Browsing by Subject "PHOTOSYNTHESIS"

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  • Lappalainen, Hanna K.; Sevanto, Sanna; Dal Maso, Miikka; Taipale, Risto; Kajos, Maija; Kolari, Pasi; Back, Jaana (2013)
  • Vesala, Timo; Launiainen, Samuli; Kolari, Pasi; Pumpanen, Jukka; Sevanto, S.; Hari, Pertti; Nikinmaa, E.; Kaski, Petteri; Mannila, Heikki; Ukkonen, Esko; Piao, S. L.; Ciais, P. (2010)
  • Minunno, Francesco; Peltoniemi, Mikko; Harkonen, Sanna; Kalliokoski, Tuomo; Makinen, Harri; Makela, Annikki (2019)
    Policy-relevant forest models must be environment and management sensitive and provide unbiased estimates of predicted variables over their intended areas of application. While empirical models derive their structure and parameters from representative data sets, process-based model (PBM) parameters should be evaluated in ranges that have a biological meaning independently of output data. At the same time PBMs should be calibrated against observations in order to obtain unbiased estimates and an understanding of their predictive capability. By means of model data assimilation, we Bayesian calibrated a forest model (PREBAS) using an extensive dataset that covered a wide range of climatic conditions, species composition and management practices. PREBAS was calibrated for three species in Finland: Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies [L.] H. Karst.) and Silver birch (Betula pendula L.). Data assimilation was strongly effective in reducing the uncertainty of PREBAS parameters and predictions. A country-generic calibration showed robust performances in predicting forest variables and the results were consistent with yield tables and national forest statistics. The posterior predictive uncertainty of the model was mainly influenced by the uncertainty of the structural and measurement error.
  • Pale, Ville; Nikkonen, Taru; Vapaavuori, Jaana; Kostiainen, Mauri; Kavakka, Jari; Selin, Jorma; Tittonen, Ilkka; Helaja, Juho (2013)
  • Sabater, Neus; Vicent, Jorge; Alonso, Luis; Verrelst, Jochem; Middleton, Elizabeth M.; Porcar-Castell, Albert; Moreno, José (2018)
    Estimates of Sun–Induced vegetation chlorophyll Fluorescence (SIF) using remote sensing techniques are commonly determined by exploiting solar and/or telluric absorption features. When SIF is retrieved in the strong oxygen (O 2 ) absorption features, atmospheric effects must always be compensated. Whereas correction of atmospheric effects is a standard airborne or satellite data processing step, there is no consensus regarding whether it is required for SIF proximal–sensing measurements nor what is the best strategy to be followed. Thus, by using simulated data, this work provides a comprehensive analysis about how atmospheric effects impact SIF estimations on proximal sensing, regarding: (1) the sensor height above the vegetated canopy; (2) the SIF retrieval technique used, e.g., Fraunhofer Line Discriminator (FLD) family or Spectral Fitting Methods (SFM); and (3) the instrument’s spectral resolution. We demonstrate that for proximal–sensing scenarios compensating for atmospheric effects by simply introducing the O 2 transmittance function into the FLD or SFM formulations improves SIF estimations. However, these simplistic corrections still lead to inaccurate SIF estimations due to the multiplication of spectrally convolved atmospheric transfer functions with absorption features. Consequently, a more rigorous oxygen compensation strategy is proposed and assessed by following a classic airborne atmospheric correction scheme adapted to proximal sensing. This approach allows compensating for the O 2 absorption effects and, at the same time, convolving the high spectral resolution data according to the corresponding Instrumental Spectral Response Function (ISRF) through the use of an atmospheric radiative transfer model. Finally, due to the key role of O 2 absorption on the evaluated proximal–sensing SIF retrieval strategies, its dependency on surface pressure (p) and air temperature (T) was also assessed. As an example, we combined simulated spectral data with p and T measurements obtained for a one–year period in the Hyytiälä Forestry Field Station in Finland. Of importance hereby is that seasonal dynamics in terms of T and p, if not appropriately considered as part of the retrieval strategy, can result in erroneous SIF seasonal trends that mimic those of known dynamics for temperature–dependent physiological responses of vegetation.
