Artificially improving traits of cultivated alfalfa (Medicago sativa L.), one of the most important forage crops, is challenging due to the lack of a reference genome and an efficient genome editing ...protocol, which mainly result from its autotetraploidy and self-incompatibility. Here, we generate an allele-aware chromosome-level genome assembly for the cultivated alfalfa consisting of 32 allelic chromosomes by integrating high-fidelity single-molecule sequencing and Hi-C data. We further establish an efficient CRISPR/Cas9-based genome editing protocol on the basis of this genome assembly and precisely introduce tetra-allelic mutations into null mutants that display obvious phenotype changes. The mutated alleles and phenotypes of null mutants can be stably inherited in generations in a transgene-free manner by cross pollination, which may help in bypassing the debate about transgenic plants. The presented genome and CRISPR/Cas9-based transgene-free genome editing protocol provide key foundations for accelerating research and molecular breeding of this important forage crop.
This study examined the influence of pyrolysis temperature on biochar characteristics and evaluated its suitability for carbon capture and energy production. Biochar was produced from corn stover ...using slow pyrolysis at 300, 400 and 500°C and 2 hrs holding time. The experimental biochars were characterized by elemental analysis, BET, FTIR, TGA/DTA, NMR (C-13). Higher heating value (HHV) of feedstock and biochars was measured using bomb calorimeter. Results show that carbon content of corn stover biochar increased from 45.5% to 64.5%, with increasing pyrolysis temperatures. A decrease in H:C and O:C ratios as well as volatile matter, coupled with increase in the concentration of aromatic carbon in the biochar as determined by FTIR and NMR (C-13) demonstrates a higher biochar carbon stability at 500°C. It was estimated that corn stover pyrolysed at 500°C could provide of 10.12 MJ/kg thermal energy. Pyrolysis is therefore a potential technology with its carbon-negative, energy positive and soil amendment benefits thus creating win- win scenario.
Dietary selection and intake affect the survival and health of mammals under extreme environmental conditions. It has been suggested that dietary composition is a key driver of gut microbiota ...variation; however, how gut microbiota respond to seasonal dietary changes under extreme natural conditions remains poorly understood. Sequencing plant trnL (UAA) region and 16S rRNA gene analysis were employed to determine dietary composition and gut microbiota in freely grazing yaks on the Tibetan plateau. Dietary composition was more diverse in winter than in summer, while Gramineae and Rosaceae were consumed frequently all year. Turnover of seasonal diet and gut microbiota composition occurred consistently. Yaks shifted enterotypes in response to dietary change between warm and cold seasons to best utilize nitrogen and energy, in particular in the harsh cold season. Our findings provide insights into understanding seasonal changes of diet-microbiota linkages in the adaptation of mammals to high altitudes.
The search for predictions of species diversity across environmental gradients has challenged ecologists for decades. The humped-back model (HBM) suggests that plant diversity peaks at intermediate ...productivity; at low productivity few species can tolerate the environmental stresses, and at high productivity a few highly competitive species dominate. Over time the HBM has become increasingly controversial, and recent studies claim to have refuted it. Here, by using data from coordinated surveys conducted throughout grasslands worldwide and comprising a wide range of site productivities, we provide evidence in support of the HBM pattern at both global and regional extents. The relationships described here provide a foundation for further research into the local, landscape, and historical factors that maintain biodiversity.
Tibetan nomads have lived since ancient times in the unique and harsh environment of the Qinghai-Tibetan Plateau with average altitudes over 4000 m. These people have been able to live and multiply ...healthily over numerous generations under the extreme stress of high-altitude environment, including cold, hypoxia, and strong ultraviolet radiation, and with a simple diet devoid of vegetables and fruits for most of the year. Their survival depends heavily on yak milk, and its products comprise the main portion of their daily diet. In this review, yak milk and its derived products are examined in detail and compared with milk from other ruminant species. Yak milk products seem to be particularly rich in functional and bioactive components, which may play a role in maintaining the health status of Tibetan nomads. This includes particular profiles of amino acids and fatty acids, and high levels of antioxidant vitamins, specific enzymes, and bacteria with probiotic activity (yoghurt is the main food). Based on that, it is proposed that the Tibetan nomads have developed a nutritional mechanism adapted to cope with the specific challenges posed by the environment of the world's highest plateau. Systematic studies are required to demonstrate this in a more mechanistic way.
Long-term active restoration is often employed to restore degraded grasslands. The establishment of a viable soil seed bank is the key to successful restoration, as it enhances the resilience of ...vegetation. However, little is known of how the soil seed bank affects vegetation resilience following long-term active restoration of degraded grasslands. We determined seed abundance and species composition of the soil seed bank and soil properties and vegetation resilience of intact, degraded, and long-term (>10 years) actively restored grasslands on the Tibetan plateau (3900–4200 m a.s.l.). The plant-soil-seed bank quality index and structural equation modelling (SEM) were used to assess the effect of the soil seed bank on vegetation resilience. After long-term (>10 years) active restoration of degraded grasslands by sowing seeds of native plant species, the densities of transient and persistent seeds increased by 5%, but seed richness (number of species) decreased by 25% when compared with degraded grasslands. This occurred largely as a result of an increase in grass but decrease in forb seeds. Persistent seeds of grasses play an important role in the productivity of restored grasslands, while the density of persistent seeds serves as an indicator of the resilience of vegetation. A combination of the plant community and soil properties determined seed density. Here, we show for the first time that long-term active restoration enhances vegetation resilience of grasslands by altering the soil seed bank. A high seed density of sown Gramineae and a low seed density of forbs in the soil seed bank is a key to the successful active restoration of degraded grasslands.
