Response of rice resistance based on the validation of rice blast to elevated CO2 concentration and temperature.

Rice (Oryza sativa) resistance is its ability to resist various stresses, the changes of which have important impacts on O. sativa yield security. However, the responses of O. sativa stress resistance to elevated atmospheric CO2 concentration and temperature are poorly understood. We conducted a field open top-chamber experiment with O. sativa (Nanjing 9108 and Jinxiangyu I) based on the CO2 and temperature automatic control platform. The experimental treatments included ambient CO2 concentration and temperature treatment (CK, control), elevated CO2 concentration treatment (C, CO2 concentration increase of 200 µmol·mol-1 above CK), elevated temperature treatment (T, temperature increase of 2 ℃ above CK) and elevated CO2 concentration and temperature (CT, CO2 concentration increase of 200 µmol·mol-1 and temperature increase of 2 ℃ above CK). At the critical growth stages of O. sativa, we measured superoxide dismutase activity, silica content, total flavanol content, malondialdehyde content, soluble sugar content, proline content, and soluble protein content by cutting the uppermost functional leaves. We obtained the rice stress resistance index (RSRI) by principal component analysis to analyze the differences in the composition of stress resistance indicators under different treatments. Considering the disease resistance of O. sativa, the spike neck blast disease was counted to verify the expression level of RSRI for O. sativa stress resistance at maturity stage. Results showed that at the elongation-booting stage, C and CT treatments significantly reduced the RSRI of Jinxiangyu I by 36.5% and 41.1%, respectively, compared with CK. T treatment significantly decreased the RSRI of the two varieties by 44.9% and 33.8%, respectively. The RSRI explained 71.9%-74.3% of the variation in the spike neck blast disease. Overall, the stress resistance of two O. sativa varieties were adversely affected by elevated temperature at the elongation-booting stage. There was an interactive effect of CO2 concentration and temperature on O. sativa stress resistance. Compared with Nanjing 9108, the stress resistance of Jinxiangyu I was more sensitive to elevated CO2 concentration.

Effect of gradual increase of atmospheric CO2 concentration on nitrification potential and communities of ammonia oxidizers in paddy fields.

Currently, the influence of elevated atmospheric CO2 concentration (eCO2) on ammonia oxidation to nitrite, the rate-limiting step of nitrification in paddy soil, is poorly known. Previous studies that simulate the effect of eCO2 on nitrification are primarily based on an abrupt increase of atmospheric CO2 concentration. However, paddy ecosystems are experiencing a gradual increase of CO2 concentration. To better understand how the nitrification potential, abundance and communities of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) respond to eCO2 in paddy ecosystems, a field experiment was conducted using the following two treatments: a gradual increase of CO2 (EC, increase of 40 ppm per year until 200 ppm above ambient) and ambient CO2 (CK). The results demonstrated that the EC treatment significantly (P < 0.05) stimulated the soil potential nitrification rate (PNR) at the jointing and milky stages, which increased by 127.83% and 27.35%, respectively, compared with CK. Furthermore, the EC treatment significantly (P < 0.05) stimulated the AOA and AOB abundance by 56.60% and 133.84%, respectively, at the jointing stage. Correlation analysis showed that the PNR correlated well with the abundance of AOB (R2 = 0.7389, P < 0.001). In addition, the EC treatment significantly (P < 0.05) altered the community structure of AOB, while it had little effect on that of AOA. A significant difference in the proportion of Nitrosospira was observed between CO2 treatments. In conclusion, the gradual increase of CO2 positively influenced the PNR and abundance of ammonia oxidizers, and AOB could be more important than AOA in nitrification under eCO2.

[Effect of gradual increase of atmospheric CO2 concentration on nitrate-dependent anaerobic methane oxidation in paddy soils]. / 大气CO2æµ“åº¦ç¼“å¢žå¯¹ç¨»ç”°ç¡é ¸ç›åž‹ç”²çƒ·åŽŒæ°§æ°§åŒ–è¿‡ç¨‹çš„å½±å“.

