Ecosystem multifunctionality is more related to the indirect effects than to the direct effects of human management in China's drylands.

Drylands provide a wide range of important ecosystem functions but are sensitive to environmental changes, especially human management. Two major land use types of drylands are grasslands and croplands, which are influenced by intensive grazing activities and agricultural management, respectively. However, little is known about whether the ecosystem functioning of these two land use types is predominated affected by human management, or environmental factors (intrinsic environmental factors and factors modified by human management). This limits our understanding of the ecosystem functions under intensive human management in drylands. Here we reported a study where we collected data from 40 grassland and 30 cropland sites along an extensive aridity gradient in China's drylands to quantify the effects of human management intensity, intrinsic environmental factors (i.e., aridity), and environmental factors modified by human management (i.e., soil bulk density and plant density) on specific ecosystem functions (ecosystem multifunctionality, productivity, carbon storage, soil water, and soil nutrients). We found that the relative importance of each function differed between croplands and grasslands. Ecosystem functions varied with human management intensity, with lower productivity and plant carbon storage in grasslands under high grazing intensity than un-grazed, while multifunctionality and carbon storage increased with greater fertilization only in arid croplands. Furthermore, among environmental factors, soil bulk density had the greatest negative effects, which directly reduced multifunctionality in grasslands and indirectly reduced multifunctionality in croplands via suppressing crop density. Crop density was the major environmental factor that positively related to multifunctionality in croplands. However, these effects would be exacerbated with increasing aridity. Our study demonstrated that compared with the direct impacts of human management, environmental factors modified by human management (e.g., soil bulk density) are the major drivers of ecosystem functions, indicating that improving soil structure by alleviating human interferences (e.g., reducing livestock trampling) would be an effective way to restore ecosystem functions in drylands under global warming and drying.

Is the threatened land crab Cardisoma guanhumi conquering human-dominated systems?

Land use changes are heralded as a major driver of biodiversity loss. However, recent findings show that cities, perhaps the most radical habitat transformation, sustain increasing numbers of threatened species. This emerging trend has been mostly chronicled for vertebrates from landlocked cities, although loss of biodiversity and rates or urbanization are higher in coastal marine systems. To advance our understanding on how threatened species may conquer human-dominated systems, we studied the threatened edible crab Cardisoma guanhumi and assessed how it is proliferating in croplands and urban systems at different spatial scales and whether populations show consequences of long-term exploitation. We gathered the data on crab populations covering the whole distribution range, including three countries reporting this as a threatened species. The abundance, distribution, and size structure of crab populations among different land uses at local scales were compared and published data for populations thriving in different habitats throughout their distribution range were compiled. We found that at local scale this species is able to thrive in natural and human-disturbed habitats, where food sources are heavily altered. At larger scales, the species showed no differences in abundance and size structure among natural and anthropogenic habitats. In areas near the southern distribution edge, crab populations were more abundant and composed of larger animals in urban areas and croplands than those in natural habitats, suggesting that human-disturbed systems are stepping stones to extend the geographic range. However, we found a long-term reduction in maximum body size, exacerbated by land use changes, that likely reflects exploitation regimes consistently targeting larger crabs. Despite its status as a threatened species, the long history of human exploitation combined with livestock farming practices may explain the proliferation of this crab in human-dominated systems, which emphasize the need to consider conservation in human-dominated systems.

Net greenhouse gas balance in U.S. croplands: How can soils be part of the climate solution?

