Night transpiration of peanut affects interspecific water complementarity and use efficiency in maize/peanut intercropping

Interspecific competition for soil water between species in intercropping is critical for understanding the mechanism of resource use and overyielding in a mixture cropping system, however, it is difficult to measure plant transpiration because of lacking direct and precise measuring methods. In this study, we aim to directly measure plant transpiration of each species using sap flow meters with the heat ratio method (HRM) and to explore the interspecific interactions in water use in intercropping. The experiment was conducted in 2021–2023 under semiarid rainfed conditions in Liaoning province, China. Three treatments were compared, i.e. sole maize, sole peanut, and maize/peanut intercropping with 2 maize rows maize and 4 rows peanut. The total transpiration (TTr) of intercropped maize was 53.5 % lower than that of monocropped maize; however, considering the land use proportion of maize in the intercropping (33 %), intercropped maize plants increased TTr by 39.5 %. The water productivity (WP), defined as the above ground dry matter produced by unit crop transpiration, for intercropped maize (8.04 g m−2 mm−1) was 43.9 % higher than that for the monoculture (5.60 g m−2 mm−1), due to its strong competitive ability for soil water, resulting from the border row effects in the intercropping. The average dry matter of intercropping maize was 1497 g m−2, which was 13.6 % higher than that of mono-cropping maize. For intercropped peanut, the TTr was 165 % of that in monocropped peanut, which was 148 % higher than the expected (67 %, land use proportion of peanut), which was probably due to a night transpiration in understory crops. The night sap velocity of intercropped peanut was 9.62 cm h−1 over three years (2021–2023), while the night sap flow of dominant species maize and sole peanut were close to zero. The WP of intercropped peanut (2.75 g m−2 mm−1) was 35.6 % lower than that of the monoculture (4.27 g m−2 mm−1). Intercropping increased maize transpiration and produced more above ground dry matter. However, it reduced peanut growth and caused more nighttime transpiration, likely due to changes in microclimate conditions. Our study provides a useful information to understand the mechanism of interspecific affiliations in water use in mixing cropping systems and helps farmers to optimize agronomy managements of intercrops. The results could also contribute to the improvements for evapotranspiration simulation models.