DOI: 10.5061/dryad.fbg79cntt
title: Tree species of wet tropical forests differ in their tissue biochemistry and effects on soil carbon dynamics

description: Given the hypothesized effects on soil organic matter (SOM) of polyphenols
 in plant tissues, differences among tree species in their biochemical
 composition could influence the turnover and accrual of SOM in various
 ways. The extent to which the biochemical composition of leaf and
 fine-root tissues differ among tropical tree species, and the effects on
 soil dynamics, are largely undocumented, however. We used cupric oxide
 analyses of plant tissues and soil in long-term, replicated, mono-dominant
 15-yr-old plantations at La Selva Biological Station, Costa Rica, to test
 for differences among six tree species. We related these results to
 companion studies in this experimental site to evaluate relationships
 between interspecific differences in tissue biochemistry and SOM dynamics.
 Newly senesced leaves and fine roots of the six species differed in their
 concentrations of three lignin-derived families of phenols, the cinnamyls,
 syringyls and vanillyls (P &lt;0.0001 for all tests). Cinnamyl and
 syringyl phenols in soil differed significantly among species (p = 0.0408,
 0.0071, respectively), whereas vanillyl phenols did not (p = 0.83). The
 degree of decomposition of syringyl and vanillyl phenols in soil also
 differed (p = 0.0015, 0.0027 respectively), as evidenced by the ratio of
 carboxylic acid to aldehyde compounds, based on the concept that
 carboxylic acids are a common by-product of oxidative decomposition of
 lignin by microorganisms. In our study in a single site, i.e., the same
 soil type, climate, and growth form of vegetation, total phenols in soil
 ranged from 5 to 21 mg g-1 organic carbon (OC) across the 20 plots, and
 the endpoints were both broad-leaved evergreen species; even the means
 across species, 7–12 mg g-1 OC, covered half the range of values reported
 in another study across a broad latitudinal range of sites. This study’s
 tree species differed in traits that influenced at least four factors that
 explained their differential effects on SOC pools: (1) Fine-root detrital
 inputs; (2) Fine-root syringyl concentrations; (3) Soil pH; and (4)
 Macroaggregate structure.  This trait-based approach provides a
 process-based understanding of how trees species influence SOC dynamics,
 and the consequences for ecosystem properties, under land-use change that
 involves shifts in species composition.
description: Data were collected from a long-term field experiment at La Selva
 Biological Station in Costa Rica over a year-long period. Phenolic
 compounds (cinnamyl, syringyl, and vanillyl phenols) of leaves and fine
 roots were measured for six tropical tree species, <i>Hieronyma
 alchorneoides</i> Allemao; <i>Pentaclethra macroloba</i>
 (Willd.) Ktze; <i>Pinus patula</i> ssp.
 <i>tecunumanii</i> (Eguiluz & J.P. Perry) Styles;
 <i>Virola koschnyi</i> Warb.; <i>Vochysia
 ferruginea</i> Mart.; and <i>Vochysia guatemalensis</i>
 Donn. Sm. These same phenolic compounds were measured in soil for all of
 the species except <i>Vochysia ferruginea</i>. Fine-root
 production was measured by the root ingrowth core method. To estimate soil
 organic carbon (SOC) pools (active, slow, resistant), their decay rates
 and mean residence times, we used methods described by Paul et al. (2001).
 This included long-term laboratory incubations of soil, coupled with
 refluxing soil subsamples in 6 M HCl at 115°C for 16 h on a
 controlled-temperature digestion block as. Total SOC was determined by dry
 combustion.   
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