Nitrate-dependent anaerobic oxidation of methane (AOM) is a new pathway to reduce methane emissions from paddy ecosystems. The elevated atmospheric CO2 concentration can affect methane emissions from paddy ecosystems, but its impact on the process of nitrate-dependent AOM is poorly known. Based on the automatic CO2 control platform with open top chambers and the 13CH4 stable isotope experiments, the responses of the activity of nitrate-dependent AOM, abundance and community composition of Candidatus Methanoperedens nitroreducens (M. nitroreducens)-like archaea to the gradual increase of CO2 concentration were investigated in paddy fields. We set up two CO2 concentration treatments, including an ambient CO2 and a gradual increase of CO2(increase of 40 µL·L-1 per year above ambient CO2 concentration until 160 µL·L-1). The results showed the nitrate-dependent AOM rate of 0.7-11.3 nmol CO2·g-1·d-1 in the studied paddy fields, and quantitative PCR showed the abundance of M. nitroreducens-like archaeal mcrA genes of 2.2×106-8.5×106 copies·g-1. Compared to the ambient CO2 treatment, the slow elevated CO2 treatment enhanced the nitrate-dependent AOM rate and stimulated the abundance of M. nitroreducens-like archaea, particularly in 5-10 cm soil layer. The gradual increased CO2 concentration treatment did not change the community composition of M. nitroreducens-like archaea, but significantly decreased their diversity. The soil organic carbon content was an important factor influencing the nitrate-dependent AOM process. Overall, our results showed that the gradual increase of CO2 concentration could promote the nitrate-dependent AOM, suggesting its positive role in mitigating methane emissions from paddy ecosystems under future climate change.

Response of nitrite-dependent anaerobic methanotrophs to elevated atmospheric CO2 concentration in paddy fields.

Nitrite-dependent anaerobic methane oxidation (n-damo) catalyzed by Candidatus Methylomirabilis oxyfera (M. oxyfera)-like bacteria is a new pathway for the regulation of methane emissions from paddy fields. Elevated atmospheric CO2 concentrations (e[CO2]) can indirectly affect the structure and function of microbial communities. However, the response of M. oxyfera-like bacteria to e[CO2] is currently unknown. Here, we investigated the effect of e[CO2] (ambient CO2 + 200 ppm) on community composition, abundance, and activity of M. oxyfera-like bacteria at different depths (0-5, 5-10, and 10-20 cm) in paddy fields across multiple rice growth stages (tillering, jointing, and flowering). High-throughput sequencing showed that e[CO2] had no significant effect on the community composition of M. oxyfera-like bacteria. However, quantitative PCR suggested that the 16S rRNA gene abundance of M. oxyfera-like bacteria increased significantly in soil under e[CO2], particularly at the tillering stage. Furthermore, 13CH4 tracer experiments showed potential n-damo activity of 0.31-8.91 nmol CO2 g-1 (dry soil) d-1. E[CO2] significantly stimulated n-damo activity, especially at the jointing and flowering stages. The n-damo activity and abundance of M. oxyfera-like bacteria increased by an average of 90.9% and 50.0%, respectively, under e[CO2]. Correlation analysis showed that the increase in soil dissolved organic carbon content caused by e[CO2] had significant effects on the activity and abundance of M. oxyfera-like bacteria. Overall, this study provides the first evidence for a positive response of M. oxyfera-like bacteria to e[CO2], which may help reduce methane emissions from paddy fields under future climate change conditions.

Different responses of ammonia-oxidizing archaea and bacteria in paddy soils to elevated CO2 concentration.