Agricultural soils play a dual role in regulating the Earth's climate by releasing or sequestering carbon dioxide (CO2 ) in soil organic carbon (SOC) and emitting non-CO2 greenhouse gases (GHGs) such as nitrous oxide (N2 O) and methane (CH4 ). To understand how agricultural soils can play a role in climate solutions requires a comprehensive assessment of net soil GHG balance (i.e., sum of SOC-sequestered CO2 and non-CO2 GHG emissions) and the underlying controls. Herein, we used a model-data integration approach to understand and quantify how natural and anthropogenic factors have affected the magnitude and spatiotemporal variations of the net soil GHG balance in U.S. croplands during 1960-2018. Specifically, we used the dynamic land ecosystem model for regional simulations and used field observations of SOC sequestration rates and N2 O and CH4 emissions to calibrate, validate, and corroborate model simulations. Results show that U.S. agricultural soils sequestered 13.2 ± 1.16 $$ 13.2\pm 1.16 $$ Tg CO2 -C year-1 in SOC (at a depth of 3.5 m) during 1960-2018 and emitted 0.39 ± 0.02 $$ 0.39\pm 0.02 $$ Tg N2 O-N year-1 and 0.21 ± 0.01 $$ 0.21\pm 0.01 $$ Tg CH4 -C year-1 , respectively. Based on the GWP100 metric (global warming potential on a 100-year time horizon), the estimated national net GHG emission rate from agricultural soils was 122.3 ± 11.46 $$ 122.3\pm 11.46 $$ Tg CO2 -eq year-1 , with the largest contribution from N2 O emissions. The sequestered SOC offset ~28% of the climate-warming effects resulting from non-CO2 GHG emissions, and this offsetting effect increased over time. Increased nitrogen fertilizer use was the dominant factor contributing to the increase in net GHG emissions during 1960-2018, explaining ~47% of total changes. In contrast, reduced cropland area, the adoption of agricultural conservation practices (e.g., reduced tillage), and rising atmospheric CO2 levels attenuated net GHG emissions from U.S. croplands. Improving management practices to mitigate N2 O emissions represents the biggest opportunity for achieving net-zero emissions in U.S. croplands. Our study highlights the importance of concurrently quantifying SOC-sequestered CO2 and non-CO2 GHG emissions for developing effective agricultural climate change mitigation measures.

Relative importance between nitrification and denitrification to N2 O from a global perspective.

Nitrous oxide (N2 O) is a potent greenhouse gas, and its mitigation is a pressing task in the coming decade. However, it remains unclear which specific process between concurrent nitrification and denitrification dominates worldwide N2 O emission. We snagged an opportunity to ascertain whence the N2 O came and which were the controlling factors on the basis of 1315 soil N2 O observations from 74 peer-reviewed articles. The average N2 O emission derived from nitrification (N2 On ) was higher than that from denitrification (N2 Od ) worldwide. The ratios of nitrification-derived N2 O to denitrification-derived N2 O, hereof N2 On :N2 Od , exhibited large variations across terrestrial ecosystems. Although soil carbon and nitrogen content, pH, moisture, and clay content accounted for a part of the geographical variations in the N2 On :N2 Od ratio, ammonia-oxidizing microorganisms (AOM):denitrifier ratio was the pivotal driver for the N2 On :N2 Od ratios, since the AOM:denitrfier ratio accounted for 53.7% of geographical variations in N2 On :N2 Od ratios. Compared with natural ecosystems, soil pH exerted a more remarkable role to dictate the N2 On :N2 Od ratio in croplands. This study emphasizes the vital role of functional soil microorganisms in geographical variations of N2 On :N2 Od ratio and lays the foundation for the incorporation of soil AOM:denitrfier ratio into models to better predict N2 On :N2 Od ratio. Identifying soil N2 O derivation will provide a global potential benchmark for N2 O mitigation by manipulating the nitrification or denitrification.

Adoption of soil and water conservation technologies and its effects on soil properties: Evidences from Southwest Ethiopia.

In Ethiopia, national wide soil and water conservation (SWC) is going on since 2010/11in all agro-climatic zones and farming systems. Therefore, this study evaluated the effects of soil bund on soil physico-chemical properties and factors determining farmers' decision on the adoption of SWC technologies in a watershed located in the sub-humid climate of southwest Ethiopia. Two sub-watersheds, namely Nada and Gulufa in the Gilgel Gibe I catchment, were selected for this study. Thirty-six soil samples were collected from non-conserved croplands and croplands conserved with soil bunds (older than 4 years) at three slope positions, namely lower (5-10%), middle (10-15%), and upper (>15%). Both composite and undisturbed top soil (0-30 cm) samples were collected and soil physicochemical properties were determined following standard laboratory procedures. The generated soil physicochemical data was analyzed using one-way ANOVA and the mean separation was carried out by the Tukey test using R-version 3.5.2. To generate survey data, 267 households were randomly selected from the two sub-watersheds and interviewed using a structured questionnaire. The collected survey data was analyzed using a binary logit model using STATA software version 13. The result showed that the implemented soil bund significantly (p < 0.05) improved soil BD, SMC, pH, SOC, TN and CEC at the three slope positions for both the Nada and Gulufa sub-watersheds. The binary logit model showed that personal, socio-economic, institutional, and physical factors influencing the decision of a farmer's adoption. This revealed the need to consider personal, socio-economic, institutional, and physical factors to enhance the willingness probability of adoption. Besides, the improvements in soil properties as a result of conservation practices can help to create awareness.

