EFFECTS OF MYCORRHIZAL INFECTION ON PLANT GROWTH, NITROGEN AND PHOSPHORUS NUTRITION IN GLASSHOUSE‐GROWN ALLIUM CEPAL.

Abstract

SUMMARYGrowth and rates of uptake of nitrogen and phosphorus (inflow) in Allium cepa L. were measured in three experiments. EfTects of mycorrhizal infection {Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe) and N and P fertilization were investigated. The experiments were carried out in a naturally-lit glasshouse, so that seasonal variations in solar radiation infiuenced experimental results.In all experiments, a large positive growth response to mycorrhizal infection was observed when soil P was low. However, at high soil P smaller growth responses to infection were observed, as expected. Infection was associated with increased inflow of P, at all levels of soil P, even when non-mycorrhizal plants grew as well as or better than mycorrhizal plants. Lower P inflow was observed when infection was low and also at low irradiance in hoth mycorrhizal and non-mycorrhizal plants. The results show that mycorrhizal fungi increase the rate at which P is absorbed from soil, even under conditions which precluded a positive growth response to infection.In plants grown in spring and summer (two experiments), mycorrhizal infection was also associated with increased N inflow. N inflows in both mycorrhizal and non-mycorrhizal plants were lower in a third experiment in late winter and mycorrhizal infection had little or no effect on N inflow in this experiment. Increased N supply increased the inflow of N, concentrations of N in plant tissues and plant growth except in plants that were severely P limited, and there was no evidence that mycorrhizal infection alleviated N stress in low N plants.The results are discussed in relation to the environmental factors limiting plant growth, in particular nutrient uptake via and carbohydrate use by the fungal symbiont.

Phosphorus efficiencies and responses of barley (Hordeum vulgare L.) to arbuscular mycorrhizal fungi grown in highly calcareous soil

“…The outcome will relate to root growth rates, root length density and propagule density, and hence the chance of a propagule hitting a root (Smith et al 1986). However, the fact that percentage colonisation in each pot size was similar for the two cultivars, despite large differences in root length and specific root length suggests that propagule density was sufficient to achieve maximum colonisation in all cases.…”

“…P uptake was found to be positively correlated with root length in high-P soil, but not in low-P soil or in soil where volume was limited (Otani and Ae 1996). Responsiveness of host plants to AMF colonisation is sensitive to soil P availability (Smith and Read 1997), and hence possibly to soil volumes of experimental pots. Facelli et al (1999) have shown that the higher the plant density (relatively small soil volume per individual plant) the lower the mycorrhizal responsiveness.…”

“…Symbiotic association between plants and arbuscular mycorrhizal fungi (AMF) is widespread and of particular importance in improving plant P uptake efficiency (Smith and Read 1997). The role of AMF in plant nutrition is likely to be important even when plants are genetically modified with other traits, such as root exudation of citrate (Lopez-Bucio et al 2000;Zhu et al 2001).…”

Seed Bank Depletion: The Key to Long-Term Downy Brome ( Bromus tectorum L.) Management

“…Another consideration to improve downy brome and Japanese brome control and enhance reclamation involves arbuscular mycorrhizal fungi (AMF), which significantly aid the growth and development of mycorrhizal plants (Allen and Allen 1984;Killham 1985;Read et al 1985;Smith et al 1986;Trappe 1981). Downy brome is a facultative mycorrhizal plant and does not have to develop such an association to survive or even dominate a site (Pendleton and Smith 1983;Trappe 1981).…”

“…AMF play a vital role n the mineral nutrition of host plants (Trappe 1981) and increase the amounts of accumulated macro-and micronutrients (Killham 1985;Read et al 1985;Smith et al 1986). Additionally, AMF colonization of herbaceous species improved drought tolerance (Allen and Allen 1984;.…”