Regeneration traits reveal new and expanded dimensions of the plant functional niche

Julie E. Larson, Department of Ecology and Evolutionary Biology; Institute of Arctic and Alpine Research, University of Colorado, Boulder, Boulder, CO and Katharine N. Suding, Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO

Background/Question/Methods
Differences in species’ niches, or ecological strategies, have long been used to understand when, where, and how plants coexist in communities. Most recently, plant functional traits have been used to describe key tradeoffs in ecological strategies (e.g., leaves that can acquire resources quickly versus those that conserve them) and characterize species’ positions in functional niche space (e.g., ‘fast’ species versus ‘slow’ species). Despite the critical role of plant regeneration in differentiating ecological strategies, however, regeneration traits remain rarely and poorly integrated as dimensions of trait space that characterize the plant functional niche.
Our objective is to explore how regeneration traits meaningfully expand or alter our understanding of the plant niche. We collected traits related to seed-based regeneration and recruitment (e.g., seed production, dormancy, germination, and establishment) for dozens of grassland species, asking: Q1) Do seed and seedling regeneration traits expand the area of trait space occupied by species, and/or create new dimensionality? Q2) How does a functional niche defined by traits across the life cycle (i.e. an ontogenetically-integrated niche [OIN]) add to one defined only by mature plant traits? Q3) Which aspects of the OIN might be important for seedbank and vegetation abundance patterns?
Results/Conclusions
Emergent seedlings generally had more acquisitive leaf attributes than mature plants, expanding the vegetative niche consistently across species; in contrast, root traits tended to shift more variably over development, expanding the vegetative niche in species-dependent ways. Separately, we identified several trait dimensions related to seed function, the strongest of which separated large-seed species from those with light-sensitive and persistent seeds. A second axis tended to separate taller species (dispersal in space) from those with more water-sensitive and/or dormant seeds (dispersal in time). When vegetative and seed dimensions were integrated into a single OIN, we found surprising alignment between several aspects of regeneration and mature plant function that added a meaningful regenerative element to classic niche schemes (e.g., Grime’s CSR; fast-slow spectrum). The most integrated axis was linked to patterns of seedbank abundance, suggesting that these dimensions may have realized functionality in regeneration.
While there are many ways for the regeneration niche to expand or add dimensions to the plant functional niche, there may also be surprising patterns of alignment between regeneration and existing niche schemes. Given the potential impact of regeneration in plant community turnover and climate adaptation, we must expand efforts to integrate the regeneration niche into functional ecology.