Organochemical Characterization of Peat Reveals Decomposition of Specific Hemicellulose Structures as the Main Cause of Organic Matter Loss in the Acrotelm

Peatlands store carbon in the form of dead organic residues. Climate change and human impact impose risks on the sustainability of the peatlands carbon balance due to increased peat decomposition. Here, we investigated molecular changes in the upper peat layers (0-40 cm), inferred from high-resolution vertical depth profiles, from a boreal peatland using two-dimensional H-1-C-13 nuclear magnetic resonance (NMR) spectroscopy, and comparison to delta C-13, delta N-15, and carbon and nitrogen content. Effects of hydrological conditions were investigated at respective sites: natural moist, drainage ditch, and natural dry. The molecular characterization revealed preferential degradation of specific side-chain linkages of xylan-type hemicelluloses within 0-14 cm at all sites, indicating organic matter losses up to 25%. In contrast, the xylan backbone, galactomannan-type hemicelluloses, and cellulose were more resistant to degradation and accumulated at the natural moist and drainage site. delta C-13, delta N-15, and carbon and nitrogen content did not correlate with specific hemicellulose structures but reflected changes in total carbohydrates. Our analysis provides novel insights into peat carbohydrate decomposition and indicates substantial organic matter losses in the acrotelm due to the degradation of specific hemicellulose structures. This suggests that variations in hemicellulose content and structure influence peat stability, which may have important implications with respect to climate change

Global CO2 fertilization of Sphagnum peat mosses via suppression of photorespiration during the twentieth century

Natural peatlands contribute significantly to global carbon sequestration and storage of biomass, most of which derives from Sphagnum peat mosses. Atmospheric CO2 levels have increased dramatically during the twentieth century, from 280 to > 400 ppm, which has affected plant carbon dynamics. Net carbon assimilation is strongly reduced by photorespiration, a process that depends on the CO2 to O-2 ratio. Here we investigate the response of the photorespiration to photosynthesis ratio in Sphagnum mosses to recent CO2 increases by comparing deuterium isotopomers of historical and contemporary Sphagnum tissues collected from 36 peat cores from five continents. Rising CO2 levels generally suppressed photorespiration relative to photosynthesis but the magnitude of suppression depended on the current water table depth. By estimating the changes in water table depth, temperature, and precipitation during the twentieth century, we excluded potential effects of these climate parameters on the observed isotopomer responses. Further, we showed that the photorespiration to photosynthesis ratio varied between Sphagnum subgenera, indicating differences in their photosynthetic capacity. The global suppression of photorespiration in Sphagnum suggests an increased net primary production potential in response to the ongoing rise in atmospheric CO2, in particular for mire structures with intermediate water table depths

Cellular Aspects of Lignin Biosynthesis in Xylem Vessels of Zinnia and Arabidopsis

Lignin is the second most abundant biopolymer on earth and is found in the wood (xylem) of vascular land plants. To transport the hydro-mineral sap, xylem forms specialized conduit cells, called tracheary elements (TEs), which are hollow dead cylinders reinforced with lateral secondary cell walls (SCW). These SCWs incorporate lignin to gain mechanical strength, water impermeability and resistance against pathogens. The aim of this thesis is to understand the spatio-temporal deposition of lignin during TE differentiation and the relationship with its neighbouring cells. In vitro TE differentiating cell cultures of Zinnia elegans and Arabidopsis thaliana are ideal tools to study this process: cells differentiate simultaneously into 30-50% TEs while the rest remain parenchymatic (non-TEs). Live-cell imaging of such TEs indicated that lignification occurs after programmed cell death (PCD), in a non-cell autonomous manner, in which the non-TEs provide the lignin monomers. This thesis confirms that lignification occurs and continues long after TE PCD in both in vitro TE cultures and whole plants using biochemical, pharmacological and cytological methods. The cooperative supply of lignin monomers by the non-TEs was demonstrated by using Zinnia and Arabidopsis in vitro TE cultures. Inhibitor experiments revealed further that the non-TEs supply reactive oxygen species (ROS) to TEs and that ROS are required for TE post-mortem lignification. Characterization of the non-TEs showed an enlarged nucleus with increased DNA content, thus indicating that non-TEs are in fact endoreplicated xylem parenchyma cells (XP). The cooperative lignification was confirmed in whole plants by using knock-out mutants in a lignin monomer synthesis gene, which exhibit reduced TE lignification. The XP specific complementation of these mutants led to nearly completely rescuing the TE lignin reduction. Using microscopic techniques, the spatial distribution of lignin was analyzed in TEs from in vitro cultures and whole plants, revealing that lignification is restricted to TE SCWs in both protoxylem and metaxylem. These specific deposition domains were established by phenoloxidases, i.e. laccases localized to SCWs and peroxidases, present in SCWs and the apoplastic space. Laccases were cell-autonomously produced by developing TEs, indicating that the deposition domains are defined before PCD. Altogether, these results highlight that the hydro-mineral sap transport through TEs is enabled by the spatially and temporally controlled lignification of the SCW. Lignification occurs post-mortem by the supply of monomers and ROS from neighbouring XP cells and is restricted to specific deposition domains, defined by the pre-mortem sequestration of phenoloxidases.    