The elevated atmospheric CO2 concentration is well known to have an important effect on soil nutrient cycling. Ammonia oxidation, mediated by ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), is the rate-limiting step in soil nitrification, which controls the availability of two key soil nutrients (ammonium and nitrate) for crops. Until now, how the AOA and AOB communities in paddy soils respond to elevated CO2 remains largely unknown. Here, we examined the communities of AOA and AOB and nitrification potential at both surface (0-5 cm) and subsurface (5-10 cm) soil layers of paddy fields under three different CO2 treatments, including CK (ambient CO2 concentration), LT (CK + 160 ppm of CO2) and HT (CK + 200 ppm of CO2). The elevated CO2 was found to have a greater impact on the community structure of AOB than that of AOA in surface soils as revealed by high-throughput sequencing of their amoA genes. However, no obvious variation of AOA or AOB communities was observed in subsurface soils among different CO2 treatments. The abundance of AOA and AOB, and nitrification potential were significantly increased in surface soils under elevated CO2. The variation of AOB abundance correlated well with the variation of nitrification potential. The soil water content and dissolved organic carbon content had important impacts on the dynamic of AOB communities and nitrification potential. Overall, our results showed different responses of AOA and AOB communities to elevated CO2 in paddy ecosystems, and AOB were more sensitive to the rising CO2 concentration.

[Effect of different levels of elevated CO2 concentration on leaf chlorophyll fluorescence cha-racteristics of Japonica rice]. / 不同CO2æµ“åº¦å‡é«˜æ°´å¹³å¯¹ç²³ç¨»å¶ç‰‡è§å ‰ç‰¹æ€§çš„å½±å“.

To examine the effects of elevated CO2 concentrations on chlorophyll fluorescence of rice leaf, a field experiment was conducted with automatic control system of CO2 concentration in open top-chambers (OTCs). There were three treatments, including atmospheric CO2 concentration (CK), CK+80 µmol·mol-1 CO2 (T1), and CK+200 µmol·mol-1 CO2 (T2). The fast chlorophyll fluorescence induction dynamic curves of flag leaves were measured using the plant efficiency analyzer at the main growth stages of rice. The results showed that T1 treatment significantly increased quantum yield for electron transfer (φEo), maximum photochemical efficiency (Fv/Fm), and performance index (PIABS), but decreased quantum yield for energy dissipation (φDo) at the flowe-ring, milk grain, ripening, and full ripeness stages. The values of φEo, Fv/Fm, and PIABS were increased by 7.3%-23.3%, 3.1%-7.1%, and 46.2%-93.0%, respectively. The φDo values were decreased by 10.3%-20.5%. T2 treatment significantly decreased φEo, Fv/Fm, PIABS by 68.7%, 41.4%, and 93.4%, respectively, but increased φDo by 78.4% at the jointing stage. T2 treatment significantly increased φEo, Fv/Fm, PIABS by 11.6%-19.8%, 4.8%-6.8%, and 53.0%-72.6%, respectively, and decreased φDo by 7.7%-19.4% at the flowering, milk grain, and ripening stages. Our results suggested that elevated CO2 concentration (80, 200 µmol·mol-1) would promote photosynthetic electron transport of PS2 in flag leaves of rice.

[Effects of Warming and Straw Application on Soil Microbial Biomass Carbon and Nitrogen and Bacterial Community Structure].

In order to investigate the effects of warming and straw application on soil microbial biomass carbon and nitrogen and bacterial community structure, a randomized block experiment was performed. Four treatments were included, namely a control (CK), warming (WA), straw application (SA), and warming and straw application (WS) treatments. The soils were sampled during the soybean (Sep. 23, 2017) and winter wheat (April 21, 2018) growing seasons. The soils were used to determine the microbial biomass C and N content using chloroform fumigation methods, and the bacterial community structure was evaluated using high-throughput sequencing (Illumina HiSeq). Results indicated that there was no significant difference in microbial biomass C between different warming and straw application treatments (P>0.05). The microbial biomass N of the warming treatment was significantly higher than that of control in the soybean field (P<0.01). There were significant differences in the most dominant soil bacteria between treatments in the soybean growing season (P<0.05) at the class, order, family, and genus levels, while there was no difference in the winter wheat growing season. The percentages of dominant Gemmatimonadales, Gemmatimonadaceae, and Sphingomonas in the CK and WA (or SA) treatments were significantly different (P<0.05) in the soybean growing season. There was a significant (P<0.05) difference in the dominant Gammaproteobacteria between the CK and WA treatments in the winter wheat growing season. The observed number of species, Shannon index, Simpson index, and Chao1 index were lowest in the warming plots in the soybean growing season and highest in the warming and straw application plots in the winter wheat growing season. The Shannon index for the WA plots was significantly higher than in the WS plots in the soybean growing season (P<0.05). The observed number of species, Shannon index, Simpson index, and Chao1 index were significantly higher in the soybean plots than in the winter wheat plots (P<0.05), while the abundance was significantly higher in the winter wheat plots than in the soybean plots (P<0.05). The soybean growing season had significantly higher diversity than the winter wheat growing season. The indexes of α diversity were highly significantly correlated with soil microbial biomass C and N in the soybean growing season (P<0.001), while there was no such correlation in the winter wheat growing season. The indices of α diversity were significantly correlated in both the soybean growing season and winter wheat growing season (P<0.05).

