Significant acidification in major Chinese croplands

Net greenhouse gas balance in response to nitrogen enrichment: perspectives from a coupled biogeochemical model

Increasing reactive nitrogen (N) input has been recognized as one of the important factors influencing climate system through affecting the uptake and emission of greenhouse gases (GHG). However, the magnitude and spatiotemporal variations of N-induced GHG fluxes at regional and global scales remain far from certain. Here we selected China as an example, and used a coupled biogeochemical model in conjunction with spatially explicit data sets (including climate, atmospheric CO2 , O3 , N deposition, land use, and land cover changes, and N fertilizer application) to simulate the concurrent impacts of increasing atmospheric and fertilized N inputs on balance of three major GHGs (CO2 , CH4 , and N2 O). Our simulations showed that these two N enrichment sources in China decreased global warming potential (GWP) through stimulating CO2 sink and suppressing CH4 emission. However, direct N2 O emission was estimated to offset 39% of N-induced carbon (C) benefit, with a net GWP of three GHGs averaging -376.3 ± 146.4 Tg CO2  eq yr(-1) (the standard deviation is interannual variability of GWP) during 2000-2008. The chemical N fertilizer uses were estimated to increase GWP by 45.6 ± 34.3 Tg CO2  eq yr(-1) in the same period, and C sink was offset by 136%. The largest C sink offset ratio due to increasing N input was found in Southeast and Central mainland of China, where rapid industrial development and intensively managed crop system are located. Although exposed to the rapidly increasing N deposition, most of the natural vegetation covers were still showing decreasing GWP. However, due to extensive overuse of N fertilizer, China's cropland was found to show the least negative GWP, or even positive GWP in recent decade. From both scientific and policy perspectives, it is essential to incorporate multiple GHGs into a coupled biogeochemical framework for fully assessing N impacts on climate changes.

Roles of organic acid anion secretion in aluminium tolerance of higher plants

Approximately 30% of the world's total land area and over 50% of the world's potential arable lands are acidic. Furthermore, the acidity of the soils is gradually increasing as a result of the environmental problems including some farming practices and acid rain. At mildly acidic or neutral soils, aluminium (Al) occurs primarily as insoluble deposits and is essentially biologically inactive. However, in many acidic soils throughout the tropics and subtropics, Al toxicity is a major factor limiting crop productivity. The Al-induced secretion of organic acid (OA) anions, mainly citrate, oxalate, and malate, from roots is the best documented mechanism of Al tolerance in higher plants. Increasing evidence shows that the Al-induced secretion of OA anions may be related to the following several factors, including (a) anion channels or transporters, (b) internal concentrations of OA anions in plant tissues, (d) temperature, (e) root plasma membrane (PM) H(+)-ATPase, (f) magnesium (Mg), and (e) phosphorus (P). Genetically modified plants and cells with higher Al tolerance by overexpressing genes for the secretion and the biosynthesis of OA anions have been obtained. In addition, some aspects needed to be further studied are also discussed.

Effects of 24-epibrassinolide on nitrogen metabolism in cucumber seedlings under Ca(NO(3))(2) stress

Ca(NO(3))(2) accumulation is a major factor that limits greenhouse production in China. The present investigation was carried out to study the effect of 24-epibrassinolide (EBL) on nitrogen metabolism (including contents of NO(3)(-), NH(4)(+) and amino acids and related enzymes activities) in cucumber seedlings (Cucumis sativus L. cv. Jinyou No. 4) under 80 mM Ca(NO(3))(2) stress. This study found that exogenous EBL significantly reduced the accumulation of NO(3)(-) and NH(4)(+) by Ca(NO(3))(2), and enhanced the inactivated enzymes activities involved in the nitrogen metabolism. In addition, EBL alleviated the inhibition of photosynthesis nitrogen-use efficiency by Ca(NO(3))(2). Increased total amino acids by EBL under stress increased the precursor of proteins biosynthesis, thus promoting the biosynthesis nitrogen containing compounds. The presence of Ca(NO(3))(2) increased polyamines level, which might result from the increased content of free putrescine that is harmful to plant growth. However, exogenous EBL induced a further increase in total polyamines. The increase is likely caused by the elevated contents of conjugated and bound forms of polyamines. In summary, exogenously EBL compensated for the damage/losses by Ca(NO(3))(2) stress to some extent through the regulation of nitrogen metabolism and metabolites.

