Phytotoxicity assessment of phenanthrene, pyrene and their mixtures by a soil-based seedling emergence test

Seedling emergence tests were conducted in a meadow brown soil using five plant species(i.e., Chinese cabbage, green onion, tomato, turnip and wheat) to determine the phytotoxicity of phenanthrene, pyrene and their mixtures. The soil was amended with up to 1000 mg/kg soil of phenanthrene or 600 mg/kg soil of pyrene. Seedling emergence and root growth were measured. The results indicated that root elongation was more sensitive than seedling emergence. Root length decreased with increasing phenanthrene or pyrene concentrations(p≤0 05). Phenanthrene was more phytotoxic than pyrene. The lowest observable adverse effect concentration(LOAEC) was 10 mg/kg for phenanthrene when tested with green onion, and 50 mg/kg for pyrene when tested with wheat. Among the five species, wheat was found to be the most sensitive. When amended jointly at or below their respective LOAEC, phenanthrene and pyrene produced a synergistic toxic effect.

Precipitation amount and frequency affect seedling emergence and growth of Reaumuria soongarica in northwestern China

Climate change is shifting the amount and frequency of precipitation in many regions, which is expected to affect seedling recruitment across ecosystems. However, the combined effects of precipitation amount and frequency on seedling recruitment remain largely unknown. An understanding of the effects of precipitation amount and frequency and their interaction on seedling emergence and growth of typical desert plants is vital for managing populations of desert plants. We conducted two experiments to study the effects of variation in precipitation on Reaumuria soongarica （Pall.） Maxim. First, greenhouse experiments were conducted to examine the effects of three precipitation amount treatments （ambient, ＋30%, and -30%） and two precipitation frequency treatments （ambient and -50%） on seedling emergence. Second, the morphological responses of R. soongarica to changes in precipitation amount and frequency were tested in a controlled field experiment. Stage-specific changes in growth were monitored by sampling in different growth seasons. Our results showed that precipitation amount significantly affected germination, seedling emergence, and growth of R. soongarica, and there was a larger effect with decreased precipitation frequency compared with ambient. Germination and seedling emergence increased as precipitation increased under the same frequency of precipitation. The highest emergence percentage was obtained with a 30% increase in precipitation amount and a 50% reduction in precipitation frequency. Compared with ambient precipitation, a 30% increase in precipitation amount increased above- and below-ground biomass accumulation of R. soongarica during the growth season. A decrease of 30% in precipitation amount also resulted in an increase in below-ground biomass and root/shoot ratio in the early stages of the growth season, however, above- and below-ground biomass showed the opposite results at the end of the growth season, with larger effects on above-ground than below-ground biomass under decreased precipitation frequency. When precipitation frequency decreased by 50%, values of all growth traits increased for a given amount of precipitation. We concluded that precipitation frequency may be as important as precipitation amount to seedling emergence and growth of R. soongarica, and that understanding the effects of precipitation variability on seedling recruitment requires the integration of both precipitation amount and frequency. In particular, the combination of a 30% increase in precipitation amount and 50% reduction in precipitation frequency increased the emergence and growth of seedlings, suggesting that alteration of amount and frequency of precipitation caused by climate change may have significant effects on seedling recruitment of R. soongarica.

Changes in Nutrient-Homeostasis and Reserves Metabolism During Rice Seed Priming:Consequences for Seedling Emergence and Growth

In this study influence of different seed priming treatments on the nutrient-homeostasis and reserve metabolism during seedling emergence and growth of rice were determined. Seed priming treatments included pre-germination, hydropriming for 48 h, osmohardening with KCl and CaCl2, ascorbate priming and hardening. All treatments shortened the emergence time and enhanced the energy and index of seedling emergence. Seedlings from primed seeds had greater length, number of roots and fresh and dry mass than control. Among the treatments, CaCl2, ascorbate and KCl proved better in enhancing emergence and seedling growth. Seed priming changed the pattern of N and Ca^2＋ homeostasis both of the seeds and seedlings, which were associated to enhancing s-amylase activity and reducing sugars content. Positive correlations of seedling attributes with nutrient content suggested that as a result of seed priming, most of N and Ca^2＋ were partitioned to embryo, which enhanced seedling emergence and subsequent growth of rice seedlings.

