Pollinators, pests and soil properties interactively shape oilseed rape yield.

[EN] Pollination, pest control, and soil properties are well known to affect agricultural production. These factors might interactively shape crop yield, but most studies focus on only one of these factors at a time. We used 15 winter oilseed rape (Brassica napus L.) fields in Sweden to study how variation among fields in pollinator visitation rates, pollen beetle attack rates and soil properties (soil texture, pH and organic carbon) interactively determined crop yield. The fields were embedded in a landscape gradient with contrasting proportions of arable and semi-natural land. In general, pollinator visitation and pest levels were negatively correlated and varied independently of soil properties. This may reflect that above- and below-ground processes react at landscape and local spatial scales, respectively. The above-ground biotic interactions and below-ground abiotic factors interactively affected crop yield. Pollinator visitation was the strongest predictor positively associated with yield. High soil pH also benefited yield, but only at lower pest loads. Surprisingly, high pest loads increased the pollinator benefits for yield. Implementing management plans at different spatial scales can create synergies among above- and below-ground ecosystem processes, but both scales are needed given that different processes react at different spatial scales.[GER] Bestäubung, Schädlingskontrolle und Bodeneigenschaften beeinflussen die Agrarproduktion. Diese Faktoren könnten interagierend den Ernteertrag beeinflussen, aber die meisten Studien konzentrieren sich auf nur einen Faktor. Wir untersuchten auf 15 Winterrapsfeldern (Brassica napus L.) in Schweden, wie die von Feld zu Feld variierenden Bestäuberbesuchsraten, Rapsglanzkäfer-Befallsraten und Bodeneigenschaften (Bodentextur, pH, organischer Kohlenstoff) wechselwirkend den Ertrag bestimmten. Die Felder repräsentierten einen Landschaftsgradienten mit unterschiedlichen Anteilen von Agrarflächen und naturnahen Arealen. Allgemein waren Bestäuberbesuch und Schädlingsbefall negativ miteinander korreliert, und sie variierten unabhängig von den Bodeneigenschaften. Dies könnte anzeigen, dass oberirdische Prozesse und Prozesse im Boden auf der Landschaftsebene bzw. der lokalen Ebene reagieren. Die oberirdischen biotischen Interaktionen und die abiotischen Bodenfaktoren beeinflussten wechselwirkend den Ertrag. Der Bestäuberbesuch war der stärkste positiv mit dem Ertrag verknüpfte Faktor. Ein hoher pH-Wert begünstigte ebenfalls den Ertrag, aber nur bei geringem Schädlingsbefall. Überraschenderweise, steigerte hoher Schädlingsbefall die positive Wirkung des Bestäuberbesuchs auf den Ertrag. Das Aufstellen von Bewirtschaftungsplänen auf unterschiedlichen räumlichen Skalen kann Synergien zwischen oberirdischen und unterirdischen Ökosystemprozessen freisetzen, aber beide Skalen werden benötigt, da unterschiedliche Prozesse auf unterschiedlichen Skalen reagierenPeer reviewe

Coordinated evaporative demand and precipitation maximize rainfed maize and soybean crop yields in the USA

To understand how climate change affects crop yields, we need to identify the climatic indices that best predict yields. Grain yields are most often predicted using precipitation and temperature in statistical models, assuming linear dependences. However, soil water availability is more influential for plant growth than precipitation and temperature, and there is ecophysiological evidence of intermediate yield maximizing conditions. Using rainfed maize and soybean yields for 1970-2010 across the USA, we tested whether the aridity index, that is, the ratio of precipitation and potential evapotranspiration seasonal totals and a proxy of soil water availability, better predicts yield than growing season precipitation total, average temperature and their interaction. We also tested for non-monotonic responses allowing for intermediate yield-maximizing conditions. The aridity index alone explained 77% and 72% of maize and soybean yield variability, compared with 78% and 73% explained by temperature, precipitation and their interaction. Yield responses were non-monotonic, with yields maximized at intermediate precipitation and temperature as well as at intermediate aridity index of 0.79 for maize and 0.98 for soybean. The yield maximizing precipitation also increased with growing season average temperature, faster in maize than soybean. The intermediate yield maximizing conditions show that rainfed maize and soybean yields could both increase and decrease depending on whether climatic conditions come closer to or deviate from the yield maximizing conditions in the future. In most counties, during 1970-2010, the precipitation and aridity index were lower and temperature higher compared with those maximizing yields, suggesting that climate change will reduce yields

The coordination of green-brown food webs and their disruption by anthropogenic nutrient inputs

Aim Our goal was to quantify nitrogen flows and stocks in green-brown food webs in different ecosystems, how they differ across ecosystems and how they respond to nutrient enrichment. Location Global. Time period Contemporary. Major taxa studied Plants, phytoplankton, macroalgae, invertebrates, vertebrates and zooplankton. Methods Data from >500 studies were combined to estimate nitrogen stocks and fluxes in green-brown food webs in forests, grasslands, brackish environments, seagrass meadows, lakes and oceans. We compared the stocks, fluxes and metabolic rates of different functional groups within each food web. We also used these estimates to build a dynamical model to test the response of the ecosystems to nutrient enrichment. Results We found surprising symmetries between the green and brown channels across ecosystems, in their stocks, fluxes and consumption coefficients and mortality rates. We also found that nitrogen enrichment, either organic or inorganic, can disrupt this balance between the green and brown channels. Main conclusions Linking green and brown food webs reveals a previously hidden symmetry between herbivory and detritivory, which appears to be a widespread property of natural ecosystems but can be disrupted by anthropogenic nitrogen additions

