Effects Of Soil Heterogeneity And Species Composition On Biomass And Competitive Ability Of Three Forages

Soil heterogeneity is prevalent in grassland ecosystems,and it significantly affects the structure and functions of plant communities.Soil heterogeneity includes two main components,namely soil quality heterogeneity and soil configurational heterogeneity.Species composition crucially affects plant dynamic processes such as plant growth.However,the effects of soil heterogeneity and species composition on plant biomass and competitive ability are still unclear.Yet,it is quite difficult to explore the effects of soil heterogeneity under natural conditions since there are many factor co-occuring with soil heterogeneity.Thus,it is necessary to investigate the effects of soil heterogeneity with controlled experiments.This thesis was to examine the effects of soil heterogeneity(i.e.soil quality heterogeneity and soil configurational heterogeneity),species composition and their interactions on the biomass and competitive ability of three forages(Festuca elata,Bromus inermis,Elymus breviaristatus)through three controlled experiments.The first experiment aimed to explore the effects of species composition on the biomass and competitive ability of three forages,and the experimental treatment was set as follows: ten species compositions was achieved by growing the abovementioned three forage species monoculturely(i.e.3treatments),two species combined(i.e.6 treatments)and three species combined(i.e.1 treatment).The second experiment targeted to investigate the effects of soil quality heterogeneity and species on the biomass and competitive ability of three forages,and the experimental treatments were set as follows: three levels of soil quality heterogeneity were developed by mixing the cultivated soil and sand with three different ratios,i.e.2:8,5:5and 8:2,while the nine plant growing treatments were achieved by growing each of the abovementioned three forages with three different densities,i.e.1 individual per pot,two individuals per pot,and three individuals per pot.The third experiment was to test the effects of soil configurational heterogeneity and species composition on the biomass and competitive ability of three forages,and the experimental treatments were set as follows: three levels of soil configurational heterogeneity were established by varying the patch size of soils(i.e.small,medium and large patch size),and ten species compositions were completed by growing the abovementioned three forages monoculturely(i.e.3 treatments),two species combined(i.e.6 treatments)and three species combined(i.e.1treatment).The main results are listed as follows.1.Effects of species composition on biomass and competitive ability of three forages.Species composition significantly affected the biomass of forages.Specifically,species composition significantly affected belowground biomass,total biomass and root: shoot ratio,while the effect of species composition on aboveground biomass was not significant.Species composition significantly influenced the competitive ability of forgaes.Specifically,intraspecific competition was stronger than interspecific competition in the combination of F.elata and B.inermis.The similar trend was also found in the combinations of F.elata and E.breviaristatus and in the combinations of B.inermis and E.breviaristatus.However,the trend of the competitive ability of the target species in this combination was F.elata>B.inermis>E.breviaristatus.2.Effects of soil quality heterogeneity and species on biomass and competitive ability of three forages.Soil quality heterogeneity(i.e.soil-sand ratio)and significantly affected forage total biomass.Specifically,forage total biomass tended to increase with the increasing of soil-sand ratio.Soil quality heterogeneity(i.e.soil-sand ratio)significantly influenced competitive ability forage.Specifically,F.elata and B.inermis had a relatively high competitive intensity at the moderate level of soil quality heterogeneity,and E.breviaristatus had a relatively high competitive intensity at the high level of soil quality heterogeneity.A similar trend was found at the other planting densities.3.Effects of soil configurational heterogeneity and species composition on biomass and competitive ability of three forages.Soil configurational heterogeneity(i.e.patch size)and species composition significantly influenced the forage biomass.Specifically,the medium patch size had significantly higher biomass than the large patch size.Thus,the moderate level of soil configurational heterogeneity could support a high level of forage biomass.Soil configurational heterogeneity(i.e.patch size)and species composition significantly affected competitive ability forage.Specifically,when species composition was the same,the combination of F.elata and E.breviaristatus showed a greater relative yield in the medium patch size than in the large patch size at a soil type of 8:2,while the combination showed a greater relative yield in the large patch size than in the medium patch size in all the other soil types.The relative yield values were all greater than 1,indicating that intraspecific competition was greater than interspecific competition.These results suggest that soil heterogeneity and species composition significantly affect biomass and competitive ability of forages.Such results are of great significance for us to understand of the stability,structure and functions of grassland plant communities,as well as the maintenance of plant diversity.In addition,future research should the synergistic effects of soil heterogeneity and plant functional groups in terms of the diverse species of plant communities in nature.