Changes In Photosynthetic Activity Research Articles

Effect of different timing of water deficit combined with foliar application of ascorbic acid on physiological variables of sour passion fruit

The objective of this study was to evaluate the effects of deficit irrigation treatments during different phenological stages and foliar application of ascorbic acid on gas exchange, photosynthetic pigments, chlorophyll fluorescence, electrolyte leakage, relative water content and yield of ‘BRS GA1’ sour passion fruit. Treatments were distributed in randomized blocks, in a split-plot scheme, with plots consisting of six deficit irrigation treatments, based on crop evapotranspiration – ETc (irrigation with 100% ETc - FULL; irrigation with 50% ETc in the vegetative stage - VEG; flowering stage - FLO; fruiting stage - FRU; successively in the vegetative/flowering stages - VEG + FLO and vegetative/fruiting stages - VEG + FRU) and subplots represented by three concentrations of ascorbic acid - AsA (0, 0.5 and 1.0 mM). Water deficit induces changes in photosynthetic activity across all developmental stages of sour passion fruit, resulting in reduced yield in the period of 160 and 200 days after transplanting. Notably, flowering exhibits the greatest physiological acclimatization to water deficit conditions, albeit with more pronounced losses in the yield. When water deficit occurs during the vegetative and fruiting stages and is coupled with foliar application of ascorbic acid at 0.5 mM, there is an enhancement in the synthesis of photosynthetic pigments in ‘BRS GA1’ sour passion fruit. Overall, foliar application of ascorbic acid at concentrations of 0.5 and 1.0 mM emerges as a viable strategy to mitigate the adverse effects of water deficit on the physiology and yield of sour passion fruit at 200 days after transplanting.

WINTER WHEAT MUTATION VARIABILITY UNDER LOW-DAMAGE ABILITY MUTAGEN ACTION

The purpose of our study was to show the possibilities of a chemical supermutagen in the regular induction of certain types of mutations. Winter wheat dry seeds of eight varieties were acted with water (control) and DAB (1.4-bisdiazoacetylbutane) action in concentrations of 0.1%, 0.1%, 0.3%. Studies have shown that the use of this mutagen is expedient from the point of view of obtaining valuable forms of low-growing, earlyripening, late-ripening, high-yielding lines, forms with high productive tillering. The mutagen by its nature has a rather low affinity, at least for this group of genotypes, however, this factor still affects the frequency of some types of mutations. Even extreme concentrations of this mutagenic agent did not lead to a significant decrease in the number of mutations; however, they reached a maximum in the spectrum of possible changes. Further studies are needed on changes in photosynthetic activity and associated persistence.

Changes in Photosynthetic Activity of the Lichen Cladonia mitis and the Moss Pleurozium schreberi under Artificial High-Energy Lighting in Laboratory Conditions

Changes in Photosynthetic Activity of the Lichen Cladonia mitis and the Moss Pleurozium schreberi under Artificial High-Energy Lighting in Laboratory Conditions

Digital Technologies for Assessing and Predicting the Impact of Spatiotemporal Distribution of Greenhouse Gases on the Photosynthetic Activity of Crops

Purpose of research: formation of a bank of models for the implementation of simulation experiments to assess and predict the values of greenhouse gas concentrations in the surface layer of the territory's atmosphere based on artificial neural networks and GIS technologies. The influence of the increased concentration of carbon dioxide in the surface layer of the atmosphere on the growth and development of agricultural plants, namely on the change in photosynthetic activity, the level of mineralization of the humus layer of the soil, which affects crop yields, is considered. The peculiarities of agricultural production determine the relevance of the creation and implementation of a new intelligent technology that will provide the opportunity to identify optimal parameters of crop production.Methods. The formation of a training sample for a neural network was carried out through numerical experiments and mathematical modeling methods. To select the best neural network topology for predicting the concentration of greenhouse gases in the territory under consideration, experiments were conducted that revealed the standard deviation and relative error. To assess the predictive abilities of the models, field experiments were conducted to measure CO2 concentrations in the surface layer of the atmosphere in the agricultural territories of the Belgorod region.Results. A software toolkit has been developed that makes it possible to visualize the dispersion and accumulation of greenhouse gases in the surface layer of the atmosphere. This makes it possible to conduct simulation experiments necessary to determine the territories that are under the influence of man-made sources. An assessment of the photosynthetic activity of plants in the selected territory was carried out, which allows us to form further recommendations for the effective use of agricultural territory aimed at increasing crop yields.Conclusion. The paradigms of neural networks were considered, experiments were conducted to identify the best topology. A software toolkit has been developed to visualize the dispersion and accumulation of greenhouse gases in the surface layer of the atmosphere for decision makers. The effects of technogenic factors on the photosynthetic apparatus of agricultural plants are analyzed, on the basis of which conclusions and practical recommendations for the cultivation of agricultural crops are formulated.

