Aridity threshold and grazing effects revealed by ecological interaction networks between leaf, root, and biomass function

•Aridity threshold were observed in the ecological interaction network.•The interaction of traits between leaf and root increased above the threshold.•The control effect of root on other plant traits increased along aridity gradient.•The grazing effect on ecosystem changed with key plant traits of interaction network. Increasing aridity and grazing have multifaceted effects on the ecosystem, of which plant traits interact with each other to coregulate the productivity function including above- and below- ground compartments of plant. The ecological interaction network among plant traits could reflect how ecosystem interact with, influence, and respond to environment change. In this study, the interaction network between leaf, root, and biomass function was revealed to indicate systemic ecosystem response to increasing aridity and grazing by sampling in enclosed plots along the aridity gradient and in neighboring grazing plots of China drylands. Systemic and abrupt changes in the network relationship between leaf, root, and biomass were observed with a threshold value of 1-AI (aridity index) ∼ 0.8. The control effect of roots on other traits and the interaction of leaf and root compartments increased in the opposite direction above the threshold. The change in the relative importance of key traits with increasing aridity caused the different grazing effects. Grazing decreased the leaf area in the area with1-AI ∼ 0.6, whereas it increased the effect of roots in the area with 1-AI ∼ 0.8, thus promoting the interaction of functional traits. This result suggests the essential role of the interaction network between plant traits in ecosystem response to environmental change, which could indicate the ecosystem change in a holistic perspective under global change.