C4 plants represent about 5% of Earth's plant biomass and 1% of its known plant species. Despite this scarcity, they account for around 30% of terrestrial carbon fixation.
From a theoretical perspective, if all you want is to maximise carbon, you can focus on plants that use C4-style photosynthesis, rather than C3. From Wikipedia:
Two of the possibilities listed on that page that particularly interest me are miscanthus gigantus and millet.
I also found a few good ideas at the links below:
It seems like placing stick wood (maybe from an alder hedge?) in the garden paths, and turning it onto the beds once it's rotten, might be a reasonable replacement for exotic chipped wood.
paul wheaton wrote:
Since this is the permaculture forum and not the organic practices forum, my obnoxious opinion is a little different.
I think the long term mission is gonna be to grow stuff that will make for a long term ling mulch. A polyculture. With the soil getting richer every year without you doing anything more.
And ... when you are first getting started, sometimes it helps to take a shortcut - especially when planting in grasses or when planting in awful soil or ... well .... there are lots of excellent reasons.
I heavily favor hay and straw. I've written here before several times why I'm against newspaper and cardboard.
Hay and straw do have the risk that they are loaded with seeds and suddenly you might be growing something you don't want. My experience is that only about 5% of the straw or hay does this. So when something pops up, I just throw more straw or hay on it.