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1.
Leaf morphology, longevity, and demography were examined in Quercus ilex and Phillyrea latifolia growing in a holm oak forest in Prades mountains (northeast Spain). Four plots (10 × 15 m) of this forest were submitted
to an experimental drought during three years (soil moisture was reduced about 15 %). Leaf area, thickness and leaf mass per
area ratio (LMA) were measured in sun and shade leaves of both species. Leaf longevity, the mean number of current-year shoots
produced per previous-year shoot (Sn/Sn-1), the mean number of current-year leaves per previous-year shoot (Ln/Sn-1), and
the percentage of previous-year shoots that developed new ones were measured once a year, just after leaf flushing. LMA and
leaf thickness increased since leaf unfolding except in summer periods, when stomatal closure imposed low photosynthetic rates
and leaves consumed their reserves. LMA, leaf area, and leaf thickness were higher in Q. ilex than in P. latifolia, but leaf density was higher in the latter species. Drought reduced the leaf thickness and the LMA of both species ca. 2.5 %. Drought also increased leaf shedding up to ca. 20 % in Phillyrea latifolia and decreased it up to ca. 20 % in Q. ilex. In the later species, Sn/Sn-1 decreased by 32 %, Ln/Sn-1 by 41 %, percentage of shoots developed new ones by 26 %, and leaf
area by 17 %. Thus the decrease of leaf number and area was stronger in the less drought-resistant Q. ilex, which, under increasingly drier conditions, might lose its current competitive advantage in these Mediterranean holm oak
forests. 相似文献
2.
The photochemical reflectance index (PRI), based on reflectance signatures at 531 and 570 nm, and associated with xanthophyll pigment inter-conversion and related thylakoid energisation, was evaluated as an indicator of photosynthetic function in a Mediterranean holm oak (Quercus ilex L.) coppice. The chlorophyll fluorescence pulse-amplitude-modulation and the eddy correlation techniques were used to estimate the photosystem 2 photochemical efficiency of leaves and the CO2 flux over the canopy, respectively. The reflectance and fluorescence techniques yielded identical estimates of the photosynthetic activity in leaves exposed to dark-light-dark cycles or to a variable irradiance in laboratory. However, there was no such correlation between photosynthetic performance and PRI when applied to a sun-exposed canopy in field conditions. Fluorescence profiles inside the canopy and especially a helpful use of multispectral reflectance imaging highlight the limitations of such method. 相似文献
3.
Yield, carbon isotope discrimination, canopy reflectance and cuticular conductance of barley isolines of differing glaucousness 总被引:2,自引:0,他引:2
Febrero A; Fernandez S; Molina-Cano J; Araus J 《Journal of experimental botany》1998,49(326):1575-1581
The roles of wax bloom (Glaucousness) in discrimination against stable
isotope 13C () and yield were studied for 2
years on a pair of near-isogenic lines of two-rowed barley
(Hordeum vulgare L.) differing in their degree of
glaucousness of the spike and the upper vegetative parts of the plant other
than leaf blades. The effects of glaucousness on canopy reflectance and
cuticular conductance were also assessed. Plants were grown under fully
irrigated and rainfed Mediterranean conditions for 2 years. Grain yield for
both years and total straw biomass measured in the second year were higher
in glaucous than non-glaucous lines under both irrigated and rainfed
conditions. followed the same pattern in both grain and straw
with the highest values in the glaucous line under irrigation and the
lowest in the non-glaucous line under rainfed conditions. Differences in
yield and between the lines were greater under irrigated than
rainfed conditions. The higher of the glaucous line suggests that
these plants had lower transpiration efficiency (net photosynthesis to
transpiration ratio) than the non-glaucous line in the long term. Canopy
reflectance at some of the wavelengths of the PAR
region (400-700 nm) was significantly higher in the glaucous than in the
non-glaucous line under both irrigated and rainfed conditions. Rainfed
conditions also increased canopy reflectance in the
PAR region. No significant effect of either
glaucousness or water regime was observed in cuticular conductance or
amount of cuticular waxes of the flag leaf blades or the
ear. 相似文献
4.
