Stress causes interspecific facilitation within a compost community

Ecological theory predicts interactions between species to become more positive under abiotic stress, while competition should prevail in benign environments. However, experimental tests of this stress gradient hypothesis natural microbial communities are lacking. We test by measuring 10 different members a bacterial community inhabiting potting compost the presence or absence toxic copper stress. found that caused significant net changes interaction signs, shifting balance towards interactions. This pattern was at least part driven copper-sensitive isolates – produced relatively small amounts metal-detoxifying siderophores benefitting from other produce extracellular detoxifying agents. As well as providing support for hypothesis, our results highlight importance community-wide public goods shaping composition.