Soil seed banks represent a critical but hidden stock for potential future plant diversity on Earth. Here we compiled and analyzed a global dataset consisting of 15,698 records of species diversity ...and density for soil seed banks in natural plant communities worldwide to quantify their environmental determinants and global patterns. Random forest models showed that absolute latitude was an important predictor for diversity of soil seed banks. Further, climate and soil were the major determinants of seed bank diversity, while net primary productivity and soil characteristics were the main predictors of seed bank density. Moreover, global mapping revealed clear spatial patterns for soil seed banks worldwide; for instance, low densities may render currently species-rich low latitude biomes (such as tropical rain-forests) less resilient to major disturbances. Our assessment provides quantitative evidence of how environmental conditions shape the distribution of soil seed banks, which enables a more accurate prediction of the resilience and vulnerabilities of plant communities and biomes under global changes.
Aim
Variations in plant traits are closely linked to the functional trade-off between resource acquisition and conservation. However, there has been little research on interspecific variations in the ...traits of fine roots with different orders and their associations with leaf traits in semiarid inland dunes.
Methods
We examined the first four root orders and leaves of 12 species (seven herbs and five shrubs), representing a broad range of taxa, co-occurring in a semiarid inland dune and evaluated their root biomass ratio and nine key morphological and chemical traits.
Results
We observed substantial variations in root traits among species and among root orders within species. The root economics spectrum (RES) spanned across the first three orders, representing a resource acquisition and conservation strategy in which specific root length, specific root area and root N concentration decreased and root diameter increased with root order. Most of the fine root and leaf traits were primarily loaded on the first and second axes of the principal component analysis. Herbs and shrubs presented resource acquisitive and conservative strategies, respectively, due to their contrasting leaf and fine root traits. Phylogenetic conservatism was stronger in roots than in leaves.
Conclusions
The leading RES in the fine roots of different orders existed in the semiarid inland dune, emphasizing the importance of interspecific and intraspecific variations in the traits of fine roots of different orders in understanding root structure, function and their coordination. Partial trait integration across leaves and fine roots implies limited support to the plant economics spectrum.
The fertile islands formed by shrubs are major drivers of the structure and function of desert ecosystems, affecting seedling establishment, plant-plant interactions, the diversity and productivity ...of plant communities, and microbial activity/diversity. Although an increasing number of studies have shown the critical importance of soil microbes in fertile island formation, how soil microbial community structure and function are affected by the different fertile island effect intensities is still unknown. As an endangered and dominant shrub species in the West Ordos Desert, Tetraena mongolica was selected for further exploration of its fertile island effect on the soil microbial community in the present study to test the following two hypotheses: (1) T. mongolica shrubs with different canopy sizes exert fertile island effects of different strengths; (2) the soil microbial community structure and function beneath the T. mongolica canopy are affected by the fertile island, and the strength of these effects varies depending on the shrub canopy size.
The contents of soil total nitrogen (TN) and available phosphorus (AVP) were significantly greater beneath T. mongolica shrub canopy than outside the shrub canopy. With increasing shrub canopy size, the enrichment of soil TN and AVP increased, indicating a stronger fertile island effect. The structure and function of soil microbial communities, including fungal, archaeal and bacterial communities, are affected by the fertile island effect. An increase in canopy size increased the relative abundance of Ascomycota (Fungi) and Thaumarchaeota (Archaea). For the soil microbial functional groups, the relative abundance of endophytes in the fungal functional groups; steroid hormone biosynthesis, sphingolipid metabolism, and steroid biosynthesis genes in the bacterial functional groups; and nonhomologous end-joining and bisphenol degradation functional genes in the archaeal functional groups increased significantly with increasing T. mongolica canopy size.
These results revealed that T. mongolica had a fertile island effect, which affected the soil microbial community structure and functions, and that the fertile island effect might increase with increasing shrub canopy size. The fertile island effect may strengthen the interaction between T. mongolica shrubs and microbes, which may be beneficial to the growth and maintenance of T. mongolica.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
1. Litter decomposition plays important roles in carbon and nutrient cycling. In dryland, both microbial decomposition and abiotic degradation (by UV light or other forces) drive variation in ...decomposition rates, but whether and how litter traits and position determine the balance between these processes is poorly understood. 2. We investigated relationships between litter quality and their decomposition rates among diverse plant species in a desert ecosystem in vertically contrasting positions representing distinct decomposition environments driven by different relative contributions of abiotic and microbial degradation. Thereto, leaf litter samples from 17 desert species were sealed into litterbags and placed on the soil surface under strong solar exposure vs. shade conditions, or buried in the soil at 10 cm depth, for a whole year. 3. Litter decomposition rates were 21% and 17% higher in burial and light-exposed treatments, respectively, than those in shade. Leaf traits, i.e. specific leaf area (SLA), litter C:N ratio and lignin concentration could predict litter decomposition to some degree, but their predictive power was dependent on litter position. However, multiple linear regressions showed that SLA, litter C and P significantly affected k values for leaf litter decomposition besides litter position, with SLA standing out as a strong determinant of litter decomposition rate as related either to solar radiation or the environment below the soil surface. Furthermore, the interspecific differences in litter decomposition rates decreased over time, implying that afterlife effects of leaf traits on decomposition were attenuated. 4. Synthesis. These findings suggest that abiotic photodegradation and soil burial mediated microbial decomposition could be responsible for higher than expected litter turnover in dryland. They point to a dual role of specific leaf area (SLA) as a promotor of decomposition rates: via relative exposure of the leaf surface to abiotic factors such as UV light vs. to soil moisture and microbes under soil burial.
