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• Warming and water addition increase L. chinensis biomass and reduce S. krylovii. • Community biomass is remained unchanged under warming and water addition. • Warming increases L. chinensis biomass by affecting SA and GA. • S. krylovii steppe may be replaced by L. chinensis in warmer and wetter future. Dominant species play a crucial role in regulating plant community structure and productivity. Climate change affects community productivity by changing plant traits and resource use efficiency. However, the response of the productivity of a dominant species to warming and precipitation addition and the related effects on community biomass production in semi-arid grasslands remain unclear. We conducted a ten-year warming and precipitation addition study of a semi-arid steppe in Inner Mongolia, China. We examined the responses of community composition, biomass production, and trait and resource use efficiency of two dominant species, Leymus chinensis (rhizome grass) and Stipa krylovii. The results show that warming and precipitation increased the biomass of L. chinensis and decreased the biomass of S. krylovii. Community biomass production was unchanged under warming and precipitation from the contrasting changes in the two dominant species. Warming significantly increased the leaf area (LA) of L. chinensis and S. krylovii compared to that in ambient conditions, while it decreased the specific leaf area (SLA) and δ13C of S. krylovii. Increases in temperature stimulated biomass production of L. chinensis by affecting salicylic acid (SA) and GA (gibberellin), and they increased its competitive ability compared with that of S. krylovii. Our results highlight the different responses of L. chinensis and S. krylovii to environmental changes, which stabilised community productivity under warming and precipitation. Our study provides evidence that S. krylovii may be replaced by L. chinensis in steppe climates in the warmer and wetter future. [ABSTRACT FROM AUTHOR]

Abstract: Climate is a driver of terrestrial ecosystem carbon exchange, which is an important product of ecosystem function. The Qinghai–Tibetan Plateau has recently been subjected to a marked increase in temperature as a consequence of global warming. To explore the effects of warming on carbon exchange in grassland ecosystems, we conducted a whole‐year warming experiment between 2012 and 2014 using open‐top chambers placed in an alpine meadow, an alpine steppe, and a cultivated grassland on the central Qinghai–Tibetan Plateau. We measured the gross primary productivity, net ecosystem CO2 exchange (NEE), ecosystem respiration, and soil respiration using a chamber‐based method during the growing season. The results show that after 3 years of warming, there was significant stimulation of carbon assimilation and emission in the alpine meadow, but both these processes declined in the alpine steppe and the cultivated grassland. Under warming conditions, the soil water content was more important in stimulating ecosystem carbon exchange in the meadow and cultivated grassland than was soil temperature. In the steppe, the soil temperature was negatively correlated with ecosystem carbon exchange. We found that the ambient soil water content was significantly correlated with the magnitude of warming‐induced change in NEE. Under high soil moisture condition, warming has a significant positive effect on NEE, while it has a negative effect under low soil moisture condition. Our results highlight that the NEE in steppe and cultivated grassland have negative responses to warming; after reclamation, the natural meadow would subject to loose more C in warmer condition. Therefore, under future warmer condition, the overextension of cultivated grassland should be avoided and scientific planning of cultivated grassland should be achieved. [ABSTRACT FROM AUTHOR]

Scaling up of farming operations by land use rights transfers has been a growing trend in China in recent years. However, little is known about the implications of this trend for greenhouse gas (GHG) emissions and soil organic carbon (SOC) stock changes. Using farm survey data from Shandong Province, a typical grain production region in China, we used a life cycle assessment (LCA) method to evaluate the impact of different farm scales on input use efficiency, grain production, SOC stock changes and GHG emissions. Large-scale farming operations (LSFO) enhanced input use efficiency by reducing fertilizer and pesticide consumption rates and energy use for irrigation. Compared with small household farming operations (SHFO), LSFO attained higher grain yield in wheat-maize and wheat-rice cropping systems. Compared with small farms, carbon footprints per unit area of large-scale farms were lower for wheat (17%) and maize (28%) in the wheat-maize cropping system and for wheat (14%) and rice (8%) in the wheat-rice cropping system. Moreover, LSFO reduced GHG emissions (7–21%) and enhanced SOC stocks (6–9%), compared with SHFO. This study highlights that in China, land use rights transfers to promote large-scale farming can help achieve cleaner grain production with less negative impact on the environment. [ABSTRACT FROM AUTHOR]

