| The root system is a key underground organ for water and nutrient utilization,and its conformation is a comprehensive reflection of the underground space and resource occupation by the plant root system,which is closely related to the resource utilization and adaptation strategies of plants to environmental changes.Lauraceae plants are important community-building species in subtropical broad-leaved evergreen forests and play a significant role in regional forest community structure and ecosystem function,yet reports on their fine root conformation are extremely scarce.In this paper,122 complete root samples containing 1-5 level fine roots were collected in the field from 7 genera and 10 species of Lauraceae with different habits in Jiulongjiang National Forest Park,Daxiong Mountain National Forest Park and Nanyue National Nature Reserve in Hunan Province,and 18 functional traits of root geometry and topology were quantitatively determined.The study investigated the traits,interspecific differences and interrelationships of the fine root conformation of Lauraceae,analysed the influence of topography,soil and other environmental factors on the fine root conformation,explored the resource utilization strategy and adaptation strategy of the fine roots of Lauraceae to the environment,and further suggested the use of Lauraceae in the ecological restoration of vegetation.The main findings are as follows:(1)There are significant interspecific differences(P<0.05)in the geometric morphological traits of the fine roots in Lauraceae plants.Average root diameter ranged from 0.60±0.05～0.90±0.05 mm,with Sassafras tzumu being the smallest;specific root length and specific surface area ranged from 5.39±0.41～22.00±2.84 m/g and 137.45 ±7.66～326.40±32.51 cm2/g,respectively,with Cinnamomum austro-sinense being the smallest and Sassafras tzumu being the largest;root tissue density ranged from 0.22±0.02～0.37±0.02 g/cm3,with the smallest being Lindera rubronervia and the largest being Cinnamomum austro-sinense.The geometric morphological traits were significantly influenced by the root order(P<0.001),with average root diameter and root tissue density increasing with the order order,while specific root length and specific surface area decreasing with the order.(2)There were no significant interspecific differences in topological traits,except for topological length,average topological length,total root length,and average connection length.The topological index TI ranged from 0.70 to 0.78,indicating that the fine roots of Lauraceae belonged to the forked-to-fishtail transitional branching pattern;The total branching rate was 2.37±0.17,and the stepwise branching rates(R1/R2,R2/R3,R3/R4,R4/R5)ranged from 2.54～3.85,2.59～3.67,1.75～3.33,1.37～3.52,respectively,and the total root length and average connecting length were 286.53±43.21 cm and 68.78± 16.16 cm,respectively,indicating that the fine root branching of Lauraceae are complexly branched and have long connection lengths.(3)The average diameter and tissue density were significantly negatively correlated with specific root length and specific surface area(P<0.01),while the specific root length and specific surface area were positively correlated(P<0.01).The average diameter and tissue density were significantly positively correlated(P<0.01).Except for Machilus phoenicis,geometric morphological traits had the same correlation among species;There was a significant positive correlation(P<0.01)between topology length,average topology length,and the number of all connections.There was a significant correlation(P<0.01)between the total number of external connections,modified topology index,and topology index.There was a significant correlation(P<0.01)between total root length and average connection length,modified topology index,and topology index.Topology configuration traits had the same correlation between species;There is a weak correlation between geometric and topological traits,and the two exhibit relatively independent variations.(4)Environmental factors have a significant impact on the fine root architecture of Lauraceae plants,especially soil organic carbon and total nitrogen,while altitude and soil total phosphorus only affect tissue density.With the increase of soil organic carbon and total nitrogen content,the specific surface area,total number of connections,number of external connections,total branching rate,gradual branching rate(R2/R3),total root length,and average connection length of Lauraceae plants increase.This indicates that Lauraceae plants mainly adapt to environmental changes by adjusting specific surface area,branching rate,and connection length.Under nutrient-rich conditions,the geometry of the fine roots of Lauraceae shows an acquisition-based resource use strategy with decreasing average diameter and tissue density and increasing specific root length and surface area,while the topological configuration shows an increase in both joint length and branching rate.In poor soil conditions,the average diameter and tissue density increase,and the specific root length and surface area decrease,which is a conservative resource use strategy. |
