Turnover of non-polymeric leaf lipids in a loamy grassland soil

Background Leaves constitute a large input of lipids to soil, yet comparatively little is known about the fate of leaf lipids in soil. Our aim was to explore the initial stages of degradation of leaf lipids, both the loss of intact lipid and subsequent mineralisation. We focussed on intracellular lipids - triacylglycerols implicated in storage, membrane lipids such as phospholipids and galactolipids, and pigments - because they collectively constitute more than 1% of leaf mass. Methods A mixture of U-C-13 lipids was extracted from leaves of wheat grown with (CO2)-C-13. The lipid mixture included the range of plant lipids soluble in organic solvent (e.g. free fatty acids, acylglycerols, pigments) but not polymeric lipids such as cutin and suberin. Mineralisation was deduced from (CO2)-C-13 efflux, while LC-MS examined degradation of intact C-13 lipids. Results There was no delay before lipids were mineralised. Instead, mineralisation was significant within minutes and reached a maximum within three hours. There was rapid loss (i.e. degradation) of a broad range of intact lipids including phospholipids, galactolipids, pigments (chlorophylls), and triacylglycerols. Around two-thirds of added lipid-C was respired over the course of 15 days, with one-third of lipid-C persisting in soil. Conclusions Our study indicates that non-polymeric leaf lipids degrade quickly in soil, yet a fraction of lipid-C likely persisted in degradation products and/or microbial biomass. Persistence of lipid-C probably also reflected the presence of lipids that are more resistant to degradation (e.g. phaeophytins), and a fraction of added lipid being protected (e.g. by interaction with clays).

Automated summary

This study aims to explore the degradation process of leaf lipids, and finds that non-polymeric leaf lipids degrade quickly in soil, with a fraction of lipids likely persisting in degradation products and/or microbial biomass.