Seasonal changes in some photosynthetic properties of Ceratonia siliqua (carob tree) leaves under natural conditions

Rates of photosynthesis and leaf conductance of the leaves of carob trees ( Ceratonia siliqua L.) growing in natural conditions were measured during the course of the seasons to define the effects of the main climatic factors limiting growth in the region: temperature during the winter and water in the summer. The highest photosynthetic rates were measured in spring and autumn and could reach 25 μmol m₋₂ s₋₁ with optimal temperature and available water. Due to lower temperatures (4 to 6°C in the night) these values were frequently around 15 μmol m₋₂ s₋₁ during winter, but the strongest depression was due to prolonged drought in summer. However a reduction in photosynthesis rate down to 5 μmol m₋₂ s₋₁ occurred only after depletion of all the available water in the soil layer up to a depth of 50 cm. In the end of the summer, leaf conductance and water potential were in the order of 20 mmol m₋₂ s₋₁ and −3 MPa respectively. Compared to other trees that make up the Mediterranean sclerophyll forest, the photosynthetic activity of carob is high, and the tree tolerates a considerable depletion of soil water.     

Photoinhibition of photosynthesis in willow leaves under field conditions

Chlorophyll fluorescence of leaves of a willow (Salix sp.) stand grown in the field in northern Sweden was measured on several occasions during the growing season of 1987. For leaves that received mostly full daylight, the F _V/F _P ratio declined roughtly 15% in the afternoon on cloudless days in July (F _P is the fluorescence at the peak of the induction curve obtained at the prevailing air temperature after 45 min of dark adaptation, and F _V is variable fluoresence, F _V=F _P-F _O, where F _O is minimal fluorescence). There was no decrease in the F _V/F _P ratio on cloudy days, while the effect was intermediate on changeable days. In view of this light dependence, together with the fact that the decline in the F _V/F _P ratio was paralleled with an equal decline in the corresponding fluorescence ratio F _V/F _M at 77K, and a similar decline in the maximum quantum yield of O₂ evolution, it is suggested that the decline in the F _V/F _P ratio represents a damage in photosyntem II attributable to photoinhibition. Recovery of the F _V/F _P ratio in dim light following a decline on a cloudless day took 7–16 h to go to completion; the F _V/F _P ratio was fully restored the following morning. When all active leaves of a peripheral shoot were compared, the F _V/F _P ratio in the afternoon of a day of bright light varied greatly from leaf to leaf, though the majority of leaves showed a decline. This variation was matched by a pronounced variation in intercepted photon flux density. When leaves developed in the shade were exposed to full sunlight by trimming of the stand an increased sensitivity to photoinhibition was observed as compared to peripheral leaves. The present study indicates that peripheral willow shoots experienced in the order of 10–20% photoinhibition during an appreciable part of their life. This occurred even though the environmental conditions were within the optimal range of photosynthesis and growth.Abbreviations and symbols F _O minimum fluorescence - F _P fluorescence at the peak of the induction curve obtained at normal ambient temperatures - F _V variable fluorescence - F _M maximum fluorescence obtained at 77K - PPFD photosynthetic photon flux density     

Degradation of aromatic compounds in plants grown under aseptic conditions

The aim of the work is to investigate the ability of higher plants to absorb and detoxify environmental pollutants - aromatic compounds via aromatic ring cleavage. Transformation of 14C specifically labelled benzene derivatives, [1-6-14C]-nitrobenzene, [1-6-(14)C]-aniline, [1-(14)C]- and [7-(14)C]-benzoic acid, in axenic seedlings of maize (Zea mays L.), kidney bean (Phaseolus vulgaris L.), pea (Pisum sativum L.) and pumpkin (Cucurbita pepo L.) were studied. After penetration in plants, the above xenobiotics are transformed by oxidative or reductive reactions, conjugation with cell endogenous compounds, and binding to biopolymers. The initial stage of oxidative degradation consists in hydroxylation reactions. The aromatic ring can then be cleaved and degraded into organic acids of the Krebs cycle. Ring cleavage is accompanied by 14CO2 evolution. Aromatic ring cleavage in plants has thus been demonstrated for different xenobiotics carrying different substitutions on their benzene ring. Conjugation with low molecular peptides is the main pathway of aromatic xenobiotics detoxification. Peptide conjugates are formed both by the initial xenobiotics (except nitrobenzene) and by intermediate transformation products. The chemical nature of the radioactive fragment and the amino acid composition of peptides participating in conjugation were identified.     