  • Wang, Fang; Robson, T Matthew; Casal, Jorge J; Aphalo, Pedro J. (2020)
    The UV-A/blue photoreceptors phototropins and cryptochromes are both known to contribute to stomatal opening (∆gs) in blue light. However, their relative contributions to maintenance of gs in blue light through the whole photoperiod remains unknown. To elucidate this question, Arabidopsis phot1 phot2 and cry1 cry2 mutants (MTs) and their respective wild types (WTs) were irradiated with 200 μmol m-2 s-1 of blue-, green- or red-light (BL, GL or RL) throughout a 11-hour photoperiod. Stomatal conductance (gs) was higher under BL, than under RL or GL. Under RL, gs was not affected by either of the photoreceptor mutations, but under GL gs was slightly lower in cry1 cry2 than its WT. Under BL, the presence of phototropins was essential for rapid stomatal opening at the beginning of the photoperiod, while maximal stomatal opening beyond 3 h of irradiation required both phototropins and cryptochromes. Time courses of whole-plant net carbon assimilation rate (Anet) and the effective quantum yield of photosystem II photochemistry (ΦPSII) were consistent with an Anet-independent contribution of BL on gs both in phot1 phot2 and cry1 cry2 mutants. The changing roles of phototropins and cryptochromes through the day may allow more flexible coordination between gs and Anet.
  • Tossavainen, Marika; Nykänen, Anne; Valkonen, Kalle Santeri; Ojala, Anne; Silja, Kostia; Romantschuk, Martin (2017)
    Growth and fatty acid production of microalga Selenastrum sp. with associated bacteria was studied in lab-scale experiments in three composting leachate liquids. Nutrient reduction in cultures was measured at different initial substrate strengths. A small, pilot-scale photobioreactor (PBR) was used to verify labscale results. Similar growth conditions supported growth of both Selenastrum and bacteria. CO2 feed enhanced the production of biomass and lipids in PBR (2.4 g L-1 and 17% DW) compared to lab-scale (0.1-1.6 g L-1 and 4.0-6.5% DW) experiments. Also prolonged cultivation time increased lipid content in PBR. At both scales, NH4-N with an initial concentration of ca. 40 mg L-1 was completely removed from the biowaste leachate. In lab-scale, maximal COD reduction was over 2000 mg L-1, indicating mixotrophic growth of Selenastrum. Co-cultures are efficient in composting leachate liquid treatment, and conversion of waste to biomass is a promising approach to improve the bioeconomy of composting plants. (C) 2017 The Authors. Published by Elsevier Ltd.
  • Mõttus, Matti; Aragão, Luiz; Bäck, Jaana; Clemente, Rocío Hernandez; Maeda, Eduardo Eiji; Markiet, Vincent Robert Leon; Nichol, Caroline; Oliveira, Raimundo Cosme; Restrepo-Coupe, Natalia (2019)
    The spectral properties of plant leaves relate to the state of their photosynthetic apparatus and the surrounding environment. An example is the well known photosynthetic downregulation, active on the time scale from minutes to hours, caused by reversible changes in the xanthophyll cycle pigments. These changes affect leaf spectral absorption and are frequently quantified using the photochemical reflectance index (PRI). This index can be used to remotely monitor the photosynthetic status of vegetation, and allows for a global satellite-based measurement of photosynthesis. Such earth observation satellites in near-polar orbits usually cover the same geographical location at the same local solar time at regular intervals. To facilitate the interpretation of these instantaneous remote PRI measurements and upscale them temporally, we measured the daily course of leaf PRI in two evergreen biomes—a European boreal forest and an Amazon rainforest. The daily course of PRI was different for the two locations: At the Amazonian forest, the PRI of Manilkara elata leaves was correlated with the average photosynthetic photon flux density (PPFD) ( R2=0.59 ) of the 40 minutes preceding the leaf measurement. In the boreal location, the variations in Pinus sylvestris needle PRI were only weakly ( R2=0.27) correlated with mean PPFD of the preceding two hours; for Betula pendula, the correlation was insignificant regardless of the averaging period. The measured daily PRI curves were specific to species and/or environmental conditions. Hence, for a proper interpretation of satellite-measured instantaneous photosynthesis, the scaling of PRI measurements should be supported with information on its correlation with PPFD.
