Nutrient cycling in forests

Abstract

SUMMARY Studies of nutrient cycling in forests span more than 100 yr. In earlier years, most attention was given to the measurement of the pools of nutrients in plants and soil and of the return of nutrients from plant to soil in litterfall. The past 20 yr or so have seen a major concentration on the processes of nutrient cycling, with particular emphasis on those processes by which the supply of nutrients to the growing forest is sustained. In the more highly productive forests, up to 10 tonnes of litter of low nutritional quality is deposited annually on the forest floor. The decomposition of this litter, the mineralization of the nutrients it holds, and the uptake of nutrients by tree roots in the carbon‐rich environment which results are the themes of this review. Studies of decomposition of litter in forests have been dominated by the role of nitrogen as a limiting factor, a domination which reflects the preponderance of studies of temperate forests in the Northern Hemisphere. For many forests of the world growing on soils of considerable age, it seems more probable that growth and nutrient cycling are limited by phosphorus (or some other element). There is increasing evidence for a number of forests that phosphorus is immobilized in the first stages of decomposition to a significantly greater extent than is nitrogen. Advances in research will depend, as with studies of soil organic matter, in denning and developing analytical techniques for studying biologically active forms of potentially limiting nutrients, rather than total elemental concentrations. The availability of phosphorus in forests is sustained by phosphorus cycling. More than 50% of the total phosphorus in the surface soils is in organic forms and much of the more labile phosphorus is in the form of diesters. Phosphorus availability is determined by competition between biological and geochemical sinks, and it is clear that the sinks in the rhizosphere (plant roots, microorganisms, soil mineral and organic components) are extensively modified by active processes (e.g. production of exudates, nutrient storage in a variety of organic or polymeric forms and nutrient transport away from sites of uptake). There is abundant evidence that roots of many species exude compounds which have the ability to solubilize sources of phosphorus of otherwise low availability. The significance of root exudates (for example, phosphatases, organic acids) in the functioning of perennial ecosystems has yet to be quantified and there are conflicting reports as to the effects of simple organic acids on phosphorus availability. The distribution of phosphorus sinks and their relative competitiveness and their modification are topics of fundamental importance for future research. In contrast to the mineralization of phosphorus, our knowledge of transformations and availability of nitrogen in forest soils is well‐developed. Net nitrogen mineralization rates approximate rates of nitrogen return in litterfall but the contribution of nitrification is variable. Nitrification is ...

Contribution of litter layer to soil greenhouse gas emissions in a temperate beech forest

“…Mobile N forms like NO 3 − , NH 4 + and amino acids are quickly immobilized by microorganisms and plant roots in the mineral soil (Inselsbacher et al 2010). Litter-derived P can be adsorbed to the mineral matrix (Tiessen 2008) or taken up by plant roots before it enters the mineral soil (Attiwill and Adams 1993). It is therefore possible that because DOC, inorganic N and P were either adsorbed to the mineral matrix or turned over quickly, in the present study changes in these pools caused by litter manipulation were not detectable with standard soil extraction methods that target plant-accessible compounds.…”

Forms and Availability of Soil Phosphorus in Temperate Forests in Southern Chile and Flanders

“…Nitrogen and phosphorus are thought to be the key elements in limiting primary productivity in temperate forests (Attiwell & Adams 1993). Our understanding of the role of P in the functioning of forest ecosystems is however severely hampered by difficulties in identifying and quantifying available P fractions in forest soils.…”

Phytotoxicity, not nitrogen immobilization, explains plant litter inhibitory effects: evidence from solid‐state 13C NMR spectroscopy

“…In this context, factors affecting litter decomposition rates and related nutrient dynamics have been thoroughly investigated in relation to environmental conditions and litter chemical characteristics (Vitousek & Sanford, 1986;Attiwill & Adams, 1993). The accumulation of plant litter has an important role in affecting plant community structure.…”