Seminar: Craig See

Описание: 2025 Spring Seminar Series
Department of Soil, Water, and Climate at the University of Minnesota

Seminar: Craig See, PhD | Researcher, UMN Agronomy & Plant Genetics | Nitrogen is mobile, but phosphorus is set in stone: are soil N stocks driven by P availability in terrestrial ecosystems?

Abstract: Nitrogen (N) and phosphorus (P) availability co-limit critical carbon cycling processes, and N and P cycles are inherently coupled by biological stoichiometry. However, the N cycle is more open than the P cycle in most terrestrial systems. New N enters soil through multiple pathways, and is readily lost when it is in excess of biological demand. In contrast, new biologically available P is supplied from slower cycling P fractions already present in soils, and is largely retained when P availability exceeds biological demand. Consequently, as N and P cycles synchronize over successional timescales, spatial patterns of soil N accumulation are likely to reflect the pre-existing spatial distribution of soil P. To test this hypothesis, we compiled a dataset of soil P fractions from mineral soils across sites in the US LTER network, and compared them with co located estimates of total soil N. We found consistent within-site correlations between total P and total N across a diverse suite of ecosystems which varied widely in soil age and P content (tropical forests, temperate forests, arid grasslands, tundra). Critically, similar positive correlations were present between total soil N and slowly-cycling (mineral) P fractions. Thus, while the observed coupling of N and P in these ecosystems may proximately reflect spatial differences in organic matter accumulation, our findings demonstrate that this pattern is ultimately driven by natural variation in geochemical P across these landscapes. This supports the emerging theory that rates of ecosystem N cycling often adjust to the P cycle in terrestrial soils, highlighting the potential importance of soil P as a constraint on ecosystem responses to global change.