High-latitude Areas Research Articles

Effects of climate warming and human activities on the distribution patterns of Fritillaria unibracteata in eastern Qinghai-Tibetan Plateau

Fritillaria unibracteata is an endangered medicinal material species endemic to the Qinghai Tibet Plateau, and belongs to the national Class III endangered plant. In addition to expelling wind and removing damne, it also warms menstruation and relieves pain in clinic use of tranditional Chinese medicine. In recent years, affected by the destruction of shrubs and climate change, the habitat of F. unibracteata wild resources has been seriously damaged, indicating of great significance to predict its potential suitable habitat using MaxEnt model. The AUC values without human activities were 0.983 ± 0.013–0.988 ± 0.001, while it is 0.982 ± 0.015–0.989 ± 0.000 with human activities, justifying their applications for predicting the potential areas of F. unibracteata. Without human activities, there were 8.47 × 104 km2 of highly suitable habitats in northern Sichuan, southern Gansu and southeastern Qinghai. But the poorly, moderately and highly suitable areas of F. unibracteata have decreased to 33.8 × 104 km2, 9.66 × 104 km2 and 6.64 × 104 km2 due to human activities. Environmental variables affecting F. unibracteata distribution included the minimum temperature in the coldest month (−16.89–−4.96 °C), annual precipitation (416.64–866.96 mm), temperature annual range (24.83–31.97 °C), elevation (2879.69–3981.82 m), human footprint (2.58–23.66) and mean UV-B of highest month (7381.92–8574.27 kJ/m2). In the 2050s and 2090s, human activities would significantly reduce the highly suitable habitats of F. unibracteata. Under SSP1-2.6, SSP2-4.5 and SSP5-8.5 scenarios, the centroid would move to the low latitude area from the current position first, and then to a high latitude area. Wild resources of F. unibracteata in China can be effectively conserved based on our results.

Physiological and transcriptomic analyses reveal tea plant (Camellia sinensis L.) adapts to extreme freezing stress during winter by regulating cell wall structure

Tea plants grown in high-latitude areas are often damaged by extreme freezing temperatures in winter, leading to huge economic losses. Here, the physiological and gene expression characteristics of two tea cultivars (Xinyang No. 10 (XY10), a freezing-tolerant cultivar and Fudingdabaicha (FDDB), a freezing-sensitive cultivar) during overwintering in northern China were studied to better understand the regulation mechanisms of tea plants in response to natural freezing stress. Samples were collected at a chill (D1), freezing (D2) and recovery (D3) temperature in winter. TEM analysis of integrated leaf ultrastructure at D2 revealed lower malondialdehyde and relative electrical conductivity in XY10 than in FDDB, with serious cell structure damage in the latter, indicating XY10 was more resistant to freezing stress. Differential gene expression analysis among the different samples over winter time highlighted the following gene functions in cell wall metabolism (CesAs, COBLs, XTHs, PGs, PMEs), transcription factors (ERF1B and MYC2), and signal transduction (CDPKs and CMLs). The expression pattern of cellulose and pectin-related genes suggested higher accumulation of cellulosic and pectic materials in the cell wall of XY10, agreeing with the results of cell wall and its components. These results indicated that under the regulation of cell wall genes, the freezing-resistant tea cultivar can better maintain a well-knit cell wall structure with sufficient substances to survive natural freezing damage. This study demonstrated the crucial role of cell wall in tea plant resistance to natural freezing stress and provided important candidate genes for breeding of freezing-resistant tea cultivars.

The incidence of asthma attributable to temperature variability: An ecological study based on 1990–2019 GBD data

