Title：Rhizosphere shape of lentil and maize: Spatial distribution of enzyme activities.
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Abstract: The rhizosphere, the small soil volume that surrounds and is influenced by plant roots, is one of the most dynamic biological interfaces on Earth. Enzymes, produced by both roots and microorganisms, are the main biological drivers of SOM decomposition. In situ soil zymography was applied to test hypotheses that 1) the spatial pattern of rhizosphere activity is enzyme-specific and 2) the distribution of enzyme activity along the roots is dependent on root system and plant species. Lentil (Lens culinaris) and maize (Zea mays L.), two species with contrasting root physiology, were chosen to test their effects on spatial distribution of activities of β-glucosidase, cellobiohydrolase, leucine-aminopeptidase and phosphatase.
The extent of the rhizosphere for each enzyme and plant species was estimated as a function of distance from the root. For the first time, we demonstrated plant-specific patterns of exoenzyme distribution: these were uniform along the lentil roots, whereas in the rhizosphere of maize, the enzyme activities were higher at the apical or proximal root parts. We conclude that the shape and extent of the rhizosphere for enzyme activities is plant species specific and varies due to different rhizosphere processes (e.g. root exudation) and functions (e.g. nutrient mobilization abilities). The extension of enzyme activity into the rhizosphere soil was minimal (1 mm) for enzymes responsible for the C cycle and maximal (3.5 mm) for enzymes of the phosphorus cycle. This should be considered in assessments and modeling of rhizosphere extension and the corresponding effects on soil properties and functions.
Main conetnts:
We aimed at quantitative imaging of enzyme activities in soil as a function of distance along and outward from the root to clarify 1) whether spatial distributions of enzyme activity show enzyme specific patterns along the root, 2) whether enzyme activity is associated mainly with root tips, and 3) to estimate the extent of the rhizosphere for each enzyme and plant species as a radial distance from the root.
Results:
Fig. 1 The distribution of enzyme activities, a. leucine aminopeptidase, b. acid phosphatase, c. b-glucosidase and d. cellobiohydrolase, along the lentil roots. Values obtained from analysis of five individual roots as replicates. Black curves present fitting of enzyme activity as a function of distance from root tip by non-linear regression. Dotted arrow on the zymogram shows direction.
Fig. 2 The distribution of enzyme activities, a. leucine aminopeptidase, b. acid phosphatase, c. b-glucosidase and d. cellobiohydrolase, along the maize roots was not uniform. This observation was consistent in five root samples. Black curves present fitting of enzyme activity as a function of distance from root tip by non-linear regression. Dotted arrow on the zymogram shows direction. Note that the (x) axis of plot (d) is distance to the root tip.
Fig. 3 General pattern of distribution of enzyme activity along the roots of lentil and maize. High enzyme activity is focused at root tips for maize. Relatively uniformly distributed enzyme activity along the root for lentil.
Conclusion:
Overall, for the first time, we visualized the enzyme-specific distribution patterns in soil and in the rhizosphere of different plants with contrasting root physiology. The shape and extent of
the rhizosphere for enzyme activities varies with “super-active” sites at the growing root tip and proximal parts. Depending on the tested enzyme, the rhizosphere extension varied from 1 to 3.5 mm. In conclusion, the rhizosphere shape is plant- and enzyme-specific and reflects the soil volume, from which roots and associated mi-croorganisms mobilize nutrients and utilize carbon.
From: Yang Yinghui