Short-term physiological plasticity.Trade-off between drought and recovery responses in three Mediterranean cistus species

Short-term physiological plasticity allows plants to thrive in highly variable environments such as the Mediterranean ecosystems. In such context, plants that maximize physiological performance under favorable conditions, such as Cistus spp., are generally reported to have a great cost in terms of plasticity (i.e., a high short-term physiological plasticity) due to the severe reduction of physiological performance when stress factors occur. However, Cistus spp. also show a noticeable resilience ability in response to stress factors. We hypothesized that in Cistus species the short-term physiological response to stress and that to subsequent recovery can show a positive trade-off to offset the costs of the photosynthetic decline under drought. Gas exchange, chlorophyll fluorescence, and water relations were measured in C. salvifolius, C. monspeliensis, and C. creticus subsp. eriocephalus during an imposed experimental drought and subsequent recovery. Plants were grown outdoor in common garden conditions from seeds of different provenances. The short-term physiological response to stress and that to recovery were quantified via phenotypic plasticity index (PIstress and PIrecovery, respectively). A linear regression analysis was used to identify the hypothesized trade-off PIstress-PIrecovery. Accordingly, we found a positive trade-off between PIstress and PIrecovery, which was consistent across species and provenances. This result contributes in explaining the profit, more than the cost, of a higher physiological plasticity in response to short-term stress imposition for Cistus spp because the costs of a higher PIstress are payed back by an as much higher PIrecovery. The absence of leaf shedding during short-term drought supports this view. The trade-off well described the relative variations of gas exchange and water relation parameters. Moreover, the results were in accordance with the ecology of this species and provide the first evidence of a consistent trade-off between the short-term physiological responses to drought and recovery phases in Mediterranean species

Phenotypic plasticity of two invasive alien plant species inside a deciduous forest in a strict nature reserve in Italy

ABSTRACTInvasive alien plant species (IAPs) represent one of the main biological threats to biodiversity worldwide. Information about their phenotypic plasticity are needed to increase awareness ab..

Carbon Dioxide (CO2) Sequestration and Air Temperature Amelioration Provided by Urban Parks in Rome

Abstract Urban landscapes are rapidly expanding globally and transforming the structure and function of urban areas, thereby influencing the quality of life. Cities account for more than 70% of the energy related to global greenhouse gases, which is expected to rise up to 76% by 2030. Taking into account that over 50% of the world's population lives in cities and more than two thirds are expected by 2050, the problem of mitigating the atmospheric CO 2 concentration is considerable. The urban areas covered by parks, gardens, tree-lined avenues, sport fields, and hedges are important sinks for carbon dioxide (CO 2 ) by storing carbon through photosynthesis to form plant biomass. Despite plant CO 2 sequestration is an important ecosystem service, the relationship between urban park vegetation and CO 2 emission reduction is not completely clarified. In this context, the main objective of our research was to evaluate the role of urban park vegetation in improving air quality in Rome in terms of CO 2 concentration and air temperature. In particular, we analyzed the relationship among the different vegetation types, size and position of an historical urban park in Rome. Moreover, since the presence of buildings within urban parks determines CO 2 emissions closely related to their purpose of use, it is important to evaluate their impact in order to set instruments for their retrofit, considering the necessity of a compromise among the energy audit, the use of renewable energy systems and preservation of cultural heritage

Carbon gain optimization in five broadleaf deciduous trees in response to light variation within the crown: correlations among morphological, anatomical and physiological leaf traits

Leaf trait variations in five deciduous species (Quercus robur, Corylus avellana, Populus alba, Acer campestre, Robinia pseudoacacia) growing in an old broadleaf deciduous forest in response to light variation within the tree crown was analyzed. Net photosynthetic rate (PN), leaf respiration rate (R) and the photosynthetic nitrogen use efficiency were, on average, more than 100% higher in sun than in shade leaves. A. campestre and C. avellana sun leaves had the highest specific leaf area (SLA, 156.0 ± 17.9 cm2 g–1) and the lowest total leaf thickness (L, 101.9 ± 8.8 ?m) underlining their shade-tolerance. Among the shade- intolerant species (Q. robur, P. alba and R. pseudoacacia), Q. robur had the lowest SLA and the highest L in sun leaves (130.6 ± 10.0 cm2 g–1 and 160.8 ± 9.6 ?m, respectively) since shade-intolerant species typically have thicker leaves. The higher PN decrease in respect to R decrease from sun to shade leaves attested the higher sensitivity of PN than R to light variations within the crown. This determined a 69% lower R/PN in sun than in shade leaves. This result is further attested by the significant correlation between PN and the relative photosynthetic photon flux density. The shade-tolerant species have a 76% higher R/PN ratio than the shade-intolerant ones. The measured leaf phenotypic plasticity (PI = 0.35) was in the range of broadleaf deciduous species. Plasticity is a key trait useful to quantify plant response to environmental stimuli. It is defined as the ability of a genotype to produce different phenotypes depending on the environment. Among the considered species, Q. robur showed the highest PI (0.39) and P. alba the lowest (0.29). Knowledge on phenotypic plasticity is important in making hypotheses about the dynamics of the studied forest in consideration of environmental stress factors, including invasive species competition and global climate change