A duplex TiC and γ′-Ni
3
(Al,Ti) reinforced nickel composite was fabricated through hot-press sintering a 30 vol% Ti
2
AlC–Ni mixtures followed by thermal treatment method. Detailed microstructural ...detection was performed by adopting the route of high-resolution transmission electron microscopy. In situ generated submicron TiC particulate and nanosized L1
2
-γ′ were homogeneously distributed in a fcc γ-Ni matrix. The high temperature tensile and compression behaviors of the TiC-γ′/Ni composites were evaluated in the temperature range of 25–800 °C. The results indicated that ultimate tensile and compression properties exhibited the dependence of temperatures. The tensile properties of the composite determined at 600 °C was 945 MPa, decreasing by 28.1% and 23.0% for elongation, compared to those of measured at room temperature (UTS = 1305 MPa, elongation = 5.35%). However, the yield strength exhibited the temperature independent until to 600 °C. The yield strength of the TiC-γ′/Ni composite are comparable with conventional superalloy under 600 °C, proving that TiC and γ′ particles constitute efficient reinforcements for Ni matrix according to thermal expansion dislocations strengthening, load-transfer and coherent strengthening mechanisms. The monotonic temperature dependence of yield strength at 600–800 °C indicates that plastic deformation of TiC-γ′/Ni composite follows the thermally activated mechanism. The TiC-γ′/Ni composite exhibited superior mechanical properties both at room and high temperatures, which can be ascribed to the synergistic strengthening effect in term of dislocation density, Orowan, coherent and atomic ordering strengthening mechanisms. The present work reveals the deformation behaviors of in situ TiC-γ′/Ni composite from room to high temperatures, which is critical to predict the failure and thereby optimize the microstructure to further enhance the high temperature properties of TiC-γ′/Ni composite.
Graphic Abstract
Studies on the ecological importance of seed coat mucilage have provided valuable information about its roles in critical stages of the plant life cycle. Seed mucilage may, by providing a moist ...environment and maintaining metabolic activity in the seed, promote seed development. In seed dispersal, seed mucilage influences topochory, epizoochory, endozoochory and hydrochory by anchorage of seeds to soil surface, lubrication or changing the specific weight of the seed. In arid environments, seed mucilage can prevent seeds from drying or initiate DNA repair mechanisms, thereby maintaining the soil seed bank. Seed mucilage reduces oxygen diffusion to the seed and thus has a role in regulating seed dormancy. Due to it being hydrophilous, acting as a physical barrier and containing chemicals, seed mucilage is proposed to promote seed germination in favorable environments. In seedling growth, seed mucilage may lubricate the radicle as it penetrates the soil and be degraded by soil microfloras and thus promote seedling growth. Further investigation of seed mucilage for more species in diverse habitats from the perspectives of evolution, genetics, proteomics, phylogeny and plant–microbe interactions would contribute substantially to our understanding about its ecological importance.
