Unprecedented levels of nitrogen (N) have entered terrestrial ecosystems over the past century, which substantially influences the carbon (C) exchange between the atmosphere and biosphere. Temperature and moisture are generally regarded as the major controllers over the N effects on ecosystem C uptake and release. N-phosphorous (P) stoichiometry regulates the growth and metabolisms of plants and soil organisms, thereby affecting many ecosystem C processes. However, it remains unclear how the N-induced shift in the plant N:P ratio affects ecosystem production and C fluxes and its relative importance. We conducted a field manipulative experiment with eight N addition levels in a Tibetan alpine steppe and assessed the influences of N on aboveground net primary production (ANPP), gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem exchange (NEE); we used linear mixed-effects models to further determine the relative contributions of various factors to the N-induced changes in these parameters. Our results showed that the ANPP, GEP, ER, and NEE all exhibited nonlinear responses to increasing N additions. Further analysis demonstrated that the plant N:P ratio played a dominate role in shaping these C exchange processes. There was a positive relationship between the N-induced changes in ANPP (ΔANPP) and the plant N:P ratio (ΔN:P), whereas the ΔGEP, ΔER, and ΔNEE exhibited quadratic correlations with the ΔN:P. In contrast, soil temperature and moisture were only secondary predictors for the changes in ecosystem production and C fluxes along the N addition gradient. These findings highlight the importance of plant N:P ratio in regulating ecosystem C exchange, which is crucial for improving our understanding of C cycles under the scenarios of global N enrichment.

Nitrogen (N) availability is a key regulator of carbon (C) cycling in terrestrial ecosystems. Anthropogenic N input, such as N deposition and fertilization, increases N availability in soil, which has important implications for an ecosystem's C storage and loss. Soil respiration (Rs), which is the second largest C flux from terrestrial ecosystems to the atmosphere, plays an important role in terrestrial C cycles. The direction and magnitude of the responses of Rs and its components to N addition have been widely evaluated, but it remains unclear how these processes change across multiple N addition levels. Here we conducted a two-year field experiment to examine the changes of Rs and its autotrophic respiration (Ra) and heterotrophic respiration (Rh) components along a gradient of eight N levels (0, 1 2, 4, 8, 16, 24, 32 g m À2 yr À1 ) in a Tibetan alpine steppe, and used structural equation modeling (SEM) to explore the relative contributions of biotic and abiotic variables and their direct and indirect pathways regulating the Ra and Rh. Our results indicated that both Rs and Ra exhibited first increasing and then subsequent decreasing trends at the threshold of 8 g N m À2 yr À1 . In contrast, the Rh declined linearly with the N addition rate continuously increasing. SEM analysis revealed that, among various environmental factors, soil temperature was the most important one modulating Rs, which not only had a direct effect on the two Rs components, but also indirectly regulated the Ra and Rh via root and microbial biomass. These findings suggest that the nonlinear response patterns of Rs should be considered for better predicting terrestrial C balance, given that anthropogenic N input to the terrestrial ecosystems is increasing continuously.

Exploring the mechanisms underlying the change in ecosystem productivity under anthropogenic nitrogen (N) inputs is of fundamental ecological interest. It has been proposed that functional traits, environmental factors and species richness are central drivers linking ecosystem productivity with environmental change. However, few studies have considered the joint effects of functional traits, environmental factors and species richness on ecosystem productivity under increasing N inputs. We established a N‐manipulation experiment in a Tibetan alpine steppe in 2013. Using structural equation models, we assessed the effects of N‐induced changes in environmental factors, species richness and trait metrics (mean, variance, skewness and kurtosis of trait distribution) on gross ecosystem productivity as well as three resource use efficiencies (water, light and phosphorus (P) use efficiencies), based on measurements during the peak growing season in 2016. We found that both light and P use efficiencies decreased under N enrichment, largely due to the N‐induced decline in functional diversity of leaf P concentration. However, both gross ecosystem productivity and water use efficiency exhibited initial increases and subsequent slight decreases with N addition. These nonlinear patterns were closely associated with both the increased morphological trait (i.e. mean of leaf area) and decreased diversity of leaf P concentration. Synthesis. Our results illustrate how N‐induced changes in functional traits may have dual effects on ecosystem productivity: the stimulating effects of the dominant trait identity via increasing canopy light interception versus the inhibiting effect of decreasing trait diversity via declining resource use efficiencies. Our results highlight the importance of including functional traits in land surface models to improve predictions of the response of ecosystem function to N inputs.

