Boreal peatlands are highly important sinks for carbon (C). This function is enabled largely by one peat-forming plant, the Sphagnum moss. In addition to slowing the decomposition by gradually creating ombrotrophic conditions, it gives a shelter for the organisms mitigating the emissions of methane (CH4) – an effective greenhouse gas formed in submerged, anoxic peat layers. These organisms, methane oxidizing bacteria (methanotrophs, MOB), inhabit the dead, water-filled hyaline cells of the Sphagnum and provide the plant carbon dioxide (CO2) derived from the CH4 oxidation. While several studies have confirmed the presence of Sphagnum-associated methanotrophs (SAM), it is still unclear how dependent they are on the mosses and how environmental conditions affect their community composition and activity. This thesis evaluated SAM dynamics in the different stages of peatland development on both pristine and disturbed areas. Studies were based mainly on molecular methods, targeting the MOB-specific pmoA gene, and laboratory incubations, including stable isotope probing. In the first study, the connection between the SAM and the mosses was assessed by testing whether the SAM will disperse through the water phase. This trait, considered to represent a facultative symbiosis, was demonstrated in two experiments. In the field, mosses inactive in CH4 oxidation were transplanted next to active ones. Within a month, SAM communities of the neighboring mosses become more similar. The water-based colonization was further confirmed by bathing inactive mosses in flark pore water that showed high CH4 oxidation activity. Within just 11 h, activity was induced and the SAM abundance significantly increased in the treated mosses. The other two studies revealed similar SAM community composition patterns on a pristine chronosequence and on a gradient of re-vegetating cutover peatlands. Instead of the Sphagnum species, the general environmental conditions seemed to control the SAM community composition. Different types of SAM seemed to have their preferred environmental niches, with the type Ia MOB present and active especially in the young succession stages and the type II MOB in the older, hydrologically more stable stages. Despite the community differences, the potential CH4 oxidation did not differ along the gradients, suggesting functional redundancy. Only some drier bog samples did not show any detectable CH4 oxidation, demonstrating the regulatory role of the water table level on the SAM activity. The peat layers of the cutover gradient showed similar MOB community patterns but the potential CH4 oxidation increased with succession. The ability to disperse through the water provides a recovery mechanism from disturbances such as droughts, which are predicted to increase with climate warming. In addition, the diversity and functional redundancy of the SAM communities enhance the resilience of this important CH4 biofilter formed by the living Sphagnum mosses. The poten
{"title":"Sphagnum-associated methanotrophs : a resilient CH4 biofilter in pristine and disturbed peatlands","authors":"A. Putkinen","doi":"10.14214/df.252","DOIUrl":"https://doi.org/10.14214/df.252","url":null,"abstract":"Boreal peatlands are highly important sinks for carbon (C). This function is enabled largely by one peat-forming plant, the Sphagnum moss. In addition to slowing the decomposition by gradually creating ombrotrophic conditions, it gives a shelter for the organisms mitigating the emissions of methane (CH4) – an effective greenhouse gas formed in submerged, anoxic peat layers. These organisms, methane oxidizing bacteria (methanotrophs, MOB), inhabit the dead, water-filled hyaline cells of the Sphagnum and provide the plant carbon dioxide (CO2) derived from the CH4 oxidation. While several studies have confirmed the presence of Sphagnum-associated methanotrophs (SAM), it is still unclear how dependent they are on the mosses and how environmental conditions affect their community composition and activity. This thesis evaluated SAM dynamics in the different stages of peatland development on both pristine and disturbed areas. Studies were based mainly on molecular methods, targeting the MOB-specific pmoA gene, and laboratory incubations, including stable isotope probing. In the first study, the connection between the SAM and the mosses was assessed by testing whether the SAM will disperse through the water phase. This trait, considered to represent a facultative symbiosis, was demonstrated in two experiments. In the field, mosses inactive in CH4 oxidation were transplanted next to active ones. Within a month, SAM communities of the neighboring mosses become more similar. The water-based colonization was further confirmed by bathing inactive mosses in flark pore water that showed high CH4 oxidation activity. Within just 11 h, activity was induced and the SAM abundance significantly increased in the treated mosses. The other two studies revealed similar SAM community composition patterns on a pristine chronosequence and on a gradient of re-vegetating cutover peatlands. Instead of the Sphagnum species, the general environmental conditions seemed to control the SAM community composition. Different types of SAM seemed to have their preferred environmental niches, with the type Ia MOB present and active especially in the young succession stages and the type II MOB in the older, hydrologically more stable stages. Despite the community differences, the potential CH4 oxidation did not differ along the