Globally accelerating trends in societal development and human environmental impacts since the mid-twentieth century are known as the Great Acceleration and have been discussed as a key indicator of the onset of the Anthropocene epoch . While reports on ecological responses (for example, changes in species range or local extinctions) to the Great Acceleration are multiplying , it is unknown whether such biotic responses are undergoing a similar acceleration over time. This knowledge gap stems from the limited availability of time series data on biodiversity changes across large temporal and geographical extents. Here we use a dataset of repeated plant surveys from 302 mountain summits across Europe, spanning 145 years of observation, to assess the temporal trajectory of mountain biodiversity changes as a globally coherent imprint of the Anthropocene. We find a continent-wide acceleration in the rate of increase in plant species richness, with five times as much species enrichment between 2007 and 2016 as fifty years ago, between 1957 and 1966. This acceleration is strikingly synchronized with accelerated global warming and is not linked to alternative global change drivers. The accelerating increases in species richness on mountain summits across this broad spatial extent demonstrate that acceleration in climate-induced biotic change is occurring even in remote places on Earth, with potentially far-ranging consequences not only for biodiversity, but also for ecosystem functioning and services.

Plants store large amounts of non-structural carbohydrates (NSC). While multiple functions of NSC have long been recognized, the interpretation of NSC seasonal dynamics is often based on the idea that stored NSC is a reservoir of carbon that fluctuates depending on the balance between supply via photosynthesis and demand for growth and respiration (the source-sink dynamics concept). Consequently, relatively high NSC concentrations in some plants have been interpreted to reflect excess supply relative to demand. An alternative view, however, is that NSC accumulation reflects the relatively high NSC levels required for plant survival; an important issue that remains highly controversial. Here, we assembled a new global database to examine broad patterns of seasonal NSC variation across organs (leaves, stems, and belowground), plant functional types (coniferous, drought-deciduous angiosperms, winter deciduous angiosperms, evergreen angiosperms, and herbaceous) and biomes (boreal, temperate, Mediterranean, and tropical). We compiled data from 121 studies, including seasonal measurements for 177 species under natural conditions. Our results showed that, on average, NSC account for ~10% of dry plant biomass and are highest in leaves and lowest in stems, whereas belowground organs show intermediate concentrations. Total NSC, starch, and soluble sugars (SS) varied seasonally, with a strong depletion of starch during the growing season and a general increase during winter months, particularly in boreal and temperate biomes. Across functional types, NSC concentrations were highest and most variable in herbaceous species and in conifer needles. Conifers showed the lowest stem and belowground NSC concentrations. Minimum NSC values were relatively high (46% of seasonal maximums on average for total NSC) and, in contrast to average values, were similar among biomes and functional types. Overall, although starch depletion was relatively common, seasonal depletion of total NSC or SS was rare. These results are consistent with a dual view of NSC function: whereas starch acts mostly as a reservoir for future use, soluble sugars perform immediate functions (e.g., osmoregulation) and are kept above some critical threshold. If confirmed, this dual function of NSC will have important implications for the way we understand and model plant carbon allocation and survival under stress.

Abstract. The terrestrial carbon (C) cycle has received increasing interest over the past few decades, however, there is still a lack of understanding of the fate of newly assimilated C allocated within plants and to the soil, stored within ecosystems and lost to the atmosphere. Stable carbon isotope studies can give novel insights into these issues. In this review we provide an overview of an emerging picture of plant-soil-atmosphere C fluxes, as based on C isotopeCorrespondence to: N. Brüggemann (n.brueggemann@fz-juelich.de) studies, and identify processes determining related C isotope signatures. The first part of the review focuses on isotopic fractionation processes within plants during and after photosynthesis. The second major part elaborates on plantinternal and plant-rhizosphere C allocation patterns at different time scales (diel, seasonal, interannual), including the speed of C transfer and time lags in the coupling of assimilation and respiration, as well as the magnitude and controls of plant-soil C allocation and respiratory fluxes. Plant responses to changing environmental conditions, the functional relationship between the physiological and phenological status of plants and C transfer, and interactions between Published by Copernicus Publications on behalf of the European Geosciences Union. 3458 N. Brüggemann et al.: Plant-soil-atmosphere C fluxes C, water and nutrient dynamics are discussed. The role of the C counterflow from the rhizosphere to the aboveground parts of the plants, e.g. via CO 2 dissolved in the xylem water or as xylem-transported sugars, is highlighted. The third part is centered around belowground C turnover, focusing especially on above-and belowground litter inputs, soil organic matter formation and turnover, production and loss of dissolved organic C, soil respiration and CO 2 fixation by soil microbes. Furthermore, plant controls on microbial communities and activity via exudates and litter production as well as microbial community effects on C mineralization are reviewed. A further part of the paper is dedicated to physical interactions between soil CO 2 and the soil matrix, such as CO 2 diffusion and dissolution processes within the soil profile. Finally, we highlight state-of-the-art stable isotope methodologies and their latest developments. From the presented evidence we conclude that there exists a tight coupling of physical, chemical and biological processes involved in C cycling and C isotope fluxes in the plant-soil-atmosphere system. Generally, research using information from C isotopes allows an integrated view of the different processes involved. However, complex interactions among the range of processes complicate or currently impede the interpretation of isotopic signals in CO 2 or organic compounds at the plant and ecosystem level. This review tries to identify present knowledge gaps in correctly interpreting carbon stable isotope signals in the plant-soil-atmosphere system and how future research approaches could contribute to closing these gaps.

