Tree species of wet tropical forests differ in their tissue biochemistry and effects on soil carbon dynamics

Authors: RUSSELL, ANN - Iowa State University; MAREK, RACHEL - University Of Iowa; Olk, Daniel - Dan

Submitted to: Frontiers in Forests and Global Change
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2021
Publication Date: 5/5/2021
Citation: Russell, A.E., Marek, R.F., Olk, D.C. 2021. Tree species of wet tropical forests differ in their tissue biochemistry and effects on soil carbon dynamics. Frontiers in Forests and Global Change. 4. Article 674213. https://doi.org/10.3389/ffgc.2021.674213.
DOI: https://doi.org/10.3389/ffgc.2021.674213

Interpretive Summary: Soil organic matter plays important roles in several soil functions, yet we understand only partially what controls its formation and accumulation in soil. Here we studied the factors that affected the amount and type of soil organic matter that accumulated in long-term forestry plots, each having a different type of tree. We found that the amounts of roots produced by the trees and their chemical contents were among the most important factors that affected properties of the accumulated soil organic matter. Other factors were tree effects on soil pH and the physical structure of soil. These results will help better understand how forest management can improve soil properties and organic matter accumulation. The results will be of value to forest managers, soil scientists who study organic matter accumulation, and scientists who study global carbon cycling.

Technical Abstract: 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 effect on soil dynamics, is 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 <0.0001 for all tests). Cinnamyls and syringyls in soil differed significantly among species (p = 0.0408, 0.0071, respectively), whereas vanillyls did not (p = 0.83). The degree of decomposition of syringyls and vanillyls 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 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. At least four factors explained the differences among tree species in SOC pools and dynamics, differences in: (1) Fine-root detrital inputs to the soil pool; (2) Fine-root syringyl concentrations; (3) Effects on soil pH; and (4) Effects on macroaggregate structure. Our study illustrates that a trait-based approach can provide a process-based understanding of how trees species can influence SOC dynamics, and the consequences for ecosystem properties such as SOC pools.