11 research outputs found
Carbon sequestration in Mediterranean ecosystems: critical aspects related to plant respiration, wildfires and nitrogen budget
La producci贸 prim脿ria neta (NPP) de la biosfera est脿 limitada pels baixos nivells actuals de CO2 atmosf猫ric (Ca). Per conseq眉ent, l'augment de Ca degut a l'activitat humana, considerat la causa principal del canvi clim脿tic, s'hauria de traduir en un augment de la NPP i, per tant, en un augment del segrestament de Ca a la biomassa. Els augments de NPP i del segrestament de Ca ja s贸n detectables en boscos boreals i tropicals. L'augment de Ca produeix tamb茅 una disminuci贸 de la respiraci贸 vegetal ?un 17 % de mitjana?, fet que podria provocar que el segrestament de Ca fos m茅s gran que no s'havia previst. Aquests resultats han fet que alguns autors ofereixin visions for莽a optimistes sobre la capacitat dels ecosistemes terrestres per compensar l'exc茅s de Ca. No obstant aix貌, l'augment de Ca no es tradueix nom茅s en un augment de la NPP (diferent per a cada esp猫cie), sin贸 tamb茅 en canvis en la morfologia de la planta (tamb茅 diferents per a cada esp猫cie), que comportaran canvis en els patrons d'ocupaci贸 de l'espai, que fan dif铆cil predir en quin sentit canviar脿 la NPP a llarg termini en l'ecosistema sencer. No 茅s gens clar que aquestes previsions optimistes siguin aplicables als ecosistemes terrestres mediterranis, en els quals la sequera ?principal factor limitant de la NPP? s'espera que s'agreugi en un futur, com a conseq眉猫ncia del canvi clim脿tic. L'agreujament de la sequera es pot traduir en un augment del risc d'incendi, fet que pot conduir els ecosistemes mediterranis a una situaci贸 de gran inestabilitat, en cas que la periodicitat i la intensitat dels focs superin llur capacitat de recuperaci贸 (per germinaci贸 o rebrot). L'incendi implica p猫rdues importants de N i P per volatilitzaci贸; tamb茅 provoca un fort augment de la disponibilitat de nutrients (sobretot N) i, doncs, un augment de la fertilitat del s貌l. Moltes esp猫cies mediterr脿nies, i en concret l'alzina (Quercus ilex), tenen una gran capacitat d'acumular N en 貌rgans basals, probablement per facilitar un rebrot r脿pNet primary production (NPP) in the biosphere is limited by the current low atmospheric CO2 concentration (Ca). Hence, the increase in Ca due to anthropogenic activities, which is thought to be the main cause of climate change, is expected to result in an increase in NPP, and therefore in an increased Ca sequestration in the biomass. Increases in NPP and Ca sequestration in the biota are already detectable in boreal and tropical forests. Increased Ca results in a decrease in plant respiration ?on average, about 17%?, and therefore the increase in Ca sequestration could be higher than previously assumed. This has led some authors to publish highly optimistic views about the capacity of terrestrial ecosystems to compensate for the excess of Ca. Nevertheless, increased Ca results not only in an increase in NPP (different for every plant species), but also in changes in plant morphology (also different for every plant species); these will result in changes in the patterns of space occupation by plants, which make it difficult to predict how the NPP will change in the long term, at a whole-ecosystem level. It is not clear that such optimistic views can be applied to Mediterranean terrestrial ecosystems, in which drought ?the main constraint for NPP? is expected to increase in the future as a result of climate change. Increased drought is expected to lead to a greater risk of wildfires, which can generate a highly unstable situation in the ecosystem if the periodicity and intensity of fire events surpasses its capacity to recover (either by resprouting or seeding). Wildfires cause significant losses of N and P by volatilization. They also result in a strong increase in the availability of nutrients (mainly N), and hence an increase in soil fertility