To evaluate long-term effect of biochar application on yield-scaled greenhouse gas emissions (YSGE) in a paddy rice cropping system, a 4-year field experiment by static chamber - gas chromatograph method was conducted in South China. Principal component analysis and terminal restriction fragment length polymorphism (T-RFLP) and real-time qPCR was used to unravel the microbial mechanisms of biochar addition. Six treatments were included: control (CK), application of 5 t ha − 1 biochar (BC1), application of 10 t ha − 1 biochar (BC2), application of 10 t ha − 1 biochar (BC3), rice straw return at 2400 kg ha − 1 (RS) and inoculated rice straw return at 2400 kg ha − 1 (RI). The results indicated that biochar amendment significantly decreased methane (CH 4 ) and gross greenhouse gas (GHG) emissions. This may primarily be ascribed to the stimulated biodiversity and abundance of methanotrophic microbes, increased soil pH and improved aeration by reducing bulk density after biochar incorporation. Compared with CK, RS and RI, 26.18%, 70.02%, 66.47% of CH 4 flux and 26.14%, 70.16%, 66.46% of gross GHG emissions were reduced by biochar (mean of three biochar treatments), respectively. Furthermore, biochar significantly increased harvest index of double rice production ( p < 0.05). In comparison with CK, RS and RI, 29.14%, 68.04%, 62.28% of YSGE was reduced by biochar, respectively, and the highest biochar addition rate (20 t ha − 1 ) contributed most to the mitigation of GHG emissions (36.24% decrease compared to CK) and improvement of rice yield (7.65% increase compared to CK). Results of our study suggested that long-term application of biochar should be the potential way to mitigate GHGs emissions and simultaneously improve rice productivity in the paddy rice system. [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]

Our understanding on how soil organic carbon (SOC) storage, crop yield, and yield stability are influenced by climate is limited. To critically examine this, the impact of long-term (≥10 years) application of nutrient management practices on SOC storage, crop productivity, and yield stability were evaluated under different climatic conditions in China using a meta-analysis approach. The cropping area of China was divided into four distinct groups based on local climatic conditions (warm dry, DW; warm moist, WM; cool dry, CD; cool moist, CM). Results indicated that the impact of nutrient management practices on SOC storage, crop yield, and yield stability varies under different climatic zone in China. The use of unbalanced mineral fertilizer (UMF), and balanced mineral fertilizer (BMF) led to a loss in SOC storage by 6%, and 11% under CM climatic zone and gains in DW, WM, and CD climates. Organic fertilizers (OF), combined unbalanced mineral and organic fertilizers (UMOF), and combined balanced mineral and organic fertilizers (BMOF) were able to sustain and enhance SOC storage under all climatic conditions. However, the largest increase in SOC storage across all climates was seen for BMOF. Further, corresponding values of crop productivity and yield stability were also highest for BMOF among all the nutrient management treatments. A linear-plateau model indicated that maximal yield responsive SOC stock (C opt) levels ranged from 33.43 to 45.51 Mg C ha−1 for rice (Oryza sativa), maize (Zea mays), and wheat (Triticum aestivum) production. To enhance and sustain SOC storage, and crop productivity of croplands under different climates, BMOF appears to be the most appropriate nutrient management strategy. Our findings demonstrate that it is essential to optimize nutrient management strategies according to the local climate to protect soil from SOC losses, and for achieving sustainable crop production. • The impact of nutrient managements on SOC storage, crop yield, and yield stability varies under different climatic zones. • Unbalanced mineral, and balanced mineral fertilizer led to a loss in SOC storage by 6%, and 11% under cool moist climate. • Combined balanced mineral with organic inputs is crucial for maximal SOC storage and crop yields under different climates. • Maximal yield responsive SOC stock levels ranged from 33.43 to 45.51 Mg C ha−1 for rice, maize, and wheat production. [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]

