Plant δ15N reflects the high landscape-scale heterogeneity of soil fertility and vegetation productivity in a Mediterranean semiarid ecosystem

• Published in: The New phytologist 2016-12, Vol.212 (4), p.1030-1043
• Main Authors: Ruiz-Navarro, Antonio, Barberá, Gonzalo G, Albaladejo, Juan, Querejeta, José I
• Format: Article
• Language: English
• Subjects: drylands; landscape heterogeneity; normalized difference vegetation index (NDVI); Pinus halepensis; Rosmarinus officinalis; soil fertility; stable isotope biogeochemistry; Stipa tenacissima
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.14091

We investigated the magnitude and drivers of spatial variability in soil and plant δ15N across the landscape in a topographically complex semiarid ecosystem. We hypothesized that large spatial heterogeneity in water availability, soil fertility and vegetation cover would be positively linked to high local-scale variability in δ15N. We measured foliar δ15N in three dominant plant species representing contrasting plant functional types (tree, shrub, grass) and mycorrhizal association types (ectomycorrhizal or arbuscular mycorrhizal). This allowed us to investigate whether δ15N responds to landscape-scale environmental heterogeneity in a consistent way across species. Leaf δ15N varied greatly within species across the landscape and was strongly spatially correlated among co-occurring individuals of the three species. Plant δ15N correlated tightly with soil δ15N and key measures of soil fertility, water availability and vegetation productivity, including soil nitrogen (N), organic carbon (C), plant-available phosphorus (P), water-holding capacity, topographic moisture indices and normalized difference vegetation index. Multiple regression models accounted for 62–83% of within-species variation in δ15N across the landscape. The tight spatial coupling and interdependence of the water, N and C cycles in drylands may allow the use of leaf δ15N as an integrative measure of variations in moisture availability, biogeochemical activity, soil fertility and vegetation productivity (or ‘site quality’) across the landscape.