[Effects of Organic Fertilizer Replacing Chemical Fertilizer on Organic Carbon Mineralization and Active Organic Carbon in Dryland Yellow Soil].

At present, the effect characteristics and mechanism of organic fertilizer replacing chemical fertilizer on organic carbon mineralization and active organic carbon in dryland yellow soil remain unclear. In order to explore the effect of organic fertilizer replacing chemical fertilizer on organic carbon mineralization and active organic carbon in dryland yellow soil, we used soil with no fertilization (CK), only chemical fertilizer (NP), 50% organic fertilizer replacing chemical fertilizer (1/2(NPM)), and 100% organic fertilizer replacing chemical fertilizer (M). We examined the indoor mineralization culture of organic carbon and explored the characteristics of soil organic carbon and the change in active organic carbon under the condition of organic fertilizer replacing chemical fertilizer. The results showed that organic fertilizer replacing chemical fertilizer increased soil pH, organic carbon (SOC), total nitrogen (TN), and C/N. During the culture period, the soil organic carbon mineralization rate of all treatments decreased sharply in the initial stage (2-4 days), decreased slightly in the middle stage (4-20 days), and tended to be stable in the last stage (20-60 days). After fertilization, the cumulative mineralization of soil organic carbon significantly increased by 7.9%-27.7%. Compared with that in the NP treatment, the cumulative mineralization of soil organic carbon decreased by 5.2% in the 1/2(NPM) treatment and increased by 12.2% in the 1/2(NPM) treatment. Before mineralization culture, the substitution of organic fertilizer for chemical fertilizer had no significant effect on soil recalcitrant organic carbon (ROC) but significantly increased the content of microbial biomass carbon (MBC). The content of dissolved organic carbon (DOC) was significantly increased in the 1/2(NPM) treatment and decreased in the M treatment. After 60 days of culture, the content of soil active organic carbon in all treatments decreased compared with the initial content, of which MBC decreased the most (30.6%-41.2%). The accumulated mineralization of organic carbon was significantly positively correlated with soil pH and SOC and significantly positively correlated with the initial value of MBC and the change value before and after culture. To summarize, 100% organic fertilizer replacing chemical fertilizer significantly promoted soil organic carbon mineralization and reduced soil organic carbon stability; 50% organic fertilizer replacing chemical fertilizer inhibited soil organic carbon mineralization, which was beneficial to soil sequestration and fertilization; and 50% organic fertilizer replacing chemical fertilizer significantly increased soil active organic carbon content, and MBC was used as the main carbon source in the process of soil organic carbon mineralization.

Propelling COPII vesicle biogenesis at the endoplasmic reticulum.

COPII vesicle biogenesis at the endoplasmic reticulum requires activation of the Sar1 GTPase, which recruits the COP II coat protein complex to drive membrane budding. In this issue of Structure, Joiner and Fromme (2021) investigate the enigmatic structural basis for Sar1 activation by the Sec12 guanine nucleotide exchange factor.

[Effects of chemical N fertilizer reduction combined with biochar application on soil organic carbon active components and mineralization in paddy fields of yellow soil.] / æ°®è‚¥å‡é‡é æ–½ç”Ÿç‰©ç‚­å¯¹é»„å£¤ç¨»ç”°åœŸå£¤æœ‰æœºç¢³æ´»æ€§ç»„åˆ†å’ŒçŸ¿åŒ–çš„å½±å“.

Reducing the application of chemical fertilizer and increasing fertilizer efficiency can contribute to the sustainable development of agriculture. To evaluate the impacts of N fertilizer reduction and biochar application on soil organic carbon active components and mineralization in yellow soil, an experiment was carried out with five different substitution rates of chemical N fertilizer by biochar under the same rate of N input, i.e., 0, 10%, 20%, 30%, 40% (CK, T1-T4). The results showed that chemical N fertilizer reduction combined with biochar application could significantly improve soil organic carbon (SOC), the magnitude of which was proportional to the amount of biochar application. Under the condition of 20% substitution rate (T2), soil microbial biomass carbon (MBC) and readily oxidized carbon (ROC) were the highest with 293.68 mg·kg-1 and 250.00 mg·kg-1, respectively, but the concentration of soil dissolved organic carbon (DOC) was the lowest. SOC mineralization rate reached the highest on the third day of incubation. Then, it decreased rapidly in the early period (day 3 of incubation to day 6), decreased slowly in the middle period (day 6 of incubation to day 18), and stabilized in the later period (day 18 of incubation to day 30). There was a logarithmic relationship between mineralization rate of soil organic carbon and incubation time. SOC cumulative mineralization amount and cumulative mineralization rate were the lowest in the T2 treatment with 0.66-0.86 g·kg-1 and 2.9%-4.0%, respectively. As the substitution rate of chemical N fertilizer by biochar increased, rice yield increased firstly and then decreased. Rice yield in the T2 treatment was the highest, which increased by 13.4% compared with the CK. The substitution of 20% chemical N fertilizer with biochar (5 t·hm-2) could effectively improve the contents of SOC, MBC, ROC, and rice yield, reduce the cumulative mineralization amount of organic carbon and cumulative mineralization rate, and enhance the capacity of soil carbon sequestration. Hence, it could be the most effective fertilizer practice for improving soil fertility and rice yield in paddy field of yellow soil in Guizhou Province.

Effects of nitrogen fertilization and bioenergy crop species on central tendency and spatial heterogeneity of soil glycosidase activities.

Extracellular glycosidases in soil, produced by microorganisms, act as major agents for decomposing labile soil organic carbon (e.g., cellulose). Soil extracellular glycosidases are significantly affected by nitrogen (N) fertilization but fertilization effects on spatial distributions of soil glycosidases have not been well addressed. Whether the effects of N fertilization vary with bioenergy crop species also remains unclear. Based on a 3-year fertilization experiment in Middle Tennessee, USA, a total of 288 soil samples in topsoil (0-15 cm) were collected from two 15 m2 plots under three fertilization treatments in switchgrass (SG: Panicum virgatum L.) and gamagrass (GG: Tripsacum dactyloides L.) using a spatially explicit design. Four glycosidases, α-glucosidase (AG), ß-glucosidase (BG), ß-xylosidase (BX), cellobiohydrolase (CBH), and their sum associated with C acquisition (Cacq) were quantified. The three fertilization treatments were no N input (NN), low N input (LN: 84 kg N ha-1 year-1 in urea) and high N input (HN: 168 kg N ha-1 year-1 in urea). The descriptive and geostatistical approaches were used to evaluate their central tendency and spatial heterogeneity. Results showed significant interactive effects of N fertilization and crop type on BX such that LN and HN significantly enhanced BX by 14% and 44% in SG, respectively. The significant effect of crop type was identified and glycosidase activities were 15-39% higher in GG than those in SG except AG. Within-plot variances of glycosidases appeared higher in SG than GG but little differed with N fertilization due to large plot-plot variation. Spatial patterns were generally more evident in LN or HN plots than NN plots for BG in SG and CBH in GG. This study suggested that N fertilization elevated central tendency and spatial heterogeneity of glycosidase activities in surficial soil horizons and these effects however varied with crop and enzyme types. Future studies need to focus on specific enzyme in certain bioenergy cropland soil when N fertilization effect is evaluated.

TRAPPing a Rab GTPase by the Tail.

GEFs play a key role in activation and membrane targeting of Rab GTPases. In this issue of Developmental Cell, Thomas et al. (2018) demonstrate how two TRAPP complexes with a common GEF core select distinct Rab substrates through a steric gating mechanism involving their hypervariable tails.