The role of partner species in the crop cocultures: A meta- analysis

Crop cocultures (the growing of one crop with another plant or animal species as partner) are known to increase yield and other ecosystem services. However, whether and how partner species (i.e., the species grown together with the focal crop) affect coculture effects is poorly understood. Here, we test the effects of partner species using a meta-analysis. Two types of cocultures (i.e., crop-crop and rice-fish cocultures) with 19 cereals as focal crops were considered, and 136 plant or animal species were involved. We found that cocultures increased focal crop yield, the land equivalent ratio and soil organic matter (SOM), and decreased insect pest infestation. Farming practices (i.e., fertilization, pesticide use, and irrigation) did not alter these coculture effects on yield, but fertilization decreased the coculture effect on SOM, and pesticide use reduced the coculture effect on pest control. Without irrigation, cocultures increased yield under drought conditions compared to normal moisture conditions. Beneficial coculture effects were obtained with both plant and animal partner species and under both patterns of partner species grown with focal crops (species addition and species replacement). Functional types of partner plants (i.e., C3, C4, legume and non-legume plants) and taxonomic groups of partner animals (i.e., crabs, fish, shrimps, and turtles) affected coculture effects on yield, SOM, and insect pests. Both multiple functional trait distance and single functional trait distance between the focal crops and plant partners correlated with coculture effect on yield. The results suggest that biological types of partner species are important in obtaining beneficial effects of cocultures.