Effects of Iron Valence on the Growth, Photosynthesis, and Fatty Acid Composition of Phaeodactylum tricornutum

Iron is a limiting factor that controls the phytoplankton biomass of the ocean and plays an important role in the lipid production of microalgae. Elucidating the effects of different iron valences on microalgae is helpful for their commercial production. We investigated the growth, photosynthesis, and fatty acid profile of the model diatom Phaeodactylum tricornutum cultured with depleted Fe, Fe2+, Fe2+/Fe3+, and Fe3+. Samples were taken every 24 h for 8 days, and their cell density, photosynthetic pigment content, chlorophyll fluorescence, total fatty acid content, and fatty acid composition were analyzed. The cell densities of the Fe2+ and Fe2+/Fe3+ groups were significantly higher than those of the control and Fe3+ groups (p < 0.05). They were 1.26 times and 1.23 times higher than those in the Fe-depleted group. The contents of chlorophyll a and c in the Fe2+ group were significantly higher than those in the Fe-depleted group (p < 0.05). The chlorophyll fluorescence results show that Fe2+ enhanced the photosynthesis of P. tricornutum to a greater extent than Fe3+. On the eighth day of harvest, Fv/Fm and Y(II) in the Fe2+ group were 0.672 and 0.476, respectively, being 1.10 and 1.19 times greater than those in the Fe3+ group and 1.15 and 1.33 times greater than those in the Fe-depleted group, respectively. Compared with the control group, the levels of saturated fatty acids of the Fe2+/Fe3+ and Fe3+ groups were significantly higher (p < 0.05) at 21.36 ± 1.24% and 21.20 ± 0.13%, respectively. The levels of polyunsaturated fatty acids of the Fe2+/Fe3+ group were significantly lower (p < 0.05) at 29.82 ± 2.75%. Our results show that P. tricornutum exhibited physiological plasticity, including changes in photosynthetic activities and shifts in fatty acid composition, in response to different iron valences and that Fe2+ was more beneficial to the biomass production of this species than Fe3+. These findings are applicable to the production of biomass and polyunsaturated fatty acids.

Changes in the photosynthetic performance, the activity of enzymes of nitrogen metabolism, and proline content in the leaves of wheat plants after exposure to low CO<sub>2</sub> concentration

The changes in photosynthetic activity, as well as the activity of nitrogen-metabolism enzymes, the intensity of lipid peroxidation, and proline content were studied in <i>Triticum aestivum</i> L. plants after their incubation at a low CO₂ concentration in a sealed chamber for 10 d. CO₂ deficiency (-CO₂) compared to normal CO₂ concentration (control) led to a decrease in the rate of O₂ gas exchange at the plateau of the light curve and quantum yield of photosynthesis. The maximum and effective quantum photochemical yields also decreased. CO₂ deficiency reduced the activity of nitrate reductase, but increased the activities of nitrite reductase, glutamine synthetase, and glutamate dehydrogenase, and promoted proline accumulation. It is assumed that with a lack of CO₂, an excess of nitrogen-containing compounds occurs, which must be removed from metabolic processes. Also, we suggest the partial storage of nitrogen in the form of nitrogen-containing compounds such as proline.