Interspecific Differences of Leaf Gas Exchange and Water Relations of Three Evergreen Mediterranean Shrub Species 总被引:1,自引:1,他引:0
Leaf gas exchange and plant water relations of three co-occurring evergreen Mediterranean shrubs species, Quercus ilex L. and Phillyrea latifolia L. (typical evergreen sclerophyllous shrubs) and Cistus incanus L. (a drought semi-deciduous shrub), were investigated in order to evaluate possible differences in their adaptive strategies, in particular with respect to drought stress. C. incanus showed the highest annual rate of net photosynthetic rate (P
N) and stomatal conductance (g
s) decreasing by 67 and 69 %, respectively, in summer. P. latifolia and Q. ilex showed lower annual maximum P
N and g
s, although P
N was less lowered in summer (40 and 37 %, respectively). P. latifolia reached the lowest midday leaf water potential (1) during the drought period (–3.54±0.36 MPa), 11 % lower than in C. incanus and 19 % lower than in Q. ilex. Leaf relative water content (RWC) showed the same trend as 1. C. incanus showed the lowest RWC values during the drought period (60 %) while they were never below 76 % in P. latifolia and Q. ilex; moreover C. incanus showed the lowest recovery of 1 at sunset. Hence the studied species are well adapted to the prevailing environment in Mediterranean climate areas, but they show different adaptive strategies that may be useful for their co-occurrence in the same habitat. However, Q. ilex and P. latifolia by their water use strategy seem to be less sensitive to drought stress than C. incanus. 相似文献
5.
Contribution of physiological and morphological adjustments to drought resistance in two Mediterranean tree species 总被引:1,自引:0,他引:1
Plant water potential (ψ), its components, and gas exchange data of two Mediterranean co-occurring woody species (Quercus ilex L. and Phillyrea latifolia L.) were measured in response to seasonal changes in water availability over two consecutive years. The relative contribution
of physiological and morphological adjustments to drought resistance was assessed through Principal Component Analyses. There
were large adjustments in stomatal conductance (∼36 % of accounted variance). Net photosynthetic rate and water use efficiency
were closely tuned to water availability and accounted for ∼17 % of variance. The slope of the water potential vs. relative water content (dψ/dRWC0) below zero pressure potential increased as a result of seasonal and ontogenic increases in apoplastic water fraction and
accounted for ∼20 % variance. This tolerance mechanism was accompanied by an increased range of positive pressure potential,
suggesting a functional role of sclerophylly in these Mediterranean evergreens. Similarly, changes in the slope of dψ/dRWC
in the range of positive pressure potential (∼13 % of accounted variance) were associated to variations in cell wall elasticity
and resulted in lower RWC at zero pressure potential. When considering the species studied separately, the results indicated
the primary role of stomatal regulation in the drought resistance of Qilex, while increased apoplastic water fraction had a major contribution in the drought resistance of P. latifolia.
This research was supported by Spanish CICYT grants CLI99-0479 and REN-2002-00633. L.S. acknowledges the financial support
from Ministerio de Ciencia y Tecnologia (“Ramon y Cajal” program, Spain).
An erratum to this article is available at . 相似文献
6.
Nitrogen deficiency reduces the photosynthetic capacity of both C3 and C4
plants. The regulation of photosynthetic gas exchange in eight clones of
the C4 grass, sugarcane (Saccharum spp.), grown at
three levels of N availability was studied to determine whether N stress
diminishes the efficiency of the C4 CO2 concentrating system in addition to
reducing overall rates of photosynthesis. The quantum yield for CO2 uptake
decreased linearly with decreasing leaf N content. Genetic variation in
quantum yield at a given level of N supply was also observed. Leaf tissue
carbon isotope discrimination () increased linearly with
decreasing quantum yield. Concurrent determinations of the prevailing ratio
of intercellular to ambient partial pressure of CO 2
(pi/pa) during leaf gas exchange
suggested that the observed variation in was almost entirely
attributable to variation in bundle sheath leakiness to CO2 ()
rather than pi/pa. Taken
together, these results point to substantial environmental and genetic
variation in the efficiency of the CO2 concentrating system in sugarcane.
