Background and Aims Root hairs are single-cell extensions of the epidermis that face into the soil and increase the root–soil contact surface. Root hairs enlarge the rhizosphere radially and are very important for taking up water and sparingly soluble nutrients, such as the poorly soil-mobile phosphate. In order to quantify the importance of root hairs for maize, a mutant and the corresponding wild type were compared. Methods The rth2 maize mutant with very short root hairs was assayed for growth and phosphorus (P) acquisition in a slightly alkaline soil with low P and limited water supply in the absence of mycorrhization and with ample P supply. Key Results Root and shoot growth was additively impaired under P deficiency and drought. Internal P concentrations declined with reduced water and P supply, whereas micronutrients (iron, zinc) were little affected. The very short root hairs in rth2 did not affect internal P concentrations, but the P content of juvenile plants was halved under combined stress. The rth2 plants had more fine roots and increased specific root length, but P mobilization traits (root organic carbon and phosphatase exudation) differed little. Conclusions The results confirm the importance of root hairs for maize P uptake and content, but not for internal P concentrations. Furthermore, the performance of root hair mutants may be biased by secondary effects, such as altered root growth.

Background and Aims An increase in the root hair length and density, as well as the development of arbuscular mycorrhiza symbiosis, are two alternative strategies of most plants to increase the root-soil surface area under phosphorus (P) deficiency. Across many plant species, root hair length and mycorrhization density are inversely correlated. Root architectures, rooting density and physiology also differ between species. This study aims to understand the relationship among root hairs, arbuscular mycorrhizal fungi (AMF) colonisation, plant growth, P acquisition, and mycorrhizal-specific Pi transporter gene expression of maize Methods Using nearly isogenic maize lines, the B73 wild type and the rth3 root hairless mutant, we quantified the effect of root hairs and AMF infection in a calcareous soil under P-deficiency through a combined analysis of morphological, physiological and molecular factors Key Results Wild type root hairs extended the rhizosphere for acid phosphatase activity by 0.5 mm compared to the rth3 hairless mutant, as measured by in situ zymography. Total root length of the wild type was longer than rth3 under P-deficiency. Higher AMF colonisation and mycorrhiza-induced phosphate transporter gene expression were identified in the mutant under P-deficiency, but plant growth and P acquisition were similar between mutant and the wild type. Ultimately, the mycorrhizal dependency of maize was 33% higher than the root hair dependency Conclusions The results identified a larger mycorrhizal dependency than root hair dependency under P-deficiency in maize. Root hairs and AMF inoculation are two alternative ways to increase Pi acquisition under P-deficiency, but these two strategies compete with each other

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Improved management and breeding increased maize (Zea mays L.) yields over the last century, but nutritional efficiency was usually not the focus. This study investigates whether old and recently released flint and dent maize seedlings vary in the phosphorus (P) acquisition and utilization. P use efficiency (PUE) and related traits were measured and compared at two P levels in a calcareous soil. PUE and P acquisition efficiency (PAE) from founder flints to elite flints declined over the last decades. This was associated with smaller root systems, reduced ability to exploit external P, decreased rhizosphere pH and shorter root hairs in low P. Comparing flints with doubled haploid landraces (DH_LR), old and elite dents and hybrids revealed that dents started to acquire exogenous P earlier and had improved PUE. Most DH_LRs had similar PUE as elite flints. When evaluating root traits associated with P efficiency, seed P was also critical, and it is important to stack different root traits to optimize PUE, P utilization efficiency (PUtE) and PAE in breeding programmes. The root hair length, the ability to acidify the rhizosphere and the root diameter in flint and dent pools may be utilized to improve P use in maize germplasm.