[Effects of Simulated Precipitation Reduction on Soil Respiration in a Soybean-Winter Wheat Rotation Cropland].

To investigate the effects of precipitation reduction on soil respiration in rainfed croplands, a field experiment was performed in a soybean-winter wheat cropland. A randomized block design including three treatments, viz. control (CK), 20% precipitation reduction (P20%), and 40% precipitation reduction (P40%), was used. Seasonal variabilities in soil respiration, soil temperature, and soil moisture were measured. Rates of soil CO2 production, nitrification and denitrification, and harvested crop biomass were also measured. Results indicated that the seasonal mean soil respiration rates for CK, P20%, and P40% treatments in the soybean growing season were (4.91±0.67), (4.19±0.39), and (4.35±0.32) µmol·(m2·s)-1, respectively. There was no significant difference (P>0.05) in the mean soil respiration rates between treatments during the soybean growing season. The seasonal mean soil respiration rates for CK, P20%, and P40% treatments during the winter wheat growing season were (2.39±0.17), (2.03±0.02), and (1.94±0.05) µmol·(m2·s)-1, respectively. There was a significant (P<0.05) difference in the mean soil respiration rates between treatments during the winter wheat growing season. Precipitation reduction decreased the soil CO2 production rates, but had no obvious impacts on soil nitrification and denitrification rates. Precipitation reduction had no significant (P>0.05) effects on the root, shoot, and seed biomass of soybean, but significantly (P<0.05) decreased the root, shoot, and seed biomass of winter wheat. Soil temperature was the main driver of the seasonal variation in soil respiration. Soil respiration increased exponentially with the increase in soil temperature. There was no significant (P>0.05) difference in the coefficient of temperature sensitivity (Q10) between different treatments. Based on the precipitation reduction experiments of duration longer than one year in previous studies and in our present study, a significant linear regression relationship between the amount of reduced soil respiration and the amount of precipitation reduction was found, indicating that substantial precipitation reduction showed more obvious inhibition effects on soil respiration. This study also suggested that the effects of precipitation reduction on soil respiration varied between crop growing seasons, which may be attributed to the different precipitation intensities in different growing seasons.

[CH4 Emissions Characteristics and Its Influencing Factors in an Eutrophic Lake].

In order to identify methane (CH4) diffusion emissions characteristics and their impact factors in an eutrophic lake, CH4 flux across the lake-air interface was observed in Meiliang Bay and the central zone of Lake Taihu over one year. The relationships between CH4 flux and environmental factors and water quality indices were analyzed. The results indicated that the annual mean CH4 diffusion flux in the eutrophic zone was significantly higher than that in the central zone, which were 0.140 mmol·(m2·d)-1 and 0.024 mmol·(m2·d)-1, respectively. Additionally, the highest CH4 flux appeared in the eutrophic littoral zone. The CH4 flux varied seasonally, which was consistent with water temperature that peaked in summer. Furthermore, the difference in CH4 flux between seasons was an order of magnitude. The temporal variation in CH4 flux was mostly driven by wind speed and water temperature. The spatial correlation between CH4 flux and dissolved organic carbon concentration was highly significant (R2=0.62, P<0.01). Observing temporal and spatial patterns of CH4 flux was necessary to accurately estimate whole-lake CH4 emissions due to large variability across time and space.

