Phosphorus limitation on CO_(2)fertilization effect in tropical forests informed by a coupled biogeochemical model

Tropical forests store more than half of the world's terrestrial carbon(C)pool and account for one-third of global net primary productivity(NPP).Many terrestrial biosphere models(TBMs)estimate increased productivity in tropical forests throughout the 21st century due to CO_(2)fertilization.However,phosphorus(P)liaitations on vegetation photosynthesis and productivity could significantly reduce the CO_(2)fertilization effect.Here,we used a carbon-nitrogen-phosphorus coupled model(Dynamic Land Ecosystem Model;DLEM-CNP)with heterogeneous maximum carboxylation rates to examine how P limitation has affected C fluxes in tropical forests during1860-2018.Our model results showed that the inclusion of the P processes enhanced model performance in simulating ecosystem productivity.We further compared the simulations from DLEM-CNP,DLEM-CN,and DLEMC and the results showed that the inclusion of P processes reduced the CO_(2)fertilization effect on gross primary production(GPP)by 25%and 45%,and net ecosystem production(NEP)by 28%and 41%,respectively,relative to CN-only and C-on ly models.From the 1860s to the 2010s,the DLEM-CNP estimated that in tropical forests GPP increased by 17%,plant respiration(Ra)increased by 18%,ecosystem respiration(Rh)increased by 13%,NEP increased by 121%per unit area,respectively.Additionally,factorial experiments with DLEM-CNP showed that the enhanced NPP benefiting from the CO_(2) fertilization effect had been offset by 135%due to deforestation from the 1860s to the 2010s.Our study highlights the importance of P limitation on the C cycle and the weakened CO_(2)fertilization effect resulting from P limitation in tropical forests.

Global pattern and change of cropland soil organic carbon during 1901-2010: Roles of climate, atmospheric chemistry, land use and management

Soil organic carbon(SOC)in croplands is a key property of soil quality for ensuring food security and agricultural sustainability,and also plays a central role in the global carbon(C)budget.When managed sustainably,soils may play a critical role in mitigating climate change by sequestering C and decreasing greenhouse gas emissions into the atmosphere.However,the magnitude and spatio-temporal patterns of global cropland SOC are far from well constrained due to high land surface heterogeneity,complicated mechanisms,and multiple influencing factors.Here,we use a process-based agroecosystem model(DLEM-Ag)in combination with diverse spatially-explicit gridded environmental data to quantify the long-term trend of SOC storage in global cropland area during 1901-2010 and identify the relative impacts of climate change,elevated CO2,nitrogen deposition,land cover change,and land management practices such as nitrogen fertilizer use and irrigation.Model results show that the total SOC and SOC density in the 2000s increased by 125%and 48.8%,respectively,compared to the early 20th century.This SOC increase was primarily attributed to cropland expansion and nitrogen fertilizer use.Factorial analysis suggests that climate change reduced approximately 3.2%(or 2,166 Tg C)of the total SOC over the past 110 years.Our results indicate that croplands have a large potential to sequester C through implementing better land use management practices,which may partially offset SOC loss caused by climate change.

Global convergence in terrestrial gross primary production response to atmospheric vapor pressure deficit

Atmospheric vapor pressure deficit(VPD)increases with climate warming and may limit plant growth.However,gross primary production(GPP)responses to VPD remain a mystery,offering a significant source of uncertainty in the estimation of global terrestrial ecosystems carbon dynamics.In this study,in-situ measurements,satellite-derived data,and Earth System Models(ESMs)simulations were analysed to show that the GPP of most ecosystems has a similar threshold in response to VPD:first increasing and then declining.When VPD exceeds these thresholds,atmospheric drought stress reduces soil moisture and stomatal conductance,thereby decreasing the productivity of terrestrial ecosystems.Current ESMs underscore CO_(2) fertilization effects but predict significant GPP decline in low-latitude ecosystems when VPD exceeds the thresholds.These results emphasize the impacts of climate warming on VPD and propose limitations to future ecosystems productivity caused by increased atmospheric water demand.Incorporating VPD,soil moisture,and canopy conductance interactions into ESMs enhances the prediction of terrestrial ecosystem responses to climate change.