Proteomic analysis revealed nitrogen-mediated metabolic, developmental, and hormonal regulation of maize (Zea mays L.) ear growth

Optimal nitrogen (N) supply is critical for achieving high grain yield of maize. It is well established that N deficiency significantly reduces grain yield and N oversupply reduces N use efficiency without significant yield increase. However, the underlying proteomic mechanism remains poorly understood. The present field study showed that N deficiency significantly reduced ear size and dry matter accumulation in the cob and grain, directly resulting in a significant decrease in grain yield. The N content, biomass accumulation, and proteomic variations were further analysed in young ears at the silking stage under different N regimes. N deficiency significantly reduced N content and biomass accumulation in young ears of maize plants. Proteomic analysis identified 47 proteins with significant differential accumulation in young ears under different N treatments. Eighteen proteins also responded to other abiotic and biotic stresses, suggesting that N nutritional imbalance triggered a general stress response. Importantly, 24 proteins are involved in regulation of hormonal metabolism and functions, ear development, and C/N metabolism in young ears, indicating profound impacts of N nutrition on ear growth and grain yield at the proteomic level.

Nitrogen addition regulates soil nematode community composition through ammonium suppression

Nitrogen (N) enrichment resulting from anthropogenic activities has greatly changed the composition and functioning of soil communities. Nematodes are one of the most abundant and diverse groups of soil organisms, and they occupy key trophic positions in the soil detritus food web. Nematodes have therefore been proposed as useful indicators for shifts in soil ecosystem functioning under N enrichment. Here, we monitored temporal dynamics of the soil nematode community using a multi-level N addition experiment in an Inner Mongolia grassland. Measurements were made three years after the start of the experiment. We used structural equation modeling (SEM) to explore the mechanisms regulating nematode responses to N enrichment. Across the N enrichment gradient, significant reductions in total nematode abundance, diversity (H' and taxonomic richness), maturity index (MI), and the abundance of root herbivores, fungivores and omnivores-predators were found in August. Root herbivores recovered in September, contributing to the temporal variation of total nematode abundance across the N gradient. Bacterivores showed a hump-shaped relationship with N addition rate, both in August and September. Ammonium concentration was negatively correlated with the abundance of total and herbivorous nematodes in August, but not in September. Ammonium suppression explained 61% of the variation in nematode richness and 43% of the variation in nematode trophic group composition. Ammonium toxicity may occur when herbivorous nematodes feed on root fluid, providing a possible explanation for the negative relationship between herbivorous nematodes and ammonium concentration in August. We found a significantly positive relationship between fungivores and fungal phospholipid fatty acids (PLFA), suggesting bottom-up control of fungivores. No such relationship was found between bacterivorous nematodes and bacterial PLFA. Our findings contribute to the understanding of effects of N enrichment in semiarid grassland on soil nematode trophic groups, and the cascading effects in the detrital soil food web.

Effects of soil properties on the transfer of cadmium from soil to wheat in the Yangtze River delta region, China--a typical industry-agriculture transition area

In order to identify the effects of soil properties on the transfer of Cd from soil to wheat under actual field conditions, 126 pairs of topsoil and wheat samples were collected from the Yangtze River delta region, China. Relevant parameters (Cd, Ca, Mg, Fe, Mn, Zn, N, P, K, S, pH, total organic carbon, and speciation of soil Cd) in soil and wheat tissues were analyzed, and the results were treated by statistical methods. Soil samples (19.8%) and 14.3% of the wheat grain samples exceeded the relevant maximum permissible Cd concentrations in China for agricultural soil and wheat grain, respectively. The major speciations of Cd in soil were exchangeable, bound to carbonates and fulvic and humic acid fraction, and they were readily affected by soil pH, total Ca, Mg, S and P, DTPA-Fe, Ex-Ca, and Ex-Mg. Cadmium showed a strong correlation with Fe, S, and P present in the grain and the soil, whereas there was no significant correlation in the straw or root. Generally, soil pH, Ca, Mg, Mn, P, and slowly available K restricted Cd transfer from soil to wheat, whereas soil S, N, Zn, DTPA-Fe, and total organic carbon enhance Cd uptake by wheat.

Agricultural non-point source pollution in China: causes and mitigation measures

Non-point source (NPS) pollution has been increasingly serious in China since the 1990s. The increases of agricultural NPS pollution in China is evaluated for the period 2000-2008 by surveying the literature on water and soil pollution from fertilizers and pesticides, and assessing the surplus nitrogen balance within provinces. The main causes for NPS pollution were excessive inputs of nitrogen fertilizer and pesticides, which were partly the result of the inadequate agricultural extension services and the rapid expansion of intensive livestock production with little of waste management. The annual application of synthetic nitrogen fertilizers and pesticides in China increased by 50.7 and 119.7%, respectively, during 1991-2008. The mitigation measures to reduce NPS pollution include: correct distortion in fertilizer prices; improve incentives for the recycling of organic manure; provide farmers with better information on the sound use of agro-chemicals; and tighten the regulations and national standards on organic waste disposal and pesticides use.

