Simulated Environmental Change Research Articles

Fungal Communities Are More Sensitive to the Simulated Environmental Changes than Bacterial Communities in a Subtropical Forest: the Single and Interactive Effects of Nitrogen Addition and Precipitation Seasonality Change.

Increased nitrogen deposition (N factor) and changes in precipitation patterns (W factor) can greatly impact soil microbial communities in tropical/subtropical forests. Although knowledge about the effects of a single factor on soil microbial communities is growing rapidly, little is understood about the interactive effects of these two environmental change factors. In this study, we investigated the responses of soil bacterial and fungal communities to the short-term simulated environmental changes (nitrogen addition, precipitation seasonality change, and their combination) in a subtropical forest in South China. The interaction between N and W factors was detected significant for affecting some soil physicochemical properties (such as pH, soil water, and NO3- contents). Fungi were more susceptible to treatment than bacteria in a variety of community traits (alpha, beta diversity, and network topological features). The N and W factors act antagonistically to affect fungal alpha diversity, and the interaction effect was detected significant for the dry season. The topological features of the meta-community (containing both bacteria and fungi) network overrode the alpha and beta diversity of bacterial or fungal communities in explaining the variation of soil enzyme activities. The associations between Ascomycota fungi and Gammaproteobacteria or Alphaproteobacteria might be important in mediating the inter-kingdom interactions. In summary, our results suggested that fungal communities were more sensitive to N and W factors (and their interaction) than bacterial communities, and the treatments' effects were more prominent in the dry season, which may have great consequences in soil processes and ecosystem functions in subtropical forests.

Woody plant encroachment constrains regeneration of ground‐layer species in a neotropical savanna from seeds

AbstractWoody plants have been encroaching into savannas on a global scale. Global climatic changes, along with changes to disturbance regimes, are considered to be the main drivers of this process. Particularly, many formerly open physiognomies of the Brazilian savanna have become encroached by woody species over the course of a few decades under fire suppression. In this scenario, many typical savanna species of the ground‐layer are reducing their above‐ground presence, possibly due to change in environmental filtering as a result of encroachment. Consequently, at encroachment sites, changes to microhabitats occur, such as less incident light to the soil surface, reduced red:far‐red ratios and soil surface temperatures, and increased litter deposition. These changes may hinder the regenerative capacity of ground‐layer savanna species. This study investigated the role of encroachment‐induced environmental changes as filters for the recruitment ability of ground‐layer savanna species. We examined the germination and seedling emergence of 12 species under controlled conditions, simulating natural aspects of encroached and non‐encroached sites of the Brazilian savanna. The germination and/or seedling emergence of all species examined were/was negatively affected by the simulated environmental filtering changes. Increased litter deposition reduced seedling emergence more than temperature and light affected germination. Filtering changes caused by woody encroachment represent a bottleneck for the regeneration from seeds of ground‐layer savanna species. Filtering changes by woody encroachment is one of the underlying mechanism explaining changes in species presence in savannas, and it ultimately leads to positive feedback loops wherein woody encroachment begets more woody encroachment.

Effects of temperature mode and the substrate/inoculum ratio on anaerobic digestion of Tibetan food waste

AbstractBACKGROUNDThe research and applications of anaerobic digestion (AD) in plateau areas are limited by the specific climatic conditions (e.g., low temperature, large temperature difference). To explore feasible and economical strategies of AD in these regions, the effects of different temperature modes (constant mode: 35, 25, 15 °C; stepwise changes mode that simulated daily environmental temperature changes: 35–25 °C, 25–15 °C) and substrate/inoculum (S/I) ratios (1: 1, 1: 2, 1: 4) on Tibetan food waste (FW) digestion performance and microbial community structure were analyzed. Besides this, the energy balance of AD under different conditions was estimated.RESULTSThe methane yields (335–463 mL g−1 VS) of FW at temperature changes mode with less energy consumption could reach the same level or even slightly higher than the methane yields at 35 °C. Kinetic analysis revealed that, compared with 25 °C, methane production performance was not greatly affected by temperature fluctuations around 25 °C. The relative abundance of acetoclastic methanogens (e.g., Methanosaeta) were dominant over hydrogenotrophic methanogens (e.g., Methanobacterium, Methanospirillum) at 35 °C. The opposite was true at 15 °C.CONCLUSIONThe decrease in temperature caused the digestion pathway to shift from acetoclastic to the hydrogenotrophic pathway. The effect of temperature on the microbial community structure was more pronounced than the S/I ratio. Energy balance calculations showed that psychrophilic conditions and AD without temperature control were likely to be more economically competitive than mesophilic conditions for small‐scale AD in cold regions. © 2021 Society of Chemical Industry (SCI).