BackgroundAsthma, the second leading cause of death from chronic respiratory diseases, is associated with climate change, especially temperature changes. It is currently unclear about the relationship between long-term temperature variability and the incidence of asthma on a global scale. MethodsWe used asthma incidence, demographic and socioeconomic data from the Global Burden of Disease (GBD) Results Database, and environmental and geographical statistics from TerraClimate between 1990 and 2019 to determine the association between maximum temperature variability and asthma incidence. We also predicted the incidence of heat-related asthma in the future (2020−2100) under four shared socioeconomic pathways (SSPs: 126, 245, 370, and 585). ResultsBetween 1990 and 2019, the global median incidence of asthma was 402.0 per 100,000 with a higher incidence (median: 1380.3 per 100,000) in children under 10 years old. We found that every 1 °C increase in maximum temperature variability increased the risk of asthma globally by 5.0 %, and the effect was robust for individuals living in high-latitude areas or aged from 50 to 70 years. By 2100, the average incidence of asthma is estimated to be reduced by 95.55 %, 79.32 %, and 40.02 % under the SSP126, SSP245, and SSP370 scenarios, respectively, compared to the SSP585 at latitudes >60°. ConclusionOur study provides evidence that maximum temperature variability is associated with asthma incidence. These findings suggest that implementing stricter mitigation and adaptation strategies may be importment in reducing asthma cases caused by climate change.

GPS tracking analyses reveal finely-tuned shorebird space use and movement patterns throughout the non-breeding season in high-latitude austral intertidal areas

BackgroundLong-distance migratory birds spend most of their annual cycle in non-breeding areas. During this period birds must meet their daily nutritional needs and acquire additional energy intake to deal with future events of the annual cycle. Therefore, patterns of space use and movement may emerge as an efficient strategy to maintain a trade-off between acquisition and conservation of energy during the non-breeding season. However, there is still a paucity of research addressing this issue, especially in trans-hemispheric migratory birds.MethodsUsing GPS-tracking data and a recently developed continuous-time stochastic process modeling framework, we analyzed fine-scale movements in a non-breeding population of Hudsonian godwits (Limosa haemastica), a gregarious long-distance migratory shorebird. Specifically, we evaluated if these extreme migrants exhibit restricted, shared, and periodic patterns of space use on one of their main non-breeding grounds in southern South America. Finally, via a generalized additive model, we tested if the observed patterns were consistent within a circadian cycle.ResultsOverall, godwits showed finely-tuned range-residence and periodic movements (each 24–72 h), being similar between day and night. Remarkably, range-resident individuals segregated spatially into three groups. In contrast, a smaller fraction of godwits displayed unpredictable and irregular movements, adding functional connectivity within the population.ConclusionsIn coastal non-breeding areas where resource availability is highly predictable due to tidal cycles, range-resident strategies during both the day and night are the common pattern in a long-distance shorebird population. Alternative patterns exhibited by a fraction of non-resident godwits provide functional connectivity and suggest that the exploratory tendency may be essential for information acquisition and associated with individual traits. The methodological approach we have used contributes to elucidate how the composition of movement phases operates during the non-breeding season in migratory species and can be replicated in non-migratory species as well. Finally, our results highlight the importance of considering movement as a continuum within the annual cycle.

Horizontal and vertical distribution of nitrate-driven anaerobic methane oxidation process in coastal wetlands under different plant species cover across southeast China

Coastal wetlands are an important methane emission source. Nitrate-driven anaerobic oxidation of methane (AOM), catalyzing via a novel clade of anaerobic methanotrophic archaea (ANME-2d), is a potentially important process for methane emission mitigation in coastal wetlands. However, the influence of regional and local environmental conditions, as well as plant species cover on this AOM process, remains unclear. Here, we investigated the horizontal and vertical distribution of nitrate-driven AOM activity and ANME-2d archaeal community in four coastal wetlands under both native and invasive plant species across southeast China. It was estimated that this AOM process could potentially reduce 5.7–9.5% methane emissions from the studied wetlands. Generalized linear mixed-effects model showed that sampling locations and sediment layers had greater impact on nitrate-driven AOM activity than plant species cover, and all these factors significantly affected the abundance of ANME-2d archaea. Nitrate-driven AOM activity was higher in low-latitude coastal wetlands than in high-latitude areas, and the activity positively correlated with mean annual temperature. Furthermore, both nitrate-driven AOM activity and ANME-2d archaeal abundance showed significant vertical variations along sediment profiles, with higher values in the slightly alkaline surface sediment. The plant species cover was found to impact the ANME-2d archaeal abundance and diversity by regulating the availability of substrates for the archaea. Overall, our study provides valuable insights into effects of regional and local environmental parameters and plant species cover on the horizontal and vertical distribution of nitrate-driven AOM activity and ANME-2d archaeal community in coastal wetlands.