Seasonal patterns of terpene content and emission from seven Mediterranean woody species in field conditions

The seasonal pattern of terpene content and emission by seven Mediterranean woody species was studied under field conditions. Emission rates were normalized at 30°C and 1000 μmol·m·s PFD (photosynthetic photon flux density). Bupleurum fruticosum, Pinus halepensis, and Cistus albidus stored large amounts of terpenes (0.01-1.77% [dry matter]) with maximum values in autumn and minimum values in spring. They emitted large amounts of terpenes (2-40 μg·g DM·h), but with no clear seasonal trend except for Cistus albidus, which had maximum values in spring and minimum values in autumn. The nonstoring species Arbutus unedo, Erica arborea, Quercus coccifera and Quercus ilex also emitted large amounts of terpenes (0-40 μg·g DM·h) and also tended to present maximum emission rates in spring, although this trend was significant only for A. unedo. At the seasonal scale, emission rates did not follow changes in photosynthetic rates; instead, they mostly followed changes in temperature. From autumn to spring, the least volatile monoterpenes such as limonene were emitted at highest rates, whereas the most volatile monoterpenes such as α-pinene and β-pinene were the most emitted in summer. The monoterpene emission rates represented a greater percentage of the photosynthetic carbon fixation in summer (from 0.51% in Arbutus unedo to 5.64% in Quercus coccifera) than in the rest of the seasons. All these seasonality trends must be considered when inventorying and modeling annual emission rates in Mediterranean ecosystems.     

Seasonal fluctuations in Vitis vinifera root respiration in the field

We studied the seasonal fluctuation of soil respiration (R(S)), and its root-dependent (R(R)) and basal (R(B)) components, in a Vitis vinifera (Chardonnay) vineyard. The R(S) components were estimated through independent field methods (y-intercept and trenching) and modeled on the basis of a Q(10) response to soil temperature, and fine and coarse root respiration coefficients. The effect of assimilate availability on R(R) was assessed through a trunk girdling treatment. The apparent Q(10) for R(R) was twice that of R(B) (3.5 vs 1.6) and increased linearly with increasing vine root biomass. The fastest R(R) of fine roots was during rapid fruit growth and the fastest R(R) of coarse roots was immediately following fruit development. R(S) was estimated at 32.6 kg ha(-1) d(-1) (69% as a result of R(R) ) for the hottest month and at 7.6 kg ha(-1) d(-1) (18% as a result of R(R)) during winter dormancy. Annual R(S) was low compared with other natural and cultivated ecosystems: 5.4 Mg ha(-1) (46% as a result of R(R)). Our estimates of annual vineyard R(S) are the first for any horticultural crop and suggest that the assumption that they are similar to those of annual crops or forest trees might lead to an overestimation.     

Evaluation of transgenic canola plants under field conditions.

Eleven independent transgenic canola (Brassica napus ssp. oleifera L. cv. Westar and Regent) lines were evaluated in the field. The plants carried a neomycin phosphotransferase (NPTII) gene for kanamycin resistance that was introduced via Agrobacterium-mediated transformation. NPTII enzyme assays, Southern blot by hybridizations and progeny analysis, confirmed the stable, heritable integration and expression of the introduced NPTII gene. A number of agronomic characteristics evaluated under field conditions, including maturity yield, and oil and protein content, were all statistically comparable between the transformed and nontransforemd platns. These results indicate that canola can be genetically engineered successfully, and that the Agrobacterium-based transformation system employed does not induced any adverse effects on the intrinsic agronomic and qualitative traits critical to the agricultural industry.     