Response of forage plants to alteration of temperature and spring thaw date: implications for geese in a warming Arctic

AbstractChanges in summer temperatures in Arctic Alaska have led to longer and warmer growing seasons over the last three decades. Corresponding with these changes in climate, the abundance and distributions of geese have increased and expanded over the same period. We used an experimental approach to assess the response of goose forage plants to simulated environmental change. We subjected Carex subspathacea, a preferred goose forage growing on the Arctic Coastal Plain (ACP) of Alaska, to manipulations of temperature and timing of spring thaw to measure potential effects in terms of plant nitrogen concentration, aboveground biomass, and total nitrogen availability. Carex subspathacea responded to warming in a dynamic fashion. Increases in temperature led to decreases in leaf nitrogen concentration but increases in aboveground biomass. The increase in biomass was stronger than the decline in nitrogen concentration such that total nitrogen availability was increased with temperature for the first 35–40 d of the season. Grazing removal accounted for only minimal offtake of biomass, and we found no indication that grazing maintained elevated levels of nitrogen concentration longer in the season as reported in other studies. Based on demonstrated relationships in the literature between forage nitrogen concentrations and gosling growth rates, we conclude that there is currently abundant high‐quality forage available across the ACP. This finding fits with recent evidence of high gosling growth rates and increasing trends in goose abundance on the ACP. Our results suggest that with climate warming of a few degrees, nitrogen concentration of forage may decrease, but forage biomass and total nitrogen availability will increase. Our data suggest that nitrogen concentration will not fall below the minimum threshold required by geese in the near future. As such, we suggest that there is currently no bottom‐up limitation to goose numbers on the ACP.

Independent effects of warming and altered precipitation pattern on nematode community structure in an arable field

Global environmental change is causing increases in soil temperatures and alternations in precipitation patterns, which are affecting soil biota in natural and managed systems. Arable soils, generally disturbed due to management practice, are particularly sensitive to a changing environment. However, little is known how warming interacts with precipitation pattern to affect soil fauna and thereby ecosystem functions. In an arable system, we investigated the interactions of soil warming and altered precipitation amount and frequency on soil conditions and health using nematodes as bioindicators. Our findings showed that the nematode population density was significantly increased by warming and decreased by reduced precipitation frequency. Warming mainly fostered the density of fungal feeders and obligatory plant parasites, with the latter suggesting higher crop damage. Root-associated plant feeders were further affected by changes in precipitation pattern; their density declined with reduced precipitation frequency and increased with the alternated precipitation amount. The nematode abundance was generally low in the arable ecosystem and remained stable under the simulated environmental change. In response to warming, the major soil decomposition channel via bacteria was reduced, and the fungal mediated pathway fostered, implying more fungal dominated depleted and degraded soil conditions. Soil decomposition pathways were not affected by altered precipitation pattern, neither by amount nor by frequency. Overall, warming and precipitation independently altered the soil nematode fauna and the functioning of belowground food webs. Therefore, our study highlights the need for more research considering the interactions of environmental variables to see if this lack is a general pattern and to develop strategies for agroecosystem's management under climate change.

