Abstract

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 (K_h) was measured with a high-pressure flow meter, and values were normalized by total leaf area (leaf specific conductance, K_l), xylem cross-section area (xylem specific conductance, K_s), total root area (root specific conductance, K_r) and the area of fine roots (fine root specific conductance, K_fr). 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 K_l and K_s, but increased K_h, K_r and especially K_fr. The positive effect of N on K_r and K_fr 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 (K_l and K_s) reflected opposite responses to K_r and K_fr. This indicates that the normalization criteria determine the interpretation of the effect of N on plant hydraulics, which can limit species and treatment comparisons.

中文翻译：

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归一化标准确定了氮对松树幼苗根系水力学影响的解释。

摘要

植物液压系统是植物生存和生长的关键，因为它与气体交换和抗旱性有关。尽管环境影响植物的水力学，但对于氮（N）供应的影响尚无明确共识，其部分原因可能是由于不同的水力传导率标准化标准和所研究的物种。这项研究的目的是使用三种归一化施肥方案对四种松树的几种标准化标准比较根系水力特性的变化。我们研究了四个密切相关但在生态上截然不同的物种：黑松JF Arnold，松木针叶松，松树松和哈勒皮松。根水力传导率（K用高压流量计测量_h），并通过总叶面积（叶比电导，K _l），木质部横截面积（木质部比电导，K _s），总根面积（根比电导）对值进行归一化，K _r）和细根的面积（细根比电导，K _fr）。通过控制器官的大小差异，可以比较施肥处理和物种间根系提供或吸收水分的水力效率。氮对根系水力效率的影响取决于归一化标准。N可用性的提高减少了K _l和K_s，但增加了K _h，K _r，尤其是K _fr。氮上的积极作用ķ _[R和ķ _FR呈正相关，幼苗相对生长率，也与在种间的水平，因此植物液压是正相关的光合作用和蒸腾速率快速增长公布的结果一致。相反，通过叶面积和木质部横截面积（K _l和K _s）进行归一化反映了对K _r和K _fr的相反响应。这表明归一化标准决定了氮对植物水力学影响的解释，这可能会限制物种和处理方法的比较。