Killer whales at northern Patagonia, Argentina: Evidence of different foraging groups from stable isotopes

AbstractKiller whales (Orcinus orca) are highly mobile, large marine apex predators that inhabit all oceans. Despite being the most conspicuous top predator, little is known about their ecology along Patagonia, Argentina. Here, we used carbon (δ13C) and nitrogen (δ15N) isotope analysis of bone and dentine collagen from killer whales (n = 13) stranded in northern Patagonia during the period 1970–2014 to assess their trophic ecology. A model‐based clustering analysis identified three distinct groups related with three large marine ecosystems: the Patagonia (P), Subtropical (ST), and Antarctica (A) groups. Group P (n = 8) is characterized by individuals with high δ13C and δ15N values fitting within the isotopic ratios observed over the Patagonian shelf. Group ST (n = 3) is composed of individuals with high δ13C and low δ15N values, similar to those reported for conspecifics in southern Brazil. Group A (n = 2) is composed of individuals with low δ13C and δ15N values, typical from high latitude areas like sub‐Antarctic/Antarctic waters. The finding of different killer whales' isotopic groups over the Patagonian shelf suggests the existence of individuals or groups exploiting different habitats. Our results expand the limited ecological knowledge for the species while presenting the basis to infer more complex ecological hypotheses.

Prediction of potential distribution areas and priority protected areas of Agastache rugosa based on Maxent model and Marxan model.

Agastache rugosa (Fisch. & C. A. Mey.) Kuntze has been widely studied because of its high medicinal and edible value. Establishing the priority protected area of wild A. rugosa can provide scientific basis for the protection of germplasm resources. In this study, we predicted the potential suitability distribution area of A. rugosa under the current and future climate scenarios with the MaxEnt model, and the dominant climate factors affecting the distribution of A. rugosa were analyzed. Based on the above results, we predicted the priority protected areas of A. rugosa with the Marxan model. The results showed that A. rugosa is mainly distributed in the eastern and central regions of China at present. In future, the suitable area of A. rugosa will increase, otherwise a few areas will shrink back and migrate to the high latitude areas as a whole. Hydrothermal conditions are the main environmental factors affecting the distribution of A. rugosa. The priority protected areas of A. rugosa are mainly distributed in Chongqing, eastern Sichuan, southern Guizhou, western Hunan and Hubei and southwestern Shaanxi, which are basically consistent with the highly suitable areas predicted by Maxent model. The results of this study are of great significance for the protection and rational utilization of species of Agastache.

A Global Comparison of Marine Chlorophyll Variability Observed in Eulerian and Lagrangian Perspectives

AbstractOcean chlorophyll time series exhibit temporal variability on a range of timescales due to environmental change, ecological interactions, dispersal, and other factors. The differences in chlorophyll temporal variability observed at stationary locations (Eulerian perspective) or following water parcels (Lagrangian perspective) are poorly understood. Here we contrasted the temporal variability of ocean chlorophyll in these two observational perspectives, using global drifter trajectories and satellite chlorophyll to generate matched pairs of Eulerian‐Lagrangian time series. We found that for most ocean locations, chlorophyll variances measured in Eulerian and Lagrangian perspectives are not statistically different. In high latitude areas, the two perspectives may capture similar variability due to the large spatial scale of chlorophyll patches. In localized regions of the ocean, however, chlorophyll variability measured in these two perspectives may significantly differ. For example, in some western boundary currents, temporal chlorophyll variability in the Lagrangian perspective was greater than in the Eulerian perspective. In these cases, the observing platform travels rapidly across strong environmental gradients and constrained by the shelf topography, potentially leading to greater Lagrangian variability in chlorophyll. In contrast, we found that Eulerian chlorophyll variability exceeded Lagrangian variability in some key upwelling zones and boundary current extensions. In these cases, variability in the nutrient supply may generate intermittent chlorophyll anomalies in the Eulerian perspective, while the Lagrangian perspective sees the transport of such anomalies off‐shore. These findings aid with the interpretation of chlorophyll time series from different sampling methodologies, inform observational network design, and guide validation of marine ecosystem models.

