An Investigation Of The Effect Of Phosphine On Physiological And Biochemical Responses And Phosphorus Availability Of Rice Seedlings In Paddy Fields

Phosphorus (P), one of the major mineral nutrients of plants, is quite important to thebiogeochemical cycle. The phosphorus in soils significantly influences the development andproductivity of plants and has been regarded as a common limiting nutrient for plant growth.Phosphorus availability has been a key factor that limits the development of agriculture inChina. Phosphine (PH3), a highly toxic reducing gas, is a ubiquitous trace gas in theatmosphere and a significant constituent of the phosphorus biogeochemistry cycle. Althoughthe precise source and distribution of phosphine in the natural environment remains unclear,paddy fields are major sources responsible for the production and emission of phosphine tothe atmosphere. In addition, the concentration of phosphine in paddy fields is relatively higherthan that in the atmosphere. As an important pathway for phosphorus transport, PH3in thepaddy fields might both positively and negatively affect crop growth. As a toxic reducing gas,phosphine can rapidly inhibit aerobic respiration in many insects and mammals. On the otherside, PH3is an intermediate of soil anaerobic processes, and its subsequent oxidation tophosphoric acid is actually an activation process of soil phosphorus that was originallyunavailable to plants. Some researchers have recently hypothesized that if phosphine can bepartially or totally converted into plant-absorbable phosphate, phosphorus availability willincrease, thus significantly improving crop growth.Simulated experiments were conducted to explore the effect of phosphine on thephysiological and biochemical responses and phosphorus availability of rice seedlings.Antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase(CAT); and lipid peroxidation measured through via malondialdehyde (MDA) weredetermined as indicators of the physiological and biochemical responses of the rice seedlingsto phosphine exposure. To explore the effect of high concentrations of phosphine on the Pavailability of crops in paddy fields, the contents of MBP, total phosphorus (TP), inorganicphosphorus (IP), and organic phosphorus (OP) in soil samples from rice cultivation, the Pcontent in the leaves of seedlings and the root system activity were determined under varyingphosphine concentrations.The exposure lowered the CAT and SOD activities and increased POD activity in thetreated rice seeds compared with controls. The MDA content exhibited a slow increase trendwith the increase of phosphine concentration. These results suggest that phosphine exposurecaused oxidative stress in the seeds. The antioxidant enzymes could play a pivotal role againstoxidative injury. Increasing concentrations of phosphine treatment enhanced the activity of SOD, POD,and CAT. In addition, the MDA content increased with increasing concentrations ofphosphine. These results suggested that antioxidant enzymes played important roles inprotecting rice seedlings from ROS damage. Moreover, rice seedlings were able to cope withthe oxidative stress induced by low concentrations of phosphine via an increase in antioxidantenzymatic activities. However, oxidative stress may not fully be prevented when the plantswere exposed to high concentrations of phosphine.Phosphine treatment enhanced the contents of MBP, TP, IP in soil samples, and as wellas the root system activity of the rice seedlings with the increasing of phosphineconcentrations. This study showed that higher concentrations of phosphine promoted thecontents of MBP in soil. The content of P in rice seedlings and the activity of root systemstimulated with the increasing of phosphine concentrations in the study. Thus, the higherconcentrations of phosphine in paddy fields might have a positive effect on P availability inrice plants.