Individual study: The effects of partial root removal and soil moisture regime on Nuttall oak Quercus nuttallii seedling growth: a laboratory experiment, University of Memphis, Tennessee, USA
Farmer J.W. & Pezeshki S.R. (2004) Effects of periodic flooding and root pruning on Quercus nuttallii seedlings. Wetlands Ecology and Management, 12, 205-214
In the southern USA, much emphasis in bottomland hardwood restoration is placed on establishing an oak-dominated forest. Regeneration of deforested areas and where a desirable seed source is not present, by planting nursery-grown seedlings is one available reforestation technique. Currently the usual procedure for seedling preparation is to prune the roots prior to transplanting in the field. However, it is not fully known what effect(s) root pruning has on transplanted seedlings. Secondly, bottomland restoration efforts inherently take place on floodplains, but the potential interaction between root pruning and flooding on seedling performance is not known. This study consisted of two separate but related laboratory experiments. The first experiment, a quantification of the effects of various amounts of root removal and varying soil moisture regimes on transplanted Nuttall oak Quercus nuttallii seedlings, is summarised here.
(For a summary of the effects of varying degrees of root pruning on new root formation of Nuttall oak Quercus nuttallii seedlings, please see: http://www.conservationevidence.com/ViewEntry.asp?ID=1026).
One hundred and fifty bareroot Nuttall oak seedlings were obtained from a State nursery at Pinson, Tennessee, 48 of similar size were selected for root pruning.
Root pruning treatments consisted of removal of roots at 0%, 25% and 75%, after which seedlings were placed in 2.5 l plastic pots in a sand/field soil (1:2) mix. A soil moisture regime of non-flooded or periodically flooded conditions, was maintained. The seedlings were randomly arranged in the laboratory under artificial lighting.
Plant gas exchange, growth, and survival were measured up to 108 days after root pruning.
Root pruning alone had adverse effects on height growth during the first 72 days following transplanting (no pruning c. 10 cm cumulative height growth; 75% pruning c.7 cm growth; 25% pruning 5 cm growth). Periodic flooding also produced adverse effects on stomatal conductance, height growth and survival.
As pruning intensified in the periodically flooded seedlings, photosynthetic rates decreased. In contrast, as pruning intensified in the non-flooded seedlings, photosynthesis increased. This demonstrated that pruning rate had a varying effect on photosynthesis dependent upon soil moisture conditions.
Conclusions: Results indicated that root pruning had no detectable long-term adverse effects on growth and survival of seedlings under drained soil conditions; however, if seedlings were planted in periodically flooded conditions, root pruning produced adverse effects. This indicates that if using oak seedling transplants in restoration efforts, the planting strategy and pruning rate should be evaluated based on the knowledge of hydrology of the site to be planted. Alternatively, on sites with unpredictable flooding both pruned and unpruned seedlings may be used to ensure survival, or placed in appropriate zones more liable or less liable to flooding.
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