Distinct impacts of air and root-zone temperatures on leaf and root features of cucumber seedlings: resource acquisition capacity, organ size and carbon-nitrogen balance

Both low air (Tair) and root-zone (Troot) temperatures can inhibit resource (e.g. carbon and nutrients) acquisition by leaves and roots through various aspects, such as morphology, biomass allocation and assimilation/absorption capacity. However, it is still ambiguous whether Tair and Troot influence carbon (C) and nutrient acquisition via the same approach. To this end, in this study, cucumber (Cucumis sativus L.) seedlings were hydroponically grown under treatments arranged in complete factorial combination of two levels of Tair (26/18°C and 20/12°C, day/night) and two levels of Troot (19°C and 13°C, constant). In general, both Tair and Troot affected leaf and root sizes mainly by regulating their morphology rather than biomass investment. Under low Tair conditions (20/18°C), elevated Troot (compare 19°C versus 13°C) did not influence C acquisition, but increased nitrogen (N) acquisition mainly due to an increase in relative root length, resulting in decreased C : N acquisition ratio. However, under low Troot conditions (13°C), elevated Tair (compare 26/18°C versus 20/12°C) enhanced both C and N acquisition mainly because of an increase of both C assimilation in leaves and N absorption by roots, resulting in relatively constant C : N acquisition ratio. In addition, the Tair and Troot interaction was mainly observed in relative growth rate and root growth-related variables. Our results infer that Tair and Troot have distinct impacts on resource acquisition and carbon-nitrogen balance in plants.