Unearthing soil-plant-microbiota crosstalk: Looking back to move forward

Abstract

The soil is vital for life on Earth and its biodiversity. However, being a non-renewable and threatened resource, preserving soil quality is crucial to maintain a range of ecosystem services critical to ecological balances, food production and human health. In an agricultural context, soil quality is often perceived as the ability to support field production, and thus soil quality and fertility are strictly interconnected. The concept of, as well as the ways to assess, soil fertility has undergone big changes over the years. Crop performance has been historically used as an indicator for soil quality and fertility. Then, analysis of a range of physico-chemical parameters has been used to routinely assess soil quality. Today it is becoming evident that soil quality must be evaluated by combining parameters that refer both to the physico-chemical and the biological levels. However, it can be challenging to find adequate indexes for evaluating soil quality that are both predictive and easy to measure in situ. An ideal soil quality assessment method should be flexible, sensitive enough to detect changes in soil functions, management and climate, and should allow comparability among sites. In this review, we discuss the current status of soil quality indicators and existing databases of harmonized, open-access topsoil data. We also explore the connections between soil biotic and abiotic features and crop performance in an agricultural context. Finally, based on current knowledge and technical advancements, we argue that the use of plant health traits represents a powerful way to assess soil physico-chemical and biological properties. These plant health parameters can serve as proxies for different soil features that characterize soil quality both at the physico-chemical and at the microbiological level, including soil quality, fertility and composition of soil microbial communities.

Keywords: microbiome; plant health; soil database; soil indicators; soil quality; soil-microbe-plant system.

Figure 1

Number of European/world soil databases released from 2007 to 2022.

Figure 2

Plant health indicators as a proxy of soil quality. A combination of plant health parameters such as photosynthesis, yield and resilience can represent a powerful ‘‘lens’’ to evaluate soil quality and differentiate between a “good”, healthy soil and a “bad” soil, with properties not supporting plant growth. In a “good” soil, a diverse and balanced microbiome is present, along with optimal physico-chemical parameters and air and water movement, while different nutrients are available for the plant and support its growth, health and resilience. In contrast, a “bad” soil is characterized by a dysbiotic microbiome, reduced water and air movement, limited nutrient availability and suboptimal physico-chemical parameters, which negatively affect various plant traits. Using different methods and analyzing multiple indicators, we can determine the relationship between soil parameters and selected traits of plant health.