gradients, suggesting functional redundancy. Only some drier bog samples did not show any detectable CH4 oxidation, demonstrating the regulatory role of the water table level on the SAM activity. The peat layers of the cutover gradient showed similar MOB community patterns but the potential CH4 oxidation increased with succession. The ability to disperse through the water provides a recovery mechanism from disturbances such as droughts, which are predicted to increase with climate warming. In addition, the diversity and functional redundancy of the SAM communities enhance the resilience of this important CH4 biofilter formed by the living Sphagnum mosses. The poten","PeriodicalId":375560,"journal":{"name":"Dissertationes Forestales","volume":"61 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125606184","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
(1) School of Forest Sciences, University of Eastern Finland, Joensuu, Finland (aino.korrensalo@uef.fi), (2) Department of Physics, University of Helsinki, Helsinki, Finland , (3) Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic, (4) Natural Resources Institute Finland, Helsinki, Finland, (5) School of Computing, University of Eastern Finland, Joensuu, Finland, (6) Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden, (7) Department of Forest Sciences, University of Helsinki, Finland
{"title":"Behind the stability of boreal bog carbon sink: Compositional and functional variation of vegetation across temporal and spatial scales","authors":"A. Korrensalo","doi":"10.14214/DF.240","DOIUrl":"https://doi.org/10.14214/DF.240","url":null,"abstract":"(1) School of Forest Sciences, University of Eastern Finland, Joensuu, Finland (aino.korrensalo@uef.fi), (2) Department of Physics, University of Helsinki, Helsinki, Finland , (3) Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic, (4) Natural Resources Institute Finland, Helsinki, Finland, (5) School of Computing, University of Eastern Finland, Joensuu, Finland, (6) Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden, (7) Department of Forest Sciences, University of Helsinki, Finland","PeriodicalId":375560,"journal":{"name":"Dissertationes Forestales","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117020206","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Photosynthesis requires a balance between its light-dependent and light-independent reactions so that the energy input through photochemistry matches its consumption. Biochemical and physiological processes help to achieve this balance, as certain processes regulate the activity of light-dependent photochemical reactions, whilst others regulate the activity of temperature-dependent biochemical reactions. Biochemical and physiological processes also modulate the absorbed energy available for photosynthesis by diverting a fraction into non-photochemical pathways that dissipate energy as heat and fluorescence. Interestingly, certain biochemical and physiological processes behind the dynamics of photosynthesis correlate with leaf optical properties (LOPs), which represent an approach to characterising the dynamics of photosynthesis. Yet, how solid is our knowledge concerning the biochemical and physiological processes influencing LOPs, and how accurately do LOPs and the biochemical and physiological processes behind photosynthetic dynamics correlate when investigated across various spatio-temporal scales? This thesis investigated whether reflectance-based and fluorescence-based LOPs adequately correlate with the biochemical and physiological processes behind photosynthetic dynamics, and whether their correlations hold true at various spatio-temporal scales. This thesis demonstrates the validity of reflectance-based and fluorescence-based LOPs as optical proxies for investigating the dynamics of photosynthesis. However, it also identifies sources of variability that cause the correlations between photosynthesis and LOPs to break down. This thesis classifies the sources of variability in terms of methodological (i.e. over-simplification and technical/instrumental constraints) and spatiotemporal limitations. The over-simplification of processes behind the dynamics of photosynthesis and LOPs was addressed by studying the absorption of photosynthetically active radiation (PAR) by conifer needles. PAR absorption is generally considered to be chlorophyll concentration-dependent, yet this thesis shows it to be additionally modulated by the effect that waxes have on needle PAR reflectance. Due to the difficulties of directly measuring needle PAR absorption, PAR reflectance was used as a proxy of PAR absorption. To solve this technical/instrumental constraint, this thesis presents a new methodology that facilitates the direct estimation of PAR absorption. This thesis also demonstrates that certain LOPs appear to be insensitive to detecting the dynamics of certain biochemical and physiological processes over time. This was true for the photochemical reflectance index (PRI), which failed to detect zeaxanthin-independent processes behind the thermal dissipation of the absorbed PAR. Lastly, this thesis shows that LOPs can also be influenced by leaf morphology, which could affect the optically-based monitoring of largerthan-leaf scales. Despite the caveats highligh
