Question

Using your data and the fact that plants are roughly 44.5% carbon, calculate how many days it would take for all of the carbon in your leaves to be respired if microbes continue to metabolize at the rate you measured. Now, think back to a just-fallen leaf outside. Considering how many days you estimate it would take your leaves to disappear, do you think there are enough days that are moist and warm enough to allow complete metabolism of leaves between fall and spring, say between November 1 and May 15? Explain.

Answer 1

Soil organic C is known to be protected by three main processes in soils - chemically, physically, and biochemically. Among the biochemical characteristics of an organic material, C/N is among the ones that show a great influence on its decomposition rate. A material with lower C/N ratio, like soybean residue, compared to a corn residue for example (higher C/N), would be much easier to be decomposed by the microorganisms, being known as a more labile material. But an interesting fact showed recently by a group of researchers is that the stoichiometry of the organic material being decomposed is determinant on how much CO2 would be released during decomposition. The microorganisms have a fixed nutrient ratio (C/N/P) and, during the decomposition process they impose its own stoichiometry to the transformed material. It means that, a diet rich in C causes microorganisms to release more C as CO2 into the atmosphere as the microbes try to maintain their healthy C/nutrients ratio...it would take approximately 31 days for all of the carbon in the leaves to be respired if microbes continue to metabolize.

there are enough days that are moist and warm enough to allow complete metabolism of leaves between fall and spring, say between November 1 and May 15

litter traits are a mere legacy of live leaf traits; nitrogen (N) and lignin are the key litter traits controlling decomposition; and favourable climatic conditions result in rapid decomposition in tropical forests.Substantial interspecific variation in litter phosphorus (P) was found to be unrelated to variation in green leaves. Litter nutrients explained no variation in decomposition, which instead was controlled primarily by nonlignin litter C compounds at low concentrations with important soil fauna effects. Despite near‐optimal climatic conditions, tropical litter decomposition proceeded more slowly than in a climatically less favourable temperate forest. ... slow decomposition in the studied rainforest results from a syndrome of poor litter C quality beyond a simple lignin control, enforcing energy starvation of decomposers ...the litter trait syndrome in nutrient‐poor tropical rainforests may have evolved to increase plant access to limiting nutrients via mycorrhizal associations.