Epiphytes improve host plant water use by microenvironment modification

1. Epiphytes have the potential to modify the canopy environments in which they grow. Accurately evaluating the impact of epiphytes can be challenging, since plants without epiphytes may also otherwise differ from host plants, and experimental removal is impractical and difficult to replicate in many forests. 2. We studied the impacts of epiphytes (primarily fruticose lichens and Tillandsia spp.) on host plants (Eulychnia saint-pieana and Caesalpinia spinosa) in two fog ecosystems in Chile (Pan de Azucar) and Peru (Atiquipa). These desert ecosystems sustain very high epiphyte loads and depend heavily on fog-water inputs. Using a combination of artificial substrates and epiphyte removals we show significant impacts of epiphytes on their host plants. 3. The presence of epiphytes reduced throughfall volumes, reducing fog and rainfall inputs to the soil beneath host plant canopies. 4. Soil moisture loss rate was increased below cacti after removal of epiphytes from sun-facing but not shade-facing branches. This suggests epiphyte effects on hosts are microclimatic. 5. Epiphytes also buffered temperature fluctuations and reduced daytime vapour pressure deficit (VPD). 6. Epiphytes can have strong effects on host plant ecophysiology and forest ecosystem processes, making them an important component for models and studies of canopy environments.

1. 附生植物（Epiphytes）具有改造其生长所处冠层环境的潜力。准确评估附生植物的影响颇具挑战：一方面，无附生植物的植株本身可能与宿主植物存在固有差异；另一方面，在多数森林生态系统中，实验移除附生植物的操作既不切实际，也难以重复。
2. 我们针对智利帕纳苏卡尔（Pan de Azucar）与秘鲁阿蒂基帕（Atiquipa）的两处雾生荒漠生态系统，研究了附生植物（主要为枝状地衣与铁兰属（Tillandsia spp.）植物）对宿主植物（圣皮尤壶花柱（Eulychnia saint-pieana）与刺云实（Caesalpinia spinosa））的影响。这类荒漠生态系统承载着极高的附生植物负荷，且高度依赖雾水输入。我们结合人工基质设置与附生植物移除实验，证实了附生植物对宿主植物存在显著影响。
3. 附生植物的存在会减少穿透雨量，降低宿主冠层下方土壤所获得的雾水与降雨输入量。
4. 移除向阳枝条上的附生植物后，仙人掌冠层下方的土壤水分流失速率会加快，但荫蔽枝条上并未出现该现象。这表明附生植物对宿主的影响是通过调控微气候实现的。
5. 附生植物还能缓冲温度波动，并降低日间水汽压差（Vapour Pressure Deficit, VPD）。
6. 附生植物可对宿主植物的生理生态特征与森林生态系统过程产生显著影响，因此它们是冠层环境模型与相关研究的重要组成部分。