Depth-dependent responses of soil organic carbon under nitrogen deposition.

Emerging evidence points out that the responses of soil organic carbon (SOC) to nitrogen (N) addition differ along the soil profile, highlighting the importance of synthesizing results from different soil layers. Here, using a global meta-analysis, we found that N addition significantly enhanced topsoil (0-30 cm) SOC by 3.7% (±1.4%) in forests and grasslands. In contrast, SOC in the subsoil (30-100 cm) initially increased with N addition but decreased over time. The model selection analysis revealed that experimental duration and vegetation type are among the most important predictors across a wide range of climatic, environmental, and edaphic variables. The contrasting responses of SOC to N addition indicate the importance of considering deep soil layers, particularly for long-term continuous N deposition. Finally, the lack of depth-dependent SOC responses to N addition in experimental and modeling frameworks has likely resulted in the overestimation of changes in SOC storage under enhanced N deposition.

Shifts in soil ammonia-oxidizing community maintain the nitrogen stimulation of nitrification across climatic conditions.

Anthropogenic nitrogen (N) loading alters soil ammonia-oxidizing archaea (AOA) and bacteria (AOB) abundances, likely leading to substantial changes in soil nitrification. However, the factors and mechanisms determining the responses of soil AOA:AOB and nitrification to N loading are still unclear, making it difficult to predict future changes in soil nitrification. Herein, we synthesize 68 field studies around the world to evaluate the impacts of N loading on soil ammonia oxidizers and nitrification. Across a wide range of biotic and abiotic factors, climate is the most important driver of the responses of AOA:AOB to N loading. Climate does not directly affect the N-stimulation of nitrification, but does so via climate-related shifts in AOA:AOB. Specifically, climate modulates the responses of AOA:AOB to N loading by affecting soil pH, N-availability and moisture. AOB play a dominant role in affecting nitrification in dry climates, while the impacts from AOA can exceed AOB in humid climates. Together, these results suggest that climate-related shifts in soil ammonia-oxidizing community maintain the N-stimulation of nitrification, highlighting the importance of microbial community composition in mediating the responses of the soil N cycle to N loading.

Challenges in upscaling laboratory studies to ecosystems in soil microbiology research.

Soil microbiology has entered into the big data era, but the challenges in bridging laboratory-, field-, and model-based studies of ecosystem functions still remain. Indeed, the limitation of factors in laboratory experiments disregards interactions of a broad range of in situ environmental drivers leading to frequent contradictions between laboratory- and field-based studies, which may consequently mislead model development and projections. Upscaling soil microbiology research from laboratory to ecosystems represents one of the grand challenges facing environmental scientists, but with great potential to inform policymakers toward climate-smart and resource-efficient ecosystems. The upscaling is not only a scale problem, but also requires disentangling functional relationships and processes on each level. We point to three potential reasons for the gaps between laboratory- and field-based studies (i.e., spatiotemporal dynamics, sampling disturbances, and plant-soil-microbial feedbacks), and three key issues of caution when bridging observations and model predictions (i.e., across-scale effect, complex-process coupling, and multi-factor regulation). Field-based studies only cover a limited range of environmental variation that must be supplemented by laboratory and mesocosm manipulative studies when revealing the underlying mechanisms. The knowledge gaps in upscaling soil microbiology from laboratory to ecosystems should motivate interdisciplinary collaboration across experimental, observational, theoretic, and modeling research.

Replacing chemical fertilizer with manure reduces N2O emissions in winter wheat - summer maize cropping system under limited irrigation.

Nitrous oxide (N2O) emissions from agroecosystems are a major contributor to global warming and stratospheric ozone depletion. However, knowledge concerning the hotspots and hot moments of soil N2O emissions with manure application and irrigation, as well as the underlying mechanisms remain incomplete. Here, a 3-year field experiment was conducted with the combination of fertilization (no fertilizer, F0; 100% chemical fertilizer N, Fc; 50% chemical N + 50% manure N, Fc + m; and 100% manure N, Fm) and irrigation (with irrigation, W1; and without irrigation, W0; at wheat jointing stage) for winter wheat - summer maize cropping system in the North China Plain. Results showed that irrigation did not affect annual N2O emissions of the wheat-maize system. Manure application (Fc + m and Fm) reduced annual N2O emissions by 25-51% compared with Fc, which mainly occurred during 2 weeks after fertilization combined with irrigation (or heavy rainfall). In particular, Fc + m reduced the cumulative N2O emissions during 2 weeks after winter wheat sowing and summer maize top dressing by 0.28 and 0.11 kg ha-1, respectively, compared with Fc. Meanwhile, Fm maintained the grain N yield and Fc + m increased grain N yield by 8% compared with Fc under W1. Overall, Fm maintained the annual grain N yield and lower N2O emissions compared to Fc under W0, and Fc + m increased the annual grain N yield and maintained N2O emissions compared with Fc under W1, respectively. Our results provide scientific support for using manure to minimize N2O emissions while maintaining crop N yield under optimal irrigation to support the green transition in agricultural production.

