Plant diversity and community history shift colonization success from early- to mid-successional species

Aims Functional traits are supposed to play an important role in determining the colonization success of new species into established communities. Short-term experimental studies have documented higher resistance of more diverse grasslands against colonization by new species. However, little is known about which traits colonizers should have to successfully invade diverse plant communities in the longer term and how community history may modify the resistance of diverse communities against colonization. Methods In a grassland biodiversity experiment (Jena Experiment) established with different species richness (SR; 1, 2, 4, 8 and 16) and functional group (FG) number and composition (1 to 4; legumes, grasses, small herbs, tall herbs), we studied colonization of naturally dispersed species in split-plots (i) with different duration of weeding (never weeded, weeded for 3 or 6 years and then un-weeded for 1 year) and (ii) with different duration of colonization (7 years, 4 years and 1 year after cessation of weeding). Important Findings Resistance against colonization by new species declined with increased duration of weeding (on average 13, 17 and 22 colonizer species in 1-, 4- and 7-year-old communities, respectively). Communities established at low diversity accumulated more colonizer species with a longer duration of weeding than more diverse communities. Duration of colonization had only small effects on the number of colonizer species. Colonizers with early successional traits, i.e. annual life cycle, reproduction by seeds, small seeds, long-lived seeds and an earlier start of a longer flowering period, were favoured in species-poor newly established experimental plant communities (short duration of weeding) and early after cessation of weeding (short duration of colonization). A change from early- to mid-successional traits, i.e. taller growth, perennial life cycle, vegetative reproduction, characterized colonization at increased plant diversity and in communities with legumes or without grasses. Legume absence/grass presence and increased duration of weeding led to a shift in colonizer strategies from rapid nutrient uptake and cycling (higher specific leaf area) to nutrient retention and symbiotic N2 fixation. Our study shows that non-random trait spectra of naturally dispersed colonizers encompass trade-offs between different functions (reproduction, persistence, growth) reflected in a change from early- to mid-successional traits at increasing plant diversity, with a longer duration of weeding and a longer time of colonizatio

Differential effects of plant diversity on functional trait variation of grass species

Background and Aims Functional trait differences and trait adjustment in response to influences of the biotic environment could reflect niche partitioning among species. In this study, we tested how variation in above-ground plant traits, chosen as indicators for light and nitrogen acquisition and use, differs among taxonomically closely related species (Poaceae) to assess their potential for niche segregation at increasing plant diversity. Methods Traits of 12 grass species were measured in experimental grasslands (Jena Experiment) of varying species richness (from 1 to 60) and presence of particular functional groups (grasses, legumes, tall herbs and small herbs). Key Results Grass species increased shoot and leaf length, investment into supporting tissue (stem mass fraction) and specific leaf area as well as reduced foliar δ13C values with increasing species richness, indicating higher efforts for light acquisition. These species-richness effects could in part be explained by a higher probability of legume presence in more diverse communities. Leaf nitrogen concentrations increased and biomas s : N ratios in shoots decreased when grasses grew with legumes, indicating an improved nitrogen nutrition. Foliar δ15N values of grasses decreased when growing with legumes suggesting the use of depleted legume-derived N, while decreasing δ15N values with increasing species richness indicated a shift in the uptake of different N sources. However, efforts to optimize light and nitrogen acquisition by plastic adjustment of traits in response to species richness and legume presence, varied significantly among grass species. It was possible to show further that trait adjustment of grass species increased niche segregation in more diverse plant communities but that complementarity through niche separation may differ between light and nutrient acquisition. Conclusions The results suggest that even among closely related species such as grasses different strategies are used to cope with neighbours. This lack in redundancy in turn may facilitate complementary resource use and coexistenc

The climate benefit of carbon sequestration

Ecosystems play a fundamental role in climate change mitigation by photosynthetically fixing carbon from the atmosphere and storing it for a period of time in organic matter. Although climate impacts of carbon emissions by sources can be quantified by global warming potentials, the appropriate formal metrics to assess climate benefits of carbon removals by sinks are unclear. We introduce here the climate benefit of sequestration (CBS), a metric that quantifies the radiative effect of fixing carbon dioxide from the atmosphere and retaining it for a period of time in an ecosystem before releasing it back as the result of respiratory processes and disturbances. In order to quantify CBS, we present a formal definition of carbon sequestration (CS) as the integral of an amount of carbon removed from the atmosphere stored over the time horizon it remains within an ecosystem. Both metrics incorporate the separate effects of (i) inputs (amount of atmospheric carbon removal) and (ii) transit time (time of carbon retention) on carbon sinks, which can vary largely for different ecosystems or forms of management. These metrics can be useful for comparing the climate impacts of carbon removals by different sinks over specific time horizons, to assess the climate impacts of ecosystem management, and to obtain direct quantifications of climate impacts as the net effect of carbon emissions by sources versus removals by sinks.Peer reviewe

