Human production of food and energy is the dominant continental process that breaks the triple bond in molecular nitrogen (N 2

This paper examines the impact of food and energy production on the global N cycle by contrasting N flows in the late-19th century with those of the late-20th century. We have a good understanding of the amounts of reactive N created by humans, and the primary points of loss to the environment. However, we have a poor understanding of nitrogen's rate of accumulation in environmental reservoirs, which is problematic because of the cascading effects of accumulated N in the environment. The substantial regional variability in reactive nitrogen creation, its degree of distribution, and the likelihood of increased rates of reactive-N formation (especially in Asia) in the future creates a situation that calls for the development of a Total Reactive Nitrogen Approach that will optimize food and energy production and protect environmental systems.

Keywords Milled wood lignin Cellulolytic enzyme lignin Enzyme lignin Liquidambar styraciflua Picea abies Sweetgum Spruce Schlüsselwörter (Sachgebiete) B j örkman-Lignin Cellulolytisch.es Enzym-Lignin Enzym-Lignin Liquidambar styraciflua Picea abies Amberbaum Fichte Comparative Studies on Cellulolytic Enzyme Lignin and Milled Wood Lignin of Sweetgum and Spruce SummaryMilled wood lignin (MWL) and Cellulolytic enzyme lignin (CEL) were isolated from the same batch of ball milled sapwood of sweetgum and Norway spruce. Ball milling decreased the molecular weight and increased the -carbonyl and the phenolic-hydroxyl content of lignin. Thus, the content of these functional groups in the original lignin in wood is less than that of isolated MWL and CEL. Compared to MWL, CEL of each species was very similar in elemental composition and both UV and IR spectra. A slightly greater extent of condensation and, in the case of sweetgum, a slightly smaller ratio of syringyl-to guaiacyl-propane units were found in MWL than in CEL. This indicates probable structural differences in lignin in various regions of wood cell walls. Despite these small differences, however, we conclude that MWL is adequately representative of the total lignin in wood but CEL is preferable for future studies of lignin structure because it is more representative of the total lignin in wood and can be obtained in good yield with less degradation due to ball milling. Vergleichende Untersuchungen an Cellulase-Enzym-Lignin und Björkman-Lignin von Sweetgum und Fichtenholz ZusammenfassungSplintholz von Sweetgum (Liquidambar styraciflua L.) und Fichte (Picea abies L.) wurde in einer Kugelschwingmühle gemahlen. Aus jeweils denselben Ansätzen wurde Björkman-Lignin ("Milled Wood Lignin", MWL) und durch Ein Wirkung von Cellulase freigelegtes Lignin (Cellulolytisches Enzym-Lignin, CEL) isoliert. Der Mahlvorgang führte zur Verminderung des Molekulargewichts und zur Erhöhung des Gehaltes an a-Carbonylgruppen und phenolischem Hydroxyl der untersuchten Lignine. Der Vergleich von MWL mit CEL beider Arten zeigte die große Ähnlichkeit dieser Ligninpräparate in bezug auf Elementarzusammensetzung und spektrale Eigenschaften (IR, UV). Die MWL zeigten einen etwas höheren Kondensationsgrad und das MWL von Sweetgum ein etwas niedrigeres Verhältnis von Syringylpropan-zu Guajacylpropaneinheiten als die CEL. Dies dürfte auf die unterschiedliche Zusammensetzung der Lignine in verschiedenen Teilen der Zellwand zurückzuführen sein. Trotz dieser geringen Unterschiede ergibt sich, daß MWL zureichend repräsentativ für das gesamte Lignin des Holzes ist. Trotzdem ist CEL dem MWL vorzuziehen, da es in noch höherem Grade dem Lignin in situ entspricht und außerdem in guten Ausbeuten auch bei geringerer Mahldauer auf schonende Weise erhalten werden kann.

