The Similarity between Species Composition of Vegetation and Soil Seed Bank of Grasslands in Inner Mongolia, China: Implications for the Asymmetric Response to Precipitation

The asymmetric response of productivity to precipitation was recently proposed as an early warning signal for the shifts in temperate grassland function in China. It was hypothesized that the asymmetry was influenced by the increased growth of the newly emerged seedlings from the soil seed bank. Therefore, the seed density in the soil seed bank and the similarity between species composition of the vegetation and the soil seed bank should be maximized where asymmetry was maximized. However, this knowledge was still limited and unconfirmed. In this study, the desert steppe, typical steppe and the transition zone between them (with the highest asymmetry) were selected for studying the similarity index in both 2018 (dry year) and 2019 (wet year). Plant species composition was monitored in situ using an unmanned aerial vehicle. Soil seed bank samples were collected, and the seed bank density and species composition were then examined and identified in the laboratory. Results showed that: (1) The variation in vegetation species richness between the two years was the highest (41%) in the transition zone (p < 0.05), while it was only 7% and 13% for the desert steppe and typical steppe, respectively. The presence of herbaceous species mainly caused the differences in variation among three grassland types. (2) Seed density was the highest in the transition zone (114 seeds/m2 and 68 seeds/m2 in the transient and persistent soil seed bank, respectively) (p < 0.05). Additionally, herbaceous species were the main components of the soil seed bank. (3) The similarity index was the highest in the transition zone (p < 0.05), with 38%/44% and 33%/44% for the transient/persistent soil seed bank in 2018 and 2019, respectively. Our study demonstrated that variation in vegetation species composition was very similar to the composition of the seeds accumulated in the soil seed bank. These results warrant further investigation for the mechanism of asymmetric response of productivity to precipitation.

Effect of temperature and moist conditions on seed dormancy cycling of two sympatric limestone species, Begonia guishanensis and Paraisometrum mileense, in southern China

Information about seed dormancy cycling and germination in relation to temperature and moisture conditions in the natural environment is important for the conservation and restoration of rare species, including Begonia guishanensis and Paraisometrum mileense, two sympatric perennial limestone (karst) species. Dry afterripening (DAR) and wet and dry (WD) cycles at 15/5 and 25/15°C as well as moist chilling (MC) at 15/5°C were used to mimic the natural environment at different times of the year. A field experiment was conducted to monitor seasonal changes in germination responses of the seeds. About 40–65% of B. guishanensis and 5% of P. mileense seeds were dormant at maturity. DAR at 25/15 and 15/5°C as well as MC and WD cycles at 15/5°C alleviated dormancy for B. guishanensis but not P. mileense, and WD cycles at 25/15°C induced a deeper conditional dormancy for both species. Seeds of B. guishanensis exhibited dormancy cycling in the field, with increased dormancy under natural WD cycles at relatively high temperatures during the transition from the dry to the wet season in April to May and decreased dormancy during the wet season from June to October. KNO3 mitigated the dormancy-inducing effect of both artificial and natural WD cycles at relatively high temperatures for B. guishanensis. The field experiment indicated that seeds of B. guishanensis may be able to form a persistent soil seed bank, while almost all seeds of P. mileense germinate at the beginning of the wet season in the field.

The role of soil temperature and seed dormancy in the creation and maintenance of persistent seed banks of Nassella trichotoma (serrated tussock) on the Northern Tablelands of New South Wales

A large and persistent soil seed bank characterises many important grass weeds, including Nassella trichotoma (Nees) Hack. ex Arechav. (serrated tussock), a major weed in Australia and other countries. In the present study we examined the effects of constant and alternating temperatures in regulating primary and secondary dormancy and the creation and maintenance of its soil seed bank in northern NSW, Australia. One-month-old seeds were stored at 4, 25°C, 40/10°C and 40°C, in a laboratory, and germination tests were conducted every two weeks. Few seeds germinated following storage at 4°C, compared with seeds stored at 25°C, 40/10°C and 40°C. Nylon bags containing freshly harvested seeds were buried among N. trichotoma stands in early summer, and germination tests conducted following exhumation after each season over the next 12 months. Seeds buried over summer and summer plus autumn had higher germination than seeds buried over summer plus autumn plus winter, but germination increased again in the subsequent spring. Seeds stored for zero, three, six and 12 months at laboratory temperatures were placed on a thermogradient plate with 81 temperature combinations, followed by incubation at constant 25°C of un-germinated seeds. Constant high or low temperatures prolonged primary dormancy or induced secondary dormancy whereas alternating temperatures tended to break dormancy. Few temperature combinations resulted in more than 80% germination.

