黄栌幼苗根系构型对土壤养分胁迫环境的适应性研究

李金航; 周玫; 朱济友; 徐程扬

doi:10.12171/j.1000-1522.20190218

黄栌幼苗根系构型对土壤养分胁迫环境的适应性研究

Adaptability response of root architecture of Cotinus coggygria seedlings to soil nutrient stress

摘要

摘要:
目的通过研究黄栌幼苗根系构型对土壤养分胁迫环境的适应性，探讨黄栌根系构型在土壤养分供应不足环境中的适应对策。
方法试验材料为一年生黄栌幼苗，采用盆栽模拟控制试验，设置养分充足（即全土，土壤含沙比例0，CK），轻度养分胁迫（土壤含沙比例30%，N₁），中度养分胁迫（土壤含沙比例50%，N₂），重度养分胁迫（土壤含沙比例70%，N₃）和极度养分胁迫（即全沙，土壤含沙比例100%，N₄）5个梯度，分别在移栽后第31、38、45、52和59天取样，研究幼苗根系分枝模式、几何特征和不同径级细根形态在上述养分环境中的变化规律。
结果（1）CK处理幼苗的根系拓扑指数（TI和DBI）最大，最长链接路径的链接数（a）、根系外部链接数（μ）以及所有链接路径的链接总数（P_e）最小。N₁环境中，幼苗的TI和DBI最小，a、μ和P_e最大，分别比CK高53.2%、131.6%和194.7%。（2）N₁、N₂、N₃和N₄处理中：幼苗比根长（SRL）、比表面积（SRA）和分枝密度（RBI）逐渐增大，其中，N₄处理幼苗的SRL、SRA和RBI分别比CK高67.7% ~ 157.4%、52.3% ~ 120.7%和14.7% ~ 42.1%；根尖数量（RT）、根链接数量（RLN）、根链接总长度（RLTL）和分枝数量（RF）逐渐减小，以N₁处理为最大，分别比CK高95.0% ~ 279.6%、104.3% ~ 247.4%、77.4% ~ 193.5%和102.6% ~ 235.0%；根链接平均长度（RLAL）、根链接平均直径（RLAD）和根组织密度（RTID）均呈减小趋势，以N₄处理最小，分别比CK低15.2% ~ 22.7%、9.3% ~ 21.4%和32.4% ~ 42.7%。（3）CK环境中，SRL和SRA的正相关系数最大（0.951），N₄环境中，RF与RLN之间和RLAL和RLAD之间的正相关系数最大（分别为0.989、0.904）。N₁、N₂和N₃处理的RBI和RLAL之间的负相关系数分别为− 0.915、− 0.889和− 0.893。（4）N₃和N₄处理中，0 ~ 0.50 mm范围内细根的平均长度比例、平均表面积比例、平均体积比例和平均根尖数量比例均高于其他处理，分别达86.3%和86.1%、67.6%和66.7%、40.2%和38.1%、98.6%和98.4%，而上述指标在CK处理中均为最低，分别为80.9%、59.4%、32.2%和97.2%。
结论（1）土壤养分充足时，黄栌根系最接近分枝少且结构相对简单的鲱鱼骨分枝模式，具有向土壤深处延伸生长的倾向。轻度胁迫环境中，黄栌构建了分枝多、次级根重叠度高的叉状分枝模式，主、侧根尽可能地主动向距离根基较远的土壤中拓展以吸收更大范围内的养分。中度、重度和极度胁迫环境中，幼苗为减少碳消耗而采取相对简单化的根系结构对策，根系通过形成短而细的密集横向分枝（以细根为主）而加强原位利用养分能力。（2）改变根系构型几何特征参数间的协同或权衡关系、实现自身资源利用的经济化，也是黄栌应对不同土壤养分环境的重要方面。（3）从全土到极端严重胁迫环境，0 ~ 0.50 mm范围细根的分化明显增强。重度胁迫逆境时，0 ~ 0.50 mm的细根是幼苗吸收养分的重要活跃位点。极度胁迫逆境时，黄栌通过促进产生一定数量的寿命相对较长、周转速率相对较慢的细根（0.50 ~ 2.00 mm）以减少细根周转对碳的消耗，从而维持根系资源利用效率。

