Seasonal photosynthesis, respiration, and calcification of a temperate Maërl bed in southern Portugal

Rhodolith (maerl) beds are biodiversity hotspots with a worldwide distribution. Maerl is the general term for free-living non-geniculate rhodoliths or coralline red algae. In southern Portugal, maerl beds are mainly composed of Phymatolithon lusitanicum, recently identified as a new species and commonly misidentified as Phymatolithon calcareum. Photosynthesis, respiration, and growth rates of the algae were measured seasonally, as well as the photosynthetic pigment composition. To characterize the seasonal and interannual patterns of key abiotic conditions in the largest described maerl bed of the Portuguese coast, temperature, irradiance, and dissolved oxygen were continuously monitored over a 2-year period. At the bed depth (22 m), temperature ranged between 14 degrees C in winter and 24 degrees C in summer, irradiance varied from 5 to 75 mu.mol m(-2) s(-1) , and dissolved oxygen from 5.8 to 7.25 mg O-2 L-1. We found a strong linear relationship (r(2) = 0.95) between gross primary production (GPP) and relative electron transport rates (rETRs). Both methods led to similar results and an average molar ratio of 0.24. Photosynthesis and respiration increased in summer and decreased in autumn and winter. In the summer of 2013, the growth rates were twofold higher (1.34 mu.mol CaCO3 g(-1) day(-1)) than in the other seasons. In winter and spring, to compensate for light deprivation and low temperature, algae increased their chlorophyll a and carotenoid concentrations while also decreasing their phycobilin concentration, in this case probably due to nutrient limitation. To isolate the role of temperature on the algae's metabolism, the photosynthetic and respiration rates of individual thalli were measured at eight different temperatures in the laboratory (from 12 degrees C to 26 degrees C). Phymatolithon lusitanicum photosynthesis increased twofold after a threshold of 18 degrees C (from 2.2 at 18 degrees C to 3.87 mu mol O-2 m(-2) s(-1) at 20 degrees C), whereas respiration increased fourfold with temperature after a threshold of 22 degrees C (from -0.38 at 18 degrees C to -1.81 (mu mol O-2 m(-2) s(-1) at 24 degrees C). The significant increases on respiration, photosynthetic rates, and maximum growth with temperature reveal that the metabolic rates of P. lusitanicum are highly sensitive to ocean warming.UIDB/04326/2020info:eu-repo/semantics/publishedVersio

Efeitos a posteriori dos défices hídricos sobre a actividade fotossintética: mecanismos de fotoprotecção e sistema enzimático antioxidante

Tese de dout., Biologia (Fisiologia Vegetal), Faculdade de Engenharia dos Recursos Naturais, Univ. do Algarve, 2005A resposta dos mecanismos fotossintéticos à duração e intensidade do défice hídrico e posterior rehidratação foi investigada em plantas envasadas de Helianthus annuus L. e Lupinus albus L. A rega foi manipulada de modo a induzir diferentes intensidades de défice hídrico e posterior rehidratação. Nas plantas de H. annuus foram analisadas comparativamente folhas jovens e folhas maduras, tendo-se também avaliado nas folhas jovens o efeito da diminuição temporária da intensidade luminosa nas plantas em défice hídrico e rehidratação. Foram também avaliados comparativamente os efeitos dos défices hídricos e da rehidratação na actividade fotossintética e no sistema antioxidante em folhas de H. annuus e L. albus, espécies com estratégias diferentes perante o défice hídrico (H. annuus é tolerante ao défice hídrico e L. albus evita o défice hídrico). Os resultados obtidos indicam que, apesar de as taxas de fotossíntese terem diminuído em resposta ao défice hídrico, não ocorreu fotoinibição crónica nem foi induzida senescência foliar nas folhas de H. annuus amostradas. Nestas plantas, em situação de défice hídrico, ocorreram limitações metabólicas à actividade fotossintética, que nas folhas maduras podem ter incluído a activação da reacção de Mehler e da fotorrespiração. As folhas jovens revelaram possuir a capacidade de reforçar a sua protecção antioxidante em resposta ao défice hídrico, através do aumento do teor foliar em carotenóides. No entanto, as diferenças registadas entre as folhas jovens e as folhas maduras nas plantas em défice hídrico não se repercutiram na sua capacidade de recuperação da actividade fotossintética após rehidratação, que foi semelhante. Os dados obtidos mostraram que o aumento do ‘quenching’ não fotoquímico nem sempre está directamente relacionado com o aumento do índice de desepoxidação do ciclo das xantofilas e confirmaram a relação de dependência entre ambos os parâmetros e a densidade de fluxo quântico. Nas plantas em défice hídrico transferidas para intensidade luminosa baixa, a ausência de stresse oxidativo pode ter implicado falhas na sinalização interna das plantas, enquanto o estímulo aparente da exportação de fotoassimilados durante a rehidratação pode ter conduzido à inibição do crescimento, pelo que não se observaram vantagens na imposição do défice hídrico e da rehidratação a baixas densidades de fluxo quântico. A manutenção de altos teores foliares de sacarose nas plantas rehidratadas sob irradiância alta não evitou que estas não recuperassem completamente a actividade fotossintética. O défice hídrico induziu senescência foliar em L. albus. Esta pode ter resultado do stresse oxidativo induzido nas plantas em défice hídrico, aparentemente devido ao desequilíbrio entre as actividades da dismutase do superóxido e da peroxidase do ascorbato. Os resultados mostram que o défice hídrico pode, por si só, induzir respostas normalmente associadas à ocorrência conjunta de défice hídrico e intensidade luminosa alta, tais como o stresse oxidativo e o aumento no teor foliar em pigmentos antioxidantes