[Effects of Simulated Acid Rain on Soil Respiration and Heterotrophic Respiration in a Secondary Forest].

In order to investigate the effects of simulated acid rain on soil respiration and heterotrophic respiration in a secondary forest, a field experiment was carried out. A split-plot experiment was arranged in field. There were 4 blocks; each block had two main plots which were trenched and un-trenched plots. In each main plot, 4 simulated acid rain treatments of control (CK), pH 4.0 (A1), pH 3.0 (A2), and pH 2.0 (A3) were randomly assigned. Soil respiration in the un-trenched plots and heterotrophic respiration in the trenched plots were measured weekly. Soil temperature and moisture at a depth of 5 cm were measured during the respiration measurements. The results indicated that different simulated acid rain treatments exhibited similar seasonal patterns of soil respiration and heterotrophic respiration. Heterotrophic respiration in the trenched plots was significantly lower than soil respiration in the un-trenched plots. The annual mean soil respiration rates for the CK, A1, A2, and A3 treatments in the un-trenched plots were (2.47±0.31), (2.52±0.22), (2.38±0.17), and (2.43±0.22) µmol·(m2·s)-1, respectively, while the annual mean heterotrophic respiration rates for the 4 treatments in the trenched plots were (1.55±0.10), (1.65±0.22), (1.77±0.08), and (1.78±0.27) µmol·(m2·s)-1, respectively. ANOVA showed that simulated acid rain had no significant effects on soil respiration in the un-trenched plots and heterotrophic respiration in the trenched plots. Regression analysis suggested that there was a significant linear regression relationship between soil respiration and heterotrophic respiration. Simulated acid rain significantly (P<0.001) decreased the ratio of soil respiration to heterotrophic respiration. Soil temperature was the main controlling factor regulating the seasonal patterns of soil respiration and heterotrophic respiration for each of the SAR treatment, while soil moisture had no significant effects on the seasonal variability in soil respiration and heterotrophic respiration.

[Effects of Short-time Conservation Tillage Managements on Greenhouse Gases Emissions from Soybean-Winter Wheat Rotation System].

Field experiments including one soybean growing season and one winter-wheat growing season were adopted. The experimental field was divided into four equal-area sub-blocks which differed from each other only in tillage managements, which were conventional tillage (T) , no-tillage with no straw cover ( NT) , conventional tillage with straw cover (TS) , and no-tillage with straw cover (NTS). CO2 and N2O emission fluxes from soil-crop system were measured by static chamber-gas chromatograph technique. The results showed that: compared with T, in the soybean growing season, NTS significantly increased the cumulative amount of CO2 (CAC) from soil-soybean system by 27.9% (P = 0.045) during the flowering-podding stage, while NT significantly declined CAC by 28.9% (P = 0.043) during the grain filling-maturity stage. Compared with T, NT significantly declined the cumulative amount of N2O (CAN) by 28.3% (P = 0.042) during the grain filling-maturity stage. In the winter-wheat growing season, compared with T, TS and NT significantly declined CAC by 24.3% (P = 0.032) and 36.0% (P = 0.041) during the elongation-booting stage, and also declined CAC by 26.8% (P = 0.027) and 33.1% (P = 0.038) during the maturity stage. During the turning-green stage, compared with T treatment, NT, NTS, and TS treatments had no significant effect on CAN, while NTS significant declined CAN by 42.0% (P = 0.035) compared with NT. Our findings suggested that conservation tillage managements had a more significant impact on CO2 emission than 20 emission from soil-crop system.

[Effects of Warming and Straw Application on Soil Respiration and Enzyme Activity in a Winter Wheat Cropland].

