Genotypic Diversity Affects Age Structure of Tiller and Rhizome of Leymus chinensis Population,But Not Age Structure of Bud

The effect of genotypic diversity on the age structure and bud bank of the Leymus chinensis population has not yet been demonstrated.This experiment was designed to study the age structure of the tiller,rhizome,and bud of L.chinensis at genotypic diversity levels of 1,2,4,8,and 12.A total of 64 communities were established in this experiment,following the principle of randomized block experimental design.The results indicated that genotypic diversity had a significant or obviously significant effect on the cumulative length of rhizomes of 2a and 4a,dry matter accumulation of rhizomes of 1a and 2a,tiller number of 1a,tiller productivity of 3a,but had no significant effect age structure of buds.As the levels of genotypic diversity increased,the proportion of the cumulative length of rhizomes with 4a decreased and then increased,and dry matter accumulation of rhizomes with 1a and 2a gradually increased while the number of tillers with 1a gradually decreased,when the gradient of genotypic diversity increased.At the 1,2,4,8,and 12 genotype diversity levels,the number of tillers,the cumulative length of rhizomes,and dry matter accumulation in rhizomes and buds were all age structures of expanding type.However,tiller productivity was an expanding or stable age structure at levels of 1,2,4,8 genotypic diversity,while it was a declining age structure at the 12 genotype diversity gradient.An appropriate genotypic diversity is conducive to maintaining the growth and stability of the age structure of L.chinensis population,but too high a gradient of genotypic diversity can have a negative impact on the population age structure.This study provided that an appropriate number of genotypic diversity contributes to the stability of the population.

Morphological and physiological plasticity response to low nitrogen stress in black cottonwood(Populus deltoides Marsh.)

It is important to evaluate nitrogen use efficiency and nitrogen tolerance of trees in order to improve their productivity.In this study,both were evaluated for 338 Populus deltoides genotypes from six provenances.The plants were cultured under normal nitrogen(750μM NH_4 NO_3)and low nitrogen(5μM NH_4 NO_3)conditions for 3 months.Growth,chlorophyll content and glutamine synthetase activity of each genotype were measured.Under low nitrogen,heights,ground diameter,leaf area,leaf and root biomass,and chlorophyll contents were significantly lower than those under normal nitrogen level.Correlation analysis showed that nutrient distribution changed under different nitrogen treatments.There was a negative correlation between leaf traits and root biomass under normal nitrogen level,however,the correlation became positive in low nitrogen treatment.Moreover,with the decrease of nitrogen level,the negative correlation between leaf morphology and chlorophyll levels became weakened.The growth of the genotypes under the two treatments was evaluated by combining principal component analysis with a fuzzy mathematical membership function;the results showed that leaf traits accounted for a large proportion of the variation in the evaluation model.According to the results of comprehensive evaluation of plants under the two treatments,the 338 P.deltoides genotypes could be divided into nine categories,with wide genotypic diversity in nitrogen use efficiency and low nitrogen tolerance.As a result,26 N-efficient genotypes and 24 N-inefficient genotypes were selected.By comparative analysis of their morphological and physiological traits under the two treatments,leaf traits could be significant indicators for nitrogen use efficiency and nitrogen tolerance,which is of considerable significance for breeding poplar varieties with high nitrogen use efficiencies.

Small-scale genotypic richness stabilizes plot biomass and increases phenotypic variance in the invasive grass Phalaris arundinacea

Aims We aim to understand how small-scale genotypic richness and gen-otypic interactions influence the biomass and potential invasiveness of the invasive grass,Phalaris arundinacea under two different dis-turbance treatments:intact plots and disturbed plots,where all the native vegetation has been removed.Specifically,we address the following questions(i)Does genotypic richness increase biomass production?(ii)Do genotypic interactions promote or reduce bio-mass production?(iii)Does the effect of genotypic richness and gen-otypic interactions differ in different disturbance treatments?Finally(iv)Is phenotypic variation greater as genotypic richness increases?Methods We conducted a 2-year common garden experiment in which we manipulated genotype richness using eight genotypes planted under both intact and disturbed conditions in a wetland in Burlington,Vermont(44°27′23″N,73°11′29″W).The experiment consisted of a randomized complete block design of three blocks,each containing 20 plots(0.5 m2)per disturbed treatment.We calculated total plot biomass and partitioned the net biodiversity effect into three com-ponents:dominance effect,trait-dependent complementarity and trait-independent complementarity.We calculated the phenotypic variance for each different genotype richness treatment under the two disturbance treatments.Important Findings Our results indicate that local genotypic richness does not increase total biomass production of the invasive grass P.arundinacea in either intact or disturbed treatments.However,genotypic interactions underlying the responses showed very different patterns in response to increasing genotypic richness.In the intact treatment,genotypic interactions resulted in the observed biomass being greater than the predicted biomass from monoculture plots(e.g.,overyielding)and this was driven by facilitation.However,facilitation was reduced as genotypic richness increased.In the disturbed treatment,genotypic interactions resulted in underyielding with observed biomass being slightly less than expected from the performance of genotypes in monocultures;however,underyielding was reduced as genotypic richness increased.Thus,in both treatments,higher genotypic rich-ness resulted in plot biomass nearing the additive biomass from indi-vidual monocultures.In general,higher genotypic richness buffered populations against interactions that would have reduced biomass and potentially spread.Phenotypic variance also had contrasting patterns in intact and disturbed treatments.In the intact treatment,phenotypic variance was low across all genotypic richness levels,while in the disturbed treatment,phenotypic variance estimates increased as genotypic richness increased.Thus,under the dis-turbed treatment,plots with higher genotypic richness had a greater potential response to selection.Therefore,limiting the introduction of new genotypes,even if existing genotypes of the invasive species are already present,should be considered a desirable management strategy to limit the invasive behavior of alien species.