Julia Cooke

One function of plant Si is ameliorating stress, including drought and salinity stress, which can induce active Si uptake in addition to passive uptake via transpiration. However, the interactions and feedbacks between stress, water movement and Si uptake remain unknown. To examine this gap, we compiled papers reporting transpiration and/or stomatal conductance of plants exposed to stresses while varying Si availability. Our meta‐analysis (34 studies, excluding rice) showed that stress alters the role of Si in controlling water movement across diverse plant groups. Increased Si availability significantly increased water movement in stressed plants, particularly stomatal conductance ( p < 0.001, k = 84) in plants exposed to salinity ( p < 0.05, k = 20) and drought ( p < 0.05, k = 45) stress. This signal of increased conductance was most apparent in C4 plants ( p < 0.001, k = 41) and Poales ( p < 0.001, k = 47). These findings have implications for plants under increasing water and salinity stress, particularly for Poales , where survival in affected ecosystems could be mediated by soil Si availability, and in agricultural systems, supplying Si to water‐stressed plants could increase productivity. Intriguingly, Si addition to unstressed plants had no consistent impact on water movement, with reduction of water movement with Si addition to unstressed plants in 50% of studies, mostly those involving non‐Poales species. This is an important first broad‐scale Si cost quantification, as the costs of Si for plants have remained stubbornly mysterious, hampering evolutionary and functional understanding of plant Si use. Read the free Plain Language Summary for this article on the Journal blog.