Natural Terrestrial Ecosystems Research Articles

Total environment sentinels: Dragonflies as ambivalent/amphibiotic bioindicators of damage to soil and freshwater

Discerning the impact of anthropogenic impacts requires the implementation of bioindicators that quantify the susceptibilities and vulnerabilities of natural terrestrial and aquatic ecosystems to perturbation and transformation. Although legal regulations in Brazil recognize the value of bioindicators in monitoring water quality, the depreciation of soil conditions has yet to receive adequate attention. Thus, our study aimed to evaluate the potential of odonates (dragonflies and damselflies) as amphibiotic bioindicators to reflect the correlation between the degradation of aquatic and terrestrial habitats in pasture-dominated landscapes. We assessed the relationship between the biotic indices of Odonata and the conservation status of preserved riparian landscapes adjacent to anthropogenically altered pastures in 40 streams in the Brazilian savannah. Our results support the hypothesis that Odonata species composition may be a surrogate indicator for soil and water integrity, making them promising sentinels for detecting environmental degradation and guiding conservation strategies in human-altered landscapes. Importantly, while the Zygoptera/Anisoptera species ratio is a useful bioindicator tool in Brazilian forest, it is less effective in the open savannah here, and so an alternative index is required. Importantly, while the Zygoptera/Anisoptera species ratio is a useful bioindicator tool in Brazilian forest, it is less effective in the open savannah here, and so an alternative index is required. On the other hand, our results showed the Dragonfly Biotic Index to be a suitable tool for assessing freshwater habitats in Brazilian savannah. We also identified certain bioindicator species at both ends of the environment intactness spectrum.

Effects of long-term nitrogen addition on the shift of nitrogen cycle from open to closed along an age gradient of larch plantations in North China

The 15N:14N ratio (δ15N) is often used as an integrated indicator of nitrogen (N) status in natural terrestrial ecosystems. However, the mechanisms by which long-term N addition affects N cycling and status in temperate plantations with different ages remain poorly understood. Here, we used an approach of leaf–soil continuum of δ15N with the combination of incubation experiments to evaluate the effects of three rates of decadal N addition (urea) on N status in young, intermediate, and mature larch (Larix principis-rupprechtii) plantations in northern China. We found that leaf δ15N decreased significantly from 1.6‰ in young trees to −0.5‰ and −1.0‰ in intermediate and mature trees, respectively, due to increases in the use of NO– 3-N relative to NH+ 4-N with stand age, and probably a shift in N acquisition from mineral soil in the young plantation to organic and/or surface mineral soil layers in the intermediate and mature plantations. Decadal N addition decreased leaf δ15N, which was likely to be due to the direct imprints of 15N-depleted urea input, the inhibition of soil net mineralization, and nitrification, and greater dependence on N absorption by ectomycorrhizal fungi after N addition. Soil δ15N decreased with stand age, which was likely to be due to reduced soil N transformation (e.g., mineralization) and/or relative abundance of ectomycorrhizal fungi along the chronosequence; however, soil δ15N was not affected by long-term N inputs. Combined with the decreased enrichment factor (ε = δ15Nleaf – δ15Nsoil), these results suggest a shift from more open N cycling (potentially greater ecosystem N losses) in young plantation to more closed N cycling (facilitation of ecosystem N retention) in mature plantation, which showed negative response to decadal N addition. These findings provide new insights into N acquisition strategies and cycling in the typically N-limited temperate plantations under heightened atmospheric N deposition.

A meta-analysis highlights globally widespread potassium limitation in terrestrial ecosystems.

Potassium (K+ ) is the most abundant inorganic cation in plant cells, playing a critical role in various plant functions. However, the impacts of K on natural terrestrial ecosystems have been less studied compared with nitrogen (N) and phosphorus (P). Here, we present a global meta-analysis aimed at quantifying the response of aboveground production to K addition. This analysis is based on 144 field K fertilization experiments. We also investigate the influences of climate, soil properties, ecosystem types, and fertilizer regimes on the responses of aboveground production. We find that: K addition significantly increases aboveground production by 12.3% (95% CI: 7.4-17.5%), suggesting a widespread occurrence of K limitation across terrestrial ecosystems; K limitation is more prominent in regions with humid climates, acidic soils, or weathered soils; the effect size of K addition varies among climate zones/regions, and is influenced by multiple factors; and previous N : K and K : P thresholds utilized to detect K limitation in wetlands cannot be applied to other biomes. Our findings emphasize the role of K in limiting terrestrial productivity, which should be integrated into future terrestrial ecosystems models.

