Exudation of organic acid anions by tropical grasses in response to low phosphorus availability

Abstract

It has been suggested that some tropical grasses can acquire phosphorus (P) from hematite and gypsite by exuding organic acid anions (OAs). However, it remains to be determined exactly which OAs could be involved in each case. The objective of this study was to verify the exudation OAs by ruzigrass (Urochloa ruziziensis), palisade grass (U. brizantha), and Guinea grass (Megathyrsus maximus) as a response to P deficiency. The grasses were grown in leachate columns with adequate and deficient P nutrient solutions. The concentration of OAs in the leacheate and root surface, as well as shoot and root dry matter, and P uptake were determined. Citrate, isocitrate, and malate concentration in leachates and root surfaces increased with P starvation, mainly for the Urochloa grasses. Oxalate exudation was similar for the grasses under adequate P supply, but was lower in Guinea grass under P starvation. Palisade grass showed a higher concentration of total OAs in the root surface than the other species due to a great production of oxalate and isocitrate. Palisade grass showed greater dry matter yields regardless of P deficiency, and Guinea grass always had the higher shoot:root ratio. Urochloa grasses have a higher capacity to cope with low P availability by exuding OAs along with a lower shoot:root ratio than Guinea grass.

Potassium Bioavailability in a Tropical Kaolinitic Soil

“…Another uncertainty in assessing the actual importance of microbes in soil K solubilization is the survival of these microorganisms in unfavorable environments [50]. However, organic acid exudates may have had a considerable effect in the present experiment, since ruzigrass roots have been shown to release significant amounts of organic acids such as citrate, isocitrate, and oxalate [53]. Therefore, we infer that the ruzigrass DM yields without K fertilizer were, proportionally, less affected by successive crops than those of maize and soybean (Figure 1B) due to exudation of organic acids that promoted soil K release.…”

Differential metabolic rearrangements in the roots and leaves of Cicer arietinum caused by single or double nitrate and/or phosphate deficiencies

“…The accumulation of OAs, such as citramalate, citrate, α‐ketoglutarate, malate, malonate, succinate and isocitrate, increased in the roots but not in the leaves (with the exception α‐ketoglutarate whose level increased) of chickpea plants in response to Pi deficiency (Figures 4, 7 and S8; Table S1). The exudation of these OAs, which could contribute to Pi‐solubilization, into the rhizosphere and apoplastic spaces of the roots is a highly effective strategy for improving Pi acquisition efficiency (Almeida et al., 2020; Pant et al., 2015; Pueyo et al., 2021). Interestingly, pyruvate, which is the end‐product of glycolysis and is involved in adjusting the flow of glycolytic metabolites into the TCA cycle (Fataftah et al., 2018), showed decreased levels in the roots of chickpea plants under Pi deficiency (Figures 4 and S8; Table S1), suggesting that it might have been transformed to acetyl‐CoA at a higher rate under such stress conditions for entering into the TCA cycle.…”

Transformation of phosphorus forms and its regulation on phosphorus availability across differently degraded marsh soils

“…For Ca-P forms, a remarkable change was observed in the concentration and proportion of available Ca 2 -P increased under marsh degradation, whereas those of unavailable Ca 10 -P decreased (Figures 3a-d and 4a-b). This is because marsh desiccation accompanied by the transition of the plant community or overgrazing may enhance the activity and/or quantity of phosphate-dissolving bacteria, such as Pseudomonas , Bacillus, and Erwini (Liu et al, 2015;Susilowati et al, 2019) and increase the organic acids from plants, microbes, and/or livestock excreta (Almeida et al, 2020;Gyaneshwar et al, 2002;Miao et al, 2013;Nuryana et al, 2019). Improved phosphate-dissolving bacteria and organic acids can further stimulate the transformation of Ca 10 -P to other labile inorganic P forms such as Ca 2 -P, Ca 8 -P, and Al-P (Almeida et al, 2020;Susilowati et al, 2019).…”

“…This is because marsh desiccation accompanied by the transition of the plant community or overgrazing may enhance the activity and/or quantity of phosphate-dissolving bacteria, such as Pseudomonas , Bacillus, and Erwini (Liu et al, 2015;Susilowati et al, 2019) and increase the organic acids from plants, microbes, and/or livestock excreta (Almeida et al, 2020;Gyaneshwar et al, 2002;Miao et al, 2013;Nuryana et al, 2019). Improved phosphate-dissolving bacteria and organic acids can further stimulate the transformation of Ca 10 -P to other labile inorganic P forms such as Ca 2 -P, Ca 8 -P, and Al-P (Almeida et al, 2020;Susilowati et al, 2019). Similarly, Jamil et al (2016) revealed that Calcisols with greater biological activity under sugarcane crop cover had a high concentration of Ca 2 -P in the estuary plains of Pakistan.…”

“…Meanwhile, non-occluded P is easy to be mobilized into labile P (e.g. Ca 2 -P) due to the activation of organic acids and phosphate-dissolving bacteria (Almeida et al, 2020;Susilowati et al, 2019), and indirectly regulate available P (Hou et al, 2016). Hence, soil non-occluded P was the second P form of regulating available P (Figures 6 a-b).…”