Photosynthetic patterns during autumn in three different Salix cultivars grown on a brownfield site

Leaf senescence at the end of the growing season is a complex process stimulated by changes in daylength and temperature that prepares deciduous trees for winter by reducing photosynthetic rates and remobilization of nutrients. Extending the duration of photosynthetic activity could have important consequences for the translocation of heavy metals in the phytoremediation of contaminated sites using deciduous trees like willow. In the present study, three Salix cultivars (‘India,’ ‘SX67,’ and ‘Fish Creek’) that were observed to maintain green leaves late into autumn were evaluated over an 11-week period extending from mid-September to mid-November on a brownfield site in Montreal, Canada. Gas exchange rates, chlorophyll fluorescence, and leaf pigments were measured weekly. A general trend of declining stomatal conductance and transpiration were observed early in the trial, followed by reductions in photosynthetic efficiency and concentrations of chl a, chl b, and carotenoids, in agreement with other studies. In particular, the cultivar ‘Fish Creek’ had higher rates of gas exchange and pigment concentrations than either ‘SX67’ or ‘India,’ but values for these parameters also declined more rapidly over the course of the trial. Both photoperiod and soil and air temperatures were strong drivers of changes in photosynthetic activity in all three of these cultivars according to correlation analyses. Further studies should focus on their biomass production and heavy metal accumulation capacity in light of the observed variation in photosynthetic activity stimulated by seasonal changes in light and temperature.

The circadian night depression of photosynthesis analyzed in a herb, Pulmonaria vallarsae. Day/night quantitative relationships

Although many photosynthesis related processes are known to be controlled by the circadian system, consequent changes in photosynthetic activities are poorly understood. Photosynthesis was investigated during the daily cycle by chlorophyll fluorescence using a PAM fluorometer in Pulmonaria vallarsae subsp. apennina, an understory herb. A standard test consists of a light induction pretreatment followed by light response curve (LRC). Comparison of the major diagnostic parameters collected during day and night showed a nocturnal drop of photosynthetic responses, more evident in water-limited plants and consisting of: (i) strong reduction of flash-induced fluorescence peaks (FIP), maximum linear electron transport rate (Jmax, ETREM) and effective PSII quantum yield (ΦPSII); (ii) strong enhancement of nonphotochemical quenching (NPQ) and (iii) little or no change in photochemical quenching qP, maximum quantum yield of linear electron transport (Φ), and shape of LRC (θ). A remarkable feature of day/night LRCs at moderate to high irradiance was their linear-parallel course in double-reciprocal plots. Photosynthesis was also monitored in plants subjected to 2–3 days of continuous darkness (“long night”). In such conditions, plants exhibited high but declining peaks of photosynthetic activity during subjective days and a low, constant value with elevated NPQ during subjective night tests. The photosynthetic parameters recorded in subjective days in artificial darkness resembled those under natural day conditions. On the basis of the evidence, we suggest a circadian component and a biochemical feedback inhibition to explain the night depression of photosynthesis in P. vallarsae.

Land use and land cover changes resulting from the urban El Molinito reservoir in the drying Sonoran River Basin

ABSTRACT Although the impacts of dams on the environment and human populations have been widely documented, many developing countries continue constructing large dams. In Mexico, impact studies have neglected to analyze downstream effects of dams. Thus, we analyzed land use and land cover (LULC) changes downstream of El Molinito dam, constructed on the Sonora River in northwest Mexico. We used Landsat Thematic Mapper (TM) to generate classifications (for 1993, 2002 and 2011), from which an assessment is performed to identify the principal changes. In addition, we analyzed changes in photosynthetic activity using the simple but informative Normalized Difference Vegetation Index (NDVI). We found a drastic decline between 1993 and 2011 in agricultural LULC because of water diversions from El Molinito. This study demonstrates the need for agencies responsible for water management to better assess the negative effects of dam construction and operation, especially on the livelihoods of downstream rural communities.

The Reactions of Photosynthetic Capacity and Plant Metabolites of Sedum hybridum L. in Response to Mild and Moderate Abiotic Stresses.

