Mass, nutrient pool, and mineralization of litter and fine roots in a tropical mountain cloud forest.

ABSTRACT

We used fine root and litter mass from a tropical mountain cloud forest to assess their relative contribution to nutrient content and to examine mineralization processes during a laboratory incubation experiment. Our results showed that average fine root mass density ranged from 2.86kgm-3 to 11.59kgm-3, while litter mass density ranged from 72.5kgm-3 to 177.3kgm-3. On average, fine root mass density represented 4.7% of the mass density of the O horizon. Fine root mass density followed an exponentially declining trend with soil depth. On average, 83% of fine root mass density within the soil profile was concentrated in the O horizon. Mean element pools in litter decreased from 44.08mgcm-3 to 0.49µgcm-3 in the following sequence C>N>Fe>S>Ca>P>K>Mg>Na>Mn>Zn>Cu. For fine roots, a different mean element pool sequence (C>N>Ca>K>Fe>S>Mg>Na>P>Mn>Zn>Cu) in decreasing abundance (from 2.88mgcm-3 to 0.13µgcm-3) was observed with respect to litter. Regarding C, litter mineralized faster than fine roots, with a mean k value of 0.25d-1 for litter and 0.13d-1 for fine roots. Principal component analysis (PCA) combined with stepwise regression analysis revealed that the main mass density predictors were N, S, Zn, and Mn for litter (p<0.0001, R2=0.92), and S and C/N ratio for fine roots (p<0.0001, R2=0.82). These results demonstrate the potential of chemical composition to influence the mineralization of fine root and litter mass and therefore the nutrient availability and C sequestration.