Testing the interaction between inter-sexual competition and phosphorus availability in a dioecious grass

Spatial segregation of the sexes (SSS) occurs in many dioecious plants, usually along an environmental gradient. However, little data is available on how male and female plants of species with SSS respond to environmental conditions along these gradients. We examined whether male and female plants of Distichlis spicata (L.) Greene, a dioecious grass species that exhibits extreme SSS along a phosphorus gradient, differed in their responses to phosphorus and competition treatments in the greenhouse. We found little evidence that phosphorus plays a role in SSS in D. spicata. However, supporting earlier work, we found that plants subject to inter-sexual competition were significantly more likely to have high root/shoot ratios than plants subject to intra-sexual competition, suggesting that competition is an important driver of SSS in this species.