References

1. … On Predicting Root Decomposition Kim H. Ludovici USDA Forest Service, SRS-4160 Abstract Quantification of root decomposition remains controversial because researchers can not control the process. The literature provides examples in which researchers have limited the size, age and species of roots used in studies, or controlled the onset of decomposition. Others have controlled ambient and/or soil conditions during root growth and decomposition. Still, there is not one quintessential root decomposition methodology that can be utilized across species or ecotomes. Using data from available publications, decay curves will be generated with consideration given to tree species, stand age, root size, temperature and methodology. Discussion Research studies have been conducted on every continent, and on many of the most economically important species. The 2 phase pattern of decomposition, often reported for fine roots, supports the idea that root structure and complexity control nutrient release rates from roots, however, most studies include only roots < 5mm in diameter, and last only a year or two (approximately the duration of a Master’s project). Consideration that most decomposition work is conducted on a small percentage of the root system (just 5 – 15% of the total tree biomass), and has a duration far shorter than the lifespan of a fine root, is necessary. Root decomposition and nutrient release are also traditionally estimated from dried root tissues, and while it is unlikely that roots dehydrate prior to decomposition in-situ, the limited studies disagree on the cause and effect. • Results • Summarization across species, ecotomes and methodologies suggest: • Root decomposition rate does not differ by soil depth • Soil temperature may, or may not be positively related to decomposition rate • Root decomposition is affected by soil texture • Site fertility is not a predictor of decomposition rate • Soil biota are always important for root decomposition • Ambient temperature and CO2 level do not strongly impact root decomposition rates • Decomposition is negatively related to root diameter • Nutrient concentrations in roots may or may not be related to decomposition rate • Decomposition is negatively related to root lignin and carbohydrate concentrations • Root decomposition rates vary widely between species Table 1. Summary of literature review including root size and species, and decomposition rate constants (k-values) when published. PC2 Scores All Soils 0-20 cm PC1 Conclusions We are seriously over estimating the amount of root decomposition that occurs over a forest rotation. Additional studies are required to test the mechanisms of nutrient loss, and the long-term decomposition rates of larger roots. Table 2. Summary of root decomposition rate response to within-species manipulations and/or direct tests of site effects. • References • Yavitt, J.B. and T.J. Fahey. 1982. Loss of mass and nutrient changes of decaying woody roots in lodgepole pine forests, southeastern Wyoming. Can. J. For. Res. 12:745-752 • McClaugherty, C.A., J.D. Aber and J.M. Melillo. 1984. Decomposition dynamics of fine roots in forested ecosystems. Oikos 42:378-386 • Fahey, T.J., J.W. Hughes, Mou Pu and M.A. Arthur. 1988. Root Decomposition and Nutrient Flux Following Whole-Tree Harvest of Northern Hardwood Forest. For. Sci. 34(3):744-768 • Bloomfield, J., K.A. Vogt and D.J. Vogt. 1993. Decay rate and substrate quality of fine roots and foliage of two tropical tree species in the Luquillo Experimental Forest, Puerto Rico. Plant and Soil 150:233-245 • Ruark, G.A. 1993. Modeling Soil Temperature Effects on In Situ Decomposition Rates for Fine Roots of Loblolly Pine. For. Sci. 39(1):118-129 • Silver, W.L. and K.A. Vogt. 1993. Fine root dynamics following single and multiple disturbances in a subtropical wet forest ecosystem. J. Ecology. 81:729-738 • Scheu, S. and J. Schauermann. 1994.Decomposition of roots and twigs: Effects of wood type (beech and ash), diameter, site of exposure and macrofauna exclusion. Plant and Soil 163:13-24 • Lohmus,K. and M. Ivask. 1995.Decomposition and nitrogen dynamics of fine roots of Norway spruce (Picea abies (L.) Karst.) at different sites. Plant and Soil 168:89-94 • King, J.S.. H.L. Allen, P.M. Dougherty and B.R. Strain. 1997. Decomposition of roots in loblolly pine: Effects of nutrient and water availability and root size class on mass loss and nutrient dynamics. Plant and Soil 195:171-184 • Mun, H.T. and W.G. Whitford. 