Coupling between tree water use and calcium accumulation

Although it is well-known that transpiration is the major driving force for plant nutrient uptake/transport, the coupling between these two processes has not been well-established. Calcium (Ca) is a good candidate to evaluate the coupling between transpiration (water use) and nutrient accumulation as Ca uptake is a passive process without relocation once incorporated, thus avoiding the confounding effects of active regulation and translocation. Here we developed a novel theoretical equation to use soil-to-plant calcium ratio (SCa/BCa) to predict plant water use efficiency (WUE) derived from δ13C. We tested this relationship with two conifer and one angiosperm tree species across their native habitats in China and a controlled greenhouse experiment with soil Ca concentrations manipulated. A linear relationship between WUE and SCa/BCa was found in all three species across their natural distribution ranges and in the greenhouse experiment. SCa/BCa was also strongly related to the precipita...