Stabilization of the Metastable Pre-Fusion Conformation of the SARS-CoV-2 Spike Glycoprotein through N-Linked Glycosylation of the S2 Subunit.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the novel coronavirus responsible for the coronavirus disease 2019 (COVID-19) pandemic, represents a serious threat to public health. The spike (S) glycoprotein of SARS-CoV-2 mediates viral entry into host cells and is heavily glycosylated. In this study, we systemically analyzed the roles of 22 putative N-linked glycans in SARS-CoV-2 S protein expression, membrane fusion, viral entry, and stability. Using the α-glycosidase inhibitors castanospermine and NB-DNJ, we confirmed that disruption of N-linked glycosylation blocked the maturation of the S protein, leading to the impairment of S protein-mediated membrane fusion. Single-amino-acid substitution of each of the 22 N-linked glycosylation sites with glutamine revealed that 9 out of the 22 N-linked glycosylation sites were critical for S protein folding and maturation. Thus, substitution at these sites resulted in reduced S protein-mediated cell-cell fusion and viral entry. Notably, the N1074Q mutation markedly affected S protein stability and induced significant receptor-independent syncytium (RIS) formation in HEK293T/hACE2-KO cells. Additionally, the removal of the furin cleavage site partially compensated for the instability induced by the N1074Q mutation. Although the corresponding mutation in the SARS-CoV S protein (N1056Q) did not induce RIS in HEK293T cells, the N669Q and N1080Q mutants exhibited increased fusogenic activity and did induce syncytium formation in HEK293T cells. Therefore, N-glycans on the SARS-CoV and SARS-CoV-2 S2 subunits are highly important for maintaining the pre-fusion state of the S protein. This study revealed the critical roles of N-glycans in S protein maturation and stability, information that has implications for the design of vaccines and antiviral strategies.

Preventable burden of head and neck cancer attributable to tobacco and alcohol between 1990 and 2039 in China.

Tobacco use and heavy alcohol consumption are risk factors for head and neck cancer (HNC), including oral, pharynx, and larynx cancer. No study has investigated the preventable burden of HNC attributable to tobacco and alcohol in China. We extracted data from 1990 to 2019 from the Global Burden of Disease. The preventable burden attributable to tobacco and alcohol was estimated by subtracting the overlapping fraction derived from a literature search. Descriptive analyses were performed initially, followed by joinpoint regression and age-period-cohort (APC) analysis. The future burden was forecasted using a Bayesian APC model. The crude burden increased significantly, while the age-standardized rates showed a downward trend from 1990 to 2019 in China. Both all-age and age-standardized population attributable fractions rose significantly, potentially due to the poor prognosis of tobacco- and alcohol-associated HNC. The absolute burden would continue to climb in the next 20 years from 2019, largely due to population aging. For site-specific burden, compared with total, pharynx, and larynx cancer burden, the substantial upward trend of oral cancer burden indicated a strong interaction with risk factors such as genetic susceptibility, betel nut chewing, oral microbiota, and human papillomavirus. The burden of oral cancer attributable to tobacco and alcohol is a major concern and is anticipated to become more severe than cancer in other anatomic sites. Altogether, our study provides useful information to rethink the current restrictions on tobacco and alcohol, lean healthcare resources, and develop effective HNC prevention and control strategies.

Genomic characterization of a novel torradovirus infecting Arctium lappa L. in China.

Burdock (Arctium lappa L.) is not only a popular vegetable crop but also an important medicinal plant. In burdock plants with symptoms of leaf mosaic, a novel torradovirus tentatively named "burdock mosaic virus" (BdMV) was identified by high-throughput sequencing. The complete genomic sequence of BdMV was further determined using RT-PCR and the rapid amplification of cDNA ends (RACE) method. The genome is composed of two positive-sense single-stranded RNAs. RNA1 (6991 nt) encodes a polyprotein of 2186 aa, and RNA2 (4700 nt) encodes a protein of 201 aa and a polyprotein of 1212 aa that is predicted to be processed into one movement protein (MP) and three coat proteins (CPs). The Pro-Pol region of RNA1 and the CP region of RNA2 shared the highest amino acid sequence identity of 74.0% and 70.6%, respectively, with the corresponding sequences of lettuce necrotic leaf curl virus (LNLCV) isolate JG3. Phylogenetic analysis based on the amino acid sequences of the Pro-Pol and CP regions showed that BdMV clustered with other non-tomato-infecting torradoviruses. Taken together, these results suggest that BdMV is a new member of the genus Torradovirus.

