Understanding phosphorus (P) dynamics in the rhizosphere is crucial for sustainable crop production. P mobilization processes in the rhizosphere include the release of plant and microbially-derived protons and extracellular phosphatases. We investigated the effect of root hairs and soil texture on the spatial distribution and intensity of P mobilizing processes in the rhizosphere of Zea mays L. root-hair defective mutant (rth3) and wild-type (WT) grown in two substrates (loam, sand). We applied 2D-chemical imaging methods in custom-designed root windows installed in the field to visualize soil pH (optodes), acid phosphatase activity (zymography), and labile P and Mn fluxes (diffusive gradients in thin films, DGT).

The average rhizosphere extent for phosphatase activity and pH was greater in sand than in loam, while the presence of root-hairs had no impact. Acidification was significantly stronger at young root tissue (<2 cm from root cap) than at older root segments (>4 cm from root cap) and stronger in WT than rth3. Accompanied with stronger acidification, higher P flux was observed mainly around young, actively growing root tissues for both genotypes. Our results indicate that acidification was linked to root growth and created a pH optimum for acid phosphatase activity, i.e., mineralization of organic P, especially at young root tissues which are major sites of P uptake. Both genotypes grew better in loam than in sand; however, the presence of root hairs generally resulted in higher shoot P concentrations and greater shoot biomass of WT compared to rth3. We conclude that soil substrate had a larger impact on the extent and intensity of P solubilization processes in the rhizosphere of maize than the presence of root hairs. For the first time, we combined 2D-imaging of soil pH, phosphatase activity, and nutrient gradients in the field and demonstrated a novel approach of stepwise data integration revealing the interplay of various P solubilizing processes in situ.

了解根际磷 (P) 动态对于可持续作物生产至关重要。根际磷动员过程包括植物和微生物来源的质子和细胞外磷酸酶的释放。我们研究了根毛和土壤质地对玉米根毛缺陷突变体（rth3）和野生型（ WT ）在两种基质（壤土、壤土、沙）。我们在现场安装的定制设计的根窗中应用了二维化学成像方法，以可视化土壤 pH 值（光极）、酸性磷酸酶活性（酶谱）和不稳定的 P 和 Mn 通量（薄膜中的扩散梯度，DGT）。

沙子中磷酸酶活性和 pH 值的平均根际范围大于壤土，而根毛的存在没有影响。幼根组织（距根冠<2 cm）的酸化明显强于老根段（距根冠>4 cm），WT 中的酸化强于rth3。伴随着更强的酸化，两种基因型的主要在年轻、活跃生长的根组织周围观察到更高的 P 通量。我们的结果表明酸化与根系生长有关，并为酸性磷酸酶活性创造了最佳 pH 值，即., 有机磷的矿化，特别是在幼根组织中，这些组织是磷吸收的主要部位。两种基因型在壤土中比在沙土中生长得更好；然而，与rth3相比，根毛的存在通常导致 WT 更高的枝条 P 浓度和更大的枝条生物量。我们得出结论，与根毛的存在相比，土壤基质对玉米根际磷溶解过程的程度和强度的影响更大。我们首次将土壤 pH 值、磷酸酶活性和养分梯度的二维成像结合起来，并展示了一种新的逐步数据集成方法，揭示了原位各种 P 溶解过程的相互作用。