Seed Health Status of Sweet Corn (Zea mays L. saccharata Sturt) from Five Areas in China and Effect on Field Seedling Emergence

The health status of 18 sweet corn (Zea mays L. saccharata Sturt) hybrids classified to two types, collected from five areas in China, was examined by PDA method, and factors influencing seed health and relationships between seed health and field seedling emergence were studied. Seventeen fungal genera were isolated and Fusarium was the most frequently isolated. There were significant differences both in incidence of Fusarium and in percentage of infected seeds among 18 hybrids. Research also showed that significant and consistent differences both in seed-borne fungal taxa and in percentage of infected seeds existed between two types of sweet corn. Sugar enhanced corn is more slightly infected than super sweet corn both in fungal taxa (13 and 16, respectively) and in percentage of infected seeds (62.0 and 79.2%, respectively). There were also significant differences both in seed-borne fungal taxa and in percentage of infected seeds among five areas. Seeds from South China were most severely infected, for there were 14 fungal genera detected and the percentage of infected seeds was highly 99.1% while those from Northwest China were slightly infected, for there were 10 fungal genera detected and the percentage of infected seeds was only 14.3%. Further research showed that there were significant negative correlations both between incidence of Fusarium and percentage of field seedling emergence and between percentage of infected seeds and percentage of field seedling emergence. Percentage of field seedling emergence could be estimated by regression equations built by regression analysis.

Pre-emergence herbicides affect seedling emergence of tropical forest tree species

Testing techniques to reduce weed infestation is a crucial step in developing direct tree seeding systems. The use of pre-emergence herbicides may be an alternative to manual weeding techniques, but so far, information on how they affect the seeds of native tree species is scarce. We established a greenhouse experiment to evaluate the effects of four pre-emergence herbicides (atrazine, diuron, isoxaflutole and oxyfluorfen) on weed suppression and seedling emergence and early growth of seven tropical forest tree species (Annona coriacea Mart., Citharexylum myrianthum Cham., Cordia ecalyculata Vell., Peltophorum dubium (Spreng.) Taub., Psidium guajava L., Pterogyne nitens Tul. and Schinus terebinthifolia Raddi). The experimental design was a randomized complete block design with five treatments and five replicates. The treatments consisted of a single dose of each pre-emergence herbicide and a control. Throughout the 60?days after sowing we evaluated weed cover and seedling emergence and early growth of tree species. Overall, our results suggest that all tested herbicides reduced weed cover; however, they also negatively affected tree species seedling emergence. Of the four herbicides tested, atrazine and diuron showed the greatest effects on tree seedling emergence, oxyfluorfen was least aggressive towards native species and isoxaflutole was most effective in weed control. Native tree species varied in their responses to herbicides, indicating that future experiments should increase the number of species tested as well as investigate how seed traits can affect the species responses to different herbicides.

Responses of Caryopsis Germination, Seedling Emergence, and Development to Sand Water Content of Agropyron cristatum （L.） Gaertn. and Bromus inermis Leyss.

Responses of caryopsis germination, seedling emergence, and development of Agropyron cristatum （L.） Gaertn. （Gramineae） and Bromus inermis Leyss. （Gramineae）, two dominant perennial grasses in the Otindag Sandland of China, to different sand water content （SWC; 1%, 2%, 3%, 4%, 6%, 8%, 12%, 16%, and 20%） were studied comparatively. The results showed that the germination responses of the two grasses to SWC were similar （i.e. caryopses could not germinate when the SWC was below 3%; at SWC ranging from 3% to 12%, the higher the SWC, the higher the germination percentage; and at a SWC of 12%-20%, germination reached similarly high percentages）. At a sand burial depth of 0.5 cm, the threshold of SWC for seedling emergence was 6% forA. cristatum and 8% forB. inermis; at 12%-20% SWC, the seedling emergence of both species reached similarly high percentages. The seedling growth responses of these two species to SWC gradients were different. For A. cristatum, the biomass of seedlings increased with SWC from 6% to 12%, and decreased with SWC from 12% to 20%. For B. inermis, the biomass of seedlings always increased with SWC from 8% to 20%. The results also showed that the seedlings of both species allocated more biomass to the roots with decreases in SWC. The SWC changes from April to October in natural microhabitats of both species suggested that the SWC may play an important role in caryopsis germination, seedling emergence, and the growth characteristics of the two grasses. The responses of caryopsis germination, seedling emergence, and the growth characteristics of these two species to SWC may determine their distribution pattems in the Otindag Sandland.

