Publications

Phosphorus (P) is essential for life but is often poorly available to plants, limiting biological processes in ecosystems. Microbial transformations increase P availability through enzymatic hydrolysis of organic P compounds; however, these processes are metabolically and energetically costly and occur predominantly in microbial hotspots, such as the rhizosphere and other microsites with elevated microbial activity. Microorganisms invest cellular energy, primarily in the form of ATP, to produce phosphatase enzymes required for P mineralisation.This study aimed to quantify the energetic and metabolic costs of enzymatic hydrolysis of organic P compounds of increasing complexity within microbial hotspots. We hypothesized that (i) energy investment for enzyme production increases with substrate complexity and its interaction with soil minerals, and (ii) enzyme-mediated P mineralization requires higher energy input than direct P uptake. To test these hypotheses, a soil–sand mixture was incubated with different P substrates while measuring heat dissipation (microcalorimetry), enzyme activities, soil ATP content, and available P.Four treatments were applied: inorganic P (control), glycerol phosphate, DNA, and phytic acid (phytate). Heat release increased with substrate complexity, from phosphomonoester to DNA, indicating higher energetic investment. Microorganisms invested more energy in enzyme production than in P uptake, and phosphomonoesterase activity increased with substrate complexity. In contrast, phosphodiester hydrolysis was constrained by low phosphodiesterase activity, reflecting higher metabolic costs.These results demonstrate that microbial hotspot activity governs the energetic efficiency of organic P transformations in soils, highlighting the importance of microscale processes for soil P cycling.Acknowledgments and Funding: This work was funded by the German Research Foundation (DFG, BI 2570/1-1), project number 525137622.

No abstract is provided for this article.

Abstract Reliable predictions of dryland carbon fluxes require understanding the persistence and turnover of soil organic carbon (SOC). We measure radiocarbon to quantify the age of SOC and CO 2 released from soil respiration at 97 dryland sites across six continents. Here we show that bulk SOC contains little C fixed in the past 60 years, while respired CO 2 originates from both bomb-derived recent C and millennia-old C, challenging the idea that old C is chemically or physically protected. Radiocarbon suggests mean ages of ~2100 years for bulk SOC and ~520 years for respired CO 2 , the latter far older than machine-learning (<50 years) or Earth system models predict. Aridity, net primary productivity, and SOC content are dominant predictors for radiocarbon signatures, with abrupt shifts to older C beyond an aridity threshold of ~0.87. Our findings underscore the need to incorporate the vulnerability of older carbon into models and land management strategies.

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, 14 C 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 ( V max and K m ) 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.

<title>Abstract</title> <bold>Background and aims</bold> Integrating biochar (BC) into agriculture promotes sustainable management of farm residues and carbon sequestration in soil. This study evaluates a novel approach combining suspended biochar with phosphorus (P) fertilizer to assess its effectiveness in promoting P nutrition during early maize (<italic>Zea mays </italic>L<italic>.</italic>) growth. <bold>Methods</bold> Biochar suspension (equivalent to 300 kg dry biochar ha^-1) was mixed with liquid P fertilizer (30 kg P ha^-1, ³³P-labeled) and band-applied to maize in the rhizobox experiment. Five treatments—control without fertilizer, BC only, P fertilizer only, and combined BC+P with and without plants—aimed to assess the effect of biochar on soil P dynamics and plant P uptake. <bold>Results</bold> Our findings demonstrate that liquid P fertilizer can be effectively combined with biochar suspension without reducing P availability. After 38 days, up to 25% of fertilizer-P was recovered in the soil’s available P pool, regardless of BC presence. ³³P-imaging confirmed that P movement from the fertilizer band was not restricted by BC. Fertilizer increased plant P uptake, height, biomass, leaf area, root length and volume. Biochar significantly increased fertilizer-P recovery in plants from 14.9% to 17.6%, supporting nutrient cycling and fertilizer efficiency. ³³P-imaging revealed higher activity of ³³P in maize roots with BC+P co-application, though P redistribution patterns remained unchanged; plant roots showed neither preference nor suppression near biochar, even upon direct contact. <bold>Conclusion</bold> Localized co-application of biochar and P in suspension promotes maize growth during critical early stages and increases phosphorus use efficiency, supporting sustainable agriculture and a circular economy.

