Use of service plants with fruit trees: Impacts on tree development and soil functioning

Agroforestry (AF) applied to fruit trees is promising for helping to cope with major global challenges, such as climate change and biodiversity loss. However, knowledge about such systems takes a very long time to acquire, and mature AF orchards in temperate regions are very scarce. To circumvent this issue, a mesocosm experiment was created in which a pear tree is accompanied by four different perennial herbaceous plants at varying modalities of density and management. One of the tested hypotheses comes from ’syntropic‘ agriculture, which suggests that intensive use of companion plants at very high density with frequent pruning can be beneficial for plant development and soil health. Our results overall show that in our (constrained) system, the growth of pear trees is not favored by the presence of companion plants, but that the competition for resources that they trigger can be entirely offset by frequent management (pruning + mulching with the chopped material). Furthermore, mineral nutrition and certain soil functions related to nutrient cycling seem to be enhanced by the presence of companion plants, even though nitrogen appears as a major potential bottleneck.