COS 38-10
Effects of altered litter inputs and nutrient additions on rapidly- and slowly-cycling soil carbon in a tropical forest

Tuesday, August 12, 2014: 4:40 PM
309/310, Sacramento Convention Center
Sarah Halterman, Geography, University of California, Los Angeles, Los Angeles, CA
Daniela Cusack, Geography, University of California - Los Angeles, Los Angeles, CA
Benjamin L. Turner, Smithsonian Tropical Research Institute, Ancon, Panama
S. Joseph Wright, Smithsonian Tropical Research Institute, Panama

Tropical forests contain a considerable fraction of the global soil carbon (C) stock, but the response of tropical soil C to predicted changes in primary productivity remains poorly understood. Drastic changes in soil C storage and loss are likely to occur if global change alters plant net primary production (NPP). Because litterfall production is one of the main pathways of transport of organic matter from plants to soil, changes in litter inputs to tropical systems can have large effects on soil C cycles. We assessed the effects of a decade of litter removal and addition on soil C storage in a tropical seasonal forest in Panama. To distinguish the effect of changes in organic matter inputs from parallel changes in litter nutrients, we included soils that received long-term additions of nitrogen (N), phosphorus (P), and potassium (K). Because soil C is not homogenous, we used a density fractionation scheme to assess manipulation effects on rapidly and slowly cycling pools of C. Soil samples were collected from 0-5 cm and 5-10 cm depths in 15- 45x45 m plots with litter removal, 2x litter addition, and control (n=5), and from 32- 40x40 m plots with factorial additions of N, P, and K.


Bulk soil results validate the importance of changes in litter for soil C dynamics. Litter addition plots contained 5.94±0.35% soil C (mean ± one standard error) at 0-5 cm depth and 3.39±0.13% at 5-10 cm, litter removal plots had 4.19±0.18% (0-5 cm) and 2.79±0.06% (5-10 cm) soil C, and control plots had 5.15±0.23% (0-5 cm) and 3.02±0.20% (5-10 cm) soil C, representing a significant decline with litter removal and increase with litter additions relative to control plots. We found that the "free light" fraction, or rapidly cycling soil C pool, was significantly different among the three litter treatments, with this fraction comprising 4.3 ± 0.3 % of soil mass in the litter addition plots, 2.7 ± 0.3 % in control plots, and 1.1 ± 0.1 % in litter removal plots at the 0-5cm depth, after 10 years (means ± one standard error, n = 5). These results demonstrate that changes in primary productivity have the potential to alter the storage and cycling of C in lowland tropical forest soils.