• Energy Research

Excessive nitrogen fertilizer application in greenhouses could cause a significant variation in the nitrogen-use efficiency at the regional scale. This study aims to quantify agronomic nitrogen-use efficiency (AEN) and identify its driving factors across Chinese greenhouse tomato cultivation. Three hundred and forty-eight AEN values were obtained from 64 papers, including mineral nitrogen (MN) and mineral combined with organic nitrogen (MON) treatments. The average AEN values for the MN and MON treatments were 56.6 ± 7.0 kg kg−1 and 34.6 ± 3.5 kg kg−1, respectively. The AEN of the MN treatment was higher than that of the MON treatment for cultivation using soil with an organic matter content of less than 10 g kg−1 and the drip fertigation method. The AENs of the MN and MON treatments were divided into two segments according to the nitrogen application rate. The inflection points of the nitrogen application rate were 290 and 1100 kg N ha−1 for the MN and MON treatments, respectively. When the ratio of organic nitrogen to total nitrogen was less than 0.4, it was beneficial for improving the AEN. The soil organic matter content and the nitrogen application rate were the most critical factors determining the AEN. These results suggest that rationally reducing the nitrogen input and partially substituting mineral nitrogen with organic nitrogen can help improve the nitrogen-use efficiency.

Excessive nitrogen fertilizer application in greenhouses could cause a significant variation in the nitrogen-use efficiency at the regional scale. This study aims to quantify agronomic nitrogen-use efficiency (AEN) and identify its driving factors across Chinese greenhouse tomato cultivation. Three hundred and forty-eight AEN values were obtained from 64 papers, including mineral nitrogen (MN) and mineral combined with organic nitrogen (MON) treatments. The average AEN values for the MN and MON treatments were 56.6 ± 7.0 kg kg−1 and 34.6 ± 3.5 kg kg−1, respectively. The AEN of the MN treatment was higher than that of the MON treatment for cultivation using soil with an organic matter content of less than 10 g kg−1 and the drip fertigation method. The AENs of the MN and MON treatments were divided into two segments according to the nitrogen application rate. The inflection points of the nitrogen application rate were 290 and 1100 kg N ha−1 for the MN and MON treatments, respectively. When the ratio of organic nitrogen to total nitrogen was less than 0.4, it was beneficial for improving the AEN. The soil organic matter content and the nitrogen application rate were the most critical factors determining the AEN. These results suggest that rationally reducing the nitrogen input and partially substituting mineral nitrogen with organic nitrogen can help improve the nitrogen-use efficiency.

AbstractDetection and identification of the impacts of climate change on ecosystems have been core issues in climate change research in recent years. In this study, we compared average annual values of the normalized difference vegetation index (NDVI) with theoretical net primary productivity (NPP) values based on temperature and precipitation to determine the effect of historic climate change on global grassland productivity from 1982 to 2011. Comparison of trends in actual productivity (NDVI) with climate-induced potential productivity showed that the trends in average productivity in nearly 40% of global grassland areas have been significantly affected by climate change. The contribution of climate change to variability in grassland productivity was 15.2–71.2% during 1982–2011. Climate change contributed significantly to long-term trends in grassland productivity mainly in North America, central Eurasia, central Africa, and Oceania; these regions will be more sensitive to future climate change impacts. The impacts of climate change on variability in grassland productivity were greater in the Western Hemisphere than the Eastern Hemisphere. Confirmation of the observed trends requires long-term controlled experiments and multi-model ensembles to reduce uncertainties and explain mechanisms.

AbstractDetection and identification of the impacts of climate change on ecosystems have been core issues in climate change research in recent years. In this study, we compared average annual values of the normalized difference vegetation index (NDVI) with theoretical net primary productivity (NPP) values based on temperature and precipitation to determine the effect of historic climate change on global grassland productivity from 1982 to 2011. Comparison of trends in actual productivity (NDVI) with climate-induced potential productivity showed that the trends in average productivity in nearly 40% of global grassland areas have been significantly affected by climate change. The contribution of climate change to variability in grassland productivity was 15.2–71.2% during 1982–2011. Climate change contributed significantly to long-term trends in grassland productivity mainly in North America, central Eurasia, central Africa, and Oceania; these regions will be more sensitive to future climate change impacts. The impacts of climate change on variability in grassland productivity were greater in the Western Hemisphere than the Eastern Hemisphere. Confirmation of the observed trends requires long-term controlled experiments and multi-model ensembles to reduce uncertainties and explain mechanisms.