Reduced partitioning of carboxylase activity to ribulose-1,5-bisphosphate
carboxylase relative to phosphoenolpyruvate carboxylase in N-deficient
plants suggested that the associated increase in and decline in
quantum yield may have been attributable largely to a decline in C3 cycle
activity in the bundle sheath relative to C4 cycle activity in the
mesophyll. Quantum yield and intrinsic water use efficiency (WUE) were
negatively correlated. In contrast with the trade-off between intrinsic
light- and water use efficiency, photosynthetic nitrogen-use efficiency and
intrinsic WUE were positively correlated. 相似文献
7.
Tissue-water relations were used to characterize the responses of two Mediterranean co-occurring woody species (Quercus ilex L. and Phillyrea latifolia L.) to seasonal and experimental drought conditions. Soil water availability was reduced 15% by partially excluding rain throughfall and lateral flow (water runoff). Seasonal and experimental drought elicited physiological and morphological adaptations other than osmotic adjustment: both species showed large increases in cell-wall elasticity and decreased saturated-to-dry-mass ratio. Increased elasticity (lower elastic modulus) resulted in concurrent decreases in relative water content at turgor loss. In addition, P. latifolia showed significant increases in apoplastic water fraction. Decreased saturated-to-dry-mass ratio and increased apoplastic water fraction were accompanied by an increased range of turgor maintenance, which indicates that leaf sclerophyllous traits might be advantageous in drier scenarios. In contrast, the degree of sclerophylly (as assessed by the leaf mass-to-area ratio) was not related to tissue elasticity. An 15% reduction in soil water availability resulted in significant reductions in diameter growth when compared to control plants in both species. Moreover, although P. latifolia underwent larger changes in tissue water-related traits than Q. ilex in response to decreasing water availability, growth was more sensitive to water stress in P. latifolia than in Q. ilex. Differences in diameter growth between species might be partially linked to the effects of cell-wall elasticity and turgor pressure on growth, since Q. ilex showed higher tissue elasticity and higher intrinsic tolerance to water deficit (as indicated by lower relative water content at turgor loss) than P. latifolia. 相似文献
8.
We conducted a 6-year field manipulation drought experiment in an evergreen Quercus ilex forest where we simulated the drought predicted by GCM and ecophysiological models for the coming decades (an average of
15% soil moisture reduction). We thereby tested the hypothesis that enhanced drought will change Ca, Fe, Mg, Mo and S availability,
concentrations and accumulation patterns in Mediterranean ecosystems. The strongest effects of drought occurred in the soil.
Drought increased the total soil concentrations of S, the soil extract concentrations of Fe, Mg and S, the Mg saturation in
the soil exchangeable complex and tended to increase the percentage base saturation of the soil exchangeable complex. These
increased soil concentrations were related to a decrease of plant uptake capacity and not to an increase of soil enzyme activity,
which in fact decreased under drier conditions. Drought increased leaf Mg concentrations in the three dominant species although
only significantly in Quercus ilex and Arbutus unedo (20 and 14%, respectively). In contrast, drought tended to decrease Ca in Phillyrea latifolia (18%) and Ca and Fe concentrations in the wood of all three species. Drought increased Ca and Fe concentrations in the roots
of Quercus ilex (26 and 127%). There was a slight general trend to decrease total biomass accumulation of nutrients that depend on water
flux such as Mg, Fe and S. This effect was related to a decrease of soil moisture that reduced soil flow, and to a decrease
in photosynthetic capacity, sap flow, transpiration and growth, and therefore plant uptake capacity under drought observed
in Quercus ilex and Arbutus unedo. On the contrary, drought increased Mo accumulation in aboveground biomass in Phillyrea latifolia and reduced Mo accumulation in Arbutus unedo by reducing growth and wood Mo concentrations (51%). Phillyrea latifolia showed a great capacity to adapt to drier conditions, with no decrease in growth, an increase of Mo uptake capacity and a
decrease in leaf Ca concentration, which was related to a decrease in transpiration under drought. The results indicate asymmetrical
changes in species capacity to accumulate these elements, which are likely to produce changes in inter-specific competitive
relations among dominant plant species and in their nutritional quality as food sources. The results also indicate that drought
tended to decrease nutrient content in aboveground biomass, mainly through the decrease in growth and transpiration of the
most sensitive species and caused an increase in the availability of these nutrients in soil. Thus, drought decreased the
ecosystem’s capacity to retain Mg, Fe and S, facilitating their loss in torrential rainfalls. 相似文献
9.
