Leaf age does not justify its early removal in Carica papaya L

Abstract

AbstractThis study evaluated gas exchange and therefore sink/source condition of papaya leaves as they age in order to determine the right moment for leaf blade removal under two different strategies of climate control in greenhouses of Almería (SE Spain): Passive control (PCC; climate control of the greenhouse consisting of natural ventilation by only lateral and roof windows) versus active control (ACC; in addition to the natural ventilation, the greenhouse also incorporated a nebulization and a heating system). The effects of improved climate control were determined on papaya leaves distributed in five different positions in the canopy: S1, S2, S3, S4, S5, where S1 represented the youngest leaf, whereas S5 was the oldest (senescent) leaf present in the plant canopy. We observed that all age leaves presented positive values of net photosynthesis (Anet) despite reduced light availability under plastic greenhouses. In order to separate the effects of limited light availability from the leaf age (position in the canopy), we then repeated gas exchange measurements using artificial light (400 μmol m2 s−1) equal for all treatments and observed that the leaves of the ACC increased up to 96% their photosynthetic rates with respect to natural light. ACC plants presented also higher Anet/gs, showing better intrinsic water use efficiency. Based on these results, we discourage blade removal of papaya leaves when light availability above 400 μmol m2 s−1 is assured by correct plant spacing and cultural management.