Digital mapping of the global soil δ15N at 0.1° × 0.1° resolution using random forest regression with climate classification

Spatial information of the natural abundance of soil nitrogen stable isotope (δ15N) is beneficial for deeply understanding the terrestrial nitrogen (N) cycle. However, to date, the precise global map of soil δ15N still lacks. In this study, based on the measured soil δ15N data by Craine et al. (2015) (https://doi.org/10.1038/srep08280) and related environmental variables including soil, topography, vegetation, and climate, we constructed the optimal relationship model between soil δ15N and environmental variables, and mapped the global pattern of soil δ15N at 0.1° × 0.1° resolution (in natural terrestrial ecosystem). Results indicated that satisfied performance was achieved (R2 = 0.68 and RMSE = 1.26‰) by separately building the optimal relationship models for soil δ15N in each of five climate zones (Tropical, Arid, Temperate, Cold and Polar) using the random forest regression algorithm. In addition, critical controls of the soil δ15N in different climate zones were thus identified based on the variable importance calculated by each random forest regression model. In the Tropical zone, soil δ15N might be primarily regulated by microbial N loss, and soil pH and organic matter were identified as two most important factors. In the Arid zone, abiotically gaseous N loss regulated by solar radiation would be the critical controls of soil δ15N. In the Temperate zone, temperature-related variables were identified as the critical controlling factors, and in the Cold zone, soil water and heat conditions had the equally greater importance, and bulk density was the dominated factor in the Polar zone. Furthermore, the predicted global soil δ15N ranged from −0.44‰ to 12.59‰, with the mean value of 5.06‰, and the standard deviation of 1.74‰. Significantly higher soil δ15N (P < 0.05) were observed in the Tropical and Arid zones with mean values of 6.52‰ and 6.11‰, respectively. This indicated that the soil N cycles were more open than those in the Temperate, Cold and Polar zones (mean soil δ15N of 4.37‰, 3.67‰ and 2.76‰, respectively). This study provides clues for potential environmental regulations on terrestrial N cycle in different climates, and the global soil δ15N map can be a reliable data support for future research.

Soil Water Regime, Air Temperature, and Precipitation as the Main Drivers of the Future Greenhouse Gas Emissions from West Siberian Peatlands

This modeling study intended to solve a part of the global scientific problem related to increased concentrations of carbon dioxide in the atmosphere via emissions from terrestrial ecosystems that, along with anthropogenic emissions, make notable contributions to the processes of climate change on the planet. The main stream of CO2 from natural terrestrial ecosystems is related to the activation of biological processes, such as the production/destruction of plant biomass. In this study, the Wetland-DNDC computer simulation model with a focus on nitrogen and carbon biogeochemical cycles was used to study the effect of hydrothermal conditions on greenhouse gas fluxes in West Siberian peatlands. The study was implemented on the site of the world’s largest pristine wetland/peatland system, the Great Vasyugan Mire (GVM). The study was carried out based on data from permanent measurements at meteo stations and our own in situ measurements of hydrological and thermal parameters on sites, which allowed for testing different scenarios of changes in environmental conditions (temperature, precipitation, groundwater level) together with a change in GHG fluxes. The study revealed the air temperature and the level of groundwater as the main drivers controlling CO2 fluxes. The study of different scenarios of change in annual air temperature revealed the threshold of change in the wetland/peatland ecosystem from carbon sink to carbon source to the atmosphere to happen with an increase in the average annual air temperature by 3 °C with reference to the average annual air temperature values in 2019. Also, we found that the wetland/peatland ecosystem turned to act as an active carbon sink with about 7 cm increase in annual groundwater level, compared with its base level of −21 cm.

Soil bacteria and fungi communities are shaped by elevation influences in Colombian forest and páramo natural ecosystems.

