Shiqing Li

Taibaiella smilacinae gen. nov., sp. nov., an endophytic member of the family Chitinophagaceae isolated from the stem of Smilacina japonica, and emended description of Flavihumibacter petaseus

A light-yellow-coloured bacterium, designated strain PTJT-5(T), was isolated from the stem of Smilacina japonica A. Gray collected from Taibai Mountain in Shaanxi Province, north-west China, and was subjected to a taxonomic study by using a polyphasic approach. The novel isolate grew optimally at 25-28 °C and pH 6.0-7.0. Flexirubin-type pigments were produced. Cells were Gram-reaction-negative, strictly aerobic, rod-shaped and non-motile. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain PTJT-5(T) was a member of the phylum Bacteroidetes, exhibiting the highest sequence similarity to Lacibacter cauensis NJ-8(T) (87.7 %). The major cellular fatty acids were iso-C15 : 0, iso-C15 : 1 G, iso-C17 : 0 and iso-C17 : 0 3-OH. The only polyamine was homospermidine and the major polar lipid was phosphatidylethanolamine. The only respiratory quinone was MK-7 and the DNA G+C content was 40.3 mol%. Based on the phenotypic, phylogenetic and genotypic data, strain PTJT-5(T) is considered to represent a novel species of a new genus in the family Chitinophagaceae, for which the name Taibaiella smilacinae gen. nov., sp. nov. is proposed. The type strain of Taibaiella smilacinae is PTJT-5(T) ( = CCTCC AB 2013017(T) = KCTC 32316(T)). An emended description of Flavihumibacter petaseus is also proposed.

Effects of land-cover type and topography on soil organic carbon storage on Northern Loess Plateau, China

Abstract Changes in land cover from cropland to conservation can sequester carbon in soil. On the Loess Plateau of China, vast areas of sloping cropland were converted into forest and grassland to control soil erosion. The northern plateau is a topographically heterogeneous, semi-arid region. A good understanding of the change of soil organic carbon (SOC) storage on the plateau in the process of land-cover change is important for assessing environmental changes and planning future land cover. We selected four land-cover types (cropland, planted grassland, abandoned orchard, and secondary grassland), and two vegetation covers (Stipa bungeana and Caragana korshinskii) on shady and sunny slopes, to analyse the effects of land cover and slope aspect on SOC storage. Soil C in the top 100 cm was significantly (P<0.05) greater in artificial grassland (2.49 kg m−2) and secondary grassland (2.98 kg m−2) than in cropland (1.69 kg m−2). The SOC pool in the surface soil and throughout the 1-m profile followed the order secondary grassland>artificial grassland>abandoned orchards>cropland. Sequestration extended to deep soil (80–100 cm). Slope aspect affected SOC concentration: wind erosion of the shady slope marginally reduced surface SOC relative to the sunny slope. In deep soil, responses of SOC concentration to slope aspect differed between vegetation covers: under C. korshinskii, SOC concentration was significantly greater on the shady slope (P<0.05), but no difference was found under S. bungeana.

Diurnal and seasonal soil CO2 flux patterns in spring maize fields on the Loess Plateau, China.

Abstract Carbon dioxide flux from the soil to the atmosphere is an important component of terrestrial C cycling, and accurate estimates of CO2-C fluxes are crucial for estimating C budgets. A field study was conducted (i) to examine the diurnal and seasonal soil CO2 flux pattern in spring maize fields on the Loess Plateau, and (ii) to determine the effects of soil characteristics affected by various cultivation practices on CO2 flux from the soil surface to the atmosphere. Soil surface CO2 flux was determined with an LI-8100 Automated Soil Flux System, and related environmental factors were also measured, including near-ground air temperature and relative humidity, soil moisture (0–15 cm), soil temperature (at depths of 5, 10, 15, and 20 cm), and leaf area index. Diurnal soil CO2 flux showed a single peak between 12-00 h and 16-00 h, and reached a minimum in the early morning, at about 4-00 h. During the crops growing season, soil CO2 flux increased during the rapid vegetative growth stages, reached its maximum during the peak reproductive stages, and then declined as the plants senesced. Time series analysis showed that the temporal dynamics of the CO2 flux were more closely related to air temperature than to soil temperature; this may be because a substantial portion of the CO2 originated from surface residues. The time-averaged mean soil CO2 flux for different cultivation practices over the growing season was ranked as follows: plastic film mulching (3.980 µmol m−2s−1) > corn straw mulching (3.464 µmol m−2s−1) > supplementary irrigating (3.157 µmol m−2s−1) > rain-fed (2.371 µmol m−2s−1) > bare ground (1.934 µmol m−2s−1). Different cultivation practices affected plant and microbial activities, and soil hydrothermal conditions, and caused different patterns of soil surface CO2 flux in spring maize fields on the Loess Plateau.

