Plant Competition Of Abandoned Old-Field Community Binding Species With Different Soil Moisture Treatment In Loess Hilly Region

Water is an essential restricted factor of plant growth in loess hilly region, and interspecific competition refers to the relationship between species competing for resource, which is critical to community succession and vegetation recovery. Previous studies mostly focused on the individual level interaction between species and water environment. Little was known about the community coexisting interspecific competition on the community level for the relationship of water condition and community structure, dynamic. Thus, studying that coexistence of soil moisture and community interaction and the influence of soil moisture on interspecific competition will provide theoretical basis for vegetation restoration and reconstruction in loess hilly region.The pot experiment with phytometer approach of pair-wise method and addition series experiment method and the field experiment with community density series method(CDS) were conducted by weighing the effects on ten binding species(Artemisia scoparia, Artemisia sacrorum, Artemisia giraladii, Bothriochloa ischaemum, Oxytropis glabra, Lespedeza dahumrica, Agropyron cristatum, Cleistogenes chinensis, Cleistogenes songorica, Potentilla chinensis)competition on soil moisture treatment in loess hilly region. Compared the competitive ability of eight species’ pair-wise and competition intensity and competitive hierarchy of ten coexisting species on community level, analyzed the relationship of mortality in drought stress and growth variation in water-welled period, the main conclusions were as follows:1. Species competition of pair-wise response to soil moisture change of competition:Interspecific competition affected the plant growth as growth condition of pair-wise were different from monoculture. Although interspecific competition enhanced A.cristatum biomass increase, it was inhibited by water stress contrary to L.dahumrica. The growth of A.sacrorum and A.giraladii were benefited from concurrence of interspecific competition and mild water stress. Aboveground biomass could react better soil moisture changes on the influence of biomass, and underground biomass were more sensitive to soil moisture feedback. The influence of test species density change on target species growth was first increased and then decreased along with water well.Competition intensity was larger under severe water stress. Change trend of relative biomass or height competition intensity was almost the opposite. In water stress, total competitive ability of O.glabra > A.cristatum and A.sacrorum > A.giraladii, total biomass competitive ability of L.dahumrica >B.ischaemum and A.scoparia > C.songorica, meanwhile the biomass competitive ability were stronger of A.sacrorum, L.dahumrica, B.ischaemum and A.giraladii, contrary to A.cristatum, A.scoparia,C.songorica. It was roughly in line with the succession niche theory, that is, with the decrease of soil moisture in the process of succession, the competition ability of resistance to water stress was the late succession species > early in succession. The influence of test species density change on target species per-gram competitive ability of biomass was same with its growth. Per-gram competition intensity of height was <0.01 basically.2. Competitive hierarchy of community binding species was effected to soil moisture:Except for O.glabra, C.chinensis,C.songorica, aboveground biomass were largest in medium water and height were highest water. Except for B.ischaemum, A.cristatum, relative biomass in low water stress were decreased along with community density increased, and the relationship of community density and relative biomass had been seen positively in medium water. P.chinensis were not suitable for the regeneration after transplanting. Relative biomass of A.giraladii were maximum in low and medium water, A.sacrorum in high water.Interspecific competitive hierarchy were variable and changed with environment. With soil moisture stress, total competitive ability of A.cristatum,C.songorica were higher,then B.ischaemum, A.sacrorum, A.giraladii, and A.scoparia, O.glabra, P.chinensis were lower. With water better, competitive ability of A.sacrorum increased significantly and decreased of B.ischaemum, A.sacrorum, A.giraladii. Competitive advantage of L.dahumrica were weak in water stress.3. Relationship of growth variation and mortality: Except for A.scoparia, L.dahumrica, height were lager in water-welled period. Community density was higher, growth variation of A.scoparia, B.ischaemum, A.cristatum was smaller, individual size was more uniform, shaping action was the stronger of the competition for the size of individual plants. Growth variation was maximum in high density of A.sacrorum, L.dahumrica, C.chinensis,P.chinensis, and in medium density of A.giraladii, C.songorica.In drought period, height and biomass of ten species were decreased with community density increased. Species did not reduce, individual death number increased significantly, the death rate increased with the population density increase after drought treatment. When water stress and competition coexist, mortality were higher of A.scoparia,O.glabra,P.chinensis,C.chinensis, and lower of B.ischaemum, L.dahumrica, A.cristatum.The relationship was positive between growth variation and mortality in drought period. It could explain 12% growth performance which was caused by competition in water-welled period lead to mortality rate changes of drought.