Browsing by Subject "Photosynthesis"

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  • Durand, Maxime; Murchie, Erik H.; Lindfors, Anders; Urban, Otmar; Aphalo, Pedro J.; Robson, T. Matthew (2021)
    The sunlight received by plants is affected by cloudiness and pollution. Future changes in cloud cover will differ among regions, while aerosol concentrations are expected to continue increasing globally as a result of wildfires, fossil fuel combustion, and industrial pollution. Clouds and aerosols increase the diffuse fraction and modify the spectral composition of incident solar radiation, and both will affect photosynthesis and terrestrial ecosystem productivity. Thus, an assessment of how canopy and leaf-level processes respond to these changes is needed as part of accurately forecasting future global carbon assimilation. To review these processes and their implications: first, we discuss the physical basis of the effect of clouds and aerosols on solar radiation as it penetrates the atmosphere; second, we consider how direct and diffuse radiation are absorbed and transmitted by plant canopies and their leaves; and finally, we assess the consequences for photosynthesis at the canopy and ecosystem levels. Photobiology will be affected at the atmospheric level by a shift in spectral composition toward shorter or longer wavelengths under clouds or aerosols, respectively, due to different scattering. Changes in the microclimate and spectral composition of radiation due to an enhanced diffuse fraction also depend on the acclimation of canopy architectural and physiological traits, such as leaf area index, orientation, and clumping. Together with an enhancement of light-use efficiency, this makes the effect of diffuse solar radiation on canopy photosynthesis a multilayered phenomenon, requiring experimental testing to capture those complex interactions that will determine whether it produces the persistent enhancement in carbon assimilation that land-surface models currently predict.
  • Gauranvi (Helsingin yliopisto, 2021)
    It is important to study the factors which inhibit the cultivation of major crops which serve as a source of food and feed, with various other medicinal values as well. One of these factors is soil degradation and infertility which could be due to high amounts of toxic elements or unfavourable pH conditions. Faba bean is one such crop and is widely affected by the acidity and aluminium toxicity in soil. In this study, an effort has been made to observe the varying tolerance of faba bean accessions and understand the underlying mechanisms used by them under stress conditions. The accessions selected were Aurora, Babylon and Kassa. Each accession was subjected to three treatments and were grown in pH 7 (control), pH 4.5 (acid treatment) and pH 4.5 + Al3+ (aluminium treatment). The pH of peat for acidic treatment was reduced to 4.5 using Sulphuric acid (H2SO4) and for aluminium treatment, Aluminium sulphate (Al2(SO4)3) was added in addition to the acid. At 16 Day after Sowing (DAS) and 30 DAS the physiological data was collected which comprised of chlorophyll concentration (SPAD value), stomatal conductance, leaf temperature and photosynthesis rate. At 35 DAS, the experiment terminated and the shoot data (fresh and dry weights of leaves and stem; and leaf area) of each plant was recorded. Then the root data (tap root length, quality and quantity of nodules and photographs of roots) was taken for each plant. ICP samples for peat, shoot and shoot were also analysed. The data collected were subjected to analysis of variance using R version 4.0.3. (means separated by 5% significance level). From the plant data, Aurora was found to be tolerant. Kassa was sensitive (especially the roots) and Babylon was sensitive to both acid and aluminium treatments. The ICP results provided the reason for this tolerance pattern and a higher concentration of elements needed for plant growth such as P and S were found to be higher in aluminium and acid treatments.
  • Lukaszewicz, German; Iturburu, Fernando G.; Garanzini, Daniela S.; Menone, Mirta L.; Pflugmacher, Stephan (2019)
    Imidacloprid (IMI) is a neonicotinoid insecticide widely used in agricultural activities all around the world. This compound is transported from croplands to surrounding freshwater ecosystems, producing adverse effects on non-target organisms. Because of the relevance of aquatic macrophytes in the above-mentioned environments and the lack of studies of potential effects of IMI on them, this work aimed to assess the mitotic process and potential genotoxicity in the aquatic macrophyte Bidens laevis L. Although the analysis of the Mitotic Index (MI) showed that IMI was not cytotoxic, the Cell Proliferation Kinetics (CPK) frequencies evidenced modifications in the kinetics of the mitotic process. Indeed, the anaphases ratio decreased at 10 and 100 mu g/L IMI, while at 1000 mu g/L an increase of prophases ratio and a decrease of metaphases ratio were observed. Regarding genotoxicity, IMI produced an increase of the abnormal metaphases frequency from 10 mu g/L to 1000 mu g/L as well as an increase in clastogenic anaphases-telophases frequency at 100 and 1000 mu g/L. In addition, aneugenic anaphases-telophases and C-mitosis frequencies also increased at 1000 mu g/L, confirming the effects on the mitotic spindle. Considering the genotoxic effects on B. laevis through two different mechanisms (aneugenic and clastogenic) and the wide spread use of IMI in agriculture, these mechanisms of toxicity on macrophytes should be considered among other recognized effects of this insecticide on aquatic biota.
