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

ABSTRACTBoth 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 whetherTairandTrootinfluence carbon (C) and nutrient acquisition via the same approach. To this end, in this study, cucumber (Cucumis sativusL.) seedlings were hydroponically grown under treatments arranged in complete factorial combination of two levels ofTair(26/18°C and 20/12°C, day/night) and two levels ofTroot(19°C and 13°C, constant). In general, bothTairandTrootaffected leaf and root sizes mainly by regulating their morphology rather than biomass investment. Under lowTairconditions (20/18°C), elevatedTroot(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 lowTrootconditions (13°C), elevatedTair(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, theTairandTrootinteraction was mainly observed in relative growth rate and root growth-related variables. Our results infer thatTairandTroothave distinct impacts on resource acquisition and carbon-nitrogen balance in plants.