气候变化领域集成服务门户

Natural abundance of the stable nitrogen (N) isotope N-15 can elucidate shifts in plant N acquisition and ecosystem N cycling following disturbance events. This study examined the potential relationship between foliar delta N-15 and depth of plant N acquisition (surface organic vs. mineral soil) and nitrification as conifer stands develop following stand-replacing wildfire.

We measured foliar delta N-15 along an 18-site chronosequence of jack pine (Pinus banksiana) stands, 1 to 72 years in age post-wildfire. Foliar delta N-15 was compared to total delta N-15 of the organic (Oe + Oa) and mineral (0-15 cm) soil horizons, and organic horizon N mineralization and nitrification as functions of total mineralization.

Foliar delta N-15 declined with stand age, yet wildfire effects were heterogeneous. Jack pine seedlings on burned, mineral soil patches in the youngest stand were significantly more enriched than those on unburned, organic patches (P = 0.007). High foliar values in the youngest stands relative to mineral-horizon delta N-15 indicate that nitrification also likely contributed to seedling enrichment.

Our results suggest jack pine seedlings on burned patches obtain N from the mineral soil with potentially high nitrification rates, whereas seedlings on unburned patches and increasingly N-limited, mature jack pine acquire relatively more N from organic horizons.