Using machine learning and remote sensing to track land use/land cover changes due to armed conflict.

Armed conflicts have detrimental impacts on the environment, including land systems. The prevailing understanding of the relation between Land Use/Land Cover (LULC) and armed conflict fails to fully recognize the complexity of their dynamics - a shortcoming that could undermine food security and sustainable land/water resources management in conflict settings. The Syrian portion of the transboundary Orontes River Basin (ORB) has been a site of violent conflict since 2013. Correspondingly, the Lebanese and Turkish portions of the ORB have seen large influxes of refugees. A major challenge in any geoscientific investigation in this region, specifically the Syrian portion, is the unavailability of directly-measured "ground truth" data. To circumvent this problem, we develop a novel methodology that combines remote sensing products, machine learning techniques and quasi-experimental statistical analysis to better understand LULC changes in the ORB between 2004 and 2022. Through analysis of the resulting annual LULC maps, we can draw several quantitative conclusions. Cropland areas decreased by 21-24 % in Syria's conflict hotspot zones after 2013, whereas a 3.4-fold increase was detected in Lebanon. The development of refugee settlements was also tracked in Lebanon and on the Syrian/Turkish borders, revealing different LULC patterns that depend on settlement dynamics. The results highlight the importance of understanding the heterogenous spatio-temporal LULC changes in conflict-affected and refugee-hosting countries. The developed methodology is a flexible, cloud-based approach that can be applied to wide variety of LULC investigations related to conflict, policy and climate.

Negative effects of the spatial clumping of thermal resources on lizard thermoregulation in a fragmented habitat.

In ecosystems threatened by the expansion of croplands, habitat fragmentation and climate change, two of the main extinction drivers, may have thermoregulation-mediated interacting effects on demographic trends of terrestrial ectotherms. We studied the thermal biology of a metapopulation of the widespread Mediterranean lacertid Psammodromus algirus in ten fragments of evergreen or deciduous oak forests interspersed among cereal fields. We obtained thermoregulation statistics (selected temperature range, body and operative temperatures, thermal quality of the habitat, and precision, accuracy, and effectiveness of thermoregulation) that could be compared among fragments and with conspecific populations living in unfragmented habitat. We also measured the selection (use vs. availability) and spatial distribution of sunlit and shaded patches used for behavioral thermoregulation in fragments, and we estimated operative temperatures and thermal habitat quality in the agricultural matrix surrounding the fragments. Variation of the thermal environment was much larger within fragments than among them, and thermoregulation was accurate, precise, and efficient throughout the fragmented landscape; its effectiveness was similar to that of previously studied unfragmented populations. The average distance between sunlit and shaded patches was shorter in deciduous than in evergreen fragments, producing a more clumped distribution of the mosaic of thermal resources. Consequently, in evergreen habitat the cost of thermoregulation was higher, because lizards were more selective in their choice of sunlit sites (i.e. they used sunlit patches closer to shade and refuge than expected at random, and the extent of such selection was larger than at deciduous habitat). Temperatures available in croplands were too high to allow lizard dispersal, at least in the post-breeding season. This result confirms the role of croplands as a thermal barrier that promotes inbreeding and associated fitness losses in isolated fragments, and it forecasts a dark future for populations of forest lizards in agricultural landscapes under the combined effects of habitat fragmentation and global warming.

Impact of extreme weather events on cropland inundation over Indian subcontinent.

