Zinc biofortification potential for wheat of green manure and mycorrhiza in calcareous, saline soil

Abstract

2 root and fungal hyphal involvement in plant Zn acquisition (3), a study carried out in a compartmented growth system in which root access to a fertilization/labeling compartment was controlled by a mesh barrier. The study on the response of the two wheat cultivars to application of mineral Zn fertilizer and mycorrhization (1) demonstrated that shoot Zn concentrations and contents can, indeed, be raised with increasing doses of ZnSO4 fertilizer, but that biomass production may not necessarily increase. The roots of the growth-impaired plants and those of the Zn fertilizerresponsive wheat cultivar, Back Cross Rushan, were more heavily colonized by naturally occurring AMF than those of normally growing plants or of the Zn fertilizer unresponsive cultivar, Kavir. The Zn fertilizer-responsive wheat cultivar was also that which showed positive N, P, and Zn uptake responses to mycorrhization. This suggests that genetic cultivardependent differences in Zn-efficiency in field trials may be at least partially explained by differences in the degree of mycorrhization. The study on the effects of green manure on plant Zn uptake (2) showed that green manure mixed to soil can, indeed, mobilize considerable amounts of Zn from the soil’s own stock and thereby essentially substitute probably for some time any Zn, which otherwise would have to be introduced as mineral Zn fertilizer from externally. The study found green manure prepared of sunflower to be more effective than such prepared of red clover in stimulating Zn uptake. In this experiment, the non-indigenous AMF inoculant, but not the native AMF assemblage, reduced the overall Zn uptake from soil. These findings show that mixing green manure to soil does, indeed, liberate Zn from the existing soil stock and that it allows locally adapted AMF to become useful support agents in Zn uptake. The study on root and fungal hyphal Zn uptake (3) let to the discovery of synergistic facilitative Zn uptake, which must have resulted from positive root-AMF hyphal interference in mineral nutrient-rich and ZnSO4 fertilizerand green manure-enriched soil. The overall Zn uptake by roots and AMF hyphae foraging in the same volume of soil was higher than predicted, if the uptakes via roots and via hyphae each foraging alone had been strictly additive. Mycorrhizal fungal hyphal Zn uptake became, however, only quantitatively significant after ZnSO4 fertilizer and/or green manure were added to the soil. All evidence together suggests that Zn uptake by AMF depends on bioavailable soil Zn. It seems likely that