Climate, mineralogy, and depth control soil organic matter composition and soil carbon storage in Hawaiian tropical montane wet forests

Tayo, Malissa Ann Gueco

Climate, mineralogy, and depth control soil organic matter composition and soil carbon storage in Hawaiian tropical montane wet forests

Files

Tayo_hawii_0085O_12016.pdf (2.12 MB)

Date

2023

Authors

Tayo, Malissa Ann Gueco

Advisor

Litton, Creighton M.
Giardina, Christian P.

Department

Natural Resources and Environmental Management

Abstract

The formation and stabilization of soil carbon (C) in tropical forests are key processes influencing the global C cycle. Both climate and mineralogy are known to exert important control over these processes, especially at depth in tropical soils. However, recent work suggests plant litter quality-controlled microbial assimilation also plays an important role in the stabilization of soil C. The Microbial Efficiency Matrix Stabilization (MEMS) framework describes the formation and stabilization of soil organic matter (SOM) by identifying significant C pools within soil and linking those pools to plant quality input pools. The MEMS framework, however, fails to incorporate important emerging concepts such as mineralogical content. In this study, I utilized a highly constrained (constant vegetation, geology/substrate/soils, soil moisture, and disturbance history), long-term, whole-ecosystem mean annual temperature (MAT) gradient spanning 4.3°C located in Hawaiian tropical montane wet forests to evaluate the controls on soil C storage and formation. To do this, I measured above- and belowground plant litter quality pools, and SOM composition, mineralogy, and age to 1 m depth across this MAT gradient. Overall, the data presented here show varying support of the tested hypothesis that all examined controls collectively control complex SOM C dynamics and storage in tropical montane wet forests. Multi-model averaging revealed that the combination of MAT, depth, and mineralogy best explain changes in SOM C pool composition and age. Specifically, these variables explained 82% of the variation in SOM composition for light-particulate organic matter (LPOM), 40% for heavy-POM (HPOM), and 56% for mineral-associated OM (MAOM). Specifically, the primary mineral displaying most control over the C stock of the LPOM, HPOM, and MAOM, respectively, was poorly- and non-crystalline minerals (PNCM), crystalline iron (Fe) and organo-aluminum. With increasing MAT, LPOM C declined in the surface soils. Deeper within the soil profile, MAOM C, a critical component of longer-term soil C storage, decreased. However, an inverse relationship was observed for HPOM C indicating transitions of mineral control from PNCM to crystalline Fe. This highlight HPOM fraction as a primary control on stable SOM storage with increasing MAT and depth in mineral rich tropical ecosystems. All of these result together support the need to create a new modeling framework (e.g., in MEMS) to account for the formation of mineral rich tropical SOM that includes: the impact of changes in MAT on mineralogy; linking plant quality to surface soils and mineralogy to deep SOM formation; quantifying all important SOM fractions to depth and, importantly, separating LPOM and HPOM; utilizing new data analysis methods that model all of these important factors (i.e., climate, plant quality and quantity, mineralogy, depth).

Keywords

Biogeochemistry, climate change, soil carbon, soil organic matter fractions, tropical soils

URI

https://hdl.handle.net/10125/107941

Extent

82 pages

Rights

All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.

Collections

M.S. - Natural Resources and Environmental Management

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