Somatic embryogenesis (SE) is an effective approach of in vitro regeneration that depends on plant cell totipotency. However, largely unknown of molecular mechanisms of SE in woody plants such as Chinese chestnut (Castanea mollissima Blume), limits the development of the woody plant industry. Here, we report the MADS-box transcription factor CmAGL11 in Chinese chestnut. CmAGL11 transcripts specifically accumulated in the globular embryo. Overexpression of CmAGL11 in chestnut callus enhanced its SE capacity, and the development of somatic embryos occurred significantly faster than in the control. RNA-seq results showed that CmAGL11 affects the expression of several genes related to the gibberellin, auxin, and ethylene pathways. Moreover, the analysis of DNA methylation status indicated that the promoter methylation plays a role in regulation of CmAGL11 expression during SE. Our results demonstrated that CmAGL11 plays an important role in the SE process in Chinese chestnut, possibly by regulating gibberellin, auxin, and ethylene pathways. It will help establish an efficient platform to accelerate genetic improvement and germplasm innovation in Chinese chestnut.

Seasonal soil freeze-thaw events may enhance soil nitrogen transformation and thus stimulate nitrous oxide (N₂O) emissions in cold regions.  However, the mechanisms of soil N₂O emission during the freeze-thaw cycling in the field remain unclear.  We evaluated N₂O emissions and soil biotic and abiotic factors in maize and paddy fields over 20 months in Northeast China, and the structural equation model (SEM) was used to determine which factors affected N₂O production during non-growing season.  Our results verified that the seasonal freeze-thaw cycles mitigated the available soil nitrogen and carbon limitation during spring thawing period, but simultaneously increased the gaseous N₂O-N losses at the annual time scale under field condition.  The N₂O-N cumulative losses during the non-growing season amounted to 0.71 and 0.55 kg N ha^–1 for the paddy and maize fields, respectively, and contributed to 66 and 18% of the annual total.  The highest emission rates (199.2–257.4 μg m^–2 h^–1) were observed during soil thawing for both fields, but we did not observe an emission peak during soil freezing in early winter.  Although the pulses of N₂O emission in spring were short-lived (18 d), it resulted in approximately 80% of the non-growing season N₂O-N loss.  The N₂O burst during the spring thawing was triggered by the combined impact of high soil moisture, flush available nitrogen and carbon, and rapid recovery of microbial biomass.  SEM analysis indicated that the soil moisture, available substrates including NH₄⁺ and dissolved organic carbon (DOC), and microbial biomass nitrogen (MBN) explained 32, 36, 16 and 51% of the N₂O flux variation, respectively, during the non-growing season.  Our results suggested that N₂O emission during the spring thawing make a vital contribution of the annual nitrogen budget, and the vast seasonally frozen and snow-covered croplands will have high potential to exert a positive feedback on climate change considering the sensitive response of nitrogen biogeochemical cycling to the freeze-thaw disturbance.   

    Following a rice or wheat harvest, a large amount of crop residue (straw) is retained in fields. The straw is often incorporated into the soil in order to increase the soil organic carbon storage and to reduce soil erosion. However, it has become apparent that the incorporated straw can significantly alter soil shear properties, which can dramatically affect energy inputs for tilling and other soil management practices. In this study, laboratory-remolded wheat straw-soil samples were compared with field-collected straw-soil samples; we found high correlations for the cohesion (R²=0.9084) and internal friction angle (R²=0.9548) properties of the samples. Shear tests on rice and wheat straw with different moisture content levels clearly demonstrated the relatively higher shear strength of wheat straw compared to rice straw. The cohesion of remolded rice and wheat straw-soil samples exhibited an increasing linear trend with an increase in densities, whereas the internal friction angle data for these samples exhibited a quadratic trend. Overlapping the cohesion curves revealed that the wheat straw-soil and rice straw-soil samples had the same cohesion at a straw density of 0.63%. Similar results were obtained when the internal fraction angle curves overlapped; the resultant point of intersection was observed at a straw density of 0.46%. As a whole, the remolded sample methodology was found suitable to simulate the shear properties of soils sampled directly from fields.

