The number of catalytic sites in acetylcholinesterase

By using two methods of titration, the number of active sites in acetylcholinesterase was determined. Either stepwise inhibition of the enzyme by an irreversible inhibitor, namely di-isopropyl phosphorofluoridate, or direct measurement of the concentration of active sites by titration with o-nitrophenyl dimethylcarbamate yielded an equivalent weight of approx. 130000 for an active site in acetylcholinesterase. This indicates two sites per molecule, since the native enzyme has a molecular weight of 260000.     

Peculiar tooth renewal in a Jurassic ray-finned fish (Lepisosteiformes, †Scheenstia sp.)

Tooth replacement in vertebrates is extremely diverse, and its study in extinct taxa gives insights into the evolution of the different dental renewal modes. Based on μ-CT scans of a left lower jaw of the extinct fish †Scheenstia (Actinopterygii, Lepisosteiformes), we describe in detail a peculiar tooth replacement mode that is, as far as we could ascertain from the literature, unique among vertebrates. The formation of the replacement teeth comprises a 180° rotation of their acrodin cap that occurs intraosseously within bony crypts, and their setting up appears to be synchronous. We propose a model for the dental renewal process and identify complementary anatomical features visible in the tomography such as the junction between the different tooth-bearing bones (prearticular–coronoid and dentary), as well as cavities corresponding to intraosseous crypts, nervous and/or vascular canals. The location of the cavities and their subsequent identification (e.g. Meckel's cavity, mandibular sensory canal) help us to identify the function of pores visible on the bone surface and understand their relation to internal anatomical features. Finally, recognition of this tooth replacement mode raises the question of whether it is specific to †Scheenstia or related to a particular dentition type and thus potentially occurs in other lineages.     

Water relations determine short time leaf growth patterns in the mangrove Avicennia marina (Forssk.) Vierh.

High‐resolution leaf growth is rarely studied despite its importance as a metric for plant performance and resource use efficiency. This is in part due to methodological challenges. Here, we present a method for in situ leaf growth measurements in a natural environment. We measured instantaneous leaf growth on a mature Avicennia marina subsp. australasica tree over several weeks. We measured leaf expansion by taking time‐lapse images and analysing them using marker tracking software. A custom‐made instrument was designed to enable long‐term field studies. We detected a distinct diel growth pattern with leaf area shrinkage in the morning and leaf expansion in the afternoon and at night. On average, the observed daily shrinkage was 37% of the net growth. Most of the net growth occurred at night. Diel leaf area shrinkage and recovery continued after growth cessation. The amount of daily growth was negatively correlated with shrinkage, and instantaneous leaf growth and shrinkage were correlated with changes in leaf turgor. We conclude that, at least in this tree species, instantaneous leaf growth patterns are very strongly linked to, and most likely driven by, leaf water relations, suggesting decoupling of short‐term growth patterns from carbon assimilation.     

Stomatal conductance in mature deciduous forest trees exposed to elevated CO<Subscript>2</Subscript>

Stomatal conductance (g _s) of mature trees exposed to elevated CO₂ concentrations was examined in a diverse deciduous forest stand in NW Switzerland. Measurements of g _s were carried out on upper canopy foliage before noon, over four growing seasons, including an exceptionally dry summer (2003). Across all species reductions in stomatal conductance were smaller than 25% most likely around 10%, with much variation among species and trees. Given the large heterogeneity in light conditions within a tree crown, this signal was not statistically significant, but the responses within species were surprisingly consistent throughout the study period. Except during a severe drought, stomatal conductance was always lower in trees of Carpinus betulus exposed to elevated CO₂ compared to Carpinus trees in ambient air, but the difference was only statistically significant on 2 out of 15 days. In contrast, stomatal responses in Fagus sylvatica and Quercus petraea varied around zero with no consistent trend in relation to CO₂ treatment. During the 2003 drought in the third treatment year, the CO₂ effect became reversed in Carpinus, resulting in higher g _s in trees exposed to elevated CO₂ compared to control trees, most likely due to better water supply because of the previous soil water savings. This was supported by less negative predawn leaf water potential in CO₂ enriched Carpinus trees, indicating an improved water status. These findings illustrate (1) smaller than expected CO₂-effects on stomata of mature deciduous forest trees, and (2) the possibility of soil moisture feedback on canopy water relations under elevated CO₂.     