Light and colour of cirrus, translucent, and opaque dust in the high-latitude area of LDN 1642

ABSTRACT We have performed a 5-colour surface photometric study of the high-galactic-latitude area of dark nebula LDN 1642. Scattered light properties are presented of diffuse, translucent, and opaque dust over the range of 3500–5500 Å . Far infrared absolute photometry at 200 µm improves the precision of and provides a zero point to the extinction. The intensity of the scattered light depends on dust column density in a characteristic way: for optically thin dust the intensity first increases linearly, then turns to a saturation value; at still larger extinctions the intensity turns down to a slow decrease. The AV value of the saturated intensity maximum shifts in a systematic way, from AV ≈ 1.5 mag at 3500 Å to ∼3 mag at 5500 Å . The intensity curves offer a straight-forward explanation for the behaviour of the scattered-light colours. At the intensity peak the colour agrees with the integrated starlight colour, while it is bluer at the low- and redder at the high-column-density side of the peak, respectively. These colour changes are a direct consequence of the wavelength dependence of the extinction. We have compared the colours of the LDN 1642 area with other relevant observational studies: high-latitude diffuse/translucent clouds, wide-field cirrus dust; and externally illuminated AGB-star envelopes. For extragalactic low-surface-brightness sources cirrus is an unwanted foreground contaminant. Our results for cirrus colours can help to distinguish cases where a diffuse plume or stream, apparently associated with a galaxy or a group or cluster, is more likely a local cirrus structure.

Climate Potential for Apple Growing in Norway—Part 1: Zoning of Areas with Heat Conditions Favorable for Apple Growing under Observed Climate Change

Agricultural production is already, and obviously, affected by climate change. Adapting to climate change includes reducing future risks to ensure yield quality and quantity and considers seizing any potential opportunities induced by climate change. In higher latitude areas, such as Norway, cold climate limits the cultivation of fruits. An increase in temperature offers more favorable conditions for fruit production. In this study, using available phenological observations (full blooming) and harvest dates, and meteorological data from the experimental orchard of NIBIO Ullensvang, the minimum heat requirements for growing different apple varieties are determined. Those criteria are used for zoning of the areas with heat favorable conditions for apple growing. Data on six varieties were used, with lower and higher requirements for heat for fruit development (Discovery, Gravenstein, Summerred, Aroma, Rubinstep, and Elstar). High resolution daily temperature data were generated and used for zoning of the areas with heat favorable conditions for apple growing within the selected domain, which includes Western Norway, Southern Norway, Eastern Norway, and the western part of Trøndelag, Mid-Norway. Dynamics of the change in such surfaces was assessed for the period of 1961–2020. The total surface with favorable heat conditions for growing the varieties with lesser requirement for heat increased three times during this period. The growing of more heat-demanding varieties increased from near zero to about 2.5% of the studied land surface. In the period of 2011–2020, surface area with favorable heat conditions for apple growing was almost 27,000 km2, and a surface area of about 4600 km2 can sustain growing of more heat-demanding varieties. The presented results show the increasing potential of the climate of Norway for apple cultivation and highlight the importance of implementation of fruit production planned according to climate change trends, including the assessment of potential risks from climate hazards. However, the methodology for determining heat requirements can be improved by using phenological ripening dates if available, rather than harvest dates which are impacted by human decision. Zoning of areas with the potential of sustainable apple growing requires the use of future climate change assessments and information on land-related features.

Potential of grid-connected decentralized rooftop PV systems in Sweden

Solar power generation in Sweden is far from required capacity to help with transition towards 100% renewables in the power sector by 2040. Decentralized PV system attracts attentions given the conflicts of future increasing demands and land scarcity in the urban areas. However, it is not easy to implement it due to challenges on local conditions and lack of references.This paper aims to propose an overview of the potential of small-scale grid-connected PV systems in a Swedish context and offer an example for urban PV system planning in Sweden or high latitude areas. A model considering weather, space, infrastructures and economics is developed and implemented with a real case in the Swedish context.The findings verify the technical and economic feasibility of urban decentralized rooftop PV systems in the Swedish context. It is found that this kind of system does have considerable power potential in the Swedish context without land requirements. This kind of PV system could be a promising option for future power generation which satisfies part of demands and reduces pressure on external grids. The full potential could be only achieved with improved infrastructures, and the profitability of the system relies heavily on market and political conditions. This study can be a refence for other high latitude areas.