Stimulation of ammonia oxidizer and denitrifier abundances by nitrogen loading: Poor predictability for increased soil N2 O emission.

Unprecedented nitrogen (N) inputs into terrestrial ecosystems have profoundly altered soil N cycling. Ammonia oxidizers and denitrifiers are the main producers of nitrous oxide (N2 O), but it remains unclear how ammonia oxidizer and denitrifier abundances will respond to N loading and whether their responses can predict N-induced changes in soil N2 O emission. By synthesizing 101 field studies worldwide, we showed that N loading significantly increased ammonia oxidizer abundance by 107% and denitrifier abundance by 45%. The increases in both ammonia oxidizer and denitrifier abundances were primarily explained by N loading form, and more specifically, organic N loading had stronger effects on their abundances than mineral N loading. Nitrogen loading increased soil N2 O emission by 261%, whereas there was no clear relationship between changes in soil N2 O emission and shifts in ammonia oxidizer and denitrifier abundances. Our field-based results challenge the laboratory-based hypothesis that increased ammonia oxidizer and denitrifier abundances by N loading would directly cause higher soil N2 O emission. Instead, key abiotic factors (mean annual precipitation, soil pH, soil C:N ratio, and ecosystem type) explained N-induced changes in soil N2 O emission. Altogether, these findings highlight the need for considering the roles of key abiotic factors in regulating soil N transformations under N loading to better understand the microbially mediated soil N2 O emission.

Effect of wind speed variation on rainfed wheat production evaluated by the CERES-Wheat model.

Climate is one of the major factors affecting crop phenology and yield. In most previous studies, impacts of temperature (T) and rainfall (R) on crop development, growth, and yield were investigated, while the effect of wind speed (WS) has so far not been assessed. In this study, the influence of WS alteration on rainfed wheat production was evaluated in arid and semi-arid environments during a 25-year period in northeast Iran. In so doing, various climatic scenarios were defined using T, R, and WS changes, and then applied to the CERES-Wheat model included in DSSAT v4.7.5. The results showed that WS variation can alter total ET (planting to harvest) from -12.1 to +8.9%, aboveground biomass from -8.4 to +11.0%, water use efficiency from -13.4 to +19.7%, and grain yield from -11.2 to +15.3%. These changes were in many cases related to the climatic conditions. It was also revealed that in a greater amount of rainfall and shorter growing season (i.e., less drought stress), the WS variation had the stronger impact on total ET; while for aboveground biomass, water use efficiency, and grain yield, the greatest effect of WS variation was detected under the water scarcity conditions (i.e., low rainfall). The results demonstrate that wind speed needs to be better considered in climate change impact studies, in particular in water-scarce regions.

Climate change impact and adaptation for wheat protein.

Wheat grain protein concentration is an important determinant of wheat quality for human nutrition that is often overlooked in efforts to improve crop production. We tested and applied a 32-multi-model ensemble to simulate global wheat yield and quality in a changing climate. Potential benefits of elevated atmospheric CO2 concentration by 2050 on global wheat grain and protein yield are likely to be negated by impacts from rising temperature and changes in rainfall, but with considerable disparities between regions. Grain and protein yields are expected to be lower and more variable in most low-rainfall regions, with nitrogen availability limiting growth stimulus from elevated CO2 . Introducing genotypes adapted to warmer temperatures (and also considering changes in CO2 and rainfall) could boost global wheat yield by 7% and protein yield by 2%, but grain protein concentration would be reduced by -1.1 percentage points, representing a relative change of -8.6%. Climate change adaptations that benefit grain yield are not always positive for grain quality, putting additional pressure on global wheat production.

Targeted set-aside: Benefits from reduced nitrogen loading in Danish aquatic environments.

