Schmitz Nele, Jansen Steven, Verheyden Anouk, Kairo James Gitundu, Beeckman Hans, Koedam Nico
Vrije Universiteit Brussel, Laboratory for General Botany and Nature Management (APNA), Pleinlaan 2, 1050 Brussels, Belgium.
Ann Bot. 2007 Aug;100(2):271-81. doi: 10.1093/aob/mcm103. Epub 2007 Jun 11.
According to the air-seeding hypothesis, embolism vulnerability in xylem elements is linked directly to bordered pit structure and functioning. To elucidate the adaptive potential of intervessel pits towards fluctuating environmental conditions, two mangrove species with a distinct ecological distribution growing along a natural salinity gradient were investigated.
Scanning and transmission electron microscopic observations were conducted to obtain qualitative and quantitative characteristics of alternate intervessel pits in A. marina and scalariform intervessel pits in Rhizophora mucronata. Wood samples from three to six trees were collected at seven and five sites for A. marina and R. mucronata, respectively, with considerable differences between sites in soil water salinity.
Vestured pits without visible pores in the pit membrane were observed in A. marina, the mangrove species with the widest geographical distribution on global as well as local scale. Their thick pit membranes (on average 370 nm) and minute pit apertures may contribute to reduced vulnerability to cavitation of this highly salt-tolerant species. The smaller ecological distribution of R. mucronata was in accordance with wide pit apertures and a slightly higher pitfield fraction (67 % vs. 60 % in A. marina). Nonetheless, its outer pit apertures were observed to be funnel-shaped shielding non-porous pit membranes. No trends in intervessel pit size were observed with increasing soil water salinity of the site.
The contrasting ecological distribution of two mangrove species was reflected in the geometry and pit membrane characteristics of their intervessel pits. Within species, intervessel pit size seemed to be independent of spatial variations in environmental conditions and was only weakly correlated with vessel diameter. Further research on pit formation and function has to clarify the large variations in intervessel pit size within trees and even within single vessels.
根据气穴播种假说，木质部细胞中的栓塞脆弱性与具缘纹孔的结构和功能直接相关。为了阐明导管间纹孔对波动环境条件的适应潜力，研究了沿着自然盐度梯度生长的两种具有不同生态分布的红树林物种。
进行扫描和透射电子显微镜观察，以获取滨海白骨壤中交替排列的导管间纹孔和红树中梯状导管间纹孔的定性和定量特征。分别在七个和五个地点采集了滨海白骨壤和红树的三到六棵树的木材样本，各地点土壤水盐度存在显著差异。
在全球和局部尺度上地理分布最广的红树林物种滨海白骨壤中，观察到纹孔膜上没有可见孔隙的具瘤纹孔。其较厚的纹孔膜（平均370纳米）和微小的纹孔口可能有助于降低这种高度耐盐物种发生空化的脆弱性。红树较小的生态分布与其较宽的纹孔口和略高的纹孔场比例（滨海白骨壤为60%，红树为67%）相一致。尽管如此，观察到其外部纹孔口呈漏斗状，可保护无孔的纹孔膜。未观察到导管间纹孔大小随采样地点土壤水盐度增加而呈现的变化趋势。
两种红树林物种截然不同的生态分布反映在其导管间纹孔的几何形状和纹孔膜特征上。在物种内部，导管间纹孔大小似乎与环境条件的空间变化无关，且仅与导管直径弱相关。关于纹孔形成和功能的进一步研究必须阐明树木内部甚至单个导管内部导管间纹孔大小的巨大差异。
