Plant sulfur isotopic compositions are altered by marine fertilizers

Abstract

This study presents sulfur isotope compositions (δ34S) for plants grown in a series of growth chamber and field experiments under controlled conditions. Maize, beans, and squash fertilized with a marine fertilizer (seabird guano) were significantly enriched in 34S relative to the unfertilized control plants (by +4.0 to +7.2‰) in the growth chamber experiments. No 34S enrichment was detected in the plants from the field experiment, which likely relates to the recent use of ammonium sulfate fertilizer in these fields and the retention of residual sulfate with a comparatively low δ34S. The field experiment provided a basis to estimate the apparent fractionation between soil and plant S associated with uptake and assimilation (Δ34S), which ranged between −4 and −6‰ depending on the taxon and tissue. The use of marine fertilizers has the capacity to increase plant δ34S values and complicate quantitative reconstructions of ancient diet based on bulk stable isotope data.