Best Sunlight to Biomass Plant

Given that all leaves have a net sunlight to energy efficiency conversion ratio of just 5.4%.

100% sunlight → non-bioavailable photons waste is 47%, leaving
53% (in the 400–700 nm range) → 30% of photons are lost due to incomplete absorption, leaving
37% (absorbed photon energy) → 24% is lost due to wavelength-mismatch degradation to 700 nm energy, leaving
28.2% (sunlight energy collected by chlorophyl) → 32% efficient conversion of ATP and NADPH to d-glucose, leaving
9% (collected as sugar) → 35–40% of sugar is recycled/consumed by the leaf in dark and photo-respiration, leaving
5.4% net leaf efficiency.

Which plants store that energy in the best package for carbon farming?

Elephant grass ? I know this is grown as a fuel in the UK . http://recrops.com/miscanthus
You could grow your own fuel annually
Imagine if you could use it in your rocket heater
Carbon neutral free heating even if you have no trees plus it perrrenial you just chop it down and it grows from the roots next year

David

You have ample rainfall so I think hybrid poplars would be hard to beat. Even when you harvest them above ground you are leaving tons of biomass below ground, and you can coppice them annually or more than annually if you want to control their size. Cheap, easy to propagate and require almost zero care to keep them alive.

That 5.4% is an average.

There have been some good suggestions already, but I'd like to add one to the mix.

Find plants using the C4 photosynthetic pathway. Under drought and high temperature conditions, these plants fix carbon much more efficiently than plants using the C3 pathway.

Plants using the C4 pathway account for 3% of species, 5% of total biomass (because they tend to be annuals, not perennials) and account for 30% of annual terrestrial carbon fixation (only partly because they are concentrated in the tropics and subtropics, where there is more light).

The C4 pathway seems to have evolved relatively recently, but independently. Around 46% of grasses use the C4 pathway, including maize, sugarcane, millet and sorghum.

Some members of the amaranth and cabbage families do as well, and plant breeding from non-crop varieties of these might be considered a priority.

The main problem with this suggestion is that they account for, as I say, only 3% of species. You could stack your plant list towards them, but at the expense of overall diversity.

The general rule is: anything perennial. Bonus points for woody perennial. Extra bonus points for dense, diverse plantings of long – lived woody perennials.

I note Neil you state that the 5.4% is an average there fore some plants will do better and some not so good .
So I wonder which gets the highest %
Or is this more condition dependent ?
Should this not be better put which plant has the highest potential

David

OK guys, I've asked once. Please keep stuff on topic. This forum is about carbon farming. If you want to make it about climate change, it has to go into the cider press.

Eastern gamagrass was suggested in another thread. I have a couple clumps of it in my kitchen garden, which isn't ideal for it as it would like more space, but it's a pretty cool plant:

http://agresearchmag.ars.usda.gov/2005/sep/carbon

http://www.actahort.org/books/638/638_40.htm

http://images.library.wisc.edu/EcoNatRes/EFacs/NAPC/NAPC07/reference/econatres.napc07.mbender2.pdf

David Livingston wrote:I note Neil you state that the 5.4% is an average there fore some plants will do better and some not so good .
So I wonder which gets the highest %
Or is this more condition dependent ?
Should this not be better put which plant has the highest potential

David

Actually, that's an easy one.

Sugarcane (Saccharum spp, mainly officinarum), with peak efficiencies around 8%. Efficiencies of sweet sorghum (Sorghum bicolor), and maize (Zea mays) approach this. The theoretical maximum is around 10%.

It's worth bearing in mind that monoculture sugarcane has its own problems, and there are issues to consider besides gross efficiency, so I would stand by Eric's more general advice above.

Although there may be ONE species that has the best ratio of sunlight to biomass conversion, we know, and Tyler has already said that monocropping sugar cane brings its own problems. So, even where sugar cane can grow, it needs its friends and protectors.