Convergence of DNA Methylation Profiles of the Reef Coral Porites astreoides in a Novel Environment

Phenotypic acclimatization is an organismal response to environmental change that may be rooted in epigenetic mechanisms. In reef building corals, organisms that are severely threatened by environmental change, some evidence suggests that DNA methylation is an environmentally responsive mediator of acclimatization. We investigated changes in DNA methylation of the reef coral Porites astreoides in response to simulated environmental change. Coral colonies were sampled from a variety of habitats on the Belize Barrier Reef and transplanted to a common garden for one year. We used restriction site associated DNA sequencing, including a methylation-sensitive variant, to subsample the genome and assess changes in DNA methylation levels after a year in the common garden. Methylation changes among the 629 CpG loci we recovered were subtle, yet coral methylomes were more similar to each other after a year in the common garden together, indicating convergence of methylation profiles in the common environment. Differentially methylated loci showed matches with both coding and non-coding RNA sequences with putative roles in intracellular signaling, apoptosis, gene regulation, and epigenetic crosstalk. There was a positive and significant relationship between genetic and epigenetic variation, providing evidence of methylation heritability. Altogether, our results suggest that DNA methylation in P. astreoides is at least somewhat responsive to environmental change, reflective of the environment, and heritable, characteristics necessary for methylation to be implicated as part of potential transgenerational acclimatization responses.

Plant communities are more sensitive than soil microbial communities to multiple environmental changes in the Eurasian steppe

Understanding species responsiveness to anthropogenic environmental changes benefits the guide to manage biodiversity. Microbes are traditionally thought to be more sensitive to environmental changes than plants. However, this hypothesis is supported by little empirical evidence. We compared plant and microbial responses to 13 types of simulated environmental changes (mowing (M), adding nitrogen (N), adding phosphorus (P), watering (W), warming (T) and combinations of these) in a steppe ecosystem. Contrary to our hypothesis, the microbial responses were generally smaller than the plant responses to different types of environmental changes, both at the community-abundance level and species/operational taxonomic unit (OTU)/gene level. This might be ascribed to the soil buffering capacity to environmental changes, and the rapid evolutionary adaptation for microbial communities. Furthermore, the responses at the community-abundance level were larger than at the species/OTU/gene level to 13 types of environmental changes, both in plant and microbial communities. Given that the community abundance representing the total number of all individuals of the organism within the community, the responses to environmental changes at the community-abundance level is likely to be larger than at the species/OTU/gene level. Plant biomass was more responsive to N addition, particularly in such N- limiting grassland ecosystem. Our findings highlight that plant communities are more responsive to environmental changes than microbial communities, contrary to the traditional viewpoint. Therefore, plant communities could be used as ecological indicators of anthropogenic environmental changes in grasslands.

Microbial community response to environmental changes in a technosol historically contaminated by the burning of chemical ammunitions

The burning of chemical weapons in the 1926–1928 period produced polluted technosols with elevated levels of arsenic, zinc, lead and copper. During an eight-month mesocosm experiment, these soils were submitted to two controlled environmental changes, namely the alternation of dry and water-saturated conditions and the addition of fragmented organic forest litter to the surface soil. We investigated, by sequencing the gene coding 16S rRNA and 18S rRNA, (1) the structure of the prokaryotic and eukaryotic community in this polluted technosol and (2) their response to the simulated environmental changes, in the four distinct layers of the mesocosm. In spite of the high concentrations of toxic elements, microbial diversity was found to be similar to that of non-polluted soils. The bacterial community was dominated by Proteobacteria, Acidobacteria and Bacteroidetes, while the fungal community was dominated by Ascomicota. Amongst the most abundant bacterial Operational Taxonomic Units (OTUs), including Sphingomonas as a major genus, some were common to soil environments in general whereas a few, such as organisms related to Leptospirillum and Acidiferrobacter, seemed to be more specific to the geochemical context. Evolution of the microbial abundance and community structures shed light on modifications induced by water saturation and the addition of forest litter to the soil surface. Co-inertia analysis suggests a relationship between the physico-chemical parameters total organic carbon, Zn, NH4+ and As(III) concentrations and the bacterial community structure. Both these results imply that microbial community dynamics linked to environmental changes should be considered as factors influencing the behavior of toxic elements on former ammunition burning sites.