No abstract

The adaptation of plants to particular soil types has long intrigued biologists. Gypsum soils occupy large areas in many regions of the world and host a striking biological diversity, but their vegetation has been much less studied than that developing over serpentine or saline soils. Herein, we review all aspects of plant life on gypsum ecosystems, discuss the main processes driving their structure and functioning, and highlight the main conservation threats that they face. Plant communities in gypsum habitats typically show distinctive bands at very small spatial scales, which are mainly determined by topography. Plants living on gypsum soils can be classified into three categories: (i) wide gypsophiles are specialists that can penetrate the physical soil crust during early life stages and have physiological adjustments to cope with the chemical limitations imposed by gypsum soils; (ii) narrow gypsophiles are refugee plants which successfully deal with the physical soil crust and can tolerate these chemical limitations but do not show specific adaptations for this type of soils; and (iii) gypsovags are non-specialist gypsum plants that can only thrive in gypsum soils when the physical crust is absent or reduced. Their ability to survive in gypsum soils may also be mediated by below-ground interactions with soil microorganisms. Gypsophiles and gypsovags show efficient germination at low temperatures, seed and fruit heteromorphism within and among populations, and variation in seed dormancy among plants and populations. In gypsum ecosystems, spatio-temporal changes in the composition and structure of above-ground vegetation are closely related to those of the soil seed bank. Biological soil crusts (BSCs) dominated by cyanobacteria, lichens and mosses are conspicuous in gypsum environments worldwide, and are important drivers of ecosystem processes such as carbon and nitrogen cycling, water infiltration and run-off and soil stability. These organisms are also important determinants of the structure of annual plant communities living on gypsum soils. The short-distance seed dispersal of gypsophiles is responsible for the high number of very narrow endemisms typically found in gypsum outcrops, and suggests that these species are evolutionarily old taxa due to the time they need to colonize isolated gypsum outcrops by chance. Climate change and habitat fragmentation negatively affect both plants and BSCs in gypsum habitats, and are among the major threats to these ecosystems. Gypsum habitats and specialists offer the chance to advance our knowledge on restrictive soils, and are ideal models not only to test important evolutionary questions such as tolerance to low Ca/Mg proportions in soils, but also to improve the theoretical framework of community ecology and ecosystem functioning.

Summary Stable isotopes are extensively used as tracers for the study of plant‐water sources. Isotope‐ratio infrared spectroscopy (IRIS) offers a cheaper alternative to isotope‐ratio mass spectroscopy (IRMS), but its use in studying plant and soil water is limited by the spectral interference caused by organic contaminants. Here, we examine two approaches to cope with contaminated samples in IRIS: on‐line oxidation of organic compounds (MCM) and post‐processing correction. We assessed these methods compared to IRMS across 136 samples of xylem and soil water, and a set of ethanol– and methanol–water mixtures. A post‐processing correction significantly improved IRIS accuracy in both natural samples and alcohol dilutions, being effective with concentrations up to 8% of ethanol and 0.4% of methanol. MCM outperformed the post‐processing correction in removing methanol interference, but did not effectively remove interference for high concentrations of ethanol. By using both approaches, IRIS can overcome with reasonable accuracy the analytical uncertainties associated with most organic contaminants found in soil and xylem water. We recommend the post‐processing correction as the first choice for analysis of samples of unknown contamination. Nevertheless, MCM can be more effective for evaluating samples containing contaminants responsible for strong spectral interferences at low concentrations, such as methanol.