Potentiality of Different Seed Priming Agents to Mitigate Cold Stress of Winter Rice Seedling

Seed priming has proved to be an effective pre-germination seed invigoration technique for different crops to improve seed and seedling performance under different abiotic stresses.In Bangladesh,winter rice is very often exposed to cold waves just after sowing in the nursery bed resulting in poor seed germination and seedling emergence,yellowish and thin seedlings production,and a very low survival rate.Seed priming may mitigate the cold stress during seed germination and seedling emergence and helps in the quality seedling production of winter rice.To evaluate the efficacy of different seed priming techniques in increasing seedling emergence,growth,vigor and survivability of winter rice cultivars under cold stress,a pot experiment was conducted at the Department of Agronomy,Bangladesh Agricultural University during December 2018 to January 2019.The experiment comprised two factors,(A)Winter rice variety namely,(i)BRRI dhan29 and (ii)BRRI dhan36;(B)Seed priming agent namely (i)Control(no priming),(ii)20000 ppm NaCl,(iii)30000 ppm NaCl,(iv)20000 ppm KCl,(v)30000 ppm KCl,(vi)20000 ppm CaCl2,(vii)30000 ppm CaCl2,(viii)50 ppm CuSO4,(ix)75 ppm CuSO_(4),(x)10000 ppm ZnSO4,(xi)15000 ppm ZnSO4,(xii)2 ppm Na2MoO4,(xiii)3 ppm Na2MoO4,(xiv)100 ppm PEG(Polyethylene glycol 4000)and (xv)150 ppm PEG.Seeds were sown on two different dates viz.,1st December and 1st January so that seedlings are exposed to cold stress at different stages.The experiment was laid out in a completely randomized design(CRD)with three replications.Results indicated that(in most of the cases)seed priming has a positive impact on seedling emergence rate(%),root length,shoot length,root shoot ratio,root dry weight,shoot dry weight,seedling dry weight and survival rate(%).Among the priming agents,KCl and CaCl2 performed best;while priming with NaCl and PEG showed no advantages over no priming for both the sowing dates.In general,BRRI dhan36 performed better than BRRI dhan29 in terms of seedling growth because of its higher tolerance to cold stress.But,both the varieties performed similarly in terms of emergence rate and survival rate.Thus,priming is an effective tool to increase seed germination,better seedling growth,and higher seedling survivability of winter rice under cold stress,and KCl(20000 ppm)or CaCl2(20000 ppm)can be considered as a viable priming agent.

Preliminary Research on Radiation Breeding of Pteroceltis tatarinowii Maxim.

In order to explore the effect of radiation breeding on new germplasm innovation of Pteroceltis tatarinowii,the dry seeds of P.tatarinowii from Lingyan Temple were used as test materials in this study,which were irradiated by ^(60)Co-γ rays with different radiation doses.The results showed that the emergence rate decreased with the increase of radiation dose,the emergence rate of low dose below 200 Gy decreased slowly,and the emergence rate of high dose above 200 Gy decreased sharply;when the radiation dose ranged from 100 to 200 Gy,the mutagenic effect of P.tatarinowii seeds was the best;and radiation obviously affected the leaf color and leaf shape of seedlings.This study provides original materials for the cultivation of new P.tatarinowii varieties and the study of color-changing mechanism.

