摘要： 水是植物生存与生长的基础条件, 水分有效性影响植物木质部解剖结构、水力功能, 使之形成特定的适应特征。因此, 对比自然与人工生境中同一植物的水力功能与解剖结构差异, 有助于理解植物对水分环境的适应机理。该研究以湿润区三角槭(Acer buergerianum)、青冈(Cyclobalanopsis glauca)和女贞(Ligustrum lucidum)为研究材料, 对比分析了自然和人工生境中各物种的栓塞抗性(导水率损失50%时的水势(P50))、输水效率(比导率(Ks))和解剖结构(导管直径(D)、导管壁厚(T)、导管密度(N)、木质部密度(WD)、厚度跨度比(t/b)2)特征, 探究了同生境种内与跨生境、跨物种水平的效率-安全权衡关系, 量化分析了水力功能与解剖结构的关系。结果发现: 1) 3种被子植物在自然生境中Ks更大, P50更小, 与其更大的D、更小的(t/b)2有关。2)同生境种内Ks与P50不存在权衡。3)功能性状和解剖结构相关分析表明: 同生境种内D与P50不存在显著的相关关系; 除自然生境女贞外, T、(t/b)2均与P50正相关。相对于人工生境, 在水分有效性低或无额外浇灌的自然生境中, 植物通过增大导管直径显著提高其输水效率, 从而避免水势下降、降低潜在栓塞风险。
水是植物生存与生长的基础条件, 水分有效性影响植物木质部解剖结构、水力功能, 使之形成特定的适应特征。因此, 对比自然与人工生境中同一植物的水力功能与解剖结构差异, 有助于理解植物对水分环境的适应机理。该研究以湿润区三角槭(Acer buergerianum)、青冈(Cyclobalanopsis glauca)和女贞(Ligustrum lucidum)为研究材料, 对比分析了自然和人工生境中各物种的栓塞抗性(导水率损失50%时的水势(P50))、输水效率(比导率(Ks))和解剖结构(导管直径(D)、导管壁厚(T)、导管密度(N)、木质部密度(WD)、厚度跨度比(t/b)2)特征, 探究了同生境种内与跨生境、跨物种水平的效率-安全权衡关系, 量化分析了水力功能与解剖结构的关系。结果发现: 1) 3种被子植物在自然生境中Ks更大, P50更小, 与其更大的D、更小的(t/b)2有关。2)同生境种内Ks与P50不存在权衡。3)功能性状和解剖结构相关分析表明: 同生境种内D与P50不存在显著的相关关系; 除自然生境女贞外, T、(t/b)2均与P50正相关。相对于人工生境, 在水分有效性低或无额外浇灌的自然生境中, 植物通过增大导管直径显著提高其输水效率, 从而避免水势下降、降低潜在栓塞风险。
Abstract: Aims Water is essential for plant survival and growth. Water availability affects the anatomical structure and hydraulic function of xylem, and finally makes trees form specific acclimating characters. Therefore, comparing the differences of hydraulic function and anatomical structure between plants growing in field and garden habitats, can facilitate a better understanding on the acclimation of plants to water conditions. Methods We compared hydraulic safety (water potential at 50% loss of conductivity, P50), hydraulic efficiency (specific hydraulic conductivity, Ks) and xylem anatomy (vessel diameter (D), double thickness of vessel wall (T), vessel density (N), xylem density (WD) and thickness-to-span ratio of vessels ((t/b)2)), between field and garden plants of Acer buergerianum, Cyclobalanopsis glauca and Ligustrum lucidum. We also analyzed the differences of the relationship between xylem hydraulic function and anatomical structure in field and garden habitats. Important findings We found that: 1) The Ks was higher and P50 was lower in field habitat of the three angiosperms, which were related to the larger D and smaller (t/b)2. 2) The intraspecific correlation analysis between Ks and P50 showed that there were no efficiency-safety trade-offs. 3) Intraspecific correlation analysis of anatomical structure and functional traits showed that there was no significant correlation between D and P50; except for L. lucidum in garden habitat, the T and (t/b)2of the other trees was positively correlated with P50. Comparing to garden habitat, plants in field habitat with low water availability or no additional irrigation increased their diameter of vessels to improve water transport efficiency, so as to avoid the decrease of water potential and effectively reduce the potential risk of embolism.
Aims Water is essential for plant survival and growth. Water availability affects the anatomical structure and hydraulic function of xylem, and finally makes trees form specific acclimating characters. Therefore, comparing the differences of hydraulic function and anatomical structure between plants growing in field and garden habitats, can facilitate a better understanding on the acclimation of plants to water conditions.