Carbon Balance of Mediterranean Evergreen Species

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.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

Morphological and physiological adaptive traits of Mediterranean narrow endemic plants: The case of Centaurea gymnocarpa (Capraia Island, Italy)

A case study on Centaurea gymnocarpa Moris & De Not., a narrow endemic species, was carried out by analyzing its morphological, anatomical, and physiological traits in response to natural habitat stress factors under Mediterranean climate conditions. The results underline that the species is particularly adapted to the environment where it naturally grows. At the plant level, the above-ground/below-ground dry mass (1.73 +/- 0.60) shows its investment predominately in the above-ground structure with a resulting total leaf area per plant of 1399 +/- 94 cm(2). The senescent attached leaves at the base of the plant contribute to limit leaf transpiration by shading soil around the plant. Moreover, the dense C gymnocarpa leaf pubescence, leaf rolling, the relatively high leaf mass area (LMA = 12.3 +/- 1.3 mg cm(-2)) and leaf tissue density (LTD = 427 +/- 44 mg cm(-3)) contribute to limit leaf transpiration, also postponing leaf death under dry conditions. At the physiological level, a relatively low respiration/photosynthesis ratio (R/P-N) in spring results from high R [2.26 +/- 0.59 mu mol (CO2) m(-2) s(-1)] and P-N [12.3 +/- 1.5 mu mol (CO2) m(-2) s(-1)]. The high photosynthetic nitrogen use efficiency [PNUE = 15.5 +/- 0.4 mu mol (CO2) g(-1) (N)s(-1)] shows the large amount of nitrogen (N) invested in the photosynthetic machinery of new leaves, associated to a high chlorophyll content (Chl = 35 +/- 5 SPAD units). On the contrary, the highest R/PN ratio (1.75 +/- 0.19) in summer is due to a significant PM decrease and increase of R in response to drought. The low PNUE [1.5 +/- 0.2 mu mol (CO2) g(-1) (N) s(-1)] in this season is indicative of a greater N investment in leaf cell walls which may contribute to limit transpiration. On the contrary, the low RIPN ratio (0.05 +/- 0.02) in winter is resulting from the limited enzyme activity of the respiratory apparatus [R = 0.23 +/- 0.08 mu mol (CO2) m(-2) s(-1)] while the low PNUE [3.5 +/- 0.2 mu mol (CO2) g(-1) (N) s(-1)] suggests that low temperatures additionally limit plant production. The experiment of the imposed water stress confirms that the C gymnocaipa growth capability is in conformity with the severe conditions of its natural habitat, likewise as it may be the case with others narrow endemic species that have occupied niches with similar extreme conditions

Variations in leaf respiration and photosynthesis ratio in response to air temperature and water availability among Mediterranean evergreen species

Net photosynthesis (P-N) and leaf respiration (R-L) of the evergreen species co-occurring in the Mediterranean maquis in response to water availability and air temperature variations were analyzed. The results underlined that the ratio R-L/P-N of the considered species ranged from 0.15 +/- 0.08 (in winter) to 1.32 +/- 0.80 (in summer). Variations of R-L and P-N 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 P-N and R-L rates and low leaf mass area (LMA) and leaf tissue density (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 P-N rates in drought and the lowest P-N 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 R-L 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 R-L rates. (C) 2013 Elsevier Ltd. All rights reserved

Physiological, morphological and anatomical trait variations between winter and summer leaves of Cistus species