Oxidative stress and quantum yield efficiency in the intertidal seagrass zostera noltii

We investigated the combined effects of several environmental stressors in the photosynthetic performance and in the activation of biochemical defense mechanisms in the intertidal seagrass Zostera noltii in Ria Formosa coastal lagoon (southern Portugal). The maximum (Fv/Fm) and the effective (F’v/F’m) quantum use efficiencies of PSII were sampled monthly in both neap and spring tides over one year. Other fluorescence parameters, such as the Stern-Volmer non-photochemical quenching (NPQ) and the novel parameter LNP (which expresses the general decrease in PSII photochemical activity in the light) were derived from quantum use efficiency measurements. Sampling for antioxidant enzymes activity, pigments, soluble protein and malondialdehyde (MDA) was conducted in parallel. Reactive oxygen species (ROS) are formed as a normal part of the metabolism. An increment on ROS formation is a common response to those stresses and can cause several types of damage, namely lipid peroxidation. MDA is a product of the peroxidation of membrane lipids and thus is commonly used as an indicator of oxidative stress. Carotenoids and antioxidant enzymes such as ascorbate peroxidase (APx) are part of the plants’ antioxidative system. Higher content of carotenoids indicate a higher photoprotection and increased activities of ROS scavenging enzymes such as APx are correlated with stress tolerance. The relationships among critical environmental parameters (irradiance, temperature, air exposure), oxidative stress, antioxidative responses and quantum use efficiency in Z. noltii were explored through multifactorial analysis

Physiological and morphological effects of a marine heatwave on the seagrass Cymodocea nodosa

Marine heatwaves (MHWs) are increasing in frequency and intensity as part of climate change, yet their impact on seagrass is poorly known. The present work evaluated the physiological and morphological responses of Cymodocea nodosa to a MHW. C. nodosa shoots were transplanted into a mesocosm facility. To simulate a MHW, water temperature was raised from 20 to 28 degrees C, kept 7 days at 28 degrees C, cooled down back to 20 degrees C and then maintained at 20 degrees C during an 8-day recovery period. The potentially stressful effects of the simulated heatwave on the photosynthetic performance, antioxidative-stress level and area vs dry weight ratio of leaves were investigated. The maximum quantum yield of photosystem II (phi PSII) increased during the heatwave, allowing the plants to maintain their photosynthetic activity at control level. Negative effects on the photosynthetic performance and leaf biomass of C. nodosa were observed during the recovery period. No significant oxidative stress was observed throughout the experiment. Overall, although C. nodosa showed a relative tolerance to MHWs compared to other species, its population in Ria Formosa is likely to be negatively affected by the forecasted climate change scenarios.info:eu-repo/semantics/publishedVersio

Influence of nutrient availability on drought-induced changes in the activity of antioxidant enzymes in sunflower leaves

We aimed to evaluate if plants with different nutrient availability evidenced a different capacity to overcome drought-induced oxidative stress. Membrane peroxidative damages as MDA concentration and the activity of several antioxidant enzymes were determined in leaves of well watered (WW) and water stressed (WS) H. annuus plants grown either with adequate (Adeq Nutr) or limited (Limit Nutr) nutrient regimes. Constitutive capacity to eliminate ROS was not overall changed by growing plants with different nutrient supply regimes, but a diverse enzyme-dependent response was observed. In response to drought SOD and DHAR activity increased only in plants with limited nutrient supply, while in plants with adequate nutrient supply the activity of these enzymes did not change and were constitutively higher, but the activity APX increased by 50%. The subtle observed changes in the activity of the antioxidant enzymes are discussed, given that no oxidative damage was observed

Fotossíntese e acumulação de ácido abcísico em Lupinus albus sujeito a stress hídrico

The objective of the present work was to assess whether the depression of photosynthetic activity in droughted Lupinus albus L. plants was more closely associated with carbohydrate build-up or ABA accumulation. With that purpose we have measured the concomitant drought-induced changes in photosynthetic capacity and the concentrations of Rubisco, chlorophylls, non-structural carbohydrates and ABA in young and old leaves of white lupin plants. Although Rubisco and chlorophylls contents did not decrease with water stress, the photosynthetic capacity was decreased by soil drying, the decline in photosynthesis being more tighly related with ABA accumulation than with sugar content. In contrast to droughted plants, ABA feeding to intact plants resulted in a significant decrease in Rubisco and chlorophyll content. However, no increase in shoot ABA content was detected in ABA-fed plants. Therefore this work is not conclusive as to the correlation between photosynthetic capacity and ABA accumulation in droughted white lupin plants being causal or not