{"title":"Leaf optical properties and dynamics of photosynthetic activity","authors":"B. Olascoaga","doi":"10.14214/DF.247","DOIUrl":"https://doi.org/10.14214/DF.247","url":null,"abstract":"Photosynthesis requires a balance between its light-dependent and light-independent reactions so that the energy input through photochemistry matches its consumption. Biochemical and physiological processes help to achieve this balance, as certain processes regulate the activity of light-dependent photochemical reactions, whilst others regulate the activity of temperature-dependent biochemical reactions. Biochemical and physiological processes also modulate the absorbed energy available for photosynthesis by diverting a fraction into non-photochemical pathways that dissipate energy as heat and fluorescence. Interestingly, certain biochemical and physiological processes behind the dynamics of photosynthesis correlate with leaf optical properties (LOPs), which represent an approach to characterising the dynamics of photosynthesis. Yet, how solid is our knowledge concerning the biochemical and physiological processes influencing LOPs, and how accurately do LOPs and the biochemical and physiological processes behind photosynthetic dynamics correlate when investigated across various spatio-temporal scales? This thesis investigated whether reflectance-based and fluorescence-based LOPs adequately correlate with the biochemical and physiological processes behind photosynthetic dynamics, and whether their correlations hold true at various spatio-temporal scales. This thesis demonstrates the validity of reflectance-based and fluorescence-based LOPs as optical proxies for investigating the dynamics of photosynthesis. However, it also identifies sources of variability that cause the correlations between photosynthesis and LOPs to break down. This thesis classifies the sources of variability in terms of methodological (i.e. over-simplification and technical/instrumental constraints) and spatiotemporal limitations. The over-simplification of processes behind the dynamics of photosynthesis and LOPs was addressed by studying the absorption of photosynthetically active radiation (PAR) by conifer needles. PAR absorption is generally considered to be chlorophyll concentration-dependent, yet this thesis shows it to be additionally modulated by the effect that waxes have on needle PAR reflectance. Due to the difficulties of directly measuring needle PAR absorption, PAR reflectance was used as a proxy of PAR absorption. To solve this technical/instrumental constraint, this thesis presents a new methodology that facilitates the direct estimation of PAR absorption. This thesis also demonstrates that certain LOPs appear to be insensitive to detecting the dynamics of certain biochemical and physiological processes over time. This was true for the photochemical reflectance index (PRI), which failed to detect zeaxanthin-independent processes behind the thermal dissipation of the absorbed PAR. Lastly, this thesis shows that LOPs can also be influenced by leaf morphology, which could affect the optically-based monitoring of largerthan-leaf scales. Despite the caveats highligh","PeriodicalId":375560,"journal":{"name":"Dissertationes Forestales","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-03-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126655657","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"On the economics of boreal Scots pine management under climate change","authors":"Sampo Pihlainen","doi":"10.14214/DF.246","DOIUrl":"https://doi.org/10.14214/DF.246","url":null,"abstract":"","PeriodicalId":375560,"journal":{"name":"Dissertationes Forestales","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134021931","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Disturbances, caused by abiotic and biotic agents, are discrete events in time disrupting the ecosystem and resulting in the reduction of plant biomass. They play a key role in forest ecosystems, but in the managed forests pose a risk to forest productivity. The projected climate change is expected to increase the risk of various disturbances in the boreal forests. In Europe, the major risks threatening the Norway spruce (Picea abies) dominated stands are caused by Heterobasidion root rot, wind storms, and European spruce bark beetle (Ips typographus). Heterobasidion root rot causes growth losses, mortality and decreases the timber quality. It also decreases the mechanical stability of the tree against wind load and increases the stand vulnerability for wind damages. Bark beetles benefit from the low resistance breeding material, i.e., wind damaged trees, when the population is low and can emerge as outbreaks in the right conditions. This thesis presents a simulation framework WINDROT to simulate the interactive dynamics of these disturbance agents. WINDROT consists of four simulation models, each responsible for either the dynamics of the host or one of the disturbance agents. A stand level decision support system, MOTTI, simulates the growth and dynamics of tree stands as affected by forest management, and provides inputs for mechanistic models Hmodel, HWIND and BBDYN simulating the dynamics and effects of disturbance agents. The model performance analyses in tree and stand scale showed that; i) the Heterobasidion dynamics are driven by primary and secondary infections on large stumps; ii) increasing intensity of Heterobasidion root rot damages increases the risk for wind damages; and iii) the increasing wind damages increased the subsequent bark beetle damages. The simulation framework can be used to analyze the sensitivity of different forest management regimes to the risks posed by these damages alone and in various combinations.