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Radial gradients in nitrogen content across stems of three hardwoods and two softwoods followed similar patterns. Sapwood and inner bark contained a higher proportion of the total nitrogen in cross sections than heartwood and outer bark, respectively. Nitrogen content of individual annual increments decreased progressively from the cambium to the transition zone between sapwood and heartwood, or, in species without heartwood, to the increments nearest the pith. In some cases, an abrupt decrease in nitrogen content was observed across the sapwood–heartwood boundary. The diminution of nitrogen content across the sapwood was associated with death of parenchyma cells. As the cells die, nitrogen in their cytoplasm apparently is retrieved for possible reuse elsewhere in the tree. Pith contained more nitrogen by weight than heartwood and in some cases more than sapwood. Nitrogen content was correlated directly with parenchyma volume for sapwood but not for heartwood of 16 species of angiosperms.Nitrogen extractable from sapwood with neutral solvents consisted in part of free amino acids but only traces of these acids were detected in heartwood. Hydrolysates of sapwood and heartwood prepared with 6 N HCl contained many typical protein amino acids.

Because of its serious large-scale effects on ecosystems and its transboundary nature, acid rain received for a few decades at the end of the last century wide scientific and public interest, leading to coordinated policy actions in Europe and North America. Through these actions, in particular those under the UNECE Convention on Long-range Transboundary Air Pollution, air emissions were substantially reduced, and ecosystem impacts decreased. Widespread scientific research, long-term monitoring, and integrated assessment modelling formed the basis for the policy agreements. In this paper, which is based on an international symposium organised to commemorate 50 years of successful integration of air pollution research and policy, we briefly describe the scientific findings that provided the foundation for the policy development. We also discuss important characteristics of the science-policy interactions, such as the critical loads concept and the large-scale ecosystem field studies. Finally, acid rain and air pollution are set in the context of future societal developments and needs, e.g. the UN's Sustainable Development Goals. We also highlight the need to maintain and develop supporting scientific infrastructures.

Isoprene emissions were studied in one-year old sweetgum (Liquidambar styraciflua L.) seedlings during nine drying-rewatering cycles extending over five months. Each drying cycle lasted to the point of leaf wilting. Growth was essentially stopped in response to the first drying cycle, though seedling survival and capacity to recover turgor on rewatering remained high throughout the entire nine cycles. Photosynthetic rates of leaves were inhibited by the drying treatments. Under severe drought, isoprene emission rates of leaves were also inhibited, though isoprene emission was generally less sensitive to drought than photosynthesis. The lower drought sensitivity of isoprene emission compared with photosynthesis resulted in a higher percentage of fixed carbon lost as isoprene as seedlings became more stressed. During the recovery phase of the drying-rewatering cycles, isoprene emission rates in several seedlings were higher than in well-watered control seedlings. Following the ninth drying-rewatering cycle, sustained daily watering resulted in recovery of isoprene emission rates to control values within four days. Photosynthetic rates only recovered to 50% of control values after seven days. We conclude that the mechanisms regulating photosynthetic rate and isoprene emission rate are differentially influenced by limited water supplies. The results are consistent with past studies that predict a protective role for isoprene emission during stress, particularly protection from excessive leaf temperatures during drought.

Based on present knowledge of the origin, amounts, chemical form, and distribution of nitrogen ( N ) in wood, hypotheses are proposed to explain radial gradients in N content that exist across the xylem cylinder of tree stems: (1) N in the cytoplasn~ of developing wood cells is diluted by apposition of cell wall substances; (2) after maturation of wood fiber cells, N in their cytoplasm is removed by elution into the transpiration stream; (3) death of xylem parenchyma cells during aging of sapwood and forination of heartwood is accompanied by reinoval of much of the X in their cytoplasm. Hypotheses 2 and 3 above suggest strongly that trees possess an internal recycling mechanism for conservation and reuse of the N in the cytoplasm of xylary cells.Although the supply of N in wood is meager, wood-destroying fungi readily inetabolize the carbon-rich coilstituents of wood and produce large fruiting structures that release vast numbers of spores in nature. To account for these capacities, we postulate that these fungi employ one or more of the following three mechanisms: (1) preferential allocation of N obtainable from wood to substances and pathways highly efficient in the use of wood constituents; (2) reuse of N obtainable from wood by a dynamic and continuous process of autolysis and reuse without significant loss of N ; (3) utilization of N sources outside the wood itself, for example, by fixation of atlnospheric N.