The influence of elevation on natural terrestrial ecosystems determines the arrangements of microbial communities in soils to be associated with biotic and abiotic factors. To evaluate changes of fungi and bacteria at the community level along an elevational gradient (between 1000 and 3800 m.a.s.l.), physicochemical measurements of soils, taxonomic identifications of plants, and metabarcoding sequences of the 16S rRNA gene for bacteria and the ITS1 region for fungi were obtained. The bacterial taxonomic composition showed that Acidobacteriota increased in abundance with elevation, while Actinobacteriota and Verrucomicrobiota decreased. Furthermore, Firmicutes and Proteobacteria maintained maximum levels of abundance at intermediate elevations (1200 and 2400 m.a.s.l.). In fungi, Ascomycota was more abundant at higher elevations, Basidiomycota tended to dominate at lower elevations, and Mortierellomycota had a greater presence at intermediate sites. These results correlated with the edaphic parameters of decreasing pH and increasing organic carbon and available nitrogen with elevation. In addition, the Shannon index found a greater diversity in bacteria than fungi, but both showed a unimodal pattern with maximum values in the Andean Forest at 2400 m.a.s.l. Through the microbial characterization of the ecosystems, the elevational gradient, soil properties, and vegetation were found to exert significant effects on microbial communities and alpha diversity indices. We conclude that the most abundant soil microorganisms at the sampling points differed in abundance and diversity according to the variations in factors influencing ecological communities.

Construction and Application of a Regional Kilometer-Scale Carbon Source and Sink Assimilation Inversion System (CCMVS-R)

CO2 is one of the most important greenhouse gases (GHGs) in the earth’s atmosphere. Since the industrial era, anthropogenic activities have emitted excessive quantities of GHGs into the atmosphere, resulting in climate warming since the 1950s and leading to an increased frequency of extreme weather and climate events. In 2020, China committed to striving for carbon neutrality by 2060. This commitment and China’s consequent actions will result in significant changes in global and regional anthropogenic carbon emissions and therefore require timely, comprehensive, and objective monitoring and verification support (MVS) systems. The MVS approach relies on the top-down assimilation and inversion of atmospheric CO2 concentrations, as recommended by the Intergovernmental Panel on Climate Change (IPCC) Inventory Guidelines in 2019. However, the regional high-resolution assimilation and inversion method is still in its initial stage of development. Here, we have constructed an inverse system for carbon sources and sinks at the kilometer level by coupling proper orthogonal decomposition (POD) with four-dimensional variational (4DVar) data assimilation based on the weather research and forecasting–greenhouse gas (WRF-GHG) model. Our China Carbon Monitoring and Verification Support at the Regional level (CCMVS-R) system can continuously assimilate information on atmospheric CO2 and other related information and realize the inversion of regional and local anthropogenic carbon emissions and natural terrestrial ecosystem carbon exchange. Atmospheric CO2 data were collected from six ground-based monitoring sites in Shanxi Province, China to verify the inversion effect of regional anthropogenic carbon emissions by setting ideal and real experiments using a two-layer nesting method (at 27 and 9 km). The uncertainty of the simulated atmospheric CO2 decreased significantly, with a root-mean-square error of CO2 concentration values between the ideal value and the simulated after assimilation was close to 0. The total anthropogenic carbon emissions in Shanxi Province in 2019 from the assimilated inversions were approximately 28.6% (17%–38%) higher than the mean of five emission inventories using the bottom-up method, showing that the top-down CCMVS-R system can obtain more comprehensive information on anthropogenic carbon emissions.

Science school in ecological parasitology in Karelia

The ecological concept of parasitism as a general biology phenomenon underlies the understanding of the role of parasites in terrestrial and aquatic ecosystems. The review gives an account of the current positioning of parasitology in the system of biological sciences, the subject and tasks of ecological parasitology. We relate the history of the science school in parasitology at the Institute of Biology KarRC RAS, which took shape under the leadership of pupils of the founder of the Russian school in ecological parasitology, outstanding scholar from Leningrad V. A. Dogiel. Major stages and areas of research and methodological approaches to the study of parasites and host-parasite relationships are described, covering a wide range of objects: blood-sucking arthropods, parasites of fish, birds, mammals, and plants. Studies deal with the formation and dynamics of parasitic communities in natural and disturbed terrestrial and aquatic ecosystems (eutrophication, industrial pollution, alien species invasions, aquaculture). The results of these studies are of high theoretical significance and have been published in monographs and in articles in Russian and international journals. Practical recommendations are widely applied in nature management, veterinary and agricultural practices, and are annually published in the Republic of Karelia State Report on the Environment. Today, the science school in ecological parasitology in Karelia is represented by qualified specialists, who investigate a wide range of both basic and applied topics, including those of special relevance for the region.

