Pasteurisation of soil from an extremely phosphorus-impoverished environment increases phosphorus availability and enhances the facilitative effect of cluster-rooted species on Agonis flexuosa (Myrtaceae)

Soil pasteurisation is commonly used to remove biotic factors that influence plant growth, but it can unavoidably affect some soil abiotic properties. These abiotic changes are often overlooked in extremely phosphorus (P)-impoverished soils, where even slight increases in P availability can influence both plant growth and interspecific interactions. Therefore, we aimed to determine whether pasteurisation of extremely P-impoverished soil affects the growth of Agonis flexuosa and its interaction with Banksia attenuata. In a controlled glasshouse experiment, we evaluated plant growth, root morphological and physiological traits of target species A. flexuosa grown either in monoculture or mixed culture with B. attenuata, in a pasteurised soil treatment (PST) and an inoculated soil treatment (IST), where one-third of the pasteurised soil was replaced with unpasteurised field soil. Soil resin P concentration was 20% higher in PST than in IST. In PST compared with IST, A. flexuosa had two-fold higher leaf P concentration, greater total biomass, developed thicker roots with lower tissue density, and showed higher rhizosheath carboxylate concentrations. Under PST, the total biomass of A. flexuosa was greater when grown with B. attenuata, accompanied by lower rhizosheath acid phosphatase activity than in the absence of B. attenuata. Under IST, the biomass of A. flexuosa was indistinguishable in the presence or absence of B. attenuata. Moreover, in the presence of Banksia, its biomass under PST was only 49% of that under IST. Pasteurisation of soil from extremely P-impoverished soils increased P availability, leading A. flexuosa root traits more towards nutrient absorption and enhancing its facilitation by B. attenuata. These effects were likely due to the release of P from microbial biomass and lower competition for P from microbes. These results demonstrate that attention should be paid to changes in soil nutrient availability due to pasteurisation to avoid misattributing plant responses to other factors.

土壤巴氏杀菌（pasteurisation）常用于去除影响植物生长的生物因子，但不可避免地会改变某些土壤非生物特性。在极度缺磷（P）的土壤中，这些非生物变化常被忽视——在这类土壤中，磷有效性的轻微提升即可影响植物生长及种间相互作用。因此，本研究旨在明确极度缺磷土壤的巴氏杀菌是否会影响Agonis flexuosa的生长及其与Banksia attenuata的种间相互作用。在受控温室实验中，我们评估了目标物种A. flexuosa在单作或与B. attenuata混作条件下，于巴氏杀菌土壤处理（PST）和接种土壤处理（IST，即将三分之一巴氏杀菌土壤替换为未杀菌田间土壤）中的生长状况、根系形态及生理性状。PST处理的土壤树脂磷浓度较IST处理高20%。与IST相比，PST处理下A. flexuosa的叶片磷浓度提升一倍，总生物量增加，根系更粗且组织密度更低，根鞘羧酸盐浓度亦更高。PST处理下，A. flexuosa与B. attenuata混作时的总生物量高于单作，且根鞘酸性磷酸酶活性低于单作组。IST处理下，A. flexuosa在有无B. attenuata伴生时的生物量无显著差异。此外，在有Banksia伴生时，PST处理下A. flexuosa的生物量仅为IST处理的49%。极度缺磷土壤的巴氏杀菌提高了磷有效性，使A. flexuosa的根系性状更倾向于养分吸收，并增强了B. attenuata对其的促进作用。这些效应可能源于微生物生物量磷的释放及微生物对磷的竞争减弱。研究结果表明，需关注巴氏杀菌引发的土壤养分有效性变化，以避免将植物响应误归因于其他因素。