Distribution of phosphatase activity and various bacterial phyla in the rhizosphere of Hordeum vulgare L. depending on P availability

Abstract

a b s t r a c tDespite the importance of the rhizosphere for nutrient turnover, little is known about the spatial patterns of organic phosphorus mineralization by plants and by microorganisms in the rhizosphere. Therefore, the distribution of acid and alkaline phosphatase activity and the abundance of bacteria belonging to various bacterial phyla were investigated in the rhizosphere of barley (Hordeum vulgare L.) as dependent on the availability of inorganic P. For this purpose, we conducted a greenhouse experiment with barley growing in inclined boxes that can be opened to the bottom side (rhizoboxes), and applied soil zymography and fluorescence-in situ-hybridization (FISH). Acid phosphatase activity was strongly associated with the root and was highest at the root tips. Due to P fertilization, acid phosphatase activity decreased in the bulk soil, and less strongly in the rhizosphere. Alkaline phosphatase activity, i.e., microbial phosphatase activity was high throughout the soil in the control treatment and was reduced due to inorganic P fertilization especially in the rhizosphere and less strongly in the bulk soil. P-fertilization slightly increased the total number of bacteria in the rhizosphere. Moreover, P-fertilization decreased the abundance of Firmicutes and increased the abundances of Beta-and Gamma-Proteobacteria. The total number of bacterial cells was significantly higher at the root surface than at the root tip and at a distance of 30 mm from the root surface. Our results show that alkaline phosphatase activity decreased more strongly in the rhizosphere than in the bulk soil due to P fertilization, which might be because of greater C deficiency in the bulk soil compared to the rhizosphere. Furthermore, the results indicate a spatial separation between hotspots of acid phosphatase activity and hotspots of bacteria in the rhizosphere of H. vulgare. Taken together, our study shows that bacteria and phosphatase activity were very heterogeneously distributed in soil, and that the effects of P fertilization on phosphatase activity differed strongly between bulk soil and rhizosphere as well as between various zones of the rhizosphere.

Effects of phosphorus-mobilizing bacteria on tomato growth and soil microbial activity

“…They determined the PA in the rhizosphere of barley grown under low and adequate P soil conditions and observed a similarity of approximately 90% between alkaline and acid PA. In contrast to the experiment of Spohn et al (2015), we observed no distinct separation between roots and surrounding soil (Fig. S2) and also generally lower PA (Fig.…”

“…These findings suggest increased P mineralization by microbial phosphatases produced by viable RU47. In general, zymography revealed similar activity levels for alkaline and acid PA, which is in accordance with Spohn et al (2015). They determined the PA in the rhizosphere of barley grown under low and adequate P soil conditions and observed a similarity of approximately 90% between alkaline and acid PA.…”

“…This may be attributable to the comparatively fine roots of tomato plants as compared to barley. Lower enzyme activity levels in comparison to the values of Spohn et al (2015) may have been due to the addition of quartz sand in the present experiment. PA data determined by soil in situ zymography indicated the spatial and temporal distribution of enzyme activity in the rhizosphere (soil area) during different growth stages of the tomato plants.…”

“…Using zymography in a rhizobox experiment, demonstrated the spatial separation of acid and alkaline phosphatase activity (PA) in the rhizosphere of lupines. While acid PA was associated with the root, alkaline PA was more widely distributed in the bulk soil Spohn et al 2015;Hofmann et al 2016). Microbial phosphatases comprise the major share of phosphatases in soil (Tabatabai 1994;Tarafdar et al 2001), contributing significantly to the P supply of plants (Frossard et al 2000;Oehl et al 2004).…”

Effects of strategic tillage and plant hormone treatments on wheat-associated microbial communities

“…Soil zymography works for a large range of hydrolases Spohn and Kuzyakov, 2014]. The method has been especially useful for determining the distribution of enzyme activity in the rhizosphere Kuzyakov, 2013, 2014], and it has already been combined with other imaging methods, such as 14 C imaging and fluorescent in situ hybridisation [Spohn et al, 2015] to gain insights into rhizosphere processes (Fig. 2).…”