The effect of soil compaction on growth and P uptake by Trifolium subterraneum: interactions with mycorrhizal colonisation

Abstract

The effects of vesicular-arbuscular mycorrhizal (VAM) colonisation on phosphorus (P) uptake and growth of clover (Trifolium subterraneum L.) in response to soil compaction were studied in three pot experiments. P uptake and growth of the plants decreased as the bulk density of the soil increased from 1.0 to 1.6 Mg m -3. The strongest effects of soil compaction on P uptake and plant growth were observed at the highest P application (60 mg kg-1 soil). The main observation of this study was that at low P application (15 mg kg -l soil), P uptake and shoot dry weight of the plants colonised by Glomus intraradices were greater than those of non-mycorrhizal plants at similar levels of compaction of the soil. However, the mycorrhizal growth response decreased proportionately as soil compaction was increased. Decreased total P uptake and shoot dry weight of mycorrhizal clover in compacted soil were attributed to the reduction in the root length. Soil compaction had no significant effect on the percentage of root length colonised. However, total root length colonised was lower (6.6 m pot-l) in highly compacted soil than in slightly compacted soil (27.8 m pot-z). The oxygen content of the soil atmosphere measured shortly before the plants were harvested varied from 0.18 m3m -3 in slightly compacted soil (1.0 Mg m -3) to 0.10 m3m -3 in highly compacted soil (1.6 Mg m-3).

Interactive effects of arbuscular mycorrhizal symbiosis, intraspecific competition and resource availability on Trifolium subterraneum cv. Mt. Barker

“…Barker plants were grown in autoclaved soil collected from a Mediterranean type Eucalyptus forest (Waite Hill Face Reserve, Adelaide, Australia) with a very low extractable P concentration (Colwell, 1963), 6 µg −" of NaHCO $ extractable P and a neutral pH (pH 6.4 in 10 mM CaCl # ). This concentration of available P has been reported to limit growth of T. subterraneum in previous pot experiments (Nadian et al, 1996). Autoclaving this soil had no toxic effect on T. subterraneum (E. Facelli, unpublished data).…”

“…We selected T. subterraneum as the host because the response of single plants of this species to mycorrhizal infection under different concentrations of P and light intensities has been studied in detail (Smith, 1982 ;Tester et al, 1985Tester et al, , 1986Nadian et al, 1996).…”

Enhancement of the effectiveness of indigenous arbuscular mycorrhizal fungi by inorganic soil amendments

“…Nadian et al (1996) showed that the mycorrhizal growth response, the effect of AM fungi on P uptake and growth of the host plant, decreased as the bulk density of the soil increased. Compacted soil decreased the percentage of large (> 30 fJ.-m) soil pores (Nadian et al 1996) and inhibited the elongation of the roots (Nadian et al 1996;Yano et al 1998) and also hyphae of the AM fungi (E. Drew, personal communication). In this study, soil compaction might occur in the absence of the soil amendments and suppress mycorrhizal function as a P supplier.…”

Characterization of two arbuscular mycorrhizal fungi in symbiosis with Allium porrum: inflow and flux of phosphate across the symbiotic interface

“…These values lie within the range previously reported. Estimates of hyphal P inflow vary considerably, ranging from 1-19i10 −"$ mol m −" (root) s −" (Jakobsen et al, 1992a) to 238i10 −"$ mol m −" (root) s −" (Nadian, 1998). Apart from uncertainty about the assumptions behind the calculations, these values are of course influenced by many factors, including levels of soil P, the fungal isolates, host plants and soil used, production of external hyphae, extent of colonization, and the time period used for the calculation.…”