University of Copenhagen, Department of Plant & Environmental Sciences, Thorvaldsensvej 40, 1821 Frederiksberg, Denmark.
Aarhus University, Department of Environmental Science, Frederiksborgvej 399, 4000 Roskilde, Denmark.
Sci Total Environ. 2023 Dec 20;905:166888. doi: 10.1016/j.scitotenv.2023.166888. Epub 2023 Sep 18.
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.
从农业废水中回收磷（P）对于减少过量 P 对环境的负面影响和不可持续地开采地质 P 资源至关重要。污水污泥（SS）是 P 的重要来源；然而，SS 在农业中的处理和应用存在一些问题。因此，对 SS 进行热解等后处理，将其转化为生物炭（BC），可以解决其中的一些问题。在这里，我们阐明了与 SS 相比，土壤中 SS 斑块如何与小麦的活根相互作用，并影响重要的与 P 相关的根际过程。小麦植株在带砂壤土的根盒中生长，将 1 cm Ø 的 SS 或 BC 斑块放置在距种子 10 cm 以下的位置。包括一个阴性对照（CK）。平面光学位移传感器用于可视化 40 天植物生长过程中的时空 pH 变化，扩散梯度薄膜（DGT）用于绘制可利用 P，并用同工酶技术可视化酸性（ACP）和碱性（ALP）磷酸酶活性的空间分布。此外，还对土壤有效 P、pH 和 ACP 活性进行了批量测量。最后，在斑块区域根际中测定了细菌 P 循环基因（phoD、phoX、phnK）的相对丰度。仅在 SS 斑块区域观察到可利用 P，SS 进一步刺激了根系增殖，并与根系相互作用增加了 ACP 和 ALP 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，BC 根际中 phoD 和 phnK 基因的相对丰度低于 CK。因此，需要优化 BC 的性质，以提高 BC 从 SS 作为 P 肥料的短期效率。