Potential impacts of climate change on the spatial distribution of Chinese ski resorts

Chinese skiing tourism is rapidly developing, but it will be potentially affected by snow resources and climate conditions. This study systematically analysed the spatial characteristics of snow resources, climatic conditions and ski resorts in China; revealed the potential impacts of climatic environment on current ski resorts by using Regional Climate Model (RegCM4.4); and proposed suggestions for climate resource assessment and spatial planning of ski resorts. The mean snow depth and snow cover days are more than 4.50 cm and 150 d between the years 2000 and 2014, respectively, in high-latitude areas, where fewer ski resorts are located. In the middle-low latitude areas, the mean snow depth and snow cover days are less than 3.00 cm and 100 d, respectively, with ski resorts being intensively distributed. In most of these areas, the pronounced climate warming exceeded 0.50 °C during the ski period of 2009–2015 relative to 1961–2015, and mean annual precipitation was less than 800 mm, with some even less than 400 mm. In the 2030s and 2050s, the regions with drastic temperature increases are mainly in the Qinghai–Tibetan Plateau, Northeast China, and the Yangtze River Basin. The upper and middle reaches of the Yangtze River are expected to experience reduced snowfalland temperature increases with an almost 1–1.6 °C, respectively. In this context, some ski resorts will face major threats because of shortened skiing durations and rising management costs. Skiing tourism should not pursue a one-sided growth rate in the number of ski resorts in areas with short snowpack periods. Instead, it should rely highly on snow resources, climatic conditions, geographical environment, population and economic basis, and rationalise its spatial layout to promote the industry towards sustainable development.

Adaptation to high latitudes through a novel allele of Hd3a strongly promoting heading date in rice.

A novel Hd3a allele strongly promoting rice heading date was identified, and it functions through florigen activation complex (FAC) and was selected during the spread of rice cultivation to high-latitude areas. Heading date is a critical agronomic trait for rice that determines the utilization of light and temperature conditions and thereby affects grain yield. Rice is a short day (SD) plant, and its photoperiodic information is processed by complex pathways and integrated by florigens to control flowering. In this study, we identified a novel allele for the florigen gene Heading date 3a (Hd3a), characterized by a C435G substitution in its coding region, by a genome-wide association study (GWAS) approach in a panel of 199 high-latitude japonica rice varieties. The C435G substitution induces plants to flower 10days earlier in high-latitude area (long day condition). Then, we mutated C435 to G in Hd3a by prime editing and found the point mutation plants flowered 12days earlier. Further molecular experiments showed the novel Hd3a protein can interact with GF14b protein and increase the expression of OsMADS14, the output gene of florigen activation complex (FAC). Molecular signatures of selection indicated that the novel Hd3a allele was selected during the process of rice cultivation expansion into high-latitude areas. Collectively, these results provide new insights into heading date regulation in high-latitude areas and advance improvements to rice adaptability to enhance crop yield.

Research on Airspace Conflict Detection Method Based on Spherical Discrete Grid Representation

With the continuous development of general aviation, the contradiction between the air demand of general aviation low-altitude airspace and civil aviation routes is sharp. The difficulty of airspace planning is complex and changeable, and the existing working mode of simply using computer mapping and manually finding airspace conflict contradictions can no longer meet the large-scale air use demand. In response to the existing spatial representation model of longitude and latitude grid, which has large grid deformation in high latitude areas, and the problem of slow computation speed of the conflict detection (CD) algorithm that determines whether the airspace boundary coordinates overlap, we propose a grid model that represents airspace with a spherical rhombic discrete grid of positive icosahedron and design a matrix-based digital representation method of airspace, which uses matrix product operation. The matrix product operation is used to quickly determine whether there is a conflict between airspace and airspace and between airspace and routes.