In order to investigate the effects of warming and straw application on soil respiration and enzyme activity, a field experiment was performed from November 2014 to May 2015. Four treatments, which were control (CK), warming, straw application, and warming and straw application, were arranged in field. Seasonal variability in soil respiration, soil temperature and soil moisture for different treatments were measured. Urease, invertase, and catalase activities for different treatments were measured at the elongation, booting, and anthesis stages. The results showed that soil respiration in different treatments had similar seasonal variation patterns. Seasonal mean soil respiration rates for the CK, warming, straw application, and warming and straw application treatments were 1.46, 1.96, 1.92, and 2.45 micromol x (m2 x s)(-1), respectively. ANOVA indicated that both warming and straw applications significantly (P < 0.05) enhanced soil respiration compared to the control treatment. The relationship between soil respiration and soil temperature in different treatments fitted with the exponential regression function. The exponential regression functions explained 34.3%, 28.1%, 24.6%, and 32.0% variations of soil respiration for CK, warming, straw application, and warming and straw application treatments, respectively. Warming and straw applications significantly (P < 0.05) enhanced urease, invertase, and catalase activities compared to CK. The relationship between soil respiration and urease activity fitted with a linear regression function, with the P value of 0.061. The relationship between soil respiration and invertase (P = 0.013), and between soil respiration and catalase activity (P = 0.002) fitted well with linear regression functions.

[Effects of Reduced Water and Diurnal Warming on Winter-Wheat Biomass and Soil Respiration].

Field experiments were conducted in winter wheat-growing season to investigate the effect of reduced water and diurnal warming on wheat biomass and soil respiration. The experimental treatments included the control (CK), 30% reduced water (W), diurnal warming (T, enhanced 2 degrees C), and the combined treatment (TW, 30% reduced water plus diurnal warming 2 degrees C). Soil respiration rate was measured using a static chamber-gas chromatograph technique. The results showed that in the winter wheat-growing season, compared to CK, T and TW treatments significantly increased shoot biomass by 46.0% (P = 0.002) and 19.8% (P = 0.032) during the elongation-booting stage, respectively. T and TW treatments also significantly increased the harvested shoot biomass by 19.8% (P = 0.050) and 34.6% (P = 0.028), respectively. On the other hand, W treatment had no significant effect on shoot biomass, and W, T, and TW treatments didn't significantly change the root biomass. T and W treatments had no significant effect on the mean respiration rate (MRR) of soil (P > 0.05). TW treatment significantly decreased soil MRR by 22.4% (P = 0.049). We also found T treatment decreased the temperature sensitivity coefficients of soil respiration (Q10). The results of our study suggested that compared to the single treatment (reduced water or diurnal warming), the combined treatment (reduced water plus diurnal warming) may have different effects on agroecosystem.

[Soil Microbial Respiration Under Different Soil Temperature Conditions and Its Relationship to Soil Dissolved Organic Carbon and Invertase].

In order to investigate the soil microbial respiration under different temperature conditions and its relationship to soil dissolved organic carbon ( DOC) and invertase, an indoor incubation experiment was performed. The soil samples used for the experiment were taken from Laoshan, Zijinshan, and Baohuashan. The responses of soil microbial respiration to the increasing temperature were studied. The soil DOC content and invertase activity were also measured at the end of incubation. Results showed that relationships between cumulative microbial respiration of different soils and soil temperature could be explained by exponential functions, which had P values lower than 0.001. The coefficient of temperature sensitivity (Q10 value) varied from 1.762 to 1.895. The Q10 value of cumulative microbial respiration decreased with the increase of soil temperature for all soils. The Q10 value of microbial respiration on 27 days after incubation was close to that of 1 day after incubation, indicating that the temperature sensitivity of recalcitrant organic carbon may be similar to that of labile organic carbon. For all soils, a highly significant ( P = 0.003 ) linear relationship between cumulative soil microbial respiration and soil DOC content could be observed. Soil DOC content could explain 31.6% variances of cumulative soil microbial respiration. For the individual soil and all soils, the relationship between cumulative soil microbial respiration and invertase activity could be explained by a highly significant (P < 0.01) linear regression function, which suggested that invertase was a good indicator of the magnitude of soil microbial respiration.

[Impacts of elevated ozone concentration on N2O emission from arid farmland].

