The carbon cycle is a complex thing. There is carbon in the air (carbon dioxide), carbon in plants and animals, dissolved carbon in the sea and carbon in the soil that is constantly circulating to and from. Elevated levels of atmospheric carbon dioxide may accelerate carbon cycling and soil carbon loss in forests, as found in new research led by an Indiana University biologist. The new evidence supports an emerging view that although forests remove a substantial amount of carbon dioxide from the atmosphere, much of the carbon is being stored in living woody biomass rather than as dead organic matter in soils.
Soil carbon is the generic name for carbon held within the soil, primarily in association with its organic content. Soil carbon is the largest terrestrial pool of carbon. Soil carbon plays a key role in the carbon cycle and thus is important in global climate models.
Richard P. Phillips, lead author on the paper said that after nearly two decades of research on forest ecosystem responses to global change, some of the uncertainty has been lifted about how forests are storing carbon in the wake of rising carbon dioxide levels.
“It’s been suggested that as trees take up more carbon dioxide from the atmosphere, a greater amount of carbon will go to roots and fungi to acquire nutrients, but our results show that little of this carbon accumulates in soil because the decomposition of root and fungal detritus is also increased,” he said.
Carbon stored in soils, as opposed to in the wood of trees, is desirable from a management perspective in that soils are more stable over time, so carbon can be locked away for hundreds to thousands of years and not contribute to atmospheric carbon dioxide increases.
The research was conducted at the Duke Forest Free Air Carbon Dioxide Enrichment site in North Carolina. At this site, mature loblolly pine trees were exposed to increased levels of carbon dioxide for 14 years, making it one of the longest-running carbon dioxide enrichment experiments in the world. Researchers were able to calculate the age of the carbon cycling through the soil by growing roots and fungi into mesh bags that contained uniquely labeled soils. The soils were then analyzed for their organic composition.
The authors also report that nitrogen cycled faster in this forest as the demand for nutrients by trees and microbes became greater under elevated CO2.
“The growth of trees is limited by the availability of nitrogen at this site, so it makes sense that trees are using the extra carbon taken up under elevated CO2 to prime microbes to release nitrogen bound up in organic matter,” Phillips said. “What is surprising is that the trees seem to be getting much of their nitrogen by decomposing root and fungal detritus that is less than a year old.”
The two-fold effects of microbial priming, where microbes are stimulated to decompose old soil organic matter via an increase in new carbon and other energy sources, and the faster turnover of recently fixed root and fungal carbon, are enough to explain the rapid carbon and nitrogen cycling that is occurring at the Duke Forest site.
“Most ecosystem models have limited representations of roots, and none of them include processes such as priming. Our results demonstrate that interactions between roots and soil microbes play an under appreciated role in determining how much carbon is stored and how fast nitrogen is cycled. So including these processes in models should lead to improved projections of long-term carbon storage in forests in response to global environmental change” he said.
The research article was published July 9 in the online early addition of Ecology Letters. Free access to the research article will be available until October.
For further information see Forest Soil.
Article by Andy Soos, appearing courtesy Environmental News Network.