Interspecific plant competition mediates the metabolic and ecological signature of a plant–herbivore interaction under warming and elevated CO2

Abstract Biotic interactions shape community evolution, but we lack mechanistic insights on how metabolic and ecological processes under climate change are altered by biotic interactions. We used a two‐trophic model community consisting of the aphid Dysaphis plantaginea feeding on the forb Plantago lanceolata, and a grass competitor Lolium perenne that does not experience herbivory by the aphid. Monocultures and mixtures were exposed to the herbivory treatment and to three relevant simulated environmental changes as prevalent under current climate change (increased temperature, CO2, and increased temperature and CO2) Elevated CO2 reduced the nitrogen content of P. lanceolata, while simultaneous increases of CO2 and temperature modified the plant metabolic component and the magnitude of these responses in different directions. Elevated CO2 enhanced defence systems in P. lanceolata, but these effects were not altered by warming. Interspecific plant competition did, however, neutralize these responses. There were no indirect effects of climate change on aphid population growth despite changes in plant defence, nutritional quality and biomass induced by our environmental change scenarios. We thus demonstrate interactions between abiotic and biotic processes on plant metabolite profiles, but more importantly, that climate change effects on a selection of the metabolic pathways are altered by herbivory and competition. Our experiment under semi‐natural conditions thus demonstrates the non‐additive and often neutralizing effects of biotic interactions on plant metabolism and species performance under climate‐associated environmental change. A free Plain Language Summary can be found within the Supporting Information of this article.

Decoupling of nutrient cycles in a Eucalyptus woodland under elevated CO2

Abstract Elevated atmospheric [CO2] (eCO2) is currently altering nutrient cycling and availability in ecosystems worldwide. If the availabilities and turnover rates of macro‐ and micronutrients are differentially affected, then nutrient cycles may become out of sync (i.e., decoupled). We evaluated the impacts of 3 years of eCO2 (550 µmol CO2/mol) on the availability, stability and coupling of eleven essential macro and micronutrients in a mature, P‐limited Eucalyptus woodland from Eastern Australia (EucFACE). Despite increases in N and P availability in the first 18 months of study, nutrient availabilities and their stoichiometric ratios were unaffected by eCO2 across the study period (26–57 months of experimental duration). In contrast, the stability of nutrient availability increased under eCO2, which was concomitant with a reduction in the degree of biogeochemical coupling. Synthesis. We demonstrate that macro‐ and micro‐nutrient cycles can quickly become out of sync (i.e., decoupled) under eCO2 in a low‐nutrient Australian eucalypt woodland, despite the lack of consistent effects on nutrient availability; such decoupling of nutrient cycles may have unpredicted consequences in terms of ecosystem functioning under the widely assumed positive relationship between biogeochemical coupling and ecosystem functioning.

Warming limits daytime but not nighttime activity of epigeic microarthropods in Songnen grasslands

Both climate warming and nitrogen addition have the potential to affect soil fauna. The effect of these changes on the diel variation of soil microarthropods motility remains unknown. In northeastern China, in temperate grasslands with limited moisture and nutrients, epigeic microarthropods were captured by pitfall traps and activity-density and species richness of epigeic Collembola and Oribatida were calculated after four years of simulated environmental change by warming and/or nitrogen addition both in daytime and nighttime. Warming with or without nitrogen addition reduced the total activity-density of epigeic Collembola. However, this effect was pronounced only in daytime, but not nighttime. Epigeic Oribatida was not impacted by warming treatment. Nitrogen addition had no effect on epigeic Oribatida and Collembola. Our results indicate that warming has a pronounced, adverse effect on epigeic Collembola in water-limited temperate grassland and that the effect was microarthropod taxon-specific. We conclude that warming could limit the activity-density of epigeic microarthropods' species that are not resistant to water deficiency and these alterations would not be alleviated by concurrent nitrogen deposition.

