Large differences in ammonia emission factors between greenhouse and open-field systems under different practices across Chinese vegetable cultivation.

Estimating ammonia (NH3) emission factors (EFs) for vegetable production can support assessment of potential atmospheric pollution risk and provide information for mitigating NH3 volatilization. The EFs in greenhouse and open-field systems under different fertilization, irrigation regimes, vegetable types and soil properties in both greenhouse and open-field vegetable production systems in China are poorly understood. An integrated analysis was performed, including 282 field measurements of NH3 volatilization from 54 field studies, to quantify ammonia EFs under different management practices and soil properties. The results showed that the mean ammonia EF across all measurements was 4.2 % (3.6 %-4.8 %). The EFs of greenhouse and open-field systems were 2.0 % (1.5 %-2.5 %) and 6.3 % (5.4 %-7.2 %), respectively. There was a power function relationship between nitrogen application rate and ammonia EF in greenhouses. No relationship was identified between nitrogen application rate and ammonia EF in the open-field system. The EFs of organic fertilizers were lower than those of both chemical fertilizers and the combination of chemical and organic fertilizers. EFs of leafy vegetables, cabbages, solanaceous vegetables and melons were 2.7 %, 2.9 %, 1.4 % and 1.4 % in the greenhouse system, and 5.2 %, 5.7 %, 7.6 % and 9.7 % in the open-field system, respectively. The EFs of the greenhouse production system increased with increasing soil organic matter. Boosted regression tree analysis showed that N application rate, pH and soil organic matter were the main driving factors of EFs in the greenhouse system. Vegetable type, pH and soil organic matter were the main driving factors in the open-field system. In this study, the EFs were evaluated and distinguished across greenhouse and open-field systems, and the results provided accurate EFs under different management practices and soil properties for vegetable production in both greenhouse and open-field systems.

[Tracing the sources of sedimentary organic matter in Nanyue small watershed based on 13C, 15N and C/N]. / 基于13C、15N和C/N识别南岳小流域沉积有机质的来源.

Losses of organic matter in agricultural watersheds result in eutrophication and land degra-dation, which not only threaten water quality and food security, but also lead to environmental problems such as the greenhouse gases emission. We used 13C, 15N and C/N as fingerprint markers to trace the sources of sedimentary organic matter at the outlet in the Nanyue small watershed. We analyzed the spatial distribution in watershed sedimentary organic matter and soils of typical land use types, including forest, paddy field, and vegetable fields. The Bayesian stable isotope mixing model was used to quantitatively estimate the contribution of different sources. The results showed that there was significant spatial variation of δ13C. The δ13C of sediment organic matter (-22.6‰±0.53‰) and forest soil (-23.13‰±1.71‰) was significantly higher than that of paddy soil (-25.24‰±1.4‰). The differences of δ15N among the sources were not significant, with sediment having the maximum (4.37±0.83)‰ and forest soil having the minimum (2.38±1.97)‰. Forest soil had the highest C/N of 16.66±7.18, while paddy soil had the lowest C/N of 11.95±0.92. The results of the Bayesian stable isotope mixture model showed that the contribution rates of forest land, paddy fields and vegetable fields to the organic matter deposited at the outlet in the watershed were 19.6%, 15.7%, and 64.7%, respectively. Paddy filed and vegetable field had a combined contribution rate of 80.4%. It was concluded that, soils of agricultural land were the main sources of organic matter deposited in the Nanyue small watershed, and that nutrient loss in the watershed would be effectively controlled by optimizing farmland management.

Air warming and CO2 enrichment cause more ammonia volatilization from rice paddies: An OTC field study.

Ammonia (NH3) volatilization in rice paddies may be affected by elevated atmospheric CO2 concentration ([CO2]) and temperature due to changes in plant and soil nitrogen (N) metabolism. At present, little is known about the individual and combined effects of CO2 enrichment and warming on NH3 volatilization under field conditions. An experiment was conducted in a rice paddy in Central China, after 4 years of warming and CO2 enrichment using open-top chamber (OTC) devices. Compared with ambient conditions, elevated [CO2] had no significant effects on NH3 volatilization, although increases in soil pH and urease activity were observed. The stimulation on plant N assimilation under CO2 enrichment might offset the possible enhancement on NH3 volatilization, as more soil N was absorbed by plant thus reducing NH3 loss potential. Elevated temperature increased NH3 volatilization significantly, which could be attributed to increased soil ammonium nitrogen (NH4+-N) concentration, pH, and urease activity. Combination of CO2 enrichment and warming caused the highest cumulative NH3 loss, which increased by 26.5% compared with ambient conditions, but the interaction was not significant. Higher plant N uptake, soil NH4+-N concentration, pH and urease activity were also observed with co-elevation of [CO2] and temperature, but the combined effects were variable and not synergistic. Our findings confirm that field warming and CO2 enrichment cause more NH3 volatilization in rice paddies, among which warming effects are dominant, and suggest that improved N management or field practices are required to reduce NH3 losses under future climate change.