Seasonal variability of diurnal in-stream nitrate concentration oscillations under hydrologically stable conditions

Seasonal and diurnal variations of in-stream NO₃-N concentration oscillations were studied through high-frequency measurements of streamwater’s physical, chemical parameters (in-stream NO₃-N concentration, water temperature, dissolved oxygen, pH) and hydrometeorological variables (stream discharge, solar radiation) under hydrologically stable conditions. The study was carried out in 2006, within the 42 km² forested Pade? stream watershed in the southwestern part of Slovenia, which is characterized by distinctive hydrogeological settings (flysch) and climate conditions (transitional area between the Mediterranean and continental climate). Fine temporal data resolution (15-min interval) enabled identification of the factors responsible for seasonal variability in the diurnal pattern of the streamwater NO₃-N concentrations versus seasonal and diurnal behavior of meteorological and other water chemistry constituents. The observed seasonal variability of in-stream NO₃-N daily oscillations indicates the important role of primary production uptake, particularly during seasons when deciduous vegetation is dormant and light levels in the stream are high. Highest daily NO₃-N concentration amplitudes (0.3 mg/l-N) and daily changes in the NO₃-N flux (0.4–0.5 g/s-N) were observed in spring; the NO₃-N concentration oscillations in summer showed a considerably smaller effect of the in-stream uptake (maximum NO₃-N daily concentration amplitude 0.1 mg/l-N; daily change in the NO₃-N flux 0.02 g/s-N). Seasonal shifts in the timing of daily maximum (up to 6 h) and minimum NO₃-N concentrations (between 1 and 3 h) provided some additional indications of seasonal changes in the in-stream primary production uptake and its relation to the terrestrial component of the forested watershed.     

Estimation of the distribution of living roots of plants under field conditions

Summary A method is described for estimating the relative distribution of living roots of graminaceous plants growing under normal field conditions and which does not involve separation of roots from soil.It has been shown that 24 hours after rubidium-86 has been injected into the base of shoots its concentration is sufficiently uniform throughout the root system for the volume of roots in different zones of soil to be inferred from their content of the tracer. During this period outward diffusion from the root system is negligible and no rubidium-86 enters dead roots.The energy of the gamma radiation from rubidium-86 enables it to be measured accurately in soil samples of appreciable size (e.g. 3kg). Consequently it is possible, using suitable analytical equipment, to obtain representative information on root distribution at different depths in soil by combining the appropriate sections of numerous cores which have been withdrawn from the soil in the neighbourhood of injected plants. The advantages of this procedure lie in the fact that losses of root in the separation of the soil are avoided and that living roots of the species under investigation are alone measured, the time taken in this operation compares favourably with that occupied in the manual separation of roots from soil provided suitable analytical equipment is available.     

Seasonal changes of lipid content in the leaves of some ferns

Seasonal distribution of total lipids, of total and individual phospholipids as well as of one betaine lipid, diacylglyceryl-N,N,N-trimethylhomoserine (DGTS), found in the leaves of Dryopteris carthusiana, Dryopteris filix-mas, Matteuccia struthiopteris and Pteridium aquilinum was studied. Using thin-layer chromatography it was shown that lipid composition was different in these species and changed substantially throughout the development of scrolls (unrolled young leaves) to vegetatively mature leaves. The maximum concentration of DGTS for all the examined species was found in scrolls. DGTS then decreased to its minimum level or entirely disappeared to reappear at later stages of leaf development. This may indicate a specific role of DGTS in the plant membrane.     

Seasonal fluctuations of the mineral concentration of alder (Alnus glutinosa (L.) Gaertn.) from the field

Summary The seasonal fluctuation of N, P, K, Ca, Mg, Fe, Mn, Mo, and Co, in leaves, roots and nodules of 40–50 year oldAlnus glutinosa trees growing at four different locations along the banks of the Tormes river, in the province of Salamanca, was studied. Also, the evolution of the soil organic matter under the trees sampled was evaluated. The data obtained for the various nutrient elements in the three plant parts are statistically treated at the significance levels of 99–95 per cent, and some remarks as to the nutritional status of the European alder in respect to the nutrients and its contribution to soil nutrient-cycling are provided. A positive correlation was found between N–P, N–K, N–Mg, and N–Mo, in leaves, and between N–P, N–K, N–Fe, N–Mn, and N–Mo in root nodules. In roots only, no significance at any level was obtained between N and any of the elements analyzed.     

