Project at a Glance

Title: Effects of acid rain on plant microbial associations in California

Principal Investigator / Author(s): Paul, E. A.

Contractor: Department of Plant and Soil Biology, UC Berkeley

Contract Number: a2-087-32

Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Acid Deposition, Ecosystem Impacts


The effects of simulated acid rain of pH 5.6 to 3.0, with ionic composition similar to that found in California, on Trifolium repens, Lupinus densiflorus and L. benthamii grown in two soils were tested. The interactions of treatment intensity, soil type, phosphorus uptake and mycorrhizal influences on growth, carbon fixation and allocation and nitrogen fixation were determined. Acidic treatments generally decreased plant growth, nodulation and nitrogenase activity. The exposure of plants to a large number of simulated rainfall conditions of shorter duration did not result in the negative growth effects. Plants adequately supplied with P, either as fertilizer or by mycorrhizal fungi, were much more resistant to conditions caused by acidic precipitation and in some cases growth increases were found. Measurements of carbon incorporation rates, beneath ground respiration and carbon allocation in established plants (10 to 12 weeks) was conducted in a specially designed growth chamber which allowed exposure of above ground plant parts to carefully controlled levels of 14CO2. Beneath ground respiration could then be measured separately. These measurements showed only a 25% decrease due to the observed acid rain treatment and did not account for the two-three fold differences in plant yield. This was attributable at least in part to a decrease in sensitivity to the acid rain treatments in the older plants used for the 14C studies. Internal turnover rates of carbon under acidic conditions were very high but the effect of this on long-term growth has not been clearly delineated. Lupines and clovers were found to be acid sensitive associations that occur widely in California rangelands on soils that vary in acid sensitivity. This work has shown that further field studies of the physiological processes involved in growth and plant nutrition should lead to much better criteria regarding acidic inputs into natural environments.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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