Seed heteromorphism is a plant strategy that an individual plant produces two or more distinct types of diaspores, which have diverse morphology, dispersal ability, ecological functions and different ...effects on plant life history traits. The aim of this study was to test the effects of seasonal soil salinity and burial depth on the dynamics of dormancy/germination and persistence/depletion of buried trimorphic diaspores of a desert annual halophyte Atriplex centralasiatica. We investigated the effects of salinity and seasonal fluctuations of temperature on germination, recovery of germination and mortality of types A, B, C diaspores of A. centralasiatica in the laboratory and buried diaspores in situ at four soil salinities and three depths. Diaspores were collected monthly from the seedbank from December 2016 to November 2018, and the number of viable diaspores remaining (not depleted) and their germinability were determined. Non-dormant type A diaspores were depleted in the low salinity "window" in the first year. Dormant diaspore types B and C germinated to high percentages at 0.3 and 0.1 mol L.sup.-1 soil salinity, respectively. High salinity and shallow burial delayed depletion of diaspore types B and C. High salinity delayed depletion time of the three diaspore types and delayed dormancy release of types B and C diaspores from autumn to spring. Soil salinity modified the response of diaspores in the seedbank by delaying seed dormancy release in autum and winter and by providing a low-salt concentration window for germination of non-dormant diaspores in spring and early summer. Buried trimorphic diaspores of annual desert halophyte A. centralasiatica exhibited diverse dormancy/germination behavior in respond to seasonal soil salinity fluctuation. Prolonging persistence of the seedbank and delaying depletion of diaspores under salt stress in situ primarily is due to inhibition of dormancy-break. The differences in dormancy/germination and seed persistence in the soil seedbank may be a bet-hadging strategy adapted to stressful temporal and spatial heterogeneity, and allows A. centralasiatica to persist in the unpredictable cold desert enevironment.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Clonal plants can successfully adapt to various ecosystems. A trade-off between sexual and clonal reproduction is generally assumed in clonal plants, which may be influenced both by the ...characteristics of the plant itself and environmental conditions. Currently, it is unclear how climate change, and specifically warming and increased precipitation, might affect sexual and clonal reproduction in clonal plants. Therefore, this study aimed to investigate both the sexual and clonal reproduction responses of Stipa breviflora to warming and increased precipitation. A controlled experiment was conducted by inducing increases in precipitation (ambient condition, 25% and 50% increases) and warming (ambient temperature, 1.5 degreesC and 3.0 degreesC increases). Warming significantly influenced both the ratio of reproductive ramet shoot biomass to total shoot biomass, and the ratio of reproductive ramet number to total ramet number. Additionally, the ratio of reproductive ramet shoot biomass to total shoot biomass was also significantly affected by increased precipitation. Increased precipitation benefited sexual reproduction, while effects of warming on reproductive and/or vegetative ramets varied from negative to positive depending on precipitation conditions. There was no relationship between the number or shoot biomass of reproductive ramets and vegetative ramets. Reproductive ramets displayed greater sensitivity to climate change than vegetative ramets. The findings of our study suggest that there was no trade-off between sexual and clonal reproduction in S. breviflora. The combined impact of warming and increased precipitation promoted sexual reproduction but did not inhibit clonal reproduction. Clonal plants with the capacity for both sexual and clonal reproduction, may cope with climate change well via clonal reproduction, ensuring their survival.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Main conclusion
Individuals of the annual halophyte
Atriplex centralasiatica
produce three kinds of diaspores that differ in dispersal, dormancy/germination response and type of seed bank formed, ...which likely is a bet-hedging strategy in the rainfall-unpredictable environment on the semi-arid, saline Ordos Plateau in Inner Mongolia, China.
Seasonal fluctuations in environmental conditions provide germination cues for the establishment of seedlings at the right time and place to ensure plant survival and population regeneration. Diaspore heteromorphism is a phenomenon in which diaspores with stark qualitative differences in morphology and ecology are produced by the same maternal plant. Germination responses and dispersal times of the annual halophyte
Atriplex centralasiatica
were examined to determine the role of diaspore heteromorphism in its adaptation to salt desert conditions.
A. centralasiatica
is a tumbleweed that produces three types of diaspores that differ in morphology and ecophysiology. The relative potential dispersal ability and intensity of dormancy of the three diaspore types was type A (fan-shaped diaspores with yellow fruits) < type B (fan-shaped diaspores with black fruits) < type C (globular diaspores with black fruits). In the field, type A retained high germinability, but all of them were depleted from the (transient) soil seedbank in the first growing season. Types B and C cycled between dormancy and nondormancy, and 0 and > 90.0% remained in the soil seedbank 2 years after dispersal, respectively. The dormancy, dispersal and salt tolerance of type B diaspores were intermediate between those of A and C. Type A exhibited low dispersal–nondormancy, type B exhibited intermediate dispersal–intermediate dormancy and type C exhibited high dispersal ability–high dormancy. In the unpredictable salt desert habitat, the functional differences in germination and dispersal of the three diaspores act as a bet-hedging mechanism and ensure population establishment in different years by spreading germination over time and space.
Artemisia sphaerocephala (Asteraceae) is one of the pioneer species in moving and semi-stable sand dunes in the deserts of northwest China. The outer surface of
A. sphaerocephala achenes contains a ...pectinaceous mucilage layer that can imbibe a large amount of water when wetted. We hypothesized that the mucilage can aid achene germination in heterogeneous environments. Germination of both intact achenes and those from which the mucilage had been removed (demucilaged) declined with increasing osmotic potential and NaCl concentration. However, the germination percentage of intact achenes was significantly higher than that of demucilaged achenes. The early seedling growth of intact achenes did not differ significantly from that of demucilaged achenes in either osmotic potential or NaCl solutions. Achene mucilage presumably plays an ecologically important role in the life cycle of
A. sphaerocephala by aiding germination in osmotically- and saline-stressful habitats of the cold desert environment.
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