Abstract
ABSTRACT: In tropical regions, climate conditions favor fast decomposition of soil organic matter (SOM), releasing into the soil organic composts in solid, liquid, and gaseous forms with variable compositions. Dissolved organic matter (DOM), a complex mixture of thousands of organic compounds, is only a small fraction of the decomposition products; however, it is highly mobile and reactive to the soil. Therefore, DOM play a key role in soil aggregation (formation of organometallic complexes), energy source for microorganisms, as well as C storage, cycling, and provision of plant-available nutrients. DOM multifunctionality to sustain soil functions and important ecosystem services have raised global scientific interest in studies on DOM fractions. However, previous studies were conducted predominantly under temperate soil conditions in natural ecosystems. Therefore, there is paucity of information on tropical soil conditions under agricultural systems, where DOM turnover is intensified by management practices. This review synthesized information in the literature to identify and discuss the main sources, transformations, and future of DOM in soils. We also discussed the importance of this fraction in C cycling and other soil properties and processes, emphasizing agricultural systems in tropical soils. Gaps and opportunities were identified to guide future studies on DOM in tropical soils.
Highlights
Dissolved organic matter (DOM) is one of the most active and mobile C pools and has an important role in global C cycling (Kalbitz et al, 2000)
A global study showed that 80 % of C in rainfall is in the organic form (DOC), corresponding to 430 × 1012 g C yr–1, and 20 % in the inorganic form (DIC), corresponding to 80 × 1012 g C yr–1, totaling 510 × 1012 g C yr–1, from which 70 % is deposited over land (Willey et al, 2000)
Desorption varies according to the mineral and all dissolved organic carbon (DOC) adsorbed by kaolinite is completely desorbed, while only 28 to 35 % of adsorbed DOC is desorbed by Fe-oxides
Summary
Dissolved organic matter (DOM) is one of the most active and mobile C pools and has an important role in global C cycling (Kalbitz et al, 2000). DOM studies in the soil systems, especially in agricultural soils are uncommon in Brazil To illustrate this contrast between the number of publications on DOM/ DOC in Brazil and abroad, we performed a simplified bibliometric study in the Web of Science (WoS) database. The number of publications decreased further when the word “soil” was added (i.e., “DOC” and “Brazil” and “soil”), resulting in 38 publications until 2017 (Figure 2C), but only 14 publications showed results from soil experiments (Table 1), and only a few had DOC fluxes as the main variables of study or evalu-. Only one article evaluated DOC in the soil in Brazil recently (2018) (Table 1) Complementary to this search in Web of Science database, the same search was performed in the Scopus and Scielo databases (i.e., databases that comprise scientific papers published in Brazilian and some Latino-American journals). In the Scielo database, the aim was to find publications in Portuguese; the addition of the terms “dissolved organic carbon” and “soil” showed only
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