Plant diversity and community history shift colonization success from early- to mid-successional species

Aims Functional traits are supposed to play an important role in determining the colonization success of new species into established communities. Short-term experimental studies have documented higher resistance of more diverse grasslands against colonization by new species. However, little is known about which traits colonizers should have to successfully invade diverse plant communities in the longer term and how community history may modify the resistance of diverse communities against colonization. Methods In a grassland biodiversity experiment (Jena Experiment) established with different species richness (SR; 1, 2, 4, 8 and 16) and functional group (FG) number and composition (1 to 4; legumes, grasses, small herbs, tall herbs), we studied colonization of naturally dispersed species in split-plots (i) with different duration of weeding (never weeded, weeded for 3 or 6 years and then un-weeded for 1 year) and (ii) with different duration of colonization (7 years, 4 years and 1 year after cessation of weeding). Important Findings Resistance against colonization by new species declined with increased duration of weeding (on average 13, 17 and 22 colonizer species in 1-, 4- and 7-year-old communities, respectively). Communities established at low diversity accumulated more colonizer species with a longer duration of weeding than more diverse communities. Duration of colonization had only small effects on the number of colonizer species. Colonizers with early successional traits, i.e. annual life cycle, reproduction by seeds, small seeds, long-lived seeds and an earlier start of a longer flowering period, were favoured in species-poor newly established experimental plant communities (short duration of weeding) and early after cessation of weeding (short duration of colonization). A change from early- to mid-successional traits, i.e. taller growth, perennial life cycle, vegetative reproduction, characterized colonization at increased plant diversity and in communities with legumes or without grasses. Legume absence/grass presence and increased duration of weeding led to a shift in colonizer strategies from rapid nutrient uptake and cycling (higher specific leaf area) to nutrient retention and symbiotic N2 fixation. Our study shows that non-random trait spectra of naturally dispersed colonizers encompass trade-offs between different functions (reproduction, persistence, growth) reflected in a change from early- to mid-successional traits at increasing plant diversity, with a longer duration of weeding and a longer time of colonization

Cryogenic Displacement and Accumulation of Biogenic Methane in Frozen Soils

Evidences of highly localized methane fluxes are reported from the Arctic shelf, hot spots of methane emissions in thermokarst lakes, and are believed to evolve to features like Yamal crater on land. The origin of large methane outbursts is problematic. Here we show, that the biogenic methane (δ13C ≤ −71‰) which formed before and during soil freezing is presently held in the permafrost. Field and experimental observations show that methane tends to accumulate at the permafrost table or in the coarse-grained lithological pockets surrounded by the sediments less-permeable for gas. Our field observations, radiocarbon dating, laboratory tests and theory all suggest that depending on the soil structure and freezing dynamics, this methane may have been displaced downwards tens of meters during freezing and has accumulated in the lithological pockets. The initial flux of methane from the one pocket disclosed by drilling was at a rate of more than 2.5 kg C(CH4) m−2 h−1. The age of the methane was 8–18 thousand years younger than the age of the sediments, suggesting that it was displaced tens of meters during freezing. The theoretical background provided the insight on the cryogenic displacement of methane in support of the field and experimental data. Upon freezing of sediments, methane follows water migration and either dissipates in the freezing soils or concentrates at certain places controlled by the freezing rate, initial methane distribution and soil structure

Trait means, trait plasticity and trait differences to other species jointly explain species performances in grasslands of varying diversity

