| Rice (Oryza sativa L) is the main foodstuffs in south China. However, conventional rice cultivation consumes plentiful of water and flooded paddy field is a main methane emission source. It is important to seek an alternative rice cultivation style which could keep high rice yield but lower water consumption and methane emission. Thus, many experiments were conducted to investigate the relationship between the water management and rice yield and try to explore new rice cultivation style which could keep high rice yield but low water consumption in rice cultivation. The results suggested that non-flooded with straw mulching could reduce the water consumption, and keep high crop yield or even improve the crop yield. Unfortunately, straw application could increase CH4emission largely in paddy field in previous studies. However, mid-season drainage or intermittent drainage management in paddy field could reduce the methane emission significantly. So the methane emission from non-flooded with straw mulching paddy field may much less than the flooded with straw mulching paddy field. However, there was no information about the methane emission from non-flooded with straw mulching paddy field.No-till is widely used as conservation tillage practice in dry land farming systems, but there were fewer reports in paddy field. The recent studies showed that no-till could reduce methane emission significantly, but the mechanism was not clearly.Methanogens, which belong to the Euruarchaeota in archaeal, catalyze the last step in the anoxic degradation of organic matter for the formation of CH4. So, it is important to reveal the ecology of methanogenic archaeal in paddy field soil.Thus, a water management field experiment was conducted in Yujiang County, Jiangxi Province in the southeast of China (N28°15, E116°55). The treatments included conventional flooded cultivation (F), non-flooded cultivation without straw mulching (NF-ZM) and with straw mulching (NF-M). We investigated the methane emission pattern in non-flooded with and without rice straw mulching paddy field. We also discussed the integrated effects of non-flooded with straw mulching rice cultivation style by investigating the rice yield, biomass accumulation, water use efficiency and soil nutrient balance.A tillage practice field experiment with late rice no-till was conducted in a rice-rice crop system. We investigated the methane emission pattern in a double-rice cropping system under the contrasting tillage systems. Meanwhile, we investigated the soil organic carbon and dissolved organic carbon content and soil bulk density in order to validate whether the dissolved organic carbon content reduced under no-tillage as speculated in previous studies.We also studied the methanogens community structure by PCR-DGGE and the population dynamic of specific species methanogens by fluorescence in situ hybridization (FISH) in different rice growing period under double rice cropping system and different field managements’paddy field.The main results were followed:First, the methane emission pattern and mechanisms in double rice cropping system under conventional and low tillage1. The seasonal amount methane emission in the early rice growing period of T-T and T-NT was9.28g-m-2and9.51g·m-2, respectively. The T-NT didn’t increase methane emission significantly after tillage in no-tillage field. The maximum emission rate of T-T and T-NT was18.52mg·m-2·h-1and7.32mg·m-2·h-1, respectively in late rice. The methane emission rate of T-NT was significant lower than T-T in the late rice growing period analysis by paired-sample T test. The seasonal amount methane emission of T-T and T-NT was7.78g·m-2and3.04g·m-2, respectively in late rice. The T-NT leads to a61%reduction of the total methane emission compared to the T-T treatment in late rice.2. The no-till increased the surface soil organic matter content, but not significantly. But the increased soil organic matter reduced with the tillage and rice growth. No-till reduced soil active organic carbon content, especially the dissolved organic carbon (DOC). No-till significantly also increased the surface soil (0-10cm) bulk density. Meanwhile, the root parameters under no-till were lower than conventional tillage, and the differences were significant in last half rice growing period. The lower methane emission flux under no-till may due to the increased soil bulk density, lower dissolved organic carbon content, the lower number of methanogens and the restriction of root growth. 3. Compared to early rice growing period, the seasonal amount methane emission in late rice of T-T and T-NT reduced16%and68%, respectively. This may be due to the five months’fallow after last season late rice and long time rain before early rice transplanting.Second, the methane emission pattern in non-flooded with straw mulching paddy field and the perspective of non-flooded with straw mulching rice cultivation1. The peak methane flux appeared approximately2-3weeks after transplanting in all the treatments. The seasonal amount methane emission of the conventional flooded cultivation (F), non-flooded cultivation without straw mulching (NF-ZM) and with straw mulching (NF-M) was7.78g·m-2,4.23g·m-2and11.12g·m-2, respectively. In comparison with F, NF-M increased seasonal CH4emissions by43%, but NF-ZM reduced seasonal CH4emissions by46%. For the non-flooded treatments, the seasonal amount methane emissions of NF-M were2.62times higher than that of NF-ZM in this study.2. The water content of10cm depth soil of NF-M was significant higher than that of NF-ZM in this study. Straw mulching can debase the surface soil temperature, which can reduce the damage of hot temperature on plant growth in summer. In comparison with F, the NF-M increased the soil organic matter content, soil total N and available K content significantly. The soil AH-N and Olsen-P of NF-M were also higher than F, but not significantly. All the soil nutrients investigated in this study of NF-M were significant higher than that of NF-ZM. These indicated that straw mulching could maintain and improve soil quality.3. The yield of the NF-M, F and NF-ZM was9.60t·ha-1,9.75t-ha’and8.15t·ha-1respectively. This indicated that straw mulching could improve rice growth and maintain rice yield under non-flooded condition. The straw mulching could mitigate the water stress under non-flooded paddy field, there were no significant differences in rice growth character compared to F. The biomasses of NF-M were significantly higher than NF-ZM and F.4. The