Tree species of moist tropical forests differ in their detrital biochemistry and effects on soil carbon dynamics.
Russell, Ann*,1, Olk, Dan2, Marek, Rachel3, 1 Dept. of Natural Resource Ecology and Management, Ames, IA, USA2 National Soil Tilth Laboratory, USDA/ARS, Ames, IA, USA3 Grinnell College, Grinnell, IA, USA
ABSTRACT- In 15-yr-old experimental plantations at La Selva Biological Station, Costa Rica, six tree species differed in their effects on soil organic carbon (SOC) sequestration and soil pH. In initial studies to identify some of the underlying mechanisms, we measured several biochemical attributes of fine roots, senesced leaves and soil for each of six species. Tissues of the species differed in lignin content, and in three lignin-derived families of phenols, the cinnamyls, syringyls and vanillins. Amounts of cinnamyls and syringyls in soil differed significantly among species, whereas vanillins did not. Because carboxylic acids are a common by-product of oxidative decomposition of lignin by microorganisms, the ratio of carboxylic acid to aldehyde compounds within the vanillin and the syringyl families represent the degree of decomposition of these phenols. For syringyls, this ratio was significantly higher in soils under Pinus patula than under Pentaclethra macroloba, Hyeronima alchorneoides, Virola koschnyi, Vochysia ferruginea, and V. guatemalensis. For the vanillins, this ratio varied, with Virola < Vochysia guatemalensis, V. ferruginea < Hyeronima, Pentaclethra < Pinus. Thus, if cumulative quantities of organic matter inputs were similar under all species, then these biochemical data indicate that detritus is more decomposed under Pinus. In an independent measure of SOC decomposition, potential mineralization of labile C determined from 30-day laboratory incubations, CO2-C released was lower under Virola, Pinus, and Pentaclethra compared with the other species. With the exception of Virola, these data are consistent with the biochemical data that indicated that SOC under Pinus and Pentaclethra was more decomposed. We modeled with CENTURY to integrate data regarding organic matter inputs, detrital biochemistry, and potential mineralization, and to provide insights into plant-mediated controls over soil carbon sequestration.
Key words: phenolic compounds, soil organic matter decomposition, soil carbon sequestration, tropical trees
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