Do global change experiments overestimate impacts on terrestrial ecosystems?

In recent decades, many climate manipulation experiments have investigated biosphere responses to global change. These experiments typically examined effects of elevated atmospheric CO(2), warming or drought (driver variables) on ecosystem processes such as the carbon and water cycle (response variables). Because experiments are inevitably constrained in the number of driver variables tested simultaneously, as well as in time and space, a key question is how results are scaled up to predict net ecosystem responses. In this review, we argue that there might be a general trend for the magnitude of the responses to decline with higher-order interactions, longer time periods and larger spatial scales. This means that on average, both positive and negative global change impacts on the biosphere might be dampened more than previously assumed.     

Herpes simplex virus 1 envelopment follows two diverse pathways

Herpesvirus envelopment is assumed to follow an uneconomical pathway including primary envelopment at the inner nuclear membrane, de-envelopment at the outer nuclear membrane, and reenvelopment at the trans-Golgi network. In contrast to the hypothesis of de-envelopment by fusion of the primary envelope with the outer nuclear membrane, virions were demonstrated to be transported from the perinuclear space to rough endoplasmic reticulum (RER) cisternae. Here we show by high-resolution microscopy that herpes simplex virus 1 envelopment follows two diverse pathways. First, nuclear envelopment includes budding of capsids at the inner nuclear membrane into the perinuclear space whereby tegument and a thick electron dense envelope are acquired. The substance responsible for the dense envelope is speculated to enable intraluminal transportation of virions via RER into Golgi cisternae. Within Golgi cisternae, virions are packaged into transport vacuoles containing one or several virions. Second, for cytoplasmic envelopment, capsids gain direct access from the nucleus to the cytoplasm via impaired nuclear pores. Cytoplasmic capsids could bud at the outer nuclear membrane, at membranes of RER, Golgi cisternae, and large vacuoles, and at banana-shaped membranous entities that were found to continue into Golgi membranes. Envelopes originating by budding at the outer nuclear membrane and RER membrane also acquire a dense substance. Budding at Golgi stacks, designated wrapping, results in single virions within small vacuoles that contain electron-dense substances between envelope and vacuolar membranes.     

Long-term 13C labeling provides evidence for temporal and spatial carbon allocation patterns in mature Picea abies

There is evidence of continued stimulation of foliage photosynthesis in trees exposed to elevated atmospheric CO₂ concentrations; however, this is mostly without a proportional growth response. Consequently, we lack information on the fate of this extra carbon (C) acquired. By a steady application of a ¹³CO₂ label in a free air CO₂ enrichment (FACE) experiment, we traced the fate of C in 37-m-tall, ca. 110-year-old Picea abies trees in a natural forest in Switzerland. Hence, we are not reporting tree responses to elevated CO₂ (which would require equally ¹³C labeled controls), but are providing insights into assimilate processing in such trees. Sunlit needles and branchlets grow almost exclusively from current assimilates, whereas shaded parts of the crowns also rely on stored C. Only 2.5 years after FACE initiation, tree rings contained 100 % new C. Stem-respiratory CO₂ averaged 50 % of new C over the entire FACE period. Fine roots and mycorrhizal fungi contained 49–56 and 26–43 % new C, respectively, after 2.5 years. The isotopic signals in soil CO₂ arrived 12 days after the onset of FACE, yet it contained only ca. 15 % new C thereafter. We conclude that new C first feeds into fast turnover C pools in the canopy and becomes increasingly mixed with older C sources as one moves away (downward) from the crown. We speculate that enhanced C turnover (its metabolic cost) along the phloem path, as evidenced by basipetal isotope signal depletion, explains part of the ‘missing carbon’ in trees that assimilated more C under elevated CO₂.     

