Phosphorus alleviation of nitrogen-suppressed methane sink in global grasslands.

Grassland ecosystems account for more than 10% of the global CH4 sink in soils. A 4-year field experiment found that addition of P alone did not affect CH4 uptake and experimental addition of N alone significantly suppressed CH4 uptake, whereas concurrent N and P additions suppressed CH4 uptake to a lesser degree. A meta-analysis including 382 data points in global grasslands corroborated these findings. Global extrapolation with an empirical modelling approach estimated that contemporary N addition suppresses CH4 sink in global grassland by 11.4% and concurrent N and P deposition alleviates this suppression to 5.8%. The P alleviation of N-suppressed CH4 sink is primarily attributed to substrate competition, defined as the competition between ammonium and CH4 for the methane mono-oxygenase enzyme. The N and P impacts on CH4 uptake indicate that projected increases in N and P depositions might substantially affect CH4 uptake and alter the global CH4 cycle.

A new model of two-sown regime for oat forage production in an alpine region of northern China.

Demand for high forage production and quality has been increased markedly by development of animal husbandry in China. The lack of efficient planting regimes and key technologies greatly limits production of high-quality forage. Oat has become an important forage in animal husbandry in China due to its high nutritional value and forage yield as well as its great adaptation to harsh environment. To maximize oat forage production in an alpine region, we developed a new model of oat forage production known as two-sown regime, i.e., the first spring-sown and the second summer-sown, during a single growing season in an alpine region of Hulun Buir, Inner Mongolia Autonomous Region, China, using two early-matured oat species, Avena sativa (cv. Qinghai444, winner oat cultivar) and A. nuda (cv. Huazao2, spring oat cultivar). The key technologies and the underlying agronomic mechanisms were investigated across three experimental years of 2017-2019. The main results were as follows: (1) dry weight yield, crude protein yield, and relative feed value of forage in the two-sown regime were significantly increased by 53.6%, 48.9%, and 70.6% relative to traditional one-sown regime across the 3 years, respectively; (2) forage production was mainly achieved by an increase in plant height at the first spring-sown; and (3) forage yield resulted mainly from an increase in tiller density by increasing seeding rate under no-tillage treatment in the second summer-sown. The key technologies of the two-sown regime were the first spring-sown at the soil thawing depth 10-13 cm, followed by the second summer-sown with increasing seeding rate under no-tillage treatment. These findings highlight that the two-sown regime of oat forage can be widely used as an effective planting regime to maximize forage production in large alpine regions of northern China as well as in regions with similar climates.

Aerobic and anaerobic nonmicrobial methane emissions from plant material.

Methane (CH(4)) may be generated via microbial and nonmicrobial mechanisms. Nonmicrobial CH(4) is also ubiquitous in nature, such as in biomass burning, the Earth's crust, plants, and animals. Relative to microbial CH(4), nonmicrobial CH(4) is less understood. Using fresh (living) and dried (dead) leaves and commercial structural compounds (dead) of plants, a series of laboratory experiments have been conducted to investigate CH(4) emissions under aerobic and anaerobic conditions. CH(4) emissions from fresh leaves incubated at ambient temperatures were nonmicrobial and enhanced by anaerobic conditions. CH(4) emissions from dried leaves incubated at rising temperature ruled out a microbial-mediated formation pathway and were plant-species-dependent with three categories of response to oxygen levels: enhanced by aerobic conditions, similar under aerobic and anaerobic conditions, and enhanced by anaerobic conditions. CH(4) emissions in plant structural compounds may help to fully understand nonmicrobial CH(4) formation in plant leaves. Experiments of reactive oxygen species (ROS) generator and scavengers indicate that ROS had a significant role in nonmicrobial CH(4) formation in plant material under aerobic and anaerobic conditions. However, the detailed mechanisms of the ROS were uncertain.

Transgenerational effect alters the interspecific competition between two dominant species in a temperate steppe.

