[How Different Ratios of Straw Incorporation to Nitrogen Fertilization Influence Endogenous and Exogenous Carbon Release from Agricultural Soils].

The adjustment of the C/N ratio by straw combined with fertilizer nitrogen (N) not only affects straw decomposition but also affects soil organic carbon (SOC) decomposition, i.e. the priming effects. Therefore, it is doubly important to study how the ratios of straw to N fertilizer influence the release of endogenous and exogenous C for greenhouse gas emission reduction and soil fertility improvement. We conducted a 32-week laboratory incubation experiment with 13C labeled maize straw under different N levels in farmland soil collected from fields in Huantai County to investigate the effect of the ratios of straw to N fertilizer on straw decomposition and the priming effects. Four treatments were set up, including CK, corn straw (S), corn straw+low urea rates (SN1), and corn straw+high urea rates (SN2). Dynamic sampling was conducted during the early stage (0-10 d), the middle stage (11-43 d), and the later stage (44-224 d) of straw decomposition. The approach was based on using a two-source mixing model to differentiate two sources of soil CO2 (straw and soil-derived C). With an increase in the incubation time, the contribution of SOC decomposition to soil CO2 emissions first decreased and then increased. On the contrary, the contribution of straw mineralization to soil CO2 emissions first increased and then decreased. By the end of the incubation time, the contribution of SOC and straw decomposition to soil CO2 emissions was 0.84-0.86 and 0.14-0.16, respectively. Over the whole incubation period, the effects of N fertilization on straw decomposition first increased and then decreased. The promotion degree of high and low N fertilization on straw decomposition was up to 15.8% and 7.9%, respectively. Over the whole incubation period, the inhibition degree of low N fertilization reached up to 7.1%, while high N fertilization showed a slight promotion trend of 0.7%. Therefore, the regulation of C:N by straw combined with fertilizer N not only affected the contribution of exogenous straw to SOC but also influenced the decomposition of endogenous SOC, and then influenced soil C fixation. Over the whole incubation period, straw C retention could not compensate for CO2 released by the priming effects, which led to a net loss of SOC.

[Impacts of Nitrogen Application on Ammonia Volatilization During Maize Season in Northern China].

Ammonia volatilization is one of the major paths of nitrogen (N) loss and may exert a substantial impact on air quality. This study aims to explore the effects of nitrogen (N) fertilizer types, fertilization rate, and application timing and gas collection method on NH3 volatilization during the maize season in Northern China. This study collected the publications on the NH3 volatilization from maize farming which were conducted in Northern China from 1980 to 2018, and undertook a systematic analysis. The study found that with the increase of N rate, the total and net NH3 volatilization at the basal and topdressing fertilization stages increased at exponential and power function, respectively. When the ratio of basal/topdressing N rate was 1/1, the total and net NH3 volatilization during the topdressing stage (58.4% of the whole season emission) was significantly higher than that in the basal fertilization stage (41.6%) (P<0.05). The priming effect first showed a negative effect and then gradually turned into a positive effect with the increase of N rate. Due to the positive priming effect, the net NH3 volatilization, without considering the priming effect, was overestimated under the conventional N application (>297 kg·hm-2). There is a significant difference between the NH3 volatilization measured by the venting method and the sponge absorption method, and the data from the venting method are more stable (P<0.01). Compared with conventional urea, slow-release urea may reduce NH3 volatilization by 20% to 50%. Control fertilizer N rate at the topdressing stage is more efficient in reducing the NH3 volatilization from maize production in Northern China, and the venting method is more suitable for the quantification of NH3 volatilization than the sponge absorption method under a high rate of fertilizer N.

Identification of BTG1 Status in Solid Cancer for Future Researches Using a System Review and Meta-analysis.

Abundant studies have been conducted to identify how B-cell translocation gene 1 protein (BTG1) gene affects the differentiation, proliferation, metastasis of cancer cells, and how it further regulates the generation or development of diseases to influence the prognosis of patients. However, the data from single research were not powerful enough. The correlations between BTG1 expression and mechanisms of tumorigenesis or prognosis of patients are still in controversial. Our system review and meta-analysis provided a complete explanation about the association between BTG1 expression and clinicopathological features or prognosis of patients, which further laid a foundation for future research on BTG1. Fifteen eligible studies consisting of 1992 participants were included. We uncovered that BTG1 expression in solid tumors was associated with lymph node status (RR=0.66, 95% CI: 0.58-0.75, P=0.142), TMN stage status (RR=2.13, 95% CI: 1.71-2.65, P=0.001), T category (RR=1.90, 95% CI: 1.20-3.00, P=0.000), histological differentiation (RR=1.91, 95% CI: 1.55-2.37, P=0.012), vascular invasion (RR=0.90, 95% CI: 0.57-1.41, P=0.001). BTG1 low expression was significantly associated with overall survival (OS) (HR=0.47, 95% CI: 0.38-0.67, P=0.000). It concluded that BTG1 possessed the potential value for future research and could be recommended as a significant biomarker in solid tumor.

