Global Patterns of Potential Future Plant Diversity Hidden in Soil Seed Banks

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

Arbuscular mycorrhizal and dark septate endophyte colonization in Artemisia roots responds differently to environmental gradients in eastern and central China

Arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) are two types of root symbiotic fungi that enhance nutrient uptake by host plants and their resistance to biotic and abiotic stresses. However, it remains unclear whether AMF and DSE are synergistic or antagonistic in the presence of host plants to environmental gradients, especially on large geographical scales. To determine the relationships between AMF and DSE and their adaptability on a regional scale, we measured AMF and DSE colonization in the roots of 1023 plants of different species within the Artemisia genus collected from 81 sites across central and eastern China. We used general linear mixed models to analyze the relationships between colonization, and temperature and precipitation conditions. We found no significant correlation between AMF and DSE. The AMF colonization rate followed a significant longitudinal trend, but there was no latitudinal pattern. DSE colonization did not follow any geographical pattern. The AMF colonization rate was positively correlated with temperature and precipitation, whereas it was not significantly correlated with soil. There was no significant correlation between DSE colonization and climate or soil. Our results suggest that AMF and DSE play independent roles in the response of Artemisia to the regional environment. Therefore, studies on mycorrhizal symbiosis should discern the differential responses between AMF and DSE to climate and soil when evaluating the adaptability of the two types of symbiosis on large geographical scales. (c) 2021 Published by Elsevier B.V

Effects of rainfall pattern on the growth and fecundity of a dominant dune annual in a semi-arid ecosystem

Current and future changes in rainfall patterns - amount and frequency - may particularly impact annual plants in semi-arid ecosystems. The aim of this study was to investigate how changes in rainfall patterns affect the growth and fecundity of sand dune annuals. The effects of gradients in five rainfall amounts and five frequencies, based on historical and predicted values, on growth and fecundity of Agriophyllum squarrosum, a dominant annual in Mu Us Sandland, were examined in the near natural habitat. Rainfall amount and frequency significantly affected all vegetative and reproductive traits. With decreased amount of rainfall, height, biomass, seed number, seed mass and reproductive effort decreased, while root/shoot ratio increased. Except for the two extreme frequencies (1- and 120-day intervals), values of all vegetative and reproductive traits increased with the increase of rainfall frequencies. Germinability of offspring seeds tended to increase with increasing aridity, suggesting that a maternal effect may have been present. Our study shows that the plastic response in growth and fecundity of A. squarrosum to rainfall fluctuation allows the plant to survive and reproduce under current unpredictable environments as well as the increased variability predicted with climate change in semi-arid regions

Aerial and soil seed banks enable populations of an annual species to cope with an unpredictable dune ecosystem

BACKGROUND AND AIMS: Simultaneous formation of aerial and soil seed banks by a species provides a mechanism for population maintenance in unpredictable environments. Eolian activity greatly affects growth and regeneration of plants in a sand dune system, but we know little about the difference in the contributions of these two seed banks to population dynamics in sand dunes. METHODS: Seed release, germination, seedling emergence and survival of a desert annual, Agriophyllum squarrosum (Chenopodiaceae), inhabiting the Ordos Sandland in China, were determined in order to explore the different functions of the aerial and soil seed banks. KEY RESULTS: The size of the aerial seed bank was higher than that of the soil seed bank throughout the growing season. Seed release was positively related to wind velocity. Compared with the soil seed bank, seed germination from the aerial seed bank was lower at low temperature (5/15 °C night/day) but higher in the light. Seedling emergence from the soil seed bank was earlier than that from the aerial seed bank. Early-emerged (15 April–15 May) seedlings died due to frost, but seedlings that emerged during the following months survived to reproduce successfully. CONCLUSIONS: The timing of seed release and different germination behaviour resulted in a temporal heterogeneity of seedling emergence and establishment between the two seed banks. The study suggests that a bet-hedging strategy for the two seed banks enables A. squarrosum populations to cope successfully with the unpredictable desert environment

Soil salt and NaCl have different effects on seed germination of the halophyte Suaeda salsa

Seed germination is a key life-history stage of halophytes. Most studies on seed germination of halophytes have focused on the effects of a single salt, while little information is available on the effects of mixed salt in the natural habitat. Due to the contribution of multiple ions in saline soil, we hypothesized that the effect of mixed salt on seed germination will differ from that of a single salt and the mechanism of how germination is affected will differ as well. The effects of mixed salt and NaCl on germination, water imbibition, and ionic concentrations of seeds of Suaeda salsa (L.) Pall. were compared at various salinity levels. Germination percentage (GP) and rate (GR) decreased with increasing salinity level, regardless of salt type. There was no difference in GP or GR between mixed salt and NaCl when the salinity level was below 20 dS m(-1). Above 20dS m(-1), GP and GR in NaCl were lower than those in mixed salt. At the same salinity level, Na+ concentration in seeds was higher in NaCl than that in mixed salt, but the reverse was true for Ca2+ and Mg2+ concentrations. Imbibition rate for seeds in NaCl was lower than that in mixed salt at the same salinity level. Addition of Ca2+ and Mg2+ alleviated the inhibition of NaCl on seed germination. In conclusion, our results suggest that the effects of soil salts and NaCl on seed germination are different, and using NaCl instead of soil salt might not be realistic to show the effect of saline stress on seed germination of halophytes in the natural habitat