{"title":"Integrating mechanistic disturbance models and stand dynamics of Norway spruce","authors":"Juha Honkaniemi","doi":"10.14214/DF.241","DOIUrl":"https://doi.org/10.14214/DF.241","url":null,"abstract":"Disturbances, caused by abiotic and biotic agents, are discrete events in time disrupting the ecosystem and resulting in the reduction of plant biomass. They play a key role in forest ecosystems, but in the managed forests pose a risk to forest productivity. The projected climate change is expected to increase the risk of various disturbances in the boreal forests. In Europe, the major risks threatening the Norway spruce (Picea abies) dominated stands are caused by Heterobasidion root rot, wind storms, and European spruce bark beetle (Ips typographus). Heterobasidion root rot causes growth losses, mortality and decreases the timber quality. It also decreases the mechanical stability of the tree against wind load and increases the stand vulnerability for wind damages. Bark beetles benefit from the low resistance breeding material, i.e., wind damaged trees, when the population is low and can emerge as outbreaks in the right conditions. This thesis presents a simulation framework WINDROT to simulate the interactive dynamics of these disturbance agents. WINDROT consists of four simulation models, each responsible for either the dynamics of the host or one of the disturbance agents. A stand level decision support system, MOTTI, simulates the growth and dynamics of tree stands as affected by forest management, and provides inputs for mechanistic models Hmodel, HWIND and BBDYN simulating the dynamics and effects of disturbance agents. The model performance analyses in tree and stand scale showed that; i) the Heterobasidion dynamics are driven by primary and secondary infections on large stumps; ii) increasing intensity of Heterobasidion root rot damages increases the risk for wind damages; and iii) the increasing wind damages increased the subsequent bark beetle damages. The simulation framework can be used to analyze the sensitivity of different forest management regimes to the risks posed by these damages alone and in various combinations.","PeriodicalId":375560,"journal":{"name":"Dissertationes Forestales","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132757102","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The demand for mechanized tree planting is expected to increase in the future. This dissertation assessed mechanized tree planting in Finland and suggests ways to improve its current productivity. The work on which this thesis is based was described in five peerreviewed articles (I–V) addressing four specific research questions (SQs) that focus on productivity and cost-competitiveness, automation, capacity utilization, and the quality of planting work. While productivity of mechanized planting is higher than manual methods, it is not yet cost-competitive. However, increasing efficiency by skilled operators and worksite selection make it possible for mechanized planting costs to remain lower than those of excavator spot mounding followed by manual planting. Increasing productivity and reducing operating costs are possible with an effective automatic seedling feeding system, although the Risutec APC is not yet sufficiently developed to reach that goal. Planting machine capacity is underutilized and could be utilized more effective to enhance productivity and cost-efficiency. Technical availability of planting machines in Finland is good, and the quality of mechanized planting work is high. Optimization and integration of the entire mechanized planting chain from the nursery to outplanting is important to minimize total cost. In summary, for mechanized planting to be effective the following criteria must be satisfied: machine reliability; highly-skilled machine operator; suitable worksite; seedling quality, availability, and supply to worksite. In the future, it is important to continue developing new and existing machines to enhance productivity, e.g., by continuously working planting machines.