Response patterns of simulated corn yield and soil nitrous oxide emission to precipitation change

Background Precipitation plays an important role in crop production and soil greenhouse gas emissions.However,how crop yield and soil nitrous oxide(N_(2)O)emission respond to precipitation change,particularly with different background precipitations(dry,normal,and wet years),has not been well investigated.In this study,we examined the impacts of precipitation changes on corn yield and soil N_(2)O emission using a long-term(1981-2020,40 years)climate dataset as well as seven manipulated precipitation treatments with different background precipitations using the DeNitrification-DeComposition(DNDC)model.Results Results showed large variations of corn yield and precipitation but small variation of soil N_(2)O emission among 40 years.Both corn yield and soil N_(2)O emission showed near linear relationships with precipitation based on the long-term precipitation data,but with different response patters of corn yield and soil N_(2)O emission to precipitation manipulations.Corn yield showed a positive linear response to precipitation manipulations in the dry year,but no response to increases in precipitation in the normal year,and a trend of decrease in the wet year.The extreme drought treatments reduced corn yield sharply in both normal and wet years.In contrast,soil N_(2)O emission mostly responded linearly to precipitation manipulations.Decreases in precipitation in the dry year reduced more soil N_(2)O emission than those in the normal and wet years,while increases in precipitation increased more soil N_(2)O emission in the normal and wet years than in the dry year.Conclusions This study revealed different response patterns of corn yield and soil N_(2)O emission to precipitation and highlights that mitigation strategy for soil N_(2)O emission reduction should consider different background climate conditions.

Recent leveling off of vegetation greenness and primary production reveals the increasing soil water limitations on the greening Earth

Global vegetation photosynthesis and productivity have increased substantially since the 1980s,but this trend is heterogeneous in both time and space.Here,we categorize the secular trend in global vegetation greenness into sustained greening,sustained browning and greening-to-browning.We found that by 2016,increased global vegetation greenness had begun to level off,with the area of browning increasing in the last decade,reaching 39.0 million km^(2)(35.9%of the world’s vegetated area).This area is larger than the area with sustained increasing growth(27.8 million km^(2),26.4%);thus,12.0%±3.1%(0.019±0.004 NDVI a^(-1))of the previous earlier increase has been offset since 2010(2010–2016,P<0.05).Global gross primary production also leveled off,following the trend in vegetation greenness in time and space.This leveling off was caused by increasing soil water limitations due to the spatial expansion of drought,whose impact dominated over the impacts of temperature and solar radiation.This response of global gross primary production to soil water limitation was not identified by land submodels within Earth system models.Our results provide empirical evidence that global vegetation greenness and primary production are offset by water stress and suggest that as global warming continues,land submodels may overestimate the world’s capacity to take up carbon with global vegetation greening.

Global methane and nitrous oxide emissions from terrestrial ecosystems due to multiple environmental changes

Greenhouse gas(GHG)-induced climate change is among the most pressing sustainability challenges facing humanity today,posing serious risks for ecosystem health.Methane(CH_(4))and nitrous oxide(N_(2)O)are the two most important GHGs after carbon dioxide(CO_(2)),but their regional and global budgets are not well known.In this study,we applied a process-based coupled biogeochemical model to concurrently estimate the magnitude and spatial and temporal patterns of CH_(4)and N_(2)O fluxes as driven by multiple environmental changes,including climate variability,rising atmospheric CO_(2),increasing nitrogen deposition,tropospheric ozone pollution,land use change,and nitrogen fertilizer use.The estimated CH_(4)and N_(2)O emissions from global land ecosystems during 1981-2010 were 144.39±12.90 Tg C/yr(mean 62 SE;1 Tg=1012 g)and 12.52±0.74 Tg N/yr,respectively.Our simulations indicated a significant(P,0.01)annually increasing trend for CH_(4)(0.43±0.06 Tg C/yr)and N_(2)O(0.14±0.02 Tg N/yr)in the study period.CH_(4)and N_(2)O emissions increased significantly in most climatic zones and continents,especially in the tropical regions and Asia.The most rapid increase in CH_(4)emission was found in natural wetlands and rice fields due to increased rice cultivation area and climate warming.N_(2)O emission increased substantially in all the biome types and the largest increase occurred in upland crops due to increasing air temperature and nitrogen fertilizer use.Clearly,the three major GHGs(CH_(4),N_(2)O,and CO_(2))should be simultaneously considered when evaluating if a policy is effective to mitigate climate change.

Climate change induced eutrophication of cold-water lake in an ecologically fragile nature reserve

Aquatic ecosystem sustainability around the globe is facing crucial challenges because of increasing anthropogenic and natural disturbances. In this study, the Tianchi Lake, a typical cold-water lake and a UNESCO/MAB(Man and Biosphere) nature reserve located in high latitude and elevation with the relatively low intensity of human activity was chosen as a system to examine the linkages between climate change and eutrophication. As a part of the UNESCO Bogda Man and Biosphere Reserve, Tianchi Lake has been well preserved for prevention from human intervention, but why has it been infected with eutrophication recent years? Our results show that climate change played a significant role in the eutrophication in the Tianchi Lake. Increased temperature, changed precipitation pattern and wind-induced hydrodynamic fluctuations in the summer season were suggested to make a major contribution to the accelerated eutrophication. The results also showed that the local temperature and precipitation changes were closely linked to the large-scale atmospheric circulation, which opens the door for the method to be applied in other regions without local climatic information. This study suggests that there is an urgent need to take into consideration of climate change adaptation into the conservation and management of cold-water lakes globally.

