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Summary: Root hairs and soil water content are crucial in controlling the release and diffusion of root exudates and shaping profiles of biochemical properties in the rhizosphere. But whether root hairs can offset the negative impacts of drought on microbial activity remains unknown.Soil zymography, 14C imaging and neutron radiography were combined to identify how root hairs and soil moisture affect rhizosphere biochemical properties. To achieve this, we cultivated two maize genotypes (wild‐type and root‐hair‐defective rth3 mutant) under ambient and drought conditions.Root hairs and optimal soil moisture increased hotspot area, rhizosphere extent and kinetic parameters (Vmax and Km) of β‐glucosidase activities. Drought enlarged the rhizosphere extent of root exudates and water content. Colocalization analysis showed that enzymatic hotspots were more colocalized with root exudate hotspots under optimal moisture, whereas they showed higher dependency on water hotspots when soil water and carbon were scarce.We conclude that root hairs are essential in adapting rhizosphere properties under drought to maintain plant nutrition when a continuous mass flow of water transporting nutrients to the root is interrupted. In the rhizosphere, soil water was more important than root exudates for hydrolytic enzyme activities under water and carbon colimitation. See also the Commentary on this article by Zhang et al., 237: 707–709. [ABSTRACT FROM AUTHOR]

The rhizosphere and detritusphere are hotspots of soil enzyme-mediated microbial processes, but little is known about their spatio-temporal distribution and interactions in situ , especially after straw incorporation. To answer this question, we planted maize in rhizoboxes with three wheat straw localizations: a) straw incorporated in the upper 2 cm of soil (straw localized); b) straw mixed with all the soil (straw homogenized); and 3) without straw (control). Zymography was used to investigate the spatio-temporal distribution of soil C- and N- acquiring enzyme activities in the rhizosphere (living roots) and detritusphere (straw induced), which depends on straw localization (localized vs. homogenized) and time (7 vs. 15 days after planting). The hotspot area of enzyme activities was similar in the detritusphere compared to the rhizosphere at the early stage (day 7), suggesting the importance of detritusphere in driving C and N cycling. Compared with homogenized straw, higher C- and N-acquiring enzyme activities in detritusphere were observed in the treatment with localized straw, which indicates that straw localization had a marked impact on the enzyme activity in the detritusphere. Although enzyme activities in rhizosphere and detritusphere decreased with time from straw application, straw incorporation increased the enzyme activities in the rhizosphere (especially with localized straw) compared to control at the late stage (day 15). Furthermore, homogenized straw greatly reduced plant height (−36 %), leaf area (−49 %), SPAD (−49 %), and shoot weight (−53 %) than control at the late stage, but localized straw had little impact on plant performance. In conclusion, straw incorporation forms another soil enzyme activity hotspot (detritusphere) and promotes enzyme activities in the rhizosphere and soil profile. Collectively, homogenized straw incorporation intensified nutrient competition between microorganisms and roots and restricted plant performance. [Display omitted] • The hotspot area of enzyme activity was similar in rhizosphere and detritusphere. • Enzyme activities in rhizosphere and detritusphere decreased over time. • Straw incorporation increased the enzyme activity in rhizosphere and soil surface. • Straw homogenized inhibited plant growth as nutrient competition between roots and microbes. [ABSTRACT FROM AUTHOR]

Climate change impacts soil microbial communities, activities and functionality. Nonetheless, responses of the microbiome in soil microenvironments with contrasting substrate availability in the rhizosphere to climatic stresses such as drought are largely unknown. To fill this knowledge gap, we coupled soil zymography with site-specific micro-sampling of the soil and subsequent high-throughput sequencing. This helped identify how the bacterial community structure and the genes encoding N-cycling enzymes (leucine aminopeptidase and chitinase) in rhizosphere hotspots and coldspots (microsites with activities in the range of bulk soil but localized within the rhizosphere) of maize respond to drought (20% WHC, two weeks). The elevated activities of leucine aminopeptidase and chitinase in rhizosphere hotspots were caused by the tight collaborative relationships between bacteria and their stable network structure rather than by any significant shift in bacterial community structure or enzyme-encoding gene copies. Despite the similarity in bacterial community structure in soil under drought and optimal moisture, functional predictions indicated the increased relative abundance of genera belonging to Actinobacteria capable of leucine aminopeptidase and chitinase production, especially Streptomyces , Nocardioides , Marmoricola, and Knoellia. Accordingly, the number of gene copies encoded by Actinobacteria for these two enzymes increased by 5.0–17% under drought. Among the bacteria with increased relative abundance under drought, Luedemannella played a crucial role in mediating nutrients and energy fluxes between bacteria. This was reflected in a 35–70% increase in leucine aminopeptidase and chitinase activities under drought. The resistance of enzyme activities to drought was higher in hotpots than that in coldspots. These results revealed that rhizosphere bacterial community composition remained stable, and that the number of gene copies encoded by Actinobacteria responsible for N-cycling enzymes increased under drought. The expected reduction of processes of N cycle was absent. Instead, bacteria increased N mining rate in those hotspots remaining active despite water scarcity. [Display omitted] • Soil zymography is combined with high-throughput sequencing • "Rhizosphere enzymatic coldspots" is for the first time localized • Enzyme activity in hotspots was more resistant than that in coldspots to drought • Bacterial community composition was stable between rhizosphere hot- and coldspots • Enzyme-related genes encoded by bacteria were affected by drought [ABSTRACT FROM AUTHOR]

