Forest Ecology and Restoration Group, Departamento de Ciencias de la Vida, Universidad de Alcalá, Apdo 20, Alcalá de Henares, Madrid 28805, Spain.
Department of Forestry and Natural Resources, Hardwood Tree Improvement and Regeneration Center, Purdue University, 715 West State Street, West Lafayette, IN 47907, USA.
Tree Physiol. 2020 Oct 7;40(10):1381-1391. doi: 10.1093/treephys/tpaa068.
Plant hydraulics is key for plant survival and growth because it is linked to gas exchange and drought resistance. Although the environment influences plant hydraulics, there is no clear consensus on the effect of nitrogen (N) supply, which may be, in part, due to different hydraulic conductance normalization criteria and studied species. The objective of this study was to compare the variation of root hydraulic properties using several normalization criteria in four pine species in response to three contrasting N fertilization regimes. We studied four closely related, yet ecologically distinct species: Pinus nigra J.F. Arnold, Pinus pinaster Ait., Pinus pinea L. and Pinus halepensis Mill. Root hydraulic conductance (Kh) was measured with a high-pressure flow meter, and values were normalized by total leaf area (leaf specific conductance, Kl), xylem cross-section area (xylem specific conductance, Ks), total root area (root specific conductance, Kr) and the area of fine roots (fine root specific conductance, Kfr). Controlling for organ size differences allowed comparison of the hydraulic efficiency of roots to supply or absorb water among fertilization treatments and species. The effect of N on the root hydraulic efficiency depended on the normalization criteria. Increasing N availability reduced Kl and Ks, but increased Kh, Kr and especially Kfr. The positive effect of N on Kr and Kfr was positively related to seedling relative growth rate and was also consistent with published results at the interspecific level, whereby plant hydraulics is positively linked to photosynthesis and transpiration rate and fast growth. In contrast, normalization by leaf area and xylem cross-sectional area (Kl and Ks) reflected opposite responses to Kr and Kfr. This indicates that the normalization criteria determine the interpretation of the effect of N on plant hydraulics, which can limit species and treatment comparisons.
植物水力学对于植物的生存和生长至关重要，因为它与气体交换和抗旱性有关。尽管环境会影响植物水力学，但对于氮（N）供应的影响尚无明确共识，这可能部分是由于不同的水力传导率归一化标准和研究的物种。本研究的目的是比较使用几种归一化标准的四个松树种的根系水力特性的变化，以响应三种不同的氮施肥制度。我们研究了四个密切相关但生态上不同的物种：黑松（Pinus nigra J.F. Arnold）、地中海松（Pinus pinaster Ait.）、欧洲赤松（Pinus pinea L.）和欧洲黑松（Pinus halepensis Mill.）。使用高压流量计测量根系水力传导率（Kh），并通过总叶面积（叶比导率，Kl）、木质部横截面面积（木质部比导率，Ks）、总根面积（根比导率，Kr）和细根面积（细根比导率，Kfr）进行归一化。控制器官大小差异可以比较不同施肥处理和物种根系供应或吸收水分的水力效率。N 对根系水力效率的影响取决于归一化标准。增加 N 的可利用性会降低 Kl 和 Ks，但会增加 Kh、Kr 尤其是 Kfr。N 对 Kr 和 Kfr 的积极影响与幼苗相对生长率呈正相关，这与种间水平上发表的结果一致，即植物水力学与光合作用和蒸腾速率以及快速生长呈正相关。相比之下，通过叶面积和木质部横截面积（Kl 和 Ks）归一化反映了 Kr 和 Kfr 的相反反应。这表明归一化标准决定了 N 对植物水力学的影响的解释，这可能限制了物种和处理的比较。
