Shiiba Research Forest, Kyushu University,Ohkawauchi, Shiiba-son, Miyazaki, Japan.
Field Science Education and Research Center, Kyoto University, Kyoto , Japan.
Tree Physiol. 2017 Jan 31;37(1):61-70. doi: 10.1093/treephys/tpw076.
Biomass allocation to fine roots often increases under soil nutrient deficiency, but the fine root biomass does not often increase in old stands, even under nutrient limitation. Therefore, in old stands, the morphology, anatomy, branching architecture and mycorrhization of fine roots may compensate efficiently for nutrient acquisition by the low fine root biomass. In this study, changes in the morphology, anatomy and arbuscular mycorrhizal infection at each branching position of fine root clusters were evaluated in relation to stand age. A chronosequence (6–90 years of age) of stands in a Cryptomeria japonica D. Don plantation was used for these analyses. The fine root size parameters, such as length, weight and tip numbers of fine root clusters, increased with stand age. The specific root tip length (SRTL) decreased with increasing stand age, suggesting that the allocation to root active portions decreased with stand age. From the anatomical observation, the ephemeral root tips increased with stand age, suggesting that root tip turnover within a root cluster was high in old stands. The proportions of proto-xylem groups among branching positions indicated that the life cycles in branching hierarchy should be clearer in old stands than that in younger stands. The increasing in the mycorrhizal infection of root tips in old stands should enhance the root tip absorptive functions. The SRTL was correlated with the wood/needle ratio, suggesting that carbon limitation as the stand ages may result in decline of carbon allocation to maintain active root tips. However, increasing of the ephemeral tips and mycorrhizal infection rates may compensate the declines of tip allocation in old stands.
生物量分配到细根通常会在土壤养分缺乏时增加，但在老林中，即使在养分限制下，细根生物量也不会增加。因此，在老林中，细根的形态、解剖结构、分枝结构和菌根可能会有效地弥补低细根生物量对养分获取的不足。在这项研究中，评估了细根丛在每个分枝位置的形态、解剖结构和丛枝菌根感染的变化与林龄的关系。使用了日本柳杉种植园中 6-90 年生的林龄序列来进行这些分析。细根大小参数，如细根丛的长度、重量和根尖数量，随林龄增加而增加。比根尖端长度（SRTL）随林龄增加而降低，表明根活跃部分的分配随林龄增加而减少。从解剖观察，短命根尖随林龄增加而增加，表明老林中根丛内根尖周转较高。分枝位置的原木质部组的比例表明，老林中的分枝层次的生命周期应该比年轻林中更清晰。老林中根尖菌根感染比例的增加应增强根尖吸收功能。SRTL 与木材/针叶比相关，表明随着林龄的增长，碳限制可能导致维持活跃根尖的碳分配减少。然而，短命根尖和菌根感染率的增加可能会弥补老林中根尖分配的减少。