Earthworms promote greater richness and abundance in the emergence of plant species across a grassland-forest ecotone

Aims Chalk grasslands are subject to vegetation dynamics that range from species-rich open grasslands to tall and encroached grasslands,and woods and forests.In grasslands,earthworms impact plant communities and ecosystem functioning through the modification of soil physical,chemical and microbiological properties,but also through their selective ingestion and vertical transportation of seeds from the soil seed bank.Laboratory experiments showed that seed-earthworm interactions are species specific,but little is known on the impact of seed-earthworm interactions in the field.The overall aim of this study was to better understand seed-earthworm interactions and their impact on the plant community.First we analyzed the composition of seedlings emerging from casts after earthworm ingestion.Then we compared seedling composition in casts to the plant composition of emerging seedlings from the soil and of the aboveground vegetation along four stages of the secondary succession of chalk grasslands.Methods Four stages of the secondary succession of a chalk grassland—from open sward to woods—were sampled in Upper Normandy,France,in February 2010.Within each successional stage(×3 replicates),we sampled the standing vegetation,soil seed bank at three soil depths(0-2,2-5 and 5-10 cm)and earthworm surface casts along transects.Soil and cast samples were water sieved before samples were spread onto trays and placed into a greenhouse.Emerging seedlings were counted and identified.Effect of successional stage and origin of samples on mean and variability of abundance and species richness of seedlings emerging from casts and soil seed banks were analyzed.Plant compositions were compared between all sample types.We used generalized mixed-effect models and a distance-based redundancy multivariate analysis.Important Findings Seedling abundance was always higher in earthworm casts than in the soil seed bank and increased up to 5-fold,4-fold and 3.5-fold,respectively,in the tall grassland,woods and encroached grassland compared to the soil surface layer.Species richness was also higher in earthworm casts than in the soil seed bank in all successional stages,with a 4-fold increase in the encroached grassland.The plant composition of the standing vegetation was more similar to that of seedlings from casts than to that of seedlings from the soil seed bank.Seedlings diversity emerging from casts in the tall and encroached grasslands tended toward the diversity found in woods.Our results indicate that earthworms may promote the emergence of seedlings.We also suggest that the loss of some plant species in the seed bank and the tall grass vegetation in intermediary successional stages modify the local conditions and prevent the further establishment of early-successional plant species.

Ecological role of physical dormancy in seeds of Oxytropis racemosa in a semiarid sandland with unpredictable rainfall

Aims Seed dormancy and the soil seed bank are crucial to plant regeneration strategy,especially in semiarid ecosystems with unpredictable precipi-tation.the aim of this study was to investigate how seed dormancy is controlled by environmental factors and how it is correlated with the soil seed bank and regeneration of the perennial legume Oxytropis race-mosa,a dominant perennial herb in Mu Us Sandland of semiarid China.Methods Germination and imbibition experiments on fresh intact and scarified seeds of O.racemosa were used to identify physical dormancy(PY)in seeds of this species.Soil seed bank dynamics,timing of seedling emer-gence and the fate of buried seeds in the natural habitat were investigated.Important Findings PY was broken by mechanical scarification or wet heat/ice water cycles but not solely by dry heat or wet heat treatment.the soil seed bank exhibited seasonal changes in the number of seeds,which was highest in September and lowest in July.Seeds buried at different sand depths gradually lost dormancy;20-42%of the seeds remained dormant after 20 months of burial.Dormancy break occurs grad-ually throughout the year.Our results indicate that O.racemosa exhibits hardcoatedness heterogeneity that spreads germination of a seed cohort between seasons and years in the semiarid environ-ment,where the amount of precipitation during the growing season is highly variable.

Effects of the allelopathic plant Artemisia herba-alba Asso on the soil seed bank of a semi-arid plant community

