Fine Root Biomass and Its Relationship to Evapotranspiration in Woody and Grassy Vegetation Covers for Ecological Restoration of Waste Storage and Mining Landscapes |
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Authors: | Isa A M Yunusa Sepideh Zolfaghar Melanie J B Zeppel Zheng Li Anthony R Palmer Derek Eamus |
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Institution: | (1) School of Environmental & Rural Sciences, University of New England, Armidale, New South Wales, 2350, Australia;(2) Plant Functional Biology & Climate Change Cluster, University of Technology, Broadway, Sydney, New South Wales, 2007, Australia;(3) Department of Biological Sciences, Macquarie University, Sydney, New South Wales, 2109, Australia;(4) Centre for African Conservation Ecology, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth, 4000, South Africa |
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Abstract: | Production and distribution of fine roots (≤2.0 mm diameter) are central to belowground ecological processes. This is especially
true where vegetation serves as a pump to prevent saturation of soil and possible drainage of excess water into or from potentially
toxic waste material stored underground or in mounds aboveground. In this study undertaken near Sydney in Australia, we determined
fine root biomass and evapotranspiration (ET) on a waste disposal site restored with either a 15-year-old grass sward or plantations
of mixed woody species that were either 5 years old (plantation-5) with a vigorous groundcover of pasture legumes and grasses,
or 3 years old (plantation-3) with sparse groundcover. These sites were compared with nearby remnant woodland; all four were
located within 0.5-km radius at the same site. Ranking of fine root biomass was in the order woodland (12.3 Mg ha−1) > plantation-5 (8.3 Mg ha−1) > grass (4.9 Mg ha−1) > plantation-3 (1.2 Mg ha−1) and was not correlated with nutrient contents in soil or plants, but reflected the form and age of the vegetation covers.
Trends in root length density (RLD) and root area index (RAI) followed those in root biomass, but the differences in RAI were
larger than those in biomass amongst the vegetation covers. Annual ET in the dry year of 2009 was similar in the three woody
vegetation covers (652–683 mm) and was at least 15% larger than for the grass (555 mm), which experienced restrained growth
in winter and periodic mowing. This resulted in drainage from the grass cover while there was no drainage from any of the
woody vegetation covers. In plantation-5, root biomass, RAI and RLD were reduced in the rain shadow side of the tree rows.
Similarly, the amount and depth of rooting in the groundcover were reduced close to the trees compared to midway between rows.
Differences in the root variables were larger than those in ET, which suggested that more roots were produced than were needed
for water uptake and/or presence of considerable amounts of necromass. We conclude that vegetation covers, such as plantation-5
consisting of widely spaced trees and a heavy groundcover containing winter-active pasture legumes, will promote year-round
water-use with a reduced risk of deep rooting that could breach buried wastes. This function could be sustained through progressive
thinning of trees to account for not more than 25% of the whole canopy cover; this will minimize competition for limited soil-water
and thereby constrain deep rooting as vegetation ages and attains climax. |
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