The excessive nitrogen (N) fertilizer input coupled with flood irrigation might result in higher N leaching and lower nitrogen recovery efficiency (NRE). Under an intensive rice system in the Ningxia irrigation region, China, environmental friendly N management practices are heavily needed to balance the amount of N input for optimum crop production while minimize the nitrogen loss. The objective of this study was to determine the influences of side-dressing (SD) technique in mechanical transplanting systems on the NRE, N leaching losses and rice yield in anthropogenic-alluvial soil during two rice growing seasons (2010-2011). Four fertilizer N treatments were established, including conventional urea rate (CU, 300 kg ha–1 yr–1); higher SD of controlled-release N fertilizer rate (SD1, 176 kg ha–1 yr–1); lower SD of controlled-release N fertilizer rate (SD2, 125 kg ha–1 yr–1); and control (CK, no N fertilizer). Field lysimeters were used to quantify drainage from undisturbed soil during six rice growing stages. Meanwhile, the temporal variations of total nitrigen (TN), NO3 –-N, and NH4 +-N concentrations in percolation water were examined. The results showed that SD1 substantially improved NRE and reduced N leaching losses while maintaining rice yields. Across two years, the averaged NRE under SD1 treatment increased by 25.5% as relative to CU, but yet the rice yield was similar between two treatments. On average, the nitrogen loss defined as TN, NH4 +-N, and NO3 –-N under the SD1 treatment reduced by 27.4, 37.2 and 24.1%, respectively, when compared with CU during the study periods. Although the SD2 treatment could further reduce N leaching loss to some extent, this technique would sharply decline rice yield, with the magnitude of as high as 21.0% relative to CU treatment. Additionally, the average NRE under SD2 was 11.2% lower than that under SD1 treatment. Overall, the present study concluded that the SD technique is an effective strategy to reduce N leaching and increase NRE, thus potentially mitigate local environmental threat. We propose SD1 as a novel alternative fertilizer technique under an irrigated rice-based system in Ningxia irrigation region when higher yields are under consideration.

Organic amendment is considered as an effective way to increase soil organic carbon (SOC) stock in croplands. To better understand its potential for SOC sequestration, whether SOC saturation could be observed in an intensive agricultural ecosystem receiving long-term composted manure were examined. Different SOC pools were isolated by physical fractionation techniques of a Cambisol soil under a long-term manure experiment with wheat-maize cropping in North China Plain. A field experiment was initiated in 1993, with 6 treatments including control (i.e., without fertilization), chemical fertilizer only, low rate of traditional composted manure (7.5 t ha-1), high rate of traditional composted manure (15 t ha-1), low rate of bio-composted manure (7.5 t ha-1) and high rate of bio-composted manure (15 t ha-1). The results showed that consecutive (for up to 20 years) composted manure amendments significantly improved soil macro-aggregation, aggregate associated SOC concentration, and soil structure stability. In detail, SOC concentration in the sand-sized fraction (>53 μm) continued to increase with manure application rate, while the silt (2-53 μm) and clay (<2 μm) particles showed no further increase with greater C inputs, exhibiting the C saturation. Further physical separation of small macro-aggregates (250-2 000 μm) into subpools showed that the non-protected coarse particulate organic matter (cPOM, >250 μm) was the fraction in which SOC continued to increase with increasing manure application rate. In contrast, the chemical and physical protected C pools (i.e., micro-aggregates and silt-clay occluded in the small macroaggregates) exhibited no additional C sequestration when the manure application rate was increased. It can be concluded that repeated manure amendments can increase soil macro-aggregation and lead to the increase in relatively stable C pools, showing hierarchical saturation behavior in the intensive cropping system of North China Plain.

While the shortage of water and energy is a well-recognized worldwide natural resources issue, little attention has been given to irrigation energy efficiency. In this paper, we examine the potential energy savings that can be achieved by implementing improved irrigation technologies in China. The use of improved irrigation management measures such as a flow meter, irrigation scheduling, and/or regular maintenance and upgrades, typically reduces the amount of water pumped over the course of a growing season. The total energy saved by applying these improved measures could reach 20%, as compared with traditional irrigation methods. Two methods of irrigation water conveyance by traditional earth canal and low pressure pipeline irrigation (LPPI) were also evaluated. Our study indicated that LPPI could save 6.48×109 kWh yr-1 when applied to 11 Chinese provinces. Also, the CO2 emission was reduced by 6.72 metric tons per year. Among these 11 surveyed provinces, the energy saving potential for two provinces, Hebei and Shandong, could reach 1.45×109 kWh yr-1. Using LPPI, potential energy saved and CO2 emissions reduced in the other 20 Chinese provinces were estimated at about 2.97×109 kWh yr-1 and 2.69 metric tons per year, respectively. The energy saving potential for Heilongjiang, a major agriculture province, could reach 1.77×109 kWh yr-1, which is the largest in all provinces. If LPPI is applied to the entire country, average annual energy saving of more than 9 billion kWh and average annual CO2 emission reduction of more than 9.0 metric tons could be realized. Rice is one of the largest users of the world’s fresh water resources. Compared with continuous flooding irrigation, intermittent irrigation (ITI) can improve yield and water-use efficiency in paddy fields. The total increments of net output energy and yield by ITI in paddy fields across China could reach 2.5×1016 calories and 107 tons, respectively. So far only a small part of agricultural land in China has adopted water and energy saving technologies. Therefore, potential water and energy savings in China by adapting improved irrigation technology could be significant and should be carefully studied and applied.

