Long‐term patterns of mass loss during the decomposition of leaf and fine root litter: an intersite comparison

Abstract

Decomposition is a critical process in global carbon cycling. During decomposition, leaf and fine root litter may undergo a later, relatively slow phase; past long-term experiments indicate this phase occurs, but whether it is a general phenomenon has not been examined. Data from Long-term Intersite Decomposition Experiment Team, representing 27 sites and nine litter types (for a total of 234 cases) was used to test the frequency of this later, slow phase of decomposition. Litter mass remaining after up to 10 years of decomposition was fit to models that included (dual exponential and asymptotic) or excluded (single exponential) a slow phase. The resultant regression equations were evaluated for goodness of fit as well as biological realism. Regression analysis indicated that while the dual exponential and asymptotic models statistically and biologically fit more of the litter type-site combinations than the single exponential model, the latter was biologically reasonable for 27-65% of the cases depending on the test used. This implies that a slow phase is common, but not universal. Moreover, estimates of the decomposition rate of the slowly decomposing component averaged 0.139-0.221 year À1 (depending on method), higher than generally observed for mineral soil organic matter, but one-third of the faster phase of litter decomposition. Thus, this material may be slower than the earlier phases of litter decomposition, but not as slow as mineral soil organic matter. Comparison of the long-term integrated decomposition rate (which included all phases of decomposition) to that for the first year of decomposition indicated the former was on average 75% that of the latter, consistent with the presence of a slow phase of decomposition. These results indicate that the global store of litter estimated using short-term decomposition rates would be underestimated by at least one-third.

Soil Biology Research across Latitude, Elevation and Disturbance Gradients: A Review of Forest Studies from Puerto Rico during the Past 25 Years

“…Biotic interactions between plants and detrital communities have also been seen in cross-site leaf decomposition studies. Home-field advantage has been observed where detrital processing and mass loss was faster in the forest type of origin than when translocated to other forest types in the same region or across latitudinal gradients [25,105,106]. Basidiomycete fungi soften decomposing leaves by degrading lignocellulose, so are more important for preconditioning of tough leaves to make them palatable to invertebrates.…”

Improvement of global litter turnover rate predictions using a Bayesian MCMC approach

“…Most of the turnover rates from the LIDET data were obtained from 10-year decomposition records, whereas the maximum length of decomposition records included in the Zhang et al (2008) dataset was three years. Some studies argue that leaf litter turnover rates are best represented by two or three turnover rate components: fast, slow, and passive (Adair et al 2008, Harmon et al 2009) with the impact of slower components on the total leaf litter turnover rates dependent on litter quality (Adair et al 2008). Comparison of the LIDET turnover rates with the estimates from our calibrated best-fitting model revealed no significant relationships neither between the model's residuals and lignin:N ratios (Fig.…”

“…Therefore lignin:N ratios remained a source of uncertainty for the global leaf litter turnover rates distribution. Long-term (10-year) litter decomposition rates have been reported to be lower than short term (1-year) decay rates on average by 22-30% (Harmon et al 2009). The longest observation period for litter decomposition in Zhang et al (2008) that was used in our study was three years, therefore litter decomposition rates might have been overestimated, causing underestimation of the litter pools.…”

“…3d), even a 30% decrease in the litter turnover rates would lead to approximately a 43% increase in the litter pools, which would not be enough to compensate for ;6-fold underprediction of litter pools. To address a potential issue with the data used for model calibration we used the leaf litter turnover rates from the Long-term Intersite Decomposition Experiment Team (LIDET) observed across multiple biomes and substrates (Harmon et al 2009) for additional model validation. We calculated the leaf litter turnover rates from the temperatures and lignin:N ratios at the 27 LIDET sites distributed across North and Central America using the original and our best-fitting model, and compared them to the turnover rates from Harmon et al (2009).…”

“…Litter mass loss is usually represented as an exponential decay process (Olson 1963, Aber et al 1990, Harmon et al 2009):…”