  • Atherton, J.; MacArthur, A.; Hakala, T.; Maseyk, K.; Robinson, I.; Liu, W.; Honkavaara, E.; Porcar-Castell, A. (IEEE, 2018)
    IEEE International Symposium on Geoscience and Remote Sensing IGARSS
    Solar induced chlorophyll fluorescence (SIF) emitted from plant canopies is now retrievable from space. In addition, SIF is now also routinely measured from fixed tower platforms. However there is a scale gap between temporally continuous tower measurements and spatially coarse satellite retrievals that is now being bridged by drone technology. Drone retrievals of SIF can be used to help unravel the structural and species component dependencies that occur across space on the scale of meters in heterogeneous vegetation types. Also when flown at sufficient altitude, drones can be used to simulate, and potentially validate satellite retrievals of SIF. We flew a dual field of view spectrometer system, the Piccolo doppio, above a boreal forest with the aim of retrieving SIF. Our flights were designed to assess both spatial heterogeneity of SIF driven by changes in vegetation cover type and to simulate satellite pixels by flying at a relatively high altitude.
  • Vesala, Timo; Sevanto, Sanna; Grönholm, Tiia; Salmon, Yann; Nikinmaa, Eero; Hari, Pertti; Hölttä, Teemu (2017)
    The pull of water from the soil to the leaves causes water in the transpiration stream to be under negative pressure decreasing the water potential below zero. The osmotic concentration also contributes to the decrease in leaf water potential but withmuch lesser extent. Thus, the surface tension force is approximately balanced by a force induced by negative water potential resulting in concavely curved water-air interfaces in leaves. The lowered water potential causes a reduction in the equilibrium water vapor pressure in internal (sub-stomatal/ intercellular) cavities in relation to that over water with the potential of zero, i.e., over the flat surface. The curved surface causes a reduction also in the equilibrium vapor pressure of dissolved CO2, thus enhancing its physical solubility to water. Although the water vapor reduction is acknowledged by plant physiologists its consequences for water vapor exchange at low water potential values have received very little attention. Consequences of the enhanced CO2 solubility to a leaf water-carbon budget have not been considered at all before this study. We use theoretical calculations and modeling to show how the reduction in the vapor pressures affects transpiration and carbon assimilation rates. Our results indicate that the reduction in vapor pressures of water and CO2 could enhance plant water use efficiency up to about 10% at a leaf water potential of -2 MPa, and much more when water potential decreases further. The low water potential allows for a direct stomatal water vapor uptake from the ambient air even at sub-100% relative humidity values. This alone could explain the observed rates of foliar water uptake by e.g., the coastal redwood in the fog belt region of coastal California provided the stomata are sufficiently open. The omission of the reduction in the water vapor pressure causes a bias in the estimates of the stomatal conductance and leaf internal CO2 concentration based on leaf gas exchange measurements. Manufactures of leaf gas exchange measurement systems should incorporate leaf water potentials in measurement set-ups.
  • Pour-Aboughadareh, Alireza; Omidi, Mansour; Naghavi, Mohammad Reza; Etminan, Alireza; Mehrabi, Ali Ashraf; Poczai, Péter; Bayat, Hamid (2019)
    Wild relatives of wheat serve as an extraordinary source of variability for breeding programs due to their capabilities to respond to various environmental stresses. Here, we investigated some species possessing a D genome (T. aestivum, Ae. tauschii, Ae. crassa and Ae. cylindrica) in terms of relative water content (RWC), stomatal conductance (Gs), relative chlorophyll content, initial fluorescence (Fo), maximum quantum yield of PSII (Fv/Fm), maximum primary yield of PSII photochemistry (Fv/Fo), as well as shoot fresh and dry biomasses under control and water deficit conditions. Our results revealed that water deficit negatively affected all traits; shoot fresh weight, Gs and RWC showed the highest reduction compared to the control condition. Principal component analysis (PCA) identified two PCs that accounted for 53.36% of the total variation in the water deficit conditions. Correlation analysis and PCA-based biplots showed that stress tolerance index (STI) is significantly associated with Fv/Fm and Fv/Fo under water stress conditions, suggesting that these are the best parameters to evaluate when screening for tolerant samples at the seedling stage. We identified 19 accessions from Ae. crassa and one from Ae. tauschii as the most tolerant samples. In conclusion, Ae. crassa might provide an ideal genetic resource for drought-tolerant wheat breeds.