The complete genomic sequence of a Pakistani isolate of Sugarcane streak mosaic virus (SCSMV-PAK) is determined to be 9782 nucleotides in length, excluding the 3' poly(A) tail, and it comprises a large open reading frame encoding a polyprotein of 3130 amino acid residues. The deduced polyprotein is likely to be cleaved at nine putative protease sites by three viral proteases to ten mature proteins. Conserved motifs of orthologous proteins of other potyviruses are identified in corresponding positions of SCSMV-PAK. The genomic organization is virtually identical to the genera Ipomovirus, Potyvirus, Rymovirus, and Tritimovirus in the family Potyviridae. Sequence analyses indicate that the SCSMV-PAK genomic sequence is different from those of Sugarcane mosaic virus and Sorghum mosaic virus, two viruses with very similar symptoms and host range to SCSMV-PAK. SCSMV-PAK shares 52.7% identity with Triticum mosaic virus (TriMV) and 26.4-31.5% identities with species of the existing genera and unassigned viruses in the Potyviridae at the polyprotein sequence level. Phylogenetic analyses of the polyprotein and deduced mature protein amino acid sequences reveal that SCSMV, together with TriMV, forms a distinct group in the family at the genus level. Therefore, SCSMV should represent a new genus, Susmovirus, in the Potyviridae.

Biomass partitioning has been explored across various biomes. However, the strategies of allocation in plants still remain contentious. This study investigated allocation patterns of above- and belowground biomass at the community level, using biomass survey from the Tibetan Plateau. We explored above- and belowground biomass by conducting three consecutive sampling campaigns across shrub biomes on the northeast Tibetan Plateau during 2011–2013. We then documented the above-ground biomass (AGB), below-ground biomass (BGB) and root: shoot ratio (R/S) and the relationships between R/S and environment factors using data from 201 plots surveyed from 67 sites. We further examined relationships between above-ground and below-ground biomass across various shrub types. Our results indicated that the median values of AGB, BGB, and R/S in Tibetan shrub were 1102.55, 874.91 g m-2, and 0.85, respectively. R/S showed significant trend with mean annual precipitation (MAP), while decreased with mean annual temperature (MAT). Reduced major axis analysis indicated that the slope of the log-log relationship between above- and belowground biomass revealed a significant difference from 1.0 over space, supporting the optimal hypothesis. Interestingly, the slopes of the allometric relationship between log AGB and log BGB differed significantly between alpine and desert shrub. Our findings supported the optimal theory of above- and belowground biomass partitioning in Tibetan shrub, while the isometric hypothesis for alpine shrub at the community level.

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This study presents an efficient strategy based on liquid-liquid extraction, high-speed counter-current chromatography, and preparative HPLC for the rapid enrichment, separation, and purification of four anthraquinones from Rheum tanguticum. A new solvent system composed of petroleum ether/ethyl acetate/water (4:2:1, v/v/v) was developed for the liquid-liquid extraction of the crude extract from R. tanguticum. As a result, emodin, aloe-emodin, physcion, and chrysophanol were greatly enriched in the organic layer. In addition, an efficient method was successfully established to separate and purify the above anthraquinones by high-speed counter-current chromatography and preparative HPLC. This study supplies a new alternative method for the rapid enrichment, separation, and purification of emodin, aloe-emodin, physcione, and chrysophanol.

Anthraquinone glycosides, such as chrysophanol 1-O-β-d-glucoside, chrysophanol 8-O-β-d-glucoside, and physion 8-O-β-d-glucoside, are the accepted important active components of Rheum tanguticum Maxim. ex Balf. due to their pharmacological properties: antifungal, antimicrobial, cytotoxic, and antioxidant activities. However, an effective method for the separation of the above-mentioned anthraquinone glycosides from this herb is not currently available. Especially, greater difficulty existed in the separation of the two isomers chrysophanol 1-O-β-d-glucoside and chrysophanol 8-O-β-d-glucoside. This study demonstrated an efficient strategy based on preparative high-performance liquid chromatography and high-speed countercurrent chromatography for the separation of the above-mentioned anthraquinone glycosides from Rheum tanguticum Maxim.ex Balf.