Grassland degradation can alter the structure and function of ecosystem and soil seed bank. Therefore, estimating the role of soil seed bank in vegetation regeneration of degraded grasslands is ...crucial. We selected grasslands with three levels of degradation, namely non-degraded (ND), mildly degraded (MD), and heavily degraded (HD) to analyze the effect of grassland degradation on soil seed bank, as well as the role of soil seed bank on vegetation regeneration of the alpine grasslands, China. Soil samples from each level were collected in May, before seedling emergence, in August, after completion of transient seed bank germination, and in December, after seed dispersal, to determine the seed density and species composition through germination experiment. Result showed that a total of 35 plant species was identified, including 15 species observed in both soil seed bank and above-ground vegetation. A total of 19, 15, and 14 species of soil seed bank were identified in December, May, and August, respectively. The most abundant species in soil seed bank were Compositae (5 species), followed by Poaceae (4 species), and Cyperaceae (3 species). Degradation level has no significant impact on species richness and Shannon-Wiener index of soil seed bank. In addition, sampling month and grassland degradation affected soil seed bank density, in which December>May>August, and ND>MD>HD, indicating that density of transient seed bank was greater than persistent seed bank. Soil seed bank density of surface layer (0–5 cm) accounting for 42%–72% of the total density, which was significantly higher than that of deep layer (5–10 cm). Similarity of species composition between vegetation and soil seed bank was low, and it increased with degradation level (ranged from 0.14 to 0.69). We concluded that grassland degradation affects soil seed bank density more than species diversity, and soil seed bank contributed slightly to vegetation regeneration of degraded alpine grassland. Therefore, it is unlikely that degraded alpine meadow can be restored solely through soil seed bank.
Elymus natans is a dominant native species widely planted to restore the heavily degraded alpine meadows in Qinghai-Tibetan plateau. The objective of this study was to determine how E. natans ...establishment affected the quality and fertility of a heavily degraded soil. Soil samples (at depths of 0-10, 10-20 and 20-30 cm) were collected from the 3- and 7-year-old E. natans re-vegetated grasslands, and in the heavily degraded alpine meadow (control). The establishment of E. natans promoted plant cover and aboveground biomass. Compared to the non-reseeded meadow, the concentration of total organic C increased by 13% in the soil under 3-year-old reseeded E. natans grassland at 0-10 cm, and by 7-33% in the soil under 7-year-old reseeded E. natans grassland at 0-10, 10-20 and 20-30 cm depths. Rapid increases in total and available N were also observed in two E. natans re-vegetated grasslands, especially in the 0-10 cm soil layer. Across three sampling depths, total P concentration was increased by 17-35% and 18-54% in 3- and 7-year-old reseeded soil respectively, compared to the soil of control. After 3 years of E. natans growth, microbial biomass C increased by 13-58% at 0-10 and 10-20 cm layers; while it increased by 43-87% in 7-year-old reseeded treatment at 0-10, 10-20 and 20-30 cm depths relative to control. A similar increasing trend was observed for microbial biomass N and P generally. Significant increase in neutral phosphatase, urease, catalase and dehydrogenase was also found in 3- and 7-year-old re-vegetated grasslands compared with heavily degraded meadow. Our results suggest a significant positive impact of E. natans establishment on soil quality. Thus, E. natans establishment could be an effective and applicable measure in restoring heavily degraded alpine meadow in the region of Qinghai-Tibetan Plateau.
Accurate information on grassland above-ground biomass (AGB) is critical to better understanding the carbon cycle and conserve grassland resources. As a climate-sensitive key ecological function ...area, it is important to accurately estimate the grassland AGB of the Tibetan Plateau. Sentinel-2 (S2) images have advantages in reducing mixed pixels and the scale effect for remote sensing, while the data volume is correspondingly larger. In order to improve the estimation accuracy while reducing the data volume required for AGB estimation and improving the computational efficiency, this study used the Recursive Feature Elimination (RFE) algorithm to find the optimal feature set and compared the performance of the Cubist, Gradient Boosting Regression Tree (GBRT), random forest (RF) and eXtreme Gradient Boosting (XGBoost) algorithms for estimating AGB. In this study, ten S2 bands, ten S2-derived vegetation indexes, 218 pieces of AGB field survey data, four types of meteorological data and three types of topographic data were used as the alternative input features for the AGB estimation model. The impurity and permutation importance were used as the feature importance calculation method input to the RFE, and the Cubist, GBRT, RF and XGBoost algorithms were used to construct the AGB estimation models. The results showed that the RF algorithm based on the monthly average temperature (T), elevation, Normalized Difference Phenology Index (NDPI), Normalized Difference Infrared Index (NDII) and Palmer Drought Severity Index (PDSI) performed best (R2 = 0.8838, RMSE = 35.05 g/m2, LCCC = 2.44, RPPD = 0.91). The above findings suggest that the RF model based on the features related to temperature, altitude, humidity and leaf water content is beneficial to estimate the grassland AGB on the Tibetan Plateau.
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