Cooperative lignification of xylem tracheary elements

The development of xylem tracheary elements (TEs) – the hydro-mineral sap conducting cells - has been an evolutionary breakthrough to enable long distance nutrition and upright growth of vascular land plants. To allow sap conduction, TEs form hollow laterally reinforced cylinders by combining programmed cell death and secondary cell wall formation. To ensure their structural resistance for sap conduction, TE cell walls are reinforced with the phenolic polymer lignin, which is deposited after TE cell death by the cooperative supply of monomers and other substrates from the surrounding living cells

Теоретические основы электротехники: Ч. 1. Электрические цепи постоянного и однофазного переменного тока

Электронный учебно-методический комплекс дисциплины

Different combinations of laccase paralogs nonredundantly control the amount and composition of lignin in specific cell types and cell wall layers in Arabidopsis

Vascular plants reinforce the cell walls of the different xylem cell types with lignin phenolic polymers. Distinct lignin chemistries differ between each cell wall layer and each cell type to support their specific functions. Yet the mechanisms controlling the tight spatial localization of specific lignin chemistries remain unclear. Current hypotheses focus on control by monomer biosynthesis and/or export, while cell wall polymerization is viewed as random and nonlimiting. Here, we show that combinations of multiple individual laccases (LACs) are nonredundantly and specifically required to set the lignin chemistry in different cell types and their distinct cell wall layers. We dissected the roles of Arabidopsis thaliana LAC4, 5, 10, 12, and 17 by generating quadruple and quintuple loss-of-function mutants. Loss of these LACs in different combinations led to specific changes in lignin chemistry affecting both residue ring structures and/or aliphatic tails in specific cell types and cell wall layers. Moreover, we showed that LAC-mediated lignification has distinct functions in specific cell types, waterproofing fibers, and strengthening vessels. Altogether, we propose that the spatial control of lignin chemistry depends on different combinations of LACs with nonredundant activities immobilized in specific cell types and cell wall layers

Intramolecular stable isotope variation : Consequences for conventional isotope measurements and elucidation of new ecophysiological signals

Isotope ratios (13C/12C and 2H/1H) have long been used in plant ecophysiology and for reconstruction of environmental variables. For decades it has also been known that heavy isotopes are distributed unevenly IN biological metabolites. In other words, the isotopomers of metabolites have unequal abundances. Consequently, conventional δ values are whole-molecule averages over varying intramolecular values. However, this biochemical knowledge has not been applied in plant ecophysiology or biogeochemistry, because the first measurements of intramolecular isotope distributions were extremely cumbersome, requiring breakdown of metabolites into small molecules and IRMS measurements on those. Since then, NMR methodology has advanced so that intramolecular isotope distributions can routinely be measured (Chaintreau et al., Anal. Chim. Acta 2013), although large samples are needed. Here we demonstrate the importance of intramolecular isotope distributions with several examples. 1. We show that 13C is distributed unevenly in tree-ring cellulose. While this is not surprising given previous observations, it has important consequences: When wood enters soil organic matter and is broken down, the δ13C of respired CO2 will only follow δ13C of cellulose if the glucose units are fully respired. If part of the glucose molecules enters other pathways, such as the oxidative pentose phosphate pathway, δ13C of liberated CO2 can deviate markedly from the whole-molecule value. This may have consequences for using δ13C of CO2 to unravel ecosystem C exchange fluxes. 2. Intramolecular isotope distributions are created by enzyme isotope effects, hence they constitute fingerprints of biosynthetic pathways and can report on regulation of metabolism on time scales up to millennia. As particular advantage, this information can be encoded in ratios of isotopomer abundances (Augusti et al., Chem. Geol. 2008), and can be extracted independent of the isotope ratio of the whole molecule, and of the isotope source (Ehlers et al., PNAS 2015). 3. We demonstrate that intramolecular 13C distributions of the glucose units of tree-ring cellulose vary over time. This implies that 13C fractionations mechanisms beyond the well-known stomata-Rubisco mechanism exist. The time-dependent intramolecular variation constitutes new ecophysiological information. 4. When δ13C or δD are used as proxies for ecophysiological parameters, correlation coefficients between both quantities are restricted to low values, limiting the power of isotope-based reconstructions. We show that this limitation is at least partly caused by intramolecular isotope variation. Conversely, higher correlation coefficients can be observed between intramolecular isotope parameters – position-specific carbon isotope ratios or deuterium isotopomer ratios – and ecophysiological parameters. Thus, intramolecular isotope data allow for more powerful reconstructions of physiological and environmental parameter

Intramolecular stable isotope variation : Consequences for conventional isotope measurements and elucidation of new ecophysiological signals