Cyclonic storms and extreme precipitation lead to loss of lives and significant damage to land and property, crop productivity, etc. The "Gulab" cyclonic storm formed on the 24th of September 2021 in the Bay of Bengal (BoB), hit the eastern Indian coasts on the 26th of September and caused massive damage and water inundation. This study used Integrated Multi-satellite Retrievals for GPM (IMERG) satellite precipitation data for daily to monthly scale assessments focusing on the "Gulab" cyclonic event. The Otsu's thresholding approach was applied to Sentinel-1 data to map water inundation. Standardized Precipitation Index (SPI) was employed to analyze the precipitation deviation compared to the 20 years mean climatology across India from June to November 2021 on a monthly scale. The water-inundated areas were overlaid on a recent publicly available high-resolution land use land cover (LULC) map to demarcate crop area damage in four eastern Indian states such as Andhra Pradesh, Chhattisgarh, Odisha, and Telangana. The maximum water inundation and crop area damages were observed in Andhra Pradesh (~2700 km2), followed by Telangana (~2040 km2) and Odisha (~1132 km2), and the least in Chhattisgarh (~93.75 km2). This study has potential implications for an emergency response to extreme weather events, such as cyclones, extreme precipitation, and flood. The spatio-temporal data layers and rapid assessment methodology can be helpful to various users such as disaster management authorities, mitigation and response teams, and crop insurance scheme development. The relevant satellite data, products, and cloud-computing facility could operationalize systematic disaster monitoring under the rising threats of extreme weather events in the coming years.

Fertilization regime shifts the molecular diversity and chlorine reactivity of soil dissolved organic matter from tropical croplands.

Soil-derived dissolved organic matter (SDOM) is an important site-specific disinfection byproduct (DBP) precursor in watersheds. However, it remains unclear how fertilization regime shifts the molecular diversity and chlorine reactivity of SDOM in cropland-impacted watersheds. Here, we analyzed the spectroscopic and molecular-level characteristics of the SDOM from croplands that had different fertilization regimes (i.e., non-fertilization, chemical fertilization, straw return, and chemical fertilization plus straw return) for 5 years and evaluated the chlorine reactivity of the SDOM by determining the 24-h chlorine consumption and specific DBP formation potential (SDBP-FP). The SDOM level decreased by chemical fertilization and was not significantly altered by straw return alone or combined with chemical fertilizer. However, all fertilization regimes elevated the molecular diversity of SDOM by increasing the abundance of protein-, lignin-, and tannin-like compounds. The chlorine reactivity of SDOM was reduced by chemical fertilization, but was significantly increased by straw return. Typically, straw return increased the formation potential of specific trihalomethane and chloral hydrate by 339% and 56% via increasing the aromatics in SDOM, whereas chemical fertilization could effectively decrease about 231% of the increased specific trihalomethane formation potential caused by straw return. This study highlights that fertilization regime can significantly shape the molecular diversity and chlorine reactivity of the SDOM in croplands and that partially replacing chemical fertilizer with crop straw is an advantageous practice for reducing DBP risks in drinking water in cropland-impacted watersheds.

Impacts of climate change and evapotranspiration on shrinkage of Aral Sea.

The massive desiccation of the Aral Sea, the fourth largest lake in the world, has led to severe ecological problems, expansion of cropland was thought to be the main factor driving that shrinkage. But this study performed a long-term land cover and use change assessment for Aral Sea Basin (ASB) to show that the cropland has stopped expanding in 2000, of which the cropland in the ASB plain area has decreased significantly (-140 km2/year) from 2001 to 2019. By contrast, this study finds the hydrological cycle in the ASB has intensified through a spatial and temporal scale approach based on Earth observation. Specifically, there is a 7.21 % (+304.56 × 108 m3) increase in annual total precipitation and a 10.13 % (+376.21 × 108 m3) increase in annual total actual evapotranspiration (AET) for the whole ASB during 1980-2019. In particular, the total annual AET in the ASB plain area has increased by 37.81 % (+718.92 × 108 m3), which almost depletes the water that should have flowed into the Aral Sea. Therefore, the Aral Sea shrank by 5625 × 108 m3 (or 42,944.32km2) from 1980 to 2019. Changing climate and increasing AET have accelerated the desiccation of the Aral Sea, and the expansion of cropland is no longer the main factor of that shrinkage. After more water was conserved in the ASB plain area, evapotranspiration plays a more vital role in the Aral Sea shrinkage. Reducing AET and unproductive water losses are key initiatives in future projects to save the Aral Sea. This study explores the causes of Aral Sea shrinkage from an integrated perspective of climate-land-water-ecological change across the ASB, bridging the limitations of previous studies that have focused on Aral Sea waters and subbasins.