<title>Abstract</title> Context Analysing root traits to identify below ground acquisition mechanisms and relating them to above ground traits, such as leaf phenology, can improve the understanding and design of resource use efficient and drought resilient agroforestry systems. Objectives To determine how fine root traits are associated with different shade tree functional groups and their influence on climate resilience Methods Two key roots traits, i.e. fine root length density and fine root diameter of shade trees and cocoa are evaluated for the 13 most common shade tree species belonging to six functional (leaf phenology) groups under farmer field conditions. Fine root samples were acquired for four replicates of each shade tree species through extensive root coring up to 60 cm depth and at three horizontal shade tree impact zones. Results All cocoa plants irrespective of their associated shade tree functional group exhibited resource acquisitive fine root traits, i.e. higher root length density and smaller diameter. Similarly, shade trees in the ‘brevi deciduous during dry season’ functional group, i.e. characterized by higher, leaf area-related, water uptake in the dry season exhibited acquisitive fine root traits. Evergreen and complete deciduous functional groups showed a conservative fine root trait, i.e. with lower fine root length density and larger diameter. Conclusion Pairing acquisitive root traits in cocoa with conservative fine root trait shade trees optimize agroforestry systems.

While well-described for soil properties, we barely know how microbial traits determine the availability of various phosphorus (P) forms to crops. We trace

Plants and microorganisms, besides the climate, drive nitrogen (N) cycling in ecosystems. Our objective was to investigate N losses and N acquisition strategies along a unique ecosystem-sequence (ecosequence) ranging from arid shrubland through Mediterranean woodland to temperate rainforest. These ecosystems differ in mean annual precipitation, mean annual temperate, and vegetation cover, but developed on similar granitoid soil parent material, were addressed using a combination of molecular biology and soil biogeochemical tools. Soil N and carbon (C) contents, δ 15 N signatures, activities of N acquiring extracellular enzymes as well as the abundance of soil bacteria and fungi, and diazotrophs in bulk topsoil and rhizosphere were determined. Relative fungal abundance in the rhizosphere was higher under woodland and forest than under shrubland. This indicates toward plants' higher C investment into fungi in the Mediterranean and temperate rainforest sites than in the arid site. Fungi are likely to decompose lignified forest litter for efficient recycling of litter-derived N and further nutrients. Rhizosphere—a hotspot for the N fixation—was enriched in diazotrophs (factor 8 to 16 in comparison to bulk topsoil) emphasizing the general importance of root/microbe association in N cycle. These results show that the temperate rainforest is an N acquiring ecosystem, whereas N in the arid shrubland is strongly recycled. Simultaneously, the strongest 15 N enrichment with decreasing N content with depth was detected in the Mediterranean woodland, indicating that N mineralization and loss is highest (and likely the fastest) in the woodland across the continental transect. Higher relative aminopeptidase activities in the woodland than in the forest enabled a fast N mineralization. Relative aminopeptidase activities were highest in the arid shrubland. The highest absolute chitinase activities were observed in the forest. This likely demonstrates that (a) plants and microorganisms in the arid shrubland invest largely into mobilization and reutilization of organically bound N by exoenzymes, and (b) that the ecosystem N nutrition shifts from a peptide-based N in the arid shrubland to a peptide- and chitin-based N nutrition in the temperate rainforest, where the high N demand is complemented by intensive N fixation in the rhizosphere.

