Peláez Marta, López-Sánchez Aida, Fernandes Geraldo Wilson, Dirzo Rodolfo, Rodríguez-Calcerrada Jesús, Perea Ramón
Plant and Animal EcoLogy LAb (PAELLA), Centro para la Conservación de la Biodiversidad y el Desarrollo Sostenible (CBDS), Universidad Politécnica de Madrid, C/ José Antonio Novais 10, Madrid, 28040, Spain.
Departments of Biology and Earth Systems Science, Stanford University, 327 Campus Drive, Stanford, CA 94305, USA.
Ann Bot. 2025 Feb 8;135(1-2):341-356. doi: 10.1093/aob/mcae178.
Anthropogenic disturbances are causing a co-occurring increase in biotic (ungulate herbivory) and abiotic (drought) stressors, threatening plant reproduction in oak-dominated ecosystems. However, could herbivory compensate for the adverse impact of drought by reducing evapotranspiration? Thus, we investigated the isolated and joint effects of herbivory and drought on oak seedlings of two contrasting Mediterranean species that differ in leaf habit and drought resistance.
California oak seedlings from the evergreen, and more drought-resistant, Quercus agrifolia and the deciduous Q. lobata (n = 387) were assigned to a fully crossed factorial design with herbivory and drought as stress factors. Seedlings were assigned in a glasshouse to three to four clipping levels simulating herbivory and three to four watering levels, depending on the species. We measured survival, growth and leaf attributes (chlorophyll, secondary metabolites, leaf area and weight) once a month (May-September) and harvested above- and below-ground biomass at the end of the growing season.
For both oak species, simulated herbivory enhanced seedling survival during severe drought or delayed its adverse effects, probably due to reduced transpiration resulting from herbivory-induced leaf area reduction and compensatory root growth. Seedlings from the deciduous, and less drought-resistant species benefited from herbivory at lower levels of water stress, suggesting different response across species. We also found complex interactions between herbivory and drought on their impact on leaf attributes. In contrast to chlorophyll content which was not affected by herbivory, anthocyanins increased with herbivory - although water stress reduced differences in anthocyanins due to herbivory.
Herbivory seems to allow Mediterranean oak seedlings to withstand summer drought, potentially alleviating a key bottleneck in the oak recruitment process. Our study highlights the need to consider ontogenetic stages and species-specific traits in understanding complex relationships between herbivory and drought stressors for the persistence and restoration of multi-species oak savannas.
人为干扰正导致生物（有蹄类食草动物啃食）和非生物（干旱）胁迫因子同时增加，威胁着以橡树为主的生态系统中的植物繁殖。然而，食草作用能否通过减少蒸散来补偿干旱的不利影响呢？因此，我们研究了食草作用和干旱对两种叶习性和抗旱性不同的地中海地区橡树幼苗的单独及联合影响。
将常绿且抗旱性更强的加州栎（Quercus agrifolia）和落叶的加州白栎（Q. lobata）的幼苗（n = 387）分配到一个完全交叉的析因设计中，以食草作用和干旱作为胁迫因子。根据物种不同，在温室中将幼苗分配到三到四个模拟食草作用的修剪水平和三到四个浇水水平。我们每月（5月至9月）测量一次存活率、生长情况和叶片属性（叶绿素、次生代谢产物、叶面积和重量），并在生长季节结束时收获地上和地下生物量。
对于这两种橡树，模拟食草作用提高了严重干旱期间的幼苗存活率或延迟了其不利影响，这可能是由于食草作用导致叶面积减少和根系补偿性生长从而降低了蒸腾作用。来自落叶且抗旱性较差物种的幼苗在较低水平的水分胁迫下从食草作用中受益，这表明不同物种的反应不同。我们还发现食草作用和干旱对叶片属性的影响之间存在复杂的相互作用。与不受食草作用影响的叶绿素含量不同，花青素含量随食草作用增加——尽管水分胁迫减少了因食草作用导致的花青素差异。
食草作用似乎使地中海地区的橡树幼苗能够抵御夏季干旱，这可能缓解了橡树更新过程中的一个关键瓶颈。我们的研究强调，在理解食草作用和干旱胁迫因子之间的复杂关系以实现多物种橡树稀树草原的存续和恢复时，需要考虑个体发育阶段和物种特异性特征。
