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Title: The nature of high altitude precipitation and its effect on Scots pine (Pinus sylvestris L.) and Sitka spruce (Picea sitchensis (Bong.) (Carr.))
Author: Henderson, Callum George McKenzie
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1990
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The nature of high altitude precipitation and its effect on Scots pine (Pinus sylvestris L.) and Sitka spruce (Picea sitchensis (Bong.) Carr.) was investigated. Scots pine and Sitka spruce are important British forestry species and the effect of acidic cloud on these has been inadequately investigated. At a field site in the Scottish Southern Uplands, impacted cloudwater was either collected from, or measured with a microelectrode in situ on, artificial polypropylene snoots which closely mimicked live shoots. Temporal variation of pH within cloud deposition events was strong and the potential for damage by acid clouds was seen to be high. Impacted cloudwater was also collected from, or measured in situ on, live shoots and the interchange of ions between shoots and cloudwater investigated. Leaching of basic cations was considerable but not sufficient to neutralize cloudwater acidity. Dry deposition on live shoots appeared to increase the acidity of impacted cloudwater on shoots. The change in pH of evaporating droplets was measured in situ with the microelectrode. Droplet acidity increased dramatically as a result of evaporation. The potential for damage by snow was investigated by collecting and analysing snowmelt. Ground snowpack showed an initial flush of ions (including H+) on melting, followed by a steep decline to very low ion concentrations. Meltwater from live shoots did not show this flush/decline but did exhibit higher acidity levels which were also related to the pathway of the snowmelt through the snowpack. A series of four glasshouse experiments were undertaken in which a system for applying simulated acid cloud (SAC) was developed. Six to eight-year-old Scots pine and Sitka spruce were subjected to SAC at pH 5.6, 3.0 and 2.5. Considerable leaching of Ca, Mg, K, NO~-N and PO~-P occurred and showed an increasing response to increasing acidity of SAC. Both extension growth and needle area declined with increasing acidity but the decline was statistically insignificant. Visible injury on Scots pine needles was limited to those subjected to SAC at pH 2.0. Sitka spruce damage occurred to a very small extent at pH 2.5 but was again largely restricted to pH 2.0. Artificial abrasion of needles did not increase susceptibility to acid damage. Acid damage generally progressed from tip to base and at the junction of the brown and green tissue a darker brown band formed. Tissue underlying brown areas was subject to cell collapse and underneath the dark bown band the extracellular spaces were filled with an unknown material and the cells had not collapsed. The structure of the epicuticular wax was not affected by SAC acidity and even over necrotic areas the crystalline wax remained intact. The functional integrity of the cuticle, investigated by measuring cuticular conductance and contact angles, was unaffected by SAC. Controlled experiments on the changing acidity of evaporating droplets took place with three-year-old Scots pine and Sitka spruce in a large wind-tunnel, again with the use of the microelectrode. Droplet acidity again increased dramatically evaporation and there was also a close relationship between the increase of acidity of the droplet and that predicted by a direct relationship to the amount of water evaporated. Scots pine and Sitka spruce thus appear to be resistant to direct effects of acid cloud at pH 3.0 which is the lowest generally encountered in the Scottish Southern Uplands. However acidity enhancement through evaporation, extreme pH values at the start or finish of cloud events and high acidity flushes at the start of snowmelt may all expose trees to pH levels approaching those causing direct damage. In addition, the nutrient budgeting of trees may be adversely affected and lead to long term reductions in growth.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available