Soil temperature and moisture regulate seed dormancy cycling of a dune annual in a temperate desert

Plants have evolved diverse strategies to ensure their survival and regeneration in specific environments. Although temperature and soil moisture control seed dormancy, most studies have concentrated on temperature and little is known about the influence of moisture for species in the arid region. Responses of seed dormancy and germination of Agriophyllum squarrosun (Amaranthaceae), a pioneer and dominant species in Mu Us Sandland in northern China, to variations in soil moisture and temperature were examined. Our study showed that (1) freshly harvested seeds were in non-deep physiological (conditional) dormancy; (2) seeds in the soil exhibited dormancy cycling being non-dormant in spring and dormant from summer to autumn; (3) dry conditions at cold or warm temperatures alleviated dormancy; (4) germination was promoted by wetting-drying cycles; and (5) dormancy was induced by warm temperature (15/25 degrees) and particularly low soil moisture less than 14.0%. The seasonal pattern of seed dormancy/germination was regulated by seasonal rainfall and soil temperature. At the same time, a range of conditions enable dormancy break and germination regardless of soil moisture conditions allowing the species to persist in an unpredictable environment

Allometry rather than abiotic drivers explains biomass allocation among leaves, stems and roots of Artemisia across a large environmental gradient in China

Biomass allocation patterns reflect the adaptive strategies of plants growing in different environments, which is a central issue in comparative plant ecology and evolution. However, the factors underpinning specific allocation patterns across organs and the existence of general rules governing allocation remain contentious. Optimal partitioning theory (OPT) states that plants can respond to resource availability by allocating relatively more biomass to the organ that captures the most limiting resources to optimize growth. In contrast, allometric partitioning theory (APT) postulates that biomass allocation among organs is a power function of plant size independently of environmental variation. As phylogenetic and growth form constraints (e.g. formation of inert heartwood in tree clades) may also affect biomass allocation, comparison among and within closely related taxa of rather similar growth form may enable a more direct testing of which of these two theories prevails. To test whether OPT or APT was prevalent at wide geographical scale, we investigated biomass allocation patterns among leaves, stems and roots of 1,022 plants of 62 Artemisia species (Asteraceae) collected along broad climate (annual mean temperature range: −4.9 to 18.0°C, annual mean precipitation range: 193–1,668 mm) and soil gradients (soil carbon content range: 1.6–15.4 kg C m−2) in central and eastern China. There were strong allometric relationships among leaf mass (ML), stem mass (MS) and root mass (MR) at both interspecific and intraspecific levels. Moreover, the interspecific and intraspecific patterns were not different from general patterns for pooled plants, that is, ML/MR and ML/MS, but not MS/MR, generally decreased with plant size. However, the three organ mass ratios were not responsive to broad climatic or soil gradients after the effect of plant size was removed. Synthesis. Our results generally support APT instead of OPT, suggesting that Artemisia plants have evolved an allometric strategy rather than relying on adjustment of allocation among organs to adapt to the broadly varying environments at the regional scale. For follow-up research, we hypothesize that the strong allometric constraints on biomass allocation should depend on strong physiological adaptive responses of the different organs of Artemisia to environmental gradients

Seed dormancy and germination of a critically endangered plant, Elaeagnus mollis, on the Loess Plateau of China

Elaeagnus mollis is an endangered species narrowly distributed on the south-eastern Loess Plateau of China. Natural regeneration of populations is highly restricted by low seed germination. The aim of this study was to explore why germination is low and how to enhance germination of the species. Field and laboratory experiments were carried out to examine the effects of temperature, light, drought and NaCl on seed germination and the effects of the seed coat, GA(3), cold and warm stratification and after-ripening on dormancy release. Our results showed that (1) fruits (0.65 g/fruit) and seeds (0.14 g/seed) were relatively large, the embryo was surrounded by a hard and permeable seed coat and a lignified calyx tube, and more than half of the fresh seeds were not viable; (2) fresh, intact seeds did not germinate, but germination of scarified seeds was highest at 5/15 degrees C in continuous darkness; (3) dormancy was not released by GA(3) and cold stratification (5 degrees C), but significantly released by variable temperature stratification and field burial, indicating that seeds had deep physiological dormancy; and (4) germination was significantly enhanced by median drought (-0.6 MPa) and NaCl (0.34 M), and decay was inhibited beyond -0.4 MPa osmotic potential and 0.225 M NaCl. Our results suggested that, with habitat loss and climate warming, regeneration from seeds in natural populations will continue to be negatively affected, and the range of the populations will further contract

Global patterns of potential future plant diversity hidden in soil seed banks

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