One of the key aims of global change studies is to predict more accurately how plant community composition responds to future environmental changes. Although interspecific relationship is one of the most important forces structuring plant communities, it remains a challenge to integrate long-term consequences at the plant community level. As an increasing number of studies have shown that maternal environment affects offspring phenotypic plasticity as a response to global environment change through transgenerational effects, we speculated that the transgenerational effect would influence offspring competitive relationships. We conducted a 10-year field experiment and a greenhouse experiment in a temperate grassland in an Inner Mongolian grassland to examine the effects of maternal and immediate nitrogen addition (N) and increased precipitation (Pr) on offspring growth and the interspecific relationship between the two dominant species, Stipa krylovii and Artemisia frigida. According to our results, Stipa kryloii suppressed A. frigida growth and population development when they grew in mixture, although immediate N and Pr stimulated S. kryloii and A. frigida growth simultaneously. Maternal N and Pr declined S. krylovii dominance and decreased A. frigida competitive suppression to some extent. The transgenerational effect should further facilitate the coexistence of the two species under scenarios of increased nitrogen input and precipitation. If we predicted these species' interspecific relationships based only on immediate environmental effects, we would overestimate S. krylovii's competitive advantage and population development, and underestimate competitive outcome and population development of A. frigida. In conclusion, our results demonstrated that the transgenerational effect of maternal environment on offspring interspecific competition must be considered when evaluating population dynamics and community composition under the global change scenario.

Agronomic and economical characterizations of a two-harvest regime for oat forage in cold regions of Northern China.

The natural grasslands in northern China have been seriously degraded due mainly to overgrazing and climate change in recent decades, leading to shortage of forage supply to animal husbandry. To maximize forage production, we developed a two-harvest regime of oat forage by sowing in spring in an alpine region of Hulun Buir, northern China, using two oat early maturation species. The agronomic characteristics and forage quality of the two-harvest regime were evaluated across three constructive years from 2017 to 2019. Compared to the traditional one-harvest regime, the production, resource use efficiency, and economic benefits were compared and quantified for both oat species across the 3 years. Dry weight forage by the two-harvest regime was increased by 17.5-18.5%, while crude protein was increased by 25.1-30.0%. Growing days by the two-harvest regime was increased by 36.7% on average, nitrogen fertilizer use efficiency was enhanced by 25.1-30.0%, while water use efficiency was not significantly changed. The two-harvest regime also increased the net profit by 28.0%. Taken together, our results reveal that the two-harvest regime of forage production in the cold region of northern China is a promising practice with high forage yield, nutritional value, and nitrogen fertilizer use efficiency as well as economic profit.

Spatiotemporal patterns and drivers of methane uptake across a climate transect in Inner Mongolia Steppe.

Steppe soils are important biological sinks for atmospheric methane (CH4), but the strength of CH4 uptake remains uncertain due to large spatiotemporal variation and the lack of in situ measurements at regional scale. Here, we report the seasonal and spatial patterns of CH4 uptake across a 1200 km transect in arid and semi-arid steppe ecosystems in Inner Mongolia, ranging from meadow steppe in the east plain to typical and desert steppes on the west plateau. In general, seasonal patterns of CH4 uptake were site specific, with unimodal seasonal curves in meadow and typical steppes and a decreasing seasonal trend in desert steppe. Soil moisture was the dominant factor explaining the seasonal patterns of CH4 uptake, and CH4 uptake rate decreased with an increase in soil moisture. Across the transect, CH4 uptake showed a skewed unimodal spatial pattern, with the peak rate observed in the typical steppe sites and with generally higher uptake rates in the west plateau than in the east plain. Soil moisture, together with soil temperature, soil total carbon, and aboveground plant biomass, were the main drivers of the regional patterns of CH4 uptake rate. These findings are important for model development to more precisely estimate the soil CH4 sink capacity in arid and semi-arid regions.

Effects of water and nitrogen addition on ecosystem respiration across three types of steppe: The role of plant and microbial biomass.

Evaluating the regional variation of ecosystem respiration (Reco) in its response to the changes of soil water and nitrogen (N) availability is crucial for fully understanding ecosystem carbon (C) exchange and its feedbacks to global changes. Here, we examined the responses of Reco, plant community aboveground biomass (AB), microbial biomass carbon (MBC) and soil moisture (SM) to water and N addition, using intact soil monoliths from three different temperate steppes along a precipitation gradient, including meadow steppe, typical steppe, and desert steppe in northern China. We found that the meadow steppe held the highest value of Reco. Water addition significantly enhanced Reco while N addition had no effect on Reco in all three ecosystems. The response of Reco in the typical steppe was more sensitive than the other two ecosystems. The changes of plant community AB exhibited a much stronger explanatory power than that of MBC for Reco in the typical steppe. In contrast, MBC was the dominant factor explaining the variation of Reco in the desert steppe and the meadow steppe. These findings contribute to our understanding of regional patterns of ecosystem C exchange under scenarios of global changes and highlight the importance of water availability in regulating ecosystem processes in temperate steppe grasslands.

