Benefits for nurse and facilitated plants emerge when interactions are considered along the entire life-span

Abstract

The structure of plant communities is often influenced by facilitative interactions where ‘facilitated’ plants benefit from growing associated with ‘nurse’ plants. Facilitation has been mostly studied from the facilitated plant's perspective, and bidirectional effects between nurse and facilitated plants have received less attention. We hypothesized that reciprocal benefits in plant-plant interactions may emerge when interactions are considered along the life-span of the plants involved. Over one spring, we selected five species with similar life-form and growth strategy, and using a full factorial design, we compared different fitness components along the plants’ life-span (seedling establishment, juvenile growth and reproductive investment in adult plants). We compared: a) plants growing in solitary stands and associated with other plants in vegetation patches; and b) plants that originally functioned as nurse plant (the largest plant of the vegetation patch) and as facilitated (not the largest plant of the vegetation patch). At an early developmental stage, facilitated plants growing in vegetation patches displayed higher seedling establishment and juvenile growth compared to solitary conspecific plants. At a later developmental stage, nurse plants in vegetation patches experienced higher reproductive investment (measured as flower production relative to plant size) compared to solitary plants, while the originally facilitated plants showed similar reproductive investment compared to their solitary pair of similar size. Facilitation is likely a complex interaction in which reciprocal benefits for both facilitated and nurse plants can be detected when interactions are considered along the plants’ life-span. Our results suggest that mutual benefits in plant-plant interactions could be important to sustain diversity in plant communities, but they appeared overlooked and deserve further attention.