Land cover diversity: Reshaping the socioeconomic value of land.

The land is a vital resource to support economic growth. Previous studies have mainly taken urban and agricultural areas as the major factors of economic boost. However, the supporting role of diversified land in sustainable economy has not been fully valued. This study analyzed the relationship between land cover diversity and socioeconomic outputs from 1992 to 2019 on up to 2086 counties in China. The results showed the regional disparity in the eastern and western counties. In the western counties, land cover diversity was positively correlated with per area socioeconomic indicators throughout the period. In the eastern counties, the correlation with per area indicators has gradually changed from negative to positive. The correlation with per capita indicators was more significant in the east than west. The regional disparity and temporal trends may come from the influence of water resources, demographic pressure and other constraints in different regions. The refreshed land value can help to achieve sustainable development and improve human well-being in the long term.

Analysis and Evaluation of the Flagellin Activity of Bacillus amyloliquefaciens Ba168 Antimicrobial Proteins against Penicillium expansum.

Blue mold caused by Penicillium expansum is one of the most common apple diseases, and it is becoming a serious threat in apple production. The strain Bacillus amyloliquefaciens Ba168 showed high levels of antimicrobial activity in our previous study. To analyze the antimicrobial protein of Ba168, a high-resolution LC-MS/MS proteomic analysis was performed. A total of 1155 proteins were identified from 5233 unique peptides. A total of 16 potential antimicrobial-activity-related proteins were identified; 10 of these proteins have direct antimicrobial effects, while 6 of these proteins are associated with the formation of antimicrobial substances. Then, an antifungal protein of Ba168 was isolated and purified by the sequential chromatography of DEAE Bio-sep FF anion exchange and Sephadex G-75. The single protein, named BP8-2, showed antifungal activity towards Penicillium expansum. The peptide mass fingerprinting of the protein band of BP8-2 had a high similarity with the amino acid sequences of flagellin protein. The results showed that BP8-2 significantly inhibited the growth of P. expansum and slowed the spread of apple blue mold. The results indicated that flagellin is one of the important antimicrobial substances from Ba168.

AlkB RNA demethylase homologues and N6 -methyladenosine are involved in Potyvirus infection.

Proteins of the alkylation B (AlkB) superfamily show RNA demethylase activity removing methyl adducts from N6 -methyladenosine (m6 A). m6 A is a reversible epigenetic mark of RNA that regulates human virus replication but has unclear roles in plant virus infection. We focused on Potyvirus-the largest genus of plant RNA viruses-and report here the identification of AlkB domains within P1 of endive necrotic mosaic virus (ENMV) and an additional virus of a putative novel species within Potyvirus. We show that Nicotiana benthamiana m6 A levels are reduced by infection of plum pox virus (PPV) and potato virus Y (PVY). The two potyviruses lack AlkB and the results suggest a general involvement of RNA methylation in potyvirus infection and evolution. Methylated RNA immunoprecipitation sequencing of virus-infected samples showed that m6 A peaks are enriched in plant transcript 3' untranslated regions and in discrete internal and 3' terminal regions of PPV and PVY genomes. Down-regulation of N. benthamiana AlkB homologues of the plant-specific ALKBH9 clade caused a significant decrease in PPV and PVY accumulation. In summary, our study provides evolutionary and experimental evidence that supports the m6 A implication and the proviral roles of AlkB homologues in Potyvirus infection.

The Teaching Design Methods Under Educational Psychology Based on Deep Learning and Artificial Intelligence.