Dissolved methane in groundwater of domestic wells and its potential emissions in arid and semi-arid regions of Inner Mongolia, China.

Methane (CH4) is widely present in groundwater. Dissolved CH4 in groundwater is less understood when compared with that in wetlands. In this study, the concentrations and origin of dissolved CH4 in groundwater were investigated and the potential importance of groundwater CH4 emissions in arid and semi-arid regions of Inner Mongolia was discussed. Groundwater was extracted from domestic wells using a submersible pump or manual power and was analyzed for CH4 concentrations, δ13C-CH4, and physico-chemical variables. The results show that the concentrations of dissolved CH4 in groundwater had large spatial variability, ranging from 0 to 0.10 mg L-1 with a mean of 0.01 mg L-1 in Xilingol and from 0 to 8.99 mg L-1 with a mean of 1.44 mg L-1 in Xingan-Tongliao. Substantial CH4 concentrations of about 2.5-5.5 mg L-1 were found in central areas of Xingan-Tongliao in the winter and the summer. The δ13C-CH4 of about -85‰ was highly depleted while CH4 concentration was significantly negatively correlated with SO42- concentration, indicating that dissolved CH4 in groundwater was microbial in origin. This study suggests that groundwater as a source of CH4 might have great implications in arid and semi-arid regions worldwide and should deserve more research.

Response of soil methane uptake to simulated nitrogen deposition and grazing management across three types of steppe in Inner Mongolia, China.

The response of soil methane (CH4) uptake to increased nitrogen (N) deposition and grazing management was studied in three types of steppe (i.e., meadow steppe, typical steppe, and desert steppe) in Inner Mongolia, China. The experiment was designed with four simulated N deposition rates such as 0, 50, 100, and 200kgNha-1, respectively, under grazed and fenced management treatments. Results showed that the investigated steppes were significant sinks for CH4, with an uptake flux of 1.12-3.36kgha-1 over the grass growing season and that the magnitude of CH4 uptake significantly (P<0.05) decreased with increasing N deposition rates. The soil CH4 uptake rates were highest in the desert steppe, moderate in the typical steppe, and lowest in the meadow steppe. Compared with grazed plots, fencing increased the CH4 uptake by 4.7-40.2% with a mean value of 20.2% across the three different steppe types. The responses of soil CH4 uptake to N deposition in the continental steppe varied depending on the N deposition rate, steppe type, and grazing management. A significantly positive correlation between CH4 uptake and soil temperature was found in this study, whereas no significant relationship between soil moisture and CH4 uptake occurred. Our results may contribute to the improvement of model parameterization for simulating biosphere-atmosphere CH4 exchange processes and for evaluating the climate change feedback on CH4 soil uptake.

Effects of Increased Nitrogen and Phosphorus Deposition on Offspring Performance of Two Dominant Species in a Temperate Steppe Ecosystem.

Plants adapt to environment by plastic growth which will be transferred to offspring through transgenerational effect. Performance and response of maternal and offspring plant will affect population dynamics and community composition. However, it is scarcely understood how maternal nutrient environment affect the performance and response of offspring through transgenerational effect. Here we studied the impacts of nitrogen (N) and phosphorus (P) enrichment on maternal and offspring performances and responses of Stipa krylovii and Artemisia frigida. Seeds were collected from maternal plant experiencing N or/and P addition for three years in Inner Mongolia grassland. We found that maternal nutrient addition significantly affected seed traits, offspring biomass, and offspring responses of A. frigida. Maternal N addition significantly affected maternal reproductive biomass, seed traits of S. kryloii. Maternal P addition of S. kryloii significantly affected seed qualities, seedling biomass and seeding response to N addition. Our results suggested that transgenerational effects of N and P enrichment to the two dominant plant species existed in this ecosystem. Furthermore, the two species exhibited different adaptive strategies to future nutrient addition. These findings indicate that maternal environmental effect should be considered into the model projection of vegetation dynamics in response to ongoing environmental change.