Ecology of vegetative regeneration after coppicing in macchia stands in central Italy 总被引:1,自引:0,他引:1
Vegetative regeneration after coppicing of Quercus ilex, Phillyrea latifolia, and Fraxinus ornus in two macchia stands in the Maremma Nature Park (Grosseto, Italy) has been studied.Observations during the first three years after the cut showed that horizontal space occupation by shoots is rapid (95% of the available space being reoccupied within 3 yrs.) and stool mortality very low. We observed differences among species in resprouting, growth pattern and shoot differentiation. Q. ilex and P. latifolia had a longer budburst period than F. ornus. There were no considerable differences in height growth among the three species in the first year. During the second and third years the height increments decreased. F. ornus average height increments were higher than those of Q. ilex and P. latifolia. These two species produced proleptic flushes from the first year on, while F. ornus only showed spring flush. The examination of proleptic shoots and of summer and autumn rainfall seem to show that the latter control Q. ilex growth and shoot differentiation more than that of other species. Differentiation among shoots of the same stool occurs from the first year onwards and the initial vigour differences amongst shoots remain during the following years. Resprouting, space occupation and shoot differentiation have been discussed in relation to rainfall and temperature.The high stool survival and the strong link between stool vigour parameters before and after coppicing confirm a certain stability in successional dynamics following a single coppicing event.Abbreviations CA
Crown Projection Area
- DBH
Diameter at Breast Height (1.30 m)
-
F. ornus
Fraxinus ornus
- G
Basal area at Breast Height (1.30 m)
- HD
Height of the dominant shoot per stool
- ND
Number of the dominant shoots per stool
-
P. latifolia
Phillyrea latifolia
-
Q. ilex
Quercus ilex 相似文献
10.
Romà Ogaya Josep PeñuelasDolores Asensio Joan Llusià 《Environmental and Experimental Botany》2011,71(2):123-127
A rain exclusion experiment simulating drought conditions expected in Mediterranean areas for the following decades (15% decrease in soil moisture) is being conducted since 1999 in a Mediterranean holm oak forest to study its response to the forecasted climatic changes for the coming decades. The maximum PSII quantum yield of primary photochemistry (Fv/Fm) was measured in Quercus ilex, and Phillyrea latifolia, the co-dominant species of the studied forest, from 1999 to 2009 in four plots: two of them were control plots and the other two plots received the rain exclusion treatment. In both species, the Fv/Fm values were highly dependent on air temperatures, and in a second term, in water availability. P. latifolia was the species with the larger decrease in Fv/Fm values induced by low air temperatures, while in hot seasons, the Fv/Fm values in P. latifolia were even higher than in Q. ilex. Rainfall exclusion decrease Fv/Fm values significantly only in few monitoring dates. The most drought resistant species P. latifolia was more affected by the experimental rainfall exclusion than Q. ilex that instead lost number of leaves per tree. There was a synergic effect of drought stress and winter cold in P. latifolia not observed in Q. ilex, but a more conservative strategy in P. latifolia maintaining leaves with a down-regulation of the linear photosynthetic electron transport. These results indicate that, although other physiological and reproductive strategies at whole plant level must be also taken into account, the warmer and drier environment expected for the following decades could favour the species more sensitive to cold and more resistant to drought, the shrub P. latifolia, in detriment of the tree Q. ilex as already observed in the field after severe heat-drought episodes. 相似文献
11.
