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• The relative abundance of soil rare biosphere was stable under climate changes. • The specific soil microbial taxa strongly related to soil rare biosphere. • The rare biosphere strongly explained variations of soil available nitrogen. Ecological roles of "rare biosphere" (RB) were rarely discussed in alpine grassland ecosystems. We explored the roles of RB and specific taxa of soil bacteria and fungi in regulating soil nutrients and aboveground biomass of an alpine meadow and alpine steppe under warming and enhanced rainfall scenarios on the Qinghai-Tibetan plateau. In the context of alpine meadow and alpine steppe, the relative abundance of bacterial RB was ∼40% in the bacterial community, and it was <10% for fungal RB in the fungal community. The relative abundance of the RB of soil bacteria and fungi were not changed by warming or enhanced rainfall. All specific bacterial taxa and over 90% specific fungal taxa belonged to the RB. The RB, including the most specific taxa, explained many more variations in the contents of soil NO 3 -N and NH 4 -N than the high abundant microbial species under warming and enhanced rainfall conditions. The aboveground biomass of the alpine meadow and steppe were strongly affected by the contents of soil NO 3 -N, available phosphorus and total nitrogen under the condition of warming and enhanced rainfall. Our findings suggest that the robust soil microbial RB plays an important role in regulating the content of soil available nitrogen, which could profoundly affect aboveground plant biomass of alpine grassland ecosystems under climate change conditions. [ABSTRACT FROM AUTHOR]

Atmospheric concentrations of nitrous oxide (N 2 O) have increased over the last 150 years due to human activities. Soils are important source of N 2 O where its production is largely regulated by biological processes. Nitrogen (N) deposition can alter the processes of autotrophic nitrification and denitrification, thus affecting the rate and direction of the soil N 2 O exchange with the atmosphere. It is obvious that atmospheric N deposition has influenced a dry alpine meadow in the Qinghai–Tibetan Plateau (QTP). Therefore, we investigated the effects of N deposition on the annual N 2 O emissions in an alpine meadow of the QTP. The N 2 O flux was measured for 2 years using static chambers and gas chromatography methods at four treatments (N0, background level; N7, add 7 kg N ha −1  yr −1 ; N20, add 20 kg N ha −1  yr −1 ; N40, add 40 kg N ha −1  yr −1 ). We found that high N deposition increased the N 2 O flux, not only in the growing season but also in winter and the spring thaw period. The average annual N 2 O fluxes at N0 and N40 plots were 3.1 and 6.1 μg m −2  h −1 , respectively. Compared with N0, the average annual N 2 O fluxes increased at N7, N20, and N40 plots by 13.7%, 47.6%, and 98.7%, respectively, the N 2 O fluxes in N40 plots increased by 113.6%, 41.6%, and 78.7% during the growing season, winter and spring thaw period, respectively. The emission of N 2 O during the growing season, winter and spring thaw period accounted for 63.2%, 29.9% and 6.9% of annual total emission of N 2 O, respectively. The N 2 O flux correlated significantly with air temperature, soil temperature, soil water content, total nitrogen, total organic carbon, and soil NH 4 + –N content in the alpine meadow. [ABSTRACT FROM AUTHOR]

Practical nitrogen fertilizers are required that simultaneously increase yield and reduce greenhouse gas (GHG) emissions from rice ( Oryza sativa L.) paddies. A field experiment was conducted to measure methane (CH 4 ) and nitrous oxide (N 2 O) fluxes in situ during two double rice-winter fallow rotations (2012–2014) under five different nitrogen fertilizer treatments: traditional urea (CK), polymer-coated controlled release urea (CRU), urea with N-Sever nitrapyrin (NU), urea with 3,4-dimethylpyrazole phosphate (DMPP), and urea with effective microorganisms (EM). The results revealed that GHG emissions ranged between 77.2 and 178.2 kg CH 4 ha −1 and 4.18 and 10.11 kg N 2 O ha −1 averagely over the whole rotation, and significant differences ( P < 0.05) among treatments and seasons were found. N 2 O emissions accounted for 26.6–36.9% of total GWP, and significant N 2 O emissions were observed during the winter fallow period, ranging from 3.1 to 3.88 kg N 2 O ha −1 . Compared to the GWP (7.66 and 8.85 Mg CO 2 ha −1 ) and GHGI (0.52 and 0.63 Mg CO 2 Mg −1 grain) from CK in 2012 and 2013 rotation, respectively, CRU achieved the highest reduction (48.5% for GWP and 55.4% for GHGI) in 2012, NU achieved the highest reduction (37.6% for GWP and 43.1% for GHGI) in 2013, and other treatments also realized different levels of decrease. Thus, controlled release urea, nitrification inhibitor or effective microorganisms might be effective fertilization options for low-carbon rice production with high yield. [ABSTRACT FROM AUTHOR]