  • Han, Qingquan; Luo, Jianxun; Li, Zhijun; Korpelainen, Helena; Li, Chunyang (2018)
    In this study, intergeneric grafting was employed between Populus cathayana and Salix rehderiana to investigate the grafting compatibility of the two Salicaceae plants and to reveal whether grafting can improve their drought resistance. Under different grafting combinations (P. cathayana scion with P. cathayana rootstock, P/P; P. cathayana scion with S. rehderiana rootstock, P/S; S. rehderiana scion with S. rehderiana rootstock, S/S; and S. rehderiana scion with P. cathayana rootstock, S/P), the survival and growth rate, biomass accumulation and allocation, photosynthetic traits, carbon isotope composition (delta C-13), relative water content (RWC) and nonstructural carbohydrates (NSCs) were measured. The results showed that the grafting compatibility between P. cathayana and S. rehderiana was very high, as the survival rates ranged from 76% to 100% under different grafting combinations. Drought significantly decreased growth, biomass accumulation, photosynthetic pigment contents, net photosynthesis rates (P) and RWC, and increased delta C-13 in all grafting combinations. Under drought stress, biomass accumulation, total chlorophyll, transpiration rate (E) and P-n were higher in P/P and P/S than in S/S and S/P. Compared with P/P, the growth rate, biomass accumulation, root/aboveground ratio (R/A ratio), carotenoid, RWC, starch and total soluble sugar (TSS) of P/S were less affected by drought. The height growth rate (GRH), R/A ratio, carotenoid, chlorophyll a, total chlorophyll, WUEi and TSS of S/P were lower than those of S/S under water-limited conditions. Moreover, a principal component analysis indicated that P/S and S/S had higher drought resistance than P/P and S/P under water deficits. The used method allows combining specific advantageous traits from P. cathayana and S. rehderiana, which may be a highly useful tool to enhance drought resistance in the cultivation of Salicaceae plants.
  • Bellucco, Veronica; Marras, Serena; Grimmond, C. Susan B.; Järvi, Leena; Sirca, Costantino; Spano, Donatella (2017)
    The biogenic CO2 surface atmosphere exchange is investigated and linked to vegetation cover fraction for seven sites (three urban and four non-urban) in the northern hemisphere. The non-rectangular hyperbola (NRH) is used to analyse the light-response curves during period of maximum ecophysiological processes, and to develop two models to simulate biogenic vertical CO2 fluxes. First, a generalised set of NRH coefficients is calculated after linear regression analysis across urban and non-urban ecosystems. Second, site-specific NRH coefficients are calculated for a suburban area in Helsinki, Finland. The model includes a temperature driven equation to estimate ecosystem respiration, and variation of leaf area index to modulate emissions across the year. Eddy covariance measured CO2 fluxes are used to evaluate the two models at the suburban Helsinki site and the generalised model also in Mediterranean ecosystem. Both models can simulate the mean daily trend at monthly and seasonal scales. Modelled data typically fall within the range of variability of the observations (differences of the order of 10%). Additional information improves the models performance, notably the selection of the most vegetated wind direction in Helsinki. The general model performs reasonably well during daytime but it tends to underestimate CO2 emissions at night. This reflects the model capability to catch photosynthesis processes occurring during the day, and the importance of the gross primary production (GPP) in modifying the net ecosystem exchange (NEE) of urban sites with different vegetation cover fraction. Therefore, the general model does not capture the differences in ecosystem respiration that skew nocturnal fluxes. The relation between the generalised NRH plateau parameter and vegetation cover improves (R-2 from 0.7 to 0.9) when only summer weekends with wind coming from the most vegetated sector in Helsinki and well-watered conditions for Mediterranean sites are included in the analysis. In the local model, the inclusion of a temperature driven equation for estimating the ecosystem respiration instead of a constant value, does not improve the long-term simulations. In conclusion, both the general and local models have significant potential and offer valid modelling options of biogenic components of carbon exchange in urban and non-urban ecosystems.(C) 2016 Elsevier B.V. All rights reserved.
  • Kilpeläinen, Jouni; Barbero-López, Aitor; Adamczyk, Bartosz Wojciech; Aphalo, Pedro J.; Lehto, Tarja (2019)
    Background and aims The aim was to assess possible benefits or drawbacks of arbuscular-mycorrhizal (AM) and ectomycorrhizal (EM) colonisation compared to no mycorrhizas (NM) in seedlings of the same host species. Eight broadleaf species were tested for mycorrhiza formation. Grey alder (Alnus incana) and four fungal species were selected for further experiments. Methods Grey alder seedlings were inoculated with AM fungi Rhizophagus intraradices and Glomus hoi or EM fungi Paxillus involutus plus an ascomycete isolated from Alnus roots or mock-inoculated (NM). Results EM formed in 70% of root tips and AM in 30% of root length. AM plants were smaller than EM and NM, but their specific root length (SRL) and specific leaf area (SLA) were highest. Net photosynthesis, stomatal conductance and shoot water potential did not differ between treatments. Foliar Ca, K, Mg, Mn, N, P and S concentrations (mg g−1) were highest in AM plants. However, total foliar contents (mg per plant) were lowest in AM plants, except for P, K and Zn. Conclusions The larger SRL and SLA suggest more efficient resource usage in AM plants, even though these were smaller than EM and NM plants. Grey alder is proposed as a new model species for comparisons between mycorrhiza types in cold climates.
