Abstract：
Recycling of phosphorus (P) from waste streams in agriculture is essential to reduce the negative environmental effects of surplus P and the unsustainable mining of geological P resources. Sewage sludge (SS) is an important P source; however, several issues are associated with the handling and application of SS in agriculture. Thus, post-treatments such as pyrolysis of SS into biochar (BC) could address some of these issues. Here we elucidate how patches of SS in soil interact with the living roots of wheat and affect important P-related rhizosphere processes compared to their BC counterparts. Wheat plants were grown in rhizoboxes with sandy loam soil, and 1 cm Ø patches with either SS or BC placed 10 cm below the seed. A negative control (CK) was included. Planar optode pH sensors were used to visualize spatiotemporal pH changes during 40 days of plant growth, diffusive gradients in thin films (DGT) were applied to map labile P, and zymography was used to visualize the spatial distribution of acid (ACP) and alkaline (ALP) phosphatase activity. In addition, bulk soil measurements of available P, pH, and ACP activity were conducted. Finally, the relative abundance of bacterial P-cycling genes (phoD, phoX, phnK) was determined in the patch area rhizosphere. Labile P was only observed in the area of the SS patches, and SS further triggered root proliferation and increased the activity of ACP and ALP in interaction with the roots. In contrast, BC seemed to be inert, had no visible effect on root growth, and even reduced ACP and ALP activity in the patch area. Furthermore, there was a lower relative abundance of phoD and phnK genes in the BC rhizosphere compared to the CK. Hence, optimization of BC properties is needed to increase the short-term efficiency of BC from SS as a P fertilizer.
摘要：
从农业废物流中回收磷（P）对于减少剩余磷的负面环境影响和地质磷资源的不可持续开采至关重要。污水污泥(SS)是重要的P源;然而,SS在农业中的处理和应用有几个问题。因此，后处理如将SS热解成生物炭(BC)可以解决这些问题中的一些。在这里，我们阐明了土壤中的SS斑块如何与小麦的活根相互作用，并与BC对应物相比影响重要的与P相关的根际过程。小麦植物生长在有沙壤土的根茎中，和1cmØ具有SS或BC的斑块放置在种子下方10cm处。包括阴性对照(CK)。平面光电极pH传感器用于可视化40天植物生长过程中的时空pH变化，薄膜中的扩散梯度(DGT)被应用于不稳定P，酶谱用于可视化酸（ACP）和碱性（ALP）磷酸酶活性的空间分布。此外,有效磷的散装土壤测量，pH值,并进行了ACP活动。最后,细菌P循环基因的相对丰度(phoD，phoX,phnK）在斑块区域根际中测定。仅在SS斑块区域观察到不稳定P，SS进一步触发了根系增殖，并增加了ACP和ALP与根系相互作用的活性。相比之下,BC似乎是惰性的，对根系生长没有明显影响，甚至降低了斑块区域的ACP和ALP活性。此外，与CK相比，BC根际中phoD和phnK基因的相对丰度较低。因此，需要优化BC特性以提高SS作为P肥料的BC的短期效率。
