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.

Analysis on the Growth Rhythm and Cold Tolerance of Five-Year Old <i>Eucalyptus benthamii</i>Plantation for Bioenergy

A research plot of Eucalyptus benthamii was planted to evaluate this species’ ability to supply the emerging bioenergy markets that are developing in the southern U.S. The plot was planted in two different densities to investigate the growth parameters and the cold tolerance. The stand was measured annually through five growing seasons. The results indicated that the growth difference among the young E. benthamii was noticeable. For example, the maximum and minimum value of five-year old trees at diameter breast height (DBH) was 27.9 centimeters and 1.27 centimeters;and the maximum and minimum value of tree height was 22.86 meters and 2.44 meters, respectively. The yearly change in DBH and height of E. benthamii had significant differences. The average annual survival rates of E. benthamii had differences under the two planting densities (1650 trees ha-1 and 1237 trees ha-1). The densities also had effects on the height and DBH growth of E. benthamii. The average DBH and height of 1650 trees ha-1 plantation were 11.18 centimeters and 15.03 meters, and the average DBH and height of 1237 trees ha-1 plantation were 13.46 centimeters and 16.28 meters. The volume per hectare of 1650 trees ha-1 and 1237 trees ha-1 plantation were 111.45 cubic meters and 101.15 cubic meters, respectively. Average diameter growth was almost 2.54 centimeters per year and average height growth was over 3 meters. E. benthamii plantations were considered tolerant to -7.4 degrees Celsius and a cold spell during early 2014 (-11.3 degrees Celsius for two consecutive nights) killed the plantation. The growth of E. benthamii also varied depending on surrounding conditions. The difference in growth of row seven versus row one was a good example. The reason probably was that row seven was adjacent to a loblolly pine plantation and row one was next to an open field.

Effect of genetic sources on anatomical, morphological,and mechanical properties of 14-year-old genetically improved loblolly pine families from two sites in the southern United States

Tree improvement programs on loblolly pine(Pinus taeda) in the southeastern USA has focused primarily on improving growth, form, and disease tolerance.However, due to the recent reduction of design values for visually graded southern yellow pine lumber(including loblolly pine), attention has been drawn to the material quality of genetically improved loblolly pine. In this study,we used the time-of-flight(TOF) acoustic tool to assess the effect of genetic families on diameter, slenderness, fiber length, microfibril angle(MFA), velocity and dynamic stiffness estimated using green density(DMOEG) and basic density(DMOEB) of 14-year-old loblolly pine stands selected from two sites. All the 184 and 204 trees of the selected eight half-sib genetic families on sites 1 and 2 respectively were tested using TOF acoustic tool, and two 5 mm core samples taken at breast height level(1.3 m)used to for the anatomical and physical properties analysis.The results indicated a significant positive linear relationship between dynamic MOEs(DMOEGand DMOEB)versus tree diameter, slenderness, and fiber length while dynamic MOEs negatively but nonsignificant correlated with MFA. While there was no significant difference in DMOEBbetween sites; velocity 2 for site 1 was significantly higher than site 2 but DMOEGwas higher for site 2 than site 1. Again, the mean DMOEGand DMOEBreported in the present study presents a snapshot of the expected static MOE for green and 12% moisture conditions respectively for loblolly pine. Furthermore, there were significant differences between families for most of the traits measured and this suggests that forest managers have the opportunity to select families that exhibit the desired fiber morphology for final product performance. Lastly,since the dynamic MOE based on green density(DMOEG),basic density(DMOEB) and velocity 2 present difference conclusions, practitioners of this type of acoustic technique should take care when extrapolating results across the sites.

Influence of Residual Basal Area on Longleaf Pine (<i>Pinus palustris</i>Mill.) First Year Germination and Establishment under Selection Silviculture

Even-aged silvicultural methods have been successfully used to manage longleaf pine (Pinus palustris Mill.) forests for wood production;however, successful use of uneven-aged methods to manage this ecosystem is less well documented. In this study, the effects of varying levels of residual basal area (RBA) (9.2, 13.8, and 18.4 m2·ha-1) on longleaf pine germination and establishment under selection silviculture marked using the Proportional-B method were observed. In addition to RBA, photosynthetically active radiation (PAR) was measured, and the relationships between light penetration, germination, and growth were examined. The study found an inverse relationship between RBA and the number of germinants, but the mortality of germinants was not influenced by RBA. PAR also had a significant positive effect on germination, but, did not affect mortality of germinants. In addition, RBA and PAR had no effect on mortality or growth of planted seedlings. Continued monitoring of seedling recruitment into the stand will be required to determine the efficacy of the system. However, nothing in the first year data suggests that this approach will not be successful in sustaining an uneven-aged stand.

