Monday, August 2, 2010

PS 22-173: A new functional role for diversity in agroecosystems: Mediation of soil resource pools and weed-crop competition

Richard G. Smith, David A. Mortensen, and Matthew R. Ryan. The Pennsylvania State University


We develop a new conceptual model aimed at explaining how soil resource pool diversity may mediate competition between weeds and crops in agroecosystems.  The primary tenets of the resource pool diversity hypothesis (RPDH) are that (1) in plant communities, the intensity of inter-specific competition can depend upon the degree to which niche differentiation and resource partitioning occur among species, (2) agricultural systems are unique in that management practices, such as crop rotation, source of fertility, and weed management, result in inputs to the soil, and (3) these inputs directly or indirectly become soil resource pools from which crops and weeds may partition resources.   


The RPDH leads to the novel prediction that along a gradient of increasing cropping system diversity, yield loss due to weed-crop competition (i.e. the impact on yield per unit weed density) for soil resources should decrease.  Similarly, the degree to which crops and weeds overlap in soil resource niche breadth (which is determined by species-specific functional traits for resource acquisition), will determine the extent to which weed-crop competition weakens as resource pool diversity increases. We highlight evidence from the agricultural literature that provides strong support for components of the hypothesis.  Validation of the RPDH would have important implications across a broad range of cropping systems for the development of integrated management strategies that aim to reduce yield loss impact per unit weed plant density.