Integrating major agricultural practices into the TRIPLEX-GHG model v2.0 for simulating global cropland nitrous oxide emissions: Development, sensitivity analysis and site evaluation.

Nitrous oxide (N2O) emissions from croplands are one of the most important greenhouse gas sources while the estimation of which remains large uncertainties globally. To simulate N2O emissions from global croplands, the process-based TRIPLEX-GHG model v2.0 was improved by coupling the major agricultural activities. Sensitivity experiment was used to measure the impact of the integrated processes to modeled N2O emission found chemical N fertilization have the highest relative effect sizes. While the coefficient of the NO3- consumption rate for denitrification (COEdNO3), controlling the first step of the denitrification process was identified to be the most sensitive parameter based on sensitivity analysis of model parameters. The model performed well when simulating the magnitude of the daily N2O emissions for 39 calibration sites and the continental mean of the parameters were used to producing reasonable estimations for the means of the measured daily N2O fluxes (R2 = 0.87, slope = 1.07) and emission factors (EFs, R2 = 0.70, slope = 0.72) during the experiment periods. The model reliability was further confirmed by model validation. General trend of modeled daily N2O emissions were reasonably consistent with the observations of selected validated sites. In addition, high correlations between the results of modeled and observed mean N2O emissions (R2 = 0.86, slope = 0.82) and EFs (R2 = 0.66, slope = 0.83) from 68 validation sites were obtained. Further improvement on more detailed estimations for the variation of the environmental factors, management effects as well as accurate model input model driving data are required to reduce the uncertainties of model simulations. Consequently, our simulation results demonstrate that the TRIPLEX-GHG model v2.0 can reliably estimate N2O emissions from various croplands at the global scale, which contributes to closing global N2O budget and sustainable development of agriculture.

Using nitrification inhibitors and deep placement to tackle the trade-offs between NH3 and N2 O emissions in global croplands.

Ammonia (NH3 ) and nitrous oxide (N2 O) are two important air pollutants that have major impacts on climate change and biodiversity losses. Agriculture represents their largest source and effective mitigation measures of individual gases have been well studied. However, the interactions and trade-offs between NH3 and N2 O emissions remain uncertain. Here, we report the results of a two-year field experiment in a wheat-maize rotation in the North China Plain (NCP), a global hotspot of reactive N emissions. Our analysis is supported by a literature synthesis of global croplands, to understand the interactions between NH3 and N2 O emissions and to develop the most effective approaches to jointly mitigate NH3 and N2 O emissions. Field results indicated that deep placement of urea with nitrification inhibitors (NIs) reduced both emissions of NH3 by 67% to 90% and N2 O by 73% to 100%, respectively, in comparison with surface broadcast urea which is the common farmers' practice. But, deep placement of urea, surface broadcast urea with NIs, and application of urea with urease inhibitors probably led to trade-offs between the two gases, with a mitigation potential of -201% to 101% for NH3 and -112% to 89% for N2 O. The literature synthesis showed that deep placement of urea with NIs had an emission factor of 1.53%-4.02% for NH3 and 0.22%-0.36% for N2 O, which were much lower than other fertilization regimes and the default values recommended by IPCC guidelines. This would translate to a reduction of 3.86-5.47 Tg N yr-1 of NH3 and 0.41-0.50 Tg N yr-1 of N2 O emissions, respectively, when adopting deep placement of urea with NIs (relative to current practice) in global croplands. We conclude that the combination of NIs and deep placement of urea can successfully tackle the trade-offs between NH3 and N2 O emissions, therefore avoiding N pollution swapping in global croplands.

Temporal Dynamics of Bacterial Communities along a Gradient of Disturbance in a U.S. Southern Plains Agroecosystem.