Industrial land expansion in rural China threatens environmental securities

China’s rural industrialization has been a major driver for its rapid economic growth during the recent decades,but its myriad environmental risks are yet to be fully understood.Based on a comprehensive national land-use data set,our study shows that the area of China’s rural industrial land(RIL)quadrupled during 1990–2015,reaching 39338 km2 in 2015,comparable to urbanization in magnitude but with a much greater degree of landscape fragmentation which implies stronger ecological and environmental impacts.About 91%of the protected areas in the central China were within 50 km from rural industrial land,thus exposed to industrial disturbances.Accelerated rural industrial land expansion,particularly in regions under high geo-hazard risks,led to dramatically increased environmental risks,threatening the safety and health of both rural industrial workers and residents.Moreover,negative effects from rural industrial land expansion could partially offset the crop production growth in recent decades.The underprivileged rural population in the west bears a disproportionally large share of the increased environmental risks.China urgently needs to design and implement sustainable policies to restrict and reshape its rural industrialization.This study aims to inspire policy makers and researchers to rethink the current model of industrial expansion and improve rural industrial land planning,which is important for achieving the sustainable development goals of China.

Spatiotemporal variations of carbon flux and nitrogen deposition flux linked with climate change at the centennial scale in China

The spatial and temporal variations of the vegetation carbon flux in China from 1901 to 2005 were studied using the vegetation net primary production(NPP)values from seven Earth-system models.In addition,the temporal and spatial changes in the nitrogen deposition flux in China were studied using the NHx and NOy fluxes from 1901 to 2005.The relationship between changes in the carbon flux,nitrogen flux and climate was analyzed.The results show that(1)over the past 100 years,NPP in China has shown an upward trend.The average trend coefficient is 0.88 and the NPP distribution trend is generally low in the north and high in the south,with a gradual increase from the northwest to the southeast.Temperature,precipitation and radiation are all conducive to plant growth in the direction of the gradient.The correlation coefficients between the ensemble model mean NPP and temperature,precipitation,longwave radiation and shortwave radiation are 0.88,0.73,0.91 and 0.67,respectively.(2)In the past 100 years,the NHx and NOy fluxes in China have shown an upward trend,with trend coefficients of 0.98 and 0.98,respectively,which pass the 99.9%confidence level of the t-test.NHx and NOy fluxes are also generally low in the north and high in the south,with a gradual increase from the northwest to the southeast in a step-like pattern.(3)The spatial distribution of the correlation coefficients between the NHx and NOy fluxes and air temperature is similar,with only slight differences in values.The spatial distribution of the correlation coefficients between the NHx and NOy fluxes and precipitation is similar in overall pattern,but the pattern is relatively complicated,with a positive-negative-positive-negative-positive pattern occurring across the monsoon region from north to south,and a negative-positive-negative-positive pattern occurring beyond the monsoon region from east to west.(4)The spatial distribution of the correlation coefficients between the NHx and NOy fluxes and NPP shows a generally consistent pattern,but the pattern is relatively uneven.The average distribution of the ensemble model mean is positive correlation in northeast China and southwest China,and alternating positive and negative correlation in other regions.

Climate extremes and ozone pollution:a growing threat to China’s food security

Ensuring global food security requires a sound understanding of climate and environmental controls on crop productivity.The majority of existing assessments have focused on physical climate vari-ables(i.e.,mean temperature and precipitation),but less on the increasing climate extremes(e.g.,drought)and their interactions with increasing levels of tropospheric ozone(O3).Here we quantify the combined impacts of drought and O3 on China’s crop yield using a comprehensive,process-based agricultural eco-system model in conjunction with observational data.Our results indicate that climate change/variability and O3 together led to an annual mean reduction of crop yield by 10.0%or 55 million tons per year at the national level during 1981-2010.Crop yield shows a growing threat from severe episodic droughts and in-creasing O3 concentrations since 2000,with the largest crop yield losses occurring in northern China,causing serious concerns in food supply security in China.Our results imply that reducing tropospheric O3 levels is critical for securing crop production in coping with increasing frequency and severity of extreme climate events such as droughts.Improving air quality should be a core component of climate adaptation strategies.