Morphological, anatomical and physiological summer and winter leaf traits of Cistus incanus subsp. incanus, C. salvifolius and C. monspeliensis growing at the Botanical garden of Rome were analyzed. With regard to differences between summer and winter leaves of the considered species, leaf thickness (L) was 21% higher in summer than in winter leaves (mean of the considered species) and this increase was mostly the result of the increased palisade parenchyma thickness over the spongy parenchyma one (24 and 16% higher in summer than in winter leaves, respectively). Leaf mass area (LMA) and leaf tissue density (LTD) were 38% and 17% higher in summer than in winter leaves, respectively (mean of the considered species). The photosynthetic rate (P N), stomatal conductance (g s) and chlorophyll content (Chl) of summer leaves were 54%, 17% and 14% lower, respectively, than in winter leaves. C. monspeliensis summer leaves had the highest LMA, LTD, adaxial cuticle thickness (14.6±1.8mgcm -2, 1091±94mgcm -3, and 5.8±1.7μm, respectively) and the lowest mesophyll intercellular spaces (f ias 38±3%). Moreover, C. monspeliensis had the highest P N in summer (2.6±0.1μmolm -2s -1) and C. incanus the highest P N and WUE (84% and 59% higher than the other species) in the favorable period, associated to a higher f ias (42±2%). C. salvifolius had the highest P N (54% higher than the other species) in winter. The plasticity index could allow a better interpretation of the habitat preference of the considered species. The physiological plasticity (PI p=0.39, mean value of the considered species) was higher than the morphological (PI m=0.22, mean value) and anatomical (PI a=0.13, mean value) plasticity. Moreover, among the considered species, C. salvifolius and C. incanus are characterized by a larger PI a (0.14, mean value) which seems to be correlated with their wider ecological distribution and the more favorable conditions of the environments where they naturally occur. The highest PI m (0.29) of C. monspeliensis indicates that it can play a high adaptive role in highly stressed environments, like fire degraded Mediterranean areas in which it occurs. © 2012 Elsevier GmbH

Morphological, anatomical and physiological leaf traits of Q. ilex, P. latifolia, P. lentiscus, and M. communis and their response to Mediterranean climate stress factors

Background: Limitations to plant growth imposed by the Mediterranean climate are mainly due to carbon balance in response to stress factors. In particular, water stress associated to high air temperature and irradiance in summer causes a marked decrease in CO2 assimilation. Air temperature sensitivity of photosynthesis (P-N) differs from that of leaf respiration (R-D). P-N often decreases sharply at temperature above its optimum while R-D increases exponentially over short term rises in temperature. Nevertheless, the impact of water deficit on R-D is still far from clear with reports in literature including decreases, maintenance or increases in its rates. The ratio R-D/P-N can be considered a simple approach to leaf carbon balance because it indicates the percentage of photosynthates that is respired. Results: The results underline different morphological, anatomical and physiological traits of the evergreen species co-occurring in the Mediterranean maquis which are indicative of their adaptive capability to Mediterranean stress factors. The ratio R-D/P-N varies from 0.15 +/- 0.04 in autumn, 0.24 +/- 0.05 in spring through 0.29 +/- 0.15 in winter to 0.46 +/- 0.11 in summer. The lower R-D/P-N in autumn and spring underlines the highest P-N rates during the favorable periods when resources are not limited and leaves take in roughly three to five times more CO2 than they lose by respiration. On the contrary, the highest R-D/P-N ratio in summer underlines the lowest sensitivity of respiration to drought. Among the considered species, Quercus ilex and Pistacia lentiscus have the largest tolerance to low winter temperatures while Phillyrea latifolia and Myrtus communis to drought, and Phillyrea latifolia the highest recovery capability after the first rainfall following drought. Conclusions: The Mediterranean evergreen specie shows a different tolerance to Mediterranean climate stress factors. The predicted global warming might differently affect carbon balance of the considered species, with a possible change in Mediterranean shrublands composition in the long-term. Understanding the carbon balance of plants in water limited environments is crucial in order to make informed land management decisions. Moreover, our results underline the importance of including seasonal variations of photosynthesis and respiration in carbon balance models

Relationship between net photosynthesis and leaf respiration in Mediterranean evergreen species

The relationship between net photosynthetic (P(N)) and leaf respiration ( R) rates of Quercus ilex, Phillyrea latifolia, Myrtus communis, Arbutus unedo, and Cistus incanus was monitored in the period February 2006 to February 2007. The species investigated had low R and P(N) during winter, increasing from March to May, when mean air temperature reached 19.2 degrees C. During the favourable period, C. incanus and A. unedo had a higher mean P(N) ( 16.4 +/- 2.4 mu mol m(-2) s(-1)) than P. latifolia, Q. ilex, and M. communis ( 10.0 +/- 1.3 mu mol m(-2) s(-1)). The highest R ( 1.89 +/- 0.30 mu mol m(-2) s(-1), mean of the species), associated to a significant P(N) decrease ( 62 % of the maximum, mean value of the species), was measured in July ( mean R/P(N) ratio 0.447 +/- 0.091). Q(10), indicating the respiration sensitivity to short-term temperature increase, was in the range 1.49 to 2.21. Global change might modify R/P(N) determining differences in dry matter accumulation among the species, and Q. ilex and P. latifolia might be the most favoured species by their ability to maintain sufficiently higher P(N) and lower R during stress periods