Abstract
Biotic and abiotic stressors commonly co-occur in plant communities and influence interactions between plants. However, their combined effects on plant interactions have not been widely studied and are still unclear. Here, we assessed the balance of interactions between neighboring plants along a grazing gradient and under two water regimes. We conducted a three-year-field experiment in semi-arid central Argentina with transplants of the dominant palatable grass Piptochaetium napostaense growing in Baccharis ulicina and open microsites across a gradient of grazing pressure. Additionally, we established a water addition treatment along that gradient. We recorded herbivory, size, and fecundity of P. napostaense. During the first two years, P. napostaense was consumed less and was larger below Baccharis than in the open. These differences were greatest under high grazing pressure. Differences in fecundity between microsites were only detected under high and medium grazing pressure in the first two years. In the third year, Baccharis lost their leaves for unclear reasons and provided poor herbivory protection; hence, P. napostaense plants in Baccharis were larger than those in the open only under medium and low grazing pressure, and there were no differences in fecundity between microsites under any grazing condition. Water additions exerted no effect on plant interactions. The balance of interactions changed from positive under heavy grazing to neutral at low and no grazing and water availability did not alter that balance. We conclude that herbivore pressure is an important driver of the balance of plant interactions in semi-arid environments.
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Acknowledgements
We would like to express our gratitude to Dr. Enrique Chaneton for his insightful contribution to the early development of this research. We are grateful to E. Brandoni-Bescos and J. A. Cock for their support throughout the three years of the study. We also thank A. Lozza, C. Baudino, J. Larrazabal, L. Ramírez-Brumatti, N. Icasatti, M. Chiuffo for providing field assistance. We appreciate the generosity of R. and C. Ruiz for allowing us to conduct this study in their ranch. We thank J.H. Cock for his valuable assistance in refining the narrative. This work was supported by the Neotropical Grassland Conservancy [no grant number], Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa [grant numbers CN219, B15], and Consejo Nacional de Investigaciones Científicas y Técnicas [grant number PIP11420110100206].
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MCC and JLH conceived and designed the study. MCC collected and analyzed the data. MCC and JLH wrote the manuscript.
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Cock, M.C., Hierro, J.L. Plant interactions balance under biotic and abiotic stressors: the importance of herbivory in semi-arid ecosystems. Oecologia 194, 685–694 (2020). https://doi.org/10.1007/s00442-020-04789-4
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DOI: https://doi.org/10.1007/s00442-020-04789-4