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With the increasing demands of livestock production, grasslands are under pressure from over‐intensified grazing. Phosphorus (P) and nitrogen (N) fertilization is widely employed to meet the nutrient demands of heavy grazing. Although soil ammonia‐oxidizers play a critical role in determining N dynamics after fertilizer application, their responses to fertilization are still not well understood in steppe grassland systems. Here, the individual and combined effects of N (0, 7.5 and 15 g N m−2 year−1) and P (0, 3.27, 6.55 and 13.09 g P m−2 year−1) applications on soil ammonia‐oxidizers were explored in the Tibetan alpine steppe. Ammonia‐oxidizing archaea (AOA) and bacteria (AOB) abundance and community composition were examined using qPCR, terminal restriction fragment length polymorphism and clone libraries. Results showed that AOB diversity was significantly increased by N fertilization and decreased by P fertilization. The abundance of AOB was significantly increased by N fertilization and its interactive effects with P application. In contrast, AOA community diversity and abundance remained unaffected by either N or P application. The AOB abundance and diversity were affected by the direct effects of N fertilization, as well as its indirect effects of N application through available N and ammonium (NH4+), and further analysis showed that NH4+ and pH were the main factors. The changes to the ammonia‐oxidizing community altered the total N content of plants and the N:P ratio of Gramineae. Plant P properties were influenced by P addition, which also interacted with soil pH and available N to indirectly affect AOB. Overall, AOB exhibited stronger responses to N and P fertilization of alpine steppe grassland than AOA, and appear to play a critical role in plant nutrient absorption under fertilization management. Highlights: Effects of N and P application on AOA and AOB communities were evaluated.AOB, not AOA, responded to N or P, and their interaction, and NH4+ and pH were regulators of AOB.N application affected AOB community, resulting in changes to plant nutrient absorption.P addition affected plant tissue stoichiometry, and thus affected AOB community. [ABSTRACT FROM AUTHOR]

In the alpine steppe zone on the Central Tibetan Plateau, a large amount of area has been degraded due to natural and artificial factors. N & P fertilization is widely accepted to recover degraded pastures in other regions all over the world. However, it is not clear how alpine steppe communities respond to N & P fertilization, and what is the optimal application rate, in the perspective of forage production. To attempt to explore these questions, in July 2013, two fencing sites were designed in Baingoin County with 12 treatments of different levels of nitrogen (N0: 0; N1: 7.5 g m-2 yr-1; N2: 15 g m-2 yr-1) & phosphate (P0: 0; P1: 7.5 gP2O5 m-2 yr-1; P2: 15 gP2O5 m-2 yr-1; P3: 30 gP2O5 m-2 yr-1). The results indicated N&P addition was capable to ameliorate the quality of the two sites in the Tibetan Plateau steppe. Increasing N application level resulted in significant increment in Gramineae and total biomass in the two sites. P addition significantly improved the quantity of Compositae, total biomass and the biomasss of other species in site II, while it only significantly improved the total biomass in site I. Gramineae was much more sensitive to N-induced changes than P-induced changes, and this indicated N addition was better to ameliorate the quality of plateau steppe than P-induced changes. No strong evidence was found for critical threshold within 15 g N m-2 yr-1, and there was decreasing tendency when P addition rate was above 15 g m-2 yr-1. N&P has the potential to accelerate soil acidification, which improved the content of available K, likely as a result of nonsignificant correlation between biomass and soil moisture. This work highlights the the tradeoffs that exist in N and P addition in recovering degraded steppe. [ABSTRACT FROM AUTHOR]

Aim: Species–area relationships (SAR) are widely utilized for estimating the species richness and its spatial turnover across various scales. Despite the prevalent characterization of SAR using the power law in many microbial community studies, its efficacy remains unvalidated. This study aims to characterize the microbial SAR and its mechanisms in alpine grassland soils on the Qinghai‐Tibet Plateau (QTP). Location: Qinghai‐Tibet Plateau, China. Time Period: August 2014. Major Taxa Studied: Soil bacteria. Methods: Soil samples were collected from five alpine grassland sites on the QTP. Employing a nested sampling strategy at each site, soil samples were collected in plot sizes ranging from 0.5 × 0.5 m2 to 2048 × 2048 m2. Soil bacterial communities were analysed by sequencing 16S ribosomal RNA gene amplicons using an Illumina MiSeq. Results: The bacterial SAR exhibited a logarithmic power law (R2: 0.952–0.999), outperforming the power law (R2: 0.701–0.852). Consequently, the most widely adopted power law led to an overestimation of species richness by up to 15.07% in areas >256 × 256 m2, and the regional maximum theoretical richness based on Chao1 by up to 9.88%. Mechanistically, the passive sampling hypothesis was refuted through the rarefied species richness analysis, and the disproportionate effect hypothesis was rejected based on analyses of the effective numbers of species number conversions for the probability of interspecific encounters (SPIE). Notably, Pearson and multiple linear regression analyses indicated that the spatial turnover of bacterial richness was determined by the environmental heterogeneity (R2: 0.855–0.999), rather or better than environmental variables themselves, supporting the 'environment heterogeneity hypothesis'. Main Conclusions: Soil bacterial SAR in alpine grasslands exhibited a logarithmic power relationship. Spatial turnover was primarily governed by the environmental heterogeneity. In contrast, the traditional power law leads to an overestimation of soil bacterial diversity at the regional scale. [ABSTRACT FROM AUTHOR]

