• 问题讨论 •

连作杨树细根根序形态及解剖结构

1. 1. 山东农业大学林学院 山东省高校森林培育重点实验室 泰安 271018;
2. 国家林业局泰山森林生态系统定位研究站 泰安 271018;
3. 山东省林业科学研究院 济南 250014
• 收稿日期:2013-09-27 修回日期:2014-12-10 出版日期:2015-01-25 发布日期:2015-01-23
• 通讯作者: 王延平
• 基金资助:

国家林业公益性行业科研专项(2012041017);国家自然科学基金项目(31070550, 31270670, 31170662);山东省自然科学基金(ZR2012CM033);山东省博士后创新基金项目(2014140687).

Morphological and Anatomical Traits of Poplar Fine Roots in Successive Rotation Plantations

Xu Tan1, Wang Huatian1,2, Zhu Wanrui1, Wang Yanping1,2, Li Chuanrong1,2, Jiang Yuezhong3

1. 1. Silviculture Key Lab of Shandong Province Forestry College of Shandong Agricultural University Tai'an 271018;
2. Taishan Forest Ecosystem Research Station of State Forestry Administration Tai'an 271018;
3. Shandong Academy of Forestry Jinan 250014
• Received:2013-09-27 Revised:2014-12-10 Online:2015-01-25 Published:2015-01-23

[目的]针对连作杨树人工林细根形态和解剖结构,从根序视角探讨连作杨树人工林细根生长的代际差异及其与人工林生产力衰退的联系,以期揭示连作杨树人工林衰退机制.[方法]分别在杨树人工林Ⅰ和Ⅱ代林分设立标准地,采用改良全根取样法获得杨树细根(<2 mm)并按根序进行分级,制作1~5级细根各根序石蜡切片.根系扫描仪结合分析软件获得各根序细根长度、直径,光学显微镜观察各根序细根剖面直径、皮层厚度、维管柱(中柱)直径等参数,并计算比根长、根组织密度、根长密度、维根比等.LSD分析1~5级根序形态参数的差异显著性,One-way ANOVA分析同一根序在不同代数间形态指标参数的差异显著性.[结果]杨树细根生物量表现为随根序增加而减小,且连作Ⅱ代人工林细根生物量分配高于Ⅰ代林,尤其在1,2级根序中更为显著(P<0.05);连作导致杨树1,2级细根平均长度减少而3~5级根长度增加;直径虽然在不同根序细根间差异并不显著,但Ⅱ代林显著高于Ⅰ代林;杨树细根表面积、比根长和根长密度总体表现为1,2级根显著高于3,4级根(P<0.05),但比根长在Ⅱ代林中差异不显著;连作导致杨树1,2级根表面积和根长密度显著增大,但比根长显著减小(P<0.05);细根解剖特征表明,横剖面宽度随根序逐渐增大,中柱面积占横剖面的比例随根序增加而增大,1,2级细根总体呈现初生结构的特征,从3级根开始出现木栓层且皮层开始脱落.[结论]杨树1~5级根序细根形态和功能存在显著差异,1,2级细根仅具初生结构,是杨树的吸收根,3级以上细根出现木栓层从而变为输导根.连作导致杨树细根形态发生显著变化,且低级细根生物量显著增加,表明连作导致杨树人工林对地下部分的生长投入增大,这与养分匮乏生境中植物光合产物最优分配理论相一致.伴随细根死亡和周转,连作杨树人工林细根生物量分配格局将影响人工林地上部分生产力的形成.

Abstract:

[Objective]The productivity of poplar plantation with successive rotations depleted seriously. Based on morphological and anatomical properties of the fine roots, the inter-rotation difference of fine root growth and its relation to the depletion of plantation productivity were studied to reveal mechanisms of the productivity depletion of plantation with successive rotations. [Method]Sample plots were set up in plantations respectively at the first and second rotations. Using the improved complete-root sampling method, fine roots (< 2 mm) of sample trees were collected and grouped into 1-5 classes according to orders of the roots. WINRHIZO root system analyzer (Canada) and corresponding software were used to determine the morphological properties: length and diameter. Furthermore, permanent paraffin sections of the 1-5 classes of fine roots were prepared to observe the anatomical properties: cross section diameter, cortex thickness and xylem diameter. Finally, several important parameters related to fine root morphology, i.e. specific root length (SRL), root tissue density (RTD), root length density (RLD) and percentage of xylem to cross section area were calculated. Least-significant difference (LSD) multiple comparisons were used to analyze differences of fine root morphological properties among the 1-5 root classes, and one-way ANOVA was used for the analysis of difference of the same class of fine root morphology between first and second rotations of poplar plantation (P<0.05). [Result]There were significant differences of biomass allocation among the fine root classes, and biomass allocation appeared to decrease with increase of root orders. The biomass of fine roots in the second rotation plantation was significantly higher than that in the first rotation, especially for 1,2 root classes (P <0.05). The mean root length was also significantly different among the root classes. The mean root length of 1,2 root classes was decreased and that of 3-5 root classes was increased in the second rotation plantation. Although root diameter showed no significant differences among root classes, it was still larger in the second rotation plantation. Also, the surface area, specific root length and root length density of 1,2 order roots were significantly higher than those of 3,4 order roots (P <0.05), but the specific root length showed no significant difference among orders in second rotation plantation. The surface area and root length density of 1,2 root classes displayed a significant increase in the second rotation, but specific root length was significantly decreased (P <0.05). The anatomical properties showed that the cross section diameter of all fine roots increased with root classes and the same trend was found with the area ratio of stele (or vascular cylinder) to cross section. The anatomical properties of the 1,2 root classes was characterized as primary structure in general, while phellem layer was formed from the 3rd root class and cortex layer started to fall off.[Conclusion]There were significant differences in morphology ad functions among the 1-5 classes of fine roots. Fine roots of the 1,2 root classes were of primary structure, indicating that they serve as absorbing roots, while fine roots of the 3-5 root classes formed the secondary phellem layer, indicating that they act as transporting roots for water and nutrients. Successive rotations led to significant changes of fine root morphology and significant increases of fine roots biomass, indicating that the biomass allocation to underground part was increased in poplar plantation with successive rotations. This conclusion was consistent with the theory of optimal allocation of photosynthetic products under nutrient deficiency conditions. With fine roots mortality and turnover, the allocation pattern of fine root biomass of poplar plantation with successive rotations would have a negative effect on aboveground productivity.