Isotope ratios (13C/12C and 2H/1H) have long been used in plant ecophysiology and for reconstruction of environmental variables. For decades it has also been known that heavy isotopes are distributed unevenly IN biological metabolites. In other words, the isotopomers of metabolites have unequal abundances. Consequently, conventional δ values are whole-molecule averages over varying intramolecular values. However, this biochemical knowledge has not been applied in plant ecophysiology or biogeochemistry, because the first measurements of intramolecular isotope distributions were extremely cumbersome, requiring breakdown of metabolites into small molecules and IRMS measurements on those. Since then, NMR methodology has advanced so that intramolecular isotope distributions can routinely be measured (Chaintreau et al., Anal. Chim. Acta 2013), although large samples are needed. Here we demonstrate the importance of intramolecular isotope distributions with several examples. 1. We show that 13C is distributed unevenly in tree-ring cellulose. While this is not surprising given previous observations, it has important consequences: When wood enters soil organic matter and is broken down, the δ13C of respired CO2 will only follow δ13C of cellulose if the glucose units are fully respired. If part of the glucose molecules enters other pathways, such as the oxidative pentose phosphate pathway, δ13C of liberated CO2 can deviate markedly from the whole-molecule value. This may have consequences for using δ13C of CO2 to unravel ecosystem C exchange fluxes. 2. Intramolecular isotope distributions are created by enzyme isotope effects, hence they constitute fingerprints of biosynthetic pathways and can report on regulation of metabolism on time scales up to millennia. As particular advantage, this information can be encoded in ratios of isotopomer abundances (Augusti et al., Chem. Geol. 2008), and can be extracted independent of the isotope ratio of the whole molecule, and of the isotope source (Ehlers et al., PNAS 2015). 3. We demonstrate that intramolecular 13C distributions of the glucose units of tree-ring cellulose vary over time. This implies that 13C fractionations mechanisms beyond the well-known stomata-Rubisco mechanism exist. The time-dependent intramolecular variation constitutes new ecophysiological information. 4. When δ13C or δD are used as proxies for ecophysiological parameters, correlation coefficients between both quantities are restricted to low values, limiting the power of isotope-based reconstructions. We show that this limitation is at least partly caused by intramolecular isotope variation. Conversely, higher correlation coefficients can be observed between intramolecular isotope parameters – position-specific carbon isotope ratios or deuterium isotopomer ratios – and ecophysiological parameters. Thus, intramolecular isotope data allow for more powerful reconstructions of physiological and environmental parameter

Intramolecular stable isotope variation : Consequences for conventional isotope measurements and elucidation of new ecophysiological signals

Isotope ratios (13C/12C and 2H/1H) have long been used in plant ecophysiology and for reconstruction of environmental variables. For decades it has also been known that heavy isotopes are distributed unevenly IN biological metabolites. In other words, the isotopomers of metabolites have unequal abundances. Consequently, conventional δ values are whole-molecule averages over varying intramolecular values. However, this biochemical knowledge has not been applied in plant ecophysiology or biogeochemistry, because the first measurements of intramolecular isotope distributions were extremely cumbersome, requiring breakdown of metabolites into small molecules and IRMS measurements on those. Since then, NMR methodology has advanced so that intramolecular isotope distributions can routinely be measured (Chaintreau et al., Anal. Chim. Acta 2013), although large samples are needed. Here we demonstrate the importance of intramolecular isotope distributions with several examples. 1. We show that 13C is distributed unevenly in tree-ring cellulose. While this is not surprising given previous observations, it has important consequences: When wood enters soil organic matter and is broken down, the δ13C of respired CO2 will only follow δ13C of cellulose if the glucose units are fully respired. If part of the glucose molecules enters other pathways, such as the oxidative pentose phosphate pathway, δ13C of liberated CO2 can deviate markedly from the whole-molecule value. This may have consequences for using δ13C of CO2 to unravel ecosystem C exchange fluxes. 2. Intramolecular isotope distributions are created by enzyme isotope effects, hence they constitute fingerprints of biosynthetic pathways and can report on regulation of metabolism on time scales up to millennia. As particular advantage, this information can be encoded in ratios of isotopomer abundances (Augusti et al., Chem. Geol. 2008), and can be extracted independent of the isotope ratio of the whole molecule, and of the isotope source (Ehlers et al., PNAS 2015). 3. We demonstrate that intramolecular 13C distributions of the glucose units of tree-ring cellulose vary over time. This implies that 13C fractionations mechanisms beyond the well-known stomata-Rubisco mechanism exist. The time-dependent intramolecular variation constitutes new ecophysiological information. 4. When δ13C or δD are used as proxies for ecophysiological parameters, correlation coefficients between both quantities are restricted to low values, limiting the power of isotope-based reconstructions. We show that this limitation is at least partly caused by intramolecular isotope variation. Conversely, higher correlation coefficients can be observed between intramolecular isotope parameters – position-specific carbon isotope ratios or deuterium isotopomer ratios – and ecophysiological parameters. Thus, intramolecular isotope data allow for more powerful reconstructions of physiological and environmental parameter