Land conversion for intensive agriculture produces unfavorable changes to soil ecosystems, causing global concern. Soil bacterial communities mediate essential terrestrial ecosystem processes, making it imperative to understand their responses to agricultural perturbations. Here, we used high-throughput sequencing coupled with a functional gene array to study temporal dynamics of soil bacterial communities over 1 year under different disturbance intensities across a U.S. Southern Plains agroecosystem, including tallgrass prairie, Old World bluestem pasture, no-tillage (NT) canola, and conventional tillage (CT) wheat. Land use had the greatest impact on bacterial taxonomic diversity, whereas sampling time and its interaction with land use were central to functional diversity differences. The main drivers of taxonomic diversity were tillage > sampling time > temperature, while all measured factors explained similar amounts of variations in functional diversity. Temporal differences had the strongest correlation with total nitrogen > rainfall > nitrate. Within land uses, community variations for CT wheat were attributed to nitrogen levels, whereas soil organic matter and soil water content explained community variations for NT canola. In comparison, all measured factors contributed almost equally to variations in grassland bacterial communities. Finally, functional diversity had a stronger relationship with taxonomic diversity for CT wheat compared to phylogenetic diversity in the prairie. These findings reinforce that tillage management has the greatest impact on bacterial community diversity, with sampling time also critical. Hence, our study highlights the importance of the interaction between temporal dynamics and land use in influencing soil microbiomes, providing support for reducing agricultural disturbance to conserve soil biodiversity. IMPORTANCE Agricultural sustainability relies on healthy soils and microbial diversity. Agricultural management alters soil conditions and further influences the temporal dynamics of soil microbial communities essential to ecosystem functions, including organic matter dynamics, nutrient cycling, and plant nutrient availability. Yet, the responses to agricultural management are also dependent on soil type and climatic region, emphasizing the importance of assessing sustainability at local scales. To evaluate the impact of agricultural management practices, we examined bacterial communities across a management disturbance gradient over 1 year in a U.S. Southern Plains agroecosystem and determined that intensive management disturbance and sampling time critically impacted bacterial structural diversity, while their interactive effect influenced functional diversity and other soil health indicators. Overall, this study provides insights into how reducing soil disturbance can positively impact microbial community diversity and soil properties in the U.S. Southern Plains.

Warming-induced greenhouse gas fluxes from global croplands modified by agricultural practices: A meta-analysis.

Climate warming increases the emissions of soil greenhouse gases (GHGs) by stimulating carbon (C) and nitrogen (N) processes in terrestrial ecosystems, contributing to climate change. However, the responses of soil GHG fluxes to warming from global agricultural ecosystems remain unknown. Here, we evaluate the effects of warming on soil GHG fluxes from global croplands under different agro-ecosystems, cropping systems, crop species, and N fertilizer levels, and determine the potential mechanisms through a meta-analysis of field observations. The results showed that warming (+2.0 °C on average) significantly enhanced soil carbon dioxide (CO2) emissions (i.e., soil respiration) by 14.7% and nitrous oxide (N2O) fluxes by 12.6% across croplands and increased soil methane (CH4) uptake by 21.8% in uplands and CH4 release by 23.4% in paddy fields. The responses of C gas fluxes to warming were regulated by initial C substrates, initial wetness, and changes in temperature in croplands. The responses of N2O fluxes to warming were mainly associated with changed NH4+-N and NO3--N as well as initial wetness and N fertilizer in croplands. The responses of soil GHG fluxes to warming were generally comparable among different crop species and N fertilizer levels, respectively. However, the responses of CO2 emissions and CH4 release to warming were significantly higher in upland-paddy fields than in uplands and paddy fields; the warming-induced changes in CH4 release was significantly greater in rotation cropping systems than in single- and double-cropping systems. This synthesis highlights the important role of climate warming in increasing soil GHG fluxes from croplands, underscoring the critical need for agricultural practice adjustment to mitigate climate change in the future.

An integrated assessment on the warming effects of urbanization and agriculture in highly developed urban agglomerations of China.

