PLANT‐DERIVED MACROMOLECULES IN THE SOIL

As the primary producer in terrestrial ecosystems, plants are the ultimate source of organic carbon supplied into soils and fueling microbial decomposition. Hence, plants play a key role in the formation and accumulation of soil organic matter. However, due to the complexity of plant-derived organic matter and soil processes, the fate, persistence and storage of carbon in the form of plant-derived molecules in the soil remain poorly understood. Plant-derived organic matter is composed of a wide array of organic molecules from simple organic acids and carbohydrates to polymeric molecules such as cellulose, lignin and proteins, etc. These molecules have distinct chemical structures, physiochemical properties, interactions with soil minerals and propensities to associate with soil aggregates. Such characteristics, coupled with soil environmental conditions and microbial capacities, play a decisive role on the stability and biodegradability of plant-derived molecules in the soil. In this chapter, I summarize the properties and behavior of major plant macromolecules as inputs into soils and describe various molecular-level methods to trace the transformation and turnover of plant molecules in soils, with a specific emphasis on biomarker and isotopic analyses that are specific to plant-derived molecules. Major soil processes that affect the persistence of different plant-derived compounds are also reviewed, with several aspects summarized for prioritizing future research in order to improve our understanding on the fate of plant-derived organic matter and its contribution to soil carbon storage.