COS 163-1 - Leaf sediment coatings reduce photosynthesis in a Spartina salt marsh

Abstract: Salt marshes are widely distributed ecosystems that provide abundant ecosystem services globally. Sea level rise is an increasing threat to these tidally influenced ecosystems and a great deal of research focuses on how marshes can build soil elevation to survive increasing water levels. A primary mode of elevation gain is suspended sediment deposition and subsequent accretion, which is aided by plant biomass that reduces turbulent energy in the water column that keeps sediments suspended. Thus, suspended sediment is normally represented as a positive influence on marsh accretion in models that predict marsh persistence in response to sea level. Here we present new evidence that suspended sediments contribute to forming coatings on Spartina alterniflora leaves, and that this coating reduces plant photosynthesis. Supporting observations are presented at the leaf and canopy scale using cuvette and eddy covariance measurements, respectively. Leaf coating development is largely modulated by rain, that is, coatings build during rain free periods and are rinsed by rain. This is significant because it implies that drought regulates a soil-plant linkage with the potential to reduce plant productivity. It is possible that this previously undescribed mechanisms could account for a portion of the established relationship between precipitation and marsh productivity. Our results have significant implications for detecting marsh productivity via remote sensing, since sediments obscure the color or reflectance information in underlying leaves. Further work is needed to determine whether the reduction in photosynthesis is significant enough to affect annual scale biomass accumulation and the detailed composition and formation mechanisms of these coatings.