The use of chlorophyll fluorescence excitation spectra for the non-destructive in situ assessment of UV-absorbing compounds in leaves

In this study a method was designed to assess non‐destructively the type of UV‐screening compounds present in the leaf epidermis. The method is based on the recording and calculation of the ratio of UV‐excitation spectra of chlorophyll fluorescence (FER) from the adaxial and abaxial sides of bifacial leaves, or from older and younger segments of monocotyledonous leaves. The logarithm of this ratio (logFER) matched the absorption spectrum of the UV‐absorbers present in the leaf, as confirmed by its overlap with the absorption spectrum of the methanolic extract of the leaf or of the isolated epidermis. By using the logFER approach, it was possible to demonstrate that the concentration but not the classes of compounds present in the epidermis that are responsible for UV‐screening is affected by the side and the age of the leaves. In contrast, measurements from the leaves of seven dicots and one monocot indicated large difference in the classes of these compounds between species. Finally, it was shown that the logFER in the UV is independent of the emission wavelength, and that the method can be used for quantitative measurements. This method expands to the spectral domain the use of ChlF for the estimation of the leaf epidermal transmittance.     

Growth and water requirements of some range plants under controlled conditions

Summary The growth and water requirements of ten of the native and introduced range species were compared at different levels of moisture stress between the permanent wilting percentage and the moisture equivalent.The most vigorous vegetative growth and highest dry matter production were shown byChloris gayana.The transpiration intensity of all the studied species was low and comparable with that of xerophytes living under extremely dry conditions. At the highest moisture stress which is a xeric condition, the transpiration intensity varied between 90 mg/g.h inOnonis vaginalis and 160 mg/g.h inPanicum antidotale.The osmotic pressure varied widely between 16.5 atm inPennisetum dichotomum and 30.0 atm inOryzopsis miliacea at the highest moisture stress.The present investigation revealed that all the studied species are drought resistant as shown by their transpiration intensity and osmotic pressure which are comparable with those of xerophytes. SinceChloris gayana exhibits the highest dry matter production in addition to its drought resistance therefore it can be considered as the most suitable species for cultivation in desert regions.     

Variations in the concentration of phenolic compounds in the seagrass Posidonia oceanica under conditions of competition

The concentration of phenolic compound was measured in the seagrass Posidonia oceanica when interacting with two Bryopsidophyceae, Caulerpa taxifolia and Caulerpa racemosa, between May 1999 and May 2000. These measurements were performed on adult and intermediate leaves and in sheaths of the seagrass. Sampling was carried out at three stations subject to increasing levels of interaction with Caulerpa. The number of tannin cells was also analysed. Five phenolic compounds were identified in P. oceanica, with a predominance of caffeic acid in the adult and intermediate leaves. For a given level of interaction (and for both caulerpa sp.), a significant seasonal variation in phenolic compounds was shown in the adult leaves (higher in November and lower in September and March for example for the interaction with C. taxifolia). Only for two compounds (corresponding to a mixture containing ferulic acid and the ester methyl 12-acetoxyricinoleate) were significant differences observed as a function of the level of interaction with C. taxifblia, and only in the adult leaves: higher concentrations of phenols were observed with increasing level of interaction. Thus,adult leaves gave values of 55.5 +/- 14.1 microg g(-1) dm without interaction (OCt) and 94.9 +/- 23.4 microg g(-l) dm with high interaction (2Ct),corresponding to an increase of 70%. No significant difference was observed with intermediate leaves and sheaths, or for interaction with C. racemosa. The number of tannin cells (supposed to produce the phenolic compounds) largely increased in the adult and intermediate leaves when the degree of interaction with C. taxifolia increased: 90 mm above the base of the sheath (in adult leaves), 16.7 +/- 10.6 tannin cells cm(-2) were found without interaction (OCt), and 57.8 + 21.2 tannin cells cm(-2) with high interaction (2Ct). No significant difference was found for C. racemosa interaction. It thus appears that when the seagrass P. oceanica is in interaction with C. taxifolia, it accelerates its production of secondary metabolites so as to limit invasion of the beds.     

