Studies On Reproductive Strategies Of Grasses In Temperate Grassland

Grasses act either as constructive species or dominant species in temperate grasslands,which are considered as the consequence of natural selection,also are important indicator plants both for community succession and grassland restoration.Grasses developed a diversity of reproductive strategies as adapted into environmental conditions.The main purpose of grasses is to continuously produce progenies as well as occupy space resources.Seed propagations allow plants to produce genetic variability,while vegetative reproduction can produce genetic identical progenies.Both are fundamental requirements for grasses to fill available spaces under grassland environmental conditions.Initially a group of popular grass species were divided based on differential characteristics of their reproductive strategies.Furthermore,clonal traits,bud bank types and dynamics,seed productivity and seed germination characteristics of several representative grass species were compared.The comparison not only explain different adapted abilities among diverse grass species,but also offer a theoretical knowledge about proper use of grassland resources,acceleration of grasslands restoration and understanding of community succession.The main results were as follows:1 There are four different spatial growth patterns among grasses,including “dot”,“circle radius”,“horizontal expansion”,and “space expansion”.Based on individual growth form and life form,reproductive strategies were divided into five categories,including “single-dot”,“tiller-dot”,“tiller-circle”,“rhizomatous horizontal expansion”and “rhizomatous space expansion ” and nine types,containing “point vertical solitary annual”,“point vertical solitary perennial”,“point scatter annual”,“circular radius perennial bunchgrass”,“circular radius perennial dense bunchgrass”,“multiple directions horizontal expansion short rhizomatous grass”,“multiple directions horizontal expansion long rhizomatous grass”,“double horizontal expansions long rhizomatous grass”and“spatial layer expansion long rhizomatous grass”.2.Rhizome grass had poorer ability to tiller but stronger ability to expand as compared with tillering grass.The clonal architecture of tiller grass and short rhizome grass was defined as “phalanx growth form”;The clonal architecture of “horizontal expansion long rhizome grass” was a transition form between “phalanx-guerrilla growth form”;but the clonal architecture of “spatial layer expansion long rhizome grass” was more similar to “guerrilla growth form”.3.In temperate grasslands,the bud bank of tillering grass was considered as seasonal bud banks.Stipa breviflora buds emerged at the end season(Autumn),Agropyron mongolicum buds mainly emerged at three periods: the end of early season(Spring),the beginning of middle season(Summer),and the end season(Autumn);In addition,rhizome grasses buds emerged over the entire growth season,and high precipitation was likely to be a primary factor to accelerate rhizome grass bud emergence.Pennisetum centrasiaticum and Leymus secalinus overwintered with a large amount of dormant axillary shoot buds and dormant axillary rhizome buds,whereas Bromus inermis had a small amount of axillary shoot buds to overwinter.4.Compared with nitrogen and phosphorus fertilizer addition,water addition improved clonal propagation and clonal growth for grass species.Also,water addition not only could increase tiller height for five grasses,but also could increase tiller density;Sufficient water was beneficial to rhizome growth and emergence of axillary shoot buds and apical axillary shoot buds for long rhizome grass.5.After synthetically comparing the reproductive characteristics of 5 species,the research found that grass species with low seed production were more likely to present poor germination and vigor.6.The reproductive adaptation of grass species to environments could be defined as D-S strategy(Dispersal-Spreading strategy).D-strategy(Dispersal strategy)represents grass species mainly reproduce by seeds and use seeds to establish plant population,this strategy can increase genetic variability of grass species,but restrict them to utilize limited resources and decrease resistances to adverse environmental conditions(e.g.fire and grazing);S-strategy(Spreading strategy)allows grass species to expand plant populations via individual clonal growth.This S-strategy enables grass species to quickly offset adverse environmental stresses and to make fully use of resources,but meanwhil e it make no contribution to genetic variability improvement,and increase the risk of population elimination under environmental stresses.