  • Lindroth, Anders; Holst, Jutta; Linderson, Maj-Lena; Aurela, Mika; Biermann, Tobias; Heliasz, Michal; Chi, Jinshu; Ibrom, Andreas; Kolari, Pasi; Klemedtsson, Leif; Krasnova, Alisa; Laurila, Tuomas; Lehner, Irene; Lohila, Annalea; Mammarella, Ivan; Mölder, Meelis; Lofvenius, Mikaell Ottosson; Peichl, Matthias; Pilegaard, Kim; Soosaar, Kaido; Vesala, Timo; Vestin, Patrik; Weslien, Per; Nilsson, Mats (2020)
    The Nordic region was subjected to severe drought in 2018 with a particularly long-lasting and large soil water deficit in Denmark, Southern Sweden and Estonia. Here, we analyse the impact of the drought on carbon and water fluxes in 11 forest ecosystems of different composition: spruce, pine, mixed and deciduous. We assess the impact of drought on fluxes by estimating the difference (anomaly) between year 2018 and a reference year without drought. Unexpectedly, the evaporation was only slightly reduced during 2018 compared to the reference year at two sites while it increased or was nearly unchanged at all other sites. This occurred under a 40 to 60% reduction in mean surface conductance and the concurrent increase in evaporative demand due to the warm and dry weather. The anomaly in the net ecosystem productivity (NEP) was 93% explained by a multilinear regression with the anomaly in heterotrophic respiration and the relative precipitation deficit as independent variables. Most of the variation (77%) was explained by the heterotrophic component. Six out of 11 forests reduced their annual NEP with more than 50 g C m(-2)yr(-1)during 2018 as compared to the reference year. The NEP anomaly ranged between -389 and +74 g C m(-2)yr(-1)with a median value of -59 g C m(-2)yr(-1). This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.
  • Södervik, Ilona; Nousiainen, Maija; Koponen, Ismo (2021)
    The purpose of this study is to increase the understanding about undergraduate life science students’ conceptions concerning the role of photosynthesizing plants in the ecosystem, utilizing a network analysis method. Science learning requires the integration and linking of abstract and often counterintuitive concepts successfully into multifaceted networks. The quality of these networks, together with their abilities to communicate via the language of science, influences students’ success in academic, verbal problem-solving tasks. This study contributes to investigating students’ understanding, utilizing a modern network analysis method in exploring first-year university life science students’ written answers. In this study, a total of 150 first-year life science students answered two open-ended tasks related to the role of photosynthesizing plants in the ecosystem. A network analysis tool was used in exploring the occurrence of different-level science concepts and the interrelatedness between these concepts in students’ verbal outputs. The results showed that the richness of concept networks and students’ use of macro-concepts were remarkably varied between the tasks. Higher communicability measures were connected to the more abundant existence of macro-concepts in the task concerning the role of plants from the food-chain perspective. In the answers for the task concerning the role of plants regarding the atmosphere, the students operated mainly with single facts, and there were only minor interconnections made between the central concepts. On the basis of these results, the need for more all-encompassing biology teaching concerning complex environmental and socio-economic problems became evident. Thus, methodological and pedagogical contributions are discussed.
  • Wasonga, Daniel; Kleemola, Jouko; Alakukku, Laura; Mäkelä, Pirjo (2020)
    Cassava (Manihot esculenta Crantz) experiences intermittent water deficit and suffers from potassium (K) deficiency that seriously constrains its yield in the tropics. Currently, the interaction effect between deficit irrigation and K fertigation on growth and yield of cassava is unknown, especially during the early growth phase. Therefore, pot experiments were conducted under controlled greenhouse conditions using cassava cuttings. Treatments initiated at 30 days after planting included three irrigation doses (30%, 60%, 100% pot capacity) and five K (0.01, 1, 4, 16, and 32 mM) concentrations. The plants were harvested 90 days after planting. Decreasing irrigation dose to 30% together with 16 mM K lowered the leaf water potential by 69%, leaf osmotic potential by 41%, photosynthesis by 35%, stomatal conductance by 41%, water usage by 50%, leaf area by 17%, and whole-plant dry mass by 41%, compared with full-irrigated plants. Lowering the K concentration below 16 mM reduced the values further. Notably, growth and yield were decreased the least compared with optimal, when irrigation dose was decreased to 60% together with 16 mM K. The results demonstrate that deficit irrigation strategies could be utilized to develop management practices to improve cassava productivity by means of K fertigation under low moisture conditions.
