Impact of Irrigation Strategies on Tomato Root Distribution and Rhizosphere Processes in an Organic System

Abstract

Root exploitation of soil heterogeneity and microbially mediated rhizosphere nutrient transformations play critical roles in plant resource uptake. However, how these processes change under water-saving irrigation technologies remains unclear, especially for organic systems where crops rely on soil ecological processes for plant nutrition and productivity. We conducted a field experiment and examined how water-saving subsurface drip irrigation (SDI) and concentrated organic fertilizer application altered root traits and rhizosphere processes compared to traditional furrow irrigation (FI) in an organic tomato system. We measured root distribution and morphology, the activities of C-, N-, and P-cycling enzymes in the rhizosphere, the abundance of rhizosphere microbial N-cycling genes, and root mycorrhizal colonization rate under two irrigation strategies. Tomato plants produced shorter and finer root systems with higher densities of roots around the drip line, lower activities of soil C-degrading enzymes, and shifts in the abundance of microbial N-cycling genes and mycorrhizal colonization rates in the rhizosphere of SDI plants compared to FI. SDI led to 66.4% higher irrigation water productivity than FI, but it also led to excessive vegetative growth and 28.3% lower tomato yield than FI. Our results suggest that roots and root-microbe interactions have a high potential for coordinated adaptation to water and nutrient spatial patterns to facilitate resource uptake under SDI. However, mismatches between plant needs and resource availability remain, highlighting the importance of assessing temporal dynamics of root-soil-microbe interactions to maximize their resource-mining potential for innovative irrigation systems.

Contrasting distribution of enzyme activities in the rhizosphere of European beech and Norway spruce

“…This result was explained by the more homogeneous morphological appearance of beech roots compared with spruce. The root morphological and physiological heterogeneity results in the alteration of the chemical composition of exudates ( Jaeger et al., 1999 ; Wen et al., 2022 ) or generate micro-niches, where the mucilage and other exudates may accumulate, favouring microbial activity ( Massalha et al., 2017 ; Schmidt et al., 2018 ; Li et al., 2020 ; Xiong et al., 2021 ). As the enzymes cleave complex organic compounds from rhizodeposits into absorbable nutrients for plants and microorganisms ( Nannipieri et al., 2007 ; Nannipieri et al., 2011 ), the quantity and quality of rhizodeposits are likely contributing to the spatial distribution of enzyme activities on the rhizoplane.…”

Response of the tomato rhizosphere bacterial community to water–oxygen coupling under micronanobubble oxygenated drip irrigation in mildly saline soil

“…in distinct root-microbe interactions, affect the efficiency of soil water and nutrient acquisition by the roots and indirectly result in differences in the soil EC (M. Li et al, 2020).…”

How does building healthy soils impact sustainable use of water resources in irrigated agriculture?

“…Soil health management could also help different types of root systems adapt to irrigation management and improve the effective use of water. With irrigation, crops often invest preferentially in shallow roots, especially with drip or microsprinkler systems in which applied water is more localized and does not penetrate deeply into the soil profile (Li et al, 2020). Well-structured soils with low resistance to root proliferation could help crops rapidly develop shallow axial roots with extensive lateral branching that would enable exploitation of water and nutrient resources concentrated near the soil surface (Schmidt and Gaudin, 2017).…”