Abstract
Plants in arid environments are exposed to drought stress but also may suffer herbivory by large mammals. Since this may affect plant fitness, plants may display different responses and/or defences, developing tolerance and resistance mechanisms. In this work, we experimentally investigated how drought and herbivory affect seedling growth of a forage species, Atriplex lampa, from Patagonian Monte Desert. In addition, we evaluated in a greenhouse whether simulated herbivory stress affects the presence of aphids, and in the field whether herbivory by large mammals affects insect granivory in this species. We found that drought did not affect the species growth, suggesting toleration or adaptation to drought condition, while herbivory reduced its growth. In addition, we found that a higher level of stress on seedlings and, to minor extent, on parent (seed origin) is related to a lower presence of aphids on the seedlings growth in the greenhouses. However, at field conditions, we observed that the higher the stocking rate, the higher the insect granivory. The results from the greenhouse experiment suggest that this species develops some kind of defences or a decrease in aphid attraction caused by drought stress and the simulated herbivory. In contrast, field results imply that this species does not develop any defences or that they are mainly found in stems and leaves, but not in fruits. Our results show that A. lampa has developed drought tolerance strategies but is vulnerable to herbivory. These stress factors could be exerting selection pressures on A. lampa that affect evolutionary and ecological processes and, consequently, its ecosystem services as a key forage species in the Monte Region.
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