• PAH records in Liaodong Bay provides the first detailed reconstruction of industrial activities;. • PAH variations can be divided into four episodes linked to industrialization process since 1815. • Dominant PAH sources of Northeast China shift from wood to coal and petroleum over time;. • PAH fluxes could be used to track the trend for regional anthropogenic CO 2 emissions. Polycyclic aromatic hydrocarbons (PAHs) are excellent tracers for fossil fuel combustion, natural fires and petroleum contamination, and have been widely used for reconstructing past wildfires and industrial activities at a variety of time scales. Here, for the first time, we obtain a high resolution (annual to decadal scale) record of PAHs from two parallel marine sediment cores from the Liaodong Bay, Northeastern China to reconstruct the industrial activities, spanning the past ∼ 200 years from 1815 to 2014. Our data indicate that PAH variations can be divided into four episodes: I) low (probably near background) PAHs from natural fires and domestic wood combustion during the pre-industrial period from 1815 to 1890; II) slightly increased (but with large fluctuations) PAH concentrations derived from intermittent warfare during the World War (1891–1945) and increased industrial activities after 1946 (1946–1965); III) a period of stagnation and, in some cases, reduction in PAHs during the "Cultural Revolution" (1966 to 1979); and IV) a rapid and persistent rise in PAHs post 1979 linked to fast economic development, with PAH concentrations doubled from 1979 to 2014. Changes in PAH distributions demonstrate major shifts in the dominant types of fuels over time from vegetation/wood, to coal and wood, followed by coal and petroleum (including vehicle emissions) over the past 200 years. We find that PAH records also show similar trend to domestic economy and the estimated regional Anthropocene CO 2 emissions from industrial activities, suggesting sedimentary PAH fluxes could be used as an indirect and qualitative proxy to track the trend for regional anthropogenic CO 2 emissions. [Display omitted] [ABSTRACT FROM AUTHOR]

Droughts and heat waves are increasing in magnitude and frequency, altering the carbon cycle. However, understanding of the underlying response mechanisms remains poor, especially for the combination (hot drought). We conducted a 4‐year field experiment to examine both individual and interactive effects of drought and heat wave on carbon cycling of a semiarid grassland across individual, functional group, community and ecosystem levels. Drought did not change below‐ground biomass (BGB) or above‐ground biomass (AGB) due to compensation effects between grass and non‐grass functional groups. However, consistently decreased BGB under heat waves limited such compensation effects, resulting in reduced AGB. Ecosystem CO2 fluxes were suppressed by droughts, attributed to stomatal closure‐induced reductions in leaf photosynthesis and decreased AGB of grasses, while CO2 fluxes were little affected by heat waves. Overall the hot drought produced the lowest leaf photosynthesis, AGB and ecosystem CO2 fluxes although the interactions between heat wave and drought were usually not significant. Our results highlight that the functional group compensatory effects that maintain community‐level AGB rely on feedback of root system responses, and that plant adjustments at the individual level, together with shifts in composition at the functional group level, co‐regulate ecosystem carbon sink strength under climate extremes. • It is indispensable to explore the mechanisms and impacts of climate extremes on the carbon cycle given they are increasing in magnitude and frequency.• Aboveground biomass responses to climate extremes rely on the functional group compensatory effects and feedbacks of root system responses.• Plant physiological adjustments and shifts in community composition co‐regulate ecosystem CO2 fluxes under climate extremes. [ABSTRACT FROM AUTHOR]

The microstructure evolution and mechanical properties of Mg-9Gd-3.8Y-1.9Zn-0.5Zr alloy after high-pressure torsion (HPT) were analyzed. It was found that the dislocation density increased and gradually reached saturation as the number of torsion turns increased. Its microhardness value increases with increasing strain. The microhardness of the alloy was increased to 128 HV after HPT for 15 turns and the grain size was refined from the initial ∼110 μm to ∼63 nm. The strength enhancement mainly originates from fine-grained strengthening, with a contribution of about 42 %. Additional contributions are provided by dislocation strengthening, second phase strengthening, and stacking faults strengthening. The plastic deformation of the material during the HPT process is coordinated by the interaction of multiple slip and { 10 1 ‾ 1 } compression deformation twinning. [ABSTRACT FROM AUTHOR]