Mzunguko wa kaboni ni jambo gumu. Kuna kaboni katika hewa (kaboni dioksidi), kaboni katika mimea na wanyama, kaboni iliyoyeyuka katika bahari na kaboni katika udongo ambayo inazunguka daima kwenda na kutoka. Kiwango cha juu cha kaboni dioksidi katika angahewa kinaweza kuharakisha mzunguko wa kaboni na kupoteza kaboni ya udongo katika misitu, kama ilivyopatikana katika utafiti mpya ulioongozwa na mwanabiolojia wa Chuo Kikuu cha Indiana. "Uhakika huo unaunga mkono maoni ya kwamba ingawa misitu huondoa kiasi kikubwa cha kaboni dioksidi kutoka angahewa, kaboni nyingi huhifadhiwa katika ""biomass"" ya mti hai badala ya kama vitu vya kikaboni vilivyo hai katika udongo." Kaboni ya udongo ni jina la jumla kwa kaboni iliyowekwa ndani ya udongo, hasa kuhusiana na maudhui yake ya kikaboni. Kaboni ya udongo ndiyo kaboni kubwa zaidi duniani. Kaboni ya udongo ina jukumu muhimu katika mzunguko wa kaboni na kwa hivyo ni muhimu katika mifano ya hali ya hewa ya kimataifa. "Richard P. Phillips, mwandishi mkuu wa jarida hilo, alisema: ""Baada ya karibu miongo miwili ya utafiti juu ya majibu ya mazingira ya misitu kwa mabadiliko ya ulimwengu, baadhi ya kutokuwa na uhakika umeondolewa kuhusu jinsi misitu inavyoweka kaboni katika hali ya kuongezeka kwa viwango vya kaboni dioksidi." "Imesemekana kwamba kama miti inachukua kaboni dioksidi zaidi kutoka angahewa, kiasi kikubwa cha kaboni itakwenda mizizi na kuvu kupata virutubisho, lakini matokeo yetu yanaonyesha kwamba kidogo ya kaboni hii hukusanyika katika udongo kwa sababu uharibifu wa mizizi na uharibifu wa kuvu pia huongezeka. """ Kaboni iliyohifadhiwa katika udongo, kinyume na katika mbao za miti, ni ya kutamaniwa kutoka kwa mtazamo wa usimamizi kwa kuwa udongo ni thabiti zaidi kwa muda, kwa hivyo kaboni inaweza kufungwa kwa mamia hadi maelfu ya miaka na haichangia ongezeko la kaboni dioksidi. Utafiti huo ulifanywa katika eneo la Duke Forest Free Air Carbon Dioxide Enrichment huko North Carolina. Katika eneo hili, miti ya msonobari ya loblolly ilifunuliwa kwa viwango vya juu vya kaboni dioksidi kwa miaka 14, na kuifanya kuwa moja ya majaribio ya muda mrefu zaidi ya kutajirisha kaboni dioksidi ulimwenguni. Watafiti waliweza kuhesabu umri wa mzunguko wa kaboni kupitia udongo kwa kukuza mizizi na kuvu katika mifuko ya mesh ambayo ilikuwa na udongo uliotiwa alama ya kipekee. Kisha udongo huo ulichunguzwa ili kujua ikiwa ulikuwa na viungo vya kikaboni. Kwa mfano, katika msitu wa Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa cha Kisiwa. "Ukubwa wa miti ni mdogo na upatikanaji wa nitrojeni katika eneo hili, kwa hivyo ina maana kwamba miti inatumia kaboni ya ziada iliyochukuliwa chini ya CO2 iliyoinuliwa kwa vimelea vya msingi ili kutolewa nitrojeni iliyounganishwa katika nyenzo za kikaboni. """ "Kila mtu anajua kwamba miti ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili ya asili.""" <unk>Mifano mingi ya mazingira ina uwakilishi mdogo wa mizizi, na hakuna moja yao inajumuisha michakato kama vile priming. Matokeo ya utafiti huu yanaonyesha kwamba mwingiliano kati ya mizizi na vimelea vya udongo una jukumu muhimu katika kuamua kiasi cha kaboni kinachohifadhiwa na jinsi nitrojeni inavyozunguka haraka. Kwa hiyo ikiwa ni pamoja na michakato hii katika mifano inapaswa kusababisha makadirio bora ya kuhifadhi kaboni ya muda mrefu katika misitu kwa kukabiliana na mabadiliko ya mazingira ya kimataifa. Makala ya utafiti ilichapishwa Julai 9 katika nyongeza ya mapema ya mtandaoni ya Barua za Ekolojia. Upatikanaji wa bure wa makala ya utafiti utakuwa inapatikana hadi Oktoba. Kwa habari zaidi tazama Ardhi ya Msitu. Makala na Andy Soos, kuonekana heshima Mazingira News Network.