It is good to know which are the super producers, so that we can build communities "guilds" of plants around the high performers, and not get too drawn into the idea of the one most efficient plant. We repeat that to each other often, that a single stand of plants is highly vulnerable to disease, predatory insects, nematodes etc. IMO a pure stand of a single species is a time limited thing. Diversity is key.

I grow C4 grasses and weeds in the summer, and their rate of growth is astonishing. Kochia scoparia and amaranth, both members of the chenopodiaceae have rates of growth so fast it is truly hard to believe, but our very hot season only lasts a couple of months. Here in the high desert, we have a cool season before and after summer, and the cool season grasses grow in both those seasons, with not much going on with the kochia and amaranth. And the cool seasons combined are more than twice as long as the very hot season when the C4s can do their thing.

So, in my climate, on a year round basis I wonder which plants would capture more CO2 per square cm or square inch of leaf surface, the hot season super star C4s, or the cool season plants such as orchard grass.

My conclusion is that to maximize photosynthesis on my property and in my climate, I need a mix, so that not only is something growing year round, but at higher and lower levels of surface, sub canopy and canopy, and all the intermediate levels. IMO the best "biomass plant" is a community of synergists making sure no photon of sunlight goes un-captured.

8-10% is a theoretical high end for conversion of incident solar energy to biomass.
Actual conversion efficiencies under most circumstances are closer to 1% (maybe 4% for sugarcane).

The very highest efficiencies are only reached under moderate light; even C4 plants can be come light saturated at noon on a clear day, so those photons are wasted (maybe that is the first line in the original poster's quote?).

The answer depends in part upon the goal:
-carbon sequestration into soil carbon or standing biomass?
-or total harvestable carbon
-or total usable harvestable carbon?

So, in a tropical harvest situation sugarcane is the current winner, because some strains have nitrogen fixation, and the gabasse left from sugar production can be used as fuel.
In a temperate carbon sequestration situation a tree species or perennial grass might win because it might sequester more carbon into soil.
Miscanthus is studied for temperate situations because the leaves and stalks can be harvested after yellowing, and they contain little besides carbohydrate; the nutrients are pumped down to the roots for another round of production.

I agree that theoretical peak productivity is not always the best criteria for a permaculture situation; diversity, disease resistance, pollenator support, habitat.... are all factors

Plants are 3 dimensional. Photosynthesis can use reflected sunlight and to a lesser degree sunlight that has passed thru another leaf. Photosynthesis happens in the shade. A photon might have a 5.4% chance of being used by the first leaf it hits, but if that photon isn't used by the first leaf it doesn't just cease to exist. So the actual amount of sunlight that goes to photosynthesis can be higher than the experimental figures quoted suggest.

Please don't hate me for the following suggestion, but might kudzu be a candidate?  It grows terribly fast both above and below ground.  I know it is terribly invasive, but would it not fulfill the function of carbon sequestration?  

This would NOT be my first choice, but I think it is worth some thought.  I don't like it much either and I don't want it in my back yard but I have to wonder if it could be put to good use somehow.
Maybe if it were sterile or made determinate like tomatoes.

Eric

Willow and switchgrass can produce 4-5 tons of biomass per acre per season. Both can be very difficult to eradicate if you ever want to use the land for something else.
Biomass-type alfalfa can hit 5-6 tons of biomass per acre per season. Very easy to eradicate.
The Princess Tree (Paulownia tomentosa) yields 24-30 tons of biomass per acre after 3 years, or 8-10 tons per acre per season. Easy to eradicate if harvested in year 3. Older stands can resprout from stumps or deposit seeds, making eradication more difficult.

As for annuals, Industrial hemp can produce 5-8 tons of biomass per acre per season, depending on variety. Some volunteers will sprout the following season if allowed to flower and set seeds. Easily eradicated with mowing or tillage. Or cut when flowering begins.
I don't know of other annuals that will consistently yield 5+ tons/acre

NOTE: These figures refer solely to aboveground biomass. Belowground biomass amounts to an additional 15-50%.