Browsing by Subject "stomatal conductance"

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  • 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.
  • Johansson, Karin S. L.; El-Soda, Mohamed; Pagel, Ellen; Meyer, Rhonda C.; Toldsepp, Kadri; Nilsson, Anders K.; Brosche, Mikael; Kollist, Hannes; Uddling, Johan; Andersson, Mats X. (2020)
    Background and Aims The stomatal conductance (g(s)) of most plant species decreases in response to elevated atmospheric CO2 concentration. This response could have a significant impact on plant water use in a future climate. However, the regulation of the CO2 induced stomatal closure response is not fully understood. Moreover, the potential genetic links between short-term (within minutes to hours) and long-term (within weeks to months) responses of g(s) to increased atmospheric CO2 have not been explored. Methods We used Arabidopsis thaliana recombinant inbred lines originating from accessions Col-0 (strong CO2 response) and C24 (weak CO2 response) to study short- and long-term controls of g(s) Quantitative trait locus (QTL) mapping was used to identify loci controlling short- and long-term g(s) responses to elevated CO2 as well as other stomata-related traits. Key Results Short- and long-term stomatal responses to elevated CO2 were significantly correlated. Both short-and long-term responses were associated with a QTL, at the end of chromosome 2. The location of this QTL was confirmed using near-isogonic lines and it was fine-mapped to a 410-kb region. The QTL did not correspond to any known gene involved in stomatal closure and had no effect on the responsiveness to abscisic acid. Additionally, we identified numerous other loci associated with stomatal regulation. Conclusions We identified and confirmed the effect of a strong QTL corresponding to a yet unknown regulator of stomatal closure in response to elevated CO2 concentration. The correlation between short- and long-term stomatal CO2 responses and the genetic link between these traits highlight the importance of understanding guard cell CO2 signalling to predict and manipulate plant water use in a world with increasing atmospheric CO2 concentration. This study demonstrates the power of using natural variation to unravel the genetic regulation of complex traits.
  • Lizarazo Torres, Clara Isabel (Helsingfors universitet, 2010)
    Drought is one of the most important abiotic stresses that causes significant reductions in crop yield, and thus hinders the food security of the growing world population. In consequence, it is urgent to select crops able to resist drought, maintain high yield and have a good nutritive content. The purpose of this project was to evaluate the responses of different accessions of Andean lupin to drought stress, and identify if there are significant differences in their physiological responses. To identify germplasm for further investigation, thirty accessions of Lupinus mutabilis Sweet. and one accession of L. albococcineus Hort. were screened in two sets, A of 15 and B of 16 accessions. From these sets, four lines were chosen on the basis of extreme values in the measurements, and this set of four was investigated in depth (set C). In all experiments, ten seeds of each chosen accession were sown in pots and grown in a glasshouse with 22°C, 18 h days and 18°C, 6 h nights, and were well watered until day 50 after planting. The pots were arranged in a randomized complete block design. The eight most uniform plants were chosen, and four were exposed to water stress while watering of the other four was continued. Water stress consisted of controlled water loss from the soil, 20% water holding capacity at 2% per day over 9 days, so the soil reached 2% moisture content and was held at this level for 2 days more. In all experiments, leaf temperature, stomatal conductance, relative water content, water potential, ion membrane leakage, and shoot dry weight were measured and transpiration efficiency was calculated. In set C, carbon isotope discrimination, root length, root dry matter, proline content and soluble sugar content were also determined. The analysis of set A and B revealed significant differences between treatments for all the parameters measured, except for relative water content, and there were also differences amongst accessions in certain parameters. PI 457972 and PI 457981 were selected for further investigation because of their low stomatal conductance under water stress conditions and low water use, and PI 510572 was selected as sensitive to drought stress due to its high water use, ion membrane leakage and water potential under water stress conditions. In addition AC 2792 (L. albococcineus) was selected due to its low stomatal conductance and water use, and high leaf temperature under water stress conditions. In the final experiment, PI 457981 and PI 457972 appeared to avoid drought through appropriate stomatal characteristics. PI 457981 showed low stomatal conductance, high leaf temperature and also high root length, similarly, accession PI 457972 showed low water potential, low stomatal conductance, low carbon isotope discrimination and accumulation of soluble sugars. Accession PI 510572 contrasted for these stomatal traits, but interestingly it showed low membrane ion leakage, high proline content and soluble sugars content, suggesting that it was capable of drought tolerance by osmotic adjustment. Finally, accession AC2792 showed low water use, low water potential and low carbon isotope discrimination. This survey thus identified accessions of Andean lupin that were able to avoid drought stress through stomatal traits and root traits, and other that were able to tolerate drought through the accumulation of osmotically active substances. Thus, there are good prospects for breeding of Andean lupin to improve its drought resistance.