Methane emissions from livestock in East Asia during 1961−2019

Context:East Asia is a crucial region in the global methane(CH4)budget,with significant contributions from the livestock sector.However,the long-term trend and spatial pattern of CH4 emissions from livestock in this region have not been fully assessed.Methods:Here,we estimate CH4 emissions from 10 categories of livestock in East Asia during 1961-2019 following the Tier 2 approaches suggested by the 2019 Refinement to the IPCC 2006 Guidelines.Results:livestock-sourced CH4 emission in 2019 was 13.22[11.42-15.01](mean[minimum%maximum of 95-confidence interval]Tg CH4 yr-1,accounting for an increase of 231%since 1961.The contribution of slaughtered populations to total emissions increased from 3%in 1961 to 24%in 2019.Spatially,the emission hotspots were mostly distributed in eastern China,South Korea,and parts of Japan,but they tend to shift northward after 2000.Conclusion:It is necessary to use dynamic emission factors and include slaughtered populations in the estimation of livestock CH4 emissions.Regions including Northern China,Mongolia,and South Korea deserve more attention in future CH4 mitigation efforts.

Responses of global terrestrial water use efficiency to climate change and rising atmospheric CO_(2)concentration in the twenty-first century

Terrestrial ecosystems play a significant role in global carbon and water cycles because of the substantial amount of carbon assimilated through net primary production and large amount of water loss through evapotranspiration(ET).Using a process-based ecosystem model,we investigate the potential effects of climate change and rising atmospheric CO_(2)concentration on global terrestrial ecosystem water use efficiency(WUE)during the twenty-first century.Future climate change would reduce global WUE by 16.3%under high-emission climate change scenario(A2)and 2.2%under low-emission climate scenario(B1)during 2010–2099.However,the combination of rising atmospheric CO_(2)concentration and climate change would increase global WUE by 7.9%and 9.4%under A2 and B1 climate scenarios,respectively.This suggests that rising atmospheric CO_(2)concentration could ameliorate climate change-induced WUE decline.Future WUE would increase significantly at the high-latitude regions but decrease at the low-latitude regions under combined changes in climate and atmospheric CO_(2).The largest increase of WUE would occur in tundra and boreal needleleaf deciduous forest under the combined A2 climate and atmospheric CO_(2)scenario.More accurate prediction of WUE requires deeper understanding on the responses of ET to rising atmospheric CO_(2)concentrations and its interactions with climate.

Interaction between pollution and climate change augments ecological risk to a coastal ecosystem

Pollution and climate change are among the most challenging issues for countries with developing economies,but we know little about the ecological risks that result when these pressures occur together.We explored direct effects of,and interactions between,environmental pollution and climate change on ecosystem health in the Bohai Sea region of Northern China.We developed an integrated approach to assess ecological risks to this region under four scenarios of climate change.Although ecological risks to the system from pollution alone have been declining,interactions between pollution and climate change have enhanced ecological risks to this coastal/marine ecosystem.Our results suggest that current policies focused strictly on pollution control alone should be changed to take into account the interactive effects of climate change so as to better forecast and manage potential ecological risks.

Recent patterns of terrestrial net primary production in Africa influenced by multiple environmental changes

Terrestrial net primary production(NPP)is of fundamental importance to food security and ecosystem sustainability.However,little is known about how terrestrial NPP in African ecosystems has responded to recent changes in climate and other environmental factors.Here,we used an integrated ecosystem model(the dynamic land ecosystem model;DLEM)to simulate the dynamic variations in terrestrial NPP of African ecosystems driven by climate and other environmental factors during 1980-2009.We estimate a terrestrial NPP of 10.22(minimum-maximum range of 8.9-11.3)Pg C/yr during the study period.Our results show that precipitation variability had a significant effect on terrestrial NPP,explaining 74%of interannual variations in NPP.Over the 30-yr period,African ecosystems experienced an increase in NPP of 0.03 Pg C/yr,resulting from the combined effects of climate variability,elevated atmospheric CO_(2)concentration,and nitrogen deposition.Our further analyses show that there is a difference in NPP of 1.6 Pg C/yr between wet and dry years,indicating that interannual climatic variations play an important role in determining the magnitude of terrestrial NPP.Central Africa,dominated by tropical forests,was the most productive region and accounted for 50%of the carbon sequestered as NPP in Africa.Our results indicate that warmer and wetter climatic conditions,together with elevated atmospheric CO_(2)concentration and nitrogen deposition,have resulted in a significant increase in African terrestrial NPP during 1980-2009,with the largest contribution from tropical forests.