Pacific Southwest

Title: Distribution of Quercus agrifolia mycorrhizae deep within weathered bedrock: a potential mechanism for transport of stored water

Author: Bornyasz, M.; Graham, R.; Allen, M.

Date: 2002

Source: In: Standiford, Richard B., et al, tech. editor. Proceedings of the Fifth Symposium on Oak Woodlands: Oaks in California's Challenging Landscape. Gen. Tech. Rep. PSW-GTR-184, Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture: 821-822

Station ID: GTR-PSW-184

Description: In southwestern California, Quercus agrifolia distribution closely matches regions of granitic regolith. High annual evapotranspiration demand and inherent shallow soil conditions lead to a dependence on a deep rooting system and an ability to access water from deep within the regolith. Most of the plant available water in weathered granitic rock is held within micropores, which are generally too small for roots to access. It is not clear how water held in the rock matrix reaches the roots, which are confined to the fractures. Hyphae are narrow and able to explore a greater substrate volume for resources. Our study addresses the vertical composition of both endo- and ecto-mycorrhizae in weathered granitic rock in an effort to determine if mycorrhizae are available to act as conduits to transport water from rock matrix to roots. Water status, morphology, nutrients, root and mycorrhizae distribution of three Q. agrifolia trees were characterized from a 15-meter-wide by 4-meter-deep profile consisting of 30 to 70 cm of soil and 330 to 370 cm of weathered bedrock. Plant available water within the soil fraction was depleted by the end of June; therefore plants must rely on water available within the fractured bedrock for the remainder of the growing season and during the dry season. Roots greater than 1 mm are present throughout the entire 4-meter deep profile. Fine roots <1 mm are also present in the weathered bedrock and commonly occur in root mats consisting of live and dead roots. Percent infected tips and morphotype abundance in samples collected from the soil fraction (0-10, 10-20, 20-30 cm) decreased with depth from 65 percent to 30 percent and 12 to 2, respectively. This is a similar trend to what is generally reported in the literature. However, samples collected from fractures within the weathered bedrock at and below a one-meter depth also contained infected root tips. Percent infected tips ranged from 0-64 percent and morphotype abundance ranged from 0-10. Percent-infected tips from a 3.7 m deep rock sample closely matched that of a surface soil sample (63 percent rock; 65 percent soil), however morphotype abundance was substantially lower.

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Citation

Bornyasz, M.; Graham, R.; Allen, M.  2002.  Distribution of Quercus agrifolia mycorrhizae deep within weathered bedrock: a potential mechanism for transport of stored water.   In: Standiford, Richard B., et al, tech. editor. Proceedings of the Fifth Symposium on Oak Woodlands: Oaks in California's Challenging Landscape. Gen. Tech. Rep. PSW-GTR-184, Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture: 821-822.