| Horqin Sandy Land is located in the meadow plain area of northern China,and in the history,it was once a beautiful grassland with lush grass.In the past 100 years,it has developed into a agro-pastoral transition zone.Due to long-term overgrazing,the Leymus chinensis meadow which isn't suitable to be reclaimed has been generally degraded to different degrees.In this study,a series of dominant populations in the restoration succession series of degraded L.chinensis meadows were regarded as the common object to conduct a dynamic study.After six sampling measurements in two years,a statistic analysis on the density and biomass change of dominant populations of Chloris virgata,Artemisia scoparia,Puccinellia tenuiflora and L.chinensis,as well as the number and biomass structure of plant and rhizome,the spatial change of bud age structure,the plasticity and regularity of reproductive distribution of L.chinensis in different succession communities are carried out.It not only theoretically reveals the development trend and change rule of different dominant populations in the restoration succession process of degraded L.chinensis meadows,but also provides a scientific basis for the rational utilization and management of degraded L.chinensis meadow in northern China.The main research results are as follows:1.In the restoration succession series of L.chinensis meadow,for the L.chinensis+Ch.virgata community for two years in different growth periods,the average population density of L.chinensis was 182.4-604.8 plants/m~2,and the average population density of Ch.virgata was 227.2-444.8 plants/m~2;As for the L.chinensis+A.scoparia community,the average population density of L.chinensis was 204.8-1280.0 plants/m~2,and the average population density of A.scoparia was 51.2-124.8 plants/m~2.in the L.chinensis+P.tenuiflora community,the average population density of L.chinensis was 339.2-1398.4 plants/m~2,and the average population density of P.tenuiflora was 1094.4-3238.4 plants/m~2;and there were550.4-1964.8 plants/m~2 in the single L.chinensis community.The above results indicate that among populations of restoration succession series,the perennial grass had a larger population density and a stronger tillering ability.2.In the restoration succession series of L.chinensis meadow,the community biomass of the single L.chinensis community was the highest in both July 2018 and May 2019,and they were 510.51g/m~2 and 225.19g/m~2,respectively.The community biomass of L.chinensis+P.tenuiflora community was the highest in August 2018 and July 2019,and they were565.95g/m~2 and 431.32g/m~2,respectively.In October of the two years,the community biomass of L.chinensis+A.scoparia community was the highest,and they were 282.40g/m~2and 432.74g/m~2,respectively.The biomass of L.chinensis+Ch.virgata community was significantly lower than that of other communities.The above results show that,from the perspective of community productivity,the late stage of restoration succession in which the dominant position of single L.chinensis community hadn't been reached.3.In the restoration succession series of L.chinensis meadow,the L.chinensis population in two years at different growth stages was composed of 3 to 4 age-classes,of which the number of 1a ramets accounted for 49.20%-62.85%,2a for 27.90%-35.72%,3a for9.07%-14.55%,and 4a for 0.18%-2.51%,presenting an increasing age structure.As for the biomass of ramets,1a accounted for 51.88-68.21%,2a for 23.97-36.16%,3a for7.74%-31.15%,and 4a for 0.08%-1.75%,which showed an increasing age structure.The rhizome of L.chinensis population was composed of 3 to 4 age-classes,and for the accumulated rhizome length,1a accounted for 32.70%-48.72%,2a for 30.42%-41.46%,3a for18.89%-25.37%,and 4a for 1.02-7.19%.As for the biomass of rhizome,the proportion of 1a and 2a was the largest,and they were 34.16%-52.31%and 28.30%-39.46%,respectively,with3a accounting for 17.78%-24.45%and 4a accounting for 0.97-6.24%,which presented an increasing or stable age structure.The buds of L.chinensis population were composed of 4 to5 age-classes,and 0a had an absolute advantage,accounting for 44.22%-68.89%,followed by1a,accounting for 15.31-38.66%,2a(11.19%-18.41%),and 3a(1.95%-4.44%),and 4a(0-0.49%)was only found in a few communities,which presented an increasing age structure.With the progressive increase of age,the proportion of ramets,rhizomes and buds in the old stage gradually decreased,the productivity of ramets and the storage capacity of rhizomes also decreased,and their contribution to L.chinensis population became smaller and smaller.The results indicated that,the L.chinensis population has a strong vegetative and reproductive capacity,and it can develop into a single dominant population in each succession community with the restoration succession process.4.In the restoration succession series of L.chinensis meadow,the quantitative characters of the reproductive ramets of L.chinensis of the two years had a different ecological plasticity.Among them,the plasticity of reproductive ramet growth was generally small,and the variation coefficient of inflorescence length was the largest(19.13%-19.59%),while the variation coefficient of ramet height was the smallest(13.99%-14.18%).The plasticity of material production and distribution of reproductive ramet was generally large,and the variation coefficient of inflorescence biomass was the largest(41.10%-45.89%),while the variation coefficient of reproductive distribution was the smallest(23.84-34.99%).In the four succession communities,the inflorescence length of the reproductive ramet of L.chinensis increased with the increase of ramet height and ramet biomass,and at the same time,there were two growth regulation modes,including isogony and allometry.With the increase of ramet biomass,the inflorescence biomass only presented allometry in the community of L.chinensis+Ch.virgata,and isogony and allometry coexisted in the community of L.chinensis+A.scoparia,the community of L.chinensis+P.tenuiflora as well as single L.chinensis community.The results indicated that the growth strategies of the four successional communities were common,in the case of ensuring normal growth,the reproductive ramets will provide more energy to the inflorescence.. |
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