古田山亚热带常绿阔叶林粗根空间分布特征及影响因子分析——探地雷达途径

粗根在森林生态系统内扮演重要角色，粗根空间分布不仅与环境因素有关还受到生物因素的影响，根系密度可以在一定程度上反映森林群落地下生长及种间竞争情况．根系研究一直是生态学领域极具挑战性的工作，传统的挖掘法具有费时、费力、破坏样地、不能连续测定等缺点．在自然保护区，原则上禁止使用破坏性取样方法进行研究．因此，应用非破坏性方法进行森林粗根研究具有重要的实践意义．应用探地雷达技术，对古田山自然保护区24公顷监测样地内山脊、山坡、山谷3种生境及胸径大于50cm优势树种甜槠、木荷的地下粗根密度进行研究．结果发现：（i）探地雷达探测3种生境粗根密度均值为88．04roots/m^2．粗根主要集中在地表0～40cm土层范围，土壤深度增加，粗根密度迅速下降．粗根密度集中于树种周围，较开阔样地或距树木一定距离处粗根密度较低；（ii）山脊、山坡、山谷间总粗根密度差异显著，山脊、山谷粗根密度大于山坡；优势种甜槠粗根密度大于木荷．直径〉3cm的粗根在山谷分布数量显著大于山坡、山脊，该部分粗根在20—40cm土层密度值最大；（iii）粗根密度随树种丰富度的增加而显著降低，优势树种甜槠、青冈、马尾松个体数对粗根分布有影响显著；（iv）0—40cm是粗根的“基础分布层”，大部分粗根分布于此范围，粗根密度均值为84．18roots／m^2，与地形变化、树种丰富度、稀疏树种丰富度、地上树木密度均没有显著回归关系；40—60cm土层，环境与生物因素均会影响粗根密度的大小，是森林根系减小空间重叠、邻根干扰、缓解竟争压力的“潜在分布层”．研究表明，应用探地雷达技术可以实现对粗根空间分布及影响因子较准确、有效的非破坏性研究．

Coarse root spatial distribution determined using a ground-penetrating radar technique in a subtropical evergreen broad-leaved forest,China

Coarse roots play a critical role in forest ecosystems and both abiotic and biotic factors affect their spatial distribution.To some extent,coarse root density may reflect the quantity of root biomass and biotic competition in forests.However,using traditional methods(e.g.,excavation)to study coarse roots is challenging,because those methods are time-consuming and laborious.Furthermore,these destructive methods cannot be repeated in the same forests.Therefore,the discovery of non-destructive methods for root studies will be very significant.In this study,we used a ground-penetrating radar technique to detect the coarse root density of three habitats(ridge,slope and valley)and the dominant tree species(Castanopsis eyrei and Schima superba)in a subtropical forest.We found that(i)the mean of coarse root density for these three habitats was 88.04roots m–2,with roots being mainly distributed at depths of 0–40 cm.Coarse root densities were lower in deeper soils and in areas far from the trunk.(ii)Coarse root densities differed significantly among the three habitats studied here with slope habitat having the lowest coarse root density.Compared with S.superba,C.eyrei had more roots distributed in deeper soils.Furthermore,coarse roots with a diameter>3 cm occurred more frequently in the valleys,compared with root densities in ridge and slope habitats,and most coarse roots occurred at soil depths of 20–40 cm.(iii)The coarse root density correlated negatively with tree species richness at soil depths of 40–60 cm.The abundances of the dominant species,such as C.eyrei,Cyclobalanopsis glauca,Pinus massoniana,had significant impacts on coarse root density.(iv)The soil depth of 0–40 cm was the"basic distribution layer"for coarse roots since the majority of coarse roots were found in this soil layer with an average root density of 84.18 roots m–2,which had no significant linear relationships with topography,tree species richness,rarefied tree species richness and tree density.Significant relationships between coarse root density and these factors were found at the soil depth of40–60 cm,which was the"potential distribution layer"for coarse root distribution.