To investigate the impact of elevated surface ozone (O3) concentration on nitrous oxide (N2O) emission from arid farmland, field experiments were carried out during winter-wheat and soybean growing seasons under the condition of simulating O3 concentrations, including free air (CK), 100 nL x L(-1) O3 concentration (T1), and 150 nL x L(-1) O3 concentration (T2). N2O emission fluxes were measured by static dark chamber-gas chromatograph method. The results showed that the accumulative amount of N2O (AAN) were decreased by 37.8% (P = 0.000 ) and 8.8% (P = 0.903 ) under T1 and T2 treatments, respectively, in the turning-green stage of winter wheat. In the elongation-booting stage, ANN were decreased by 15.0% (P = 0.217) and 39.1% (P = 0.000) under T1 and T2 treatments, respectively. ANN were decreased by 18.9% (P = 0.138) and 25.6% (P = 0.000) under T1 and T2 treatments, respectively, during the whole winter-wheat growing season. No significant impact of elevated O3 concentration on N2O emission from soil-soybean system was found due to the less rainfall during the soybean growing season, drought had a stronger stress on soybean than O3 concentration. The results of this study suggested that elevated O3 concentration could reduce N2O emission from arid farmland.

[Multi-year measurement of soil respiration components in a subtropical secondary forest].

A four-year field experiment was performed from March 2010 to February 2014 in order to investigate the contribution of different respiratory components to soil respiration and the temperature sensitivity of different respiratory components. Four blocks were arranged in field, and there were trenched and un-trenched plots in each block. Trenching, which can exclude roots, was performed around the trenched plots. A portable soil CO2 fluxes system ( Li-8100) was used to measure soil respiration rates. Soil temperature and soil moisture were simultaneously observed when measuring soil respiration rates. The results showed that the heterotrophic respiration rate in the trenched plots and the soil respiration rate in the un-trenched plots had the same seasonal pattern. Soil respiration rate in the un-trenched plots was significantly (P < 0.001) higher than that in the trenched plots. Mean soil respiration rates in untrenched plots and mean heterotrophic respiration rate in trenched plots were (2.59 ± 0.48 ) and (1.74 ± 0.28) µmol x (M2 x s)(-1), respectively. There was no significant (P > 0.05) difference in the mean soil respiration rate or mean heterotrophic respiration rate between measurement years. The relationship between heterotrophic respiration and soil respiration could be fitted with a proportion function. Heterotrophic and autotrophic respiration contributed 65.9% and 34.1% to the soil respiration, respectively. The main contributor to soil respiration was heterotrophic respiration. The relationship between the ratio of heterotrophic respiration to soil respiration and measurement date could be fitted with a linear function. An exponential function could be used to fit the relationship between heterotrophic respiration and soil temperature, and between autotrophic respiration and soil temperature. The temperature sensitivity coefficient (Q10) for heterotrophic respiration was lower than that for autotrophic respiration.

[Factors influencing the variability in soil heterotrophic respiration from terrestrial ecosystem in China].

Soil heterotrophic respiration is one of the key factors for estimating ecosystem carbon balance. Measurement data of soil heterotrophic respiration from terrestrial ecosystem in China were collected. Climate data (annual precipitation and annual mean air temperature) and relevant environmental factors (e. g. tree age) were also collected. Results indicated that the relationship between heterotrophic respiration and soil respiration could be explained by a power function. Heterotrophic respiration increased with the increase of soil respiration. The power function explained 73% of the variability (R2 = 0.730, P < 0.001) in heterotrophic respiration. The linear equation could be used to explain the relationship between heterotrophic respiration and annual precipitation/mean annual air temperature. The logarithmic regression equation could be employed to describe the relationship between the ratio of heterotrophic respiration to soil respiration and annual precipitation/mean annual air temperature. The ratio of heterotrophic respiration to soil respiration increased with the increase of tree age; a power function could be used to explain the relationship between the ratio of heterotrophic respiration to soil respiration and tree age. Further investigation showed that the relationship between measured annual heterotrophic respiration and modeled heterotrophic respiration by using an empirical model could be described by a linear function, indicating that the empirical model well fitted the variability in heterotrophic respiration.

