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1

Needle terpene concentrations and emissions of two coexisting subspecies of Scots pine attacked by the pine processionary moth (Thaumetopoea pityocampa)

100%
Achotegui-Castells A., Llusia J., Hodar J. A., Penuelas J.
Acta Physiologiae Plantarum
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2013
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tom 35
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nr 10
Mediterranean pine forests are often attacked by caterpillars of Thaumetopoea pityocampa (Lep., Thaumetopoidae), one of the most important defoliators in the Mediterranean region causing large economic losses and ecological effects. The needle terpene concentrations and emissions may play a key role in the defense of pines. We studied two subspecies of Pinus sylvestris, nevadensis (an endemic and relict subspecies) and iberica, with different levels of caterpillar attack in Sierra Nevada mountains (Spain). GC–MS analyses showed large total concentrations of terpenes (6 to 39 mg g-1 of dry weight) in the needles of both subspecies under field conditions. Concentrations were 25 % higher in ‘‘Non-Attacked Trees’’ (NATs) of the iberica than in the nevadensis subspecies. The branches of NATs had terpene concentrations 20 % higher than those of ‘‘Attacked Branches of attacked trees’’ (ABs). Within attacked trees, the ‘‘Non-Attacked Branches’’ (NABs) also had terpene concentrations 20 % higher than those of ABs. Mainly a-pinene and germacrene D had higher concentrations in NATs and NABs than in ABs. Some terpenes had higher concentrations in NABs than in NATs, indicating possible systemic reactions. In subsp. nevadensis, the percentage of monoterpenes relative to total terpenes was higher in ABs than in other attack states. The rates of emission in nevadensis (standardized to 30 C) were ca. three times higher in ABs than in NABs and NATs. These results suggest that the lower terpene concentrations and high percentages of monoterpenes in ABs were produced by a combination of emission losses and terpene induction in response to herbivorous attack.
2

Annual and seasonal changes in foliar terpene content and emission rates in Cistus albidus L. submitted to soil drought in Prades forest (Catalonia, NE Spain)

100%
Llusia J., Penuelas J., Ogaya R., Alessio G.
Acta Physiologiae Plantarum
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2010
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tom 32
|
nr 2
We measured the gas exchange and foliar terpene concentrations and terpene emission rates of Cistus albidus throughout the seasons of two annual periods (2003 and 2005) of contrasting precipitations (900 vs. 500 mm) and in response to experimental drought in a Mediterranean forest of southern Catalonia. C. albidus showed a typical seasonal oscillation of photosynthetic rates and stomatal conductance. Maximum photosynthetic activity appeared in the spring of the first year of the study and minimum ones in both summers. Net photosynthetic rates and stomatal conductance tended to decrease with drought treatment. In the first year, Cistus albidus presented maximum values of stored terpenes in autumn and winter and minimum values in spring and summer. Average concentrations in the first year were 154 and 96 µg g⁻¹ dry matter (d.m.) for control and drought, respectively. Average concentrations in the second year were higher, 339 and 263 µg g⁻¹ (d.m.) for control and drought, respectively. The most abundant terpene was zingiberene, followed by aromadendrene, germacrene, (-)-α-cedrene, and sesquiphellandrene. The drought treatment tended to decrease terpene content, but not significantly. Considering all the treatments together, total terpene emissions ranged between practically 0 (spring 2003) to 9 µg g⁻¹ (d.m.) h⁻¹ (winter 2003). In the second year, total terpene emission rates decreased 39% in control plants, and 29% in drought plants. Significant seasonal differences in emission rates were found. Total emission rates tended to be higher in the drought treatment, especially in spring and autumn. These results help for a better understanding of the behavior of plant volatiles in Mediterranean conditions interannualy and seasonally, an issue of great interest for forest flammability and atmospheric chemistry.
3

Methanol as a signal triggering isoprenoid emissions and photosynthetic performance in Quercus ilex