Overestimated nitrogen loss from denitrification for natural terrestrial ecosystems in CMIP6 Earth System Models

Denitrification and leaching nitrogen (N) losses are poorly constrained in Earth System Models (ESMs). Here, we produce a global map of natural soil 15N abundance and quantify soil denitrification N loss for global natural ecosystems using an isotope-benchmarking method. We show an overestimation of denitrification by almost two times in the 13 ESMs of the Sixth Phase Coupled Model Intercomparison Project (CMIP6, 73 ± 31 Tg N yr−1), compared with our estimate of 38 ± 11 Tg N yr−1, which is rooted in isotope mass balance. Moreover, we find a negative correlation between the sensitivity of plant production to rising carbon dioxide (CO2) concentration and denitrification in boreal regions, revealing that overestimated denitrification in ESMs would translate to an exaggeration of N limitation on the responses of plant growth to elevated CO2. Our study highlights the need of improving the representation of the denitrification in ESMs and better assessing the effects of terrestrial ecosystems on CO2 mitigation.

Unearthing the importance of soil development in total phosphorus distribution in China’s mountains

Phosphorus (P) as an essential limiting nutrient for primary productivity has a far-reaching impact on ecosystem carbon sequestration. Increasing studies have evaluated the distribution and stock of soil P in natural terrestrial ecosystems, yet few studies explore the large-scale P distribution from the perspective of soil development in the mountain regions. In this study, 1254 soil samples, including organic soils (O horizon), surface mineral soils (A horizon) and parent materials (C horizon), were collected from twenty-nine mountains in China according to soil development conditions. The concentration and stock of total P in the soils were analyzed to decipher the effects of soil development along with other potential drivers on the P distribution. The results showed that total P concentration decreased significantly in the order of O horizon > A horizon > C horizon, whereas total P stock displayed an opposite trend. Spatially, soil total P concentration increased from South to North China and from West to East China, irrespective of soil horizons, whereas total P stock did not present a consistent spatial trend across the soil horizons. Climate, vegetation and atmospheric active nitrogen deposition exhibited negative effects on soil P distribution directly or indirectly by affecting pedogenesis, while soil organic carbon, pH and iron had distinctly positive effects on the P accumulation in specific horizon. The results highlight the importance of soil development on soil total P distribution in mountains, and this process should be considered when evaluating soil P dynamics in the P biogeochemical cycling models.

Acoustic monitoring to evaluate the effect of anthropogenic noise within a park

The aim of this paper is to propose the use of passive acoustic monitoring (PAM) as a non-invasive method to investigate the state of communities and ecosystems. PAM operates through the study and characterization of the soundscape of an area. One of the three components of the soundscape (beside geophony and biophony) is anthrophony, which is the collection of sounds produced by human activities. This kind of sounds can have effects on natural envi-ronments and natural population. In this study, recording instruments and sampling tech-niques have been used to acquire and collect sound data for long periods (two weeks) in a nat-ural terrestrial ecosystem (Ticino Park) which is affected by road and rail traffic noise. The analysis conducted studied the trends of the eco-acoustic indices belonging to three measure-ment sites to detect the presence of characteristic trends and to evaluate the influence of the two anthropogenic noise sources at different distances.

The ecological role of native‐plant landscaping in residential yards to birds during the nonbreeding period