Interactive impacts of nitrogen input and water amendment on growing season fluxes of CO2, CH4, and N2O in a semiarid grassland, Northern China.

Nitrogen and water are two important factors influencing GHG (primarily CO2 - carbon dioxide; CH4 - methane, and N2O - nitrous oxide) fluxes in semiarid grasslands. However, the interactive effects of nitrogen and water on GHG fluxes remain elusive. A 3-year (2010-2012) manipulative experiment was conducted to investigate the individual and interactive effects of nitrogen and water additions on GHG fluxes during growing seasons (May to September) in a semiarid grassland in Northern China. Accumulated throughout growing seasons, nitrogen input stimulated CO2 uptake by 3.3±1.0gCm-2 (gN)-1, enhanced N2O emission by 1.2±0.3mgNm-2 (gN)-1, and decreased CH4 uptake by 5.2±0.9mgNm-2 (gN)-1; water amendment stimulated CO2 uptake by 0.2±0.1gCm-2 (mmH2O)-1 and N2O emission by 0.2±0.02mgNm-2 (mmH2O)-1, decreased CH4 uptake by 0.3±0.1mgCm-2 (mmH2O)-1. A synergistic effect between nitrogen and water was found on N2O flux in normal year while the additive effects of nitrogen and water additions were found on CH4 and CO2 uptakes during all experiment years, and on N2O emission in dry years. The nitrogen addition had stronger impacts than water amendment on stimulating CH4 uptake in the normal year, while water was the dominant factor affecting CH4 uptake in dry years. For N2O emission, the N-stimulating impact was stronger in un-watered than in watered plots, and the water-stimulating impact was stronger in non-fertilized than in fertilized treatments in dry years. The interactive impacts of nitrogen and water additions on GHG fluxes advance our understanding of GHG fluxes in responses to multiple environmental factors. This data source could be valuable for validating ecosystem models in simulating GHG fluxes in a multiple factors environment.

Effects of Ge-132 and GeO2 on seed germination and seedling growth of Oenothera biennis L. under NaCl stress.

To investigate the effects of ß-carboxyethyl germanium sequioxide (Ge-132) and germanium dioxide (GeO2) on improving salt tolerance of evening primrose (Oenothera biennis L.), seed germination, seedling growth, antioxidase and malondialdehyde (MDA) were observed under treatments of various concentrations (0, 5, 10, 20, 30 µM) of Ge in normal condition and in 50 mM NaCl solution. The results showed that both Ge-132 and GeO2 treatments significantly increased seed germination percentage and shoot length in dose-dependent concentrations but inhibited early root elongation growth. 5-30 µM Ge-132 and 10, 20 µM GeO2 treatments could significantly mitigate even eliminate harmful influence of salt, representing increased percentage of seed germination, root length, ratio between length of root and shoot, and decreased shoot length. These treatments also significantly decreased peroxidase (POD) and catalase (CAT) activities and MDA content. The mechanism is likely that Ge scavenges reactive oxygen species - especially hydrogen peroxide (H2O2) - by its electron configuration 4S24P2 so as to reduce lipid peroxidation. This is the first report about the comparison of bioactivity effect of Ge-132 and GeO2 on seed germination and seedling growth under salt stress. We conclude that Ge-132 is better than GeO2 on promoting salt tolerance of seed and seedling.

Contribution of the pod wall to seed grain filling in alfalfa.

Three genotypes of alfalfa viz. Medicago sativa (Zhongmu No. 1, Zhongmu No. 2) and M. varia (Caoyuan No. 3) grown in the filed were investigated for the contribution of pod wall and leaves by shading all pods and leaves on July 15, 20 and 25, respectively. Date was recorded for total pod weight (TPW), pod wall weight (PWW), seed weight per pod (SWP), seed number per pod (SNP) and single seed weight (SSW) of one-coil and two-coil spiral pods. TPW, SNP, PWW and SWP were reduced by shading all leaves or pods, whereas SSW was not significantly affected. The relative photosynthetic contribution of pod wall to SWP was 25.6-48.1% in three genotypes on July 15. The pod wall in one-coil spiral pods generated a greater relative contribution to the TPW and SWP than in two-coil spiral pods. In the last stage (July 25), the relative photosynthetic contribution of leaves to SWP sharply decreased, whereas the relative photosynthetic contribution of pod wall to SWP was stable in the late stage (July 20 and 25). In conclusion, the pod wall of alfalfa could carry out photosynthesis and the pod wall played an important role in pod filling at the late growth stage.

