Plant fitness is maximized in a complex soil environment when root growth patterns respond to cues in the soil. Two cues that have been studied but are not fully understood are nutrient patches and roots of neighbors. We tested for differences between eight local, coexisting grassland species in their root responses to nutrient patches and neighbors, and tested the effect of neighbors on responses to nutrient patches. We manipulated resources and neighbor presence in a greenhouse experiment by crossing eight focal species with two soil treatments (even vs. patchy) and three neighbor treatments (alone, Plantago, Poa). Focal plants were planted in one corner of a pot (home quadrant) and neighbors in the opposite corner. Root allocation to the remaining two, shared quadrants, and precision, the degree to which roots grew in a high-nutrient quadrant compared to a low-nutrient quadrant, were calculated. In pots with neighbors, qPCR with species-specific genetic markers was used to quantify the proportion of roots belonging to each plant.
Results/Conclusions
When Plantago was placed as a neighbor, we observed that root allocation into away quadrants was greater than our predicted values, suggesting that there was an overproduction of root in response to Plantago. The greatest response occurred with Bromus and Dactylis. With Poa as a neighbor, overproduction was not observed. This suggests that species overproduce roots when sharing a pot with a strong competitor, but not with a weak competitor. Surprisingly, overproduction was stronger in a resource poor quadrant than a resource rich quadrant giving those species lower foraging precision. These results show that plants integrate information about presence of neighbors, identity of the neighbors, and resource availability to optimize their root foraging strategies.