Rainfall variability counteracts N addition by promoting invasive Lonicera maackii and extending phenology in prairie

Although encroaching woody plants have reduced the global extent of grasslands, continuing increases in soil nitrogen availability could slow this trend by favoring resident herbaceous species. At the same time, projected increases in rainfall variability could promote woody encroachment by aligning spatiotemporal patterns of soil moisture availability with the needs of woody species. We evaluated the responses of two deciduous woody species to these simulated environmental changes by planting seedlings of Quercus palustris and Lonicera maackii into tallgrass prairie communities grown under a factorial combination of increased rainfall variability and nitrogen addition. Lonicera maackii growth was reduced 20% by nitrogen addition, and increased rainfall variability led to 33% larger seedlings, despite greater competition for light and soil resources. In contrast, Q.palustris growth showed little response to either treatment. Increased rainfall variability allowed both species to retain their leaves for an additional 6.5d in autumn, potentially in response to wetter end-of-season shallow soils. Our findings suggest increases in rainfall variability will counteract the inhibitory effect of nitrogen deposition on growth of L.maackii, extend autumn phenology, and promote the encroachment of some woody species into grasslands.

People and nature in the Fuerteventura Biosphere Reserve (Canary Islands): socio-ecological relationships under climate change

SUMMARYThis paper analyses the interdependence between environment and society in terms of socio-ecological webs, in which human and biophysical systems are linked. A quantitative model, based on canonical correlation analysis applied in Fuerteventura Island (Canary Archipelago), detected indicators of human–landscape relationships and predicted potential shifts based on simulated environmental changes. In the last few decades, the landscape of Fuerteventura Island has changed: natural components and cultural agrarian uses have decreased, while the population has increased due to immigration, mainly from mainland Spain and other European countries. The island shows a transition from a coupled local socio-ecosystem to one based on the interaction between environment and coastal tourism that decouples native inhabitants from the landscape and traditional land-use practices. As vulnerability and adaptation to climate change represent critical sets of potential interactions in Canary Islands, a model and a map of the socio-ecological system under four Intergovernmental Panel on Climate Change scenarios show rural decoupling through ‘deagrarianization’ and ‘deruralization’, as well as stronger links to the tourism system.

Resistance of plant–plant networks to biodiversity loss and secondary extinctions following simulated environmental changes

Summary Plant interactions are fundamental processes for structuring plant communities and are an important mechanism governing the response of plant species and communities to environmental changes. Thus, understanding the role played by the interaction network in modulating the impact of environmental changes on plant community composition and diversity is crucial. Here, we aimed to develop a new analytical and conceptual framework to evaluate the responses of plant communities to environmental changes. This framework uses functional traits as sensitivity measures for simulated environmental changes and assesses the consequences of microhabitat loss. We show here its application to an alpine plant community where we recorded functional traits [specific leaf area (SLA) and leaf dry matter content (LDMC)] of all plants associated with three foundation species or the surrounding open areas. We then simulated primary species loss based on different scenarios of environmental change and explored community persistence to the loss of foundation species. Generally, plant community responses differed among environmental change scenarios. In a scenario of increasing drought alone (i.e. species with lower LDMC were lost first) or increasing drought with increasing temperature (i.e. species with lower LDMC and higher SLA were lost first), the plant community resisted because drought‐tolerant foundation species tolerated those deteriorating conditions. However, in scenarios with increasing nitrogen input (i.e. species having lower SLA were lost earlier), foundation species accelerated species loss due to their early primary extinctions and the corresponding secondary extinctions of species associated to their microhabitat. The resistance of a plant community depends on the driver of environmental change, meaning that the prediction of the fate of this system is depending on the knowledge of the main driver of environmental change. Our framework provides a mechanistic understanding of an ecosystem response to such environmental changes thanks to the integration of biology‐informed criteria of species sensitivities to environmental factors into a network of interacting species. A lay summary is available for this article.

