Dados do Trabalho

Título

MONITORING WATER EXTRACTABLE ORGANIC MATTER DYNAMICS DURING SOIL INCUBATION USING UV-VIS SPECTROSCOPY

Resumo

Water-extractable organic matter (WEOM) is a dynamic fraction of soil organic matter (SOM) serving as a readily available substrate for microorganisms. Understanding the fate of WEOM is crucial for unraveling the processes driving SOM persistence. Here we employed UV-Vis spectroscopy to monitor WEOM during a soil incubation study. Two soils from similar lithology (Irati Formation sedimentary rocks) but exhibiting different degrees of development (Embryonic soil: Spolic Technosol; Mature soil: Rhodic Lixisol) were investigated. Over a 150-day period, we measured soil respiration rates while determining WEOM concentrations, SUVA254 and A2/A3. SUVA254 represents the degree of aromaticity, while A2/A3 serves as a proxy for molecular weight, with a higher A2/A3 ratio indicating lower molecular weight. The mature soil had 1.7-fold higher respiration rate than the embryonic soil, with both decreasing over time. The A2/A3 ratio increased from 2.4 and 3.7 to 5.9 and 6.1 within the first 15 days, followed by a decline to 4.6 and 3.6 after 150 days, for mature and embryonic soils, respectively. The SUVA254 initially started at similar values for both soils (~2 L mg C-1 m-1), but the embryonic soil exhibited higher values in subsequent days. Principal component analysis revealed a strong positive correlation between respiration rate and WEOM concentration, while a negative correlation was observed between respiration rate and aromaticity. However, no significant correlation was found between respiration rate and molecular weight, likely due to the erratic behavior of A2/A3. The findings indicate that microorganisms initially consumed less aromatic and higher molecular weight molecules. While aromaticity continued to increase, the mean molecular weight initially decreased and gradually rose throughout the incubation period. Our study highlights the intricate dynamics of WEOM during microbial decomposition and offers insights into the fate of this labile fraction of SOM.

Palavras-chave

Soil organic matter, Dissolved organic carbon, Soil respiration

Instituição financiadora

FAPESP (process number: 2019/18324-3)

Agradecimentos

The authors would like to express their gratitude to the CLACS organizing committee.