AbstractResidential yards are a form of urban land use that cover a considerable amount of area in cities worldwide and provide important habitat for wildlife, especially when landscaped with native plants. Nevertheless, most native‐plant landscaping and wildlife research in the northern temperate regions of the world has been conducted during the spring and summer breeding period, leaving a gap in our understanding of the importance of residential yards and native plants as habitats for animals during the nonbreeding period. To fill this gap, we quantified the ecological role of native‐landscaped yards to avifauna throughout Greater Los Angeles (LA), California, during the winter nonbreeding period, which is a time of year when the region hosts a high abundance and diversity of migratory and resident birds. We surveyed birds and habitat features from October to March of 2020 and 2021 at 22 pairs of native‐ and non‐native‐landscaped yards plus 10 additional native‐landscaped yards. We had three objectives for our study. First, we compared avifaunal communities, including feeding and nonfeeding behaviors, and habitat features between native and non‐native‐landscaped yards. Second, we quantified relationships between habitat features and bird richness, abundance, and feeding and nonfeeding behaviors—focusing on species affiliated with urban or natural terrestrial ecosystems of the region. Third, we documented feeding and nonfeeding behaviors by birds with native and non‐native plants. Native‐landscaped yards had a greater cover of native trees, shrubs, and herbaceous plants, and a higher cover of natural habitat elements, including leaf litter and bare‐ground cover. Bird richness and abundance—especially bird species affiliated with tree‐ and shrub‐dominated ecosystems—were greater in native than non‐native‐landscaped yards. Further, yards with a higher cover of native plants supported greater numbers of feeding birds, with individuals focusing their foraging behaviors on distinct native trees and shrubs, including Quercus spp. (oak), Heteromeles spp. (toyon), Arctostaphylos spp. (manzanita), and Salvia spp. (sage). Our results suggest that residential yards landscaped with native plants provide important habitat for birds during the nonbreeding period and are a viable approach for residents and cities if improving conditions for birds throughout the annual cycle is a goal.

Implementation of a new crop phenology and irrigation scheme in the ISBA land surface model using SURFEX_v8.1

Abstract. With an increase in the number of natural processes represented, global land surface models (LSMs) have become more and more accurate in representing natural terrestrial ecosystems. However, they are still limited with respect to the impact of agriculture on land surface variables. This is particularly true for agro-hydrological processes related to a strong human control on freshwater. While many LSMs consider natural processes only, the development of human-related processes, e.g. crop phenology and irrigation in LSMs, is key. In this study, we present the implementation of a new crop phenology and irrigation scheme in the ISBA (interactions between soil–biosphere–atmosphere) LSM. This highly flexible scheme is designed to account for various configurations and can be applied at different spatial scales. For each vegetation type within a model grid cell, three irrigation systems can be used at the same time. A limited number of parameters are used to control (1) the amount of water used for irrigation, (2) irrigation triggering (based on the soil moisture stress), and (3) crop seasonality (emergence and harvesting). A case study is presented over Nebraska (USA). This region is chosen for its high irrigation density and because independent observations of irrigation practices can be used to verify the simulated irrigation amounts. The ISBA simulations with and without the new crop phenology and irrigation scheme are compared to different satellite-based observations. The comparison shows that the irrigation scheme improves the simulated vegetation variables such as leaf area index, gross primary productivity, and land surface temperature. In addition to a better representation of land surface processes, the results point to potential applications of this new version of the ISBA model for water resource monitoring and climate change impact studies.

Forest Aboveground Biomass Estimation and Response to Climate Change Based on Remote Sensing Data

As the largest and most important natural terrestrial ecosystem, forest plays a crucial role in reducing the concentrations of greenhouse gases in the atmosphere, mitigating global warming, maintaining the global ecological balance, and promoting global biological evolution and community succession. The accurate and rapid assessment of forest biomass is highly significant for estimating the regional carbon budget and monitoring forest change. In this study, Landsat images and China’s National Forest Continuous Inventory data of 1999, 2004, 2009, and 2014 were used to establish extreme gradient boosting (XGBoost) models for forest aboveground biomass (AGB) estimation based on forest type in the Xiangjiang River Basin, Hunan Province, China. Kriging interpolation of the AGB residuals was used to correct the error of AGB estimation. Then, a new XGBoost model was established using the final corrected AGB maps and climate data to estimate the AGB under different climate scenarios during the 2050s and 2070s. The results indicated that AGB estimation using the XGBoost model with correction via Kriging interpolation of the AGB residuals can significantly improve the accuracy of AGB estimation. The total AGB of the study area increased over time from 1999 to 2014, indicating that the forest quality improved in the study area. Under the different climate scenarios, the total AGB during the 2050s and 2070s was predicted to decline continuously with increasing of greenhouse gas emissions, indicating that greenhouse gas emissions have a negative impact on forest growth. The results of this study can provide data support for evaluating the ecological function and value of forest ecosystems, and for formulating reasonable forest management measures to mitigate the effects of climate change.

Leaf N:P ratio does not predict productivity trends across natural terrestrial ecosystems.

