

“…At the landscape scale, P is exported mainly via streamflow either in solution or as a particulate, and in either organic or inorganic forms [3][4][5]. The magnitude and dynamics of P export fluxes from forests are determined by the availability of P from the geologic parent materials as well as from the internal cycling of P within the forest ecosystem [1,6]. In forest soils, nutrients can be easily exported via preferential flow pathways, such as macropores or at the interface between organic and mineral soil layers [7,8].…”

“…While the dynamics and magnitude of P fluxes from agricultural systems are relatively well understood, less is known about the processes in forested ecosystems [6]. For small headwater catchments in central and northern Europe under mixed oak/beech and spruce, export rates for total phosphorus (TP-P) ranging from 1.4 to 2.2 g·ha −1 ·a −1 [5] and 26 g·ha −1 ·a −1 [16] have been reported.…”