不同载畜率对短花针茅荒漠草原优势物种间关系及其空间分布特征的影响

Effects of different stocking rates on interspecific relationships among dominant species and their spatial distribution characteristics in the Stipa breviflora desert steppe

为探究不同载畜率对荒漠草原群落建群种与优势物种间的关系及其空间分布的影响,于2020年7-9月在内蒙古四子王旗短花针茅荒漠草原进行野外调查,以建群种短花针茅及优势种无芒隐子草和冷蒿为研究对象,设置不放牧对照(CK)、轻度(LG)、中度(MG)和重度放牧(HG)载畜率水平(分别放牧0、4、8和12只羊),结合常规方法与地统计学方法分析建群种及优势种出现频率、多度、种间关系强度及空间分布特征。结果表明:1)与CK相比,LG下冷蒿出现频率仅在7月显著降低了50.55%(P<0.05),而MG和HG在7-9月均显著降低(P<0.05),7-9月平均降低77.76%和97.53%;而不同处理及月份下短花针茅和无芒隐子草出现频率无显著差异(P>0.05)。2)与CK相比,各处理在7-9月时短花针茅种群多度均显著增加(P<0.05),LG、MG和HG分别在7-9月平均增加37.34%、75.72%和99.32%;冷蒿种群多度均显著降低(P<0.05),分别降低61.26%、66.32%和99.31%;无芒隐子草除LG在9月无显著变化外,各处理在7-9月时种群多度均显著增加(P<0.05)。3)短花针茅与无芒隐子草主要表现为亲和关系,而在9月时从CK的亲和关系转化为HG的竞争关系;短花针茅与冷蒿主要表现为竞争关系,放牧未改变其种间关系。4)短花针茅与无芒隐子草对冷蒿的作用强度较大,而冷蒿对短花针茅和无芒隐子草的作用强度较小。5)模拟9月物种间空间分布发现,CK中短花针茅种群多度随无芒隐子草种群多度增加而增加,随冷蒿种群多度增加而呈降低的趋势;HG中冷蒿种群多度不随短花针茅与无芒隐子草的变化而变化,但随着无芒隐子草种群多度增加,短花针茅种群多度整体上呈波动下降的趋势,表明短花针茅与无芒隐子草之间的关系由CK中的亲和关系转变为HG下的竞争关系。综上,放牧会改变物种的种群多度及物种间的关系。

The aim of this study was to explore the effects of different stocking rates on the relationships among dominant plant species and their spatial distribution in the Stipa breviflora desert steppe.A field study was conducted from July to September 2020 in the Siziwang Banner,Inner Mongolia.The constructive species S.breviflora and the dominant species Cleistogenes songorica and Artemisia frigida were selected as the research objects.Different stocking rates corresponding to the control,light grazing,moderate grazing,and heavy grazing(0,4,8,and 12 sheep grazing,respectively)were established.We analyzed the frequency,abundance,strength of interspecific relationships,and spatial distribution characteristics of the constructive and dominant species combining conventional methods and geostatistical methods.The results show that:1)The frequency of A.frigida was significantly decreased(by 50.55%)in the light grazing treatment as compared with the control(P<0.05)in July,while moderate and severe grazing significantly reduced its frequency from July to September(P<0.05).The average decreases in the frequency of A.frigida from July to September were 77.76%(moderate grazing)and 97.53%(heavy grazing).The frequency of S.breviflora and C.songorica did not differ significantly among different stocking rates and among different months(P>0.05).2)Compared with the control,the light,moderate,and heavy grazing treatments resulted in increased abundance of S.breviflora(by 37.34%,75.72%,and 99.32%,respectively),and decreased abundance of A.frigida(by 61.26%,66.32%,and 99.31%,respectively)from July to September(P<0.05).The species abundance of C.songorica increased significantly from July to September in all treatments,except for the light grazing treatment in September(P<0.05).3)S.breviflora and C.songorica mainly showed an affinity relationship,but showed a competitive relationship in the heavy grazing treatment in September.S.breviflora and A.frigida mainly showed a competitive relationship,and grazing did not change this interspecific relationship.4)S.breviflora and C.songorica had stronger effects on A.frigida,while A.frigida had weaker effects on S.breviflora and C.songorica.5)Finally,a simulation of the spatial distribution among dominant species in September revealed that the abundance of S.breviflora increased with increasing abundance of C.songorica in the control,and decreased with increasing abundance of A.frigida.In the heavy grazing treatment,the abundance of A.frigida was not affected by the abundance of S.breviflora and C.songorica.As the abundance of C.songorica increased,the abundance of S.breviflora tended to decrease,indicating that the relationship between S.breviflora and C.songorica changed from an affinity relationship in the control to a competitive relationship under heavy grazing.In summary,these results show that grazing can change intra-specific abundance and inter-specific relationships among dominant plant species.