Aims Seed bank strongly influences composition and structure of above-ground vegetation.Little attention has been paid to the role of allel-opathy driving soil seed bank dynamics,even though allelochemicals released by allelopathic plants might determine whether a species can or cannot germinate from the soil seed bank and,therefore,to co-exist in the neighborhood of the allelopathic species.Hence,the effects of allelopathic plants on community organization through the effects of allelochemicals on soil seed bank remain largely unknown.In this study,we assessed spatial heterogeneities in soil seed bank caused by the presence of allelopathic plants,and evaluated allelo-pathic effects on seed bank germination and seedling mortality.Methods We examined the effects of the allelopathic shrub Artemisia herba-alba Asso on the spatial structure(in terms of species richness and seed density)of the soil seed bank of a semi-arid ecosystem in NE Spain.Specifically,we evaluated seed bank richness and density at three microsites:under the canopy of A.herba-alba individuals,under the canopy of Salsola vermiculata L.(a non-allelopathic shrub)individuals,and in bare soil.In addition,we assessed the effects of aqueous extract of A.herba-alba on soil seed bank germination(seed-ling emergence and emergence timing)and seedling mortality.Important Findings We found that seed bank richness and density were higher under shrub canopy than they were in bare soil.A.herba-alba and S.vermiculata microsites had similar seed bank richness.However,seed bank density was higher under A.herba-alba because of the high abundance of A.herba-alba seeds.Aqueous extract reduced seedling emergence from the seed bank by 50%,and affected mortality of some emerged seedlings.On the other hand,aqueous extract did not influence the emergence timing of seedlings.We conclude that,although the presence of allelo-pathic plants does not cause relevant changes in seed bank struc-ture relative to similar non-allelopathic shrubs,their presence can actually result in a reduction of seedling emergence from the seed bank,which leads to low plant species richness and density nearby.To our knowledge,this is the first study to examine the effect of an allelopathic plant on the structure and germination in an entire soil seed bank.

Effects of soil warming history on the performances of congeneric temperate and boreal herbaceous plant species and their associations with soil biota

Aims Climate warming raises the probability of range expansions of warm-adapted temperate species into areas currently dominated by cold-adapted boreal species.Warming-induced plant range expansions could partly depend on how warming modifies relationships with soil biota that promote plant growth,such as by mineralizing nutri-ents.Here,we grew two pairs of congeneric herbaceous plants spe-cies together in soil with a 5-year warming history(ambient,+1.7℃,+3.4℃)and related their performances to plant-beneficial soil biota.Methods Each plant pair belonged to either the mid-latitude temperate climate or the higher latitude southern boreal climate.Warmed soils were extracted from a chamberless heating experiment at two field sites in the temperate-boreal ecotone of North America.To isolate poten-tial effects of different soil warming histories,air temperature for the greenhouse experiment was identical across soils.We hypothesized that soil with a 5-year warming history in the field would enhance the performance of temperate plant species more than boreal plant species and expected improved plant performances to have positive associations with plant growth-promoting soil biota(microbial-feeding nematodes and arbuscular mycorrhizal fungi).Important Findings Our main hypothesis was partly confirmed as only one temperate spe-cies performed better in soil with warming history than in soil with his-tory of ambient temperature.Further,this effect was restricted to the site with higher soil water content in the growing season of the sampling year(prior to soil collection).One of the boreal species performed con-sistently worse in previously warmed soil,whereas the other species showed neutral responses to soil warming history.We found a positive correlation between the density of microbial-feeding nematodes and the performance of one of the temperate species in previously wetter soils,but this correlation was negative at the site with previously drier soil.We found no significant correlations between the performance of the other temperate species as well as the two boreal species and any of the studied soil biota.Our results indicate that soil warming can modify the relation between certain plant species and microbial-feeding nematodes in given soil edaphic conditions,which might be important for plant performance in the temperate-boreal ecotone.

Functions of canopy-stored seeds in the dune ecosystem: conclusions from Agriophyllum squarrosum and Artemisia wudanica

Delay in seed release is found in the dune ecosystem.However,its functions have been rarely reported.We studied delayed seed release in the Agrio-phyllum squarrosum(Chenopodiaceae),an annual psam-mophyte,and the Artemisia wudanica(Asteraceae),a psammophilous subshrub in an active sand dune field in Inner Mongolia,China,to get insights into its functions in dealing with sand movement.We concluded that delay in seed release in the dune ecosystem are as follows:(1)postponing dispersal of a portion of seeds until the end of windy season and the start of growing season;(2)regulating the spatiotemporal pattern of seed bank;(3)helping psammophytes adapt to wind erosion on the active sand dune;and(4)helping psammophytes realize long-distance dispersal.