There are significant differences in leaf life-span among evergreen sclerophyllous species and drought semideciduous species growing in the Mediterranean maquis. Cistus incamus, which has a leaf life-span of four-eight months, was characterised by the highest net photosynthetic rates (P
N), while Quercus ilex and Phillyrea latifolia, which maintain their leaves two-three and two-four years, respectively, had a lower P
N. The longer leaf life-span of the two evergreen sclerophyllous species may be justified to cover the high production costs of leaf protective structures such as cuticle, hairs, and sclereids: cuticle and hairs screen radiation penetrating into the more sensitive tissues, and sclereids have a light-guiding function. Q. ilex and P. latifolia have the highest leaf mass/area ratio (LMA = 209 g m-2) and a mesophyll leaf density (2065 cells per mm2 of leaf cross section area) about two times higher than C. incanus. In the typical evergreen sclerophyllous species the steepest leaf inclination ( = 56°) reduces 42 % of radiation absorption, resulting in a reduced physiological stress at leaf level, particularly in summer. C. incanus, because of its low leaf life-span, requires a lower leaf investment in leaf protective structures. It exhibits a drastic reduction of winter leaves just before summer drought, replacing them with smaller folded leaves. The lower leaf inclination ( = 44°) and the lower LMA (119 g m-2) of C. incanus complement photosynthetic performance. Water use efficiency (WUE) showed the same trend in Q. ilex, P. latifolia, and C. incanus, decreasing 60 % from spring to summer, due to the combined effects of decreased CO2 uptake and increased transpirational water loss. 相似文献
12.
Tree growth,mortality, and above-ground biomass accumulation in a holm oak forest under a five-year experimental field drought 总被引:2,自引:0,他引:2
A holm oak forest was exposed to an experimental drought during 5 years to elucidate the growth responses of the dominant
species Quercus ilex, Arbutus unedo and Phillyrea latifolia. Soil water availability was partially reduced, about 15% as predicted for this area for the next decades by GCM and ecophysiological
models, by plastic strips intercepting rainfall and by ditch exclusion of water runoff. The stem diameter increment was highly
correlated with annual rainfall in all species, and drought treatment strongly reduced the diameter increment of Q. ilex (41%) and specially of A. unedo (63%), the species showing higher growth rates. Stem mortality rates were highly correlated with previous stem density, but
drought treatment increased mortality rates in all species. Q. ilex showed the highest mortality rates (9% and 18% in control and drought plots, respectively), and P. latifolia experienced the lowest mortality rates (1% and 3% in control and drought plots, respectively). Drought strongly reduced the
increment of live aboveground biomass during these 5 years (83%). A. unedo and Q. ilex experienced a high reduction in biomass increment by drought, whereas P. latifolia biomass increment was insensitive to drought. The different sensitivity to drought of the dominant species of the holm oak
forest may be very important determining their future development and distribution in a drier environment as expected in Mediterranean
areas for the next decades. These drier conditions could thus have strong effects on structure (species composition) and functioning
(carbon uptake and biomass accumulation) of these Mediterranean forests. 相似文献
13.
We investigated the responses of two co‐existing Mediterranean trees with different regeneration strategies (Phillyrea latifolia seedlings and Quercus ilex sprouts) to experimental drought below the forest canopy. We considered different recruitment stages and used leaf isotopic discrimination to estimate water use efficiency (WUE) and nitrogen availability and use. Drought decreased the emergence and survival of seedlings and sprouts. Survival and growth of older saplings were not influenced by drought. Seedling emergence of P. latifolia was higher than Q. ilex sprout production, but Q. ilex sprouts had higher survival and growth rates. These differences disappeared in the sapling stage. Carbon isotopic discrimination suggested that Q. ilex sprouts had higher WUE than P. latifolia seedlings. Drought increased WUE of recruits, particularly in Q. ilex. Water use regulation increased with ageing, particularly in P. latifolia. Q. ilex had higher δ15N values than P. latifolia; these were also higher under drier soil conditions. Current year seedlings had higher δ15N than saplings, particularly in P. latifolia, suggesting they exploit superficial soil layers. These results suggest that sprouts obtain benefit from resources stored in parent plants. At earlier stages, they perform better than seedlings. This response is not coupled to adult vulnerability to drought for these species, revealing the difficulty of predicting species dynamics during climate change. 相似文献
14.