Effects of agricultural land types on microplastic abundance: A nationwide meta-analysis in China

Microplastics (MPs) accumulation in agricultural land that possibly poses threats to food security and human health has recently attracted increasing attention. Land use type probably is a key factor that drives the contamination level of soil MPs. Nevertheless, few studies have performed large-scale systematic analysis of the effects in different agricultural land soils on the MPs abundance. In this study, we constructed a national MPs dataset comprising 321 observations from 28 articles, summarised the current status of microplastic pollution in five agricultural land types in China through meta-analysis, and investigated the effects and key factors of agricultural land types on microplastic abundance. The results showed that among the existing soil microplastic research, vegetable soils maintained a higher environmental exposure distribution than other agricultural lands, and with the most common trend being vegetable land > orchard land > cropland > grassland. By combining agricultural practices, demographic economic factors and geographical factors, a potential impact identification method based on subgroup analysis was established. The findings demonstrated that agricultural film mulch significantly increased soil MPs abundance, especially in orchards. Increased population and economy (carbon emissions and PM2.5 concentrations) add MPs abundance in all kinds of agricultural lands. And the significant changes of effect sizes in high-latitude and mid-altitude areas suggested that geographical space differences exerted a certain degree of impact on the soil distribution of MPs. By the proposed method, different levels of MPs risk areas in agricultural soils can be more reasonably and effectively identified, which will provide type-specific policies technical and theoretical support for the precise management of MPs in agricultural land soils.

Prediction of Potential Distribution Patterns of Three Larix Species on Qinghai-Tibet Plateau under Future Climate Scenarios

How climate change affects the plants on the Qinghai-Tibet Plateau (QTP) has become a hot research topic in recent years. It was widely recognized that Larix. are sensitive to climate change, while the corresponding research of Larix. on the QTP has been rare. Using the maximum entropy (MaxEnt) model, we predicted the potential distribution patterns of Larix potaninii Batalin, Larix griffithii and Larix speciosa on the QTP in this study under different future climate scenarios. The results demonstrated that the area of suitable habitat for Larix potaninii Batalin (Larix griffithii) presented a loss (gain) trend, while that for Larix speciosa remained unchanged on the whole. The centroids of their suitable habits all migrated to the high-altitude and high-latitude areas, suggesting the three species may take the same survival strategy in response to climate change. Annual Precipitation was the most significant environmental factor influencing the distribution pattern of Larix potaninii Batalin, while Temperature Annual Range was the most significant for Larix griffithii and Larix speciosa. The overlapping potential suitable area for the three Larix species was the maximum under the 2041–2060 SSP126 future climate scenarios and decreased with the increasing emission concentration, suggesting that the niches of these species may step towards separation. This study suggested the survival strategies of the Larix species in response to climate change and the findings may provide a reliable basis for conserving the endangered Larix species under different future climate scenarios.

Optimizing the distribution pattern of species under climate change: the protection and management of Phellodendron amurense in China

ObjectivePhellodendron amurense, a special species in Northeast Asia, is the source of the wild medicinal Phellodendri Amurensis Cortex, the second-level key protection in China. Because of its dual value of medicine and timber, it has been cut in large quantities, resulting in a sharp decline in wild resources. It has been listed as a national first-class rare tree species. Here, we aim to plan protection area and wild tending area for Chinese P. amurense in the context of climate change.MethodIn this study, based on the Biomod2 model, the main environmental factors affecting the distribution and the potentially suitable areas of the current and future were investigated. Furthermore, the correlation between the main environmental factors and the chemical components was determined by full subset regression. Habitat quality and landscape pattern change were determined by InVEST and Fragstats software based on the land use data in 1980, 2000, and 2020. Then, Zonation software was used to plan the priority protection and wild tending areas.ResultsThe results showed that in the future, the potential habitat of P. amurense will gradually move to the high latitude and high altitude areas in the northwest direction, and the high suitability area will decrease sharply. Since 1980, the habitat quality of P. amurense habitat has gradually deteriorated, and the fragmentation has gradually intensified. In the future, the central part of the Greater Khingan Mountains and the forest area of the Lesser Khingan Mountains will be the long-term stable sanctuary. Fengcheng City and Tonghua County are the most suitable for the wild tending areas.ConclusionThe existing nature reserve only contains 6.01% of the priority protection area, so we propose to expand the area to cover a larger proportion of the sanctuary and implement management and restoration plans to increase the suitability and connectivity. These results can support the protection action and provide a reference and scientific basis for further research, rational development, and utilization of P. amurense.