[Effects of diurnal warming on soil N2O emission in soybean field].

To investigate the impact of experimental warming on N2O emission from soil of soybean field, outdoor experiments with simulating diurnal warming were conducted, and static dark chamber-gas chromatograph method was used to measure N2O emission fluxes. Results indicated that: the diurnal warming did not change the seasonal pattern of N2O emissions from soil. In the whole growing season, comparing to the control treatment (CK), the warming treatment (T) significantly enhanced the N2O flux and the cumulative amount of N2O by 17.31% (P = 0.019), and 20.27% (P = 0.005), respectively. The significant correlations were found between soil N2O emission and soil temperature, moisture. The temperature sensitivity values of soil N2O emission under CK and T treatments were 3.75 and 4.10, respectively. In whole growing stage, T treatment significantly increased the crop aboveground and total biomass, the nitrate reductase activity, and total nitrogen in leaves, while significantly decreased NO3(-) -N content in leaves. T treatment significantly increased soil NO3(-) -N content, but had no significant effect on soil organic carbon and total nitrogen contents. The results of this study suggested that diurnal warming enhanced N2O emission from soil in soybean field.

[Factors influencing the spatial variability in soil respiration under different land use regimes].

In order to investigate the factors influencing the spatial variability in soil respiration under different land use regimes, field experiments were performed. Soil respiration and relevant environment, vegetation and soil factors were measured. The spatial variability in soil respiration and the relationship between soil respiration and these measured factors were investigated. Results indicated that land use regimes had significant effects on soil respiration. Soil respiration varied significantly (P < 0.001) among different land use regimes. Soil respiration rates ranged from 1.82 to 7.46 micromol x (m2 x s)(-1), with a difference of 5.62 micromol x (m2 x s)(-1) between the highest and lowest respiration rates. Soil organic carbon was a key factor controlling the spatial variability in soil respiration. In all, ecosystems studied, the relationship between soil respiration and soil organic carbon content can be described by a power function. Soil respiration increased with the increase of soil organic carbon. In forest ecosystem, the relationship between soil respiration and diameter at breast height (DBH) of trees can be explained by a natural logarithmic function. A model composed of soil organic carbon (C, %), available phosphorous (AP, g x kg(-1)) and diameter at breast height (DBH, cm) explained 92.8% spatial variability in soil respiration for forest ecosystems.

[Effects of simulated warming on soil respiration in a cropland under winter wheat-soybean rotation].

This study was aimed to investigate the effects of simulated warming on soil respiration in a cropland under winter wheat-soybean rotation. Randomized experiments were carried out in the cropland. 6 Plots were arranged and there were 2 treatments, simulated warming and control. A portable soil CO2 fluxes system (LI-8100) was used to measure soil respiration rates. Soil CO2 production rates were determined by using a Barometric Process Separation (BaPS) method. Soil temperature and soil moisture were simultaneously determined when measuring soil respiration rates. Results indicated that soil respiration rates in different treatments showed similar seasonal variability, in accordance with the variability in soil temperature. Seasonal mean soil respiration rates for simulated warming and control treatments were 3.54 and 2.49 micromol x (m2 x s)(-1), respectively, during the winter wheat growth season, while they were 4.80 and 4.14 micromol x (m2 x s)(-1), respectively, during the soybean growth season. Simulated warming significantly (P < 0.05) enhanced soil respiration during both the winter wheat and soybean growth seasons. The impact of simulated warming on soil respiration was particularly obvious during the later growth stages of winter wheat (from heading to maturity stages) and soybean (from flowing to maturity stages). Further investigations suggested that, for both the winter wheat and soybean growth seasons, the relationship between soil respiration and soil temperature could be well explained (P < 0.01) by exponential functions. The temperature sensitivity (Q10) of soil respiration in the simulated warming treatments was significantly higher than that in the control treatments. The Q10 values for the simulated warming and control treatments were 1.83 and 1.26, respectively, during the winter wheat growth season, while they were 2.85 and 1.70, respectively, during the soybean growth season. This study showed that simulated warming significantly increased soil respiration in the cropland.