• Elevated [CO 2 ] and temperature jointly stimulated leaf A net before heading. • Air warming accelerated photosynthetic down-regulation under CO 2 enrichment after heading. • G s acclimated to warming and CO 2 enrichment in parallel with A net under no stress conditions. • Earlier leaf senescence, larger sink capacity or lower rice sterility might cause photosynthetic acclimation. • Co-elevation of [CO 2 ] and temperature increased dry matter productivity in Chinese double rice cultivation. Changes in atmospheric CO 2 concentration ([CO 2 ]) and temperature have impacts on leaf photosynthesis (A net) and stomatal conductance (G s) of rice, which strongly affect dry matter productivity. Understanding of the acclimation responses of A net and G s under elevated [CO 2 ] and/or temperature is limited. A field experiment of double rice (early rice-late rice rotation) was conducted using open-top chambers from 2013 to 2016 in Hubei Province, Central China, with two levels of [CO 2 ] (ambient, ambient + 60 μmol mol−1) and two levels of temperature (ambient, ambient + 2°C). Averaging across the four-year experiment, elevated [CO 2 ] and elevated temperature increased A net by 2.4 %–9.4 % and 2.4 %–10.7 %, respectively at pre-heading stages. A positive interaction was observed between elevated [CO 2 ] and temperature in early rice which further increased A net , while the interaction was not additive in late rice. Elevated [CO 2 ] caused lower G s and partly offset the stimulation of elevated temperature on G s at tillering and jointing. At post-heading stages, photosynthetic acclimation to elevated [CO 2 ] was observed as the stimulation of A net was not continued. Elevated temperature decreased A net by 1.7 %–16.6 % and further accelerated photosynthetic down-regulation by elevated [CO 2 ]. Warming reduced G s at milking and maturity in early rice because of high ambient temperature, which resulted in stomatal limitation to photosynthesis, but its effects on G s in late rice were positive because the ambient temperature was low. Generally, G s acclimated to warming and CO 2 enrichment in parallel with A net when there were no environmental constraints. Earlier leaf senescence, decreased leaf SPAD, lower seed-setting rate or larger sink capacity caused by elevated [CO 2 ] and/or temperature might directly or indirectly explain the down-regulation on photosynthesis after heading. Our results show that warming alters the acclimation of leaf photosynthesis and stomatal conductance to CO 2 enrichment and the combined effects differ between growth stages, and indicate that co-elevation of [CO 2 ] and temperature may increase dry matter productivity in the Chinese double rice cropping system. [ABSTRACT FROM AUTHOR]

Ecosystem stability is one of the main factors maintaining ecosystem functioning and is closely related to temporal variability in productivity. Resistance and resilience reflect tolerance and recovering ability, respectively, of a plant community under perturbation, which are important for maintaining the stability of ecosystems. Generally, heavy grazing reduces the stability of grassland ecosystems, causing grassland degradation. However, how livestock grazing affects ecosystem stability is unclear in alpine steppe ecosystems. We conducted a five-year grazing experiment with Tibetan sheep in a semi-arid alpine steppe on the Qinghai-Tibetan Plateau, China. The experimental treatments included no grazing (NG), light grazing (LG, 2.4 sheep per ha), moderate grazing (MG, 3.6 sheep per ha) and heavy grazing (HG, 6.0 sheep ha). We calculated resistance and resilience of three plant functional groups and ecosystem stability under the three grazing intensities using aboveground primary productivity. The results showed that with increasing grazing intensity, aboveground biomass of each functional group significantly decreased. As grazing intensity increased, the resistance of forbs first increased then decreased. The resilience of graminoids in HG was significantly lower than in LG plots, but the resilience of legumes in HG was higher than in LG and MG plots. The resilience of graminoids was significantly higher than legume and forbs under LG and MG treatments. In HG treatments, resilience of legumes was higher than graminoids and forbs. Ecosystem stability did not change under different grazing intensities, because of dissimilar performance of the resilience and resistance of functional groups. Our results highlight how the differential resistance and resilience of different function groups facilitate the tolerance of alpine steppe to grazing under even a heavy intensity. However, the degradation risk of alpine steppe under heavy grazing still needs to be considered in grassland management due to sharp decreases of productivity. • Grazing intensity have no significant effects on plant resistance. • Resilience of graminoids under heavy grazing was lower than other treatments. • Under heavy grazing, resilience of legumes was higher than graminoids and forbs. • Ecosystem stability did not change under different grazing intensities. [ABSTRACT FROM AUTHOR]