Grazing effects on ecosystem CO2 fluxes differ among temperate steppe types in Eurasia.

Grassland ecosystems play a critical role in regulating CO2 fluxes into and out of the Earth's surface. Whereas previous studies have often addressed single fluxes of CO2 separately, few have addressed the relation among and controls of multiple CO2 sub-fluxes simultaneously. In this study, we examined the relation among and controls of individual CO2 fluxes (i.e., GEP, NEP, SR, ER, CR) in three contrasting temperate steppes of north China, as affected by livestock grazing. Our findings show that climatic controls of the seasonal patterns in CO2 fluxes were both individual flux- and steppe type-specific, with significant grazing impacts observed for canopy respiration only. In contrast, climatic controls of the annual patterns were only individual flux-specific, with minor grazing impacts on the individual fluxes. Grazing significantly reduced the mean annual soil respiration rate in the typical and desert steppes, but significantly enhanced both soil and canopy respiration in the meadow steppe. Our study suggests that a reassessment of the role of livestock grazing in regulating GHG exchanges is imperative in future studies.

Proteomic Identification of Differentially Expressed Proteins during Alfalfa (Medicago sativa L.) Flower Development.

Flower development, pollination, and fertilization are important stages in the sexual reproduction process of plants; they are also critical steps in the control of seed formation and development. During alfalfa (Medicago sativa L.) seed production, some distinct phenomena such as a low seed setting ratio, serious flower falling, and seed abortion commonly occur. However, the causes of these phenomena are complicated and largely unknown. An understanding of the mechanisms that regulate alfalfa flowering is important in order to increase seed yield. Hence, proteomic technology was used to analyze changes in protein expression during the stages of alfalfa flower development. Flower samples were collected at pre-pollination (S1), pollination (S2), and the post-pollination senescence period (S3). Twenty-four differentially expressed proteins were successfully identified, including 17 down-regulated in pollinated flowers, one up-regulated in pollinated and senesced flowers, and six up-regulated in senesced flowers. The largest proportions of the identified proteins were involved in metabolism, signal transduction, defense response, oxidation reduction, cell death, and programmed cell death (PCD). Their expression profiles demonstrated that energy metabolism, carbohydrate metabolism, and amino acid metabolism provided the nutrient foundation for pollination in alfalfa. Furthermore, there were three proteins involved in multiple metabolic pathways: dual specificity kinase splA-like protein (kinase splALs), carbonic anhydrase, and NADPH: quinone oxidoreductase-like protein. Expression patterns of these proteins indicated that MAPK cascades regulated multiple processes, such as signal transduction, stress response, and cell death. PCD also played an important role in the alfalfa flower developmental process, and regulated both pollination and flower senescence. The current study sheds some light on protein expression profiles during alfalfa flower development and contributes to the understanding of the basic molecular mechanisms during the alfalfa flowering process. These results may offer insight into potential strategies for improving seed yield, quality, and stress tolerance in alfalfa.

The effects of exogenous antioxidant germanium (Ge) on seed germination and growth of Lycium ruthenicum Murr subjected to NaCl stress.

In this paper, we present the results of a study on the effects of exogenous antioxidant germanium (Ge) on seed germination and seedling growth, and its role as a radical scavenger that regulates related enzymes, including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), under salt stress. Seeds were incubated in 0, 50, 100, 150, 200, 250 and 300 mM NaCl to determine the salt tolerance of the Lycium ruthenicum Murr seedlings and from the results, the critical and ultimate salt concentrations were chosen for the next experiment. Subsequently, two treatments (seeds soaked in Ge and Ge added to salt) with four concentrations of GeO2 (0, 5, 10 and 20 µM) were used with the critical (150 mM) and ultimate salt concentrations (250 mM). The results demonstrated that salt alone inhibited seed germination significantly (≥150 mM) and reduced seedling growth (≥200 mM). The addition of exogenous Ge to the salt solution, as well as soaking the seeds in Ge, attenuated the salt stress effects in a manner dependent on the dose of Ge, as indicated by the increased percentage of seeds that germinated and improved seedling growth. The addition of Ge also showed a significant reversal of salt stress on the activities of antioxidant enzymes, with a decrease in SOD and POD activity, but an increase in CAT activity with 150 mM NaCl, and enhancement of SOD, POD and CAT with 250 mM NaCl. Correspondingly, the level of malondialdehyde was decreased significantly by each Ge treatment under salt stress. Further, for L. ruthenicum, adding 10 Ge and seeds soaked in 5 Ge were the most effective treatments. To our knowledge, this is the first report to show the protective effects of exogenous Ge against salt-induced oxidative damage in L. ruthenicum seed germination and seedling growth. Thus, L. ruthenicum can be used in areas with salty soil and Ge can promote the plants' salt tolerance.