Post-fire invasion risk of Chinese tallow(Triadica sebifera)in a slash pine flatwood ecosystem in the Gulf of Mexico Coastal Plain,United States:mechanisms and contributing factors at the community level

The invasion of Chinese tallow(Triadica sebifera(L.)Small)is a serious threat to the endangered slash pine(Pinus elliottii)flatwood ecosystem in the Gulf of Mexico Coastal Plain,United States.Prescribed fire in combination with vegetation management has been suggested as a preferred approach for mitigating Chinese tallow invasion and restoring this endangered ecosystem.A large plot of 0.86-ha with 281 nested contiguous 30-m^(2) quadrats was established in a tallow-invaded slash pine flatwood and all tallow trees,saplings,seedlings and associated factors in each quadrat were measured to study the community-level tallow invasion processes before and after a prescribed fire and by dispersal and community factors.Classification and regression tree models show that the dispersal factors(distances to the road and to the trail)and microtopography(elevation)determine the invasion probability of tallow,but the degree of invasion(abundance)of tallow depends on the interactions of both dispersal factors and community factors such as canopy closure and grass/herbaceous coverage.Areas nearer to roads and trails,dominated by native grass/herbaceous species,and with a low elevation and canopy closure are highly susceptible to tallow invasion and establishment.The effect of fire on tallow invasion varies with overstory and understory conditions.Density of tallow seedlings and saplings increased greatly after fire in the areas dominated by slash pines in the overstory and native grass/herbaceous species in the understory.To control tallow invasion and establishment,tallow seed trees/sources should be removed from the area and vicinity to be burned.

Soil animals and nitrogen mineralization under sand-fixation plantations in Zhanggutai region,China

The effects of soil animals on soil nitrogen (N) mineralization and its availability were studied by investigating soil animal groups and their amounts of macro-faunas sorted by hand, and middle and microfaunas distinguished with Tullgren and Baermann methods under three Pinus sylvestris var. mongolica Litv. plantations in Zhanggutai sandy land, China. In addition, soil N mineralization rate was also measured with PVC closed-top tube in situ incubation method. The soil animals collected during growing season belonged to 13 orders, 5 groups, 4 phyla, whose average density was 86 249.17 individuals·m^(-2). There were significant differences in soil animal species, densities, diversities and evenness among three plantations. Permanent grazing resulted in decrease of soil animal species and diversity. The average ammonification, nitrification and mineralization rates were 0.48 g·m^(-2)·a^(-1), 3.68 g·m^(-2)·a^(-1) and 4.16 g·m^(-2)·a^(-1), respectively. The ammonification rate in near-mature forest was higher than that in middle-age forests, while the order of nitrification and net mineralization rates was: middle-age forest without grazing < middle-age forest with grazing < near-mature forest with grazing (P<0.05). Soil N mineralization rate increased with soil animal amounts, but no significant relationship with diversity. The contribution of soil animals to N mineralization was different for different ecosystems due to influences of complex factors including grazing, soil characteristics, the quality and amount of litter on N mineralization.

China's Wetland Databases Based on Remote Sensing Technology

Wetland databases can provide the basic data that necessary for the protection and management of wetlands. A large number of wetland databases have been established in the world as well as in China. In this paper, we review China's wetland databases based on remote sensing(RS) technology after introducing the background theory to the application of RS technology in wetland surveys. A key conclusion is that China's wetland databases are far from sufficient in fulfilling protection and management needs. Our recommendations focus on the use of the hyper-spectral imagery, microwave data, multi-temporal images, and automatic classifications in order to improve the accuracy and efficiency of wetland inventory. Further, attention should also be paid to detect major biophysical features of wetlands and build wetland databases in years after the 1980 s in China. Considering that great gap exists between RS experts and wetland experts, further cooperation between wetland scientists and RS scientists are needed to promote the application of RS in the foundation of wetland databases.

