Isotopic constraints on plant nitrogen acquisition strategies during ecosystem retrogression

• Published in: Oecologia Vol. 192; no. 3; pp. 603 - 614
• Main Authors: Dynarski, Katherine A., Houlton, Benjamin Z.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Science + Business Media 01.03.2020; Springer Berlin Heidelberg; Springer; Springer Nature B.V
• Subjects: Bacteria; Biomedical and Life Sciences; Ecology; Ecosystem; Ecosystems; Ectomycorrhizas; Fertility; Fixing; Foraging; Forest ecosystems; Functional groups; Fungi; HIGHLIGHTED STUDENT RESEARCH; Historic sites; Hydrology/Water Resources; Life Sciences; Mineral nutrients; Mycorrhizae; Nitrogen; Nutrient availability; Nutrient sources; Nutrients; Organic chemistry; Organic soils; Phosphorus; Plant Roots; Plant Sciences; Plants; Soil; Soil fertility; Soil nutrients; Soils; Terrestrial ecosystems; Mycorrhizal fungi; Nutrient limitation; N fixation; Stable isotopes; Ecosystem retrogression
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-020-04606-y

Plant root associations with microbes such as mycorrhizal fungi or N-fixing bacteria enable ecosystems to tap pools of nitrogen (N) that might otherwise be inaccessible, including atmospheric N or N in large soil organic molecules. Such microbially assisted N-foraging strategies may be particularly important in late-successional retrogressive ecosystems where productivity is low and soil nutrients are scarce. Here, we use natural N-stable isotopic composition to constrain pathways of N supplies to different plant functional groups across a well-studied natural soil fertility gradient that includes a highly retrogressive stage. We demonstrate that ectomycorrhizal fungi, ericoid mycorrhizal fungi, and N-fixing bacteria support forest N supplies at all stages of ecosystem succession, from relatively young, N-rich/phosphorus (P)-rich sites, to ancient sites (ca. 500 ky) where both N supplies and P supplies are exceedingly low. Microbially mediated N sources are most important in older ecosystems with very low soil nutrient availability, accounting for 75–96% of foliar N at the oldest, least fertile sites. These isotopically ground findings point to the key role of plant–microbe associations in shaping ecosystem processes and functioning, particularly in retrogressive-phase forest ecosystems.