100%
Seco R., Filella I., Llusia J., Penuelas J.
Acta Physiologiae Plantarum
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2011
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tom 33
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nr 6
Several volatile organic compounds (VOCs) have been reported as having a communication role between plants and also between plants and animals. We aimed to test whether methanol, a short-chain oxygenated VOC, could also have a signalling role between plants. We monitored photosynthetic performance and VOC exchange rates of Quercus ilex L. saplings before and after two different treatments: (a) clipping of some leaves to simulate an attack by herbivores and (b) fumigation with gaseous methanol for 5 h to simulate the amount of methanol a plant could receive from surrounding plants if those had been already attacked by herbivores. The clipping treatment enhanced the photosynthetic rates, the chlorophyll a to b ratio and the carotenoid to chlorophyll ratio of nonclipped leaves, suggesting an activation of plant protective metabolism. Also, a small but interesting systemic (in nonclipped leaves) increase in methanol emission rates was observed, which agrees with the possibility that methanol may act as a signalling cue. The methanol fumigation treatment induced an increase in the actual photochemical efficiency of PSII and also in the carotenoid to chlorophyll ratio. Methanol fumigation also promoted a 14% increase in the monoterpene emission rate, 1 day after the treatment, a similar response to the ones induced by other signalling VOCs. The enhanced monoterpene emissions could add to the blend of VOCs emitted after stress and be part of further signalling pathways, thus forwarding the message started by methanol. This study suggests that clipping and methanol fumigation at natural concentrations elicit significant neighbour plant physiological responses and further BVOC emissions.
4

Effects of long-term experimental night-time warming and drought on photosynthesis, Fv/Fm and stomatal conductance in the dominant species of a Mediterranean shrubland

88%
Prieto P., Penuelas J., Llusia J., Asensio D., Estiarte M.
Acta Physiologiae Plantarum
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2009
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tom 31
|
nr 4
We conducted a night-time warming and drought field experiment for 7 years (1999–2005) in a Mediterranean shrubland. We focused on the two dominant shrub species, Erica multiflora L. and Globularia alypum L. and the tree Pinus halepensis L. and the final years to study the effects of the experimental night-time warming and drought on Fv/Fm, photosynthesis, and stomatal conductance. Warming treatment increased mean air temperature and mean soil temperature through the years by an average of 0.7 and 0.9°C respectively, and drought treatment reduced soil moisture through the years by an average of 19%. Warming tended to increase photosynthetic rates in E. multiflora, G. alypum and P. halepensis mostly in the cold seasons, when plants were more limited by temperature, as shown by the lowest values of Fv/Fm being detected in winter in the three studied species. A negative effect of warming was only detected for E. multiflora in summer 2003. Drought treatment generated different responses of net photosynthetic rates depending on the species, season and year. Stomatal conductance showed the same pattern as photosynthesis for the three studied species, displaying seasonal and inter-annual variability, although with an overall negative effect of drought for P. halepensis. Photosynthetic rates decreased significantly in the dry winter 2005 and spring 2005 in comparison to the same seasons of 2003 and 2004. There were positive correlations between the photosynthetic rates in different seasons for E. multiflora, G. alypum and P. halepensis and the soil moisture of the week prior to measurements. The great variation in the photosynthetic rates was thus explained in a significant part by soil moisture levels. The lowest Fv/Fm values usually corresponded with lowest stomatal conductances suggesting that drought stress could be associated to stress by low temperatures in winter.
5

Effects of UV radiation and water limitation on the volatile terpene emission rates, photosynthesis rates, and stomatal conductance in four Mediterranean species

88%
Llusia J., Llorens L., Bernal M., Verdaguer D., Penuelas J.
Acta Physiologiae Plantarum
|
2012
|
tom 34
|
nr 2
This study examined the effects of the combination of UV radiation and water limitation on the leaf photosynthesis, stomatal conductance, and terpene emissions of four Mediterranean species. 1-year-old seedlings of these Mediterranean species [Daphne gnidium L., Pistacia lentiscus L., Ilex aquifolium L. and Laurus nobilis L.] were grown under one of three UV treatments (without UV, with UVA, or with UVA + UVB) and two watering regimes (high and low water supply). In general, UV treatments did not affect significantly leaf photosynthesis or stomatal conductance, although UVA and UVB radiation in September led to a reduction in leaf stomatal conductance in D. gnidium. Leaf photosynthesis rates did not differ significantly between the two watering treatments, even though, in three of the species, leaf stomatal conductance was significantly higher among the well-watered plants. The effects of UV on terpene emissions were species-specific; D. gnidium had the highest terpene emission rates when grown under UVA + UVB radiation, which was also true for L. nobilis in September. Overall, UV treatments did not have a significant effect on total terpene emission rates in I. aquifolium, but UVB and UVA in July and September, respectively, reduced emission rates in P. lentiscus. A limited water supply reduced the terpene emission rates in D. gnidium, increased emissions in L. nobilis, and did not affect the emission rates in the other two species.
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