Abstract:
ObjectiveThe study was conducted to explore the adaptability strategy of root architecture of Cotinus coggygria seedlings to soil nutrient stress environment.
MethodTaking one-year-old C. coggygria seedlings as research object and carrying out pot-culturing simulation control test, five soil nutrient gradients were set: nutrient-rich condition (sand proportion 0, CK), slight nutrient stress condition (sand proportion 30%, N₁), medium nutrient stress condition (sand proportion 50%, N₂), severe nutrient stress condition (sand proportion 70%, N₃) and extreme nutrient stress condition (sand proportion 100%, N₄). Seedlings were sampled at 31th, 38th, 45th, 52th and 59th day after transplanting to explore the changing rules of branching pattern and geometric characteristics of seedling root, fine root morphology at varied diameter classes under the above nutrient conditions.
Result(1) Topological indices (TI or DBI) under CK were higher than the other treatments, but the number of root longest link path (a), the number of root external link (μ) and the total number of all root link paths (P_e) were lowest. Seedlings in the N₁ treatment showed the lowest TI and DBI while the highest a, μ and P_e, which were higher than those in CK by 53.2%, 131.6% and 194.7%, respectively. (2) In the N₁, N₂, N₃ and N₄ treatments, specific root length (SRL), specific root surface area (SRA) and root branching index (RBI) increased gradually with the nutrient stress degree rising. Among which, SRL, SRA and SRA of seedlings under N₄ treatment were higher than those in CK by 67.7%−157.4%, 52.3%−120.7% and 14.7%−42.1%, respectively.The number of root tip (RT), the number of root link (RLN), root link total length (RLTL) and the branching number of root (RF) decreased with the nutrient stress degree rising. All these four parameters in N₁ treatment were highest, and higher than those in CK by 95.0%−279.6%, 104.3%−247.4%, 77.4%−193.5% and 102.6%−235.0%, respectively. Root link average length (RLAL), root link average diameter (RLAD) and root tissue density (RTID) had a reducing trend with the nutrient stress degree rising, and RLAL, RLAD and RTID in N₄ were lower than those in CK by 15.2%−22.7%, 9.3%−21.4% and 32.4%−42.7%, respectively. (3) The positive correlation coefficient (0.951) between SRL and SRA was highest under CK environment, and the positive correlation coefficients between RF and RLN (0.989) and between RLAL and RLAD (0.904) were highest under N₄ environment. The negative correlation coefficients under N₁, N₂ and N₃ treatments were − 0.915, − 0.889 and − 0.893, respectively. (4) The average length proportion, average surface area proportion, average volume proportion and the average tip number proportion of fine roots in 0−0.50 mm were all higher than the other treatments, and they were 86.3% and 86.1%, 67.6% and 66.7%, 40.2% and 38.1%, 98.6% and 98.4% in N3 and N4, respectively. While these parameters under CK were lowest, which were 80.9%, 59.4%, 32.2% and 97.2%, respectively.
Conclusion(1) The root system of C. coggygria in soil nutrient-rich environment is closest to the herringbone pattern with few branches and a relatively simple structure. It also has an extending tendency towards deeper layers of soil. In contrast, C. coggygria develops increased branches and a high degree of secondary root overlap in slight nutrient stress soil. Under medium, severe and extreme nutrient stress conditions, the relatively simple root structure strategy is adopted, and the root system strengthens the ability of local nutrient utilization by forming short, thin and dense lateral branches (mainly fine roots). (2) The adjustment of coordination and trade-off relationships between geometric characteristic parameters of root architecture for economizing soil resource utilization is also an important aspect for C. coggygria to cope with different soil nutrient environments. (3) The differentiation of fine roots in 0−0.50 mm is markedly enhanced from soil nutrient-rich to extreme nutrient stress environment. Fine roots in 0−0.50 mm diameter are the significantly active organs for C. coggygria to absorb nutrients in severe stress environment. When the soil is extremely poor, a certain number of fine roots of 0.50−2.00 mm diameter are promoted production to reduce the carbon consumption caused by fine root turnover, and then to maintain the root resource utilization efficiency.

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