Non-structural carbohydrates contributed to cold tolerance and regeneration of Medicago sativa L.

Soil water content only affected regeneration time, whereas the NSC content was related to the success of alfalfa regeneration. Non-structural carbohydrates (NSCs) are important factors influencing the overwintering and regeneration of alfalfa. In this study, we analyzed eight in-situ samplings at three depths of coarse roots (crown, 20 and 40cm depths) during the overwintering period and assessed the dynamic change and allocation of root NSCs under three irrigation frequencies (irrigation once every second day/4days/8days). Primary results showed that: (i) before cold acclimation, irrigation once every second day was beneficial to the accumulation of soluble sugars and starch in crown tissues, which would be maintained until the following spring and accelerate the regeneration time of alfalfa; (ii) during the overwintering process, the soluble sugars and starch contents in the crown were significantly higher than those in deeper roots, and there was an asynchronous effect caused by the change in soluble sugars and starch among roots at three depths; and (iii) the change trend of soluble sugar and starch contents was consistent with that of semi-lethal temperature, and there was a significant negativecorrelation between the content of soluble sugar (R2 = 0.8046) and starch (R2 = 0.6332) and the semi-lethal temperature. This study demonstrated that NSCs are the key driver of cold tolerance and regeneration under the three irrigation frequencies evaluated. Our results provide further insight into the allocation of NSCs in winter. This improved understanding of the mechanism of overwintering will allow for improved water management of alfalfa in high latitude areas.

Impacts of East Asian winter monsoon circulation on interannual variability of winter haze days in Guangdong Province

Haze days in Guangdong Province (GD) occur mainly in winter, with the highest number of moderate/severe haze days occurring in January. The interannual variability of winter haze days in GD is closely related to the Siberian High, the Aleutian Low, the East Asian Trough, the 850-hPa meridional wind over eastern China, and the 200-hPa East Asian Jet. We construct a winter comprehensive circulation index (WCIDX) to express the joint effects of the above regional-scale circulations on haze days in GD. The positive phase of WCIDX is closely linked to the Eurasian teleconnection pattern, which induces the abnormal southerly winds, high temperatures, and enhanced precipitation over GD by modulating the regional atmospheric circulations, localized meteorological conditions (i.e., enhanced lower specific humidity, reduced planetary boundary layer height, decreased surface wind speed, and enhanced low-level atmospheric inversion) conductive to a higher haze in GD. In addition, the positive phase of the WCIDX favors enhancement of the positive 850-hPa Eady growth rate (EGR) over the mid–high-latitude areas of East Asia, which enhances atmospheric baroclinity and results in a northward shift of the East Asian Jet. Pollutants accumulated over the Indochina Peninsula are advected to GD by the southwesterly airflows. It was found that enhanced horizontal warm advection, adiabatic heating, and diabatic heating provide conditions favorable for low-level atmospheric inversion.

Low-order fine roots of Picea asperata have different physiological mechanisms in response to seasonal freeze and freeze-thaw of soil.

Seasonal soil freezing (F) and freeze-thaw cycles (FTCs) are common natural phenomena in high latitude or altitude areas of the world, and seriously affect plant physiological processes. However, studies on the effect of soil F and FTCs on fine roots are less common, especially in subalpine coniferous forests of western Sichuan, China. We set up a controlled experiment in growth chambers to explore the effects of F and FTCs on low-order fine roots of Picea asperata and differential responses of first-order roots and the first three root orders (1st, 2nd and 3rd order roots combined as a unit). Soil F and FTCs resulted in serious damage to cell membranes and root vitality of low-order fine roots, accompanied by increased MDA content and O2 ·- production. FTCs had a stronger effect than F treatment. In turn, low-order fine roots are the unit that responds to cold stress. These roots had increased unsaturated fatty acid contents, antioxidant enzyme activities, osmolytes and plant hormones contents when acclimation to cold stress. The first-order roots were more sensitive to cold stress than the combined first three root orders for several processes (e.g. antioxidant enzymes, osmolytes and hormones) because of their specific structure and physiological activity. This study explains physiological differences in responses of fine roots of different root orders to seasonal soil freezing, which will improve the understanding of fine root heterogeneity and support agriculture and forest management.