N : P ratios influence litter decomposition and colonization by fungi and bacteria in microcosms

• Published in: Functional ecology Vol. 23; no. 1; pp. 211 - 219
• Main Authors: Güsewell, Sabine, Gessner, Mark O.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01-02-2009; Blackwell Publishing; Blackwell Publishing Ltd; Wiley-Blackwell
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Autoecology; Bacteria; Biological and medical sciences; Carex; ecological stoichiometry; Ecosystems Ecology; ergosterol; Fundamental and applied biological sciences. Psychology; fungal-to-bacterial ratio; Fungi; General aspects; Human ecology; Microcosms; nutrient immobilization; nutrient limitation; piecewise regression; Plant litter; Plant nutrition; Plants; Ratios; Soil ecology; Wetland ecology; Ergosterol; Stoichiometry; Litter; Microcosm; Immobilization; Regression; Phosphorus; Decomposition; Ecology; Nitrogen; ecological stoichiometry; Fungi; Limiting factor; fungal-to-bacterial ratio; nutrient immobilization; nutrient limitation; Bacteria; Nutrient; Ratio; Colonization; piecewise regression
• ISSN: 0269-8463; 1365-2435
• DOI: 10.1111/j.1365-2435.2008.01478.x

1. Nitrogen and phosphorus supply influences the rate of litter decomposition and nutrient dynamics during decomposition. Besides the total amount of N and P available to decomposers, their relative supply (N : P ratio) might be important, e.g. through an influence on the composition and activity of microbial communities. 2. We carried out two experiments using laboratory microcosms to test that (i) N : P ratios (in either litter or the environment) determine whether N or P limits the rate of decomposition, (ii) the 'critical' N : P ratio between N and P limitation depends on overall nutrient availability, (iii) litter colonization by fungi and bacteria depends on the N : P ratio, and (iv) N : P ratios determine if proportionately more N or P is retained or immobilized by the litter. 3. In one experiment, cellulose as a nutrient-free litter analogue was incubated on sand fertilized with varying N : P supply ratios, whereas in a second experiment, Carex leaf litter with varying N : P ratios was incubated on nutrient-free sand. 4. Results essentially support our hypotheses. Cellulose decomposition was N- or P-limited depending on the N : P supply ratio. The shift from N to P limitation occurred at N : P supply ratios of 1·7-45, depending on overall nutrient supply. Bacteria were most abundant on cellulose at low N : P supply ratios, when decomposition was N-limited, while fungi were relatively more important at high N : P ratios, when decomposition was P-limited. The amounts of mineral N and P immobilized on cellulose and those released from litter, both in absolute terms and relative to supply, depended on the type of nutrient limitation (N vs. P). 5. The N : P ratio of nutrients available to decomposers appears to be an important determinant of plant litter decomposition, the relative importance of fungi and bacteria in litter-associated microbial communities, and litter nutrient dynamics.