J. Llusià J. Peñuelas G. A. Alessio R. Ogaya 《Russian Journal of Plant Physiology》2011,58(1):126-132
Mediterranean vegetation emits large amounts of terpenes. We aimed to study the effects of the decreases in soil water availability
forecast for the next decades by global circulation models and ecophysiological models on the terpene emissions by two widely
distributed Mediterranean woody species, Phillyrea latifolia L. and Quercus ilex L. We subjected holm oak forest plots to an experimental soil drought of ca. 20% decrease in soil moisture by partial rainfall
exclusion and runoff exclusion. We measured the emission rates throughout the seasons for two years with contrasting precipitation
and soil moisture (16.6% average in 2003 vs. 6.4% as average in 2005). Among the detected volatile terpenes, only α-pinene
and limonene were present in detectable quantities in all of the studied periods. Total terpene emitted ranged from practically
zero (spring 2003) to 3.6 and 58.3 μg/(g dry wt h) (winter 2005 and summer 2003 for P. latifolia and Q. ilex, respectively). A clear seasonality was found in the emission rates (they were the highest in summer in both species) and
also in the qualitative composition of the emission mix. Maximum emissions of α-pinene occurred in spring and maximum emissions
of limonene in winter. Neither the inter-annual differences in water availability nor the rain exclusion treatment significantly
affected the emissions in P. latifolia, but Q. ilex showed by 17% lower emissions during the drier second year of study, 2005, but more than two- and threefold increases with
the drought treatment in summer 2003 and in summer 2005, respectively, showing historical accumulated effects. These results,
which show increased monoterpene emission under the moderate drought produced by the treatment and decreased emission under
the severe second year drought, and a much higher sensitivity to drought in Q. ilex than in P. latifolia, are useful in understanding the behavior of plant volatiles under Mediterranean conditions and in modeling future emission
under changing climate conditions. They show that the usage of current models could lead to under- and overestimations of
the emission under summer dry conditions, because most current algorithms are based on light and temperature only. 相似文献
15.
16.
Effects of water stress on photosystem II photochemistry and its thermostability in wheat plants 总被引:19,自引:1,他引:18
Modulated chlorophyll fluorescence, rapid fluorescence induction kinetics
and the polyphasic fluorescence transients (OJIP) were used to evaluate
PSII photochemistry in wheat plants exposed to water stress and/or heat
stress (25-45C). Water stress showed no
effects on the maximal quantum yield of PSII photochemistry
(Fv/Fm), the rapid fluorescence
induction kinetics, and the polyphasic fluorescence transients in
dark-adapted leaves, indicating that water stress had no effects on the
primary photochemistry of PSII. However, in light-adapted leaves, water
stress reduced the efficiency of excitation energycapture by open PSII
reaction centres (F'v/F'm) and
the quantum yield of PSII electron transport (PSII), increased
the non-photochemical quenching (qN) and showed no effects on the
photochemical quenching (qP). This suggests that water stress modified the
PSII photochemistry in the light-adapted leaves and such modifications may
be a mechanism to down-regulate the photosynthetic electron transport to
match a decreased CO2 assimilation. In addition, water stress also modified
the responses of PSII to heat stress. When temperature was above 35C, thermostability of PSII was strongly enhanced in
water-stressed leaves, which was reflected in a less decrease in
Fv/Fm, qP,
F'v/F'm, and PSII in
water-stressed leaves than in well-watered leaves. There were no
significant variations in the above fluorescence parameters between
moderately and severely water-stressed plants, indicating that the moderate
water-stressed plants, indicating that the moderate water stress treatment
caused the same effects on thermostability of PSII as the severe treatment.
It was found that increased thermostability of PSII may be associated with
an improvement of resistance of the O2-evolving complex and the reaction
centres in water-stressed plants to high temperature.Key
words: Chlorophyll fluorescence, heat stress, photosystem II
photochemistry, water stress, wheat (Tritium aestivum
L.).
相似文献
17.
The vegetative resprouting of mediterranean maquis shrubby species was examined eight years after fire. Post-fire regeneration occurs through the resprouting of stumps. All species (Quercus ilex L., Phillyrea latifolia L., Arbutus unedo L., Erica arborea L., Pistacia lentiscus L.) show a rapid growth in the first years after fire, and a decrease already from 4th–5th year.All the species survived the fire and reconstituted a community similar to that unburned in a relatively short time span. 相似文献
18.