Responses of CH(4), CO(2) and N(2)O fluxes to increasing nitrogen deposition in alpine grassland of the Tianshan Mountains

To assess the effects of nitrogen (N) deposition on greenhouse gas (GHG) fluxes in alpine grassland of the Tianshan Mountains in central Asia, CH(4), CO(2) and N(2)O fluxes were measured from June 2010 to May 2011. Nitrogen deposition tended to significantly increase CH(4) uptake, CO(2) and N(2)O emissions at sites receiving N addition compared with those at site without N addition during the growing season, but no significant differences were found for all sites outside the growing season. Air temperature, soil temperature and water content were the important factors that influence CO(2) and N(2)O emissions at year-round scale, indicating that increased temperature and precipitation in the future will exert greater impacts on CO(2) and N(2)O emissions in the alpine grassland. In addition, plant coverage in July was also positively correlated with CO(2) and N(2)O emissions under elevated N deposition rates. The present study will deepen our understanding of N deposition impacts on GHG balance in the alpine grassland ecosystem, and help us assess the global N effects, parameterize Earth System models and inform decision makers.

Temporal and spatial profiling of root growth revealed novel response of maize roots under various nitrogen supplies in the field

A challenge for Chinese agriculture is to limit the overapplication of nitrogen (N) without reducing grain yield. Roots take up N and participate in N assimilation, facilitating dry matter accumulation in grains. However, little is known about how the root system in soil profile responds to various N supplies. In the present study, N uptake, temporal and spatial distributions of maize roots, and soil mineral N (N_min) were thoroughly studied under field conditions in three consecutive years. The results showed that in spite of transient stimulation of growth of early initiated nodal roots, N deficiency completely suppressed growth of the later-initiated nodal roots and accelerated root death, causing an early decrease in the total root length at the rapid vegetative growth stage of maize plants. Early N excess, deficiency, or delayed N topdressing reduced plant N content, resulting in a significant decrease in dry matter accumulation and grain yield. Notably, N overapplication led to N leaching that stimulated root growth in the 40–50 cm soil layer. It was concluded that the temporal and spatial growth patterns of maize roots were controlled by shoot growth and local soil N_min, respectively. Improving N management involves not only controlling the total amount of chemical N fertilizer applied, but also synchronizing crop N demand and soil N supply by split N applications.

Biological sources and sinks of nitrous oxide and strategies to mitigate emissions

Nitrous oxide (N(2)O) is a powerful atmospheric greenhouse gas and cause of ozone layer depletion. Global emissions continue to rise. More than two-thirds of these emissions arise from bacterial and fungal denitrification and nitrification processes in soils, largely as a result of the application of nitrogenous fertilizers. This article summarizes the outcomes of an interdisciplinary meeting, 'Nitrous oxide (N(2)O) the forgotten greenhouse gas', held at the Kavli Royal Society International Centre, from 23 to 24 May 2011. It provides an introduction and background to the nature of the problem, and summarizes the conclusions reached regarding the biological sources and sinks of N(2)O in oceans, soils and wastewaters, and discusses the genetic regulation and molecular details of the enzymes responsible. Techniques for providing global and local N(2)O budgets are discussed. The findings of the meeting are drawn together in a review of strategies for mitigating N(2)O emissions, under three headings, namely: (i) managing soil chemistry and microbiology, (ii) engineering crop plants to fix nitrogen, and (iii) sustainable agricultural intensification.

Regulation of denitrification at the cellular level: a clue to the understanding of N2O emissions from soils

Denitrifying prokaryotes use NO(x) as terminal electron acceptors in response to oxygen depletion. The process emits a mixture of NO, N(2)O and N(2), depending on the relative activity of the enzymes catalysing the stepwise reduction of NO(3)(-) to N(2)O and finally to N(2). Cultured denitrifying prokaryotes show characteristic transient accumulation of NO(2)(-), NO and N(2)O during transition from oxic to anoxic respiration, when tested under standardized conditions, but this character appears unrelated to phylogeny. Thus, although the denitrifying community of soils may differ in their propensity to emit N(2)O, it may be difficult to predict such characteristics by analysis of the community composition. A common feature of strains tested in our laboratory is that the relative amounts of N(2)O produced (N(2)O/(N(2)+N(2)O) product ratio) is correlated with acidity, apparently owing to interference with the assembly of the enzyme N(2)O reductase. The same phenomenon was demonstrated for soils and microbial communities extracted from soils. Liming could be a way to reduce N(2)O emissions, but needs verification by field experiments. More sophisticated ways to reduce emissions may emerge in the future as we learn more about the regulation of denitrification at the cellular level.