Understanding the responses of soil nitrous oxide (N2O) emissions from terrestrial ecosystems to future CO2enrichment and warming is critical for the development of mitigation and adaptation policies. The effects of continuous increase in elevated CO2(EC) and elevated temperature (ET) on N2O emissions are not fully known. We synthesized 209 measurements from 70 published studies and carried out a meta‐analysis to examine individual and interactive effects of EC and ET on N2O emissions from grasslands, croplands and forests. On average, a significant increase of 23% in N2O emissions was observed under EC across all case studies. EC did not affect N2O emissions from grasslands or forests, but significantly increased N2O emissions in croplands by 38%. The extent of ET effects on N2O emissions was nonsignificant and there was no significant difference in N2O emission responses among these three terrestrial systems. ET only promoted N2O emissions in forest by about 32% when ET was less than 2°C. The interactive effect of EC and ET on N2O emissions was significantly synergistic, showing a greater increase than the sum of the effects caused by EC and ET alone. Our findings indicated that the combination of EC and ET substantially promoted soil N2O and highlighted the urgent need to explore its mechanisms to better understand N2O responses under future climate change.

Understanding the responses of soil nitrous oxide (N2O) emissions from terrestrial ecosystems to future CO2enrichment and warming is critical for the development of mitigation and adaptation policies. The effects of continuous increase in elevated CO2(EC) and elevated temperature (ET) on N2O emissions are not fully known. We synthesized 209 measurements from 70 published studies and carried out a meta‐analysis to examine individual and interactive effects of EC and ET on N2O emissions from grasslands, croplands and forests. On average, a significant increase of 23% in N2O emissions was observed under EC across all case studies. EC did not affect N2O emissions from grasslands or forests, but significantly increased N2O emissions in croplands by 38%. The extent of ET effects on N2O emissions was nonsignificant and there was no significant difference in N2O emission responses among these three terrestrial systems. ET only promoted N2O emissions in forest by about 32% when ET was less than 2°C. The interactive effect of EC and ET on N2O emissions was significantly synergistic, showing a greater increase than the sum of the effects caused by EC and ET alone. Our findings indicated that the combination of EC and ET substantially promoted soil N2O and highlighted the urgent need to explore its mechanisms to better understand N2O responses under future climate change.