荒漠短命植物的养分含量与荧光特征初探

短命植物作为荒漠植被类群中的独特类型，植物叶片的荧光生理特征和养分含量之间具有极高的相关性。分别选取5种典型短命植物东方旱麦草(Eremopyrum orientale)、卷果涩芥(Malcolmia scorpioides)、狭果鹤虱(Lappula semiglabra)、四齿芥(Tetracme quadricormis)和硬萼软紫草(Arnebiade cumbens)自然生长比较一致的叶片作为研究材料，对叶片的叶绿素和养分含量以及荧光光响应进行了测定。结果表明，短命植物的叶绿素总量为1.24~2.67 mg∙g−1之间，叶绿素a、b含量之比达到5.80~12.86。叶片含N量在3.1%以上，含P量为0.22%~0.30%，含K量在3.15%~6.24%。短命植物的实际光化学量子产量ΦPSII平均在0.4以上，ETR受光强的抑制不明显，当光合有效辐射值超过1400 mol∙m−2∙s−1时，出现下降。 Ephemerals, including annual ephemerals and ephemeroid plants, are characterized by short- term growth rhythms and specific biological traits adapted to deserts or temperate broad-leaved deciduous forests. Their fluorescence physical characteristics had a significant correlation with their leaf contents. The chlorophyll content, nutrient content and response of the photosynthetic characteristics to the simulated light environmental changes of five desert ephemerals, Eremopyrum orientale, Malcolmia scorpioides, Lappula semiglabra, Tetracme quadricormis and Arnebiade cumbens, which distributed in Northwestern China, were investigated. The results showed that the chlorophyll content of ephemerals was between 1.24 and 2.67 mg∙g−1, with extremely high chla/ chlb values reaching 5.80 - 12.86. Ephemerals growing in barren desert had extremely high nutrient use efficiency, with leaf nitrogen content all above 3.1%, leaf phosphorus content between 0.22% and 0.30%, and leaf potassium content between 3.15% and 6.24%. The ΦPSII of ephemerals on average was above 0.4. The inhibition effect of high light intensity on electron transport rate (ETR) was not obvious, with the latter decreasing only when PAR was above 1400 mol∙m−2∙s−1.

Nitrogen deposition but not climate warming promotes Deyeuxia angustifolia encroachment in alpine tundra of the Changbai Mountains, Northeast China

Vegetation in the alpine tundra area of the Changbai Mountains, one of two alpine tundra areas in China, has undergone great changes in recent decades. The aggressive herb species Deyeuxia angustifolia (Komarov) Y. L. Chang, a narrow-leaf small reed, was currently encroaching upon the alpine landscape and threatening tundra biota. The alpine tundra of the Changbai Mountains has been experiencing a warmer climate and receiving a high load of atmospheric nitrogen deposition. In this study, we aimed to assess the respective roles of climate warming and atmospheric nitrogen deposition in promoting the upward encroachment of D. angustifolia. We conducted experiments for three years to examine the response of D. angustifolia and a native alpine shrub, Rhododendron chrysanthum, to the conditions in which temperature and nitrogen were increased. Treatments consisting of temperature increase, nitrogen addition, temperature increase combined with nitrogen addition, and controls were conducted on the D. angustifolia communities with three encroachment levels (low, medium, and high levels). Results showed that 1) D. angustifolia grew in response to added nutrients but did not grow well when temperature increased. R. chrysanthum showed negligible responses to the simulated environmental changes. 2) Compared to R. chrysanthum, D. angustifolia could effectively occupy the above-ground space by increasing tillers and growing rapidly by efficiently using nitrogen. The difference in nitrogen uptake abilities between the two species contributed to expansion of D. angustifolia. 3) D. angustifolia encroachment could deeply change the biodiversity of tundra vegetation and may eventually result in the replacement of native biota, especially with nitrogen addition. Our research indicated that nutrient perturbation may be more important than temperature perturbation in promoting D. angustifolia encroachment upon the nutrient- and species-poor alpine tundra ecosystem in the Changbai Mountains.