Corrigendum to "Rhizosphere hotspots: Root hairs and warming control microbial efficiency, carbon utilization and energy production" [Soil Biol. Biochem. The monogenic maize mutant rth3 was described incorrectly in Section 2.1: it is not a maize mutant without root hairs but a root-hair defective mutant. Accordingly, the respective paragraph Section 2.1 should read as follows: - Two maize (Zea mays L.) genotypes, the root hair defective mutant rth3 (showing normal root hair initiation but disturbed root hair elongation) ([2], [3]), and the corresponding wild-type sibling were germinated for 3 days. [Extracted from the article]

Hotspot localization but not the duration of hot moments in the rhizosphere is affected by root hair lengthXiaona Song1, Xuechen Zhang1, Kazem Zamanian2, Michaela A. Dippold1, Yakov Kuzyakov2, Bahar S. Razavi21 Biogeochemistry of Agroecosystems, University of Göttingen, Büsgenweg 2, 37077 Göttingen, Germany2 Department of Agricultural Soil Science, University of Göttingen, Büsgenweg 2, 37077 Göttingen, GermanyAbstractThe rhizosphere, the narrow zone influenced by a broad range of compounds released by plant roots, is a hotspot of microbial activities. Microorganisms decompose root exudates and drive biogeochemical processes via enzymes production. Here, for the first time, we combined in situ soil zymography and the Rapid Automated Bacterial Impedance Technique system (RABIT) to localize enzymatic hotspots (β-glucosidase and leucine aminopeptidase) and estimate duration of microbial hot-moments in the rhizosphere.Wheat and soybean were selected as plants contrasting in root morphology: soybean has short root hairs while wheat has long root hairs. The zymograms and dispersion index analysis showed that the hotspots of β-glucosidase activity in wheat rhizoboxes were 6 times higher than under soybean. The hotspots of β-glucosidase activity under wheat and soybean were localized and aggregated at rhizoplane (dispersion index > 1). In contrast, the hotspot percentage of leucine aminopeptidase under wheat and soybean was similar, but spatial distribution of leucine-aminopeptidase activities under soybean demonstrated dispersed pattern in the whole rhizobox (dispersion index < 1) in contrast with wheat which were aggregated along the roots.Following zymography, rhizosphere and bulk soil was sampled by micro spatulas and CO2 emission during 72 h of incubation was quantified. For the first 18h rhizosphere respiration was higher than from bulk soil. Thereafter, the available substrate depleted and CO2 emission rate from the bulk soil was similar or even higher than of rhizosphere soil. Moreover, nutrient addition to soil decelerated the peak CO2 emission (~24 h) and extended the duration of the hot moment for a factor of 2.7 (> 32 h). For the first time, we linked enzymatic activity in rhizosphere hotspots of various extend with their CO2 emission rate. We could not prove any relation between rhizosphere hotspot extend and the duration of the hot moment of rhizodeposits decomposition. Concluding, root hairs increase hotspot percentage of enzyme activities but hotspot abundance does not affect the duration of hot moments of rhizodeposits decomposition. [ABSTRACT FROM AUTHOR]

The input of labile organics by plant roots stimulates microbial activity and therefore facilitates biochemical process rates in the rhizosphere compared to bulk soil, forming microbial hotspots. However, the extent to which the functional properties of soil microorganisms are different in the hotspots formed in soils with contrasting fertility remains unclear. We identified the hotspots related to different levels of Zea mays L. root architecture by zymography of leucine aminopeptidase in two soils with contrasting fertility. The hotspots localized by tiny wet-needle approach around first- and second-order roots were compared for parameters of microbial growth and enzyme kinetics. The pattern of hotspot distribution was more dispersed and the hotspot area was one order of magnitude smaller around first-versus second-order roots. The specific microbial growth rate (μ m) and biomass of active microorganisms were soil-specific, with no difference between the hotspots and bulk soil in the fertile soil. In contrast, in the soil poor in organic matter and nutrients, 1.2-fold higher μ m and greater growing biomass were found in the hotspots versus bulk soil. Lower enzyme affinity (1.3–2.2 times higher K m value) of β-glucosidase and leucine aminopeptidase to the substrate was detected in the hotspots versus bulk soil, whereas only β-glucosidase showed higher potential enzyme activity (V max) in the hotspots, being 1.7–2.1 times greater than that in bulk soil. Notably, the activity of C-acquiring enzyme, β-glucosidase positively correlated with the biomass of actively growing microorganisms. The fertile soil, on the whole, showed greater V max and catalytic efficiency (V max / K m) and an approximately 2.5 times shorter substrate turnover time as compared to the poor soil. Therefore, we conclude that i) the differences in microbial growth strategy between rhizosphere hotspots and bulk soil were dependent on soil fertility; ii) affinity of hydrolytic enzyme systems to substrate was mainly modulated by plant, whereas potential enzymatic activity was driven by both plant and soil quality. • The hotspots around roots were successfully localized by tiny wet-needle approach. • Stimulation on microbial growth in the hotspots was soil-specific. • Roots modulated enzyme affinity to substrate. • The fertile soil showed greater catalytic efficiency than the poor soil. [ABSTRACT FROM AUTHOR]