straw mulching non-flooded cultivation increased the methane emission, but this cultivation style could get an almost equivalent yield with the conventional flooded cultivation style besides reducing water consumption significantly, improving soil quality and maintaining soil productivity. Furthermore, it avoided the greenhouse gas emission and atmosphere pollution during the straw management by other methods. Though non-flooded without straw mulching reduced methane emission significantly, it also reduced rice yield significantly. Thus, non-flooded with straw mulching rice cultivation style may be an alternative cultivation style in water shortage area.Third, The dynamic of the community structure and population of methanogens under different field management paddy fieldsI The dynamic of the community structure and population of methanogens in the double rice cropping system of south China1. It is proper to use primer1106F-gc-1378R for PCR amplification of16S rRNA gene fragments of methanogenic archaeal for community structure analysis. The denaturant gradient range of the gel was from32to62%. The fluorescence in situ hybridization (FISH) is a feasible method to investigate the population of methanogens.2. The community structure of methanogens changed greatly in different rice growing period in both early and late rice. There were several main species in all the growing period. The methanogens richness, diversity index and evenness of early rice were21.8,2.86and0.934respectively, and the parameters of late rice were18.5,2.66and0.916respectively. The community diversity of methanogens in early rice was higher than late rice.3. The number of different methanogens species changed greatly in different rice growing period, the key methanogens varied in different rice growing period. The peak number of methanogens of early rice was1.15×10/In/g dry soil, and the lowest number was6.28×106In/g dry soil. The peak number of methanogens of late rice was7.75×106In/g dry soil. The peak number all appeared20days after transplanting. The total number of methanogens reached highest in tillering period in both early and late rice, and significantly higher than other rice growing period. There was no significantly difference in different rice growing period except tillering period.4. The key physiological group of methanogens genera was using H2/CO2and formate, the followed was using acetate and then mixture substrate.II the dynamic of the community structure and population of methanogens in a double rice cropping system under conventional and low tillage1. The community structure of methanogens changed greatly in different rice growing period under no-till in both early and late rice. There were several main species in all the growing period under no-till. The methanogens richness, diversity index and evenness under no-till in early rice were19,2.58and0.887respectively, and the parameters of late rice were21,2.78and0.884respectively. These indicated that the community structure diversity of early rice was lower than that of late rice under no-till.2. The population of different methanogens also changed greatly in different rice growing period under no-till in both early and late rice. In early rice, the total number of methanogens increased after rice transplanting and reached highest20days after rice transplanting at the density of1.14×107Ind·g-1dry soil. Thereafter, the number decreased slowly and reached lowest at the harvest time at the density of4.93×106Ind·g-1dry soil. In late rice, the the total number of methanogens also increased after rice transplanting and reached highest20days after rice transplanting at the density of6.72×106Ind·g-1dry soil. The total number of methanogens in early rice was higher than that of late rice. The peak number all appeared20days after transplanting as conventional tillage paddy field. There were no significant differences between the different rice growing periods except tillering period (about20days after transplanting).3. The community strcture diversity and population under no-till was lower than conventional tillage paddy field in early rice. The community strcture diversity under no-till was higher than that of conventional tillage paddy field in late rice, but the number was also lower than conventional tillage paddy field.4. The key physiological group of methanogens genera was using H2/CO2and formate under no-till in both early and late rice. The followed was using acetate and mixture substrate, and there was no significant difference between them.HI the dynamic of the community structure and population of methanogens under non-flooded with and without straw mulching paddy field1. The community structure of methanogens changed greatly in different rice growing period under non-flooded with straw mulching or without straw mulching. There were also several main species in all the growing period under non-flooded condition. The methanogens richness, diversity index and evenness under NF-M were25,2.89and0.950respectively, and the parameters under NF-ZM were21,2.79and0.916respectively. These indicated that the community structure diversity under NF-ZM was lower than that of NF-M.2. The significant difference of the number of methanogens under NF-ZM and NF-M only appeared21days after transplanting. The total number of methanogens under NF-M was significantly higher than that under NF-ZM according the whole rice growing season.3. In comparison with conventional flooded paddy field, the community structure diverisity and population under non-flooded with or without straw mulching were much lower. But the peak number of the three treatments all appeared21days after rice transplanting. The maximum values of diversity index of non-flooded fields were significantly late than conventional flooded one.4. The key physiological group of methanogens genera was using H2/CO2and formate under both of NF-ZM and NF-M, the followed was using mixture substrate and then acetate.IV the relationship between methane emission and the community structure and population of methanogens in paddy fieldThe methane emission rate was significant positive correation with the number of methanogens under different field managements’ paddy fields, but the methane emission rate was negative correlation with the community structure of methanogens. This indicated that methane emission rate was mainly affected by the number of methanogens rather than the community structure of methanogens in paddy field. |
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