Nitrate leaching, direct and indirect nitrous oxide fluxes from sloping cropland in the purple soil area, southwestern China

This study provides a combined dataset on N loss pathways and fluxes from sloping cropland in the purple soil area, southwestern China. A lysimeter experiment was conducted to quantify nitrate leaching (May 2004-May 2010) and N(2)O emission (May 2009-May 2010) losses. Nitrate leaching was the dominant N loss pathway and annual leaching fluxes ranged from 19.2 to 53.4 kg N ha(-1), with significant differences between individual observation years (P < 0.05). Direct N(2)O emissions due to N fertilizer use were 1.72 ± 0.34 kg N ha(-1) yr(-1), which corresponds to an emission factor of 0.58 ± 0.12%. However, indirect N(2)O emissions caused by nitrate leaching and surface runoff N losses, may contribute another 0.15-0.42 kg N ha(-1) yr(-1). Our study shows that nitrate leaching lowered direct N(2)O emissions, highlighting the importance for a better understanding of the tradeoff between direct and indirect N(2)O emissions for the development of meaningful N(2)O emission strategies.

Plant nitrogen assimilation and use efficiency

Crop productivity relies heavily on nitrogen (N) fertilization. Production and application of N fertilizers consume huge amounts of energy, and excess is detrimental to the environment; therefore, increasing plant N use efficiency (NUE) is essential for the development of sustainable agriculture. Plant NUE is inherently complex, as each step-including N uptake, translocation, assimilation, and remobilization-is governed by multiple interacting genetic and environmental factors. The limiting factors in plant metabolism for maximizing NUE are different at high and low N supplies, indicating great potential for improving the NUE of current cultivars, which were bred in well-fertilized soil. Decreasing environmental losses and increasing the productivity of crop-acquired N requires the coordination of carbohydrate and N metabolism to give high yields. Increasing both the grain and N harvest index to drive N acquisition and utilization are important approaches for breeding future high-NUE cultivars.

Effects of urea and (NH4)2SO4 on nitrification and acidification of Ultisols from southern China

The mechanisms for the effects of ammonium-based fertilizers on soil acidification in subtropical regions are not well understood. Two Ultisols collected from cropland and a tea garden in Anhui and Jiangxi Provinces in subtropical southern China, respectively, were used to study the effects of urea and (NH4)2SO4 on the nitrification and acidification of soils with incubation experiments. Nitrification occurred at very low pH with no N fertilizer added and led to lowering of the soil pH by 0.53 and 0.30 units for the soils from Jiangxi and Anhui, respectively. Addition of urea accelerated nitrification and soil acidification in both Ultisols; while nitrification was inhibited by the addition of (NH4)2SO4, and greater input of (NH4)2SO4 led to greater inhibition of nitrification. Ammonia-oxidizing bacteria (AOB) played an important role in nitrification in cropland soil under acidic conditions. Addition of urea increased the soil pH at the early stages of incubation due to hydrolysis and stimulated the increase in the AOB population, and thus accelerated nitrification and soil acidification. At the end of incubation, the pH of Ultisol from Jiangxi had decreased by 1.25, 1.54 and 1.84 units compared to maximum values for the treatments with 150, 300 and 400 mg/kg of urea-N added, respectively; the corresponding figures were 0.95, 1.25 and 1.69 for the Ultisol from Anhui. However, addition of (N-H4)2SO4 inhibited the increase in the AOB population and thus inhibited nitrification and soil acidification. Soil pH for the treatments with 300 and 400 mg/kg of (NH4)2SO4-N remained almost constant during the incubation. AOB played an important role in nitrification of the cropland soil under acidic conditions. Addition of urea stimulated the increase in the AOB population and thus accelerated nitrification and soil acidification; while addition of (NH4)2SO4 inhibited the increase in the AOB population and thus inhibited nitrification.

Improving crop productivity and resource use efficiency to ensure food security and environmental quality in China

In recent years, agricultural growth in China has accelerated remarkably, but most of this growth has been driven by increased yield per unit area rather than by expansion of the cultivated area. Looking towards 2030, to meet the demand for grain and to feed a growing population on the available arable land, it is suggested that annual crop production should be increased to around 580 Mt and that yield should increase by at least 2% annually. Crop production will become more difficult with climate change, resource scarcity (e.g. land, water, energy, and nutrients) and environmental degradation (e.g. declining soil quality, increased greenhouse gas emissions, and surface water eutrophication). To pursue the fastest and most practical route to improved yield, the near-term strategy is application and extension of existing agricultural technologies. This would lead to substantial improvement in crop and soil management practices, which are currently suboptimal. Two pivotal components are required if we are to follow new trajectories. First, the disciplines of soil management and agronomy need to be given increased emphasis in research and teaching, as part of a grand food security challenge. Second, continued genetic improvement in crop varieties will be vital. However, our view is that the biggest gains from improved technology will come most immediately from combinations of improved crops and improved agronomical practices. The objectives of this paper are to summarize the historical trend of crop production in China and to examine the main constraints to the further increase of crop productivity. The paper provides a perspective on the challenge faced by science and technology in agriculture which must be met both in terms of increased crop productivity but also in increased resource use efficiency and the protection of environmental quality.