Scale effects on the prediction of rare events in mature second-growth oak forests:a simulation study of cavity trees

The abundance of cavity trees varies greatly due to the stochastic nature of cavity formation processes and involved disturbance agents.At small spatial scales such as a stand or plot,cavity tree abundance is extraordinarily difficult to predict precisely using tree and stand factors.In this study we used resampling methods to simulate the effect of spatial scale on cavity tree density(CTD)estimation using cavity tree data collected from a long-term forest experimental project.More than 53,000 measured trees were randomly divided into two approximately equal parts:the construction and test datasets,to construct classification and regression tree(CART)and logistic regression(LR)models to predict cavity probability and to test the accuracy of CTD estimation across varying spatial scales,respectively.Simulation results showed that when the spatial scale was<10 ha,the predicted CTD varied dramatically,and with this specific dataset,CART tended to overestimate,whereas LR and the sample mean method underestimated the true CTD estimated by the construction dataset.Compared with the sample mean method,the use of tree characteristics in both CART and LR resulted in slight or moderate reduction of the relative error(RE)(<20%)when the spatial scale was<10 ha.However,CART and LR,particularly CART,could improve CTD prediction efficiency significantly at larger spatial scales.For instance,the RE of CART was only 17%of the sample mean method at a spatial scale of 50 ha.Resource managers could use this information for cavity tree sampling and monitoring.

Occurrence, spatial distribution and ecological risks of antibiotics in soil in urban agglomeration

Antibiotics in soil environment are regarded as emerging pollutants and have introduced increasing risks to soil ecosystem and human health in rapid urbanization areas. Identifying the occurrence and spatial variability of antibiotics in soils is an urgent issue in sustaining soil security. In this study, antibiotics in soils were investigated and analyzed in BeijingTianjin-Hebei urban agglomeration. The occurrence, spatial distribution, and related affecting factors of antibiotics in soils were identified and ecological risks of antibiotics in soil environment were assessed. Results showed that(1) The mean concentration of soil antibiotics in Beijing-Tianjin-Hebei urban agglomeration was 21.79 μg/kg. Land use substantially affected the occurrence and concentration of antibiotics in soils. Concentrations of antibiotics in cropland and orchard soils were 2-3 times higher than the other land use types.(2)The concentrations of antibiotics in soils in Beijing-Tianjin-Hebei urban agglomeration presented a spatial pattern of high values in southeast, and low values in northwest. Spatial variability of antibiotics in soils was closely related to the application of organic fertilizer and wastewater irrigation as well as topographical features. Furthermore, soil properties and land management policy had substantial influences on soil antibiotics, and soil heavy metals may aggravate the accumulation of antibiotics in soils.(3) Ecological risks assessment of antibiotics in soils demonstrated that erythromycin(ERY), sulfamethoxazole(SMX), and doxycycline(DOX) may introduce high risks to soil ecosystem health, and more attention should be paid to the areas with intensive human activities that had potential high risk to soil ecosystem health. This study suggests that scientific land and soil management should be considered to prevent soil antibiotic pollution and sustain soil security in urban agglomeration.

山西沁河上游河岸植被缓冲带综合评价

在对河岸带特性进行调查的基础上,针对我国北方河岸带的特点,从河流健康状况、岸坡稳定性、河岸带土壤条件、河岸带植被条件等4个方面选取16个指标,运用层次分析法,构建了河岸植被缓冲带综合评价体系,并将河岸带生态系统的状态分为4个等级:理想状态、良好状态、一般自然状态和较差状态。运用该体系对山西省沁河的一级支流赤石桥河和紫红河的河岸植被带现状进行评价,结果显示赤石桥河处于"良好状态",紫红河处于"一般状态"。

典型黑土区坡耕地退化程度诊断与评价

为了对黑土区坡耕地退化程度进行全面、综合、客观的诊断与评价,通过文献计量法和频度分析法对国内外耕地退化评价文献内的高频指标进行了统计分析,建立了适用于东北典型黑土区坡耕地退化程度诊断与评价的指标体系(TIS)。同时以拜泉县为研究区域,通过聚类分析建立了土壤退化程度诊断与评价最小指标集(MIS)。结果表明:(1)TIS共包括物理、化学、生物和侵蚀特征因子4类共11项指标:腐殖质层厚度、黏粒含量、有机质含量、pH值、坡度、垄坡角、沟壑密度、容重、水稳性大团聚体含量、土壤阳离子交换量和作物产量,其中前6项指标组成了MIS。(2)研究区未退化土壤占12%,轻度退化土壤占12%,中度及以上退化土壤占76%。坡度可能是影响研究区土壤退化的主要因素之一,坡度与垄坡角之间存在协同关系。此外,施用农药、化肥以及连作导致土壤酸化问题突出。

Does a General Temperature-Dependent Q10 Model of Soil Respiration Exist at Biome and Global Scale？