This study aims to evaluate the practical application value of the teaching method under the guidance of educational psychology and artificial intelligence (AI) design, taking the deep learning theory as the basis of teaching design. The research objects of this study involve all the teachers, students, and students' parents of Ningbo Middle School. The questionnaires are developed to survey the changes in the performance of students before and after the implementation of the teaching design and the satisfaction of all teachers, students, and parents to different teaching methods by comparing the two results and the satisfaction ratings. All objects in this study volunteer to participate in the questionnaire survey. The results suggest the following: (1) the effective return rates of the questionnaires to teachers, students, and parents are 97, 99, and 95%, respectively, before implementation; whereas those after implementation are 98, 99, and 99%, respectively. Comparison of the two return results suggests that there was no significant difference statistically (P > 0.05). (2) Proportion of scoring results before and after implementation is given as follows: the proportions of levels A, B, C, and D are 35, 40, 15, and 10% before implementation, respectively; while those after implementation are 47, 36, 12, and 5%, respectively. After the implementation, the proportion of level A is obviously higher than that before the implementation, and the proportions of other levels decreased in contrast to those before the implementation, showing statistically obvious differences (P < 0.05). (3) The change in the performance of each subject after 1 year implementation is significantly higher than that before the implementation, and the change in the average performance of each subject shows an upward trend. In summary, (1) the comparison on the effective return rate of the satisfaction survey questionnaire proves the feasibility of its scoring results. (2) The comparison of the survey scoring results shows that people are more satisfied with the new educational design teaching method. (3) The comparison of the change in the performance of each subject before and after the implementation indirectly reflects the drawbacks of partial subject education, indicating that the school should pay the same equal attention to every subject. (4) Due to various objective and subjective factors, the results of this study may be different from the actual situation slightly, and its accuracy has to be further explored in the future.

Inhibitory Effect of Osthole from Cnidium monnieri (L.) Cusson on Fusarium oxysporum, a Common Fungal Pathogen of Potato.

Fusarium wilt of potato is one of the most common diseases of potato in China, and is becoming a serious threat in potato production. It has been reported that osthole from Cnidium monnieri (L.) Cusson can inhibit plant pathogens. Here, we test the anti-fungal activity of C. monnieri osthole against Fusarium oxysporum in potatoes. The results showed that at a concentration of 5 mg/mL, osthole was able to obviously inhibit mycelial growth of F. oxysporum. We found that osthole caused changes of mycelial morphology, notably hyphal swelling and darkening. Osthole significantly reduced the spore germination of Fusarium by 57.40%. In addition, osthole also inhibited the growth of other pathogens such as Fusarium moniliforme J. Sheld, Thanatephorus cucumeris Donk, and Alternaria alternata (Fr.) Keissl, but not Alternaria solani Jonesetgrout and Valsa mali Miyabe and G. Yamada. Our results suggest that osthole has considerable potential as an agent for the prevention and treatment of potato Fusarium wilt.

Molecular and biological characterization of Potato virus Y detected in zucchini in China.

Potato virus Y (PVY) is an important viral pathogen of the plant family Solanaceae. However, it has not been reported that PVY infects zucchini (Cucurbita pepo L). Zucchini plants showing symptoms of leaf mosaic and fruit ringspot were collected from Inner Mongolia, China. Using RT-PCR, we amplified the PVY-specific bands in zucchini (PVY-Zu isolate). Further, we found that the viral pathogen could infect Nicotiana benthamiana via mechanical inoculation with the extract of the zucchini leaves. Filamentous virions were observed in infected N. benthamiana plants under a transmission electron microscope. Additionally, the complete genomic fragment of the PVY-Zu isolate was obtained via RT-PCR and RACE analysis, containing 9662 nucleotides (nt) excluding the 3'-terminal poly (A) tail. The 5' and 3' untranslated regions (UTRs) were 150 nt and 329 nt, respectively, while the putative polyprotein contained 3061 amino acids. Comparison of the PVY-Zu isolate with 19 other PVY isolates revealed that they shared nucleotide sequence identities of ~ 83.1-99.8% at the complete genomic level. Based on the complete genome sequences, phylogenetic analysis showed that PVY-Zu clustered with PVY strain N605 (X97895-PVY), a Swiss necrotic isolate of PVY. Compared with the complete genome sequence of X97895-PVY, the PVY-Zu isolate had a deletion of a 39-nt fragment in its 5' UTR and 22 mutated nucleotides without changes in the amino acids. Moreover, although the similarity in the identities of the PVY-Zu isolate and PVY N isolate N-Jg (AY166867) was about 96.2%, the former had a deletion of a 38-nt fragment in its 5' UTR and 334 mutations among the viral genome, which resulted in 61 amino acid changes. However, we could not detect any recombination throughout the PVY-Zu genome. To our knowledge, this is the first study reporting that PVY could infect zucchini plants, thus broadening the host diversity of the viral pathogen. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13337-020-00647-2.

