Jacques Le Bot

The tissues of higher plants are made up largely of organic compounds which contain carbon, hydrogen, oxygen, and nitrogen. Carbon and oxygen atoms in the form of CO₂ are taken up from the atmosphere and fixed, together with hydrogen and oxygen from water, in the dark reactions of photosynthesis. Nitrogen is absorbed as ions (NO₃ ^- or NH₄ ⁺) from the soil solution, or in the case of nodulated legumes may be fixed as molecular N₂ from the atmosphere. In addition to these elements plants also contain a number of other mineral elements which are present in lower concentration but which are essential for normal plant growth. These mineral elements include potassium, phosphorus, sulfur, calcium, magnesium, iron, manganese, copper, zinc, molybdenum, boron, and chlorine (Table 1).

Density‐ and trait‐mediated indirect interactions (DMIIs and TMIIs respectively) are important drivers of community dynamics but how plant nutrients (bottom‐up effects) affect the magnitude of such indirect interactions has been scarcely addressed. To assess the impact of bottom‐up forces on indirect interactions, we carried out laboratory and greenhouse experiments manipulating plant nutrient supplies in a four‐species diamond food web consisting of a plant (tomato), two phytophagous insects (a leafminer and an aphid) and a predator (a mirid bug) attacking both herbivores. Multiple negative indirect effects of the leafminer occurred towards the aphid. The presence of its eggs negatively affected aphid population growth through increased predator abundance (DMIIs), and larval herbivory slowed down aphid development and negatively modulated aphid behaviours, for example they spent less time feeding (TMIIs), likely owing to enhanced plant chemical defences and/or decreased plant nutritional quality. Moreover, the low plant nutrient supply further magnified TMIIs. Synthesis. Abiotic factors modulated predator‐ and plant‐mediated indirect interactions among herbivorous community members. Our study highlights the importance of using a holistic approach, from foliar chemistry to community dynamics, for disentangling interspecific interactions in a simple food web.

Variation in resource input to plants triggers bottom-up effects on plant-insect herbivore interactions. However, variation in plant intrinsic traits in response to resource availability may modify the bottom-up effects. Furthermore, the consequences also may depend on the feeding strategy of insect herbivores belonging to different feeding guilds. We evaluated the performance of two insect herbivores from distinct feeding guilds, the leaf miner Tuta absoluta and the phloem feeder Bemisia tabaci. We offered the insects two tomato cultivars growing under optimal nitrogen input vs. nitrogen limitation, or under optimal water input vs. water limitation. We found that: (i) the two cultivars differed in their responses to nitrogen and water limitation by regulating primary (leaf-gas exchange related parameters, leaf nitrogen content, and leaf C/N ratio) and secondary metabolism (main defensive compounds: glycoalkaloids); (ii) for both plant cultivars, nitrogen or water limitation significantly affected T. absoluta survival and development, while B. tabaci survival was affected only by nitrogen limitation; and surprisingly (iii) plant cultivar differences did not modify the negative bottom-up effects of resource limitation on the two insect herbivores. In conclusion, the negative effects of resource limitation cascaded up to insect herbivores even though plant cultivars exhibited various adaptive traits to resource limitation.

Plant–insect interactions are strongly modified by environmental factors. This study evaluates the influence of nitrogen fertilisation on the tomato (Solanum lycopersicumL.) cv. Santa clara and the leafminer (Tuta absoluta(Meyrick), Lepidoptera: Gelechiidae). Greenhouse‐grown tomato plants were fed hydroponically on a complete nutrient solution containing either a high nitrogen concentration (HN) sustaining maximum growth or a low nitrogen concentration (LN) limiting plant growth. Insect‐free plants were compared with plants attacked byT. absoluta. Seven and 14 days after artificial oviposition leading to efficacious hatching and larvae development, we measured total carbon, nitrogen and soluble protein as well as defence compounds (phenolics, glycoalkaloids, polyphenol oxidase activity) in theHNversusLNplants. Only in theHNtreatment didT. absolutainfestation slightly impair leaf growth and induce polyphenol oxidase (PPO) activity in the foliage. Neither the concentration of phenolic compounds and proteins nor the distribution of nitrogen within the plant was affected byT. absolutainfestation. In contrast,LNnutrition impairedT. absoluta‐inducedPPOactivity. It decreased protein and total nitrogen concentration of plant organs and enhanced the accumulation of constitutive phenolics and tomatine. Moreover,LNnutrition impairedT. absolutadevelopment by notably decreasing pupal weight and lengthening the development period from egg to adult. Adjusting the level of nitrogen nutrition may thus be a means of altering the life cycle ofT. absoluta. This study provides a comprehensive dataset concerning interrelated responses of tomato plants andT. absolutato nitrogen nutrition.