Soil respiration （SR） is commonly modeled by a Q10 （an indicator of temperature sensitivity） function in ecosystem models. Q10 is usually treated as a constant of 2 in these models, although Q10 value of SR often decreases with increasing temperatures. It remains unclear whether a general temperature- dependent Q10 model of SR exists at biome and global scale. In this paper, we have compiled the long-term Q10 data of 38 SR studies ranging from the Boreal, Temperate, to Tropical/Sublropical biome on four continents. Our analysis indicated that the general temperature-dependent biome Q10 models of SR existed, especially in the Boreal and Temperate biomes. A single-exponential model was better than a simple linear model in fitting the average Q10 values at the biome scale. Average soil temperature is a better predictor of Q10 value than average air temperature in these models, especially in the Boreal biome. Soil temperature alone could explain about 50% of the Q10 variations in both the Boreal and Temperate biome single-exponential Q10 model. Q10 value of SR decreased with increasing soil temperature but at quite different rates among the three biome Q10 models. The k values （Q10 decay rate constants） were 0.09, 0.07, and 0.02/℃ in the Boreal, Temperate, and Tropical/Subtropical biome, respectively, suggesting that Q10 value is the most sensitive to soil temperature change in the Boreal biome, the second in the Temperate biome, and the least sensitive in the Tropical/ Subtropical biome. This also indirectly confirms that acclimation of SR in many soil warming experiments probably occurs. The k value in the ＂global＂ single-exponential Q10 model which combined both the Boreal and Temperate biome data set was 0.08/℃. However, the global general temperature-dependent Q10 model developed using the data sets of the three biomes is not adequate for predicting Q10 values of SR globally. The existence of the general temperature-dependent Q10 models of SR in the Boreal and Temperate biome has important implications for modeling SR, especially in the Boreal biome. More detail model runs are needed to exactly evaluate the impact of using a fixed Q10 vs a temperature-dependent Q10 on SR estimate in ecosystem models （e.g., TEM, Biome-BGC, and PnET）.

Impacts of climate variability and extremes on global net primary production in the first decade of the 21st century

A wide variety of studies have estimated the magnitude of global terrestrial net primary production （NPP）, but its variations, both spatially and temporally, still remain uncertain. By using an improved process-based terrestrial ecosystem model （DLEM, Dynamic Land Ecosystem Model）, we provide an estimate of global terrestrial NPP induced by multiple environmental factors and examine the response of terrestrial NPP to climate variability at biome and global levels and along latitudes throughout the first decade of the 21st century. The model simulation estimates an average global terrestrial NPP of 54.6 Pg C yr-1 during 2000-2009, varying from 52.8 Pg C yr-1 in the dry year of 2002 to 56.4 Pg C yr-1 in the wet year of 2008. In wet years, a large increase in terrestrial NPP compared to the decadal mean was prevalent in Amazonia, Africa and Australia. In dry years, however, we found a 3.2% reduction in global terrestrial NPP compared to the decadal mean, primarily due to limited moisture supply in tropical regions. At a global level, precipitation explained approximately 63% of the variation in terrestrial NPP, while the rest was attributed to changes in temperature and other environmental factors. Precipitation was the major factor determining inter-annual variation in terrestrial NPP in low-latitude regions. However, in midand high-latitude regions, temperature variability largely controlled the magnitude of terrestrial NPP. Our results imply that pro- jected climate warming and increasing climate extreme events would alter the magnitude and spatiotemporal patterns of global terrestrial NPP.

自然与环境资源价值评估的误区

资源环境价值计量近年来成为资源与环境经济学的研究热点,但却因为在许多最基本的问题上迷失了方向,产生了不少似是而非的问题。被混淆的问题包括:①实物意义上的稀缺与经济学上的稀缺;②使用价值与交换价值;③边际价值与全部价值;④成本与价值;⑤个人消费者价值与社会价值。论文主要目的是通过澄清这些问题来指出如何对自然与环境资源估价。

The Ozone Component of Global Change:Potential Effects on Agricultural and Horticultural Plant Yield,Product Quality and Interactions with Invasive Species

The productivity, product quality and competitive ability of important agricultural and horticultural plants in many regions of the world may be adversely affected by current and anticipated concentrations of ground-level ozone （O_3）. Exposure to elevated O_3 typically results in suppressed photosynthesis, accelerated senescence, decreased growth and lower yields. Various approaches used to evaluate O_3 effects generally concur that current yield losses range from 5% to 15% among sensitive plants. There is, however, considerable genetic variability in plant responses to O_3.

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.

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.

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.

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 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.