Biocontrol of tobacco black shank disease (Phytophthora nicotianae) by Bacillus velezensis Ba168.

Tobacco black shank (TBS) caused by Phytophthora nicotianae is destructive to almost all tobacco cultivars and is widespread in many tobacco-growing countries. Through lab study and field test, we isolated plant growth-promoting rhizobacteria (PGPR) strain Ba168 which is a promising biocontrol strain of TBS. Ba168 was isolated from 168 soil samples and identified as Bacillus velezensis by its genetic and phenotypic characteristics. A susceptibility test indicated that the P. nicotianae antagonistic materials of Ba168 in extracellular metabolites were composed of effective and stable proteins/peptides. P. nicotianae's growth was suppressed by the ammonium sulfate precipitation of Ba168 culture filtrates (ASPBa) at a minimum inhibitory concentration of 5 µg/mL. Extracellular conductivity, pH, and the wet/dry weights of P. nicotianae's mycelia, along with scanning electron microscope analysis, suggested that Ba168-derived proteins/peptides could effectively inhibit P. nicotianae by causing irreversible damage to its cell walls and membranes. Protein identification of ASPBa supported these results and identified many key proteins responsible for various biocontrol-related pathways. Field assays of TBS control efficacy of many PGPRs and agrochemicals showed that all PGPR preparations reduced the disease index of tobacco, but Ba168 was the most effective. These results demonstrated the importance of Bacillus-derived proteins/peptides in the inhibition of P. nicotianae through irreversible damage to its cell wall and membrane; and the effectiveness of PGPR strain B. velezensis Ba168 for biocontrol of the soil-borne disease caused by P. nicotianae.

Inhibitory Effect of Osthole from Cnidium monnieri on Tobacco Mosaic Virus (TMV) Infection in Nicotiana glutinosa.

The coumarin compound of osthole was extracted from Cnidium monnieri and identified by LC-MS and 1H- and 13C-NMR. Osthole was tested for anti-virus activity against tobacco mosaic virus (TMV) using the half-leaf method. The results showed that stronger antiviral activity on TMV infection appeared in Nicotiana glutinosa than that of eugenol and ningnanmycin, with inhibitory, protective, and curative effects of 72.57%, 70.26%, and 61.97%, respectively. Through observation of the TMV particles, we found that osthole could directly affect the viral particles. Correspondingly, the level of coat protein detected by Western blot was significantly reduced when the concentrations of osthole increased in tested plants compared to that of the control. These results suggest that osthole has anti-TMV activity and may be used as a biological reagent to control the plant virus in the half-leaf method.

Family-level leaf nitrogen and phosphorus stoichiometry of global terrestrial plants.

Leaf nitrogen (N) and phosphorus (P) concentrations are critical for photosynthesis, growth, reproduction and other ecological processes of plants. Previous studies on large-scale biogeographic patterns of leaf N and P stoichiometric relationships were mostly conducted using data pooled across taxa, while family/genus-level analyses are rarely reported. Here, we examined global patterns of family-specific leaf N and P stoichiometry using a global data set of 12,716 paired leaf N and P records which includes 204 families, 1,305 genera, and 3,420 species. After determining the minimum size of samples (i.e., 35 records), we analyzed leaf N and P concentrations, N:P ratios and N∼P scaling relationships of plants for 62 families with 11,440 records. The numeric values of leaf N and P stoichiometry varied significantly across families and showed diverse trends along gradients of mean annual temperature (MAT) and mean annual precipitation (MAP). The leaf N and P concentrations and N:P ratios of 62 families ranged from 6.11 to 30.30 mg g-1, 0.27 to 2.17 mg g-1, and 10.20 to 35.40, respectively. Approximately 1/3-1/2 of the families (22-35 of 62) showed a decrease in leaf N and P concentrations and N:P ratios with increasing MAT or MAP, while the remainder either did not show a significant trend or presented the opposite pattern. Family-specific leaf N∼P scaling exponents did not converge to a certain empirical value, with a range of 0.307-0.991 for 54 out of 62 families which indicated a significant N∼P scaling relationship. Our results for the first time revealed large variation in the family-level leaf N and P stoichiometry of global terrestrial plants and that the stoichiometric relationships for at least one-third of the families were not consistent with the global trends reported previously. The numeric values of the family-specific leaf N and P stoichiometry documented in the current study provide critical synthetic parameters for biogeographic modeling and for further studies on the physiological and ecological mechanisms underlying the nutrient use strategies of plants from different phylogenetic taxa.