Ammonia-oxidizing archaea have more important role than ammonia-oxidizing bacteria in ammonia oxidation of strongly acidic soils

Increasing evidence demonstrated the involvement of ammonia-oxidizing archaea (AOA) in the global nitrogen cycle, but the relative contributions of AOA and ammonia-oxidizing bacteria (AOB) to ammonia oxidation are still in debate. Previous studies suggest that AOA would be more adapted to ammonia-limited oligotrophic conditions, which seems to be favored by protonation of ammonia, turning into ammonium in low-pH environments. Here, we investigated the autotrophic nitrification activity of AOA and AOB in five strongly acidic soils (pH<4.50) during microcosm incubation for 30 days. Significantly positive correlations between nitrate concentration and amoA gene abundance of AOA, but not of AOB, were observed during the active nitrification. (13)CO(2)-DNA-stable isotope probing results showed significant assimilation of (13)C-labeled carbon source into the amoA gene of AOA, but not of AOB, in one of the selected soil samples. High levels of thaumarchaeal amoA gene abundance were observed during the active nitrification, coupled with increasing intensity of two denaturing gradient gel electrophoresis bands for specific thaumarchaeal community. Addition of the nitrification inhibitor dicyandiamide (DCD) completely inhibited the nitrification activity and CO(2) fixation by AOA, accompanied by decreasing thaumarchaeal amoA gene abundance. Bacterial amoA gene abundance decreased in all microcosms irrespective of DCD addition, and mostly showed no correlation with nitrate concentrations. Phylogenetic analysis of thaumarchaeal amoA gene and 16S rRNA gene revealed active (13)CO(2)-labeled AOA belonged to groups 1.1a-associated and 1.1b. Taken together, these results provided strong evidence that AOA have a more important role than AOB in autotrophic ammonia oxidation in strongly acidic soils.

Genome-wide identification of microRNAs in response to low nitrate availability in maize leaves and roots

Background

Nitrate is the major source of nitrogen available for many crop plants and is often the limiting factor for plant growth and agricultural productivity especially for maize. Many studies have been done identifying the transcriptome changes under low nitrate conditions. However, the microRNAs (miRNAs) varied under nitrate limiting conditions in maize has not been reported. MiRNAs play important roles in abiotic stress responses and nutrient deprivation.

Methodology/Principal Findings

In this study, we used the SmartArray™ and GeneChip® microarray systems to perform a genome-wide search to detect miRNAs responding to the chronic and transient nitrate limiting conditions in maize. Nine miRNA families (miR164, miR169, miR172, miR397, miR398, miR399, miR408, miR528, and miR827) were identified in leaves, and nine miRNA families (miR160, miR167, miR168, miR169, miR319, miR395, miR399, miR408, and miR528) identified in roots. They were verified by real time stem loop RT-PCR, and some with additional time points of nitrate limitation. The miRNAs identified showed overlapping or unique responses to chronic and transient nitrate limitation, as well as tissue specificity. The potential target genes of these miRNAs in maize were identified. The expression of some of these was examined by qRT-PCR. The potential function of these miRNAs in responding to nitrate limitation is described.

Conclusions/Significance

Genome-wide miRNAs responding to nitrate limiting conditions in maize leaves and roots were identified. This provides an insight into the timing and tissue specificity of the transcriptional regulation to low nitrate availability in maize. The knowledge gained will help understand the important roles miRNAs play in maize responding to a nitrogen limiting environment and eventually develop strategies for the improvement of maize genetics.

Transcriptomic responses to aluminum stress in soybean roots

Aluminum (Al) toxicity is the primary limitation to crop production and plant growth in acid soils. Soybean has multiple mechanisms of Al resistance including the complexing and exclusion of Al in root apices by Al-induced citrate secretion. Microarray analysis is available for the identification of genes in soybean. In the present study, Affymetrix soybean genome array was used to identify the Al-induced differentially expressed genes in Al-resistant genotype Jiyu 70. With a cutoff of > 2.0-fold (p < 0.05) between non Al-treated and Al-treated root apices, 561 genes were upregulated and 78 genes were downregulated when roots were exposed to 30 μmol/L AlCl(3) for 4 h. Quantitative real-time PCR was used to test the microarray data. The analysis showed that nearly half of the Al-responsive genes were of unknown biological function. A higher proportion of genes related to transcription regulation and cell wall processes were observed in Al-induced up- and downregulated genes, respectively. Some genes homologous to the citrate transporter MATE family gene or C(2)H(2) family transcription factor gene, STOP1, were detected in our analysis. Some genes related to lignin deposition were upregulated, which might be related to Al-induced root elongation inhibition.

