Effects of degradation and species composition on soil seed density in the alpine grasslands, China

Grassland degradation can alter the structure and function of ecosystem and soil seed bank.Therefore,estimating the role of soil seed bank in vegetation regeneration of degraded grasslands is crucial.We selected grasslands with three levels of degradation,namely non-degraded(ND),mildly degraded(MD),and heavily degraded(HD)to analyze the effect of grassland degradation on soil seed bank,as well as the role of soil seed bank on vegetation regeneration of the alpine grasslands,China.Soil samples from each level were collected in May,before seedling emergence,in August,after completion of transient seed bank germination,and in December,after seed dispersal,to determine the seed density and species composition through germination experiment.Result showed that a total of 35 plant species was identified,including 15 species observed in both soil seed bank and above-ground vegetation.A total of 19,15,and 14 species of soil seed bank were identified in December,May,and August,respectively.The most abundant species in soil seed bank were Compositae(5 species),followed by Poaceae(4 species),and Cyperaceae(3 species).Degradation level has no significant impact on species richness and Shannon-Wiener index of soil seed bank.In addition,sampling month and grassland degradation affected soil seed bank density,in which December>May>August,and ND>MD>HD,indicating that density of transient seed bank was greater than persistent seed bank.Soil seed bank density of surface layer(0–5 cm)accounting for 42%–72%of the total density,which was significantly higher than that of deep layer(5–10 cm).Similarity of species composition between vegetation and soil seed bank was low,and it increased with degradation level(ranged from 0.14 to 0.69).We concluded that grassland degradation affects soil seed bank density more than species diversity,and soil seed bank contributed slightly to vegetation regeneration of degraded alpine grassland.Therefore,it is unlikely that degraded alpine meadow can be restored solely through soil seed bank.

Effect of Seeding Density on Mat-Type Seedling Quality for Mechanical Transplanting in Dry Season Rice

Rice transplanting with a transplanter is a cost-effective process. Due to labor shortages during the peak time of rice transplanting, it is a promising technology in Bangladesh. However, the high-quality mat-type seedling is a prerequisite factor for mechanical transplanting. The experiments were conducted at three different locations (Gazipur, Tangail, and Rangpur) during the dry season (Boro)/2019-20 to determine the best seeding density for high-quality mat-type seedlings to be prepared for mechanical rice transplanters. The effects of seeding rate on seedling quality such as survival rate, seedling strength, stem thickness of newly released boro rice varieties BRRI dhan86, BRRI dhan89, and BRRI dhan92 were studied using four seeding rates (130, 140, 150, 160 g/tray). Results revealed that BRRI dhan92 showed quick seedling emergence compared to BRRI dhan89 and BRRI dhan86. Seedling mortality was found the lowest BRRI dhan92 while the highest in BRRI dhan86. 25 - 30 days old seedling was found suitable for mechanical transplanting in terms of seedling mortality. Seedling height increased with the increase in seed density. BRRI dhan92 showed the highest stem thickness followed by BRRI dhan89 and BRRI dhan86 with seed rate 150 - 160 g per tray. The suitable seeding rate (150 - 160 g/tray) for the studied varieties was found better for raising mat-type seedlings suitable for mechanical transplanting, which could coordinate the production of larger population growth and higher harvest index to achieve high grain yield.

Determination of the Influence of the Speed of the Saw Cylinder of the Saw Gin on the Density, Speed and Composition of the Seed Roll

The article consists of studying the influence of the speed of the saw cylinder on the quality of the fiber and the productivity of the machine, as well as on the change in the density and composition of the seed roll.

Characteristics of Soil Seed Banks of Typical Plant Communities in Hilly Area of Funiu Mountain

[Objectives]The purpose was to investigate the characteristics of soil seed bank of typical plant communities in hilly area of Funiu Mountain.[Methods]The seed density,number of species and species composition of the soil seed bank of typical plant communities such as Themeda japonica,Imperata cylindrica,Vitex negundo,Quercus acutissima,Robinia pseudoacacia,Platycladus orientalis and Populus canadensis in the surface,top 0-5 and top 5-10 cm soil were studied.[Results]The seed reserves of plant communities at different succession stages were(220.00±95.39)–(2650.00±1064.52)seeds/m2.A total of 48 species were counted in the seed bank,belonging to 45 genera in 22 families.Total 27 species were identified in the above-ground vegetation,belonging to 25 genera in 14 families.In the shallow soil where the seeds gathered,the seed densities of Imperata cylindrica and Themeda japonica were relatively low.The reserves of plant communities with different naturalness degrees were(403.33±64.29)-(2110.00±356.79)seeds/m2.A total of 67 species were counted in the seed bank,belonging to 64 genera in 37 families.A total of 45 species were identified in the above-ground vegetation,belonging to 43 genera in 28 families.In the soil layers of 0-5 and 5-10 cm,the seed density of natural secondary Q.acutissima was higher than those of planted P.canadensis,P.orientalis and R.pseudoacacia.In each soil layer,the species number of natural secondary Q.acutissima forest was slightly smaller than those of planted P.canadensis,P.orientalis and R.pseudoacacia forests.[Conclusions]The seeds in the soil seed bank may not completely come from existing above-ground vegetation.Manual assistance is required for vegetation restoration or reconstruction relying on soil seed bank,to ensure the direction of community succession.