Seasonal and Spatial Variations of Bulk Nitrogen Deposition and the Impacts on the Carbon Cycle in the Arid/Semiarid Grassland of Inner Mongolia, China.

Atmospheric nitrogen (N) deposition is an important component that affects the structure and function of different terrestrial ecosystem worldwide. However, much uncertainty still remains concerning the magnitude of N deposition on grassland ecosystem in China. To study the spatial and temporal patterns of bulk N deposition, the levels of N (NH4+-N and NO3--N) concentration in rainfall were measured at 12 sites across a 1200 km grassland transect in Inner Mongolia, China, and the respective N deposition rates were estimated. The inorganic N deposition rates ranged from 4.53 kg N ha-1 to 12.21 kg N ha-1 with a mean value of 8.07 kg N ha-1 during the entire growing season, decreasing steadily from the eastern to the western regions. Inorganic N deposition occurred mainly in July and August across meadow steppe, typical steppe, and desert steppe, which corresponded to the seasonal distribution of mean annual precipitation. A positive relationship was found between inorganic N deposition and mean annual precipitation (R2 = 0.54 ~ 0.72, P < 0.0001) across the grassland transect. Annual estimation of inorganic N deposition was 0.67 Pg yr-1 in Inner Mongolia, China based on the correlation between N deposition rates and precipitation. N deposition was an important factor controlling aboveground biomass and ecosystem respiration, but has no effect on root biomass and soil respiration. We must clarify that we used the bulk deposition samplers during the entire sampling process and estimated the dissolved NH4+-N and NO3--N deposition rates during the entire growing season. Long-term N deposition monitoring networks should be constructed to study the patterns of N deposition and its potential effect on grassland ecosystem, considering various N species, i.e., gaseous N, particle N, and wet N deposition.

Influence of pericarp, cotyledon and inhibitory substances on sharp tooth oak (Quercus aliena var. acuteserrata) germination.

In order to explore the mechanism of delayed and uneven germination in sharp tooth oak (Quercus aliena var. acuteserrata) (STO), mechanical scarification techniques were used to study STO root and shoot germination and growth. The techniques used were: removing cup scar (RS), removing the pericarp (RP), and cutting off 1/2 (HC) and 2/3 (TC) cotyledons. Germination percentage and root and shoot length for Chinese cabbage (Beassica pekinensis) seeds (CCS) were also investigated for CCS cultivated in a Sanyo growth cabinet watered by distilled water and 80% methanol extracts from the acorn embryo, cotyledon and pericarp with concentrations of 1.0 g, 0.8 g, 0.6 g and 0.4 g dry acorn weight per ml methanol. The results showed that the majority of roots and shoots from acorns with RP and HC treatment emerged two weeks earlier, more simultaneously, and their total emergencies were more than 46% and 28% higher, respectively. TC accelerated root and shoot emergence time and root length, but root and shoot germination rate and shoot height had no significant difference from the control. Positive consequences were not observed on all indices of RS treatment. The germination rates of CCS watered by 1.0 g · ml(-1) methanol extracts from the embryo and cotyledon were significantly lower than those from the pericarp, and all concentrations resulted in decreased growth of root and shoot. Methanol extracts from pericarp significantly reduced root length of CCS, but presented little response in germination percentage and shoot length. The inhibitory effect was gradually increased with the increasing concentration of the methanol extract. We conclude that both the mechanical restriction of the pericarp and the presence of germination inhibitors in the embryo, cotyledon and pericarp are the causes for delayed and asynchronous germination of STO acorns.