Abstract Effects of climate warming on tree growth and physiology may be driven by direct thermal effects and/or by changes in soil moisture. Dioecious tree species usually show sexual spatial segregation along abiotic gradients; however, few studies have assessed the sex-specific responses to warming in dioecious trees. We investigated the sex-specific responses in growth, photosynthesis, nonstructural carbohydrate (NSC), water-use efficiency and whole-plant hydraulic conductance (KP) of the dioecious tree species Populus cathayana Rehd. under +4 °C elevated temperature with and without supplemental water. For both sexes, high-temperature treatments significantly decreased growth (height and biomass), photosynthetic rate (A), the ratio of A to dark respiration rate, stomatal conductance (gs), transpiration rate, NSC, leaf water potential and KP, but increased water-use efficiency (estimated from carbon isotope composition). Under warming with supplemental water, most traits of females did not change relative to ambient conditions, but traits of males decreased, resulting in greater sexual differences. Females showed a lower KP, and their gs and A responded more steeply with water-related traits than males. These results show that the effect of summer warming on growth and photosynthesis was driven mainly by soil moisture in female P. cathayana, while male performance was mainly related to temperature. Females may experience less thermal stress than males due to flexible water balance strategy via stomata regulation and water use.

This article is a Commentary on Housset et al., 218: 630–645.

Understanding mechanisms that generate range limits is central to knowing why species are found where they are and how they will respond to environmental change. There is growing awareness that biotic interactions play an important role in generating range limits. However, current theory and data overwhelmingly focus on abiotic drivers and antagonistic interactions. Here we explore the effect that mutualists have on their partner's range limits: the geographic “footprint” of mutualism. This footprint arises from two general processes: modification of a partner's niche through environment‐dependent fitness effects and, for a subset of mutualisms, dispersal opportunities that lead suitable habitats to be filled. We developed a conceptual framework that organizes different footprints of mutualism and the underlying mechanisms that shape them, and evaluated supporting empirical evidence from the primary literature. In the available literature, we found that the fitness benefits and dispersal opportunities provided by mutualism can extend species' ranges; conversely, the absence of mutualism can constrain species from otherwise suitable regions of their range. Most studies found that the footprint of mutualism is driven by changes in the frequency of mutualist partners from range core to range edge, whereas fewer found changes in interaction outcomes, the diversity of partners, or varying sensitivities of fitness to the effects of mutualists. We discuss these findings with respect to specialization, dependence, and intimacy of mutualism. Much remains unknown about the geographic footprint of mutualisms, leaving fruitful areas for future work. A particularly important future direction is to explore the role of mutualism during range shifts under global change, including the promotion of shifts at leading edges and persistence at trailing edges.

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