  • Radecker, Nils; Pogoreutz, Claudia; Gegner, Hagen M.; Cardenas, Anny; Roth, Florian; Bougoure, Jeremy; Guagliardo, Paul; Wild, Christian; Pernice, Mathieu; Raina, Jean-Baptiste; Meibom, Anders; Voolstra, Christian R. (2021)
    Recurrent mass bleaching events are pushing coral reefs world-wide to the brink of ecological collapse. While the symptoms and consequences of this breakdown of the coral-algal symbiosis have been extensively characterized, our understanding of the underlying causes remains incomplete. Here, we investigated the nutrient fluxes and the physiological as well as molecular responses of the widespread coral Stylophora pistillata to heat stress prior to the onset of bleaching to identify processes involved in the break-down of the coral-algal symbiosis. We show that altered nutrient cycling during heat stress is a primary driver of the functional breakdown of the symbiosis. Heat stress increased the metabolic energy demand of the coral host, which was compensated by the catabolic degradation of amino acids. The resulting shift from net uptake to release of ammonium by the coral holobiont subsequently promoted the growth of algal symbionts and retention of photosynthates. Together, these processes form a feedback loop that will gradually lead to the decoupling of carbon translocation from the symbiont to the host. Energy limitation and altered symbiotic nutrient cycling are thus key factors in the early heat stress response, directly contributing to the breakdown of the coral-algal symbiosis. Interpreting the stability of the coral holobiont in light of its metabolic interactions provides a missing link in our understanding of the environmental drivers of bleaching and may ultimately help uncover fundamental processes underpinning the functioning of endosymbioses in general.
  • Roth, Florian; Karcher, Denis B.; Radecker, Nils; Hohn, Sonke; Carvalho, Susana; Thomson, Timothy; Saalmann, Franziska; Voolstra, Christian R.; Kurten, Benjamin; Struck, Ulrich; Jones, Burton H.; Wild, Christian (2020)
    Following coral mortality in tropical reefs, pioneer communities dominated by filamentous and crustose algae efficiently colonize substrates previously occupied by coral tissue. This phenomenon is particularly common after mass coral mortality following prolonged bleaching events associated with marine heatwaves. Pioneer communities play an important role for the biological succession and reorganization of reefs after disturbance. However, their significance for critical ecosystem functions previously mediated by corals, such as the efficient cycling of carbon (C) and nitrogen (N) within the reef, remains uncertain. We used 96 carbonate tiles to simulate the occurrence of bare substrates after disturbance in a coral reef of the central Red Sea. We measured rates of C and dinitrogen (N-2) fixation of pioneer communities on these tiles monthly over an entire year. Coupled with elemental and stable isotope analyses, these measurements provide insights into macronutrient acquisition, export and the influence of seasonality. Pioneer communities exhibited high rates of C and N(2)fixation within 4-8 weeks after the introduction of experimental bare substrates. Ranging from 13 to 25 mu mol C cm(-2) day(-1)and 8 to 54 nmol N cm(-2) day(-1), respectively, C and N(2)fixation rates were comparable to reported values for established Red Sea coral reefs. This similarity indicates that pioneer communities may quickly compensate for the loss of benthic productivity by corals. Notably, between 40% and 85% of fixed organic C was exported into the environment, constituting a vital source of energy for the coral reef food web. Our findings suggest that benthic pioneer communities may play a crucial, yet overlooked role in the C and N dynamics of oligotrophic coral reefs by contributing to the input of new C and N after coral mortality. While not substituting other critical ecosystem functions provided by corals (e.g. structural habitat complexity and coastal protection), pioneer communities likely contribute to maintaining coral reef nutrient cycling through the accumulation of biomass and import of macronutrients following coral loss. A freePlain Language Summarycan be found within the Supporting Information of this article.