Will PM control undermine China's efforts to reduce soil acidification?

China's strategies to control acidifying pollutants and particulate matter (PM) may be in conflict for soil acidification abatement. Acidifying pollutant emissions are estimated for 2005 and 2020 with anticipated control policies. PM emissions including base cations (BCs) are evaluated with two scenarios, a base case applying existing policy to 2020, and a control case including anticipated tightened measures. Depositions of sulfur (S), nitrogen (N) and BCs are simulated and their acidification risks are evaluated with critical load (CL). In 2005, the area exceeding CL covered 15.6% of mainland China, with total exceedance of 2.2 Mt S. These values decrease in the base scenario 2020, implying partial recovery from acidification. Under more realistic PM control, the respective estimates are 17.9% and 2.4 Mt S, indicating increased acidification risks due to abatement of acid-neutralizing BCs. China's anthropogenic PM abatement will have potentially stronger chemical implications for acidification than developed countries.

Nitrogen deposition and its ecological impact in China: an overview

Nitrogen (N) deposition is an important component in the global N cycle that has induced large impacts on the health and services of terrestrial and aquatic ecosystems worldwide. Anthropogenic reactive N (N(r)) emissions to the atmosphere have increased dramatically in China due to rapid agricultural, industrial and urban development. Therefore increasing N deposition in China and its ecological impacts are of great concern since the 1980s. This paper synthesizes the data from various published papers to assess the status of the anthropogenic N(r) emissions and N deposition as well as their impacts on different ecosystems, including empirical critical loads for different ecosystems. Research challenges and policy implications on atmospheric N pollution and deposition are also discussed. China urgently needs to establish national networks for N deposition monitoring and cross-site N addition experiments in grasslands, forests and aquatic ecosystems. Critical loads and modeling tools will be further used in N(r) regulation.

Soil nitrite as a source of atmospheric HONO and OH radicals

Hydroxyl radicals (OH) are a key species in atmospheric photochemistry. In the lower atmosphere, up to ~30% of the primary OH radical production is attributed to the photolysis of nitrous acid (HONO), and field observations suggest a large missing source of HONO. We show that soil nitrite can release HONO and explain the reported strength and diurnal variation of the missing source. Fertilized soils with low pH appear to be particularly strong sources of HONO and OH. Thus, agricultural activities and land-use changes may strongly influence the oxidizing capacity of the atmosphere. Because of the widespread occurrence of nitrite-producing microbes, the release of HONO from soil may also be important in natural environments, including forests and boreal regions.

Significance, progress and prospects for research in simplified cultivation technologies for rice in China

Simplified cultivation technologies for rice have become increasingly attractive in recent years in China because of their social, economical and environmental benefits. To date, several simplified cultivation technologies, such as conventional tillage and seedling throwing (CTST), conventional tillage and direct seeding (CTDS), no-tillage and seedling throwing (NTST), no-tillage and direct seeding (NTDS) and no-tillage and transplanting (NTTP), have been developed in China. Most studies have shown that rice grown under each of these simplified cultivation technologies can produce a grain yield equal to or higher than traditional cultivation (conventional tillage and transplanting). Studies that have described the influences of agronomic practices on yield formation of rice under simplified cultivation have demonstrated that optimizing agronomy practices would increase the efficiencies of simplified cultivation systems. Further research is needed to optimize the management strategies for CTST, CTDS and NTST rice which have developed quickly in recent years, to strengthen basic research for those simplified cultivation technologies that are rarely used at present (such as NTTP and NTDS), to select and breed cultivars suitable for simplified cultivation and to compare the practicability and effectiveness of different simplified cultivation technologies in different rice production regions.

Thirty-year amendment of horse manure and chemical fertilizer on the availability of micronutrients at the aggregate scale in black soil

PURPOSE

This study evaluates manure and chemical fertilizer effects on micronutrient (Fe, Mn, Cu, and Zn) content and availability in crops.

METHODS

Seven treatments were selected, including three conventional fertilization treatments (NP, horse manure (M), and NP plus M (NPM)), three corresponding double rate fertilization (N2P2, M2, and N2P2M2), and a CK. Soil samples were collected and separated into four aggregates by wet-sieving in September 2009. Corn samples were collected and analyzed simultaneously.

