Scaling nutrient limitation from individuals to ecosystems: effects of spatial heterogeneity and Darwinian selection.
Hedin, Lars*,1, Levin, Simon, 1 Princeton University, Princeton, NJ
ABSTRACT- Even though plants assimilate nutrients locally, the concept of nutrient limitation is commonly extended to scales as large as ecosystems or biomes. Traditional theories have focused on individual plant species that compete for plant-available nutrients in local environments structured by semi-chemostat mixing kinetics. However, most natural environments are spatially more complex and include recycling feedbacks between plants and detritus pools. In addition, it is now understood that nutrients enter and leave ecosystems via pathways that can be either available or unavailable to plant uptake. We here explore the implications of spatial structure and nutrient availability for the development of nutrient limitation and the maintenance of species diversity across scales of observation. We here examine the scale-dependence of plant-nutrient interactions by combining spatially explicit models with empirical observations of nutrient cycling and limitation across biomes. Our model displays qualitatively different behavior than the more limited traditional approaches. We show that plant coexistence and nutrient limitation depends on environmental structure, including the spatial and temporal dimensions of recycling feedbacks, and whether nutrients are lost via plant-available or plant-unavailable pathways. In the case of terrestrial systems, we also show the emergence of distinct strategies of plant nutrient allocation and stoichiometry - some which are optimizing and some which are dilutive at the ecosystem level. Functional diversity appears to peak in tropical biomes, in which nitrogen fixation coexists with a diversity of growth and nutritional strategies. Our results suggest that nutrient limitation and plant coexistence are emergent properties of local-scale interactions that include selection of component species.
Key words: Nutrient limitation, Evolution, Nutrient cycles
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