China's green development has advanced national strategic requirements for excessive nitrogen application, greenhouse gas emission reduction, and efficient production in food systems. However, large challenges still exist in achieving these goals. In this study, a comprehensive meta-analysis and random forest identification were conducted to integrate nitrogen fertilization based nitrous oxide (N 2 O) emission data from field experiments in the dry farming system of China (DFSC), and to analyze the dependency of N 2 O emissions and crop yield on nitrogen inputs. We then quantified the potential reasonable nitrogen dose in the DFSC that would simultaneously reduce N 2 O emissions and favor China's green development. The results showed an absolute impact of nitrogen input on N 2 O emissions, and a significant nonlinear response between N 2 O emissions and nitrogen dose in the DFSC. However, the crop yield exhibited a different pattern: yields of cereal and cash crops in response to nitrogen input were modeled by a quadratic polynomial, especially at extremely high nitrogen rates (>300 kg N ha−1 for cereals and >600 kg N ha−1 for cash crops). The yield enhancing effect tended to be flat or even decrease. We propose to achieve a reasonable nitrogen dose by reducing the 1/3 nitrogen surplus in the DFSC, according to the various soil-climatic conditions. For cereal, cash, vegetable, tea and orchard crops, the values should be 98.72 – 133.46, 67.66 – 107.4, 258.53 – 470.57, 159.61–296.09 and 269.08–383.48 kg N ha−1, respectively. The findings of our investigation indicate that implementation of a reasonable nitrogen dosage will not give rise to a large yield decrease and will better contribute to meeting the requirements of N 2 O mitigation and a national green development strategy. • Nonlinear response of N 2 O emissions to N input exist in DFSC. • Crop yield in DFSC exhibited Quadratic polynomial correspondence to N application. • Reducing N 2 O emissions by abatement N use favors both food security and green development in China. [ABSTRACT FROM AUTHOR]

• The effect of grazing regime on functional genes were different at distinct grazing period. • Grazing regime affected the temporal variation of soil microbial functional genes. • Grazing rather than exclosure promote C fixation and decomposition and N cycling. • There existed trade-offs between plant and soil nutrients along the grazing time. • Continuous grazing promoted CH 4 metabolism. Microbial functional genes can reflect the nutrient cycle activities in soil, because they encode various enzymes involved in the material cycle. Therefore, the gene abundance variation can reveal the impact of interference on the material cycle of grassland. To study the cycle of carbon (C), nitrogen (N) and phosphorus (P) between plant and soil in grassland under different grazing regimes, we investigated the soil microbial functional genes related to C, N, and P cycling by high-throughput quantitative PCR and 16S rRNA-based Illumina sequencing analysis under grazing exclusion (GE), rotational grazing (RG), and continuous grazing (CG) in alpine meadow of the Qinghai-Tibetan Plateau, where climate is characterized by little rain and low temperature, and grassland is very sensitive to grazing. The results showed at the early grazing period, C fixtion (rbcL , korA , and frdA) and lignin degradation (abfA , xylA , exg , lig , exoPG , chiA , and glx) processes were slower under GE; CH 4 metabolism (mcrA) was faster under CG; RG and CG improved the denitrification process (narG); RG slowed down organic-P mineralization (phoD). At the late grazing period, C fixation (accA and frdA) and degradation (mnp , apu , and amyA) processes were slower under GE; CH 4 metabolism (pmoA and mxa) was faster under CG; RG and CG improved the ammonia-oxidizing (amoA2), nitrification (hao), and denitrification (nirS3 and nirK1) processes. The majority of the genes involved in C, N, and P cycling decreased, the C, N and P content in plant leaf decreased, while that of soil increased from early to late grazing period. No matter grazing or not, there were negative relationships between genes and soil nutrients, and positive relationships between genes and plant nutrients, implying a trade-off between plant nutrients and soil nutrients along the grazing time. The genes responsible for regulating C and N cycling were increased under grazing, implying that reasonable grazing is beneficial to the nutrients cycling of grassland. [ABSTRACT FROM AUTHOR]

• Three isotopic methodologies were used to quantify the biogenic CH 4 production pathway. • AM processes predominant the CH 4 production in the agricultural river network. • Long-term measurements provide the new understanding of atmospheric CH 4. Methane (CH 4) emitted from river networks provides a globally significant, yet poorly constrained barrier for the refinement of national greenhouse gas (GHG) inventories and the global CH 4 budget. This study employed three isotopic methodologies, i.e., a simple mixing model, apparent fractionation factor, and dual isotopes (δ13C−CH 4 and δD−CH 4) to identify the biogenic CH 4 production pathway (BMPP) in a typical agricultural river network in subtropical China. The results indicated that the contribution of acetoclastic methanogenesis (AM) to BMPP in the Tuojia River network (TRN) ranged from 85 to 99%, with the first reach (S1) supporting the most biogenic CH 4 production. Furthermore, the α C value ranged from 1.00 to 1.039 and increased spatially over the four reaches (S1 to S4), while the α D value varied from 1.393 to 1.394, with S1 having the lowest value. The dual isotopes of δ13C and δD reflected a mixed BMPP. Clearly, the isotopic composition of CH 4 corroborated the predominance of AM in the BMPP in the TRN. Additionally, there was a remarkable spatiotemporal variation in δ13C−CH 4 and δD−CH 4 , as well as α C and α D. In combination with the correlation between the two paired isotopic signatures (antipathetic and positive, p < 0.05, respectively), this suggested a change in the BMPP in the TRN. The findings of our study implied that there was great impact of agricultural production and residential activities on environmental behavior of stable isotopes. Consequently, we recommend that multiple isotopic measures, based on long-term in situ isotopologue monitoring, should be applied when the uncertainties of CH 4 emissions from river networks are addressed. [ABSTRACT FROM AUTHOR]