Pursuing sustainable productivity with millions of smallholder farmers

Sustainably feeding a growing population is a grand challenge, and one that is particularly difficult in regions that are dominated by smallholder farming. Despite local successes, mobilizing vast smallholder communities with science- and evidence-based management practices to simultaneously address production and pollution problems has been infeasible. Here we report the outcome of concerted efforts in engaging millions of Chinese smallholder farmers to adopt enhanced management practices for greater yield and environmental performance. First, we conducted field trials across China’s major agroecological zones to develop locally applicable recommendations using a comprehensive decision-support program. Engaging farmers to adopt those recommendations involved the collaboration of a core network of 1,152 researchers with numerous extension agents and agribusiness personnel. From 2005 to 2015, about 20.9 million farmers in 452 counties adopted enhanced management practices in fields with a total of 37.7 million cumulative hectares over the years. Average yields (maize, rice and wheat) increased by 10.8–11.5%, generating a net grain output of 33 million tonnes (Mt). At the same time, application of nitrogen decreased by 14.7–18.1%, saving 1.2 Mt of nitrogen fertilizers. The increased grain output and decreased nitrogen fertilizer use were equivalent to US

Soil amendment with biochar increases maize yields in a semi-arid region by improving soil quality and root growth

12.2 billion. Estimated reactive nitrogen losses averaged 4.5–4.7 kg nitrogen per Megagram (Mg) with the intervention compared to 6.0–6.4 kg nitrogen per Mg without. Greenhouse gas emissions were 328 kg, 812 kg and 434 kg CO2 equivalent per Mg of maize, rice and wheat produced, respectively, compared to 422 kg, 941 kg and 549 kg CO2 equivalent per Mg without the intervention. On the basis of a large-scale survey (8.6 million farmer participants) and scenario analyses, we further demonstrate the potential impacts of implementing the enhanced management practices on China’s food security and sustainability outlook.

Characteristics of N2O production and transport within soil profiles subjected to different nitrogen application rates in China.

Abstract. Biochar has been widely proposed as a relatively novel approach to improve soil quality and increase crop productivity, but its underlying mechanisms are not well understood. A large root system in plants is either a constitutive or an inducible trait dependent on the uptake of resources and the production of shoot dry matter. Here a field experiment was conducted to investigate the effects of biochar amendment on the dynamic growth and development of maize (Zea mays L.), both above- and belowground, and to explore the relationship between soil condition, root traits and shoot biomass over two growing seasons on the Loess Plateau in northern China. Biochar was added to a maize field at rates of 0, 10, 20 and 30 t ha–1 without mulching and at rates of 0 and 20 t ha–1 with film mulching before sowing the first crop. The application of straw biochar with 30 t ha–1 decreased soil bulk density by 12% and increased soil total porosity by 13% in the 0–10-cm soil layer 6 months after biochar addition. Biochar amendment increased soil organic carbon, total soil nitrogen, carbon : nitrogen ratio, and available phosphorus and potassium at the end of each growing season. Although, root growth was inhibited at a rate of 30 t ha–1 in the early stage of the first year, biochar amendment exhibited a positive effect in other stages, resulting in higher root weight density, root length density and root surface-area density. These responses led to higher growth rates, maize biomass, grain yields and uptake of nitrogen, phosphorus and potassium as the rate of biochar addition increased. Film mulching with biochar amendment achieved the greatest root and shoot biomass and grain yield in both crops, despite differences in climate conditions. Biochar aged in the field for 2 years had the same effect on soil properties and crop production, suggesting that the application of straw biochar may be a promising option for increasing productivity in semi-arid farmland.

Effect of Foliar Nitrogen Application on Nitrogen Metabolism, Water Status, and Plant Growth in Two Maize Cultivars under Short-term Moderate Stress

To better understand the effect of N fertilizer on the responses of subsoil N2O to N2O emissions in a high-yield plot, we investigated the subsurface N2O concentrations at seven mineral soil depths and analyzed the subsoil N2O fluxes between soil horizons. This study was conducted from 2012 to 2013 in farmland located in the semi-humid area of the Changwu station, Shaanxi, and the results showed that the application of N fertilizer triggered the highest amount of N2O production and effluxes in the various soil layers. With an increase of N fertilizer, N2O effluxes and production significantly increased; the mean variation of 380 kg N ha(-1) treatment was much greater than that of 250 kg N ha(-1) treatment, particularly after fertilization during the maize growing season (MS). N2O concentrations increased within 30 cm and maintained low and stable values. However, N2O fluxes and production decreased with depth (below 30 cm) and then remained low (approximately zero or even negative) at depths of 30-90 cm. The cumulative N2O fluxes in the 0-15 cm soil layer accounted for 99.0% of the total amount in the soil profile, and high fluxes coincided with periods of relatively high production rates. The cumulative production of N2O also remained in step with the cumulative fluxes. In addition, more N fertilizer was applied, greater production occurred in the topsoil. A significantly positive relationship was found between N2O fluxes and mineral N, and a negative relationship was found between the fluxes and the water-filled pore space (WFPS) in the shallow soil. N2O effluxes increased with increasing amounts of N fertilizer, which was primarily due to nitrification on the Loess Plateau.

