高寒条件下根际环境对极小种群大理白前竞争能力的影响

Effects of rhizosphere environment on the competitive ability of extremely small population of Cynanchum forrestii Schltr under alpine conditions

大理白前(Cynanchum forrestii Schltr)是中国无危极小种群野生植物,研究高寒环境下大理白前-根际土壤系统的化学计量特征及其元素吸收,有助于解析极小种群的生存策略及其对环境的适应能力。以川西九龙县高寒草甸中的大理白前为对象,研究了其种群特征、光合色素特性、植物体和土壤的化学元素、根际土/非根际土的养分和细菌多样性。结果表明:与非根际土相比,根际土P、C/P和N/P较高而C/N较低,有机质(SOM)、全磷(TP)、全氮(TN)、速效氮(AN)、速效磷(AP)、速效钾(AK)增加;大理白前根际土P与茎的N、C/P、N/P呈正相关,而与P、C/N呈负相关。高通量测序表明,根际土/非根际土的优势细菌包括6个类群。根际土的变形菌门、芽单胞菌门相对丰度较高,而酸杆菌门、拟杆菌门、放线菌门、厚壁菌门的相对丰度较低,拟杆菌门相对丰度降低了45.53%,变形菌门相对丰度增加了32.89%。RDA分析结果显示,变形菌门相对丰度与土壤C、N、P呈正相关。在高寒草甸中,大理白前株丛呈均匀分布,平均株高(27 cm)高于群落其他植物的平均水平,地上生物量占比高达41.24%,种群密度和生态位宽度较大;随着株高增加,叶面积增大,光合色素含量和Chla/Chlb先增加后下降,但比叶质量变化不大;根茎叶对土壤元素均具有富集作用,其中对Ca、Mn、Na、K、P富集能力和对P、Ca、K转移能力较强。叶的C/N、C/P和N/P高于根、茎,各器官的N/P均小于14,表明养分主要分配到根、茎且受N限制。上述结果表明,大理白前富集有益的土壤微生物以改善根际土壤养分状况,提高植物体对Ca、Mn、Na、K、P等元素的吸收和转移能力,增强抗冻和抗辐射能力,并借助株高和叶面积的优势,弥补了光合色素含量较低的缺陷,从而提高了大理白前在高寒环境中的种间竞争能力和适合度,但却加剧种内竞争,导致其株丛呈均匀分布。推测种内竞争激烈是大理白前局限分布的原因之一。

Cynanchum forrestii Schltr,an erect perennial herb of Asclepiadaceae,is a wild plant with extremely small population(WPESP)in China.This unique plant grows in a variety of habitats such as plateau and mountain at altitudes of 1000—3500 m.The root of C.forrestii is often used as a substitute for the traditional Chinese medicine“Baiwei”.In Jiulong County,Ganzi Tibetan Autonomous Prefecture,western Sichuan Province,China,this plant is confined to alpine meadows in valleys at the altitude of 3100—3500 m.The rhizosphere is a part of the soil ecosystem where plant roots,soil and the soil microorganisms interact with each other.Soil microorganisms actively participate in soil material transformation and play a leading role in nutrient cycling by influencing the transformation of mineral elements.Most of the nutrients needed of plants come from soil and enter plants through rhizosphere interaction.The chemical element characteristics of plants can reflect the supply of nutrients to the soil.The study of plant and soil stoichiometric characteristics helps to understand the growth strategies of plants and their adaptability to the environment.Investigating the stoichiometric characteristics and element enrichment of the C.forrestii-rhizosphere soil system under the alpine environment will help to analyze the survival strategies of the extremely small populations and their adaptability to the environment.In this study,we investigated the effects of rhizosphere soil nutrients and bacterial community on population characteristics and photosynthetic characteristics of C.forrestii in the alpine meadow of Jiulong County by using plot and line transect sampling methods,physiological and biochemical analysis and Illumina-MiSeq high-throughput sequencing technology.The results showed that compared with the non-rhizosphere soil,the rhizosphere soil had higher P,C/P and N/P and lower C/N,and increased soil organic matter(SOM),total phosphorus(TP),total nitrogen(TN),available nitrogen(AN),available phosphorus(AP),and available potassium(AK).The Pearson correlation analysis showed that the value of N,C/P,N/P in C.forrestii stem were significantly positively correlated with the rhizosphere soil P,while the value of P and C/N were significantly negatively correlated with the rhizosphere P.High-throughput sequencing showed that the dominant bacteria in rhizosphere soil/non-rhizosphere soil included 6 groups.Compared with non-rhizosphere soil,the relative abundance of Proteobacteria and Gemmatimonadetes in rhizosphere soil was higher,while the relative abundance of Acidobacteria,Bacteroidetes,Actinobacteria and Firmicutes was lower.The relative abundance of Bacteroidetes decreased by 45.53%,and the relative abundance of Proteobacteria increased by 32.89%.Redundancy analysis(RDA)results showed that the relative abundance of Proteobacteria was positively correlated with soil C,N and P contents.The average plant height of C.forrestii was 27 cm,which was higher than the average height of other plants in the community.The proportion of above ground biomass reached 41.24%,and the population density and niche width also were larger than those of other plants.With the increase of plant height and leaf area,the photosynthetic pigment contents and Chla/Chlb raised first and then decreased,but leaf mass per area(LMA)had little change.Plants had enrichment effect on soil elements,the relatively high enrichment capacity for Ca,Mn,Na,K and P,and high transfer capacity for P,Ca,and K.Analysis of C,N,P stoichiometry showed that the C/N,C/P and N/P in C.forrestii leaves were higher than those of roots and stems,and the N/P of each organ was less than 14,indicating that N was the limit factor.In general,C.forrestii enriched beneficial soil microorganisms to improve the nutrient status of the rhizosphere soil,enhanced the absorption and transfer of elements such as Ca,Mn,Na,K,and P in plants,and promoted the ability to resist freezing and radiation.With the advantages of plant height and leaf area,it made up for the defect of low photosynthetic pigment content,thereby improving the interspecific competition ability and fitness of C.forrestii in the alpine environment,but intraspecific competition was intensified,which resulted in uniform distribution of plant clusters.It was speculated that the intense intraspecific competition was one of the reasons for the limited distribution of C.forrestii.