Most work on root proliferation to a localized nutrient supply has ignored the possible role of mycorrhizal fungi, despite their key role in nutrient acquisition. Interactions between roots of Plantago lanceolata, an added arbuscular mycorrhiza (AM) inoculum and nitrogen capture from an organic patch (Lolium perenne shoot material) dual-labelled with 15N and 13C were investigated, to determine whether root proliferation and nitrogen (N) capture was affected by the presence of AM fungi. Decomposition of the organic patch in the presence and absence of roots peaked in all treatments at day 3, as shown by the amounts of 13CO2 detected in the soil atmosphere. Plant N concentrations were higher in the treatments with added inoculum 10 d after patch addition, but thereafter did not differ among treatments. Plant phosphorus concentrations at the end of the experiment were depressed by the addition of the organic residue in the absence of mycorrhizal inoculum. Although uninoculated plants were also colonized by mycorrhizal fungi, colonization was enhanced at all times by the added inoculum. Addition of the AM inoculum increased root production, observed in situ by the use of minirhizotron tubes, most pronouncedly within the organic patch zone. Patch N capture by the end of the experiment was c. 7.5% and was not significantly different as a result of adding an AM inoculum. Furthermore, no 13C enrichments were detected in the plant material in any of the treatments showing that intact organic compounds were not taken up. Thus, although the added AM fungal inoculum benefited P. lanceolata seedlings in terms of P concentrations of tissues it did not increase total N capture or affect the form in which N was captured by P. lanceolata roots.

To test the ability of plants to integrate small-scale imbalances in soil nitrate and phosphate patches, plant growth and acquisition of nitrate and phosphate were measured for the perennial grass Agropyron desertorum (Fisch. ex Link) Schult. and the shrub Artemisia tridentata Nutt. ssp. vaseyana (Rydb.) Beetle in soil where the principal supply of nitrate and phosphate came from two enriched patches. The soil was calcareous loamy-skeletal Typic Haploxerolls. These patches were applied in two treatments: either nitrate and phosphate were applied in both patches (balanced treatment) or one patch contained only nitrate and the other only phosphate (unbalanced treatment). The same total quantity of nutrients was applied in both treatments and these included 15N and 32P tracers. The plants were in large pots in open field conditions. There were no significant differences in total biomass production and nitrogen concentration between the two treatments, indicating that both species had the physiological ability to integrate soil nutrient resources. Artemisia was able to acquire more phosphate in the unbalanced treatment, probably due to the high local solution phosphate concentration. Generally Artemisia acquired more N and P than did Agropyron.