[Responses of net assimilation rate to elevated atmospheric CO2and temperature at different growth stages in a double rice cropping system]. / 双季稻不同生育期净同化速率对大气CO2浓度和温度升高的响应.

Effects of elevated atmospheric CO2 concentration and temperature on rice dry matter accumulation vary in planting regions and cropping systems. It remains unclear how dry matter productivity responds to factorial combination of elevated CO2 and temperature in the double rice cropping system of China. Field experiments were conducted using open-top chambers (OTC) to simulate different scenarios of elevated CO2 and/or temperature for three rotations of double rice in Jingzhou, Hubei Province. Liangyou 287 and Xiangfengyou 9 were used as rice cultivar for early rice and late rice, respectively. There were five treatments: UC, paddy field without OTC covering; CK, OTC with the similar temperature and CO2 concentration to field environment; ET, OTC with 2 ℃ temperature elevation; EC, OTC with 60 µmol·mol-1 CO2 elevation; ETEC, OTC with simu-ltaneous 2 ℃ temperature elevation and 60 µmol·mol-1 CO2 elevation. We measured aboveground biomass, leaf area index (LAI) and net assimilation rate (NAR) of dry matter under different treatments. Our results showed that elevated CO2 and/or temperature had no significant effects on NAR from transplanting to jointing, increased NAR from jointing to heading, but decreased NAR from heading to maturity (except for EC treatment in early rice). Elevated CO2 and/or temperature promoted leaf area development at all growth stages, with ETEC showing the highest increase in LAI except at maturity. Warming and CO2 enrichment jointly promoted dry matter accumulation at heading, with ETEC increasing aboveground biomass by 10.3%-39.8% and 23.6%-34.4% compared with CK in early rice and late rice, respectively. At maturity of early rice, elevated temperature partly offset the positive effects of elevated CO2 on aboveground biomass, as shown by a reduction of 3.2%-14.1% under ETEC compared with EC. Contrarily at maturity of late rice, co-elevation of CO2 and temperature further increased aboveground biomass, showing a synergistic interaction. Results from regression analysis showed that warming and CO2 enrichment had positive effects on NAR at vegetative stages of double rice, while warming showed negative effects on NAR at reproductive stages. Considering the dissimilarities in growth characteristics, growing periods and ambient temperature, elevated CO2 and temperature might increase dry matter production in the Chinese double rice cropping system.

Diffusive flux of CH4 and N2O from agricultural river networks: Regression tree and importance analysis.

River networks in subtropical agricultural hilly region become an inconvenient greenhouse gas (GHG, methane and nitrous oxide) source because of the influence of human activities, which has caused large uncertainties for refinement of national GHG inventories and their global budget. Based on field monitoring experiments at high temporal resolution, we employed regression tree and importance analysis to identify quantitatively factors that influence the diffusive flux of GHGs to provide a scientific basis for reducing GHG emissions and controlling regional carbon and nitrogen losses. The results indicate that significant spatiotemporal variation of methane (CH4) nitrous oxide (N2O) diffusion occurs in all the four reaches (W1, W2, W3 and W4) of Tuojia river networks. Among them, W1 contributed lowest CH4 (22.55 µg C m-2 h-1) and N2O (5.00 µg N m-2 h-1) diffusive flux than the other three (P < 0.05), while W4 offered highest CH4 (166.15 µg C m-2 h-1) and N2O (30.47 µg N m-2 h-1) diffusive flux but with no statistically significant difference between W2 and W3 due to homogeneous extraneous nutrition loading into the two reaches. W4 also contributed largest cumulative flux of CH4 (14.55 kg C ha-1 yr-1) and N2O (2.69 kg N ha-1 yr-1) in Tuojia River networks (P < 0.05). Furthermore, the regression tree and importance analysis indicate that, in the anaerobic environment, dissolved oxygen saturation controlled the production and diffusion for both CH4 and N2O. The findings of this investigation highlighted that decision support tools provide an effective pathway to enhance the GHG mitigation technology research in agroecosystems and simultaneously shed light on the global campaign on refinement of national GHG inventories as well as regional nutrient management.

Air warming and CO2 enrichment increase N use efficiency and decrease N surplus in a Chinese double rice cropping system.