Loretta Gratani 《Plant biosystems》2013,147(1):19-24
ABSTRACT Gas exchange temperature dependence in Quercus ilex shrubs growing in the Mediterranean maquis was analysed. The gas exchange trend was monitored during the year: photosynthetic activity (A net) reached the highest average rates in early spring and autumn (12.5 µmol m-2s-1 was the absolute maximum A net measured) and the lowest rates were monitored in the middle of June. There was a good correlation (r = 0.72) between A net and g s (A net = 4.1246 ln g s + 4316; P < 0.01), indicating that stomatal control of CO2 diffusion plays an important role in controlling photosynthetic activity. Leaf temperature allowing the highest photosynthetic and stomatal conductance rates of Quercus ilex were in the range 17.5 – 29°C. A net and gs dropped below half its maximum value when leaf temperatures were below 11.5°C and above 35.7°C. Transpiration rates (E) were strongly related to leaf temperature; E increased as leaf temperature increased and the highest E rates were monitored in June, despite a 46% decrease in g s. Leaf water loss from transpiration, during the drought period, could result in leaf water stress which would exacerbate heat effects on photosynthesis. During summer, the increase in leaf temperatures decreased g s which in turn decreased A net. Consequently, stomatal control in Quercus ilex may be considered as an adaptive strategy during drought. 相似文献
19.
Abstract Photosynthesis and photoprotective mechanisms were investigated in the field on Laurus nobilis L. and Quercus ilex L. leaves exposed to summer drought (July) and winter cold (February) conditions compared with no-stress conditions (May). In July, net photosynthetic rate (A) and stomatal conductance (g s) decreased significantly compared with May in both species; conversely the highest ETR/A ratio and no difference in non-photochemical quenching (NPQ) was observed. In February A, g s and ETR/A declined compared with May but the highest NPQ were found in both species. Our data suggest that during summer, an increase of photochemical alternative pathways to carbon reduction, were able to effectively protect the photosynthetic apparatus under drought. In winter, the thermal dissipation of excess absorbed light constitutes the main safety valve for the photosynthetic apparatus. 相似文献
20.
Photosynthetic activity of the calyx, green shoulder, pericarp, and locular parenchyma of tomato fruit 总被引:5,自引:1,他引:4
Photosynthesis of tomato fruit was studied using green fruit from six
heritage cultivars of Lycopersicon esculentum Mill.
and one of Lycopersicon pimpinellifolium. Chlorophyll
concentrations in the green shoulder, pericarp and locular parenchyma of
the fruit were determined and the apparent photosynthetic electron
transport activity (ETR) and chlorophyll fluorescence quenching
characteristics of these tissues and the calyx were compared. In all
cultivars, green shoulder formation, apparent as intense pigmentation of
the proximal pericarp shoulder, was positively related to the degree of
shading of the fruit during development. Appearing as a photosynthetic
adaptive trait for increasing the photoautotrophic capacity of fruit grown
under low light, the green shoulder contained 17-57% of the total pericarp
chlorophyll content. The pericarp below the green shoulder had lower
chlorophyll a+b. At a photon flux
density (PFD) of 1200 mol
m-2 s-1, different fruit
tissues were found to have different levels of ETR. In 'Yellow Pear', the
upper surface of the calyx had an ETR of 154 mol m-2
s-1, while the lower surface had an ETR of 88
mol m-2 s-1. On the
green shoulder, ETR was 203 mol m-2
s-1, whereas in the pericarp distal to the green
shoulder, ETR was 97 mol m-2
s-1. In the locular parenchyma, ETR was 66
mol m-2 s-1. This
trend towards a lower ETR in distal and internal fruit tissues appeared to
indicate a shift towards a more shade-type photosynthesis. Concomitant with
this shift were changes in chlorophyll fluorescence quenching
characteristics. Generally when tissues displayed reduced levels of ETR
they also displayed a faster decrease in the photochemical quenching
coefficient qp and a more rapid diversion of absorbed
photon energy to non-photosynthetic activity found in the calyx, green
shoulder, pericarp, and locular parenchyma suggest that all of these
tissues have significant roles in CO2 scavenging and the provision of
carbon assimilates. The potential role of fruit photosynthesis in
influencing the fruit acid to sugar ratio and hence fruit quality is
discussed. 相似文献