Evrona Mistletoe parasitism

Effects In desert ecosystems, the long-term soil effects of oil contamination can weaken trees, and hemiparasitic mistletoes may exacerbate this stress. We investigated how terrestrial oil spills influence host condition and mistletoe parasitism in acacia woodlands. The Evrona Nature Reserve (southern Arava, Israel) offers a time-staggered natural experiment, with sites affected by pipeline spills in 1975 and 2014 and nearby undisturbed controls. In March 2024, we surveyed Acacia raddiana and Vachellia tortilis, assessing host vitality, counting Plicosepalus acaciae infection sites, estimating the proportion of parasitized foliage from photographs, and quantifying the distance to neighboring trees. Using GLMs, we found that host condition was lower in spill-affected areas, and V. tortilis consistently exhibited poorer condition than A. raddiana. Parasitism showed a clear temporal trend, i.e., infection intensity and parasitized foliage peaked 10 years after a spill – when hosts remained present but physiologically weakened – and were lowest after 50 years, reflecting reduced host availability rather than site recovery. Greater neighborhood distance reduced both infection-site counts and parasitized foliage, indicating density-dependent spread. Together, these findings link spill history to predictable shifts in host condition and mistletoe pressure, with consistent species-level differences and a pronounced effect of local host isolation.

研究背景：在荒漠生态系统中，石油污染对土壤造成的长期影响会削弱树木长势，而半寄生性槲寄生（hemiparasitic mistletoes）可能会加剧这种胁迫压力。本研究旨在探究陆地石油泄漏如何影响金合欢林地的寄主健康状况以及槲寄生的寄生情况。位于以色列阿拉瓦谷地南部的埃夫隆自然保护区（Evrona Nature Reserve）提供了一个时间梯度错位的天然实验场地，其内部包含1975年和2014年发生过管道泄漏的受污染样地，以及附近未受干扰的对照样地。2024年3月，我们对银叶金合欢（Acacia raddiana）与扭荚金合欢（Vachellia tortilis）开展了野外调查：评估寄主活力、统计金合欢钝果寄生（Plicosepalus acaciae）的感染位点、通过影像照片估算被寄生叶片的占比，并量化目标树木与邻近树木的距离。通过广义线性模型（Generalized Linear Models，GLMs）分析，我们发现受泄漏污染区域的寄主健康状况更差，且扭荚金合欢的健康状况始终差于银叶金合欢。寄生情况呈现出明确的时间趋势：感染强度与被寄生叶片占比在泄漏发生10年后达到峰值（此时寄主仍存活但生理机能已衰退），并在泄漏发生50年后降至最低，这一结果反映的是寄主可利用性下降，而非场地本身的恢复。寄主与邻近树木的距离越大，感染位点数量与被寄生叶片占比均越低，表明寄生传播存在密度依赖效应。综合来看，本研究结果将石油泄漏历史与寄主健康状况和槲寄生寄生压力的可预测变化建立了关联，同时证实了物种水平的稳定差异以及局部寄主隔离度的显著影响。