The temperature difference between an urban space and surrounding non-urban space is called the urban heat island effect (UHI). Global terrestrial evapotranspiration (ET) can consume 1.4803×1023 joules (J) of energy annually, which is about 21.74% of the total available solar energy at the top of atmosphere, whereas annual human energy use is 4.935×1020 J, about 0.33% of annual ET energy consumption. Vegetation ET has great potential to reduce urban and global temperatures. Our literature review suggests that vegetation and urban agricultural ET can reduce urban temperatures by 0.5 to 4.0°C. Green roofs (including urban agriculture) and water bodies have also been shown to be effective ways of reducing urban temperatures. The cooling effects on the ambient temperature and the roof surface temperature can be 0.24-4.0°C and 0.8-60.0°C, respectively. The temperature of a water body (including urban aquaculture) can be lower than the temperature of the surrounding built environment by between 2 and 6°C, and a water body with a 16 m2 surface area can cool up to 2 826 m3 of nearby space by 1°C. Based on these findings, it can be concluded that the increase of evapotranspiration in cities, derived from vegetation, urban agriculture, and water body, can effectively mitigate the effect of urban heat islands.

The influences of tillage systems on soil carbon (C) stocks have been studied extensively, but the distribution of soil C within aggregate fractions is not well understood. The objective of this study was to determine the influences of various tillage systems on soil aggregation and aggregate-associated C under wheat (Triticum aestivum L.) and corn (Zea mays L.) double cropping systems in the North China Plain. The experiment was established in 2001, including four treatments: moldboard plow (MP) with residue (MP+R) and without residue (MP-R), rotary tillage with residue (RT), and no-till with residue (NT). In 2007 soil samples were collected from the 0-5, 5-10, and 10-20 cm depths, and were separated into four aggregate-size classes (>2 000, 250-2 000, 53-250, and <53 μm) by wet-sieving method. Aggregate-associated C was determined, and the relationships between total soil C concentration and aggregation-size fractions were examined. The results showed that NT and RT treatments significantly increased the proportion of macroaggregate fractions (>2 000 and 250-2 000 μm) compared with the MP-R and MP+R treatments. Averaged across all depths, mean weight diameters of aggregates (MWD) in NT and RT were 47 and 20% higher than that in MP+R. The concentration of bulk soil organic C was positively correlated with MWD (r=0.98; P=0.024) and macroaggregate fraction (r=0.96; P=0.036) in the 0-5 cm depth. In the 0-20 cm depth, comparing with MP+R, total C occluded in the >2 000 μm fraction was increased by 9 and 6% under NT and RT, respectively. We conclude that adoption of conservation tillage system, especially no-till, can increase soil macro-aggregation and total C accumulation in macroaggregates, which may improve soil C sequestration in the intensive agricultural region of the North China Plain.

In this study, an F2 segregated population obtained by hybridization between the aphid-sensitive sorghum strain Qiansan and aphid-resistant cultivar Henong 16 was used to establish an aphid-resistant pool and an aphid-sensitive pool. 192 pairs of AFLP (amplified fragment length polymorphism) marker primers were screened in these pools using BSA (bulked segregant analysis). Three pairs of EcoR I-CTG/Mse I-CCT, EcoR I-CTG/Mse I-CAT, and EcoR I-AGT/Mse I-CCC showed linkage with aphis resistance. EcoR I-CTG/Mse I-CCT-475, EcoR I-CTG/Mse I-CAT-390, and EcoR I-AGT/Mse I-CCC- 350 (E42/M52-350) were mapped within 6, 10, and 13 cM distances with the aphid-resistant gene by using Mapmaker 3.0 software. The bands amplified by EcoR I-CTG/Mse I-CCT-475 and EcoR I-CTG/Mse I-CAT-390 were extracted, cloned, and sequenced. Specific primers of SCAR (sequence characterized amplified regions) were then designed from these bands. A specific band of 300 bp was amplified by a pair of SCAR primers designed based on the sequence obtained from the EcoR I-CTG/Mse I-CAT-390 marker. The SCAR marker was named SCA50. The marker was used to detect the F2, BC1, and F2:3 populations. The selective efficiency was 86.8, 91.1, and 86.3% in the BC1, F2, and F2:3 populations, respectively. The average selective efficiency was 88.2%.