Positive feedback between acidification and organic phosphate mineralization in the rhizosphere of maize (Zea mays L.)

Abstract

To test the hypothesis that rhizosphere acidification would enhance the hydrolyzation of organic phosphates by increasing phosphatase activity. A Petri dish experiment with sterile agar and a pot experiment with a low P soil were used. In the Petri dish experiment, roots of each plant were cultured in two compartments, each of which contained agar with one of three nitrogen combinations: NH 4 + /N0 (N0 = nitrogen free), NH 4 + /NO 3 -, and NO 3 -/N0. Phytin was supplied as the sole phosphorus (P) source to all compartments. In the pot experiment, the soil in each pot was treated with N0, KNO 3 , or (NH 4 ) 2 SO 4 ) together with 0 or 75 mg kg −1 phytin-P. Dry weight, P concentration, and P content of roots were highest in the NH 4 + compartments in the Petri dish experiment. In the pot experiment, dry weight, P concentration, and P content of both shoots and roots were higher with NH 4 + than with NO 3 -. NH 4 + treatments reduced rhizosphere pH, promoted the hydrolization of phytin, enhanced acid phosphatase activity in the rhizosphere, and increased phytin-P utilization relative to N0 and NO 3 -treatments. Phosphatase activity was negatively correlated with rhizosphere pH but was positively correlated with plant P content in both experiments. Rhizosphere acidification optimized the activity of acid phosphatase excreted by maize roots and promoted phytin mineralization. NH 4 + -induced acidification in the maize rhizosphere improved the growth of maize roots by improving P uptake from phytin; the improved growth, in turn, increased NH 4 + uptake and acidification.

Phytate utilization of maize mediated by different nitrogen forms in a plant–arbuscular mycorrhizal fungus–phosphate-solubilizing bacterium system

“…These results showed that the added phytin was utilized by maize, while the plant P uptake was not affected by different N forms. It was different from a previous study that plant P uptake of maize was increased by the application of NH 4 + compared to NO 3 − (Ding et al 2011). These different results suggested that the effect of pH regulation on plant P uptake in the sterile condition was not consistent with the plant-AM fungus-PSB system.…”

“…The soil in this system was supplied with different N forms (NH 4 + and NO 3 − ). Previous studies (Li et al 1991;Ding et al 2011) reported that the addition of different N forms can decrease or increase soil pH in the rhizosphere and hyphosphere (the volume of soil influenced by the AM fungal hyphae, see Jansa et al 2013). We hypothesized that the bioavailability of organic P (phytin) and phosphatase activity from the root and/or PSB in the rhizosphere and hyphosphere increase under low pH mediated by NH 4 + fertilizer.…”

“…Phosphatase activities can be regulated by changing soil pH conditions (George et al 2008). Similarly, a number of studies have shown that phosphatase activities in rhizosphere and hyphosphere soils can be enhanced by applying NH 4 + under sterile conditions (Ding et al 2011;Wang et al 2013). The present results showed that the phosphatase activity was increased when NH 4 + was added in the plant-AM fungus-PSB system.…”

“…Different forms of nitrogen (N) fertilizer such as NH 4 + and NO 3 − have distinctive influence on rhizosphere pH. Our previous study demonstrated that rhizosphere acidification mediated by NH 4 + can enhance the phytin utilization of maize under sterile conditions (Ding et al 2011). However, plants in agricultural ecosystems are associated with soil microbes, such as arbuscular mycorrhizal (AM) fungi and phosphate-solubilizing bacteria (PSB).…”

Higher diversity of ammonia/ammonium-oxidizing prokaryotes in constructed freshwater wetland than natural coastal marine wetland

“…Plants could change the rhizosphere pH by 1–2 units (Nye 1981). For example, plants release protons when they absorb NH 4 + , which could result in the reduction of pH (Ding et al 2011). Lu et al (2007) found that mangrove roots could release low-molecular-weight organic acids that resulted in the reduction of pH by 0.2–0.5 units in the rhizosphere.…”