Research article


Milagros Bueno1, Antonia Oya2, Rafael Carrasco1, Concepción Azorit1*

Online First: January 28, 2023

Secondary metabolites are related to the defensive needs of plants and could act as indicators of the degree of stress experienced by vegetation. Understanding how individual woody plants respond chemically to different degrees of browsing would provide information applied to herbivore management in the face of environmental changes. However, very few studies compare more than two levels of browsing intensity. In addition there is very little information on joint variations in leaf nutrient and polyphenol content in response to various browsing intensities in woody plants of Mediterranean ecosystems across the different seasons. We developed an experimental procedure under natural conditions in order to explore the relationships between browsing intensity and secondary metabolites and nutrients in wild olive leaves from southern Spain. We studied total polyphenolic compounds (TPC) and condensed tannins (CT) at increasing browsing intensities from 0 to 3 ranges, throughout the year (January, June and September) according to seasonal climatic variations and the trees´ biological cycle. Variations of nutritional quality were assessed through nitrogen (N) and carbon (C) content, and their ratios (C/N), (N/TPC) and (N/CT) as palatability indices. We found stress due to Mediterranean abiotic factors driving the main variation of secondary metabolite contents, its relationship with nitrogen and carbon content, and its seasonal variations. An increase in secondary metabolite content with increasing browsing intensity was detected, but seasonal climatic variations lead to an increase in secondary metabolites to a greater extent than browsing, with the interactions also important. According to our results the efficacy of secondary compounds in preventing browsing is limited, perhaps efficient at moderate browsing levels but at more intense browsing levels the effect may be the opposite, compromising plant growth and maintenance, especially in the more restrictive seasons of the Mediterranean climate and coinciding with factors such as drought. Our findings on seasonal variations in the nutritional quality-palatability of leaves are important for understanding differential feeding behavior and plant selection of ruminants in a broad context of plant-herbivore interaction useful for herbivory management in Mediterranean ecosystems.


Animal-plant interactions, Chemical plants defense, Factorial experiment in a completely randomized design, Mediterranean environmental constraints, Palatability nutritional quality, Selective browsing