Effectiveness of N might be modified in rice cultivation under future climate change with elevated atmospheric CO2 concentration ([CO2]). At present, limited information is available to understand how plant N uptake and N use efficiency respond to elevated [CO2] and/or temperature in Chinese double rice cropping systems. A four-year field experiment was therefore conducted using open-top chambers with varying [CO2] (ambient, ambient +60 µmol mol-1) and varying temperature (ambient, ambient +2 °C) in Hubei Province, Central China. Compared with ambient conditions, elevated [CO2] increased plant N uptake and N use efficiency, as measured by fertilizer N recovery efficiency (NRE), N agronomic efficiency (NAE), N physiological efficiency (NPE) and apparent system N use efficiency (NUEsys), in both early rice and late rice. CO2 enrichment tended to decrease soil mineral N concentration since more N was assimilated by plants. Elevated temperature led to lower plant N uptake and decreased NRE and NAE in early rice, due to a reduction in grain yield induced by heat injury. In contrast, warming increased plant N uptake and N use efficiency in late rice as no heat stress existed. Warming tended to increase soil mineral N concentration in early rice but had negligible effects in late rice. When elevated [CO2] and temperature were combined, the positive effects of CO2 enrichment for N utilization were able to compensate for the negative effects of warming in early rice, while the interaction was synergetic in late rice. Hence, co-elevation of [CO2] and temperature led to higher N use efficiency (64.6% for NUEsys across four years) and decreased annual N surplus by 28.6-36.5 kg N ha-1 compared with ambient conditions. Our findings confirm that CO2 enrichment and air warming can improve N use efficiency at both crop level and system level in Chinese double rice cultivation.

Differential resistance and resilience of functional groups to livestock grazing maintain ecosystem stability in an alpine steppe on the Qinghai-Tibetan Plateau.

Ecosystem stability is one of the main factors maintaining ecosystem functioning and is closely related to temporal variability in productivity. Resistance and resilience reflect tolerance and recovering ability, respectively, of a plant community under perturbation, which are important for maintaining the stability of ecosystems. Generally, heavy grazing reduces the stability of grassland ecosystems, causing grassland degradation. However, how livestock grazing affects ecosystem stability is unclear in alpine steppe ecosystems. We conducted a five-year grazing experiment with Tibetan sheep in a semi-arid alpine steppe on the Qinghai-Tibetan Plateau, China. The experimental treatments included no grazing (NG), light grazing (LG, 2.4 sheep per ha), moderate grazing (MG, 3.6 sheep per ha) and heavy grazing (HG, 6.0 sheep ha). We calculated resistance and resilience of three plant functional groups and ecosystem stability under the three grazing intensities using aboveground primary productivity. The results showed that with increasing grazing intensity, aboveground biomass of each functional group significantly decreased. As grazing intensity increased, the resistance of forbs first increased then decreased. The resilience of graminoids in HG was significantly lower than in LG plots, but the resilience of legumes in HG was higher than in LG and MG plots. The resilience of graminoids was significantly higher than legume and forbs under LG and MG treatments. In HG treatments, resilience of legumes was higher than graminoids and forbs. Ecosystem stability did not change under different grazing intensities, because of dissimilar performance of the resilience and resistance of functional groups. Our results highlight how the differential resistance and resilience of different function groups facilitate the tolerance of alpine steppe to grazing under even a heavy intensity. However, the degradation risk of alpine steppe under heavy grazing still needs to be considered in grassland management due to sharp decreases of productivity.

Assessment of Indirect N2O Emission Factors from Agricultural River Networks Based on Long-Term Study at High Temporal Resolution.

Assessment of indirect emission factors (EF5r) of nitrous oxide (N2O) from agricultural river networks remains challenging, and results are uncertain due to limited data availability. This study compared two methods of assessing EF5r using data from long-term observations at high temporal resolution in a typical agricultural catchment in subtropical central China. The concentration method (method 1) and the Intergovernmental Panel on Climate Change (IPCC) 2006 method (method 2) were employed to evaluate the emission factor. EF5r estimated using method 1 (i.e., EF5r1) was 0.00077 ± 0.00025 (0.00038-0.00097). EF5r calculated using method 2 (i.e., EF5r2) was lower than EF5r1, with a mean value of 0.00004 (0.000015-0.00012). Both EF5r1 and EF5r2 were significantly lower than the IPCC 2006 default value of 0.0025, suggesting that N2O emissions from China and world river networks may be grossly overestimated. A complex N2O production pathway and diffusion mechanism were responsible for the transfer of N2O from the sediment to river water and then to the atmosphere. These findings provide essential data for refining national greenhouse gas inventories and contribute evidence for downward revision of indirect emission factors adopted by the IPCC.

[Key Production Process of Nitrous Oxide and Nitrogen Sources in Tuojia River].