  • Provenzale, Maria; Ojala, Anne; Heiskanen, Jouni; Erkkila, Kukka-Maaria; Mammarella, Ivan; Hari, Pertti; Vesala, Timo (2018)
    Lakes are important actors in biogeochemical cycles and a powerful natural source of CO2. However, they are not yet fully integrated in carbon global budgets, and the carbon cycle in the water is still poorly understood. In freshwater ecosystems, productivity studies have usually been carried out with traditional methods (bottle incubations, C-14 technique), which are imprecise and have a poor temporal resolution. Consequently, our ability to quantify and predict the net ecosystem productivity (NEP) is limited: the estimates are prone to errors and the NEP cannot be parameterised from environmental variables. Here we expand the testing of a free-water method based on the direct measurement of the CO2 concentration in the water. The approach was first proposed in 2008, but was tested on a very short data set (3 days) under specific conditions (autumn turnover); despite showing promising results, this method has been neglected by the scientific community. We tested the method under different conditions (summer stratification, typical summer conditions for boreal dark-water lakes) and on a much longer data set (40 days), and quantitatively validated it comparing our data and productivity models. We were able to evaluate the NEP with a high temporal resolution (minutes) and found a very good agreement (R-2 >= 0.71) with the models. We also estimated the parameters of the productivity-irradiance (PI) curves that allow the calculation of the NEP from irradiance and water temperature. Overall, our work shows that the approach is suitable for productivity studies under a wider range of conditions, and is an important step towards developing this method so that it becomes more widely used.
  • Reichel, Philipp; Munz, Sebastian; Hartung, Jens; Prager, Achim; Kotiranta, Stiina; Burgel, Lisa; Schober, Torsten; Graeff-Honninger, Simone (2021)
    Cannabis is one of the oldest cultivated plants, but plant breeding and cultivation are restricted by country specific regulations. Plant growth, morphology and metabolism can be manipulated by changing light quality and intensity. Three morphologically different strains were grown under three different light spectra with three real light repetitions. Light dispersion was included into the statistical evaluation. The light spectra considered had an influence on the morphology of the plant, especially the height. Here, the shade avoidance induced by the lower R:FR ratio under the ceramic metal halide lamp (CHD) was of particular interest. The sugar leaves seemed to be of elementary importance in the last growth phase for yield composition. Furthermore, the last four weeks of flowering were crucial to influence the yield composition of Cannabis sativa L. through light spectra. The dry flower yield was significantly higher under both LED treatments compared to the conventional CHD light source. Our results indicate that the plant morphology can be artificially manipulated by the choice of light treatment to create shorter plants with more lateral branches which seem to be beneficial for yield development. Furthermore, the choice of cultivar has to be taken into account when interpreting results of light studies, as Cannabis sativa L. subspecies and thus bred strains highly differ in their phenotypic characteristics.
  • Silfver, Tarja; Heiskanen, Lauri; Aurela, Mika; Myller, Kristiina; Karhu, Kristiina; Meyer, Nele; Tuovinen, Juha-Pekka; Oksanen, Elina; Rousi, Matti; Mikola, Juha (2020)
    Climate warming is anticipated to make high latitude ecosystems stronger C sinks through increasing plant production. This effect might, however, be dampened by insect herbivores whose damage to plants at their background, non-outbreak densities may more than double under climate warming. Here, using an open-air warming experiment among Subarctic birch forest field layer vegetation, supplemented with birch plantlets, we show that a 2.3 degrees C air and 1.2 degrees C soil temperature increase can advance the growing season by 1-4 days, enhance soil N availability, leaf chlorophyll concentrations and plant growth up to 400%, 160% and 50% respectively, and lead up to 122% greater ecosystem CO2 uptake potential. However, comparable positive effects are also found when insect herbivory is reduced, and the effect of warming on C sink potential is intensified under reduced herbivory. Our results confirm the expected warming-induced increase in high latitude plant growth and CO2 uptake, but also reveal that herbivorous insects may significantly dampen the strengthening of the CO2 sink under climate warming. Warming is expected to increase C sink capacity in high-latitude ecosystems, but plant-herbivore interactions could moderate or offset this effect. Here, Silfver and colleagues test individual and interactive effects of warming and insect herbivory in a field experiment in Subarctic forest, showing that even low intensity insect herbivory strongly reduces C sink potential.