Study On Phosphine Distribution In Paddy Field And The Effects Of Environmental Factors

Phosphorus is a restrictive factor in wetlands, and the study of phosphorusbiogeochemical cycle is one of the core issues in wetlands environmental research. As agaseous carrier for P element, phosphine is a crucial part in phosphorus cycle. And paddyfields are an important kind of constructed wetlands. Therefore, in order to known thephosphorus biogeochemical cycle in wetlands, there is a great need to known the role whichphosphine plays in this cycle. However, there is limited research on this field, especially theresearch for the distribution and the transformation of phosphine in paddy fields.In order to understand the character of phosphine distribution, the process of phosphineemission, the mechanism of phosphine transformation, and the controlling factors ofphosphine migration, the research on the distribution of phosphine and the relation betweenphosphine and related environmental factors should be made. And these works aresignificant for studying the role of phosphine in phosphorus cycle, proposing the scientificand reasonable phosphine production mechanism, and improving the theory of phosphorusbiogeochemical cycle in wetlands.In the present study, typical paddy fields in South China were taken as the researchobject, and method of cold trap enrichment before injection to capillary and GC/FID wasalso employed. The process and pathway free gas phosphine emission were studied as wellas the vertical distribution of matrix-bone phosphine (MBP) in the complete rice growingstages. Furthermore, the key factors controlling the characters of MBP distribution was alsodiscussed. The main results of the present work are as follows:1. An analysis and determination system for trace phosphine in environment was madeusing a gas chromatography-flame ionization detector coupled with two successive capillarycryo-traps for enrichment. The optimized parameters for the system were: enrichment temperature-90oC, carrier gas flow1.5mL/min, column oven temperature90oC, detectortemperature220oC. The detection limit of phosphine was0.0417pg and the RSD was4.289%. The main mechanism for the cold trap enrichment was the enrichment capillary’sabsorption to phosphine, but not cryogenic liquefaction enrichment accepted by formerresearchers.2. The present work systematically studied the temporal and spatial distribution and theemission of gas free phosphine in paddy fields. It can be figured out that the phosphineambient levels and the emission fluxes shared quit similar changing trend, through thewhole rice growth period. Two peaks emerged in tillering stage and end of rice growthstages (flowering stage and ripening stage), however the middle rice growth had a relativelylow value. As the results shown, the maximum value of phosphine ambient concentration is24.83±6.529ng m-3and happened in the rice growing stage of flowering, the minimumvalue of phosphine ambient concentration is2.368±0.6060ng m-3and happened in the ricegrowing stage of harvest, and the average is14.25±4.547ng m-3; while the maximumvalue of phosphine emission fluxes is22.54±3.897ng m-2h-1and happened in the ricegrowing stage of tillering, the minimum value of phosphine emission fluxes is7.64±4.83ng m-2h-1and happened in the rice growing stage of harvest, and the average is14.17±4.977ng m-2h-1.3. This research found for the first time that the rice plant could be one of mainpathways for phosphine in paddy fields. The maximum value of the contribution forphosphine emission fluxes through rice plant is73.73%and happened in the rice growingstage of ripening, and the average is43.00%. There is an obvious and positive relationshipbetween the contribution for phosphine emission fluxes through rice plant and the growthstages of rice. And the rice plant’s capacity of transporting phosphine decanted when thepaddy soils was flooding.4. The determination of MBP distribution in paddy soils shown that the MBP concentration is a maximum of269.7ng kg-1at the ripening stage in the layer at5-10cm, aminimum of2.314ng kg-1at the transporting stage in the layer at20-25cm, and an averageof111.6ng kg-1. The character of MBP distribution was impacted by such environmentalfactors as the growth stages, the water cover over the paddy soils and the soil temperature.5. Pearson correlation analysis and stepwise multiple regression analysis showed that Ts,ACP and TP, among eleven considered environmental factors, were the principalenvironmental factors which affected the MBP in paddy soils. This indicated that theactivities of microbes involved in the P cycles may determine the MBP behavior in paddysoils.