A global database of paired leaf nitrogen and phosphorus concentrations of terrestrial plants.

Nitrogen (N) and phosphorus (P) are essential components of the basic cell structure of plants. In particular, leaf N and P concentrations and their stoichiometric relationship largely determine the photosynthesis, growth, reproduction, and ecophysiological processes of plants. As important leaf functional traits, leaf N and P concentrations and their stoichiometric relationship play vital roles in indicating plant nutrient-use strategies and their evolution in terrestrial ecosystems. They also influence physiological and ecological processes in leaves (e.g., growth rate and energy metabolism) and productivity (e.g., net primary production and net ecosystem production) at ecosystem level. However, the lack of a comprehensive data set containing paired leaf N and P concentration records has distinctly limited research on nutrient stoichiometry and leaf functional traits. Here, we provide a global database of paired records of leaf N and P concentrations. A total of 11,354 individual records were acquired spanning 1,291 sites worldwide, including 201 families, 1,265 genera, and 3,227 species. The records span a latitudinal range of 45.28 °S to 68.35 °N and a longitudinal range of 155.5 °W to 168.0 °E. The variables provided for each individual record are (1) geographical location (longitude, latitude, and altitude); (2) matched leaf N and P concentrations and N:P ratio; (3) taxonomic information (family, genera, and species); (4) life form (angiosperm/gymnosperm, monocotyledonous/dicotyledonous and woody plants/herbaceous plants; note that woody plants were further divided into coniferous, deciduous broad-leaved, and evergreen broad-leaved woody species and that herbaceous plants were further divided into annual and perennial species); (5) mean annual temperature (MAT) and mean annual precipitation (MAP); and (6) soil N and P concentrations and pH value in some records. To date, this database is the world's largest database of paired leaf N and P concentrations, which contains matched information of geographical location, environmental factors, and taxa. We believe that the database will play a fundamental and crucial part of ecological stoichiometric studies. There are no copyright restrictions. When using this database, we kindly request that you cite this article, respecting all the authors' hard work during sample collection and data compilation.

Antifungal Effect of Magnolol and Honokiol from Magnolia officinalis on Alternaria alternata Causing Tobacco Brown Spot.

In this study, two phenol compounds, magnolol and honokiol, were extracted from Magnolia officinalis and identified by LC-MS, 1H- and 13C-NMR. The magnolol and honokiol were shown to be effective against seven pathogenic fungi, including Alternaria alternata (Fr.) Keissl, Penicillium expansum (Link) Thom, Alternaria dauci f.sp. solani, Fusarium moniliforme J. Sheld, Fusarium oxysporum Schltdl., Valsa mali Miyabe & G. Yamada, and Rhizoctonia solani J.G. Kühn, with growth inhibition of more than 57%. We also investigated the mechanisms underlying the potential antifungal activity of magnolol and honokiol. The results showed that they inhibited the growth of A. alternata in a dose-dependent manner. Moreover, magnolol and honokiol treatment resulted in distorted mycelia and increased the cell membrane permeability of A. alternata, as determined by conductivity measurements. These results suggest that magnolol and honokiol are potential antifungal agents for application against plant fungal diseases.

Effects of body size and root to shoot ratio on foliar nutrient resorption efficiency in Amaranthus mangostanus.

