LATE SUMMER WATER STATUS OF SOILS AND WEATHERED BEDROCK IN A GIANT SEQUOIA GROVE
LATE SUMMER WATER STATUS OF SOILS AND WEATHERED BEDROCK IN A GIANT SEQUOIA GROVE
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夏末巨型红杉林土壤和风化基岩的水状况
DOI：
10.1097/00010694-199512000-00007
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发表时间：
1995
期刊：
影响因子：
--
通讯作者：
D. Martynn
中科院分区：
文献类型：
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作者：
M. Anderson;R. Graham;D. Martynn
巨型红杉（Sequoiadendron giganteum）的自然分布仅限于加利福尼亚州内华达山脉西坡的中海拔地区，那里夏季降雨量可以忽略不计。本研究测量了红杉国家森林 Packsaddle Grove 中夏末风化层（土壤 + 风化基岩）剖面的水状况，以评估旱季结束时按地貌位置划分的可用水分布。 1993 年 9 月 7 日至 12 日期间，通过螺旋钻采集土壤和风化花岗岩基岩样本，采集间隔为 30 厘米，深度为 270 厘米，在整个树林中的巨型红杉和非红杉微站点的三份边坡、洼地和排水位置采集。样品储存在密封罐中，用于实验室水势和含水量测定。土壤和风化基岩水势范围为 0 至 -2.1 MPa，通常随着深度和排水位置的增加而增加（负值逐渐减小；表明湿润条件）。对于任何景观位置，两种植被类型下的水势之间没有明显的一致差异。 Cr（风化基岩）层含有大量可供植物利用的水。典型的 270 厘米厚剖面由 90 厘米土壤和 180 厘米风化基岩组成，经计算可在田间容量下容纳约 44 厘米植物可用水，其中 27 厘米储存在风化基岩内。假设径流损失为 35%，估计年降水量 <68 厘米可能无法充分补给高地（非排水）地点的风化层剖面，并导致季末缺水。过去10年中，有3年出现过这种低降水情况。生长在排水系统中的巨杉从径流和径流中吸收额外的水；因此，他们不太可能经历缺水压力。
The natural occurrence of giant sequoia (Sequoiadendron giganteum) is restricted to a mid-elevation zone on the west slope of the Sierra Nevada, California, where summer rainfall is negligible. This study measured the late summer water status of regolith (soil + weathered bedrock) profiles in the Packsaddle Grove on the Sequoia National Forest to assess the distribution of available water by geomorphic position at the end of the dry season. Soil and weathered granitic bedrock samples were collected by auger during September 7–12, 1993, at 30–cm intervals to a depth of 270 cm on triplicated sideslope, swale, and drainage positions for both giant sequoia and non-sequoia microsites throughout the grove. The samples were stored in air-tight cans and were used for water potential and water content determinations in the laboratory. Soil and weathered bedrock water potentials ranged from 0 to −2.1 MPa, generally increasing (becoming less negative; indicating moister conditions) with depth and in drainage positions. No consistent differences between water potentials under the two vegetation types were apparent for any of the landscape positions. The Cr (weathered bedrock) horizons held a substantial quantity of plant-available water. A representative 270–cm thick profile consisting of 90 cm of soil underlain by 180 cm of weathered bedrock is calculated to hold about 44 cm of plant-available water at field capacity, 27 cm of which is stored within the weathered bedrock. Assuming 35% runoff losses, it is estimated that annual precipitation of <68 cm may fail to fully recharge the regolith profile on upland (non-drainage) sites and result in late season water stress. Such conditions of low precipitation have existed in 3 of the past 10 years. Giant sequoia growing in drainages receive additional water from runoff and throughflow; thus they are less likely to experience water stress.