Pour analyser les flux de CO2 dans des conditions de changement climatique dans une prairie alpine du plateau central Qinghai-Tibétain, nous avons simulé l'effet du réchauffement à l'aide de chambres à ciel ouvert (OTC) de 2012 à 2014. Les OTC ont augmenté la température du sol de 1,62 °C (P 0,05) et a augmenté de manière significative en 2014 (P = 0,034) dans des conditions de réchauffement. La PEG était plus sensible aux variations climatiques que l'ER, ce qui a entraîné une forte augmentation de l'absorption nette de carbone en cas de réchauffement dans la prairie alpine. En cas de réchauffement, les moyennes sur 3 ans de PEG, ER et NEE ont augmenté de 19,6 %, 15,1 % et 21,1 %, respectivement. Les modèles dynamiques saisonniers de PEG et de NEE, mais pas de RE, ont été significativement impactés par le réchauffement. La biomasse aérienne, en particulier la biomasse graminoïde, a augmenté de manière significative dans des conditions de réchauffement. L'humidité du sol, la température du sol et la biomasse aérienne ont été les principaux facteurs qui ont affecté la variation des flux de CO2 de l'écosystème. L'effet du réchauffement sur les schémas inter et intra-annuels des flux de CO2 des écosystèmes et le mécanisme des différentes sensibilités de la PEG et du RE au réchauffement nécessitent des recherches plus approfondies. Para analizar los flujos de CO2 en condiciones de cambio climático en una pradera alpina en la meseta central de Qinghai-Tibetan, simulamos el efecto del calentamiento utilizando cámaras abiertas (OTC) de 2012 a 2014. Los OTC aumentaron la temperatura del suelo en 1,62 °C (P 0,05) y aumentó significativamente en 2014 (P = 0,034) en condiciones de calentamiento. El GEP fue más sensible a las variaciones climáticas que el ER, lo que resultó en un gran aumento en la absorción neta de carbono bajo el calentamiento en el prado alpino. Bajo el calentamiento, los promedios de 3 años de GEP, ER y NEE aumentaron en un 19.6%, 15.1% y 21.1%, respectivamente. Los patrones dinámicos estacionales de GEP y NEE, pero no de ER, se vieron significativamente afectados por el calentamiento. La biomasa superficial, en particular la biomasa graminoide, aumentó significativamente en condiciones de calentamiento. La humedad del suelo, la temperatura del suelo y la biomasa aérea fueron los principales factores que afectaron la variación de los flujos de CO2 del ecosistema. El efecto del calentamiento en los patrones inter e intraanuales de los flujos de CO2 del ecosistema y el mecanismo de las diferentes sensibilidades en GEP y ER al calentamiento, requieren más investigación. لتحليل تدفقات ثاني أكسيد الكربون في ظل ظروف تغير المناخ في مرج جبال الألب على هضبة تشينغهاي- التبت الوسطى، قمنا بمحاكاة تأثير الاحترار باستخدام الغرف العلوية المفتوحة (OTCs) من عام 2012 إلى عام 2014. زادت OTCS درجة حرارة التربة بمقدار 1.62 درجة مئوية (P 0.05)، وزاد بشكل كبير في عام 2014 (P = 0.034) في ظل ظروف الاحترار. كانت السياسة البيئية العالمية أكثر حساسية للتغيرات المناخية مما كانت عليه السياسة البيئية، مما أدى إلى زيادة كبيرة في صافي امتصاص الكربون في ظل الاحترار في مرج جبال الألب. في ظل الاحتباس الحراري، ارتفعت متوسطات 3 سنوات لكل من السياسة البيئية العالمية، و سياسة الطاقة المتجددة، و سياسة الطاقة الجديدة بنسبة 19.6 ٪، و 15.1 ٪، و 21.1 ٪ على التوالي. تأثرت الأنماط الديناميكية الموسمية للمساواة بين الجنسين و NEE، ولكن ليس ER، بشكل كبير بالاحترار. زادت الكتلة الحيوية فوق الأرض، وخاصة الكتلة الحيوية الجرامينية بشكل كبير في ظل ظروف الاحترار. كانت رطوبة التربة ودرجة حرارة التربة والكتلة الحيوية فوق الأرض هي العوامل الرئيسية التي أثرت على تباين تدفقات ثاني أكسيد الكربون في النظام البيئي. يتطلب تأثير الاحترار على الأنماط بين وداخل السنة لتدفقات ثاني أكسيد الكربون في النظام الإيكولوجي وآلية الحساسيات المختلفة في سياسة المساواة بين الجنسين والاستجابة لحالات الطوارئ للاحترار مزيدًا من البحث. To analyze CO2 fluxes under conditions of climate change in an alpine meadow on the central Qinghai-Tibetan Plateau, we simulated the effect of warming using open top chambers (OTCs) from 2012 to 2014. The OTCs increased soil temperature by 1.62°C (P 0.05), and increased significantly in 2014 (P = 0.034) under conditions of warming. The GEP was more sensitive to climate variations than was the ER, resulting in a large increase in net carbon uptake under warming in the alpine meadow. Under warming, the 3-year averages of GEP, ER, and NEE increased by 19.6%, 15.1%, and 21.1%, respectively. The seasonal dynamic patterns of GEP and NEE, but not ER, were significantly impacted by warming. Aboveground biomass, particularly the graminoid biomass increased significantly under conditions of warming. Soil moisture, soil temperature, and aboveground biomass were the main factors that affected the variation of the ecosystem CO2 fluxes. The effect of warming on inter- and intra-annual patterns of ecosystem CO2 fluxes and the mechanism of different sensitivities in GEP and ER to warming, require further researched.