&amp;lt;p&amp;gt;A diverse range of soil microorganisms accumulate energy to secure their future needs under resource fluctuation or deficiency. Microbial intracellular storage can substantially mediate the stress of resource variability across time, thereby supporting growth and reproduction. Microbial storage is well known in industrial applications and under pure culture conditions, yet few studies address its importance in the soil. To evaluate how widespread microbial energy storage is in soil, we quantified the contents of two intracellular storage compounds, polyhydroxybutyrate (PHB) and triacylglycerides (TAGs), from seven permanent grasslands in Germany differing in field management (grazing/mowing and fertilizing) and soil types. In winter 2021, soil was collected from two depths, 5-10 cm called topsoil, and &amp;gt;30 cm called subsoil, to capture different soil carbon inputs from grass roots. The storage compound contents were determined by gas chromatography&amp;amp;#8211;mass spectrometry (GC-MS). We hypothesized that the carbon input controls the storage compound levels. From topsoil to subsoil, as root carbon inputs (estimated from the fresh root weight) drop with depth, microbial storage levels follow suit. Dissolved organic carbon (DOC) was measured to qualify carbon availability to microorganisms, and microbial biomass carbon (MBC) was to assess microbial biomass. The root weight in the topsoil was 20-50 times higher than in the subsoil, while MBC and DOC contents were 3-4 and 1.5-2.5 times higher, respectively. Storage levels and MBC decreased with depth, and showed a positive correlation with DOC. This experiment allowed us to quantify intracellular storage occurrence in soils and to understand how its distribution related to root carbon input. These results point out that microbial intracellular carbon storage might accumulate according to the available carbon level (root carbon inputs) for microorganisms. Thus, this carbon plays a pivotal role for microbial ecology of soils as it prepares the microbial cells to survive throughout the winter when less carbon is provided by plants.&amp;lt;/p&amp;gt;

No abstract is provided for this article.

&amp;lt;p&amp;gt;Mucilage is a gelatinous high-molecular-weight substance produced by almost all plants, serving numerous functions for plants and soil. To date, research has mainly focused on the hydraulic and physical functions of mucilage in the rhizosphere. Studies on the relevance of mucilage as a microbial habitat are scarce. Microbial research has largely focused on extracellular polymeric substances (EPS), gelatinous high-molecular-weight substances produced by microorganisms. In soil, EPS support the establishment of microbial assemblages by providing a moist environment, a protective barrier, and serving as carbon and nutrient sources. Our analyses show that mucilage shares the physical and chemical properties of EPS. Mucilage covers large extents of the rhizosphere and could function similarly to the biofilm matrix. Our laboratory and theoretical analyses largely confirmed similar viscosity and surface tension as important physical properties and polysaccharide, protein, neutral monosaccharide, and uronic acid composition as major chemical properties. Our study suggests that mucilage provides functions of EPS required for biofilm formation. Mucilage offers a protected habitat optimized for nutrient mobilization and provides carbon and nutrients. We suggest that the function of mucilage as a biofilm matrix and enabler of high rhizo-microbial abundance and activity has been strongly underestimated, and should be considered as an essential component of conceptual models of the rhizosphere.&amp;amp;#160;&amp;lt;/p&amp;gt;

Multipurpose cropping is promoted to provide biomass to meet the growing demand for biorefining, but excessive biomass removal may decrease soil C stocks and ecosystem multifunctionality. Here, soil C stocks across 0–200 cm depth and soil ecosystem multifunctionality at 0–40 cm were evaluated based on a 19–year field experiment, including three multipurpose cropping systems as continuous cotton (CC), ryegrass–sweet sorghum double cropping (RS) and perennial switchgrass (SG). Compared to CC, RS and SG increased the soil C stocks by 19% and 28%, and N stocks by 19% and 23% at 0–200 cm, respectively. The soil C stocks were positively correlated with belowground C input and negatively associated with C mineralization. RS and SG increased soil ecosystem multifunctionality by 16.8 and 15.7 folds at 0–20 cm and 0.34 and 0.61 folds at 20–40 cm relative to CC, respectively. The benefit of soil C stocks and ecosystem multifunctionality was more pronounced in SG than in RS due to the deeper root system. In conclusion, relative to continuous monoculture, rotational and perennial cropping can enhance soil C sequestration, maintain soil function, and provide feedstock for bioenergy.