Increased water retention in the rhizosphere allows for high phosphatase activity in drying soil
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Background and aims
Soil drying negatively impacts several rhizosphere processes, but plant roots are capable of alleviating changes in rhizosphere water content by releasing mucilage. We propose that enhanced water retention in the rhizosphere due to mucilage and microbial extracellular polysaccharides allows for fast diffusion of enzymes and substrates, and thus high enzyme activity in the vicinity of roots.
To assess the effect of diffusion on enzyme activity, the relation between phosphatase activity and volumetric soil water content (VWC) was quantified in sterile soil. Then, barley plants were grown in rhizoboxes and subjected to a drying cycle, while VWC and phosphatase activity were monitored by neutron radiography and soil zymography.
The relation between phosphatase activity and VWC was well described by a diffusion model (R2 = 0.64), demonstrating the importance of diffusion for enzyme activity. This finding was confirmed in the experiment with plants where phosphatase activity strongly decreased upon soil drying. Enzyme activity decreased less in the rhizosphere than in the bulk soil: the ratio between phosphatase activity in the rhizosphere and bulk soil was 10 when the soil was close to saturation and 63 when the soil contained 5% water. The relationship between phosphatase activity and local soil WC were well fitted by the diffusion model (rhizosphere: R2 = 0.54, bulk: R2 = 0.63), emphasizing the effect of diffusion on soil enzyme activity.
Our results indicate that soil VWC has a significant effect on soil enzyme activity by increasing diffusion of enzymes and substrate. The higher retention of water in the rhizosphere maintains high enzyme activity around roots in drying soils, which might be beneficial for plant nutrient acquisition.
KeywordsSoil water Soil drying Plant roots Rhizosphere Phosphatase activity Soil zymography Neutron radiography Enzyme diffusion Barley (Hordeum vulgare L.)
We thank Bea Burak and Ian Dodd for providing the seeds for the experiments and Joscha Becker for advice concerning the statistical analysis. MH thanks Bahar S. Razavi for introducing her to the zymography method. The authors acknowledge the German Research Foundation for granting the projects CA 921/3-1, KU 1184/33-1 and SP1389/6-1, and the ev. Studienwerk Villigst for granting a stipend for MH.
- Ali RS, Ingwersen J, Demyan MS, Funkuin YN, Wizemann H, Kandeler E, Poll C (2015) Modelling in situ activities of enzymes as a tool to explain seasonal variation of soil respiration from agro-ecosystems. Soil Biol Biochem 81:291–303. https://doi.org/10.1016/j.soilbio.2014.12.001 CrossRefGoogle Scholar
- Allison, S.D., Weintraub, M.N., Gartner, T.B., Waldrop, M.P., 2011. Evolutionary-economic principles as regulators of soil enzyme production and ecosystem function 229–243. https://doi.org/10.1007/978-3-642-14225-3
- FAO (2012) Coping with water scarcity: an action framework for agriculture and food security. In: Water report 38. Organization. Rome, Food and AgricultureGoogle Scholar
- Feynman RP, Leighton RB, Sands M (1965) The Feynman lectures on physics, vol 3. Addison-Wesley, Reading, MAGoogle Scholar
- Grando S, Gomez MH (2005) Food barley: importance, uses, and local knowledge. International Center for Agricultural Research in the Dry Areas, Aleppo, SyriaGoogle Scholar
- Manzoni S, Schimel JP, Porporato A, Manzoni S, Schimel JP, Porporato A (2012) Responses of soil microbial communities to water stress: results from a meta-analysis. Ecology 93:930–938Google Scholar
- Nannipieri, P., Giagnoni, L., Landi, L., Renella, G., 2011. Role of phosphatase enzymes in soil, in: Bünemann E., Oberson A., F.E. (Ed.), Phosphorus in action. Springer, Berlin, Heidelberg, pp. 215–243Google Scholar
- Or, D., Phutane, S., Dechesne, A., Ection, S.P.S., 2007. Extracellular Polymeric Substances Affecting Pore-Scale Hydrologic Conditions for Bacterial Activity in Unsaturated Soils 6. https://doi.org/10.2136/vzj2006.0080
- Sanaullah, M., Blagodatskaya, E., Chabbi, A., Rumpel, C., Kuzyakov, Y., 2011. Drought effects on microbial biomass and enzyme activities in the rhizosphere of grasses depend on plant community composition. Applied Soil Ecology 48:38–44. https://doi.org/10.1016/j.apsoil.2011.02.004
- Sardans J, Peñuelas J (2005) Drought decreases soil enzyme activity in a Mediterranean Quercus ilex L. forest. Soil Biol Biochem 37:455–461. https://doi.org/10.1016/j.soilbio.2004.08.004
- Soille P (2003) Morphological image analysis: principles and applications. Spiringer Verlag, GermanyGoogle Scholar
- Zarebanadkouki M, Kim YX, Moradi AB, Vogel H-J, Kaestner A, Carminati A (2012) Quantification and modeling of local root water uptake using neutron radiography and deuterated water. Vadose Zone J 11. https://doi.org/10.2136/vzj2011.0196