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

ABSTRACT

Both low air (T_air) and root-zone (T_root) 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 T_air and T_root 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 T_air (26/18°C and 20/12°C, day/night) and two levels of T_root (19°C and 13°C, constant). In general, both T_air and T_root affected leaf and root sizes mainly by regulating their morphology rather than biomass investment. Under low T_air conditions (20/18°C), elevated T_root (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 T_root conditions (13°C), elevated T_air (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 T_air and T_root interaction was mainly observed in relative growth rate and root growth-related variables. Our results infer that T_air and T_root have distinct impacts on resource acquisition and carbon-nitrogen balance in plants.