Nitrogen (N) leaching from agricultural areas in the form of nitrate (NO3-) is one of the most dominant sources of eutrophication in coastal waters. This environmental pressure is expected to intensify with the predicted increase in food demand, highlighting the need for developing novel ways to reduce N loads from agriculture. This may be achieved by exploiting the spatial variation in N removal through denitrification in groundwater and surface water systems. Thus, agricultural intensification should occur in areas characterized by high N removal potential, whereas effective N-reduction measures such as setting aside agricultural land (set-aside) should be targeted towards areas characterized by low N removal. Simultaneously, setting aside agricultural land can potentially strengthen local nature areas. To reach the water quality targets defined by the EU Water Framework Directive (WFD), the Danish region has defined individual coastal N reduction goals for each of the existing Danish water catchments. With set-aside as an effective N-reduction measure the study aims were to: 1) evaluate the effect of targeting areas to set aside versus using no targeting and 2) evaluate whether different prioritization for targeting set-aside areas enhances multi-functionality of the landscape, while efficiently achieving the required N load reduction. Areas were selected according to three priority values: 1) high contribution to coastal N loads, 2) high nature value, and 3) low agricultural land rent. The combination of these three values per area defined three multifunctional scenarios: (GreenEnvi - N load dominates, TerreEco - nature dominates, AgroEcon - land rent dominates). Results indicate, that targeting areas with high N loads for set-aside is more beneficial (effective) for achieving multiple goals than blanket policies for entire countries (no targeting). Targeting requires only 23% of agricultural land compared to 35% when not targeting, leaving more land available for satisfying food demand. Moreover, multiple benefits can be achieved in surrounding environments by increasing set-aside to 25% according to the GreenEnvi scenario. The GreenEnvi scenario is also cheaper compared to targeting for only land rent.

Challenges and opportunities when moving food production and consumption toward sustainable diets in the Nordics: a scoping review for Nordic Nutrition Recommendations 2023.

The terms 'Nordic countries' or 'The Nordics' include the five countries Denmark, Finland, Island, Norway, and Sweden. This review includes evaluation of the Nordic countries against Food and Agricultural Organisation (FAO)/World Health Organizations' (WHO) guiding principles for healthy, sustainable diets with respect to environmental impact (principles #9 - #13) and sociocultural aspects (principles #14 - #16). A food systems perspective is taken to summarize and discuss the most important challenges and opportunities for achieving sustainable diets. Food system, food security, self-sufficiency, and resilience perspectives are applied. The information can underpin decisions when developing and implementing Food Based Dietary Guidelines (FBDG) in the Nordics. None of the Nordic countries are on track to reach the 2030 UN climate and biodiversity goals. We describe how food production, processing, and consumption contribute to these and other environmental challenges, and what kinds of dietary changes/transitions consistent with these goals are required. A major challenge is the high production and consumption of meat and too low consumption of fish, vegetables, and fruits. Meat production is a major source of emissions and, together with farmed fish, heavily dependent on imported feed ingredients, leaving a large land-use and water footprint in exporting countries while domestic land resources are not used optimally. Dietary patterns have changed drastically over the past 50 years, and in large parts of the population, meat consumption has doubled since the 1970s, rendering historic food culture less useful as a basis for present-day recommendations. The Nordics have Europe's lowest use of antibiotics in animal and fish production and have made some progress in reducing food waste along the food chain. A major opportunity is better alignment of food production and consumption based on local or regional production potentials, in conjunction with better and more constructive integration with the global food system while integrating novel technologies to reduce emissions and resource use.

Impacts of land use, climate change and hydrological model structure on nitrate fluxes: Magnitudes and uncertainties.