{"title":"Mechanized tree planting in Finland and improving its productivity","authors":"T. Laine","doi":"10.14214/DF.239","DOIUrl":"https://doi.org/10.14214/DF.239","url":null,"abstract":"The demand for mechanized tree planting is expected to increase in the future. This dissertation assessed mechanized tree planting in Finland and suggests ways to improve its current productivity. The work on which this thesis is based was described in five peerreviewed articles (I–V) addressing four specific research questions (SQs) that focus on productivity and cost-competitiveness, automation, capacity utilization, and the quality of planting work. While productivity of mechanized planting is higher than manual methods, it is not yet cost-competitive. However, increasing efficiency by skilled operators and worksite selection make it possible for mechanized planting costs to remain lower than those of excavator spot mounding followed by manual planting. Increasing productivity and reducing operating costs are possible with an effective automatic seedling feeding system, although the Risutec APC is not yet sufficiently developed to reach that goal. Planting machine capacity is underutilized and could be utilized more effective to enhance productivity and cost-efficiency. Technical availability of planting machines in Finland is good, and the quality of mechanized planting work is high. Optimization and integration of the entire mechanized planting chain from the nursery to outplanting is important to minimize total cost. In summary, for mechanized planting to be effective the following criteria must be satisfied: machine reliability; highly-skilled machine operator; suitable worksite; seedling quality, availability, and supply to worksite. In the future, it is important to continue developing new and existing machines to enhance productivity, e.g., by continuously working planting machines.","PeriodicalId":375560,"journal":{"name":"Dissertationes Forestales","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130718995","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
............................................................................................ 3 ACKNOWLEDGEMENTS ............................................................................ 4 LIST OF ORIGINAL ARTICLES ................................................................ 5 TERMS .............................................................................................................. 7
{"title":"Tropical peat decomposability expressed through physical chemical and biological properties under varying land management intensities","authors":"M. Könönen","doi":"10.14214/df.237","DOIUrl":"https://doi.org/10.14214/df.237","url":null,"abstract":"............................................................................................ 3 ACKNOWLEDGEMENTS ............................................................................ 4 LIST OF ORIGINAL ARTICLES ................................................................ 5 TERMS .............................................................................................................. 7","PeriodicalId":375560,"journal":{"name":"Dissertationes Forestales","volume":"47 29","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120836668","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Low apoplastic water potentials can affect trees by decreasing the hydraulic conductivity of xylem due to embolism and by causing dehydration stress in living cells. Low apoplastic water potentials regularly occur in trees during summer and winter. These can either be caused by loss of water due to transpiration or by freezing due to the chemical properties of ice. In this thesis the effects of low apoplastic water potential on trees were studied by causing low water potentials with three different methods: desiccation, freezing and by adjusting the osmotic concentration of xylem sap. Tree responses in this thesis were measured with stem diameter changes, leaf gas exchange, tree temperature and xylem water potential. Living parenchyma cells are thought to have negligible effect on xylem diameter changes but this thesis shows that the role of parenchyma can, in fact, be much more significant. Evidence for the major role of parenchyma cells in the diameter changes of frozen xylem also supported the theory of extracellular freezing. Furthermore, mesophyll cells were shown to react to freezing with a rapid depression of photosynthesis. It was also studied how a pressure increase in the xylem conduits, resulting from low water potentials, affects tree water relations during embolism formation and ice propagation. A gas burst was detected emerging from the tree stem during freezing. A decrease in the amount of gases in the xylem conduit can benefit trees in avoiding winter embolism. It was also experimentally confirmed that the formation of embolism in trees can temporarily even help relieve water stress due to the so called ́capacitive effect ́. Low apoplastic water potential affects both the xylem and living cells in trees, and the interconnectedness of these responses are also shown in this thesis.
{"title":"Low apoplastic water potential in trees - dehydration stress on living cells and embolism in xylem","authors":"L. Lindfors","doi":"10.14214/df.235","DOIUrl":"https://doi.org/10.14214/df.235","url":null,"abstract":"Low apoplastic water potentials can affect trees by decreasing the hydraulic conductivity of xylem due to embolism and by causing dehydration stress in living cells. Low apoplastic water potentials regularly occur in trees during summer and winter. These can either be caused by loss of water due to transpiration or by freezing due to the chemical properties of ice. In this thesis the effects of low apoplastic water potential on trees were studied by causing low water potentials with three different methods: desiccation, freezing and by adjusting the osmotic concentration of xylem sap. Tree responses in this thesis were measured with stem diameter changes, leaf gas exchange, tree temperature and xylem water potential. Living parenchyma cells are thought to have negligible effect on xylem diameter changes but this thesis shows that the role of parenchyma can, in fact, be much more significant. Evidence for the major role of parenchyma cells in the diameter changes of frozen xylem also supported the theory of extracellular freezing. Furthermore, mesophyll cells were shown to react to freezing with a rapid depression of photosynthesis. It was also studied how a pressure increase in the xylem conduits, resulting from low water potentials, affects tree water relations during embolism formation and ice propagation. A gas burst was detected emerging from the tree stem during freezing. A decrease in the amount of gases in the xylem conduit can benefit trees in avoiding winter embolism. It was also experimentally confirmed that the formation of embolism in trees can temporarily even help relieve water stress due to the so called ́capacitive effect ́. Low apoplastic water potential affects both the xylem and living cells in trees, and the interconnectedness of these responses are also shown in this thesis.","PeriodicalId":375560,"journal":{"name":"Dissertationes Forestales","volume":"117 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128364459","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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