In this article, for the first time, an experimental study of the effect of mild and moderate osmotic stress, NaCl content and the effect of low positive temperature on photosynthetic activity and composition of metabolites of immature plants Sedum hybridum L. is reported. In this representative of the genus Sedum adapted to arid conditions and having the properties of a succulent, a change in photosynthetic activity and an increase in the level of protective metabolites in the shoots were revealed when exposed to mild and moderate stress factors. The results of this study can be used in work on the adaptation of succulent plants to arid conditions, environmental monitoring and work on the directed induction of valuable secondary metabolites in succulents to obtain new herbal medicines.

Cyanophage infections reduce photosynthetic activity and expression of CO2 fixation genes in the freshwater bloom-forming cyanobacterium Aphanizomenon flos-aquae

Cyanobacteria play a significant role in ecosystem functioning as photosynthetic and CO2 fixing microorganisms. Whether and to what extent cyanophages alter these carbon and energy cycles in their cyanobacterial hosts is still poorly understood. In this study, we investigated changes in photosynthetic activity (PSII), expression of genes associated with the light phase of photosynthesis (psbA, petA, ndhK) and carbon metabolism (rbcL, zwf) as well as intracellular ATP and NADHP concentrations in freshwater bloom-forming filamentous cyanobacterium Aphanizomenon flos-aquae infected by cyanophage vB_AphaS-CL131. We found that PSII activity and expression level of rbcL genes, indicating potential for CO2 fixation, had decreased in response to cyanophage adsorption and DNA injection. During the period of viral DNA replication and assembly, PSII performance and gene expression remained at this decreased level and did not change significantly, indicating lack of transcriptional shutdown by the cyanophage. Combined, these observations suggest that although there is little to no interference between cyanophage DNA replication, host transcription and cellular metabolism, A. flos-aquae underwent a physiological state-shift toward lower efficiency of carbon and energy cycling. This further suggest potential cascading effect for co-occurring non-infected members of the microbial community.

The Spectral Compositions of Light Changes Physiological Response of Chinese Cabbage to Elevated Ozone Concentration.

The effects of ozone combined with other environmental factors remain an important topic of the research, both in connection with climate change and the possibility of using modern solutions in horticulture. In our experiment, we compared the influence of ozone (100 ppb) on photosynthesis and changes in the pigment composition of Chinese cabbage (Brassica rapa subsp. pekinensis) leaves depending on the spectral composition of light. We used white LED light (WL), a combination of red + green + blue (RGBL) with a dominant red component and white +blue (WBL) with a dominant blue component in comparison with the classic sodium lamp lighting (yellow light—YL). The values of the parameters describing the light-dependent phase of photosynthesis and the parameters of the gas exchange, as well as non-photosynthesis pigment contents, show that the spectral composition strongly differentiates the response of Chinese cabbage leaves to ozone. In general, the efficiency of photochemical reactions was the highest in YL, but after O3 fumigation, it decreased. In plants growing in WL and WBL, the increase of O3 concentration stimulated light photosynthesis reactions and led to the enhancement of transpiration, stomatal conductance and intracellular CO2 concentration. Changes in photosynthetic activity were accompanied by an increase in the content of anthocyanins and flavonols.

Photosynthesizing while hyperaccumulating nickel: Insights from the genus Odontarrhena (Brassicaceae)

Nickel-induced changes in photosynthetic activity were investigated in three Ni-hyperaccumulating Odontarrhena species with increasing Ni tolerance and accumulation capacity, O. muralis, O. moravensis, and O. chalcidica. Plantlets were grown in hydroponics at increasing NiSO4 concentrations (0, 0.25, and 1 mM) for one week, and the effects of Ni on growth, metal accumulation, photosynthesis, and nitrogen (N) allocation to components of the photosynthetic apparatus were analysed. Nickel treatments in O. chalcidica, and O. moravensis to a lesser extent, increased not only the photochemical efficiency of photosystem II (PSII) and the CO2 assimilation rate, but also CO2 diffusion from the atmosphere to the carboxylation sites. These two species displayed a specific increase and/or rearrangement of the photosynthetic pigments and a higher leaf N allocation to the photosynthetic components in the presence of the metal. Odontarrhena muralis displayed a decrease in photosynthetic performance at the lowest Ni concentration due to a combination of both stomatal and non-stomatal limitations. Our data represent the first complete investigation of the effects of Ni on the photosynthetic machinery in Ni hyperaccumulating plants. Our findings clearly indicate a stimulatory, hormetic-like, effect of the metal on both biophysics and biochemistry of photosynthesis in the species with the highest hyperaccumulation capacity.