Combined heat and drought suppress rainfed maize and soybean yields and modify irrigation benefits in the USA

Heat and water stress can drastically reduce crop yields, particularly when they co-occur, but their combined effects and the mitigating potential of irrigation have not been simultaneously assessed at the regional scale. We quantified the combined effects of temperature and precipitation on county-level maize and soybean yields from irrigated and rainfed cropping in the USA in 1970-2010, and estimated the yield changes due to expected future changes in temperature and precipitation. We hypothesized that yield reductions would be induced jointly by water and heat stress during the growing season, caused by low total precipitation (P-GS) and high mean temperatures (T-GS) over the whole growing season, or by many consecutive dry days (CDDGS) and high mean temperature during such dry spells (T-CDD) within the season. Whole growing season (T-GS, P-GS) and intra-seasonal climatic indices (T-CDD, CDDGS) had comparable explanatory power. Rainfed maize and soybean yielded least under warm and dry conditions over the season, and with longer dry spells and higher dry spell temperature. Yields were lost faster by warming under dry conditions, and by lengthening dry spells under warm conditions. For whole season climatic indices, maize yield loss per degree increase in temperature was larger in wet compared with dry conditions, and the benefit of increased precipitation greater under cooler conditions. The reverse was true for soybean. An increase of 2 degrees C in T-GS and no change in precipitation gave a predicted mean yield reduction across counties of 15.2% for maize and 27.6% for soybean. Irrigation alleviated both water and heat stresses, in maize even reverting the response to changes in temperature, but dependencies on temperature and precipitation remained. We provide carefully parameterized statistical models including interaction terms between temperature and precipitation to improve predictions of climate change effects on crop yield and context-dependent benefits of irrigation

High mobility reduces beta-diversity among orthopteran communities - implications for conservation

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Delivery of crop pollination services is an insufficient argument for wild pollinator conservation

There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and these ecosystem services have become a key argument for biodiversity conservation. However, it is unclear how much biodiversity is needed to deliver ecosystem services in a cost- effective way. Here we show that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species. Across crops, years and biogeographical regions, crop-visiting wild bee communities are dominated by a small number of common species, and threatened species are rarely observed on crops. Dominant crop pollinators persist under agricultural expansion and many are easily enhanced by simple conservation measures, suggesting that cost- effective management strategies to promote crop pollination should target a different set of species than management strategies to promote threatened bees. Conserving the biological diversity of bees therefore requires more than just ecosystem-service-based arguments

Disentangling effects of habitat diversity and area on orthopteran species with contrasting mobility

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Land-use intensity affects the potential for apparent competition within and between habitats

Arthropod communities dwelling in adjacent habitats are able to impact one another via shared natural enemies. In agricultural landscapes, drastic differences in resource availability between crop and non-crop habitats cause variation in insect herbivore densities over short distances, potentially driving inter-habitat effects. Moreover, the composition of the landscape in which the habitats are embedded likely affects realised attack rates from natural enemies via impacts on local arthropod community structure. Here, we examine indirect effects between herbivore species within and between habitat types by calculating the potential for apparent competition between multiple populations. Firstly, we aim to determine how disparities in resource availability impact the strength of the potential for apparent competition occurring between habitats, secondly to examine the impact of landscape composition upon these effects, and finally to couch these observations in reality by investigating the link between the potential for apparent competition and realised attack rates. We used DNA metabarcoding to characterise host-parasitoid interactions within two habitat types (with divergent nutrient inputs) at 11 locations with variable landscape composition within an agroecosystem context. We then used these interaction networks to estimate the potential for apparent competition between each host pair and to compare expected versus realised attack rates across the system. Shared natural enemies were found to structure host herbivore communities within and across habitat boundaries. The size of this effect was related to the resource availability of habitats, such that the habitat with high nutrient input exerted a stronger effect. The overall potential for apparent competition declined with increasing land-use intensity in the surrounding landscape and exhibited a discernible impact on realised attack rates upon herbivore species. Thus, our results suggest that increasing the proportion of perennial habitat in agroecosystems could increase the prevalence of indirect effects such as apparent competition among insect herbivore communities, potentially leading to enhanced population regulation via increased attack rates from natural enemies like parasitoid wasps.Peer reviewe

Linear infrastructure habitats increase landscape-scale diversity of plants but not of flower-visiting insects

Habitats along linear infrastructure, such as roads and electrical transmission lines, can have high local biodiversity. To determine whether these habitats also contribute to landscape-scale biodiversity, we estimated species richness, evenness and phylogenetic diversity of plant, butterfy and bumblebee communities in 32 km2 landscapes with or without power line corridors, and with contrasting areas of road verges. Landscapes with power line corridors had on average six more plant species than landscapes without power lines, but there was no such efect for butterfies and bumblebees. Plant communities displayed considerable evenness in species abundances both in landscapes with and without power lines and high and low road verge densities. We hypothesize that the higher number of plant species in landscapes with power line corridors is due to these landscapes having a higher extinction debt than the landscapes without power line corridors, such that plant diversity is declining slower in landscapes with power lines. This calls for targeted conservation actions in semi-natural grasslands within landscapes with power line corridors to maintain biodiversity and prevent imminent population extinctions