PREMISE OF THE STUDY: Nutrient resorption is essential for plant nutrient conservation. Large-bodied plants potentially have large nutrient sink pools and high nutrient flux. Whether and how nutrient resorption can be regulated by plant size and biomass allocation are yet unknown. METHODS: Using the herbaceous plant Amaranthus mangostanus in greenhouse experiments for two consecutive years, we measured plant biomass, height, and stem diameter and calculated the root to shoot biomass ratio (R/S ratio) and nutrient resorption efficiency (NuRE) to assess the effects of plant body size and biomass allocation on NuRE. NuRE was calculated as the percentage reduction in leaf nutrient concentration from green leaf to senesced leaf. KEY RESULTS: NuRE increased with plant biomass, height, and stem diameter, suggesting that the individuals with larger bodies, which led to a larger nutrient pool, tended to resorb proportionally more nutrients from the senescing leaves. NuRE decreased with increasing root to shoot ratio, which might have reflected the nutrient acquisition trade-offs between resorption from the senescent leaves and absorption from the soil. Increased root biomass allocation increased the proportion of nutrient acquisition through absorption more than through resorption. CONCLUSIONS: This study presented the first experimental evidence of how NuRE is linked to plant size (indicated by biomass, height, and stem diameter) and biomass allocation, suggesting that nutrient acquisition could be modulated by the size of the nutrient sink pool and its partitioning in plants, which can improve our understanding of a conservation mechanism for plant nutrients. The body size and root to shoot ratio effects might also partly explain previous inconsistent reports on the relationships between environmental nutrient availability and NuRE.

The structure and opto-thermo electronic properties of a new (Bi(Bi2S3)9I3)2/3 hexagonal nano-/micro-rod.

The semiconductor optoelectronic properties of an inorganic (Bi(Bi2S3)9I3)2/3 hexagonal nano-/micro-rod are firstly explored herein. Transmittance and thermoreflectance measurements show that (Bi(Bi2S3)9I3)2/3 hexagonal rods possess an indirect gap of 0.73 eV and a direct gap of 1.08 eV, respectively. Hot-probe measurements of (Bi(Bi2S3)9I3)2/3 reveal the p-type semiconductor behavior and high thermoelectric voltage. Polarized Raman measurements of the m-plane (Bi(Bi2S3)9I3)2/3 (along c and perpendicular to the c axis) identify the structural anisotropy of the hexagonal nano-/micro-rod.

Stage-dependent stoichiometric homeostasis and responses of nutrient resorption in Amaranthus mangostanus to nitrogen and phosphorus addition.

Stoichiometric homeostasis is the ability of plants remaining their element composition relatively stable regardless of changes in nutrient availability, via various physiological mechanisms. Nutrient resorption is one of such key mechanisms, but whether and how nitrogen and phosphorus homeostasis and resorption in plants would change with growth-stages under variable nutrient supply was unclear. A nitrogen (N) and phosphorus (P) fertilizer addition experiment was conducted to evaluate the dynamics of N and P homeostasis and resorption efficiency during different growth-stages of Amaranthus mangostanus in a greenhouse. The homeostasis regulation coefficient of green-leaf P varied significantly, while that of green-leaf N maintained relatively stable across growth stages. Moreover, homeostasis regulation coefficient of N was higher at seedling stage but lower at flowering stage than that of P at corresponding stages, suggesting that the growth of A. mangostanus may switch from being more N- to P-limited from vegetative to reproductive stage. N resorption efficiency (NRE) was higher and P resorption efficiency (PRE) was lower at flowering than seed-filling stage. The nutrient dynamics displayed here suggested contrasting nutrient homeostasis and resorption responses of plants to environmental nutrient availability across growth stages. These findings can improve the understanding of nutrition maintenance mechanism of plants during their growth.

Nutrient allocation strategies of woody plants: an approach from the scaling of nitrogen and phosphorus between twig stems and leaves.

Allocation of limited nutrients, such as nitrogen (N) and phosphorus (P), among plant organs reflects the influences of evolutionary and ecological processes on functional traits of plants, and thus is related to functional groups and environmental conditions. In this study, we tested this hypothesis by exploring the stoichiometric scaling of N and P concentrations between twig stems and leaves of 335 woody species from 12 forest sites across eastern China. Scaling exponents of twig stem N (or P) to leaf N (or P) varied among functional groups. With increasing latitude, these scaling exponents significantly decreased from >1 at low latitude to <1 at high latitude across the study area. These results suggested that, as plant nutrient concentration increased, plants at low latitudes showed a faster increase in twig stem nutrient concentration, whereas plants at high latitudes presented a faster increase in leaf nutrient concentration. Such shifts in nutrient allocation strategy from low to high latitudes may be controlled by temperature. Overall, our findings provide a new approach to explore plant nutrient allocation strategies by analysing the stoichiometric scaling of nutrients among organs, which could broaden our understanding of the interactions between plants and their environments.

