Cutin and suberin in mixed-wood boreal forest plants and their use as markers for origin of soil organic matter

Abstract

Quantifying above and belowground inputs to soil organic matter is important to assess forest soil health and to develop practices that increase the soil organic matter present in forest soils. Cutin and suberin are biopolymers found in leaves and roots, respectively, that protect plants from desiccation. Due to their specific locations within plant tissues, the presence of the polymers cutin and suberin in the soil is used to confirm the contributions of these leaves and roots to organic matter. Specifically, the identity of the monomers comprising these biopolymers is used to infer the contributions of leaves and roots to organic matter. However, previous studies have identified monomers in tissues of leaves or roots that do not concur with published lists of markers, highlighting the importance of using region- and species-specific markers. Cutin and suberin were extracted from leaf, root, and bark samples from the eight most dominant species in a boreal mixed-wood stand in Alberta using hydrolysis. Additionally, I sampled soils from the interface of the organic and mineral soil, treated with the same hydrolysis process to investigate if the monomers present in the plant tissue samples were also detectable in soils. The monomers were identified using GCMS and compared to published lists of cutin and suberin markers. Across the roots and leaves of the eight species, a total of 142 monomers were identified. In soil samples, only 48 monomers were observed, five of which were not present in any of the plant tissues. Due to their presence in other plant tissues aside from leaves and roots, and in microorganisms, several classes of compounds identified in this study cannot determine the origin of soil organic matter. When compared to published lists of cutin and suberin markers, I found that while a select number of markers held true for the samples analysed in this study, others are not appropriate for use in study areas with vegetation similar to the one in this study due to their presence in multiple tissue types. The inconsistencies between the monomers identified in this study and those in published reports highlight the importance of using cutin and suberin markers specific to the dominant species of plants present in the area of interest.