Grafting and Silicon Improve Photosynthesis and Nit rate Absorption in Melon ( Cucumis melo L.) Plants

Abstract

Grafting of Cucurbitaceae species to some rootstocks seems to be especially beneficial for the nitrogen nutrition of these plants. Moreove r, melons ( Cucumis melo L.) have been considered among those plants that could benefit fr om the addition of Silicon (Si) in the Nutrient Solution (NS). Thus, two experiments were carried out in the following order: (i) it was investigated how grafting affects nitrate ab sorption (following the disappearance of nitrates from NS), leaf water relations, leaf gas e xchange, chlorophyll parameters and antioxidant activity, and (ii) it was also assayed which of the aforementioned physiological factors could be associated with Si supply in melon plants at early developmental stage when metabolism is intense. Results revealed that g rafting and Si supply could improve photosynthesis, nitrate absorption, and biomass pro duction in melon plants with respect to non-grafted or plants not receiving extra Si. Gr afting melon on Cucurbita rootstock improved photosynthetic performance associated with higher antioxidant activity in melon leaves. Silicon supplementation results lend support to an active role of Si in biochemical processes at chloroplast level in melon s. Increased assimilation rates in grafted and Si treated plants (20 to 35%), resulted in higher nitrate depletion from the medium (17 to 18%), which boosted shoot biomass pro duction (23 to 26%) compared to the control plants. Our results suggest that grafti ng and Si supply in melon plants may lead to a better crop performance and a lower envir onmental impact of greenhouse fertigation effluents with respect to nitrate leach ing, in some instances. Keywords : Antioxidant activity, Biomass production, Gas exc hange, Hydroponic melons.