Residual concentrations and ecological risks of neonicotinoid insecticides in the soils of tomato and cucumber greenhouses in Shouguang, Shandong Province, East China.

Neonicotinoid insecticides (NNIs) are the most widely used insecticides in China and worldwide. Continuous use of NNIs can lead to their accumulation in soil, causing potential ecological risks due to their relatively long half-life. We used liquid chromatography-tandem mass spectrometry (LC-MS/MS) to investigate the residual levels of nine neonicotinoids in greenhouse soils in Shouguang, East China, at different soil depths and with different crops (tomato and cucumber) after varying periods of cultivation. Seven neonicotinoids were detected in the soils of the tomato greenhouses and six were detected in the soils of the cucumber greenhouses, with total concentrations ranging from 0.731 to 11.383 µg kg-1 and 0.363 to 19.224 µg kg-1, respectively. In all samples, the neonicotinoid residues in the soils cultivated for 8-9 years were lower than in those cultivated for 2 years and 14-17 years. In the tomato greenhouse soils, the residual levels of NNIs were highest in the topsoil, with progressively lower concentrations found with depth. Under cucumber cultivation, the NNI residue levels were also highest in the topsoil but there was little difference between the middle and lower soil layers. Total organic carbon (TOC) decreased with soil depth while pH showed the opposite trend, showing a significant negative correlation in both types of soils (tomato soils ρ = -0.900, p = .001; cucumber soils ρ = -0.883, p = .002). Furthermore, TOC was significantly positively correlated, and pH was negatively correlated, with total NNI concentrations in both types of soils (TOC: tomato soils ρ = 0.800, p = .010; cucumber soils ρ = 0.881, p = .004; pH: tomato soils ρ = -0.850, p = .004; cucumber soils ρ = -0.643, p = .086). The results of an ecological risk analysis showed that acetamiprid represents a particularly high toxicity risk in these soils. Based on our analysis, NNI residues in the soils of tomato greenhouses and their associated ecological risks deserve more attention than those of cucumber greenhouse soils.

Effects of pesticide residues on bacterial community diversity and structure in typical greenhouse soils with increasing cultivation years in Northern China.

The understanding of soil microbiome is important for sustainable cultivation, especially under greenhouse conditions. Here, we investigated the changes in soil pesticide residues and microbial diversity and community structure at different cultivation years under a greenhouse system. The 9-to-14 years sites were found to have the least diversity/rich microbial population as compared to sites under 8 years and over 16 years, as analyzed with alpha diversity index. In total, 42 bacterial phyla were identified across soils with different pesticide residues and cultivation ages. Proteobacteria, Acidobacteria, and Bacteroidetes represented the dominant phyla, that accounted for 34.2-43.4%, 9.7-19.3% and 9.2-16.5% of the total population, respectively. Our data prove that certain pesticides contribute to variation in soil microbial community and that soil bacteria respond differently to cultivation years under greenhouse conditions. Thus, this study provides an insight into microbial community structure changes by pesticides under greenhouse systems and natural biodegradation may have an important part in pesticides soil decontamination.

[Estimation of Winter Wheat Photosynthesized Carbon Distribution and Allocation Belowground via 13C Pulse-labeling].

Evaluating the allocation of carbon (C) photosynthesized by winter wheat belowground is essential for C sequestration in soil and crop production. During the four growth stages of winter wheat, i. e., tillering, elongation, anthesis, and grain-filling, the method of 13CO2 pulse-labeling for the wheat was adopted. Destructive samplings were undertaken at 28 d after each labeling and the total C and 13C contents of shoots, roots, soil, and rhizosphere respiration were determined. Results showed that the majority of the fixed 13C was recovered in the aboveground (straw and grain), ranging from 51.6% to 90.8% in all growth stages. The allocation of 13C photosynthesized belowground (roots, soil, and rhizosphere respiration) decreased as the wheat growth advanced, while the 13C transferred to the aboveground increased. Of the total 13C input belowground, 22.9%-65.3% was respired by the rhizosphere, 24.3%-59.3% remained in the roots, and 10.4%-17.8% was incorporated into the soil organic carbon by rhizodeposition. Respired 13C within the last 2 d of the whole chase period (28 d) only accounted for 0.7%-2.7% of the total respired 13C, indicating that 28 days were long enough to ensure a complete distribution of photosynthesized C within all the wheat and soil pools. For the whole growth season of winter wheat, the photosynthesized C allocated aboveground, to roots, soil organic carbon, and rhizosphere respiration was 78.5%, 6.0%, 3.1%, and 12.4% of the net assimilated C, respectively. Based on local wheat production, the total C transferred belowground was quantified as 1.72 t·hm-2, with 0.99 t·hm-2 respired as rhizosphere respiration, 0.48 t·hm-2 retained in roots, and 0.25 t·hm-2 incorporated into soil organic carbon.