Methods We compared hydraulic safety (water potential at 50% loss of conductivity, P50), hydraulic efficiency (specific hydraulic conductivity, Ks) and xylem anatomy (vessel diameter (D), double thickness of vessel wall (T), vessel density (N), xylem density (WD) and thickness-to-span ratio of vessels ((t/b)2)), between field and garden plants of Acer buergerianum, Cyclobalanopsis glauca and Ligustrum lucidum. We also analyzed the differences of the relationship between xylem hydraulic function and anatomical structure in field and garden habitats.
Important findings We found that: 1) The Ks was higher and P50 was lower in field habitat of the three angiosperms, which were related to the larger D and smaller (t/b)2. 2) The intraspecific correlation analysis between Ks and P50 showed that there were no efficiency-safety trade-offs. 3) Intraspecific correlation analysis of anatomical structure and functional traits showed that there was no significant correlation between D and P50; except for L. lucidum in garden habitat, the T and (t/b)2of the other trees was positively correlated with P50. Comparing to garden habitat, plants in field habitat with low water availability or no additional irrigation increased their diameter of vessels to improve water transport efficiency, so as to avoid the decrease of water potential and effectively reduce the potential risk of embolism.
表1 自然和人工生境样地的基本特征(平均值±标准误, n = 3)
Table 1 Basic characteristics for the field and garden habitats (mean ± SE, n = 3)
表2 自然和人工生境3种被子植物样树的基本特性(平均值±标准误)
Table 2 Basic characteristics of the sampled trees for the three species in field and garden habitats (mean ± SE)
图1 三种植物自然和人工生境水力功能性状图(平均值±标准误)。A, 比导率(Ks)。B, 栓塞抗性(导水率损失50%时的水势, P50)。不同小写字母表示种内差异显著(p < 0.05)。
Fig. 1 Hydraulic functional traits of three species in field and garden habitats (mean ± SE). A, The specific hydraulic conductivity (Ks). B, Embolism resistance (water potential at 50% loss of conductivity, P50). Different lowercase letters indicate significant differences within species (p < 0.05).
图2 三种植物自然和人工生境木质部解剖横切面光学显微镜图像。A, 自然生境三角槭。B, 自然生境青冈。C, 自然生境女贞。D, 人工生境三角槭。E, 人工生境青冈。F, 人工生境女贞。
Fig. 2 Examples of light microscopy images of xylem cross sections of three species in field and garden habitats. A, Acer buergerianum in the field. B, Cyclobalanopsis glauca in the field. C, Ligustrum lucidum in the field. D, A. buergerianum in the garden. E, C. glauca in the garden. F, L. lucidum in the garden.
图3 三种植物自然和人工生境木质部解剖结构特征图(平均值±标准误)。A, 导管直径(D)。B, 导管壁厚(T)。C, 导管密度(N)。D, 木质部密度(WD)。E, 厚度跨度比((t/b)2)。不同小写字母表示种内差异显著(p < 0.05)。
Fig. 3 Xylem anatomical structure traits of three species in field and garden habitats (mean ± SE). A, Vessel diameter (D). B, Double thickness of vessel wall (T). C, Vessel density (N). D, Xylem density (WD). E, Thickness-to-span ratio of vessels ((t/b)2). Different lowercase letters indicate significant differences within species (p < 0.05).
图4 三种植物自然和人工生境功能性状(Ks和P50)与解剖结构的网络分析。A, 自然生境三角槭。B, 自然生境青冈。C, 自然生境女贞。D, 人工生境三角槭。E, 人工生境青冈。F, 人工生境女贞。实线, 正相关; 虚线, 负相关。红色线条, p < 0.05; 灰色线条, p > 0.05。线条粗细表示相关系数(r)的大小。D, 导管直径(μm); Ks, 比导率(kg·m-1∙MPa-1·s-1); N, 导管密度(103∙mm-2); P50, 导水率损失50%时的水势(-MPa); T, 导管壁厚(μm); Ttob为(t/b)2, 厚度跨度比; WD, 木质部密度(g∙cm-3)。
Fig. 4 Correlation networks between functional traits (Ks and P50) and structural traits of xylem for the three species in field and garden habitat. A, Acer buergerianum in the field. B, Cyclobalanopsis glauca in the field. C, Ligustrum lucidum in the field. D, A. buergerianum in the garden. E, C. glauca in the garden. F, L. lucidum in the garden. Solid lines, positive correlations; dashed lines, negative correlations. Red lines, p < 0.05; grey lines, p > 0.05. Line thickness indicate the correlation coefficient (r) values. D, vessel diameter (μm); Ks, specific hydraulic conductivity (kg·m-1∙MPa-1·s-1); N, vessel density (103∙mm-2); P50, water potential at 50% loss of conductivity (-MPa); T, double thickness of vessel wall (μm); Ttob, thickness-to-span ratio of vessels ((t/b)2); WD, xylem density (g∙cm-3).