Dawson T E
Section of Ecology and Systematics and the Laboratory for Stable Isotope Research and Analysis at Cornell University, Ithaca, NY 14853, USA e-mail:
Oecologia. 1998 Dec;117(4):476-485. doi: 10.1007/s004420050683.
Fog has been viewed as an important source of moisture in many coastal ecosystems, yet its importance for the plants which inhabit these ecosystems is virtually unknown. Here, I report the results of a 3-year investigation of fog inputs and the use of fog water by plants inhabiting the heavily fog inundated coastal redwood (Sequoia sempervirens) forests of northern California. During the study period, 34%, on average, of the annual hydrologic input was from fog drip off the redwood trees themselves (interception input). When trees were absent, the average annual input from fog was only 17%, demonstrating that the trees significantly influence the magnitude of fog water input to the ecosystem. Stable hydrogen and oxygen isotope analyses of water from fog, rain, soil water, and xylem water extracted from the dominant plant species were used to characterize the water sources used by the plants. An isotopic mixing model was employed to then quantify how much fog water each plant used each month during the 3-year study. In summer, when fog was most frequent, ∼19% of the water within S.sempervirens, and ∼66% of the water within the understory plants came from fog after it had dripped from tree foliage into the soil; for S.sempervirens, this fog water input comprised 13-45% of its annual transpiration. For all plants, there was a significant reliance on fog as a water source, especially in summer when rainfall was absent. Dependence on fog as a moisture source was highest in the year when rainfall was lowest but fog inputs normal. Interestingly, during the mild El Niño year of 1993, when the ratio of rainfall to fog water input was significantly higher and fog inputs were lower, both the proportion and coefficient of variation in how much fog water was used by plants increased. An explanation for this is that while fog inputs were lower than normal in this El Niño year, they came at a time when plant demand for water was highest (summer). Therefore, proportional use of fog water by plants increased. The results presented suggest that fog, as a meteorological factor, plays an important role in the water relations of the plants and in the hydrology of the forest. These results demonstrate the importance of understanding the impacts of climatic factors and their oscillations on the biota. The results have important implications for ecologists, hydrologists, and forest managers interested in fog-inundated ecosystems and the plants which inhabit them.
在许多沿海生态系统中，雾被视为重要的水分来源，然而其对栖息于这些生态系统中的植物的重要性却几乎无人知晓。在此，我报告了一项为期3年的调查结果，该调查研究了加利福尼亚北部浓雾笼罩的沿海红杉（红杉）森林中雾的输入情况以及植物对雾水的利用。在研究期间，平均每年34%的水文输入来自红杉树自身的雾滴（截留输入）。当没有树木时，雾的年平均输入仅为17%，这表明树木对生态系统中雾水输入量有显著影响。对从主要植物物种中提取的雾水、雨水、土壤水和木质部水进行稳定氢氧同位素分析，以表征植物所利用的水源。然后采用同位素混合模型来量化在为期3年的研究中每种植物每月利用的雾水量。在夏季，雾最为频繁，红杉体内约19%的水分以及林下植物体内约66%的水分来自雾从树叶滴落到土壤之后；对于红杉而言，这种雾水输入占其年蒸腾量的13 - 45%。对于所有植物来说，对雾作为水源都有显著依赖，尤其是在夏季无降雨的时候。在降雨最少但雾输入正常的年份，对雾作为水分来源的依赖程度最高。有趣的是，在1993年温和的厄尔尼诺年，降雨与雾水输入的比例显著更高且雾输入更低时，植物利用的雾水量的比例和变异系数均增加。对此的一种解释是，在这个厄尔尼诺年雾输入低于正常水平，但它们出现在植物对水需求最高的时期（夏季）。因此，植物对雾水的比例性利用增加。所呈现的结果表明，雾作为一种气象因素，在植物的水分关系和森林水文学中起着重要作用。这些结果证明了理解气候因素及其波动对生物群影响的重要性。这些结果对关注雾浸生态系统及其栖息植物的生态学家、水文学家和森林管理者具有重要意义。