A Multidisciplinary Approach to Evaluate the Effects of Contaminants of Emerging Concern on Natural Freshwater and Brackish Water Phytoplankton Communities.

Simple SummaryZinc oxide nanoparticles (ZnO NPs) and potassium dichromate (K2Cr2O7) are two contaminants of emerging concern (CECs; chemicals not commonly monitored in the environment but has the potential to enter the environment and cause known or suspected adverse ecological and/or human health effects). On this path, phytoplankton species, because of their photosynthetic activity, are vital for providing oxygen, and environmental impacts on such organisms can disrupt an entire ecosystem’s integrity. Generally, ecotoxicological assays on monospecific phytoplankton cultures provide useful information about the cellular effects of toxic compounds; however, they have limited application for detecting the effects of environmental pollutants on multiple species communities like in nature. For this reason, in this study, we took for the first time an ecotoxicological (growth rate and inhibition growth rate), ecological (taxonomic identification of species and diversity in communities), and biochemical (photosynthetic pigments) approach to evaluate the effects of ZnO NPs and K2Cr2O7 on natural freshwater and brackish water phytoplankton communities. Results show that both chemicals have negative effects on natural phytoplankton communities with an alteration of the growth rate, species composition, and photosynthetic activity. However, the exposure to ZnO 10 mg/L acts as a growth stimulant for phytoplanktonic communities. Our findings provide evidence for alterations in natural phytoplankton after exposure to such CECs.Ecotoxicological assays on monospecific phytoplankton have limited application for detecting the effects of environmental pollutants on multiple species communities. With this study, we took an ecotoxicological, ecological, and biochemical approach to evaluate the effects of two contaminants of emerging concern (zinc oxide nanoparticles, ZnO NPs, and potassium dichromate, K2Cr2O7) at different concentrations (K2Cr2O7 5.6–18–50 mg/L; ZnO NPs 10–100–300 mg/L) on natural freshwater and brackish water phytoplankton communities. Cell density and absorbance values decreased in freshwater and brackish water phytoplankton communities after exposure to ZnO NPs (100 mg/L and 300 mg/L only for freshwater), whereas growth rate was increased in both freshwater and brackish water phytoplankton communities after exposure to ZnO NPs 10 mg/L. Differently, there was no clear relationship between concentration and inhibition growth after exposure to K2Cr2O7: the lowest cell density was recorded after exposure to 18 mg/L. Moreover, the evenness index value was lower compared to the other concentrations, indicating the growth of a few, albeit resistant species to higher K2Cr2O7 concentrations. Generally, Bacillariophyceae and Dinoficee were prevalent in phytoplankton cultures after exposure to ZnO NPs and K2Cr2O7. The Shannon-Wiener index was slightly higher in the negative than the positive controls, but diversity was low after all treatments in both ecotoxicological assays. The evenness index was always very close to zero, indicating the numerical predominance of one or very few species. Finally, the decrease in chlorophyll-a and pheophytin-a in both ecotoxicological assays indicated a change in photosynthetic activity. Our findings provide evidence for alterations in natural phytoplankton after exposure to emerging contaminants that can disrupt an entire ecosystem’s integrity.

Differences in lipid homeostasis and membrane lipid unsaturation confer differential tolerance to low temperatures in two Cycas species

