In-depth insight into the short-term effect of floor management practice on young apple trees development and soil microbial biodiversity and activity

PLOS One | https://doi.org/10.1371/journal.pone.0329979 August 7, 2025 2 / 15 Introduction Introduction of additional plant species or crops into an orchard within the tree row can be considered a practice that enhances the biodiversity of the entire orchard, not only by introducing new plant species, but also by recruiting pollinating insects or sheltering beneficial insects that could positively affect the fruit yield and can help reduce pests populations [1,2]. However, the introduction of additional plants can provide multi-level benefits. Legume plants, for example, could also play an addi- tional role in the agroecosystem by supplying nitrogen to the soil through symbiosis with rhizobia strains [3]. Using herbs as living mulches can also provide an additional source of income for the farmers [4,5]. Flowering species are generally used to establish flower strips on the perimeter of the orchards to provide various ecosystem services [6–9], but have seldom been exploited as living mulches, i.e., introducing them “within” the orchard. Nevertheless, when designing an agroecological orchard, it is important to consider that accompanying plants use the same environmental resources as the main crop, e.g., soil nutrients or sun light, and that the tree needs differ depending on the orchard age. Past studies on living mulches based on simple mixtures of grasses and leguminous species have generally evaluated their impact on weeds control or tree performance [10–12], and to a limited extent on the soil biological features [13].

Soil microbiome plays a crucial role in maintaining soil health and balance [14]. Microbial communities are involved in nutrient cycling, carbon sequestration, plant growth promotion and many other processes [15]. Agricultural management prac- tices, including fertilizer application, tillage, or cover crops, influence the soil microbial communities composition and function [16]. The majority of studies on the impact of cover crops on the soil microbiome are concerned with annual cropping systems, where cover crops are present in the field during fallow periods [17]. Few works on perennial crops, including orchards or vineyards, have analysed the impact of living mulches on biodiversity and microorganisms abundance during the growing season, as well as on soil enzymatic activity: in general showing their increase after apply- ing such soil management practices [13,18–20]. Nevertheless, there is the need to better understand how these practices are affecting the soil microbiome dynamics, its functions and potential provision of ecosystem services, due to the high complexity of its relationships and interactions with the plant and the environmental conditions [21–23]. Such knowledge could fill some research gaps about the interaction of living mulches with the tree crop in relation also to the plant-soil-microbiome relations and support designing a cropping system more resilient toward abiotic and biotic stresses, reducing the need of external inputs, assuring at the same time the farmer economic expectations. Such knowledge would be of utmost importance particularly

for apple cropping system, one of the most economically important fruit crops in the world and in Poland, where it accounts for about 150.000 ha, delivering about 4M tons of fruits yearly, contributing roughly 30% of the total EU apple harvest [24]. The present study investigated two very diverse plant mixtures designed for the establishment of multifunctional living mulches suitable, to a different extent, for increasing soil nutrients, reduce weeds competition, favouring pollinators and SUSCROP/II/BioHortiTech/01/2021 within the program ERA-NET Cofund SusCrop. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist.