Characterizing spatial variability in foliar carbon and nitrogen isotopes on Tenerife, Canary Islands

Background/Question/Methods

Tenerife, the largest and most biodiverse of the Canary Islands, has six ecologically unique biomes that roughly follow elevation along its northern (windward) and southern (leeward) slopes. Moving downslope, these are peak ecosystem, summit scrub, pine forest, broad-leaved evergreen forest, thermophilous woodlands, and sub-desert coastal scrub. The distribution of these biomes likely reflects variable moisture and temperature gradients due to the prevailing humid trade winds, the cool Canary Current, and the rain shadow created by El Teide. We document spatial variability in carbon isotope discrimination (Δ_leaf) and nitrogen isotope (δ¹⁵N) values of C₃ plants during the rainy season and assess the extent to which this variability is explained by mean annual precipitation (MAP), temperature (MAT), and relative humidity (RH) using stepwise linear regression models.

Results/Conclusions

Generally, plants from the northern slope had larger Δ_leaf values and lower δ¹⁵N values than those on the southern slope. Comparing biomes within each slope, we found that the sub-desert coastal scrub had significantly smaller Δ_leaf values, and broad-leaved evergreen forest had significantly larger Δ_leaf values than other biomes on the northern slope, while the summit scrub had significantly smaller Δ_leaf values than other biomes on the southern slope. Sub-desert coastal scrub had the highest δ¹⁵N values on both slopes. Sites within biomes were typically isotopically similar, although there were some differences among sub-desert coastal scrub and pine forest sites. Climate variables (specifically MAP) explain a considerable amount of the spatial variability in both Δ_leaf and δ¹⁵N values (R²_adjusted = 0.71 and 0.50-0.55, respectively). These results demonstrate that climate variables are closely related to isotopic variability across Tenerife. However, an expanded comparison of isotopic data across seasons or years and an investigation into seasonal and inter-annual variability in climate, nitrogen availability, soil age and the influence of fog-derived moisture on Tenerife would provide additional clarity.