Effects of Nitrogen Addition on Nitrogen Resorption in Temperate Shrublands in Northern China.

Nutrient resorption from senescing leaves is a key mechanism of nutrient conservation for plants. The nutrient resorption efficiency is highly dependent on leaf nutrient status, species identity and soil nutrient availability. Nitrogen is a limiting nutrient in most ecosystems, it is widely reported that nitrogen resorption efficiency (NRE) was highly dependent on the soil nitrogen availability and vary with N deposition. The effects of nitrogen deposition on NRE and nitrogen concentration in green and senescing leaves have been well established for forests and grasslands; in contrast, little is known on how plants in shrublands respond to nitrogen deposition across the world. In this study, we conducted a two-year nitrogen addition manipulation experiment to explore the responses of nitrogen concentration in green and senescing leaves, and NRE of seven dominant species, namely, Vitex negundo, Wikstroemia chamaedaphne, Carex rigescens and Cleistogenes chinensis from the Vitex negundo community, and Spirea trilobata, Armeniaca sibirica, V. negundo, C. rigescens and Spodiopogon sibiricus from the Spirea trilobata community, to nitrogen deposition in two typical shrub communities of Mt. Dongling in northern China. Results showed that NRE varied remarkably among different life forms, which was lowest in shrubs, highest in grasses, and intermediate in forbs, implying that shrubs may be most capable of obtaining nitrogen from soil, grasses may conserve more nitrogen by absorption from senescing leaves, whereas forbs may adopt both mechanisms to compete for limited nitrogen supply from the habitats. As the N addition rate increases, N concentration in senescing leaves ([N]s) increased consistent from all species from both communities, that in green leaves ([N]g) increased for all species from the Vitex negundo community, while no significant responses were found for all species from the Spirea trilobata community; NRE decreased for all species except A. sibirica from the Vitex community and W. chamaedaphn from the Spirea community. Given the substantial interspecific variations in nutrient concentration, resorption and the potentially changing community composition, and the increased soil nutrient availability due to fertilization may indirectly impact nutrient cycling in this region.

Biogeographic patterns of structural traits and C:N:P stoichiometry of tree twigs in China's forests.

There have been a number of studies on biogeographic patterns of plant leaf functional traits; however, the variations in traits of other plant organs such as twigs are rarely investigated. In this study, we sampled current-year twigs of 335 tree species from 12 forest sites across a latitudinal span of 32 degrees in China, and measured twig specific density (TSD), twig dry matter content (TDMC), and carbon (C), nitrogen (N) and phosphorous (P) contents, to explore the latitudinal and environmental patterns of these twig traits. The overall mean of TSD and TDMC was 0.37 g cm(-3) and 41%, respectively; mean twig C, N and P was 472 mg g(-1), 9.8 mg g-1 and 1.15 mg g(-1), respectively, and mean N:P mass ratio was 10.6. TSD was positively correlated with TDMC which was positively associated with twig C but negatively with twig N and P. There were no significant differences in TSD between conifer, deciduous-broadleaf and evergreen-broadleaf plants, but evergreen-broadleaf plants had the lowest and conifers the highest TDMC. Conifer twigs were lowest in C, N, P and N:P, whereas deciduous-plant twigs were highest in N and P and evergreen-plant twigs were highest in C and N:P. As latitude increased or temperature/precipitation dropped, TDMC and P increased, but N:P ratio decreased. Our results also showed that the patterns of twig P and N:P stoichiometry were consistent with those reported for leaves, but no significant trends in twig N were observed along the gradient of latitude, climate and soils. This study provides the first large-scale patterns of the twig traits and will improve our understanding of the biogeochemistry of carbon and other key nutrients in forest ecosystems.