Soil microbes play a crucial role in myriad ecological processes in terrestrial ecosystem. With increasing nitrogen (N) loading, phosphorus (P) may become more limiting for soil microbes and these processes. However, it remains unclear to what extent P addition impacts soil microbial communities and respiration at global scale, especially under different N loadings. Therefore, we used a global meta-analysis to examine the effects of phosphorus addition on soil microbes based on 2293 paired observations from 129 studies in the world. Overall, P addition increased significantly total as well as fungal, bacterial, and actinomycete (ACT) phospholipid fatty acids (PLFAs), together with Gram+ bacteria (G+) and Gram- bacteria (G-) abundance regardless of N input or not. The increments were more pronounced under higher P addition rate or places with higher mean annual temperature or mean annual precipitation. Moreover, the fungi: bacteria ratio significantly decreased along elevational gradients. Furthermore, higher P addition frequency tended to have significantly more ACT PLFAs, as well as higher G+:G-, but significantly lower fungi: bacteria ratio (F:B). However, the responses of P addition on bacterial PLFAs and F:B were larger in forest than grassland, and cropland and varied with P fertilizer forms. In addition, the responses of soil organic carbon (SOC) contents was positively correlated with those of microbial biomass carbon (MBC) and bacterial PLFAs, and all these three parameters, in addition to fungal PLFAs, correlated positively with the response of soil respiration (Rs). Our results suggest that phosphorus addition had globally positive effects on soil microbes with different N loadings, and the positive effects of soil microbial abundance tended to promote heterotrophic respiration (Rh) and Rs. These results deepen our understanding of soil microbial community structure and function dynamics under increasing P deposition. They also provide extensive evidences and bases for parameterization of soil carbon cycling models incorporating microbial responses under global climate change. • We found phosphorus addition had globally positive effects on soil microbes. • The soil microbial biomass positively correlated with phosphorus addition rate, mean annual temperature (MAT) and mean annual precipitation (MAP). • The responses of soil microbes varied with P addition forms and ecosystem types. • The positive effects of soil microbes tended to promote Rs and Rh. [ABSTRACT FROM AUTHOR]

• Non-linear patterns of microbial N genes occurred along precipitation gradient. • Breaking points were clearly related to certain soil types. • Attribution of different environmental factors varied by ecosystem. Despite the importance of microorganisms in soil nitrogen (N) cycling, studies on spatial patterns of microbial N-cycling gene abundances in temperate grasslands are still lacking, whose productivity is limited by N. Here, we investigated N functional genes in soil microorganisms from 60 sites in temperate grasslands across 1661 km in Inner Mongolia, China. Abundances of all N functional genes and 16S rDNA tended to decrease from northeast to southwest, consistent with the changing tend of precipitation but contrary to that of temperature. Non-linear saturation curves dominated patterns for abundances of most N functional genes and 16S rDNA along precipitation as they increased with the rising precipitation when <288–343 mm, but remained stable after these breaking points. Interestingly, these breaking points were clearly related to certain soil types, e.g. nifH did not change with precipitation in Chernozems and Gleysols, but increased with it in other soil types. Non-linear saturation patterns were also observed for most N functional gene and 16S rDNA abundances with temperature and soil total organic carbon. In contrast, no consistent spatial pattern for ratios of N functional genes: 16S rDNA was observed, which varied greatly by different N functional genes. Moreover, decay relationships were discovered for the abundance-based matrix of N functional genes over geographic distance. From the temperate meadows to typical steppes and to temperate desert steppes, the influence of relatively long-term environmental variables increased, but that of short-term ones decreased. Overall, we revealed non-linear patterns of N functional gene abundances along precipitation with a clear relationship with soil type, and discovered that attributions of geographic distance, plant community, historical-contingency and contemporary-disturbance to N functional gene community similarity decay were ecosystem–dependent. [ABSTRACT FROM AUTHOR]

• Drought reduced the soil respiration (SR), especially during the treatment. • Heat wave, alone or combined with drought, had little effect on SR. • Seasonal dynamic of SR was regulated soil moisture and microbial activity. • Inter-annual variation in SR was positively related to plant biomass and structure. Increasing frequency and magnitude of climate extremes could fundamentally affect terrestrial carbon (C) cycling. However, as the second-largest terrestrial C flux, soil respiration (SR) responses to climate extremes are not well understood. Here, we investigated the effects of drought, heat wave and drought plus heat wave on SR in a semiarid grassland during the growing season over 3 years. The results indicated that drought consistently reduced the growing-season mean SR, especially during the period of drought treatment, while heat wave, alone or when combined with drought, had little effect on SR. The decreased SR under drought at the intra-annual timescale could be primarily attributable to restriction of low soil moisture to microbial biomass, as there were no consistent changes in plant community (aboveground biomass, richness and abundance). In contrast, the inter-annual variation in SR was positively related to plant community abundance, richness and aboveground biomass in additional to soil water availability, but was not significantly affected by microbial biomass. Our study highlighted that incorporating microbial biomass in C cycling models can improve simulation of seasonal dynamics of soil respiration while incorporating plant community characteristics can benefit prediction of variation in SR across multiple years in semiarid grasslands. [ABSTRACT FROM AUTHOR]