Symbiotic exchange of carbon and phosphorus between cucumber and three arbuscular mycorrhizal fungi

Abstract

SUMMARYCucumber {Cucumis sativus L.) was grown in an irradiated soil:sand mixture in PVC tubes containing a root compartment, a hyphal compartment and a hyphal ''P-labelling compartment. At 23 d from sowmg 20 /<Ci of an aqueous solution of carrier-free =' ' 'P was pipetted into the hyphal labelling compartment. Just 24 h later the plants were labelled with '^CO, for 16 h. At harvest the plants were analysed for mycorrhizal colonization and distribution of ^"C and '^^P.Hyphae of G. caledonium proved to have the most rapid "'P uptake and transfer system of the three fungi studied. The host was provided with an order of magnitude more '^P than supplied by either Glomus sp. or 5. calospora. The S. calospora-co\onized plants contained the least ^^P counts of the three mycorrhizal treatments. 75 "" of the total »^P in the plant was present in the shoots of the plants colonized by G. caledonium; the corresponding figures for the shoots of S. calospora and Glomus sp. were 45 and 25%, respectively.The proportion of assimilated '^C allocated to below-ground events was 35, 32 and 25 with S. calospora, Glomus sp. and G. caledonium, respectively. The specific incorporation of "C into roots colonized by Glomus sp. was 1-8 and 31 times as high as into roots colonized by G. caledonium and S. calospora, respectively.In contrast, the specific root respiration (Bq mg-' d. wt) was similar in the mycorrhizal treatments. The »C How into external hyphae was approximately 0-8% of the total assimilated '*C for all three fungi.Based on these results, mycorrhizal efficiency was calculated as hyphal '^C use per unit ^^P transported, belowground ^^C use per unit ^"P transported, ='P transported per metre of hyphae and hyphal "C use per metre of hyphae.

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

“…They suggested that P transport was limited by processes involved in hyphal translocation and\or transfer across the symbiotic interface rather than hyphal P uptake itself. Scutellospora calospora accumulated large amounts of $#P into its hyphae but transported little to the host plant Cucumis sativus (Pearson & Jakobsen, 1993). By contrast, we have shown large increases in P uptake and plant growth in Allium porrum colonized by S. calospora and Glomus sp. '…”

Evidence that differences in phosphate metabolism in mycorrhizas formed by species of Glomus and Gigaspora might be related to their life‐cycle strategies

“…There is increasing evidence, for example, that the diversity of species of AMF (as measured by DNA sequencing in some cases) in the plant\soil environment might determine plant community structure (Clapp et al, 1995 ;Helgason et al, 1998 ;Van der Heijden et al, 1998a,b). This might reflect the unique development and life-cycle requirements of these fungi as indicated in recent studies using species of AMF from different genera (Jakobsen et al, 1992a,b ;Pearson & Jakobsen, 1993 ;Boddington & Dodd, 1998). Despite this, the majority of studies on AMF use only species of Glomus (Abbott et al, 1984 ;Amijee et al, 1993 ;Zhao et al, 1997).…”

“…The use of alkaline phosphatase activity, localized in the vacuole of the intra-radical mycelium of AMF (Gianinazzi et al, 1979), as a potential marker for phosphate metabolism in mycorrhizas is still equivocal. Other mechanisms might also be involved in phosphate metabolism that affect the uptake, translocation and\or transfer of phosphate to the plant via the fungal mycelium (Jakobsen et al, 1992a,b ;Pearson & Jakobsen, 1993 ;Harrison & Van Buuren, 1996 ;Boddington & Dodd, 1998). However, the alkaline phosphatase in the extra-radical mycelium might be an effective marker for phosphate metabolism in studies on AMF, in contrast to that in the intraradical mycelium (Dodd, 1994).…”

A comparison of arbuscular and ectomycorrhizal Eucalyptus coccifera: growth response, phosphorus uptake efficiency and external hyphal production

“…Conclusions about whether ectomycorrhizas generally have higher P uptake efficiencies than arbuscular mycorrhizas must await comparisons between larger numbers of species of each type. Obviously a considerable amount of variability, such as that found by Pearson & Jakobsen (1993), is to be expected within each of the mycorrhizal groups.…”

“…Jones et al (1991) calculated that willow ectomycorrhizal with Thelephora terrestris took up more P per unit of C than did NM plants. Pearson & Jakobsen (1993) compared the efficiency of three AM fungi by measuring hyphal "%C use per unit $#P transported and below-ground "%C use per unit $#P transported. Both Tinker et al (1994) with ECM willow and Raju et al (1990) with AM sorghum calculated costs and benefits to the mycorrhizal plant in terms of C. Tinker et al (1994) determined that ECM willow converted 85 % of the extra C fixed into shoot biomass ( l C-use efficiency).…”