Photosynthesis and respiration are the most fundamental plant physiological processes which affect carbon cycle on a scale ranging from the leaf to the globe (Cavaleri et al.,2008). Respiration and photosynthesis are strongly coupled and interdependent in leaves of higher plants (Atkin et al., 2007). The temperature sensitivity of photosynthesis differs from that of respiration, and hence the ratio between the two processes may be altered following a short-term change in temperature (Loveysetal., 2002). In this context, the main object of this research was to analyze variation in the ratio RL/PN of the species co-occurring in the Mediterranean maquis in response to water availability and air temperature during the year. Variations of the ratio RL/PN might imply change in Mediterranean species structure and productivity in the long term (Saxe et al., 2001) by causing changes in species presence and, in turn in vegetation. Improving knowledge on processes and factors influencing carbon balance is important in making accurate models of CO2 exchange between vegetation and the atmosphere (Armstrong et al., 2006). Moreover, taking into account that respiration of terrestrial ecosystems is a major flux in the global carbon cycle and a potentially important positive feedback mechanism for climate change (Schimel, 1995), data on the response of the ratio RL/PN to environmental changes is an important aspect for predicting future global atmospheric CO2 concentration. The results highlight that the ratio RL/PN of the considered species ranged from 0.16± 0.09 (in winter) to 1.44±0.93 (in summer). Variations of RL and PN during the year were attested by the PCA which was carried out using leaf physiological and morphological traits of the considered species. In particular, Cistus incanus having the highest mean yearly PN and RL rates and low LMA and LTD was furthest from the other species emphasizing its drought semi-deciduous habitus, the highest photosynthetic capability in favorable conditions (spring), but low tolerance to drought. Erica multiflora and Rosmarinus officinalis were characterized by the highest LMA and LTD, low PN rates in drought and the lowest PN ones in spring. Erica arborea, Pistacia lentiscus, Phillyrea latifolia and Quercus ilex had the highest drought tolerance. Arbutus unedo and Smilax aspera were close to this group despite lower RL rates during the year. The xeromorphic leaves of the considered evergreen species (i.e. high LMA and LTD) favor carbon gain profits over transpiration losses during drought, nevertheless, the high construction cost of these leaf type justifies the relatively high RL rates. The ratio RL/PN can be used to evaluate plant carbon gain in response to environmental factor variations. Moreover, our findings of a seasonal variation in the ratio RL/PN are consistent with those of Zaragoza-Castells et al. (2008) showing that the ratio increases in response to the increase of temperature and in drought. The hypothesized extension of the dry season in the Mediterranean area, as forecasted in the next decades by climatic models (IPCC, 2007) might favor P. latifolia, P. lentiscus, Q. ilex, A. unedo and E. arborea by their capability to maintain a lower RL/PN ratio during drought, which is indicative of a more positive carbon balance, compared to C. incanus, E. multiflora, R. officinalis and S. aspera. Thus, we can assume that the species able to keep a positive carbon balance during drought will be more adapted in dealing with stronger environmental stress. The vegetation of the Mediterranean shrublands contributes to a relevant amount of carbon sequestration at a global level (Gratani et al.,2013), and in the long term the different competitive ability could determine change in the community structure and composition, resulting in variations of the CO2 sequestration capacity.
Il bilancio del carbonio è il risultato del rapporto tra i tassi di fotosintesi e quelli di respirazione e le elevate temperature e la scarsa disponibilità idrica possono incidere negativamente su tale bilancio (Galmés et al. 2007). Comprendere la relazione tra la respirazione e l’attività fotosintetica consentirebbe di ipotizzare la capacità di risposta delle specie vegetali alla variazione dei fattori ambientali. L’obiettivo della ricerca è stato quello di valutare le variazioni del bilancio del carbonio nelle specie della macchia mediterranea alle variazioni della disponibilità idrica e della temperatura. In particolare sono state prese in considerazione le tipiche specie sclerofille (Arbutus unedo, Phillyrea latifolia, Pistacia lentiscus, Quercus ilex), le semidecidue all’aridità (Cistus incanus), le aghiformi (Erica arborea, Erica multiflora, Rosmarinus officinalis) e le lianose (Smilax aspera). I risultati nel loro insieme sottolineano un’attività fotosintetica continua nel corso dell’anno con i tassi più elevati di Pn, associati a tassi relativamente elevati tassi di R per tutte le specie considerate fra Aprile e Maggio con una temperatura media di 17.0 ± 2.3 °C e una buona disponibilità idrica. In tali condizioni il rapporto R/Pn è relativamente basso e i tassi elevati di Pn favoriscono l’accumulo di biomassa necessaria per supportare l’attività vegetativa (Gratani et al. 2008). Tra le specie esaminate, E. multiflora e R. officinalis mostrano il più alto R/Pn (0.34 ±0.04, valore medio), giustificato da alti valori di R associati a i più bassi tassi di Pn. Quest’ultimo risultato può essere messo in relazione agli elevati valori di LMA e LTD. Il basso valore di R/Pn (0.11 ±0.05) misurato in A. unedo è da mettere in relazione ad una attività fotosintetica elevata, giustificata da bassi valori di LMA e LTD (15.8 ± 0.6 mg cm-2 e 419 ± 7 mg cm-3, rispettivamente), che aumentano la capacità di diffusione della CO2 negli spazi intercellulari (Parkust, 1994). In estate, quando le elevate temperature sono associate alla minore