Improvement of the Process of Separation of Cotton Fiber from Seeds

The differential equation, obtained as a result of the theoretical study of the movement of the bare seed on the surface of the grate of the saw gin, made it possible to determine the trajectory of the movement of the seed. The rib is one of the main working bodies of the saw gin. It serves for the free passage of the saw blades through it into the working chamber, for the withdrawal of the fiber caught on the saw teeth after separating it from the seed. A number of studies have been carried out to improve the working elements of the saw gin. The purpose of the research is to create the possibility of timely withdrawal of bare seeds from the working chamber of the saw gin by creating a concavity on the working surface of the grate. The use of the Euler equation for the movement of bare cotton seed along the grate contour, taking into account its speed V, density ρ, pressure P, made it possible to obtain a graph of seed distribution along the grate contour. An experimental 30-saw gin was developed and manufactured, the research carried out on it allowed to determine the rational parameters of new grates, which are recommended for introduction into production. The dependence of the location of the rectilinear part of the general contour on the shape of its convexity and concavity is determined. Based on the above equations, using separate functions, we present the view of the grate profile in the coordinate system modeled on the MAPLE-17 program.

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.

Is the soil seed bank a reliable source for passive restoration of bush-cleared semi-arid rangelands of South Africa?

Background:Bush clearing of encroached rangelands is crucial for restoration of herbaceous cover and diversity.Regeneration after bush clearing depends largely on the soil seed bank(SSB)size and composition.To assess the potential of the SSB to facilitate post-clearing herbaceous restoration,we examined the SSB density,composition and diversity and similarity between SSB and aboveground vegetation(AGV).Methods:The study was conducted in semi-arid rangelands of Maseding and Kgomokgomo in North-West Province of South Africa.In each rangeland,all woody plants in three 1250 m^(2) plots were cut using saws and loppers,with the stumps treated with picloram.Paired observations were conducted in cleared and uncleared microsites.Soil samples were collected at three depths(0-10,10-20 and 20-30 cm)in each microsite in April(pretreatment),August,October and December 2016 and in April and August 2017.SSB was assessed using seedling emergence method,whereas pre-and post-clearing surveys of AGV were conducted in February 2016 and 2017,respectively.Results:Cleared microsites had significantly(p<0.01)higher seed bank densities(1872 and 693 seeds m^(-2) at Maseding and Kgomokgomo,respectively)relative to uncleared microsites in August 2017,with grasses accounting for higher densities than other plant functional groups in the upper 0-10 cm.Pioneer grasses(Aristida congesta subsp.barbicollis,Brachiaria eruciformis and Tragus berteronianus)and invasive forbs(Bidens pilosa and Schkuhria pinnata)dominated the SSB in cleared microsites at Maseding,whereas succulents(Portulaca spp.)and pioneer grasses(T.berteronianus and Urochloa mosambicensis)were abundant at Kgomokgomo in August 2017.SSB and AGV were dissimilar until December 2016;thereafter,similarity increased significantly(p<0.05)in cleared microsites(Sørensen’s coefficient=0.60 to 0.66 at Maseding and 0.43 to 0.52 at Kgomokgomo)compared to uncleared microsites.Species diversity was highest in August 2016 and April 2017 at Maseding,but it did not differ between two microsites(p>0.05).At Kgomokgomo,SSB was more diverse in cleared than uncleared microsites in April and August 2017.Conclusion:High seed bank densities in the upper soil layer in cleared microsites would promote passive restoration,but regeneration is likely to be initiated by early successional species.However,close monitoring and eradication of invasive forbs and succulents is necessary following bush clearing.The tendency of SSB resembling AGV over time in cleared microsites signifies that seed production from AGV is important for passive restoration following bush clearing.