BackgroundC. panzhihuaensis is more tolerant to freezing than C. bifida but the mechanisms underlying the different freezing tolerance are unclear. Photosynthesis is one of the most temperature-sensitive processes. Lipids play important roles in membrane structure, signal transduction and energy storage, which are closely related to the stress responses of plants. In this study, the chlorophyll fluorescence parameters and lipid profiles of the two species were characterized to explore the changes in photosynthetic activity and lipid metabolism following low-temperature exposure and subsequent recovery.ResultsPhotosynthetic activity significantly decreased in C. bifida with the decrease of temperatures and reached zero after recovery. Photosynthetic activity, however, was little affected in C. panzhihuaensis. The lipid composition of C. bifida was more affected by cold and freezing treatments than C. panzhihuaensis. Compared with the control, the proportions of all the lipid categories recovered to the original level in C. panzhihuaensis, but the proportions of most lipid categories changed significantly in C. bifida after 3 d of recovery. In particular, the glycerophospholipids and prenol lipids degraded severely during the recovery period of C. bifida. Changes in acyl chain length and double bond index (DBI) occurred in more lipid classes immediately after low-temperature exposure in C. panzhihuaensis compare with those in C. bifida. DBI of the total main membrane lipids of C. panzhihuaensis was significantly higher than that of C. bifida following all temperature treatments.ConclusionsThe results of chlorophyll fluorescence parameters confirmed that the freezing tolerance of C. panzhihuaensis was greater than that of C. bifida. The lipid metabolism of the two species had differential responses to low temperatures. The homeostasis and plastic adjustment of lipid metabolism and the higher level of DBI of the main membrane lipids may contribute to the greater tolerance of C. panzhihuaensis to low temperatures.

Physiological and biochemical aspects of 'Tommy Atkins' mango subjected to doses and methods of application of paclobutrazol

The paclobutrazol has been widely used to stimulate the flowering of mango trees, regulating vegetative growth and promoting changes in photosynthetic activity and in the production of photoassimilates. In this context, the objective of this study is to evaluate the effects of forms and doses of PBZ on the biochemical and physiological variables of mango, cultivar ‘Tommy Atkins,’ in the Brazilian semiarid region. The experimental design was randomized blocks in a 5 x 2 + 1 factorial design with the first factor was paclobutrazol doses applied by irrigation (0.5, 1.0, 1.5, 2.0 and 2.5 g a.i.-1, linear canopy); the second factor was two phases of collection (vegetative and flowering), and an additional treatment (control) with the application of a dose in the conventional form (2.0 g a.i.-1 linear canopy applied manually by haul), and four replications. The variables analyzed were levels of total soluble sugars, reducing sugars, non-reducing sugars, total amino acids, total soluble proteins, liquid photosynthesis, stomatal conductance, transpiration, and leaf temperature. The application of PBZ by fertigation proved more efficient than the conventional application, allowing a greater assimilation of the product by the plant and the reduction of the dose. Most biochemical characteristics showed the highest values by applying lower doses of paclobutrazol. The increase in paclobutrazol doses applied by irrigation system reduced the gas exchange of the ‘Tommy Atkins’ cultivar.

Capturing the Impact of the 2018 European Drought and Heat across Different Vegetation Types Using OCO-2 Solar-Induced Fluorescence

The European heatwave of 2018 led to record-breaking temperatures and extremely dry conditions in many parts of the continent, resulting in widespread decrease in agricultural yield, early tree-leaf senescence, and increase in forest fires in Northern Europe. Our study aims to capture the impact of the 2018 European heatwave on the terrestrial ecosystem through the lens of a high-resolution solar-induced fluorescence (SIF) data acquired from the Orbiting Carbon Observatory-2 (OCO-2) satellite. SIF is proposed to be a direct proxy for gross primary productivity (GPP) and thus can be used to draw inferences about changes in photosynthetic activity in vegetation due to extreme events. We explore spatial and temporal SIF variation and anomaly in the spring and summer months across different vegetation types (agriculture, broadleaved forest, coniferous forest, and mixed forest) during the European heatwave of 2018 and compare it to non-drought conditions (most of Southern Europe). About one-third of Europe’s land area experienced a consecutive spring and summer drought in 2018. Comparing 2018 to mean conditions (i.e., those in 2015–2017), we found a change in the intra-spring season SIF dynamics for all vegetation types, with lower SIF during the start of spring, followed by an increase in fluorescence from mid-April. Summer, however, showed a significant decrease in SIF. Our results show that particularly agricultural areas were severely affected by the hotter drought of 2018. Furthermore, the intense heat wave in Central Europe showed about a 31% decrease in SIF values during July and August as compared to the mean over the previous three years. Furthermore, our MODIS (Moderate Resolution Imaging Spectroradiometer) and OCO-2 comparative results indicate that especially for coniferous and mixed forests, OCO-2 SIF has a quicker response and a possible higher sensitivity to drought in comparison to MODIS’s fPAR (fraction of absorbed photosynthetically active radiation) and the Normalized Difference Vegetation Index (NDVI) when considering shorter reference periods, which highlights the added value of remotely sensed solar-induced fluorescence for studying the impact of drought on vegetation.

