亚热带不同演替树种米槠和马尾松细根性状对比研究

Comparison of fine-root traits between two subtropical tree species Pinus massonianaand Castanopsis carlesii differing in succession stages

选择福建省三明市中亚热带演替前期树种马尾松和演替后期树种米槠两种人工林为研究对象,采用土芯法研究两个树种细根(直径<2mm)的生物量及其垂直分布、形态以及分支结构等细根性状特征。结果表明:(1)0—80cm土层米槠的细根生物量密度(0.21±0.06)kg/m3、根表面积密度(3.15±1.25)m2/m3和根长密度(2202.84±517.03)m/m3分别为马尾松的1.6、1.2倍和2.2倍,并且3个指标均随土层深度增加而降低,但演替前期树种马尾松细根在土层间分布更均匀,而演替后期树种米槠细根更富集于表层。(2)马尾松细根的直径(0.86±0.04)mm、比表面积(191±32)cm2/g分别是米槠的1.4倍和1.3倍;米槠细根的比根长(10.73±0.46)m/g、组织密度(0.49±0.06)g/cm3分别是马尾松的1.4倍和2.0倍,马尾松细根的较大直径和低组织密度的形态结构能够迅速生长占领土壤空间和适应干旱环境,而米槠细根的较小直径、高比根长和较高的组织密度使其具有较强养分竞争能力和应对取食压力;(3)米槠的比根尖密度(4288±63)个/g、比分叉密度(1164±155)个/g均为马尾松的2.2倍,米槠细根的高分支系统能够迅速利用富养斑块。结论表明处于不同演替阶段的树种细根性状具有明显差异,可能反映了不同的资源获取策略。

The tree fine root （〈 2 mm in diameter） system is a functionally highly important compartment of forest ecosystems. Fine root traits are a result of long-term adaptation of trees to local habitat, and they strongly reflect the information of environmental changes. The objective of this study was to investigate differences in fine-root traits between two subtropical tree species, i.e., the early-succession species, Pinus massoniana （PM） , and the late-succession species, Castanopsis carlesii （MZ） in their respective monocuhure plantations in Sanming City, Fujian Province. Three 20mX20m plots were established in each forest type. Fine roots were extracted using soil core method and measured for their biomass, vertical distribution, and morphological and branching structure. The extinction coefficient （fl） from the model of vertical root distribution ： Y = 1 - βd was used to represent root distribution. The results showed that root biomass density （RBD） ,root surface area density （RSD）, and root length density （RLD） decreased with the increasing soil depth. Their levels in the. 0--80 cm soil layer of the MZ stand were （0.21±0.06） kg/m3（RBD）, （3.15±1.25） m2/m3（RSD）, and （2202.84±517.03） m/m3（RLD） , which were 1.6, 1.2, and 2.2 times higher than those in the PM stand, respectively. Soil depth had a significant effect on RBD, RSD, and RLD in both stands. Root extinction coefficients （/3） for root biomass, root surface area, and root length were each higher in the PM stand than in the MZ stand, indicating that fine roots in the PM stand were distributed more evenly along the soil profile, while those in the MZ stand were concentrated primarily in the surface layer. The average root diameter （RD） and specific root surface area （SRA） in the PM stand were （0.86±0.04） mm and （191±32） cm2/g, respectively, which were 1.4 and 1.3 times larger than those in the MZ stand, respectively. Specific root length （SRL） and root tissue density （RTD） in the MZ stand were （10.73±0.46） m/g and （0.49±0.06） g/cm3, respectively, which were 1.4 and 2.0 times higher than in the PM stand. Soil depth had significant effects on RD, RTD and SRA and little effect on SRL in the MZ stand, whereas none of these variables were significantly affected by soil depth in the PM stand. RD and RTD differed significantly between these two stands in all soil depths. Except for the 0 - 10 cm soil layer, there was no significant difference between two stands at all depths in terms of SRA and SRL. Fine roots with coarser diameter and lower tissue density in the PM stand can grow rapidly to fill the soil space, adapting to the arid soil, whereas those with thinner diameter as well as higher SRL and RTD in the MZ stand enable them to strongly compete for nutrients while avoiding herbivory. Specific root tip density （SRT） and specific root forks density （SRF） of fine roots in the MZ stand were （4288.44±63.35） ind./g and （1164.35±155.38） ind./g, respectively, which were both 2.2 times those in the PM stand. Soil depth exerted significant effect only on SRT in the MZ stand. Roots with higher branching intensity in the MZ stand can rapidly exploit nutrient-rich soil patches. We conclude that there are contrasting fine-root traits in tree species at different succession stages, probably reflecting the differences in soil foraging strategy.