Effect Of Litter On The Reproductive Strategies Of Leymus Chinensis Under The Background Of N Deposition

Reproductive strategy is a classic topic of ecological research.The study on grassland plant reproductive strategy is of great significance for understanding the dynamics of plant community structure and its responses to environmental changes.Increasing atmospheric nitrogen(N)deposition has become an important part of global change ecology.Nitrogen deposition can alter plant growth and reproduction strategies by changing environmental conditions such as soil nutrients.Litter plays a role of an ecological engineer in the grassland ecosystem.Litter decomposition returns nutrients to the soil,and litter can also affect the growth and reproduction processes of plants by changing environmental conditions such as light intensity and soil moisture.The accumulation of litter on grassland can be affect by global changes such as N deposition and human activities such as grazing.Therefore,studying the regulating of N and litter on plant reproductive strategies is of great significance for understanding the maintenance mechanism of grassland community structure and its response to global changes and human activities.Based on long-term control experiments(for 11 years),we studied the effects of N addition and litter on the asexual and sexual reproduction of Leymus chinensis,the dominant species in Songnen Grassland,and the trade-off relationships between the two reproductive strategies.We explored the mechanism how N addition and litter regulated the reproductive strategies through altering light conditions,soil physical and chemical properties,and plant community characteristics.The main research results and conclusions obtained are as following:(1)The effects of N addition and litter on the asexual reproduction changed with time.In August,N had no effect on total number and dry biomass of bud bank number and dry biomass.Litter removal increased the total number and dry biomass of bud bank,but there was no significant difference between initial litter and litter addition.In September,N addition significantly increased the total number of total bud bank in initial litter,reduced the biomass of bud bank in the litter removal treatment.Litter addition decreased the total number and biomass of bud bank,especially in the treatments with N addition.In October,N increased the total number of bud bank in the litter addition treatment and decreased its biomass in the litter removal treatment.Without N addition,the total number and biomass of bud bank in the treatment of litter removal was lower than that in other litter treatments,while with N addition,the number of bud bank in the litter addition treatment was higher than that in other litter treatments.The number of axillary shoot buds and apical rhizome buds responded similarly to N addition and litter treatments and differently from axillary rhizome bud.(2)Nitrogen addition and litter had different impacts on the quantitative and qualitative characteristics of sexual reproduction.Nitrogen reduced the spike rate in the treatments of litter removal and litter addition,the setting rate in the treatment of litter addition and the total number of seeds in the treatment of litter removal,and increased the seed weight in the treatment of litter addition.The setting rate and the number of seeds both decreased with the increase of litter treatments,and litter addition increased the seed weight when N was addition.Nitrogen addition increased the height of reproductive branches,spike length and the number of florets in the litter addition treatment,and the litter had no effects on the spike characteristics.The reproductive phenology stages were not sensitive to N addition,but it was delayed by litter addition.Among the phenological periods,the post-fruit vegetative period was most sensitive to N and litter treatments.In the treatment of litter addition,N reduced the days of post-fruit vegetative,and without N addition,litter prolonged the post-fruit vegetative period.(3)N addition and litter regulated the reproductive characteristics mainly through improving soil nutrients.Nitrogen addition increased soil nutrients and leaf area,and reduced soil p H,thereby increasing the number of bud bank and seed weight.Litter addition increased soil nutrients and reduced light conditions,community density and leaf dry matter content,which had negative effects seed number.Litter had consistent effects on the number of seeds in the treatments with or without N,but has no effects on the number of buds.This might result from the significant interaction between N addition and litter.In the plots without N addition,litter addition had an adverse effect on the bud bank,while in the treatments with N add the number and biomass of the bud bank increased with increasing litter.Nitrogen addition had stronger effects on sexual and asexual reproduction than that in other litter treatments.Litter had similar effects on the number of seeds in the treatments with and without N,but had no effect on the number of bud bank.(4)The trade-offs relationships between reproductive strategies were different between population and individual levels.At the population level,the numbers of spikes and seeds increased with increasing community density,and the total number of bud banks was not affected by the community density.At the individual level,the number of seeds per remat decreased with increasing biomass of per ramet,while the bud bank per ramet increased with increasing biomass of ramet.The number of spikes per remat was not affected by the biomass per ramet.Therefore,the vegetative growth of L.chinensis was beneficial to bud bank,and had trade-off relationship with the number of seeds.No matter at the population or individual level,there was no trade-off relationship between sexual and asexual reproduction,and N addition and litter had no influence on the reproductive strategies.In summary,both N and litter reduced the number of seeds,which had an adverse effect on the sexual reproduction of L.chinensis.Nitrogen addition and litter had a significant interactive effect on the number of bud bank.Without N addition,litter addition reduced the number of bud banks,while with N addition,the total number of bud banks was enhanced by litter addition.The population dynamics of L.chinensis mainly depended on asexual reproduction.Therefore,without N addition,litter addition reduced the density and dominance of L.chinensis by reducing the number of bud banks,while with N addition,increasing litter increased its dominance by increasing the number of bud bank,which had negative effects on plant diversity.Therefore,under the background of N deposition,moderate grazing or mowing could reduce litter accumulation and the dominance of dominant species,and increase the plant diversity on grasslands.This research showed effects of litter on plant reproductive strategies under the background of N deposition,and deeply revealed the mechanism how N application and litter influenced plant reproductive strategies through altering environmental conditions and community characteristics.This research deepened the understanding of plant reproductive strategies in response to N deposition and human activities on grassland,but also improved the scientific basis for grassland management under the background of global changes.