The importance of amino sugar turnover to C and N cycling in organic horizons of old-growth Douglas-fir forest soils colonized by ectomycorrhizal mats
- 533 Downloads
Amino sugar dynamics represent an important but under-investigated component of the carbon (C) and nitrogen (N) cycles in old-growth Douglas-fir forest soils. Because fungal biomass is high in these soils, particularly in areas colonized by rhizomorphic ectomycorrhizal fungal mats, organic matter derived from chitinous cell wall material (or the monomeric building block of chitin, N-acetylglucosamine (NAG)) could be a significant source of C or N to the soil microbiota, and thus an important driver of microbial C and N processing. This paper reports the results of incubation experiments initiated to measure chitin degradation, NAG utilization, and the contribution of these substrates to soil respiration and N mineralization rates in mat-colonized and non-mat soil organic horizons. Amendments of chitin and NAG stimulated respiration, N mineralization, and biomass accumulation in mat and non-mat soils, and responses to NAG amendment were stronger than to chitin amendment. NAG-induced respiration was consistently two-fold higher in mat soils than non-mat soils, but induced N mineralization was similar between the two soil patch types. Assimilation of both C and N into microbial biomass was apparent, biomass C:N ratio decreased in all treatments, and microbial N use efficiency (treatment means 0.25 ± 0.06–0.50 ± 0.05) was greater than C use efficiency (treatment means 0.12 ± 0.04–0.32 ± 0.02). NAGase enzyme response was non-linear and showed the same pattern in chitin and NAG amendments. Responses to NAG and chitin amendment differed between mat and non-mat soils, indicating different mechanisms driving NAG and chitin utilization or differences in saprotrophic community composition between the two soil patch types. Net chitin and NAG processing rates were 0.08–3.4 times the basal respiration rates and 0.07–14 times the ambient net N mineralization rates, high enough for the turnover of total soil amino sugars to potentially occur in days to weeks. The results support the hypotheses that amino sugars are important microbial C and N sources and drivers of C and N cycling in these soils.
KeywordsMicrobial biomass Amino sugars Forest floor Organic layer soils Ectomycorrhizae Linked C and N cycles
The H. J. Andrews Experimental Forest and LTER personnel provided site access and collaborative energy, and Rockie Yarwood, Elizabeth Brewer, Calvin Elser and Michele Noble provided valuable laboratory advice and/or assistance. Bruce Caldwell and Bob Sinsabaugh contributed thoughtful discussion on the experimental results, Peter Bottomley provided constructive feedback on the experiments, data and manuscript, and the manuscript was improved by the thoughtful comments of two anonymous reviewers. This project was funded by NSF Grant No. 0348689 to DDM.
- Amelung W (2001) Methods using amino sugars as markers for microbial residues in soil. In: Lai R, Kimble JM, Follett RF, Stewart BA (eds) Assessment methods for soil carbon. CRC Press LLC, Boca RatonGoogle Scholar
- Dixon JJ (2003) Applying GIS to soil-geomorphic landscape mapping in the Lookout Creek valley, Western Cascades, Oregon. Master’s Thesis, Department of Crop and Soil Sciences. Oregon State University, CorvallisGoogle Scholar
- Doi H, Cherif M, Iwabuchi T, Katano I, Stegen JC, Striebel M (2010) Integrating elements and energy through the metabolic dependencies of gross growth efficiency and the threshold elemental ratio. Oikos 119(5):752–765Google Scholar
- Griffiths RP, Caldwell BA, Cromack K, Morita RY (1990) Douglas-fir forest soils colonized by ectomycorrhizal mats. 1. Seasonal-variation in nitrogen chemistry and nitrogen-cycle transformation rates. Can J For Res 20(2):211–218Google Scholar
- Hart SC, Stark JM (1997) Nitrogen limitation of the microbial biomass in an old-growth forest soil. Ecoscience 4(1):91–98Google Scholar
- Lengeler J, Drews G, Schlegel H (1999) Biology of the prokaryotes. Georg Thieme, StuttgartGoogle Scholar
- Miller M, Palojarvi A, Rangger A, Reeslev M, Kjoller A (1998) The use of fluorogenic substrates to measure fungal presence and activity in soil. Appl Environ Microbiol 64(2):613–617Google Scholar
- Sinsabaugh RL, Lauber CL, Weintraub MN, Ahmed B, Allison SD, Crenshaw C, Contosta AR, Cusak D, Frey S, Gallo ME, Gartner TB, Hobbie SE, Holland K, Keeler BL, Powers JS, Stursova M, Takacs-Vesbach C, Waldrop MP, Wallenstein MD, Zak DR, Zeglin LH (2008) Stoichiometry of soil enzyme activity at global scale. Ecol Lett 11:1252–1264Google Scholar
- Stevenson FJ (1982) Organic forms of soil nitrogen. In: Stevenson FJ (ed) Nitrogen in agricultural soils, vol 22. ASA, CSSA, pp 67–122Google Scholar
- Vignon C, Plassard C, Mousain D, Salsac L (1986) Assay of fungal chitin and estimation of mycorrhizal infection. Physiol Veg 24(2):201–207Google Scholar