Nitrate pollution and eutrophication are of increasing concern in agriculturally dominated regions, and with projected future climate changes, these issues are expected to worsen for both surface and groundwater. Changes in land use and management have the potential to mitigate some of these concerns. However, to what extent these changes will interact is unknown, and are associated with significant uncertainty. Here, we estimate nitrate fluxes and contributions of major uncertainty sources (variance decomposition analysis) affecting nitrate leaching from the root zone and river load from groundwater sources for an agricultural catchment in Denmark under future changes (2080-2099) in climate (four climate models) and land use (four land use scenarios). To investigate the uncertainty from impact model choice, two different agro-hydrological models (SWAT and DAISY-MIKE SHE) both traditionally used for nitrate impact assessments are used for projecting these effects. On average, nitrate leaching from the root zone increased by 55%-123% due to different climate models, while the impact of land use scenarios showed changes between -9% and 88%, with similar projections for river loads, while the worst-case combination of the three factors yielded a fivefold increase in nitrate transport. Thus, in the future, major land use changes will be necessary to mitigate nitrate pollution likely in combination with other measures such as advanced management and farming technologies and differentiated regulation. The two agro-hydrological models showed substantially different reaction patterns and magnitude of nitrate fluxes, and while the largest uncertainty source was the land use scenarios for both models, DAISY-MIKE SHE was to a higher degree affected by climate model choice. The dominating uncertainty source was found to be the agro-hydrological model; however, both uncertainties related to land use scenario and climate model were important, thus highlighting the need to include all influential factors in future nitrate flux impact studies.

Soil N2O emission from organic and conventional cotton farming in Northern Tanzania.

The effort to increase the sustainable supply of food and fibre is challenged by the potential for increased greenhouse gas (GHG) emissions from farming systems with intensified production systems. This study aimed at quantifying soil N2O emissions from smallholder organic and conventional cotton production practices in a semi-arid area, Meatu, Northern Tanzania. Field experiments were conducted to quantify N2O emissions under (i) current practices with organic (3 Mg ha-1 farmyard manure (FYM)) and conventional (30 kg mineral N ha-1) cultivation; (ii) a high input practice with organic (5 Mg ha-1 FYM) and conventional (60 kg mineral N ha-1) cultivation; and (iii) an integrated practice with organic (3 Mg FYM + legume intercropping) and conventional (30 kg N + 3 Mg ha-1 FYM) cultivation. In both organic and conventional farming, control treatments with no fertilizer application were included. The study was performed over two growing seasons, where season 1 was rather wet and season 2 was rather dry. Static chambers were used for in-situ measurement of N2O emission from soil. The current organic and conventional cotton farming practices did not differ (P > 0.05) in cumulative area-scaled and yield-scaled N2O emissions. High input conventional cotton showed higher area scaled N2O emissions than organic cotton during the wetter season, but not during the drier season. The inorganic fertilizer + FYM combination did not differ (P > 0.05) in area- and yield-scaled N2O emissions from conventional practice. Intercropping cotton and legumes did not affect (P > 0.05) N2O emission compared to 3 Mg FYM ha-1. The emission factors for both conventional and organic systems were generally above 1% in the dry season 2, but below 1% in the wetter season 1. The use of organic and inorganic fertilizers at rates up to 60 kg N ha-1, FYM-inorganic fertilizer combination, and cotton-legume intercropping increased yields, while N2O emissions stayed low, in particular with use of mineral fertilizers.

Plants with lengthened phenophases increase their dominance under warming in an alpine plant community.

Predicting how shifts in plant phenology affect species dominance remains challenging, because plant phenology and species dominance have been largely investigated independently. Moreover, most phenological research has primarily focused on phenological firsts (leaf-out and first flower dates), leading to a lack of representation of phenological lasts (leaf senescence and last flower) and full phenological periods (growing season length and flower duration). Here, we simultaneously investigated the effects of experimental warming on different phenological events of various species and species dominance in an alpine meadow on the Tibetan Plateau. Warming significantly advanced phenological firsts for most species but had variable effects on phenological lasts. As a result, warming tended to extend species' full phenological periods, although this trend was not significant for all species. Experimental warming reduced community evenness and differentially impacted species dominance. Shifts in full phenological periods, rather than a single shift in phenological firsts or phenological lasts, were associated with changes in species dominance. Species with lengthened full phenological periods under warming increased their dominance. Our results advance the understanding of how altered species-specific phenophases relate to changes in community structure in response to climate change.

Digging Deeper for Agricultural Resources, the Value of Deep Rooting.

In the quest for sustainable intensification of crop production, we discuss the option of extending the root depth of crops to increase the volume of soil exploited by their root systems. We discuss the evidence that deeper rooting can be obtained by appropriate choice of crop species, by plant breeding, or crop management and its potential contributions to production and sustainable development goals. Many studies highlight the potentials of deeper rooting, but we evaluate its contributions to sustainable intensification of crop production, the causes of the limited research into deep rooting of crops, and the research priorities to fill the knowledge gaps.