Nitrogen (N) and phosphorus (P) are crucial nutrients for regulating plant growth. The classic growth rate hypothesis (GRH) proposes that fast-growing organisms have lower N:P ratios, and it is promising to predict net primary productivity (NPP) using the leaf N:P ratio at the community level (N:PCom ). However, whether leaf N:P ratio can predict NPP in natural ecosystems on a large scale remains nebulous. Here, we systematically calculated leaf N:PCom (community biomass-weighted mean and species arithmetic mean) using the consistently measured data of 2192 plant species-site combinations and productivity (biomass-based aboveground NPP and flux-based NPP) in 66 natural ecosystems in China. Unexpectedly, leaf N:PCom hardly predicted productivity in natural ecosystems due to their weak correlation, although significantly negative or positive relationships across different ecosystems were observed. The ambiguous relationship between leaf N:P and species dominance reflected a luxury consumption of N and P in turnover and structure in natural communities, unlike what GRH suggests. Climate, soil, and leaf nutrients (rather than N:P) influenced productivity, which highlighted the importance of external environment and nutrient constrains. Our findings pose a major challenge for leaf N:PCom as a direct parameter in productivity models and further question the direct application of classic hypotheses in short-term experiments or model species to long-term and complex natural ecosystems.

Assessment of the impacts of biological nitrogen fixation structural uncertainty in CMIP6 earth system models

Abstract. Biological nitrogen fixation is the main source of new nitrogen into natural terrestrial ecosystems and consequently in the nitrogen cycle in many earth system models. Representation of biological nitrogen fixation varies, and because of the tight coupling between the carbon and nitrogen cycles, previous studies have shown that this affects projected changes in net primary productivity. Here we present the first assessment of the performance of biological nitrogen fixation in models contributing to CMIP6 compared to observed and observation-constrained estimates of biological nitrogen fixation. We find that 9 out of 10 models represent global total biological nitrogen fixation within the uncertainty in recent global estimates. However, 6 out of 10 models overestimate the amount of fixation in the tropics and therefore the extent of the latitudinal gradient in the global distribution. For the SSP3-7.0 scenario of future climate change, models project increases in fixation over the 21st century of up to 80 %. However, while the historical range of biological nitrogen fixation amongst models is large (up to 140 kg N ha−1 yr−1 at the grid cell level and 43–208 Tg N yr−1 globally) this does not have explanatory power for variations within the model ensemble of net primary productivity or the coupled nitrogen–carbon cycle. Models with shared structures can have significant variations in both biological nitrogen fixation and other parts of the nitrogen cycle without differing in their net primary productivity. This points to systematic challenges in the representation of carbon–nitrogen model structures and the severe limitations of models using net primary productivity or evapotranspiration to project the biological nitrogen fixation response to elevated atmospheric carbon dioxide or other environmental changes.

Microbial Metabolites Beneficial to Plant Hosts Across Ecosystems.

Plants are intimately connected with their associated microorganisms. Chemical interactions via natural products between plants and their microbial symbionts form an important aspect in host health and development, both in aquatic and terrestrial ecosystems. These interactions range from negative to beneficial for microbial symbionts as well as their hosts. Symbiotic microbes synchronize their metabolism with their hosts, thus suggesting a possible coevolution among them. Metabolites, synthesized from plants and microbes due to their association and coaction, supplement the already present metabolites, thus promoting plant growth, maintaining physiological status, and countering various biotic and abiotic stress factors. However, environmental changes, such as pollution and temperature variations, as well as anthropogenic-induced monoculture settings, have a significant influence on plant-associated microbial community and its interaction with the host. In this review, we put the prominent microbial metabolites participating in plant-microbe interactions in the natural terrestrial and aquatic ecosystems in a single perspective and have discussed commonalities and differences in these interactions for adaptation to surrounding environment and how environmental changes can alter the same. We also present the status and further possibilities of employing chemical interactions for environment remediation. Our review thus underlines the importance of ecosystem-driven functional adaptations of plant-microbe interactions in natural and anthropogenically influenced ecosystems and their possible applications.

