Progress in selected areas of rhizosphere research on P acquisition

Abstract

Large reserves of P have accumulated in soils of developed countries because additions of P fertiliser to sustain agricultural production have exceeded crop removal. By contrast, in many developing countries in the tropics and subtropics, soil P reserves are gravely low and large additions are required before maintenance requirements begin to decline. In addition, the cost of P fertiliser will increase as the currently accessible deposits of high-grade phosphate rock (PR) diminish. Developing plants that efficiently tap soil P reserves and low grade PR is therefore a priority for agricultural research. For the 50th anniversary of the New Zealand Soil Science Society, this paper reviews research on P efficiency in plants, conducted by staff, students, and research associates of Massey University, in the context of other research into plant mechanisms that enhance P uptake, including effects of root geometry, mycorrhizal associations, and root-induced changes in the soil. Techniques for fractionation of soil P are highlighted. S R 0 2 1 3 0 R h i z o s p h e r e P a c q u i s i t i o n S . N . T r o l o v e e t a l .

Impact of arbuscular mycorrhizal fungi on N and P cycling in the root zone

“…Roots and several soil organisms including ectomycorrhizal fungi (Landeweert et al 2001), but not AMF (Trolove et al 2003), are known to produce organic anions to help solubilize P. A stimulating influence of AMF on P solubilizing bacteria has been observed. Villegas and Fortin (2002) have shown using in vitro culture of G. intraradices on transformed carrot roots, that the P solubilizing activities of Pseudomonas aeruginosa and P. putida were enhanced in the presence of AMF hyphae, when N was provided as NO 3 -.…”

“…Although AMF can contribute to P mineralization, the contribution of AMF-derived phosphatase to P mineralization may be insignificant (Joner et al 2000b). First, it accounts for only a few percent of total soil phosphatase and, furthermore, the phosphatase activity measured in soil exceeds inorganic P release rates suggesting that the phosphatase activity in soil is substrate limited (Trolove et al 2003).…”

“…The release in soil of phosphatase enzymes and organic anions, the heterotrophic activity (Trolove et al 2003) and the size of the soil microbial biomass (He et al 1997) are factors influencing the availability of soil P to plants. AMF influence all these factors, in addition to physically enhancing plant P extraction capabilities (Smith and Read 1997).…”

Determination of desirable properties of bacteria, fungi and their biofilm associated with rubber rhizosphere

“…Alternative possibilities other than organic acids for inorganic P solubilization have been reported. For example, extrusion of proton accompanied with the cation uptake (Khan et al, 2007b), formation of exopolysaccharide (Yi et al, 2008), production of chelating substances (Whitelaw, 2002;Kucey, 1988;Welch et al, 2002) and through exchange reactions (Gahoonia et al, 1992;Jones, 1998;Trolove et al, 2003) can be highlighted. Present study indicated that, the formation of biofilm with effective microbes has an ability to solubilized sparingly soluble CaHPO 4 more than their bacterial and fungal counterparts.…”

Soil microbial community analysis in the environmental risk assessment of transgenic plants

“…It is well known that soil microorganisms that colonize the rhizosphere assist plants in the uptake of several vital nutrients, such as phosphorous, potassium and nitrogen, from the soil (George et al 1995;Timonen et al 1996;Trolove et al 2003;Cocking 2003). Soil microbes can also exert considerable influence upon the status of a plant's health (Smith and Goodman 1999).…”