Reproductive Characteristics Of The Dominant Species Stipa Bungeana Trin.on The Loess Plateau

Stipa bungeana Trin.is a polycarpic perennial?tussock?herbaceous grass that is a dominant species in typical grasslands of semi-arid areas on the Loess Plateau and has important economic and ecological value.However,there is little information on reproductive characteristic of this species.The aims of this research were to study the reproductive allocation of S.bungeana in different habitats;determine seed dormancy,germination and seedling emergence characteristics among different populations;compare germination characteristic of S.bungeana and other Stipa species;the effects of litter and mulching on seedling establishment and soil seed banks via laboratory and field studies.This paper aims to provide theoretical basis for reproductive characteristics of S.bungeana,and the application of this species in grassland restoration and management on the Loess Plateau.The major results are as follows.1.The biomass and reproductive allocation characteristics of S.bungeana in different habitats?the foot and top of Tsuiying mountain?in Yuzhong,Gansu Province was studied for two consecutive years?2012-2013?.In both years,the aboveground biomass and the reproductive allocation at the foot of mountain were significantly?P<0.05?higher than those at the top of mountain.The average aboveground biomass,reproductive tiller biomass and seed biomass in two years at the foot of mountain were 14.65 g,7.49 g and 1.80 g,respectively,and the top of mountain were 3.38 g,0.81 g and 0.13 g,respectively.The former were 4.3 times,9.3 times and 13.9 times of latter.In 2012 and 2013,the allocation of biomass from bunch to reproductive tiller at the foot of mountain was 59.3%and 41.3%,respectively,which were 137.3%and55.7%higher than those at the top of mountain in the same year.2.Seed dormancy,germination and seedling emergence characteristic of S.bungeana seeds collected from eight populations collected in different areas of the Loess Plateau?Gansu Province and Ningxia Hui Autonomous Region?were studied for two consecutive years?2015-2016?.Seed dormancy in the same year,rate of dormancy release and seedling emergence in the field differed significantly?P<0.05?difference,and there was no consistent trend in differences among populations between collection years,indicating that the tested characteristics among populations are mainly affected by environment.Mean seed dormancy for the two years in the eight populations was 49.3%for freshly harvested seeds,and 35.1%for six-month dry stored seeds,decreased 14.1%compared to freshly harvested seeds.3.The three“cardinal temperatures”,base water potential(?_b?50?)and hydrotime constant value??_H?of Stipa bungeana,S.grandis,S.klemenzii,S.breviflora,S.glareosa,S.gobica,S.purpurea and S.penicillata were determined.The base temperature?T_b?,optimal temperature?T_o?and maximum temperature?T_c?for germination of S.bungeana seeds was 9.7°C,23.3°C and 36.9°C,respectively.Compared with seeds of other seven Stipa species,those of S.bungeana had the lowest optimal temperature and medium base temperature and maximum temperature.Seeds of S.bungeana had a low base water potential(?_b?50?)and a high hydrotime constant??_H?,which were-0.73 MPa and 173 MPa·d,respectively,indicating that seeds of this species could germinate in dry conditions/environments.4.The effect of litter on seedling establishment and soil seed bank of S.bungeana was conducted in enclosures in natural Stipa bungeana-dominated grasslands.Compared with seeds on bare soil and those on top of different amount of litter layer?80,160 and 240 g/m²?,seedling emergence of seeds placed beneath the litter layer increased.Mean seedling emergence in different amounts of litter for seeds beneath and on top of the litter layer was 32.4%and 18.8%,respectively,and seedling emergence for seeds beneath the litter layer did not differ significantly?P>0.05?among different amounts of litter.However,seedling emergence decreased for seeds on top of the litter layer with increase in litter amount?seedling emergence with low to high amount of litter was 30.1%,14.5%and 11.7%,respectively?.5.Soil seed bank formation was significantly?P<0.05?affected by litter,and seeds on top of the litter layer were more likely to form a soil seed bank than those on bare ground or beneath the litter layer,and percentage of viable seeds increased with an increase in amount of litter.For seeds positioned on top of a 240 g/m² litter layer,percentage of viable seeds was 37.2%and 22.4%after 6 and 12 months in the field,respectively.Thus,a persistent soil seed bank?i.e.seeds viable after?12 months?was formed.However,<2.0%of seeds positioned beneath the litter layer or on bare ground were viable after 12 months.