Citation:

Rygiewicz, P T., D. Zabowski, AND M. F. Skinner. SITE SITE DISTURBANCE EFFECTS ON A CLAY SOIL UNDER PINUS RADIATA - ROOT BIOMASS, MYCORRHIZAL COLONISATION, 15AMMONIUM UPTAKE, AND FOLIAR NUTRIENT LEVELS. New Zealand Journal of Forestry Science. Scion, Rotorua, New Zealand, 34(3):238-254, (2004).

Description:

Timber harvesting can result in adverse physical, chemical and biological alterations to soil. The objective of this study was to examine the effects of site disturbance to determine the extent and duration of possible harvesting impacts on soil chemical and biological properties including fine roots and ectomycorrhizas of radiata pine. The disturbance study is located on the North Island of New Zealand and was examined nine years after organic matter and compaction treatments were installed. Treatments included undisturbed control plots, O horizon removed with no compaction, and O and A horizons removed with heavy compaction. Soil was examined for soil solution nitrogen (N), extractable N, fine root biomass, ectomycorrhizal (ECM) root tips, and specific ECM root tip 15NH4+ uptake rates. Results show that total fine root biomass is reduced with loss of both organic-rich soil horizons and compaction to approximately 1/3 that of in the control treatment, but that ECM infection rates are higher (averaging over 60%). With removal of only the O horizon, the largest effect is simply the loss of rooting volume and the roots that would normally occur in this horizon, with little reduction in root biomass or change in ECM infection rates in the mineral horizons. Specific ECM root uptake rates of 15NH4+ do not appear to have been changed by the most severe disturbance treatment. However, the unaltered uptake rate may be due to the different predominant ECM morphotype found in the most severe treatment compared with the dominant morphotype found in the two less severe treatments. Reduced fine root biomass of the severe disturbance treatment correlates with reduced tree growth and foliar N.

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