disponibilità idrica, il rapporto R/Pn mostra il più alto valore misurato nel corso dell’anno, giustificato dalla maggiore riduzione dei tassi di Pn associato ai più alti valori di R. In questo periodo, E. multiflora, R. officinalis, C. incanus e S. aspera mostrano il valore più elevato di R/Pn, giustificato da una riduzione dell’85% dei tassi di Pn, associato ad elevati valori di R, giustificati da un apparato radicale poco profondo. E. arborea, P. latifolia, P. lentiscus e Q. ilex mostrano i valori più bassi del rapporto R/Pn (0.81±0.09) giustificati da una minore riduzione dei tassi di Pn favoriti da un apparato radicale profondo (Green et al. 2005) e valori relativamente alti valori di LMA e LTD, che aumentano la resistenza allo stress d’aridità (Gratani e Varone, 2006). Nell’insieme i risultati mostrano la diversa risposta delle specie ai fattori di stress tipici delle aree caratterizzate dal clima Mediterraneo. In particolare, il bilancio del carbonio durate il corso dell’anno varia da 0.16±0.09 (in l’inverno) a 0.23±0.08 (nel periodo favorevole) raggiungendo il valore più elevato (1.44±0.93) in l’estate e il rapporto R/Pn può essere utilizzato per analizzare la risposta del bilancio del carbonio alle variazioni delle condizioni ambientali. In particolare, il previsto aumento dell’ intensità del periodo di aridità nel Bacino del Mediterraneo (IPCC, 2007) potrà favorire P. latifolia, P. lentiscus, Q. ilex, A. unedo e E. arborea. Considerando che la vegetazione della macchia mediterranea contribuisce in maniera significativa al sequestro del carbonio a livello globale (Gratani et al. 2013), la diversa capacità competitiva delle specie potrebbe determinare nel lungo periodo cambiamenti nella struttura e nella composizione, determinando di conseguenza variazioni nella capacità di sequestro della CO2.
Carbon Balance of Mediterranean Evergreen Species / Catoni, Rosangela. - ELETTRONICO. - (2013).
Carbon Balance of Mediterranean Evergreen Species
CATONI, ROSANGELA
01/01/2013
Abstract
Photosynthesis and respiration are the most fundamental plant physiological processes which affect carbon cycle on a scale ranging from the leaf to the globe (Cavaleri et al.,2008). Respiration and photosynthesis are strongly coupled and interdependent in leaves of higher plants (Atkin et al., 2007). The temperature sensitivity of photosynthesis differs from that of respiration, and hence the ratio between the two processes may be altered following a short-term change in temperature (Loveysetal., 2002). In this context, the main object of this research was to analyze variation in the ratio RL/PN of the species co-occurring in the Mediterranean maquis in response to water availability and air temperature during the year. Variations of the ratio RL/PN might imply change in Mediterranean species structure and productivity in the long term (Saxe et al., 2001) by causing changes in species presence and, in turn in vegetation. Improving knowledge on processes and factors influencing carbon balance is important in making accurate models of CO2 exchange between vegetation and the atmosphere (Armstrong et al., 2006). Moreover, taking into account that respiration of terrestrial ecosystems is a major flux in the global carbon cycle and a potentially important positive feedback mechanism for climate change (Schimel, 1995), data on the response of the ratio RL/PN to environmental changes is an important aspect for predicting future global atmospheric CO2 concentration. The results highlight that the ratio RL/PN of the considered species ranged from 0.16± 0.09 (in winter) to 1.44±0.93 (in summer). Variations of RL and PN during the year were attested by the PCA which was carried out using leaf physiological and morphological traits of the considered species. In particular, Cistus incanus having the highest mean yearly PN and RL rates and low LMA and LTD was furthest from the other species emphasizing its drought semi-deciduous habitus, the highest photosynthetic capability in favorable conditions (spring), but low tolerance to drought. Erica multiflora and Rosmarinus officinalis were characterized by the highest LMA and LTD, low PN rates in drought and the lowest PN ones in spring. Erica arborea, Pistacia lentiscus, Phillyrea latifolia and Quercus ilex had the highest drought tolerance. Arbutus unedo and Smilax aspera were close to this group despite lower RL rates during the year. The xeromorphic leaves of the considered evergreen species (i.e. high LMA and LTD) favor carbon gain profits over transpiration losses during drought, nevertheless, the high construction cost of these leaf type justifies the relatively high RL rates. The ratio RL/PN can be used to evaluate plant carbon gain in response to environmental factor variations. Moreover, our findings of a seasonal variation in the ratio RL/PN are consistent with those of Zaragoza-Castells et al. (2008) showing that the ratio increases in response to the increase of temperature and in drought. The hypothesized extension of the dry season in the Mediterranean area, as forecasted in the next decades by climatic models (IPCC, 2007) might favor P. latifolia, P. lentiscus, Q. ilex, A. unedo and E. arborea by their capability to maintain a lower RL/PN ratio during drought, which is indicative of a more positive carbon balance, compared to C. incanus, E. multiflora, R. officinalis and S. aspera. Thus, we can assume that the species able to keep a positive carbon balance during drought will be more adapted in dealing with stronger environmental stress. The vegetation of the Mediterranean shrublands contributes to a relevant amount of carbon sequestration at a global level (Gratani et al.,2013), and in the long term the different competitive ability could determine change in the community structure and composition, resulting in variations of the CO2 sequestration capacity.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
