Heliophage

Over at News@nature, Mike Hopkin reports from the Ecological Society of America’s meeting in San Jose on research into tropical forest growth rates. Looking at plots in Panama and Malaysia, the researchers found that increases in mean daily minimum temperature over a couple of decades correlated with decreases in growth rates. They associate this with lower net photosynthetic activity.

The team, led by Harvard’s Ken Feeley, suggests that if this sort of effect were repeated in bigger rainforests (most of which have only experienced marginal warming to date, as I understand it) then what are now stable stores of carbon would become net sources as theworld heats up. This is obviously a considerably less optimistic scenario than the possibility that carbon-dioxide fertilisation would make them sinks. It would presumably make the net effect of the increase in soil respiration that Peter Cox and others always stress (Nature paper from 2000) an even worse problem.

It’s not a dead cert that the change is due to temperature — the paper (published in Ecology Letters) seems to suggest that increased cloudiness could be playing a role. And there could be internal botanical changes too — maybe the lianas are doing more damage? But all in all it doesn’t sound good.

Mike is blogging the conference on the newsblog.

Cross posted at Climate Feedback

This week in Nature we have a news story on an attempt to follow up Frank Keppler’s work on methane produced aerobically by green plants which we published early last year (news story | paper). The Keppler piece, which suggested that methane emissions from green plants were a significant but previously unappreciated factor in global methane emissions, caused quit a lot of fuss, understandably, in the media — since methane is a greenhouse gas which, over short time horizons, is about 75 times more powerful than carbon dioxide — and quite a lot of befuddlement among plant scientists. If it were true, it would have significant implications for the way that people model methane production, and the levels of production that one might predict in a warming world. The debate rumbled on last year (another news report, this time by my colleague Quirin).

The new work that Tom Dueck and colleagues have published in New Phytologist (paper), though , finds no methane emissions from plants at all.

Obviously, not necessarily the last word. As Mike Hopkin reports:

Both groups have criticized the other’s choice of experimental method. Dueck says that Keppler’s group kept plants in sealed plastic containers instead of flow chambers, and exposed them to sources of stress such as bright sunlight and high temperature, which could have produced methane as an artefact. Keppler retorts that the use of ¹³C is an artificial piece of chemical trickery with unknown effects on plant metabolism, and also argues that methane production can vary by up to three orders of magnitude between species.

Keppler says other teams will be publishing results that back him up on the methane; but Mike reports that at least one other team is siding strongly with Dueck.

What Mike doesn’t mention, because an evil news editor (me) wouldn’t give him the space, is that various people in the community have pointed to an interesting contrast between the way plant scientists responded to the discovery of isoprene emissions and the Keppler work. With isoprene people said oh that’s interesting, replicated, and got on with it. This work has had a far frostier welcome.

On isoprene, this is as good a place as any to mention an interesting perspective by Manuel Lerdau in Science a few weeks ago on a possible isoprene-ozone positive feedback (paper). Isoprene within leaves protects the plants that produce it against ozone. But when isoprene gets out into the air, as it will, it can react with nitrogen oxides to make ozone. Only some species produce isoprene, and so these isoprene-producing plants both protect themselves against ozone and, in Nox-rich environments, increase the ozone stress on their non-isoprene-producing neighbours.

If this effect is real, it might have significant effects on forest composition over the next century.

One last thing to note on the Keppler story: it led to Carl Zimmer saying something nice about us, and that is always a good thing. As of course is Carl.

This post cross-posted to Climate Feedback;if you want to comment head over there.