Urbanization and agriculture, the two major and concurrent land use activities, can dramatically alter land surface temperature (LST) through multiple biophysical processes. However, previous studies mainly focused on the warming effects of urbanization in large cities and/or urban core areas that may greatly underestimate the land use impacts on regional climate. Using natural forest as a reference, we assessed the LST changes of both urbanization and agriculture in the three most developed urban agglomerations of China (Jing-Jin-Ji, JJJ; Yangtze River Delta, YRD; Pearl River Delta, PRD) according to satellite observations. Results show that the urban-dominated lands warm the daytime LST substantially, especially in the south subtropical PRD (with an annual mean intensity of 5.5 °C), and the highest do not occur in the core cities. The crop-dominated lands also warm the daytime LST dramatically, especially in the temperate semi-humid JJJ (with an annual mean intensity of 3.9 °C). The daytime warming effects increase significantly from 2003 to 2018 mainly due to urban expansion in crop-dominated and mixed lands. The two land uses continue to warm the LST at night though in a lower magnitude in the PRD. However, the urban-dominated lands warm the LST slightly and the crop-dominated lands cool the LST substantially at night in the JJJ and YRD. Overall, the crop-dominated and/or mixed lands dominate the regional LST changes owing to their large areas. We further show that the daytime warming effects of the two land uses are likely caused by the changes of evapotranspiration, whereas the nighttime cooling effects might be mainly due to the changes in surface albedo and roughness. Our results highlight the importance of considering the urbanization in small-medium sized satellite cities and the more widespread agricultural activities in rural areas when assessing the regional climate change and formulating the mitigation strategies.

Deciphering the diversity and functions of plastisphere bacterial communities in plastic-mulching croplands of subtropical China.

Considering the inhomogeneity of plastisphere and surrounding soil, it is plausible that the microbial community colonizing it also varies, affecting soil services and sustainability. Herein, we analyzed the soil and film residue from fifty-five plastic-mulching croplands in the subtropical areas of China. Based on the outcomes of this analysis, we explored the diversity and functions of the associated bacterial communities. Alpha-diversity and phylogenetic diversity of the plastisphere bacterial community was significantly lower than the surrounding soil. The average net relatedness and net nearest taxa indices of samples were less than zero. Four phyla and twenty genera were enriched in the plastisphere compared to the surrounding soil. Ecological networks of the plastisphere community showed multiple nodes, but fewer interactions, and the members of Bradyrhizobium, Rhodospirillaceae, and Bacillus were indicated as the hub species. Predicted pathways related to human disease, as well as the metabolisms of cofactors, vitamins, amino acids, and xenobiotic biodegradation, were reinforced in the plastisphere, and meanwhile, accompanied by an increase in abundance of genes related to carbon, nitrogen, and phosphorus cycles. These results demonstrated the diversity and functions of the plastisphere microbiome and highlighted the necessity for exploring the ecological and health risks of plastic residue in croplands.

Spatial heterogeneity of changes in cropland ecosystem water use efficiency and responses to drought in China.

Understanding cropland ecosystem water use efficiency (eWUE) responses to drought is important for sustainable water resource management and food security. Today in China, the spatiotemporal patterns of eWUE and responses to drought across different cropland classes remain poorly quantified. In this study, we characterized the spatial temporal variability in cropland eWUE and response to drought in China from 1982 to 2017 using the satellite-retrieved evapotranspiration (ET), gross primary production (GPP), and self-calibrating Palmer Drought Severity Index (scPDSI), in conjunction with the Global Food Security-support Analysis Data product for Crop Dominance (GFSAD1KCD) data. Results indicated that (1) mean annual cropland eWUE had a spatial range from 0 to 9.94 g C kg-1 H2O, with higher values (2.06 g C kg-1 H2O) in class 4 (rainfed: wheat, rice, and soybeans dominant), whereas the lowest eWUE (1.58 g C kg-1 H2O) occurred in class 2 (irrigated mixed crop 1: wheat, rice, barley, and soybeans). (2) Annual eWUE, GPP, and ET values for croplands in China increased significantly between 1982 and 2017. Class 1 (irrigated wheat and rice) had the highest trend of 0.011 g C kg-1 H2O yr-1, and class 6 (rainfed: corn and soybeans) had the lowest of 0.0007 g C kg-1 H2O yr-1. Apart from class 4, annual GPP and ET were enhanced in most cropland classes from 1982 to 2017 (p<0.01). (3) Rainfed croplands generally had higher eWUE, GPP, and ET values than irrigated croplands. Except for rainfed cropland eWUE, all other cropland variables increased significantly (p<0.001) from 1982 to 2017. (4) Correlation analysis found that the 19.66% (15.62%) of cropland had significant negative (positive) correlations between eWUE and current-year scPDSI. The legacy effects of drought on cropland eWUE indicated that previous and current-year drought impacts on cropland eWUE were in the same direction. Our results provide insights into variability in cropland eWUE and its response to drought in China, where there is a growing demand for agricultural water resource management.

