Functional traits of hydrolytic enzymes are related to the extent of root-root interactions in the rhizosphere of maize

The rhizosphere, a region of intensive interactions between roots and microorganisms, is shaped by biological competition and physical limitations of soil environment, which also affects decomposition of organic compounds via extracellular enzymes. This study examined the influence of contrasting intensities of root-to-root interactions and root-to-physical constraints on the kinetics of four hydrolytic enzymes in the rhizosphere of two Zea mays L. genotypes: wild type and root hair-defective mutant grown in loam and sand substrates. The field setups included the following: i) unrestricted plot cultivation of maize with unhampered root-root interactions; ii) root window with root-root interactions and physical constraints; and iii) spatially restricted soil columns. Root windows demonstrated similar potential enzymatic activity to plot cultivation , but either 59.4% smoothed (N-acetylglucosaminidase) or 621% amplified (acid phosphatase) the effect of plant genotype. Soil column exhibited substantially higher activity of acid phosphatase than the other setups due to P-limited conditions induced by the restricted soil volume and elevated root length density (RLD). When normalized by RLD, plot cultivation showed higher specific V max for C- and N-acquiring enzymes than soil column. Overall, the three field setups, which differed in neighboring plants, spatial restrictions, and sampling strategy, were associated with distinct rhizosphere enzymatic responses. Our findings further highlight the importance of considering RLD when interpreting rhizosphere enzyme activities, especially for P-mobilizing enzymes under P limitation and for C- and N-acquiring enzymes when scaling across field and controlled setups.