1998. Changes in mass and chemistry of plant roots during long-term decompostion on a Chihuahuan Desert watershed. Biol. Fertil. Soils. 26:16-22 • Ostertag, R. and S.E. Hobbie 1999. Early stages of root and leaf decomposition in Hawaiian forests: effects of nutrient availability. Oecologia. 121:564-573 • Chen, Hua, M.E. Harmon, R.P. Griffiths and W. Hicks. 2000. Effects of temperature and moisture on carbon respired from decomposing woody roots. For. Ecol. And Management. 138:51-64 • Jose, S., A.R. Gillespie, J.R. Seifert, D.B. Mengel and P.E. Pope. 2000. Defining competition vectors in a temperat alley cropping system in the midwestern USA. Agrofor. Systems. 48:61-77 • Usman, S., S.P. Singh, Y.S. Rawat and S.S. Bargali. 2000. Fine root decomposition and nitrogen mineralisation patterns in Quercus leutrichophora and Pinus roxburghii forests in central Himalaya. For. Ecol. And Management. 131:191-199 • Dilustro, J.J, F.P. Day and B.G. Drake. 2001. Effects of elevated atmospheric OC2 on root decomposition in a scrub oak ecosystem. Global Change Biology. 7:581-589 • Silver W.L. and R.K. Miya. 2001. Global patterns in root decomposition: comparisons of climate and litter quality effects. Oecologia. 129:407-419 • Chen, Hua, M.E. Harmon, J. Sexton and B. Fasth. 2002. Fine-root decomposition and N dynamics in coniferous forests of the Pacific Northwest, USA. Can. J. For. Res. 32:320-331 • Dornbush, M.E., T.M. Isenhart and J. W. Raich. 2002. Quantifying Fine-root Decomposition: An alternative to buried litterbags. Ecology. 83(11): 2985-2990 • John, B., H.N. Pandey and R.S. Tripathi. 2002. Decomposition of fine roots of Pinus kesiya and turnover of organic matter, N and P of coarse and fine pine roots and herbaceous roots and rhizomes in subtropical pine forest stands of different ages. Biol. Fertil. Soil. 35:238-246 • Ludovici, K.H., S.J. Zarnoch and D.D. Richter. 2002. Modeling in-situ pine root decomposition using data from a 60-year chronosequence. Can. J. For. Res. 32:1675-1684 • Dress, W.J. and R.E.J. Boerner. 2003. Temporal and Spatial Patterns in Root Nitrogen Concentration and Root Decomposition in Relation to Prescribed Fire. The Am. Midland Natur. 129(2) 245-257 • Manlay, R.J., D. Masse, T. Chevalier, A. Russell-Smith, D. Friot and C. Feller. 2004. Post-fallow decomposition of woody roots in the West African savanna. Plant and Soil 260:123-136 • Fritz, K.M., J.W. Feminella, C. Colson, B.G. Lackaby, R. Goverbi and R.B. Rummer. 2006. Biomass and decay rates of roots and detritus in sediments of intermittent Coastal Plain streams. Hydrobiologia. 556:265-277 • Ludovici, K.H. and L.W. Kress. 2006. Decomposition and nutrient release from fresh and dried pine roots under two fertilizer regimes. Can. J. For. Res. 36:105-111 Fig. 1 Photograph of recovered root material from 55 to 70-year-old loblolly pine stumps that had been decomposing for (A) 5 years, (B) 20 years, (C) 10 years, and (D) 55 years, on a Kanhapludult in the Piedmont region of North Carolina. Reproduced from Ludovici et al. 2002 Introduction and Methods Determining what we know about root decomposition means going back through the literature, to see what has really been done, what assumptions have been made, what species and environmental conditions are included, and how the work was implemented. A literature search for peer-reviewed publications reguarding “tree and root and decomposition” identified only 58 articles published in the past 40 years (Table 1). Of those 58, only 24 publications included within-species manipulations and/or direct tests of site effects on root decomposition rate (Table 2). Post-harvest decomposition (Fig. 1) is virtually unstudied, even though large roots persist for many years (Fig. 2), and contribute a sizable pool of C to the developing forest (Fig. 3) Methodologies have varied widely, but most often utilize live, excised roots that are washed and dried prior to decomposition (Fig. 4). Studies incorporating season and root hydration (Fig. 5) suggest additional sources of variability in root decomposition rates. A B Fig. 2. Biomass of mature loblolly pine root systems recovered along a time chronosequence, Durham, NC Fig. 3. Carbon pools in decomposing roots and the soil volume surrounding them, measured along a time chronosequence, Durham, NC 2000 Fig. 5. Graph of % biomass loss (A) and carbon concentrations (B) in fine roots of Pinus taeda decomposing in-situ. Fig. 4. Photograph of a controlled environment chamber used in root incubations.