Avocado guild and grafting questions

Hi, all.  A couple of questions about avocado trees:

First, a friend has a huge, old avocado tree that has a dense canopy and resulting shade underneath.  She'd like to plant in an area under the tree that gets partial sun during the day, but was told that because avocados are surface feeders, any plants she puts under the tree will just be taking the avocado's nutrients.  Anyone have ideas about what would be good to help build a guild under the tree, both in the shade and in the partially sunny spot?

Second, the same friend found a baby avocado tree growing under the big one, scooped it up with some soil, and gave it to me.  A different friend told me yesterday that fruit trees, avocados included, must be grafted to be good fruit bearers, but that this avocado could have grown up from the root stock of the tree (it doesn't appear to be from a pit) so no grafting would be necessary.  I have never done anything with respect to grafting, so this is a totally foreign area for me.  (I thought grafting was more a commercial thing to get seedless fruits -- mother nature doesn't graft, after all -- but the conversation yesterday made me realize that all my heirloom trees are grafted, so I'm guessing I'm missing something.)  Anyone have thoughts on whether this tree will bear fruit better if it's from the root of the tree versus a pit?  (I would appreciate any wisdom you'd like to share on grafting in general, too.)

Thanks for any responses!

if the original tree is a grafted tree (and it probably is), chances are good the rootstock wouldn't produce good fruit.  so if it's a root sucker, you may as well graft onto it.  alternately, if the little tree is a seedling, chances are good that it won't produce good fruit, so you may as well graft onto it.  either way, your best odds of getting good fruit will be had by grafting.

if you like the fruit your friend's tree produces, graft a scion or bud from that tree.  if you don't like that fruit, explore other options for obtaining scion wood.  local fruit groups or NAFEX (if you're in the USA) are both good places to start, and you may well get some grafting instructions out of the deal.  otherwise, the The Grafter's Handbook or something similar should do you well.

to avoid interfering with the avocado's surface feeding roots, deep-rooted plants should make up a good part of the guild.  and if avocados are heavy feeders (I'm not very familiar with them), shallow-rooted nitrogen-fixing legumes probably wouldn't hurt.

Good points, tel.  Thank you.

A lot of forest perennials are deep rooted. Comfrey could be a good idea (it has deep roots and is great for improving the soil). Mints are also good.