Landscape-wide changes in land use and land cover correlate with, but rarely explain local biodiversity change

ContextThere is an ongoing debate whether local biodiversity is declining and what might drive this change. Changes in land use and land cover (LULC) are suspected to impact local biodiversity. However, there is little evidence for LULC changes beyond the local scale to affect biodiversity across multiple functional groups of species, thus limiting our understanding of the causes of biodiversity change.ObjectivesHere we investigate whether landscape-wide changes in LULC, defined as either trends in or abrupt changes in magnitude of photosynthetic activity, are driving bird diversity change.MethodsLinking 34 year (1984–2017) time series at 2745 breeding bird survey (BBS) routes across the conterminous United States of America with remotely-sensed Landsat imagery, we assessed for each year what proportion of the landscape surrounding each BBS route changed in photosynthetic activity and tested whether such concomitant or preceding landscape-wide changes explained changes in bird diversity, quantified as relative abundance (geometric mean) and assemblage composition (Bray–Curtis index).ResultsWe found that changes in relative abundance was negatively, and assemblage composition positively, correlated with changes in photosynthetic activity within the wider landscape. Furthermore, landscape-wide changes in LULC in preceding years explained on average more variation in bird diversity change than concomitant change. Overall, landscape-wide changes in LULC failed to explain most of the variation in bird diversity change for most BBS routes regardless whether differentiated by functional groups or ecoregions.ConclusionsOur analyses highlight the influence of preceding and concomitant landscape-wide changes in LULC on biodiversity.

Dynamics of woody plant cover in the Sahelian agroecosystems of the northern region of Burkina Faso since the 1970s–1980s droughts

This study was carried out in the northern region of Burkina Faso under Sahelian climatic conditions. The area was particularly affected by the 1970s–1980s droughts that led to the degradation of land and vegetation. Since the early 1990s, a gradual return of rainfall has been observed throughout the Sahel region. In this new environmental context, understanding the development of woody plants is important for effective conservation and management. We analyzed the dynamics of woody plant cover over the 30 years following the end of the 1970s–1980s droughts by using Landsat images from 1986, 1999, and 2015 with 30 m spatial resolution and taking into account changes in rainfall and land use. The change in the enhanced vegetation index 1 (EVI1) at the beginning of the dry season was used as a proxy for the change in photosynthetic activity of woody plants. Results showed an improvement in EVI1 on 98% of the study area, with a mean increase of 0.20 from 1986 to 2015. This improvement was accompanied by an increase in agroforestry and was weakly correlated with rainfall. The improvement in EVI1 was unstable, however, with a decline from 1999 to 2015 in the areas undergoing regreening.

Special issue in honour of Prof. Reto J. Strasser - Gradual changes in the photosynthetic apparatus triggered by nitrogen depletion during microalgae cultivation in photobioreactor

Changes of photosynthetic activity during natural depletion of nitrogen in a batch culture of Chlorella vulgaris were studied using chlorophyll a fluorescence-based methods. Complex analysis including JIP-test, multiexponential approximation, and the analysis of differential curves was carried out on the recorded fluorescence transients. Three pivot points were detected in dynamics of the JIP-test parameters during culture growing. We associated these time points with different stages of mineral stress progress. Immediately after nitrogen exhaustion in the cultivation medium, a transient increase in the efficiency of PSII was detected. During this short period, the photosynthetic apparatus acclimated to the stress by reducing the number of PSII reaction centers, simultaneously increasing the effective cross section of the light-harvesting antenna per reaction center. However, prolonged nutrient starvation impaired the structure of the photosynthetic apparatus, deactivating the oxygen-evolving complex and impairing the overall electron transport.