Study On Functional Plant Ecology In Songnen Grassland, Northeast China

With the development of functional ecology, it is more and more important inresearch on functional plant ecology, especially with regard to the role of functionaldiversity on ecosystem functioning. This dissertation based on this point and studiedon functional plant ecology of grassland in Songnen Plain. We first discussed theproperty of Songnen grassland, and then, we stated functional traits properties and thevegetation conditions from plant functional traits perspective in Songnen grassland,third, we showed the variations of Leymus chinensis traits and L. chinensiscommunity characteristics after the control experiments by disturbance treatments ofdefoliation, nitrogen fertilization, vegetation shortness and sparseness, and last, wetested the relationships between aboveground biomass and species richness,functional group richness, species diversity and functional trait diversity at natural anddisturbed grassland. The main results as follows:The soil pH, electrical conductivity, ion contents, exchangeable sodiumpercentage (ESP) of non-degraded grassland were9.1-10.2,198.7-643.5μs/cm,734.9-9297.5mg/kg,4.8-28.4%, respectively. The corresponding values were10.2-10.4,8240.3-18232.1mg/kg,459.3-1832.6μs/cm,43.0-54.0%for the degradedgrassland. The content of clay was the highest in every soil horigon. Soil clay (<0.002mm) of alkali and meadow soil was over50%in the illuvial horizon, soilphysical clay (<0.01mm) of swampy soil and meadow soil were over75%in theilluvial horizon. The aboveground biomass of the non-degraded grassland was morethan250g/m~2, and the aboveground biomass of degraded grassland was over300g/m~2. The monodominant L. chinensis communities were widely distributed, theaboveground biomass of L. chinensis made up97.2%of the community, the speciesrichness per m~2was no more than8species. The monodominant species was moreobvious in the degraded grassland, the richness was even only one per m~2for someannual plant communities. The soil salinity content was different at micro area wheregrew another mono-dominant community, therefore, the landscape of patches wasobvious in Songnen grassland. When the soil surface was disturbed and destroyed, theeluvial horizon of original salinization soil disappeared, then, the lower soil layerwhich contained higher salinity became bare surface or grew halophyte community.The disturbed land surface was the leading reason of soil salinization at Songnengrassland. The Songnen grassland were extremely different from the typical zonalsteppe soils all over the world, and it was a meadow which was determined by soilproperties.The results of the66herbaceous plants leaf traits showed that leaf thickness (LT)variation (59.1%) was the highest among the7leaf traits measured. Pearsoncorrelation showed that specific leaf area (SLA), leaf nitrogen concentration (LNC), leaf phosphorus concentration (LPC), leaf chlorophyll (a+b) content (Chl) and leafcarotenoid content (Cd) were positively significantly correlated with each other. Therewas no significant correlation between LDMC and LPC, however, LDMC wasnegatively correlated with all other leaf traits significantly. LT was only negativelycorrelated to LDMC and SLA significantly, but not with others. LDMC, SLA, LT,LNC, LPC were significantly different among the4plant functional groups analyzedby one-way ANOVA (P <0.05). There was no difference between Chl and Cd.Perennial rhizome grass (PR) and perennial bunchgrasses (PB) had no differenceamong the7leaf traits. The LDMC of PR and PB were significantly higher thanperennial forbs (PF) and annuals/biannuals (AB). SLA, LNC, LPC of PR and PB werelower than PF and AB. Leaf N and P concentrations were22.7and1.8mg/g,respectively, N: P ratio was13.0. Plants growth were limited by nitrogen in Songnengrassland.The plant community productivity and the proportion of the dominant specieswere high, and the community saturation was low in Songnen grassland. For the fourfunctional group communities, the species richness of PR and PF was highest, andthere was no significant difference of the functional group richness, and theaboveground biomass of AB was most. LDMC, SLA, LNC, LPC, plant height (PH),specific root length (SRL) were significantly different among the4plant functionalgroups. AB had high LDMC, LNC, LPC, and low SLA. The soil condition of PFcommunities were best and AB communities were worst, and there was no significantdifferent between PR and PB. The relationships between aboveground biomass anddiversity showed that the aggregated traits of PH, leaf area (LA), and LNC were betterthan other indices to predict the variation of the productivity. Our results were inagreement with the biomass ratio hypothesis. And the grassland management for themaintenance of ecosystem functioning should focus on the dominant species.The relationship between diversity and aboveground biomass was not significantboth at the reviving stage and harvesting time after different autumn defoliation time.Defoliation treatments at autumn had no effect on grassland yield and quality in thesecond year. The harvest dates should be concentrated from the middle ten days ofAugust to the first ten days in September. Grazing or defoliation didn’t influence theyield and quality of L. chinensis population and community before late May. Grazingor defoliation limited L. chinensis regrowth, and the forbs proportion in thecommunity increased at later defoliation time. There were no significant difference ofspecies richness and functional group richness both after autumn or spring defoliation.However, there was significant positive relationship between aggregated PH andaboveground biomass, and the relationship between species richness, functional grouprichness, functional diversity and aboveground biomass were not significant.Nitrogen addition had significant effected on Cha, Chb, Cd, LNC, LDMC andSRL of L. chinensis. There were significant correlations between leaf photosynthetic traits, stem specific density (SSD), and SRL. The relationships between Cha, Chb, Cd,LNC, LDMC, SSD, PH and aboveground biomass of L. chinensis were significant. Naddition had no significant effect on species richness, functional group richness, the20g/m~2treatment had highest aboveground biomass. The aboveground biomass haddecreased trend as the species richness and functional group richness increased, but itwas not significant.The different height and density of reed stalks had significant effect on SLA,SSD, PH, leaf number (LN), Cha, Chb, Cd, LNC of L. chinensis. There weresignificant correlations between the traits of L. chinensis except LT and SRL. Therewas no substantial changes of the community characters. The species richness andfunctional group richness had shown decreased trends, and soil temperaturesincreased significantly as vegetation becoming shorter and sparser. However, therewere not obvious differences of other soil properties among the treatments. The effectof vegetation height on L. chinensis traits, community and soil properties was greaterthan that of vegetation density.