## 2 Materials and Methods  
### Experimental Procedure and Plant Material  
The present study was carried out on hydroponically-grown tomato plants (_Solanum lycopersicum_ L., cultivar nano S. Marzano) and consisted of two separate experiments, addressing different but interrelated questions. The first experiment, denoted as the'synergic, antagonistic and additive effects', aimed to determine the tomato responses to the abiotic and biotic stress, single or in combination, and their temporal evolution, and also to evaluate whether the responses to the combined stress were the results of additive, synergistic or antagonistic effects of the single stress. For this purpose, we evaluated the effects of the drought plus N deficiency (abiotic stress, ABIO), or herbivory by _T. absoluta_ (biotic stress, BIO) and their combination (combined stress, COMB) with the time of exposure (0, 1, 3 and 8 days) on the morphological (leaf fresh and dry weight), physiological [water content, photosynthesis, stomatal conductance,transpiration rate and intrinsic water use efficiency (iWUE)] and metabolic traits (VOCs profile). The fresh and dry weight of the leaf are traits directly related to the plant status, while the leaf water content was strictly correlated with the plant drought tolerance [28] but also with the plant palatability [29]. The gas exchange traits (photosynthesis, stomatal conductance, transpiration and iWUE) are involved in the plant responses to drought and N deficiency [30; 31] and further the photosynthesis is \"... a plant-driven response to the perception of stress rather than a secondary physiological response to tissue damage... \" highlighting strict interactions between photosynthesis, reactive oxygen species (ROS) and hormonal signaling pathways for the plant responses to insect herbivory [32]. Finally, the VOCs, as direct and indirect defense, are emitted by plants subject to both abiotic and biotic stress [33]. Tomato plants (_Solanum Lycopersicum_ L., cultivar nano S. Marzano) (provided by BAVICCHI S.p.a., Perugia, Italy) were exposed to the abiotic (nitrogen limitation and drought stress simulated by the use of polyethylene glycol (PEG)) and biotic stress (two first instar larvae placed in a leaf), or their combination and were considered as'stress condition'. The control plants (CTR) were maintained at optimal N concentration, no drought and herbivory, considered as the 'optimal condition'. For the morpho-physiological analysis, we used a randomized block design in which the entire experiment yielded a total of 4 (treatments) \(\times\) 4 (time of exposure) \(\times\) 2 (block) \(\times\) 2 (replications) = 64 samples. The block was introduced because we used two experiments at two different times. A completely randomized design was used for the VOCs profiling, in which the entire experiment was constituted by 4 (treatments) \(\times\) 4 (time of exposure) \(\times\) 3 (replicates) \(\times\) 3 (measurements) = 144 samples. The replicates for the VOCs were obtained in three different experiments. The second experiment, denoted as the \"within-plant phenotypic plasticity\", aimed to evaluate the within-plant variation of the tomato morpho-physiological and metabolic traits and how this within-plant phenotypic plasticity changed with the treatment conditions (optimal, abiotic, biotic and combined stress). For this aim, the foliar morpho-physiological and metabolic traits were evaluated on mature leaves located at three different positions along the shoot axes for each treatment. For each treatment, we used a completely randomized design in which the entire experiments yielded a total of 3 (leaves) \(\times\) 1 (time of exposure) \(\times\) 3 (replicates) = 9 samples. For the gas exchanges traits only, we took two measurements for each leaf, hence the experiments provided 3 (leaves) \(\times\) 1 (time of exposure) \(\times\) 2 (measurements) \(\times\) 4 replicates = 24 samples. The Figure S1 reported the experimental protocol schedule of both experiments including the plant growth, treatments and analysis.