Responses of phytolith in guinea grass (Leymus chinensis) leaves to simulated warming, nitrogen deposition and elevated CO2 concentration in Songnen grassland, Northeast China

Deposited in plant cells and their intercellular space, phytoliths, a special form of silica, could be used to determine information on plant structure and physiology especially their size and content. With the hypothesis that phytolith in plant would change under variable climate and environment, the dominant plant species in Songnen grassland, guinea grass (Leymus chinensis), was treated by an open-top chamber (OTC) to elevate CO2 concentration, infrared heaters, and artificial nitrogen (N) addition for three years from 2006–2008. Phytoliths were extracted by wet-ashing method and analyzed by variance analysis and so on. We found that the responses to elevated CO2 are complicated, and warming is positive while N addition is negative to the deposition of phytoliths in L. chinensis leaves. Especially, warming could reduce the negative impact of N addition on phytolith in L. chinensis. The short cell’s taxonomic in graminea is significant because of no disappearance with simulated environmental changes. The phytolith originated in the long cell and plant intercellular space are more sensitive to elevated CO2 concentration, warming, and N addition, and could become some new indicators for environmental changes. In conclusion, different phytolith types have various responses to simulated warming, N addition and elevated CO2 concentration.

Microbial lipid and amino sugar responses to long-term simulated global environmental changes in a California annual grassland.

Global environmental change is predicted to have major consequences for carbon cycling and the functioning of soil ecosystems. However, we have limited knowledge about its impacts on the microorganisms, which act as a “valve” between carbon sequestered in soils versus released into the atmosphere. In this study we examined microbial response to continuous 9-years manipulation of three global change factors (elevated CO2, warming, and nitrogen deposition), singly and in combination using two methods: lipid and amino sugar biomarkers at the Jasper Ridge Global Change Experiment (JRGCE). The two methods yielded important distinctions. There were limited microbial lipid differences, but many significant effects for microbial amino sugars. We found that CO2 was not a direct factor influencing soil carbon and major amino sugar pools, but had a positive impact on bacterial-derived muramic acid. Likewise, warming and nitrogen deposition appeared to enrich residues specific to bacteria despite an overall depletion in total amino sugars. The results indicate that elevated CO2, warming, and nitrogen deposition all appeared to increase bacterial-derived residues, but this accumulation effect was far offset by a corresponding decline in fungal residues. The sensitivity of microbial residue biomarker amino sugars to warming and nitrogen deposition may have implications for our predictions of global change impacts on soil stored carbon.

A simulation experiment on phosphatized spherical microfossils

The identification and characterization of the phosphate preservation of the spherical microfossils in the Ediacaran Doushantuo time and the Early Cambrian has long been controversial. Modern artificial simulation experiments of phosphate animal eggs can provide scientific evidence to settle the aforementioned disputes. This experiment simulated environmental changes to observe the early morphological changes of the Bluntnose black bream eggs (Megalobrama amblycephala). It was found that the eggs can show a different morphology in the phosphate environment and that these eggs exhibited considerable morphological variations under different conditions. Thus, those eggs cannot be ascribed to the same species based only on the features. The experimental results are expected to provide a useful reference for the identification of phosphatized microfossils and provide a more empirical basis for their genesis.

Similar tree seedling responses to shrubs and to simulated environmental changes at Pyrenean and subarctic treelines

Background: Climate, land-use and disturbance regimes are key drivers of treeline dynamics worldwide, but local and regional spatio-temporal patterns indicate that additional factors play an important role. Some studies suggest that shrub-tree interactions control tree seedling recruitment patterns across the treeline ecotone, but little is known about the generality of this interaction. Aims: We established an experiment in a treeline ecotone in the central Pyrenees to investigate the role of such interactions and other environmental factors on tree seedling growth and survival. It was based on a similar experiment we completed recently in the subarctic Scandes. By comparing local phenomena between both experiments we assessed the generality of the findings across regions with different biogeographic histories and species characteristics. Methods: We followed the survival and growth of transplanted Pinus uncinata seedlings during three growing seasons in a multi-factorial design (forest vs. treeline, +/– shrub removal, +/– temperature increase and +/– nutrient addition). Results: There was better seedling growth at the treeline compared to the forest, and the presence of shrubs prevented seedling winter damage and herbivory. Both temperature and nutrient increase enhanced seedling performance. Conclusions: Although some particular details were exclusive to the Pyrenees or to the Scandes, the similarities indicated general patterns and help to interpret the underlying mechanisms of treeline dynamics in both regions. This convergence of responses points to the potential of the development of a robust mechanistically founded predictive framework for scaling up shrub impacts on treeline dynamics to other regions.