  • Iso-Kokkila, Marijke (Helsingin yliopisto, 2020)
    Barley has been cultivated throughout the world for centuries. During that time, it has experienced different climatic conditions and selective pressure. The consecutive genetic variation gives us a valuable source to explore various components of yield and stress resilience. In this research field experiments were performed on 24 European barley cultivar and landrace genotypes, as well as laboratory experiments on 15 genotypes; 13 cultivated and 2 genetically modified genotypes. The aim of the field tests was to examine the genotypic variation in Finnish weather conditions during two growth seasons in Viikki and to find out how stomatal conductance differs between varieties and whether it can be connected to yield. The aim of the laboratory tests conducted in Tartu was to examine the genotypic variation in the ability of barley seedlings’ stomata to react to changes in environmental conditions with high vapor pressure deficit and abscisic acid treatment. The reason for this study is the ongoing climate change, which challenges breeders to create new resilient varieties for future climatic conditions. In addition to genomic data and genetic tools a wide variety of genotype data is needed to capture valuable traits that different varieties possess. The hypothesis of this study was to find differences in gas exchange, that could be useful considering breeding of resilient barley cultivars adapted to future climatic conditions. The tests conducted in field and laboratory conditions demonstrated, that genotypic variation could be found among here tested barley varieties. In the experiments we found several interesting cultivars, that could be tested further to verify their usefulness in breeding resilient barley cultivars for future climatic conditions.
  • Clifton, O.E.; Paulot, F.; Fiore, A.M.; Horowitz, L.W.; Correa, G.; Baublitz, C.B.; Fares, S.; Goded, I.; Goldstein, A.H.; Gruening, C.; Hogg, A.J.; Loubet, B.; Mammarella, I.; Munger, J.W.; Neil, L.; Stella, P.; Uddling, J.; Vesala, T.; Weng, E. (2020)
    Identifying the contributions of chemistry and transport to observed ozone pollution using regional-to-global models relies on accurate representation of ozone dry deposition. We use a recently developed configuration of the NOAA GFDL chemistry-climate model - in which the atmosphere and land are coupled through dry deposition-to investigate the influence of ozone dry deposition on ozone pollution over northern midlatitudes. In our model, deposition pathways are tied to dynamic terrestrial processes, such as photosynthesis and water cycling through the canopy and soil. Small increases in winter deposition due to more process-based representation of snow and deposition to surfaces reduce hemispheric-scale ozone throughout the lower troposphere by 5-12 ppb, improving agreement with observations relative to a simulation with the standard configuration for ozone dry deposition. Declining snow cover by the end of the 21st-century tempers the previously identified influence of rising methane on winter ozone. Dynamic dry deposition changes summer surface ozone by -4 to +7 ppb. While previous studies emphasize the importance of uptake by plant stomata, new diagnostic tracking of depositional pathways reveals a widespread impact of nonstomatal deposition on ozone pollution. Daily variability in both stomatal and nonstomatal deposition contribute to daily variability in ozone pollution. Twenty-first century changes in summer deposition result from a balance among changes in individual pathways, reflecting differing responses to both high carbon dioxide (through plant physiology versus biomass accumulation) and water availability. Our findings highlight a need for constraints on the processes driving ozone dry deposition to test representation in regional-to-global models.
  • Kooijmans, Linda M. J.; Sun, Wu; Aalto, Juho; Erkkilä, Kukka-Maaria; Maseyk, Kadmiel; Seibt, Ulrike; Vesala, Timo; Mammarella, Ivan; Chen, Huilin (2019)
    Understanding climate controls on gross primary productivity (GPP) is crucial for accurate projections of the future land carbon cycle. Major uncertainties exist due to the challenge in separating GPP and respiration from observations of the carbon dioxide (CO2) flux. Carbonyl sulfide (COS) has a dominant vegetative sink, and plant COS uptake is used to infer GPP through the leaf relative uptake (LRU) ratio of COS to CO2 fluxes. However, little is known about variations of LRU under changing environmental conditions and in different phenological stages. We present COS and CO2 fluxes and LRU of Scots pine branches measured in a boreal forest in Finland during the spring recovery and summer. We find that the diurnal dynamics of COS uptake is mainly controlled by stomatal conductance, but the leaf internal conductance could significantly limit the COS uptake during the daytime and early in the season. LRU varies with light due to the differential light responses of COS and CO2 uptake, and with vapor pressure deficit (VPD) in the peak growing season, indicating a humidity-induced stomatal control. Our COS-based GPP estimates show that it is essential to incorporate the variability of LRU with environmental variables for accurate estimation of GPP on ecosystem, regional, and global scales.
