Low soil phosphorus (P) availability is presumed to limit plant growth and other ecosystems processes across a broad range of ecosystems. Ongoing increases in atmospheric CO2concentrations and reactive nitrogen (N) inputs to terrestrial ecosystems are predicted to further exacerbate P limitation globally, with potentially important consequences for the global carbon (C) cycle and the pace of climate warming. Perhaps not coincidentally, some of the most P-poor ecosystems are also characterized by very high plant diversity, high soil microbial diversity, and high diversity of functional nutrient acquisition strategies. Together, these observations suggest the likely importance of diversity in maintaining ecosystem productivity in infertile soils. However, the mechanisms that allow diverse ecosystems to remain productive in light of very low soil P supplies remain largely unknown. Here, we combine results from our own experimental work with evidence synthesized from the literature to assess the possible mechanisms that may allow diverse ecosystems to overcome low soil P fertility.
Results/Conclusions
Our analysis points to niche partitioning – i.e., the exploitation of different soil P chemicals by different plant species – as an important mechanism which may help explain how diverse ecosystems persist despite very low soil P. Perhaps not surprisingly, plant species with different nutrient acquisition strategies (e.g., ectomycorrhizae, arbuscular mycorrhizae, specialized cluster roots) seem capable of accessing different organic P pools. However, species with similar acquisition strategies (i.e., AM species) also appear to partition organic and inorganic P. For example, we found evidence that N fixing tree seedlings preferentially exploit organic P via extracellular enzymes, that non-N fixing species preferentially exploit inorganic P via AM fungi, and that regardless of the P source, N fixers may be superior competitors than non-fixers for soil P. Finally, we propose a revised conceptual model of soil P supply and partitioning that would also help reconcile high plant diversity in low fertility landscapes. Overall, our analysis suggests that soil P partitioning may create “nutrient flexibility” that allows plant communities to balance P supply with P demand. If widespread, we would predict more subtle P limitation than is currently predicted from models that rely on simple stoichiometric relationships between C, N and P supply and demand.