Cryptic contribution to N (and C) cycles

Image: Jialiang Gao, Wikimedia Commons.

Image: Jialiang Gao, Wikimedia Commons.

In this global-climate-change-obsessed world we fre­quently hear the term car­bon sink, which is a ‘nat­ural or arti­fi­cial reser­voir that accu­mu­lates and stores some carbon-containing chem­ical com­pound for an indef­in­ite period’. The emphasis on car­bon is under­stand­able since car­bon diox­ide is one of the most import­ant green­house gases (GHGs) whose accu­mu­la­tion in the atmo­sphere con­trib­utes to an increase in global tem­per­at­ures – the green­house effect. Intuitively, one way to reduce that aer­ial CO2 bur­den is to reduce the amount added to the air, and/or increase the rate at which it is removed from the atmo­sphere. And the botan­ic­ally inclined amongst you will surely sug­gest that main­tain­ing, or even increas­ing, areas of veget­a­tion – which by dint of that mar­vel­lous pho­to­bi­o­chem­ical pro­cess known as pho­to­syn­thesis con­sume CO2 – will be a desir­able thing. Which is why tra­di­tion­ally we have pre­sumed large forest areas to be such import­ant car­bon sinks – not only do they remove CO2 in pho­to­syn­thesis, but also much of that car­bon is fixed within their trunks and stored for as long as the tree con­tin­ues to grow. Hence there are major con­cerns over the rate at which forests are being removed in such areas as the Amazon. Well, it seems that in con­cen­trat­ing on the big things we have ignored the very small things that are also major play­ers in this drama and which help to make con­struc­tion of that arboreal sink pos­sible. For example, it is easy to for­get that build­ing such massive struc­tures as trees requires not only car­bon, but also nitro­gen and all of the other essen­tial plant nutri­ents. So, regard­less of how much car­bon is avail­able, the value of trees as a car­bon sink will be lim­ited by the factors that limit plant growth. That is why you should not ignore the con­tri­bu­tion of the pho­toauto­trophic cryp­to­gams – cyanobac­teria, algae, fungi, lichens and bry­ophytes. Being so small they are eas­ily over­looked, yet can cover large areas of such sur­faces as soil, rocks and even other plants, and accord­ing to Wolfgang Elbert et al., glob­ally they may account for almost 50% of ter­restrial bio­lo­gical nitro­gen fix­a­tion. Which, in turn, is neces­sary to help make atmo­spheric nitro­gen bio­lo­gic­ally avail­able to other organ­isms, such as trees, whose role as car­bon sinks is so import­ant in ameli­or­at­ing atmo­spheric car­bon levels… And we shouldn’t under­es­tim­ate the import­ance of these land– and oceanic-based car­bon sinks (in which regard, look out for my next post), whose global car­bon uptake has almost doubled in the past 50 years accord­ing to Ashley Ballantyne et al. 

Nigel Chaffey. ORCID 0000-0002-4231-9082

Nigel is a botanist and full-time academic at Bath Spa University (Bath, near Bristol, UK). As News Editor for the Annals of Botany he contributes the monthly Plant Cuttings column to that august international botanical organ. His main goal is to inform (hopefully, in an educational, and entertaining way...) about plants and plant-people interactions.

1 Response

  1. Jacques Verulam says:

    If the world really is “global-climate-change-obsessed” it’s largely due to art­icles like this one that repeat the old glib state­ments about global tem­per­at­ures increas­ing due to ‘green­house gases’. Global tem­per­at­ure is an elu­sive concept: about the closest we can come to a meas­ure of it is the aver­age (weighted, or oth­er­wise) of tem­per­at­ures meas­ured at all avail­able weather sta­tions. And this fig­ure con­tin­ues to show a com­plex pat­tern of cyc­lical rises and falls, but no under­ly­ing increase since the turn of the cen­tury, even though the tiny pro­por­tion of CO2 in the atmo­sphere con­tin­ues to creep up.

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