The terrestrial carbon (C) cycle has received increasing interest over the past few decades, however, there is still a lack of understanding of the fate of newly assimilated C allocated within plants and to the soil, stored within ecosystems and lost to the atmosphere. Stable carbon isotope studies can give novel insights into these issues. In this review we provide an overview of an emerging picture of plant-soil-atmosphere C fluxes, as based on C isotope studies, and identify processes determining related C isotope signatures. The first part of the review focuses on isotopic fractionation processes within plants during and after photosynthesis. The second major part elaborates on plant-internal and plant-rhizosphere C allocation patterns at different time scales (diel, seasonal, interannual), including the speed of C transfer and time lags in the coupling of assimilation and respiration, as well as the magnitude and controls of plant-soil C allocation and respiratory fluxes. Plant responses to changing environmental conditions, the functional relationship between the physiological and phenological status of plants and C transfer, and interactions between C, water and nutrient dynamics are discussed. The role of the C counterflow from the rhizosphere to the aboveground parts of the plants, e.g. via CO₂ dissolved in the xylem water or as xylem-transported sugars, is highlighted. The third part is centered around belowground C turnover, focusing especially on above- and belowground litter inputs, soil organic matter formation and turnover, production and loss of dissolved organic C, soil respiration and CO₂ fixation by soil microbes. Furthermore, plant controls on microbial communities and activity via exudates and litter production as well as microbial community effects on C mineralization are reviewed. The last part of the paper is dedicated to physical interactions between soil CO₂ and the soil matrix, such as CO₂ diffusion and dissolution processes within the soil profile. From the presented evidence we conclude that there exists a tight coupling of physical, chemical and biological processes involved in C cycling and C isotope fluxes in the plant-soil-atmosphere system. Generally, research using information from C isotopes allows an integrated view of the different processes involved. However, complex interactions among the range of processes complicate or impede the interpretation of isotopic signals in CO₂ or organic compounds at the plant and ecosystem level. This is where new research approaches should be aimed at

Non-structural carbohydrates (NSC) in plant tissue are frequently quantified to make inferences about plant responses to environmental conditions. Laboratories publishing estimates of NSC of woody plants use many different methods to evaluate NSC. We asked whether NSC estimates in the recent literature could be quantitatively compared among studies. We also asked whether any differences among laboratories were related to the extraction and quantification methods used to determine starch and sugar concentrations. These questions were addressed by sending sub-samples collected from five woody plant tissues, which varied in NSC content and chemical composition, to 29 laboratories. Each laboratory analyzed the samples with their laboratory-specific protocols, based on recent publications, to determine concentrations of soluble sugars, starch and their sum, total NSC. Laboratory estimates differed substantially for all samples. For example, estimates for Eucalyptus globulus leaves (EGL) varied from 23 to 116 (mean = 56) mg g(-1) for soluble sugars, 6-533 (mean = 94) mg g(-1) for starch and 53-649 (mean = 153) mg g(-1) for total NSC. Mixed model analysis of variance showed that much of the variability among laboratories was unrelated to the categories we used for extraction and quantification methods (method category R(2) = 0.05-0.12 for soluble sugars, 0.10-0.33 for starch and 0.01-0.09 for total NSC). For EGL, the difference between the highest and lowest least squares means for categories in the mixed model analysis was 33 mg g(-1) for total NSC, compared with the range of laboratory estimates of 596 mg g(-1). Laboratories were reasonably consistent in their ranks of estimates among tissues for starch (r = 0.41-0.91), but less so for total NSC (r = 0.45-0.84) and soluble sugars (r = 0.11-0.83). Our results show that NSC estimates for woody plant tissues cannot be compared among laboratories. The relative changes in NSC between treatments measured within a laboratory may be comparable within and between laboratories, especially for starch. To obtain comparable NSC estimates, we suggest that users can either adopt the reference method given in this publication, or report estimates for a portion of samples using the reference method, and report estimates for a standard reference material. Researchers interested in NSC estimates should work to identify and adopt standard methods.