Diurnal variations of photosynthesis and dew absorption by leaves in two evergreen shrubs growing in Mediterranean field conditions

The effects of summer drought, dew deposition on leaves and autumn rainfall on plant water relations and diurnal variations of photosynthesis were measured in two evergreen shrubs, rosemary ( Rosmarinus officinalis ) and lavender ( Lavandula stoechas ), grown in Mediterranean field conditions. Withholding water for 40 d caused a similar decrease in predawn shoot water potential (ψ_pd) from c. −0.4 to c. −1.3 MPa in both species, but a 50% decrease in the relative leaf water content in L. stoechas compared with 22% in R. officinalis . A similar decrease in CO₂ assimilation rates by c. 75% was observed in water-stressed plants of both species, although L. stoechas showed smaller photosynthesis: stomatal conductance ratio than R. officinalis (35 vs 45 μmol CO₂:mol H₂O). The relative quantum efficiency of photosystem II photochemistry also decreased by c. 45% at midday in water- stressed plants of both species. Nevertheless, neither L. stoechas nor R. officinalis suffered drought-induced damage to photosystem II, as indicated by the maintenance of the ratio F _v: F _m throughout the experiment, associated with an increase in the carotenoid content per unit of chlorophyll by c. 62% and c. 30%, respectively, in water-stressed plants. Only L. stoechas absorbed dew by leaves. In this species the occurrence of 6 d of dew over a 15-d period improved relative leaf water content by c. 72% and shoot water potential by c. 0.5 MPa throughout the day in water-stressed plants, although the photosynthetic capacity was not recovered until the occurrence of autumn rainfall. The ability of leaves to absorb dew allowed L. stoechas to restore plant water status, which is especially relevant in plants exposed to prolonged drought.     

Enhanced UV-B radiation increases the reproductive effort in the Mediterranean shrub Cistus creticus under field conditions

Seedlings of the Mediterranean shrub Cistus creticus L. were grown in the field under ambient or ambient plus supplemental UV-B radiation (simulating a 15% ozone depletion over Patras, 38.3°W, 29.1°E) for 20 months. During this period, measurements of photosynthetic capacity, photochemical efficiency of PS II, chlorophylls and carotenoids were performed once per season. Supplemental UV-B radiation had no significant effect on these parameters nor on the total, above ground biomass accumulation, plant height and leaf specific mass measured at plant harvest. It was observed, however, that UV-B supplementation increased the number of seeds per fruit as well as mean individual seed mass. As a result, seed number and total seed mass per plant were considerably increased. Germination rates of produced seeds were not affected. We may conclude that C. creticus is a UV-B resistant plant whose competitive ability may be improved by enhanced UV-B radiation through an increase in its reproductive effort and a higher contribution to the seed bank.     

田间条件下棉花幼叶光合特性及光保护机制

通过比较棉花(Gossypium hirsutum)幼叶和完全展开叶气体交换参数及叶绿素荧光特性的差异, 探讨高光强下幼叶的光抑制程度及明确光保护机制间的协调机理。在田间自然条件下, 以棉花刚展平的幼嫩叶片(幼叶)和面积已达到最大的完全展开叶片为研究对象, 通过测定不同发育阶段叶片气体交换参数及叶绿素a荧光参数的变化, 并运用Dual-PAM100对不同发育阶段的叶片进行快速光响应曲线的拟合。结果表明: 幼叶和完全展开叶片在光合、荧光特性方面表现出明显的差异。与完全展开叶相比, 较低的叶绿素(Chl)含量和气孔导度(G_s)是幼叶较低净光合速率(P_n)的限制因素, 从而直接导致其光系统II (PSII)实际光化学效率(Φ_PSII)和光化学猝灭系数(q_P)的降低。在1800 μmol·m^-2·s^-1光强以下, 完全展开叶具有较强的围绕PSI循环的电子流(CEF), 有利于合成ATP, 是其具有较高光合能力的原因之一。相同光强下, 幼叶较低的光饱和点(LSP)更易受光抑制, 但其PSII原初光化学效率(F_v/F_m)的日变化幅度显著小于完全展开叶, 说明强光下幼叶通过类胡萝卜素(Car)猝灭单线态氧、光呼吸(P_r)、热耗散(NPQ)以及PSI-CEF等光保护机制能有效地耗散过剩的光能, 从而避免其光合机构发生光抑制。