EFFECTS OF SPATIAL COUPLING OF WATER AND FERTILIZER APPLICATIONS ON ROOT GROWTH CHARACTERISTICS AND WATER USE OF WINTER WHEAT

ABSTRACT Two contrasting maize (Zea mays L.) cultivars, i.e. ‘Shaandan 9’ (S9) and ‘Shaandan 911’(S911) were investigated by examining foliar nitrogen (N) modulation of N metabolism, water status and plant growth under short-term moderate water stress (SMWS). On 10th day of SMWS, dry matter (DM), relative water content (RWC) and nitrate reductase activity (NRA) were significantly decreased, whereas concentrations of free proline (FP), glycinebetaine (GB) and soluble protein (SP) were increased in leaves of both cultivars. Cultivar S9 maintained greater DM, RWC and these N metabolism traits than S911 during SMWS. Foliar N application much more raised DM, RWC, NRA, and concentrations of all solutes measured under SMWS above control. These positive effects were more pronounced in S911 than those in S9 during SMWS. Greater correlations were performed amongst all parameters under SMWS than control. Hence, we suggest that foliar N should be firstly applied to drought sensitive cultivars under drought.

Nitrogen fertilization effects on nitrogen balance and use efficiency for film-mulched maize in a semiarid region

□ Root systems play vital roles, inter alia in the acquisition of water and nutrients in all plants, and hence in their growth, physiology and metabolism. However, much remains to be learned about the mechanisms affecting root distributions and uptake efficiencies. These are important aspects to understand in order to optimize water and fertilizer applications, especially in arid areas such as the Loess Plateau of China, where a key crop is winter wheat. Therefore, we have studied the effects of spatial coupling of water, nitrogen and phosphorus applications on winter wheat root growth patterns at different growth stages and in different soil layers in soil columns. Observations by minirhizotrons showed root length, surface area, volume and number to be respectively 18.9, 25.3, 29.8 and 8.0% higher under dry treatments than under wet treatments. Simultaneous application of nitrogen and phosphorus in the 0–90 or 0–30 cm layers promoted extensive spatial distributions of roots, especially in the 0–30 cm layer. In addition, water use efficiency (WUE) was found to be strongly correlated with root length, surface area, volume and number (r 2 = 0.72–0.80, n = 26), but weakly correlated with root biomass (r 2 = 0.3).

Aboveground biomass response to increasing nitrogen deposition on grassland on the northern Loess Plateau of China

Efficient nitrogen (N) applications are crucial for sustainable agricultural development. A three-year field study was conducted to evaluate the effects of N fertilization on soil NO3-N contents, N balance, grain yield, and N use efficiency of film-mulched maize (Zea mays L.) in the semiarid northwest China. Six N levels were examined: 0 (N0), 100 (N100), 200 (N200), 250 (N250), 300 (N300), and 400 (N400) kg N ha−1. Results showed that residual soil NO3-N contents after harvest and apparent N losses markedly increased with increased N fertilizer rate. High accumulations of soil NO3-N were detected in the 80–200 cm layers in the N300 and N400 treatments in 2010 and 2011, indicating that excessive N applications resulted in NO3-N leaching in this semiarid region. The N use efficiency decreased with increased N fertilizer rate, but insignificant differences in agronomic efficiency, apparent recovery efficiency, and physiological efficiency were observed between N100, N200, and N250 treatments. Maize grain yields increased with N fertilization, but it did not further increase when N application was higher than plant N requirements. A linear plateau relationship was observed between grain yield and N supply (fertilizer N plus initial soil NO3-N in the 0–100 cm layers). The minimal N supply rate required to obtain the maximum yield (13.9 Mg ha−1) was 279 kg N ha−1, which was similar to plant N uptake and simultaneously reduced apparent N losses. We conclude that N fertilizer recommendations which consider soil NO3-N contents can simultaneously provide sufficient N for high yields and improve N fertilization of film-mulched maize in the semiarid areas.