Functional traits may help to explain the great variety of species performances in plant communities, but it is not clear whether the magnitude of trait values of a focal species or trait differences to co‐occurring species are key for trait‐based predictions. In addition, trait expression within species is often plastic, but this variation has been widely neglected in trait‐based analyses. We studied functional traits and plant biomass of 59 species in 66 experimental grassland mixtures of varying species richness (Jena Experiment). We related mean species performances (species biomass and relative yield RY) and their plasticities along the diversity gradient to trait‐based pedictors involving mean species traits (Tmean), trait plasticities along the diversity gradient (Tslope), extents of trait variation across communities (TCV; coefficient of variation) and hierarchical differences (Tdiff) and trait distances (absolute values of trait differences Tdist) between focal and co‐occurring species. Tmean (30–55%) and Tdiff (30–33%) explained most variation in mean species performances and their plasticities, but Tslope (20–25%) was also important in explaining mean species performances. The mean species traits and the trait differences between focal species and neighbors with the greatest explanatory power were related to plant size and stature (shoot length, mass:height ratios) and leaf photosynthetic capacity (specific leaf area, stable carbon isotopes and leaf nitrogen concentration). The contribution of trait plasticities in explaining species performances varied in direction (positive or negative) and involved traits related to photosynthetic capacity, nitrogen acquisition (nitrogen concentrations and stable isotopes) as well as structural stability (shoot carbon concentrations). Our results suggest that incorporating plasticity in trait expression as well as trait differences to co‐occurring species is critical for extending trait‐based analyses to understand the assembly of plant communities and the contribution of individual species in structuring plant communities

Origin context of trait data matters for predictions of community performance in a grassland biodiversity experiment

Plant functional traits may explain the positive relationship between species richness and ecosystem functioning, but species‐level trait variation in response to growth conditions is often ignored in trait‐based predictions of community performance. In a large grassland biodiversity experiment (Jena Experiment), we measured traits on plants grown as solitary individuals, in monocultures or in mixtures. We calculated two measures of community‐level trait composition, i.e., community‐weighted mean traits (CWM) and trait diversity (Rao's quadratic entropy; FD) based on different contexts in which traits were measured (trait origins). CWM and FD values of the different measurement origins were then compared regarding their power to predict community biomass production and biodiversity effects quantified with the additive partitioning method. Irrespective of trait origin, models combining CWM and FD values as predictors best explained community biomass and biodiversity effects. CWM values based on monoculture, mixture‐mean or community‐specific trait data were similarly powerful predictors, but predictions became worse when trait values originated from solitary‐grown individuals. FD values based on monoculture traits were the best predictors of community biomass and net biodiversity effects, while FD values based on community‐specific traits were the best predictors for complementarity and selection effects. Traits chosen as best CWM predictors were not strongly affected by trait origin but traits chosen as best FD predictors varied strongly dependent on trait origin and altered the predictability of community performance. We conclude that by adjusting their functional traits to species richness and even specific community compositions, plants can change community‐level trait compositions, thereby also changing community biomass production and biodiversity effects. Incorporation of these plastic trait adjustments of plants in trait‐based ecology can improve its predictive power in explaining biodiversity–ecosystem functioning relationships

Insights from regional and short-term biodiversity monitoring datasets are valuable: a reply to Daskalova et al. 2021

Reports of major losses in insect biodiversity have stimulated an increasing interest in temporal population changes. Existing datasets are often limited to a small number of study sites, few points in time, a narrow range of land-use intensities and only some taxonomic groups, or they lack standardised sampling. While new monitoring programs have been initiated, they still cover rather short time periods. Daskalova et al. 2021 (Insect Conservation and Diversity, 14, 1-18) argue that temporal trends of insect populations derived from short time series are biased towards extreme trends, while their own analysis of an assembly of shorter- and longer-term time series does not support an overall insect decline. With respect to the results of Seibold et al. 2019 (Nature, 574, 671–674) based on a 10-year multi-site time series, they claim that the analysis suffers from not accounting for temporal pseudoreplication. Here, we explain why the criticism of missing statistical rigour in the analysis of Seibold et al. (2019) is not warranted. Models that include ‘year’ as random effect, as suggested by Daskalova et al. (2021), fail to detect non-linear trends and assume that consecutive years are independent samples which is questionable for insect time-series data. We agree with Daskalova et al. (2021) that the assembly and analysis of larger datasets is urgently needed, but it will take time until such datasets are available. Thus, short-term datasets are highly valuable, should be extended and analysed continually to provide a more detailed understanding of insect population changes under the influence of global change, and to trigger immediate conservation actions