Over the years, we have repeatedly seen abundant sporulation in pot cultures of a fungal community the sporulates sparsely or not at all in the field, especially in (i) pastures, (ii) semi-arid sites, and (iii) some grasslands. Relatively high sporulation can occur in the field, mostly in certain habitats such as (i) sand dunes, (ii) wetlands, and (iii) acidic minesoils, where plants are patchy and spaced widely apart. These observations indicate that interplant dynamics (with heavy involvement of interplay amongst root systems) and soil environments play an important role. Observations from different pot culture systems provide additional clues:

1. Addition of autoclaved oat kernels to a potting medium results in tremendous stimulation of shoot (and root) growth, with a 30-40 day delay in sporulation compared to the same system without oat kernels. Plant changes also are marked with mycorrhizal root length almost 1.5 times in the former than the latter. Abundance of sporulation, in spite of temporal differences, is similar in both treatments.

2. Corn growing in a 1.5 liter pot and an 8 liter pot produces more biomass in the latter. Onset of sporulation occurs 35-45 days later in the larger pot.

3. Sudangrass growing in 15-cm diameter pots (approx. 1.5 liters) will produce abundant hyphae, auxiliary cells, and a low number of spores at 90 days when colonized with Gigaspora margarita and Scutellospora heterogama, but after an additional month in which plants are somnolent (no longer growing), auxiliary cells almost disappear and sporulation increases 10-fold or more.

From the observations summarized above, we hypothesize the following is occurring in pots:

1. During the active phase of shoot and root growth, most of the carbon going to the fungi colonizing roots is invested in mycorrhizal development (where fungal growth takes advantage of ever expanding root niche space). Carbon also is allocated to external hyphal development, but mostly for hyphae that are infective (produce secondary infection units) appear to be absorptive. The fungi are not partitioning much carbon to sporulation, possibly because sink size would compromise rate and amount of mycorrhiza biomass.

2. Once roots have ceased growth because of constraints imposed by pot boundaries, mycorrhizal colonization catches up in roots and at some point also reaches stasis.

3. With continued photosynthesis in shoots, carbon is repartioned to the one niche still open to fungal growth, and that is in sporulation. This allocation continues as long as there is an active carbon source (leaves, stems). The extent of continued sporulation following stasis in plants seems to be consistently greater and longer for Gigaspora and Scutellospora species than for Glomus, Acaulospora, Entrophospora, Paraglomus, and Archaeospora spp.