A novel organic carbon accumulation mechanism in croplands in the Yellow River Delta, China.

The trends and mechanisms of organic carbon changes in coastal delta croplands are not yet clear due to the complexity physicochemical processes in soil. In this study, combing powder x-ray diffraction (XRD), microbial analysis, and density functional theory in quantum mechanics, we proposed a novel mechanism underlying OC accumulation. We investigated changes of three kinds of organic carbon (OC)-dissolved organic carbon (DOC), light fraction organic carbon (LFOC), and heavy fraction organic carbon (HFOC) in the Yellow River Delta croplands. We found that HFOC, dominant in coastal delta cropland soil, formed at different ages and its density increased with increasing reclamation time. Yet, DOC and LFOC had no significant increase or decrease tendency. Moreover, in coastal delta croplands, HFOC accumulation might be a complex progress, including the loss of indigenous OC and the accumulation of newly input OC. Based on these results, we proposed that although root exudative DOC (organic acids) could cause the indigenous OC loss by forming a specific microbial community, it still was a source of HFOC and promoted the OC accumulation. More importantly, based on density functional theory, we verified that these root exudative organic acids could adsorb on SiO2 together with crystalline Fe oxides (Fec) to form aggregates. The finding could explain the phenomenon that the XRD results showed samples were compounds of SiO2, Fec, and OC and the accumulation of HFOC in coastal delta croplands. By revealing a new OC accumulation mechanism in coastal delta croplands, this study provides novel insights into the mechanism of OC dynamics in coastal delta croplands and the global carbon budget.

Comprehensive quantification of global cropland ammonia emissions and potential abatement.

Ammonia (NH3) emissions mostly from agriculture result in air pollution and degrade human health. However, a full picture of soil NH3 emissions and associated abatement in cropping systems are not well understood. Here we present a thorough analysis of cropland NH3 emissions, discuss mitigation potential and assess associated abatement costs. Global cropland NH3 emissions account for 26% of total soil nitrogen losses, and are estimated as 22.8-31.2 Tg N yr-1 during 1996-2013 with the increase rate of 1.6% yr-1. Our results also show that, with no increase in nitrogen fertilizer, climate change can contribute to an additional 10% increase in cropland NH3 emissions in 2100 compared to the 2010 baseline. Instead, our scenario analysis show, cropland NH3 emissions will decline by 26% from 2010 to 2100 given a 0.5% yr-1 decrease in N fertilizer (with current technology and agricultural management level), considering the facts stronger control policies are expected to occur worldwide including Western Europe, the United States of America and China. The most ambitious management (with all known mitigation practices) can reduce cropland NH3 emissions by up (71%, 17.6 Tg N yr-1) at an abatement cost of US$524 billion. Our findings indicate that cropland NH3 emissions can be mitigated through adoption of appropriate human management practices with considerable economic costs, providing a critical reference for the future NH3 abatement strategies.

Cropland nitrogen dioxide emissions and effects on the ozone pollution in the North China plain.

Soil nitrogen dioxide (NOX = NO2 + NO) emissions have been measured and estimated to be the second most significant contributor to the NOX burden following the fossil fuel combustion source globally. NOX emissions from croplands are subject to being underestimated or overlooked in air pollution simulations of regional atmospheric chemistry models. With constraints of ground and space observations of NO2, the WRF-Chem model is used to investigate the cropland NOX emission and its contribution to the near-surface ozone (O3) pollution in North China Plain (NCP) during a growing season as a case study. Model simulations have revealed that the cropland NOX emissions are underestimated by around 80% without constraints of satellite measured NO2 column densities. The biogenic NOX source is estimated to account for half of the anthropogenic NOX emissions in the NCP during the growing season. Additionally, the cropland NOX source contributes around 5.0% of the maximum daily average 8h O3 concentration and 27.7% of NO2 concentration in the NCP. Our results suggest the agriculture NOX emission exerts non-negligible impacts on the summertime air quality and needs to be considered when designing emission abatement strategies.