Factors Influencing Early Performance of Leguminous Plants in Forest Soils
- M. M. Schoeneberger ,
- R. J. Volk and
- C. B. Davey
Subterranean clover (Trifolium subterraneum L.), a winter annual, and big trefoil(Lotus pedunculatus Cav.), a summer perennial, are being studied for use in forestry operations. Establishment and performance of these plants with their associated rhizobia (+RHIZ) are adversely affected by the infertile, acid conditions generally encountered in forest soils. Using the 15N isotope dilution technique, we investigated the effects of N fertilization and inoculation with the vesicular-arbuscular mycorrhizal fungus, Gigaspora margarita Becker and Hall (+VAMF) on early growth and N2-fixing capabilities of these plants in a pasteurized acid forest soil containing low levels of both P and N. In clover, dual inoculation with + RHIZ, + VAMF at 10 kg N ha−1 enhanced N derived from the atmosphere (Ndfa), both on a per-plant (350%) and a per-gram total N (151%) basis, as well as plant biomass (68%) and flower production (100%) over the corresponding values for + RHIZ plants. Increasing N to 100 kg N ha−1 resulted in greater biomass (24%) in dual-inoculated clover, but concurrently decreased the amount of Ndfa while increasing the amount of N derived from the soil (Ndfs). Compared to + RHIZ trefoil, dual inoculation of trefoil (+ RHIZ, + VAMF) resulted in greater biomass production at 100 kg N ha−1, but had no significant effect on Ndfa or Ndfs. Increasing soil N increased biomass production, but did not reduce Ndfa in dual-inoculated trefoil. The difference in response to G. margarita inoculation may be a reflection of the annual vs. perennial nature of subterranean clover and big trefoil, respectively. The shift in biomass production and Ndfa in nodulated plants at the higher N level demonstrates the need to modify site management practices in order to maximize tree growth and leguminous plant-biological N fixation benefit to the site.
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