Scrutinization of Soil Seed Bank from Arid to Mesic Habitats of Dera Ghazi Khan

The research was conducted to investigate the persistent soil seed bank composition and its relation to the above-ground vegetation of upland area (piedmont) to low land area (alluvial) landscape from arid to mesic region of Dera Ghazi Khan. A transact of 40 kilometers was laid down from arid to mesic habitat. At each 2 km a quadrate of 1 m−2 sizes was thrown in the field to collect a soil sample of 2kg from soil cores ranging 0-15 cm deep for the analysis of soil seed bank. Twenty different sites were sampled by throwing 6 quadrates at each site making a total of 120 samples. Three thousand seeds were obtained of 50 different species from all the collected samples. Soil seed bank density m−2 was higher in the alluvial plains of Dera Ghazi Khan. Most of the perennial species, which were xerophytic in nature such as Aerua persica, Calotropis procera, Fagonia indica, Leptadaenia pyrotechnica, Peganum hermala, Rhazya stricta and Suaeda fructicosa were found in the piedmont (arid) soil habitat and the soil seed bank relatively less than the species found in the alluvial (Mesic) soil habitat, which were mostly of annual life span such as Chenopodium murale, Euphorbia prostrata, Medicago denticulata, Fumaria indica, and Withania somnifera. From this study it is concluded that the similarity found between soil seed bank and above ground vegetation of both historic types of habitats piedmont (arid) and alluvial (mesic) of Dera Ghazi Khan

A quantitative analysis of seed dormancy and germination in the winter annual weed Sinapis arvensis (Brassicaceae)

The aims of this study were to determine the effects of burial on germination and longevity, and of water stress and temperature on germination and dormancy induction of the weed Sinapis arvensis L. During exposure to the high temperatures of summer, seeds buried in the field became nondormant, but low water potential and supra-optimal temperatures (constant not alternating) induced them into secondary dormancy. The threshold temperature for dormancy induction (TTDI) was about 19 °C when water was not limiting germination, and it decreased with a slope of 10 °C per MPa as water potential decreased. Seeds had minimum dormancy (Dmin) when T < TTDI, and Dmin decreased by 81.5% per MPa increase in water potential. Dormancy induction increased linearly with a slope of 13.23% for each additional centimetre of burial depth from 1.0 to 5.19 cm. Dormancy was induced to its highest level (96%) in seeds buried at a depth of ≥5.19 cm; the remaining seeds were dead or were presumed to be dead Sinapis arvensis can form a persistent soil seed bank, and either water stress or conditions associated with increased burial depth can promote induction of secondary dormancy in the seeds.

Seed rain and seed persistence of Calamagrostis epigejos (l.) roth in extreme ecotoxicological conditions at an abandoned ore-washery sedimentation basin

ABSTRACT Clonal plants are very often among the first species to establish during primary succession. They may rapidly capture available space due to efficient vegetative propagation, but the question arises whether they may also rely on seed bank or seed rain during expansion and recovery after a possible disturbance. This question becomes increasingly important in extreme conditions of industrial deposit investigated in this study. We explored the two aforementioned seed sources in a clonal grass Calamagrostis epigejos within an ecotoxicologically stressed environment - abandoned tailings containment (former sedimentation basin) - from manganese-ore mining. Density of seeds found in seed rain was 617 seeds m-2, and in soil seed bank 220 seeds m-2, based on an autumn survey. Soil seed pool was almost depleted until the following spring as only 13 seeds m-2 were present. This pattern contrasted with the capacity of C. epigejos to build a persistent soil seed bank as shown by a burial experiment. Seed rain was thus identified to be the sole reliable seed source that may assist in recovery of this species after a possible disturbance

Seed size influence on germination responses to light and temperature of seven pioneer tree species from the Central Amazon

In Amazon secondary forests are dominated by pioneer species that typically produce large amounts of small and dormant seeds that are able to form a persistent soil seed bank. Seed dormancy in this group of species is overcome by environmental conditions found in open areas, such as high irradiation or alternating temperatures. Nevertheless, a variety of germination responses to environmental factors is known among pioneers; some of them may germinate in diffuse light or in darkness condition at constant temperature. Seed mass can be considered as one of the factors that promotes this variety. Regarding species with very small seeds, it seems that the trigger for germination is light and for larger seeds temperature alternation may be a more important stimulus. In this study we established a relationship between seed mass and germination response to light and alternating temperature for a group of seven woody pioneer species from the Amazon forest. We found that an increase in seed mass was followed by a decrease in the need for light and an increase in the tolerance to alternating temperatures. Understanding germination strategies may contribute with the knowledge of species coexistence in high diverse environments and also may assist those involved in forest management and restoration.