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Plant root traits play a crucial role in resource acquisition and crop performance when soil nutrient availability is low. However, the respective trait responses are complex, particularly at the field scale, and poorly understood due to difficulties in root phenotyping monitoring, inaccurate sampling, and environmental conditions. Here, we conducted a systematic review and meta-analysis of 50 field studies to identify the effects of nitrogen (N), phosphorous (P), or potassium (K) deficiencies on the root systems of common crops. Root length and biomass were generally reduced, while root length per shoot biomass was enhanced under N and P deficiency. Root length decreased by 9% under N deficiency and by 14% under P deficiency, while root biomass was reduced by 7% in N-deficient and by 25% in Pdeficient soils. Root length per shoot biomass increased by 33% in N deficient and 51% in P deficient soils. The root-to-shoot ratio was often enhanced (44%) under N-poor conditions, but no consistent response of the root-to-shoot ratio to Pdeficiency was found. Only a few K-deficiency studies suited our approach and, in those cases, no differences inmorphological traitswere reported. We encountered the following drawbacks when performing this analysis: limited number of root traits investigated at field scale, differences in the timing and severity of nutrient deficiencies, missing data (e.g., soil nutrient status and time of stress), and the impact of other conditions in the field. Nevertheless, our analysis indicates that, in general, nutrient deficiencies increased the root-length-to-shoot-biomass ratios of crops, with impacts decreasing in the order deficient P > deficient N > deficient K. Our review resolved inconsistencies that were often found in the individual field experiments, and led to a better understanding of the physiological mechanisms underlying root plasticity in fields with low nutrient availability. [ABSTRACT FROM AUTHOR]

Background: In search for more sustainable crop production, the subsoil has recently come into focus as considerable reservoir of nutrients and water. Aims: Dimensions of subsoil phosphorus (P) reserves are yet largely unknown but crucial for identifying regions suitable to include subsoil into sustainable management strategies. Methods: We analyzed stocks of total and plant‐available (calcium acetate lactate‐extractable) P in 96 representative soil profiles of German arable land down to 1 m depth. Results: We found that the German arable soils stored, on average, 8 t ha−1 of total P, of which nearly 500 kg ha−1 were readily plant‐available. Notably, one third of plant‐available P was located below the plow layer and one fifth even at depths below 0.5 m. The depth gradients of plant‐available P stocks were affected more by major reference soil group than by texture. Generally, Chernozem but also Anthrosol, Gleysol and Fluvisol exhibited the largest P stocks in German cropland. The contribution of plant‐available P to total P stocks was larger in sandy and extremely acidic (pH < 4.5) soils compared with more fine‐grained and slightly acidic to alkaline soils, possibly because fertilization compensated for overall lower total P stocks at these sites. Generally, the more P was stored in topsoils, the more P was stored also in subsoils. Conclusions: A hypothetical crop utilization of 10% from plant‐available P stocks and 0.1% from total P stocks from shallow subsoil could compensate for P fertilization by ca. 8 kg ha−1, but the rate of plant‐available P replenishment in subsoil likely remains the crucial factor for the role of subsoil P stocks in crop nutrition. Generally, the large P reserves found in subsoil could act as an 'insurance' system for crops. [ABSTRACT FROM AUTHOR]

Rhizoliths, that is, roots fossilized by secondary carbonates, have been known for ages and are increasingly used for paleoenvironmental reconstructions. However, knowledge about their formation mechanisms remains limited. This study reports the mineralogical and chemical characterization of rhizoliths at different stages of mineralization and fossilization in the Late Pleistocene loess–paleosol sequence of Nussloch (SW Germany). Scanning electron microscopy coupled with elemental mapping and 13C solid‐state nuclear magnetic resonance were used to concomitantly characterize the mineral and organic matter of the rhizoliths. These joint analyses showed for the first time that large rhizoliths are not necessarily remains of single large roots but consist of numerous microrhizoliths as remains of fine roots, formed mainly by calcium carbonates with only low amounts of Mg and Si. They further revealed that the precipitation of secondary carbonates occurs not only around, but also within the plant root and that fossilization leads to the selective preservation of recalcitrant root biopolymers—lignin and suberin. The precipitation of secondary carbonates was observed to occur first around fine roots, the epidermis acting as a first barrier, and then within the root, within the cortex cells, and even sometimes around the phloem and within the xylem. This study suggests that the calcification of plant roots starts during the lifetime of the plant and continues after its death. This has to be systematically investigated to understand the stratigraphic context before using (micro)rhizoliths for paleoenvironmental reconstructions in terrestrial sediments. [ABSTRACT FROM AUTHOR]

• Deep soil was included in the assessment of different restoration approaches. • Soil organic carbon accrual in deep soil did not follow aboveground biomass growth. • Deep soil organic carbon stock in reforestation areas was lower than in adjacent cropland sites. Carbon (C) sequestration following land restoration is an efficient measure of climate change mitigation. However, most studies including the international "4 per 1000″ Initiative focus on topsoil C only. Here, we studied the response of deep soil C to different land restoration approaches. Samples were taken from rural sites in the Atlantic Forest Biome (Brazil), using a paired site design with triplicates of different 16-to-19-year-old restoration approaches of former arable land: reforestation, natural regeneration, and agroforestry sites. Adjacent arable land and a > 25-year-old secondary forest served as references. We determined aboveground and belowground C pools, including deep soil until 3 m depth. We did not find statistical differences among the three restoration methods for the C sequestration in the whole ecosystem. However, the C stock in the aboveground living biomass in the reforestation site was 85 ± 15 Mg ha−1, significantly exceeding the respective aboveground C in natural regeneration (40 ± 13 Mg ha−1) and agroforestry system (25 ± 5 Mg ha−1), respectively. This order, however, was reversed in soil, where reforestation caused a loss of soil organic carbon (SOC) by 27 Mg ha−1 below 40 cm depth, whereas SOC stocks in the agroforestry system and natural regeneration site increased by 41 and 25 Mg C/ha, respectively, compared to arable land. We thus conclude that deep soil carbon losses can negate aboveground carbon accrual after land restoration, which emphasizes the importance of including this pool in C sequestration studies. [ABSTRACT FROM AUTHOR]