RESULTS

Treatment N2P2 increased DTPA extractable Fe, Mn, and Cu in soil by 732%, 388%, and 42%, whereas M2 decreased the corresponding values by 26%, 22%, and 10%, respectively, compared to CK. DTPA extractable Zn in soil and Zn in corn grain were higher in the M and M2 treatments than in the other treatments, and DTPA Zn was significantly correlated with soil organic carbon (SOC) in large macroaggregate, microaggregate, and silt + clay fractions. The Mn concentrations in corn stalks and grain were significantly correlated with DTPA extractable Mn in bulk soil and microaggregates, and Zn in stalks were significantly correlated with DTPA Zn in bulk soil, microaggregates, and large macroaggregates.

CONCLUSIONS

Long-term application of horse manure could increase soil Zn availability and uptake by corn, possibly due to its activation by SOC. In contrast, chemical fertilizer application increased DTPA extractable Fe, Mn, and Cu in soil by reducing soil pH. Our results also suggest that Mn uptake by corn originated mainly in microaggregates, whereas Zn in crops was primarily sourced from large macroaggregates and microaggregates.

Integrated soil-crop system management: reducing environmental risk while increasing crop productivity and improving nutrient use efficiency in China

During the past 47 yr (1961-2007), Chinese cereal production has increased by 3.2-fold, successfully feeding 22% of the global human population with only 9% of the world's arable land, but at high environmental cost and resource consumption. Worse, crop production has been stagnant since 1996 while the population and demand for food continue to rise. New advances for sustainability of agriculture and ecosystem services will be needed during the coming 50 yr to reduce environmental risk while increasing crop productivity and improving nutrient use efficiency. Here, we advocate and develop integrated soil-crop system management (ISSM). In this approach, the key points are (i) to take all possible soil quality improvement measures into consideration, (ii) to integrate the utilization of various nutrient resources and match nutrient supply to crop requirements, and (iii) to integrate soil and nutrient management with high-yielding cultivation systems. Recent field experiments have shed light on how ISSM can lead to significant increases in crop yields while increasing nutrient use efficiency and reducing environmental risk.

Biofuel development, food security and the use of marginal land in China

With concerns of energy shortages, China, like the United States, European Union, and other countries, is promoting the development of biofuels. However, China also faces high future demand for food and feed, and so its bioenergy program must try to strike a balance between food and fuel. The goals of this paper are to provide an overview of China's current bioethanol program, identify the potential for using marginal lands for feedstock production, and measure the likely impacts of China's bioethanol development on the nation's future food self-sufficiency. Our results indicate that the potential to use marginal land for bioethanol feedstock production is limited. Applying a modeling approach based on highly disaggregated data by region, our analysis shows that the target of 10 million t of bioethanol by 2020 seems to be a prudent target, causing no major disturbances in China's food security. But the expansion of bioethanol may increase environmental pressures due to the higher levels of fertilizer use. This study shows also that if China were able to cultivate 45% of its required bioethanol feedstock on new marginal land, it would further limit negative effects of the bioethanol program on the domestic and international economy, but at the expense of having to apply another 750 thousand t of fertilizer.

Alkaline ameliorants increase nitrous oxide emission from acidified black soil in Northeastern China

Lime and plant ash are common management used to achieve optimum pH for plant growth and improve soil properties in agricultural soils. Laboratory incubation was conducted to assess N20 emissions as influenced by different soil amendments (lime and plant ash) in a slightly acidic arable soil (pH 5.34). The experimental treatments consisted of CK, lime and plant ash fertilized with NH4(+)-N or N03(-)-N as nitrogen resource. The results show that lime and plant ash dramatically increases the soil pH and N20 emission. For N03(-)-N fertilization, the cumulative N20 emissions from CK, lime and ash are 421, 1669 and 921 μg N20-N/kg, respectively. For NH4(+)-N fertilization, the cumulative N20 emissions from CK, lime and ash are 361, 576 and 559 μg N20-N/kg, respectively. N03(-)-N addition leads to more N20 emission than that of NH4(+)-N addition, and lime increases more N20 emission than that of plant ash. After incubation, N03(-)-N content decreased largely. The findings suggested that alkaline ameliorants increase N20 emissions due to enhancement of soil denitrification.

Response of surface water acidification in upper Yangtze River to SO2 emissions abatement in China

Surface waters in Europe and North America are slowly recovering from acidification following major reductions in emissions of sulfur dioxide (SO(2)) since the 1980s. In contrast, regions affected by acid rain have been reported to be growing in China. Here we show that the rapid change in surface water chemistry in the 1990s in large areas in Southwestern China, specifically the tributary rivers of the Upper Yangtze River, caused by increasing SO(2) emissions, has leveled off. During the 1990s the sulfate (SO(4)(2-)) concentrations in river water increased rapidly and, on average, doubled in only eight years. Simultaneously, calcium (Ca(2+)) concentrations increased, while pH values decreased. In the following decade (2000s), SO(2) emissions stabilized, causing a subsequent stop to the increasing SO(4)(2-) concentrations and pH decline in river water. Although a rapid response to future reduction in SO(2) emissions can be expected, a rapid increase of nitrogen (N) emissions could lead to increases in N leaching and delay recovery.