[Effects of Different Agricultural Practices on Soil Carbon Pool in North China Plain].

North China Plain is an important region of grain production.Soil fertility and grain production in this region are significantly influenced by the levels of soil carbon and nitrogen.In order to explore the effects of agricultural practices on the levels of soil carbon and nitrogen,a long-term field experiment was started in 1999 in Quzhou County,Hebei Province.Four treatments,including following nature (F),tillage without straw (N),no tillage with crushed straw incorporation (S),and tillage with crushed straw incorporation (TS),were chosen to collect soil samples at the layers of 0-20 cm and 20-40 cm in 2013.Soil organic carbon (SOC),soil inorganic carbon (SIC),total carbon (TC),total nitrogen (TN),δ13CSOC,δ13CSIC and δ15 N were analyzed.The results indicated that compared with F,SOC stocks of N,S and TS decreased by 21.6%,12.3% and 3.4% in the 0-20 cm soil layer,but the changes of SIC stocks were not significant.In the 20-40 cm soil layer,the changes of the SOC stocks were not significant,but the SIC stocks increased by 4.1%(N),7.3%(S) and 5.0%(TS) compared to F,respectively.Major contribution of SIC increase was the pedogenic inorganic carbonate (PIC),which increased by 97%-261% in the farmland soil.In the soil layer of 0-20 cm,the values of δ15N,δ13CSIC and δ13CSOC in the farmland treatments were higher than those of F,meanwhile,the values of δ13 CSOC were significantly higher than that of F.In the soil layer of 20-40 cm,the values of δ15N and δ13CSIC were lower than those of F,but the value of δ13CSOC showed the opposite trend.In North China Plain,lithogenic inorganic carbonate (LIC) of farmland soil decomposed and PIC increased by the soil-crop system,which provided CO2 for the formation of PIC,and straw returning was an effective agricultural practice to restore the soil carbon decreased by tillage.There should be more long-term monitoring and studies for the impacts of crop straw incorporation and tillage on SOC and SIC,especially for soil in deeper layers.

[Impact of land use change and cultivation measures on soil organic carbon (SOC) and its 13C values].

In Quzhou County, Hebei Province where now intensive farming system is operated, original grassland and farming land under different tillage, crop straw return and fertilization measures were studied using isotope carbon for the analysis of the impact on soil organic carbon (SOC) properties. The research indicated that after change into farmland (34 years), SOC is significantly reduced and for 1 m of soil layer, the scope of reduction is from 13.3%-35% and this decrease happens in 0-40 cm of soil layer. After 8 years of fertilization, SOC can be increased at 0.83 g x kg(-1). No-tillage can significantly increase the SOC especially in 0-10 cm but plough will increase the SOC at 10-15 cm and 15-20 cm. Change of delta13 C of SOC due to land use change mainly happens in 0-20 cm, where input of organic materials from maize stored. In soil layer of 0-5 cm, only maximum 18% of SOC is from crop residues and in 15-20 cm, this percentage is about 5%.

[Estimating photosynthesized carbon distribution and inputs into belowground in a maize soil following 13C pulse-labeling].

Evaluating the contribution of maize growth to soil organic carbon is important for the understanding of the relationship of farmland carbon balance and agriculture production. 4 times of 13C pulse-labelling were used to estimate the photosynthesized carbon distribution at different development stages (seedling, elongation, heading and grain-filling) in maize-soil system, and quantify the carbon inputs into each part of belowground in whole growth season. The result indicated that the 13C retained aboveground reached its maximum: 80.01% among net assimilated 13C at grain-filling stage labelling. For the 4 labelling stages, the 13C transferred into belowground is 43.24%, 46.46%, 30.30% and 19.99% respectively, and of the 13C input into belowground, 34.68%-77.56% was respired by rhizosphere, 16.63%-57.02% was remain in roots and 5.05%-8.30% was incorporated into soil organic carbon by rhizodeposition. During the whole growth season of maize, the photosynthesized carbon allocated to aboveground, roots, rhizosphere respiration and soil organic carbon was 62.39%, 17.88%, 17.07% and 2.67% of the net assimilated carbon. At elongation, heading and grain-filling stages, maize's rhizosphere respiration accounted for 67.07%, 63.31% and 28.82% of the total CO2 efflux from the soil respectively, during the same period rhizosphere priming effect led to 31.11%, 79.09% and 120.83% increase of decomposition of original soil organic carbon respectively. Based on the calculation of 18 t x hm(-2) dry matter of maize for farmland production and its C content is 42%, the total carbon transferred into belowground is 4.6 t x hm(-2), among which 2.1 t x hm(-2) was respired by rhizoshphere, 2.2 t x hm(-2) was retained in roots and 0.33 t x hm(-2) was incorporated into soil organic carbon.