Overyielding is accounted for partly by plasticity and dissimilarity of crop root traits in maize/legume intercropping systems

Abstract Positive biodiversity–productivity relationships have been found in biodiversity field experiments of grasslands, forests and natural terrestrial ecosystems, where diversity effects were separated by complementarity (CE) and selection effects (SE). However, we know little about how CE and SE are related to root traits and root dissimilarity. A 4‐year field experiment was carried out with a split‐plot design, where main plot was four nitrogen (N) applications (N0, N1, N2 and N3) and five cropping systems (maize Zea mays L./soybean Glycine max L. Merrill., maize/peanut Arachis hypogaea L. intercropped and the corresponding monocultures) with three replicates. Roots were sampled in the N0 and N2 treatments in 2 years. Intercropping effects were analysed based on grain yield for 4 years and roots were sampled down to 60 cm depth, and analysed with morphological parameters at different crop growth stages in 2 years. Intercropping significantly increased grain yield and above‐ground biomass in both intercropping systems under all N treatments. The partitioning of the net intercropping effects showed that yield advantage in intercropping was due to a positive CE under the N0 treatment, and to a positive SE with N application. Maize showed greater root morphological plasticity than the legumes did, with greater changes in root length density (RLD), root weight density (RWD) and total root surface (TS) in intercropping than in monoculture. Intercropped maize occupied a larger soil space, while lateral RLD distribution of legumes was decreased by maize. The RLD, RWD and TS of intercropped maize were constant or increased in later growth stages. SE showed a significantly positive relationship with root dissimilarity. Principal component analysis showed mean root depth and specific root length of legumes drove the positive CE in the absence of N fertilization. Root dissimilarity determined by maize explained the selection effects in overyielding. Complementarity effects under N0 were closely associated with specific root traits such as mean root depth and specific root length. Linking changes of root traits with intercropping effects above‐ground helps understand yield advantages in diverse agroecosystem. In general, a cereal species with strong phenotypic plasticity intercropped with a legume species with strong physiological plasticity can maximize the yield advantage of intercropping. Read the free Plain Language Summary for this article on the Journal blog.

Synchronous vegetation response to the last glacial-interglacial transition in northwest Europe

The North Atlantic region experienced abrupt high-amplitude cooling at the onset of the Younger Dryas stadial. However, due to chronological uncertainties in the available terrestrial records it is unclear whether terrestrial ecosystem response to this event was instantaneous and spatially synchronous, or whether regional or time-transgressive lags existed. Here we use new palynological results from a robustly dated lake sediment sequence retrieved from lake Hämelsee (north Germany) to show that vegetation change started at 12,820 cal. yr BP, concurrent with the onset of changes in local climate. A comparison of the Hämelsee results to a compilation of precisely dated palynological records shows instant and, within decadal-scale dating uncertainty, synchronous response of the terrestrial plant community to Late-Glacial climate change across northwest Europe. The results indicate that the environmental impact of climate cooling was more severe than previously thought and illustrates the sensitivity of natural terrestrial ecosystems to external forcing.

Effects of agricultural land use on the differentiation of nitrifier communities and functional patterns from natural terrestrial ecosystems

Human activities severely affect the global nitrogen (N) cycle. Croplands receive intensive N fertilization; consequently, cropland and natural ecosystem differentiation often results in community and functional variation in N-transforming microbes, including nitrifiers, which perform nitrification central to N cycle. However, evidence of such variation is mostly limited to ammonia oxidizers (AO) in local fields, excluding soil heterogeneity and nitrite-oxidizing bacteria (NOB); the variation under diverse climatic and soil conditions is not comprehensively understood. We conducted a large-scale survey of 131 cropland and natural sites in China. The community patterns of ammonia-oxidizing bacteria (AOB) and NOB differed significantly between croplands and some natural ecosystems, whereas ammonia-oxidizing archaea (AOA) were not affected by ecosystem type. The AOB population and nitrification potential (NP) were significantly higher in agroecosystems than in natural systems except wetlands. Fewer co-occurrence interactions involving nitrifiers were observed in croplands than in natural ecosystems except forests, systematically indicating the ecological diversification of nitrifiers in potential microbial associations among these habitats. Ecosystem type, pH, organic matter (OM), total phosphorus (TP), mean annual temperature (MAT) and mean annual precipitation (MAP) were primary drivers of nitrifier community and functional shifts. This study provides the first large-scale evidence of overall nitrifier community (i.e., AOA, AOB and NOB) and potential functional shifts between agroecosystems and natural environments, enabling predictions of terrestrial N cycle under foreseeable natural land use conversions and global climate change.