Integrated soil-crop system management for food security

China and other rapidly developing economies face the dual challenge of substantially increasing yields of cereal grains while at the same time reducing the very substantial environmental impacts of intensive agriculture. We used a model-driven integrated soil-crop system management approach to develop a maize production system that achieved mean maize yields of 13.0 t ha(-1) on 66 on-farm experimental plots--nearly twice the yield of current farmers' practices--with no increase in N fertilizer use. Such integrated soil-crop system management systems represent a priority for agricultural research and implementation, especially in rapidly growing economies.

Deposition and leaching of sulfur, nitrogen and calcium in four forested catchments in China: implications for acidification

Here we present the first detailed study on fluxes of sulfur (S), nitrogen (N), and major cations in Chinese subtropical forest catchments. Data are from four study sites, differing in inputs of atmospheric pollutants and sensitivity to acidification. Results show important differences from most sites in North America and Europe. Dry deposition of S, N, and calcium (Ca) is considerably larger than wet deposition in most cases causing deposition fluxes ranging from moderate to very high, both for acidifying compounds (S deposition 1.5-10.5 kiloequivalents per hectare and year (keq ha(-1) yr(-1)); N deposition 0.4 to 2.5 keq ha(-1) yr(-1)) and for alkaline compounds (Ca deposition 0.8 to 5.7 keq ha(-1) yr(-1)). More than half of the input of acidity is neutralized by alkalinity associated with Ca deposition. Furthermore, the retention of incoming S and N is small in the soil root zone, but considerable in the deeper soils or riparian zone. Drainage water from the root zone of the soils at the two sites with the highest deposition show pronounced acidification. For the two sites with moderate deposition inputs, the root zones are retaining some of the incoming S and buffer some of the incoming acidity. The subsoils and the riparian zonesare strong sinks for N, S, and Ca. This is associated with substantial acid neutralization at all sites. These features are of major importance for the understanding of the long-term effects of acidification in China.

Food security: increasing yield and improving resource use efficiency

Food production and security will be a major issue for supplying an increasing world population. The problem will almost certainly be exacerbated by climate change. There is a projected need to double food production by 2050. In recent times, the trend has been for incremental modest yield increases for most crops. There is an urgent need to develop integrated and sustainable approaches that will significantly increase both production per unit land area and the resource use efficiency of crops. This review considers some key processes involved in plant growth and development with some examples of ways in which molecular technology, plant breeding and genetics may increase the yield and resource use efficiency of wheat. The successful application of biotechnology to breeding is essential to provide the major increases in production required. However, each crop and each specific agricultural situation presents specific requirements and targets for optimisation. Some increases in production will come about as new varieties are developed which are able to produce satisfactory crops on marginal land presently not considered appropriate for arable crops. Other new varieties will be developed to increase both yield and resource use efficiency on the best land.

Denitrification response patterns during the transition to anoxic respiration and posttranscriptional effects of suboptimal pH on nitrous [corrected] oxide reductase in Paracoccus denitrificans

Denitrification in soil is a major source of atmospheric N(2)O. Soil pH appears to exert a strong control on the N(2)O/N(2) product ratio (high ratios at low pH), but the reasons for this are not well understood. To explore the possible mechanisms involved, we conducted an in-depth investigation of the regulation of denitrification in the model organism Paracoccus denitrificans during transition to anoxia both at pH 7 and when challenged with pHs ranging from 6 to 7.5. The kinetics of gas transformations (O(2), NO, N(2)O, and N(2)) were monitored using a robotic incubation system. Combined with quantification of gene transcription, this yields high-resolution data for direct response patterns to single factors. P. denitrificans demonstrated robustly balanced transitions from O(2) to nitric oxide-based respiration, with NO concentrations in the low nanomolar range and marginal N(2)O production at an optimal pH of 7. Transcription of nosZ (encoding N(2)O reductase) preceded that of nirS and norB (encoding nitrite and NO reductase, respectively) by 5 to 7 h, which was confirmed by observed reduction of externally supplied N(2)O. Reduction of N(2)O was severely inhibited by suboptimal pH. The relative transcription rates of nosZ versus nirS and norB were unaffected by pH, and low pH had a moderate effect on the N(2)O reductase activity in cells with a denitrification proteome assembled at pH 7. We thus concluded that the inhibition occurred during protein synthesis/assembly rather than transcription. The study shed new light on the regulation of the environmentally essential N(2)O reductase and the important role of pH in N(2)O emission.