Heatwave effects on the photosynthesis and antioxidant activity of the seagrass Cymodocea nodosa under contrasting light regimes

Global climate change, specifically the intensification of marine heatwaves, affect seagrasses. In the Ria Formosa, saturating light intensities may aggravate heatwave effects on seagrasses, particularly during low spring tides. However, the photophysiological and antioxidant responses of seagrasses to such extreme events are poorly known. Here, we evaluated the responses of Cymodocea nodosa exposed at 20 °C and 40 °C and 150 and 450 μmol quanta m−2 s−1. After four-days, we analyzed (a) photosynthetic responses to irradiance, maximum photochemical efficiency (Fv/Fm), the effective quantum yield of photosystem II (ɸPSII); (b) soluble sugars and starch; (c) photosynthetic pigments; (d) antioxidant responses (ascorbate peroxidase, APX; oxygen radical absorbance capacity, ORAC, and antioxidant capacity, TEAC); (d) oxidative damage (malondialdehyde, MDA). After four days at 40 °C, C. nodosa showed relevant changes in photosynthetic pigments, independent of light intensity. Increased TEAC and APX indicated an “investment” in the control of reactive oxygen species levels. Dark respiration and starch concentration increased, but soluble sugar concentrations were not affected, suggesting higher CO2 assimilation. Our results show that C. nodosa adjusts its photophysiological processes to successfully handle thermal stress, even under saturating light, and draws a promising perspective for C. nodosa resilience under climate change scenarios.info:eu-repo/semantics/publishedVersio

Temperature amplifies the effect of high CO2 on the photosynthesis, respiration, and calcification of the coralline algae Phymatolithon lusitanicum

The combination of ocean acidification (OA) and global warming is expected to have a significant effect on the diversity and functioning of marine ecosystems, particularly on calcifying algae such as rhodoliths (maërl) that form extensive beds worldwide, from polar to tropical regions. In addition, the increasing frequency of extreme events, such as heat waves, threatens coastal ecosystems and may affect their capacity to fix blue carbon. The few studies where the simultaneous effects of both temperature and CO2 were investigated have revealed contradictory results. To assess the effect that high temperature spells can have on the maërl beds under OA, we tested the short-time effects of temperature and CO2 on the net photosynthesis, respiration, and calcification of the recently described species Phymatolithon lusitanicum, the most common maërl species of southern Portugal. Photosynthesis, calcification, and respiration increased with temperature, and the differences among treatments were enhanced under high CO2. We found that in the short term, the metabolic rates of Phymatolithon lusitanicum will increase with CO2 and temperature as will the coupling between calcification and photosynthesis. However, under high CO2, this coupling will favor photosynthesis over calcification, which, in the long term, can have a negative effect on the blue carbon fixing capacity of the maërl beds from southern Portugal.FCT UID/Multi/04326/2019info:eu-repo/semantics/publishedVersio

Alterações sazonais da fotossíntese e do ciclo das xantófilas em alfarrobeira (Ceratonia siliqua L.)

This study aimed to follow the seasonal changes in the photosynthetic performance of two Ceratonia siliqua cultivars – Mulata and Mulata do Espargal – growing in a non-irrigated orchard in Algarve (South Portugal). Measurements and sampling (leaf water potential, leaf gas exchange, pigments and dark-adapted chlorophyll fluorescence) were taken in days with similar photon flux density, during the dry season in June and July, and in November after the first autumnal rainfalls (»91 mm) when minimum temperatures droped below 10°C. Photosynthetic rates remained low for both cvs, and did not recover in November despite the observed increase in stomatal conductance and y. Fv/Fm slowly decreased from June to November, specially at midday. This changes in Fv/Fm were attributed mainly to increasing F0 which might reflect structural changes or damages at the chloroplast membranes level. Dry season conditions seemed to have triggered some thermal photoprotective mechanisms, as indicated through the increased ratio A+Z/VAZ. In November, however, the ratio A+Z/VAZ decreased. We suggest that the lack of recovery of A associated with higher F0 measured in both cvs, either at pre-dawn or midday, could be attributed to structural changes within the membranes mediated either by rehydration and/or by chilling temperatures

Citrus Pruning in the Mediterranean climate: a review

Pruning is a common practice in citrus for various reasons. These include controlling and shaping the canopy; improving phytosanitary health, productivity, and fruit quality; and facilitating operations such as harvesting and phytosanitary treatments. Because pruning is an expensive operation, its need is sometimes questioned. However, it has been proven to be particularly important in Mediterranean citriculture, which is oriented towards producing fruits for a high-quality demanding fresh market. Herein, we summarize and explain the pruning techniques used in Mediterranean citriculture and refer to the main purposes of each pruning type, considering citrus morphology and physiology.info:eu-repo/semantics/publishedVersio