  • Le Thiec, D.; Manninen, S. (Elsevier SAS., 2003)
    The effects of ambient and elevated ozone (O3) levels on photosynthesis, growth, pigment, biomass and element contents of Aleppo pine (Pinus halepensis Mill.) were studied for two growing seasons (1997, 1998). Two-year-old seedlings were exposed to elevated O3 in open-top chambers. The treatments were charcoal-filtered air and non-filtered air + 50 nl l–1 O3 (24 h per day, 7 days per week). In summer 1998, half of the seedlings were drought-stressed (leaf water potential down to approximately –2 MPa), while the other half were kept well-watered. At the beginning of the season (1998), current (c) and previous-year (c + 1) needles under O3 stress showed an increase in stomatal conductance and net photosynthesis. During the drought period, only stomatal conductance increased in both needle age-classes, whereas the net photosynthesis decreased. At the end of the measuring period, both parameters were reduced in the O3 treatment. Both O3 and drought decreased chlorophyll a and b concentrations, growth and biomass.A carry-over effect of O3 on pigments was also observed. Needle K content was increased in the O3 treatment. Drought protected Aleppo pine against O3 (less chlorotic mottle and less decrease of stem and branch biomass).
  • Zhang, Zhaoying; Zhang, Yongguang; Porcar-Castell, Albert; Joiner, Joanna; Guanter, Luis; Yang, Xi; Migliavacca, Mirco; Ju, Weimin; Sun, Zhigang; Chen, Shiping; Martini, David; Zhang, Qian; Li, Zhaohui; Cleverly, James; Wang, Hezhou; Goulas, Yves (2020)
    Quantifying global photosynthesis remains a challenge due to a lack of accurate remote sensing proxies. Solar-induced chlorophyll fluorescence (SIF) has been shown to be a good indicator of photosynthetic activity across various spatial scales. However, a global and spatially challenging estimate of terrestrial gross primary production (GPP) based on satellite SIF remains unresolved due to the confounding effects of species-specific physical and physiological traits and external factors, such as canopy structure or photosynthetic pathway (C-3 or C-4). Here we analyze an ensemble of far-red SIF data from OCO-2 satellite and ground observations at multiple sites, using the spectral invariant theory to reduce the effects of canopy structure and to retrieve a structure-corrected total canopy SIF emission (SIFtotal). We find that the relationships between observed canopy-leaving SIF and ecosystem GPP vary significantly among biomes. In contrast, the relationships between SIFtotal and GPP converge around two unique models, one for C-3 and one for C-4 plants. We show that the two single empirical models can be used to globally scale satellite SIF observations to terrestrial GPP. We obtain an independent estimate of global terrestrial GPP of 129.56 +/- 6.54 PgC/year for the 2015-2017 period, which is consistent with the state-of-the-art data- and process-oriented models. The new GPP product shows improved sensitivity to previously undetected 'hotspots' of productivity, being able to resolve the double-peak in GPP due to rotational cropping systems. We suggest that the direct scheme to estimate GPP presented here, which is based on satellite SIF, may open up new possibilities to resolve the dynamics of global terrestrial GPP across space and time.
  • Burgess, Alexandra J.; Durand, Maxime; Gibbs, Jonathon A.; Retkute, Renata; Robson, T. Matthew; Murchie, Erik H. (2021)
    Under field conditions, plants are subject to wind-induced movement which creates fluctuations of light intensity and spectral quality reaching the leaves, defined here as windflecks. Within this study, irradiance within two contrasting wheat (Triticum aestivum) canopies during full sun conditions was measured using a spectroradiometer to determine the frequency, duration and magnitude of low- to high-light events plus the spectral composition during wind-induced movement. Similarly, a static canopy was modelled using three-dimensional reconstruction and ray tracing to determine fleck characteristics without the presence of wind. Corresponding architectural traits were measured manually and in silico including plant height, leaf area and angle plus biomechanical properties. Light intensity can differ up to 40% during a windfleck, with changes occurring on a sub-second scale compared to similar to 5 min in canopies not subject to wind. Features such as a shorter height, more erect leaf stature and having an open structure led to an increased frequency and reduced time interval of light flecks in the CMH79A canopy compared to Paragon. This finding illustrates the potential for architectural traits to be selected to improve the canopy light environment and provides the foundation to further explore the links between plant form and function in crop canopies.