The carboxylate composition of rhizosheath and root exudates from twelve species of grassland and crop legumes with special reference to the occurrence of citramalate

Abstract

Low-molecular-weight organic anions (carboxylates) influence rhizosphere processes and may enhance plant phosphorus acquisition. We examined the root exudate profile of a range of pasture and grain legumes and focused on the little-investigated carboxylate, citramalate. Methods Twelve species of pasture legumes and herbs, including four Lotus spp. and two crop legumes, Cicer arietinum and Lupinus albus, were grown in a glasshouse for six weeks. The composition and amounts of carboxylates were measured in rhizosheath soil as well as in root exudates from roots washed free of their rhizosheath. Results Citrate and malate were found in the rhizosheath of all species. However, citramalate was present in the rhizosheath of only Lotus species (10-82% of total exuded carboxylates). Cicer arietinum had the largest amount of carboxylates in its rhizosheath and fastest rate of carboxylate exudation into the trap solution. Conclusions Citrate and malate were found in the rhizosheath of all species in this study, but citramalate was only found in the root exudates and rhizosheath of Lotus spp. Further investigation into the role of citramalate in Lotus spp. is merited.

Role of Organic Anions and Phosphatase Enzymes in Phosphorus Acquisition in the Rhizospheres of Legumes and Grasses Grown in a Low Phosphorus Pasture Soil

“…One drop of concentrated orthophosphoric acid was added to each sample, which were then stored at −20 °C until analysis by HPLC. The remaining rhizosphere extract was then filtered through a Whatman number 1 filter paper and oven-dried at 70 °C for three days to determine the rhizosphere soil dry weight [ 45 , 122 ]. Organic anions were determined using a Prevail TM organic acid column (300 × 4.6 mm, 5 µm particle size, Grace Davison Discovery Sciences) with 25 mM KH 2 PO 4 (pH: 2,35) as a mobile phase, 0.6 mL min −1 as the flow rate at 50 °C, with an injection volume of 30 µl and a detection wavelength of 210 nm.…”

Rhizobium-Linked Nutritional and Phytochemical Changes Under Multitrophic Functional Contexts in Sustainable Food Systems

“…The leguminous rhizosphere is characterized by root exudation of organic compounds, enzymes, and ion exchange (Kidd et al, 2018;Preece and Peñuelas, 2020), supporting complex food webs of heterotrophic biota from various taxa (Bonkowski et al, 2009; De-la-Peña and Loyola-Vargas, 2014; Taylor et al, 2020) ( Table 2). Rhizobium has to survive both in the rhizosphere and host tissues where they still encounter diverse endophytic biota inside the root nodule microbiome (Taha, 1993;Omar and Abd-Alla, 2000;Sharaf et al, 2019;Taylor et al, 2020).…”

Vellozioid roots allow for habitat specialization among rock‐ and soil‐dwelling Velloziaceae in campos rupestres

“…Dauciform roots, sand‐binding roots forming rhizosheaths (Abrahão, Costa, Lambers, et al, ; Abrahão, Lambers, Sawaya, Mazzafera, & Oliveira, ; Oliveira et al, ) and the recently described vellozioid roots (Teodoro et al, ) are prevalent in campos rupestres . Rhizosheaths are soil sheaths strongly bound to the roots, associated with long root hairs that increase root–soil contact and mucilage release (Brown, George, Neugebauer, & White, ; North & Nobel, ; Pang, Ryan, Siddique, & Simpson, ), which enhances the uptake of poorly mobile P (Brown et al, ; Kidd et al, ; McCully, ; Zhang et al, ). Vellozioid roots (Figure c) were described in rock‐dwelling Velloziaceae, which is an ubiquitous plant family in campos rupestres ; they are capable of dissolving the quartzite rocks, releasing strongly bound P through carboxylate release and contributing to biological weathering of rocks (Porder, ; Teodoro et al, ).…”