Precipitation manipulation experiments--challenges and recommendations for the future

Climatic changes, including altered precipitation regimes, will affect key ecosystem processes, such as plant productivity and biodiversity for many terrestrial ecosystems. Past and ongoing precipitation experiments have been conducted to quantify these potential changes. An analysis of these experiments indicates that they have provided important information on how water regulates ecosystem processes. However, they do not adequately represent global biomes nor forecasted precipitation scenarios and their potential contribution to advance our understanding of ecosystem responses to precipitation changes is therefore limited, as is their potential value for the development and testing of ecosystem models. This highlights the need for new precipitation experiments in biomes and ambient climatic conditions hitherto poorly studied applying relevant complex scenarios including changes in precipitation frequency and amplitude, seasonality, extremity and interactions with other global change drivers. A systematic and holistic approach to investigate how soil and plant community characteristics change with altered precipitation regimes and the consequent effects on ecosystem processes and functioning within these experiments will greatly increase their value to the climate change and ecosystem research communities. Experiments should specifically test how changes in precipitation leading to exceedance of biological thresholds affect ecosystem resilience and acclimation.     

When things get MESI: The Manipulation Experiments Synthesis Initiative—A coordinated effort to synthesize terrestrial global change experiments

Responses of the terrestrial biosphere to rapidly changing environmental conditions are a major source of uncertainty in climate projections. In an effort to reduce this uncertainty, a wide range of global change experiments have been conducted that mimic future conditions in terrestrial ecosystems, manipulating CO₂, temperature, and nutrient and water availability. Syntheses of results across experiments provide a more general sense of ecosystem responses to global change, and help to discern the influence of background conditions such as climate and vegetation type in determining global change responses. Several independent syntheses of published data have yielded distinct databases for specific objectives. Such parallel, uncoordinated initiatives carry the risk of producing redundant data collection efforts and have led to contrasting outcomes without clarifying the underlying reason for divergence. These problems could be avoided by creating a publicly available, updatable, curated database. Here, we report on a global effort to collect and curate 57,089 treatment responses across 3644 manipulation experiments at 1145 sites, simulating elevated CO₂, warming, nutrient addition, and precipitation changes. In the resulting Manipulation Experiments Synthesis Initiative (MESI) database, effects of experimental global change drivers on carbon and nutrient cycles are included, as well as ancillary data such as background climate, vegetation type, treatment magnitude, duration, and, unique to our database, measured soil properties. Our analysis of the database indicates that most experiments are short term (one or few growing seasons), conducted in the USA, Europe, or China, and that the most abundantly reported variable is aboveground biomass. We provide the most comprehensive multifactor global change database to date, enabling the research community to tackle open research questions, vital to global policymaking. The MESI database, freely accessible at doi.org/10.5281/zenodo.7153253 , opens new avenues for model evaluation and synthesis-based understanding of how global change affects terrestrial biomes. We welcome contributions to the database on GitHub.     

Are the well-fed less thirsty? Effects of drought and salinity on New Zealand mangroves

饱食则耐渴？论干旱和盐度对新西兰红树林的影响 尽管已有大量的研究考察了非生物胁迫因素对植物的影响，但是我们对干旱造成植物死亡的机理尚无定论，而对多种胁迫因子之间的相互作用更是知之甚少。非结构性碳水化合物(NSCs)在防止或延缓因干旱造成死亡方面的作用正日益引人关注。在本研究中，我们探讨了NSCs在缓解新西兰红树林(Avicennia marina subsp. australasica)受干旱和盐度影响时所起的作用。首先，我们对植物体内的NSC 水平进行了实验调控，随后将植株置于不同的干旱和盐度组合环境中培育。研究结果表明，在高盐度且高度干旱的条件下，高NSC水平组(H-NSC)的植物生长速率和存活率分别比低NSC水平组(L-NSC)的高出2和3倍。在高盐度且高度干旱的条件下培育了12周后，H-NSC组植株的茎杆导水率(281 ± 50 mmol cm⁻¹ s⁻¹ MPa⁻¹)高于L-NSC组植株(134 ± 40 mmol cm⁻¹ s⁻¹ MPa⁻¹)。尽管淀粉含量保持相对稳定，但H-NSC组植株茎杆中的可溶性糖含量在高盐度且高度干旱条件下的第8周时比第12周时高出20%。这些研究结果表明：1) NSCs对于缓解因干旱和与之相关的高盐度造成的较低土壤水势的影响具有重要作用；2)旱、盐联合胁迫下的植株生长受到库的限制。