  • Dewar, Roderick; Mauranen, Aleksanteri; Makela, Annikki; Holtta, Teemu; Medlyn, Belinda; Vesala, Timo (2018)
    Optimization models of stomatal conductance (g(s)) attempt to explain observed stomatal behaviour in terms of cost-benefit tradeoffs. While the benefit of stomatal opening through increased CO2 uptake is clear, currently the nature of the associated cost(s) remains unclear. We explored the hypothesis that g(s) maximizes leaf photosynthesis, where the cost of stomatal opening arises from nonstomatal reductions in photosynthesis induced by leaf water stress. We analytically solved two cases, CAP and MES, in which reduced leaf water potential leads to reductions in carboxylation capacity (CAP) and mesophyll conductance (g(m)) (MES). Both CAP and MES predict the same one-parameter relationship between the intercellular:atmospheric CO2 concentration ratio (c(i)/c(a)) and vapour pressure deficit (VPD, D), viz. c(i)/c(a) approximate to xi/xi (xi+D), as that obtained from previous optimization models, with the novel feature that the parameter xi is determined unambiguously as a function of a small number of photosynthetic and hydraulic variables. These include soil-to-leaf hydraulic conductance, implying a stomatal closure response to drought. MES also predicts that g(s)/g(m) is closely related to c(i)/c(a) and is similarly conservative. These results are consistent with observations, give rise to new testable predictions, and offer new insights into the covariation of stomatal, mesophyll and hydraulic conductances.
  • Israel, David; Khan, Shandjida; Warren, Charles R; Zwiazek, Janusz J; Robson, T Matthew (2021)
    The roles of different plasma membrane aquaporins (PIPs) in leaf-level gas exchange of Arabidopsis thaliana were examined using knockout mutants. Since multiple Arabidopsis PIPs are implicated in CO2 transport across cell membranes, we focused on identifying the effects of the knockout mutations on photosynthesis, and whether they are mediated through the control of stomatal conductance of water vapour (g(s)), mesophyll conductance of CO2 (g(m)), or both. We grew Arabidopsis plants in low and high humidity environments and found that the contribution of PIPs to g s was larger under low air humidity when the evaporative demand was high, whereas any effect of a lack of PIP function was minimal under higher humidity. The pip2;4 knockout mutant had 44% higher g(s) than wild-type plants under low humidity, which in turn resulted in an increased net photosynthetic rate (A(net)). We also observed a 23% increase in whole-plant transpiration (E) for this knockout mutant. The lack of functional plasma membrane aquaporin AtPIP2;5 did not affect g(s) or E, but resulted in homeostasis of g(m) despite changes in humidity, indicating a possible role in regulating CO2 membrane permeability. CO2 transport measurements in yeast expressing AtPIP2;5 confirmed that this aquaporin is indeed permeable to CO2.
  • Liu, Che; Hölttä, Teemu; Tian, Xianglin; Berninger, Frank; Mäkelä, Annikki (2020)
    Age-related effects on whole-tree hydraulics are one of the key challenges to better predicting the production and growth of old-growth forests. Previous models have described the optimal state of stomatal behaviour, and field studies have implied on age/size-induced trends in tree ecophysiology related to hydraulics. On these bases, we built a Bayesian hierarchical model to link sap flow density and drivers of transpiration directly. The model included parameters with physiological meanings and accounted for variations in leaf-sapwood area ratio and the time lag between sap flow and transpiration. The model well-simulated the daily pattern of sap flow density and the variation between tree age groups. The results of parameterization show that (1) the usually higher stomatal conductance in young than old trees during mid-summer was mainly because the sap flow of young trees were more activated at low to medium light intensity, and (2) leaf-sapwood area ratio linearly decreased while time lag linearly increased with increasing tree height. Uncertainty partitioning and cross-validation, respectively, indicated a reliable and fairly robust parameter estimation. The model performance may be further improved by higher data quality and more process-based expressions of the internal dynamics of trees.