Abstract

For a better understanding of plant nutrition processes, it is important to study the flux of nutrients within plants. However, existing xylem sap sampling methods are typically destructive and do not allow for repeated, highly frequent measurements of nutrient concentration. In this paper, we present a novel use of microdialysis (MD) for characterizing xylem sap phosphate (PO₄³⁻) concentration as a possible alternative to destructive sampling. First, MD probes were tested under laboratory conditions in vitro, in a stirred solution test, and in vivo, using beech tree stem segments. Exponential decline in the relative recovery (RR) with an increasing MD pumping rate allows for determining an optimal sampling interval (i.e., the maximum amount of sample volume with the minimum required concentration). The RR changed only minimally, with a change in the simulated sap flow velocity during the in vivo stem segment test. This suggests that MD can be applied over a range of naturally occurring sap flow velocities. Differences in the ionic strength between the xylem sap and the perfusate pumped through the MD did not influence the RR. Then, MD was successfully applied in a 24 h field campaign in two beech trees of different ages and allowed for in situ assessments of the diurnal variation of PO₄³⁻ concentration and (together with xylem flow measurements) flux variability in living trees. Both beech trees exhibited the same diurnal pattern in PO₄³⁻ concentrations with higher concentrations in the younger tree. The xylem PO₄³⁻ concentration measured with MD was in the same order of magnitude as that received through destructive sampling in the younger tree. The MD probes did not show a decline in RR after the field application. We showed that MD can be applied to capture the PO₄³⁻ concentration dynamics in the xylem sap with bihourly resolution under field conditions.

中文翻译：

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使用微透析的木质部汁液磷采样-一种无损的高采样频率方法，在实验室和现场条件下进行了测试。

摘要

为了更好地了解植物的营养过程，研究植物内营养的通量很重要。但是，现有的木质部树液采样方法通常具有破坏性，并且不允许重复，频繁地测量营养物浓度。在本文中，我们介绍了微透析（MD）用于表征木质部树液磷酸酯（PO ₄ ^3-）作为破坏性采样的一种可能替代方法。首先，使用山毛榉树茎段在体外，搅拌溶液测试和体内实验室条件下测试MD探针。相对回收率（RR）随MD泵送速率的增加而呈指数下降，可以确定最佳采样间隔（即，具有最小所需浓度的最大样品量）。在体内茎节测试期间，RR的变化很小，模拟的树液流速也发生了变化。这表明MD可以应用于一系列自然发生的树液流速。木质部汁液和通过MD泵送的灌注液之间的离子强度差异不会影响RR。然后，₄ ³⁻浓度和（与木质部流量测量一起）活树中的通量变异性。两种山毛榉树在PO ₄ ^3-浓度下都表现出相同的昼夜模式，而幼树中的浓度更高。用MD测量的木质部PO ₄ ^3-浓度与在幼树中通过破坏性采样所获得的木质素PO ₄ ^3-浓度相同。在现场应用后，MD探针未显示出RR下降。我们表明，在田间条件下，MD可应用于捕获植物木质部汁液中的PO ₄ ^3-浓度动力学，且每两小时解析一次。