The nitrogen (N) pollution of water is a common global problem. To understand the key production process of N2 O and identify the dominant N sources, Tuojia River, a typical agricultural watershed in a subtropical area, was investigated. To analyze the characteristics of dual nitrate isotopes (δ15N-NO3-,δ18O-NO3-) in water, and N isotope (δ15Norg) and carbon-nitrogen ratio (C/N) in sediment organic matter from four reaches(S1-S4), the stable isotopes method was used. The results showed that the sources of nitrate varied significantly among river segments and were affected by agricultural production and human habitation on the land surface. The average δ15N-NO3- in reaches S1, S2, S3, and S4 were 1.72‰, 2.62‰, 4.10‰, and -1.28‰, respectively, while the average δ18O-NO3- were 2.60‰,-0.06‰, 0.85‰, and -0.62‰. The N in terrestrial soil made a large contribution to nitrate sources in reach S1, while soil N, ammonium N fertilizer, and manure played a main role in reaches S2 and S3. Most of the nitrate came from ammonium N fertilizer in reach S4. We also found that δ15Norg in sediment organic matter ranged from -0.69‰ to 11.21‰, and C/N was between 7.30 and 12.02. The mean δ15Norg in reaches S1-S4 were 1.91‰, 2.96‰, 4.72‰, and 3.23‰, respectively, and the mean C/N values were 10.62, 8.63, 9.05, and 9.22, respectively. Although there were some differences in δ15Norg among reaches S2-S4, the dominant N source was sewage in those reaches. However, soil organic matter was the main N source in the sediments of reach S1. The mean δ18O-NO3- in reaches S1-S4 were -7.01‰,-0.17‰,-0.28‰, and -0.60‰, respectively, indicating that nitrification was the key N2 O production process in these reaches. The ratios of δ15N-NO3- and δ18O-NO3- were 0.66,-41.01,-30.23, and 9.39 in reaches S1-S4, respectively. Finally, we found that there was a positive correlation between NO3--N and δ15N-NO3-. To summarize, the N transformation and N2 O production could be dominated by the nitrification process in Tuojia River.

Temperature leads to annual changes of plant community composition in alpine grasslands on the Qinghai-Tibetan Plateau.

In most grassland ecosystems, the effects of mean temperature increase on plant communities have been investigated; however, the effects of climate fluctuations on local plant community metrics are much less well understood. We conducted a nine-year survey in alpine meadow and alpine steppe to investigate the effects of inter-annual temperature and precipitation variation on plant community composition, species richness, and species diversity on the central Qinghai-Tibetan Plateau, China. We unexpectedly found that annual variability of growing season temperature, and not precipitation, is a driver of plant composition and species diversity in both habitats. Generally, increasing temperature had a negative effect on species diversity in meadow (r2 = 0.94) and steppe (r2 = 0.95). In the meadow habitat, the proportion of grass decreased with increasing temperature and ultimately had positive impacts on the proportion of sedges. In steppe habitat, legumes increased and forbs decreased with the increase of growing season temperature; both legumes and forbs negatively affected proportion of grass and resulted in grass remaining stable under temperature change. Our results provide evidence that responses of functional group composition and species richness to temporal change of temperature are very different from those responses to mean temperature increase on the central Qinghai-Tibetan Plateau. In our results, temperature is a main regulator for annual variation of functional group composition and species richness, while soil water content is a dominant regulator for community responses in other experimental warming studies.

Different responses of ecosystem carbon exchange to warming in three types of alpine grassland on the central Qinghai-Tibetan Plateau.

Climate is a driver of terrestrial ecosystem carbon exchange, which is an important product of ecosystem function. The Qinghai-Tibetan Plateau has recently been subjected to a marked increase in temperature as a consequence of global warming. To explore the effects of warming on carbon exchange in grassland ecosystems, we conducted a whole-year warming experiment between 2012 and 2014 using open-top chambers placed in an alpine meadow, an alpine steppe, and a cultivated grassland on the central Qinghai-Tibetan Plateau. We measured the gross primary productivity, net ecosystem CO 2 exchange (NEE), ecosystem respiration, and soil respiration using a chamber-based method during the growing season. The results show that after 3 years of warming, there was significant stimulation of carbon assimilation and emission in the alpine meadow, but both these processes declined in the alpine steppe and the cultivated grassland. Under warming conditions, the soil water content was more important in stimulating ecosystem carbon exchange in the meadow and cultivated grassland than was soil temperature. In the steppe, the soil temperature was negatively correlated with ecosystem carbon exchange. We found that the ambient soil water content was significantly correlated with the magnitude of warming-induced change in NEE. Under high soil moisture condition, warming has a significant positive effect on NEE, while it has a negative effect under low soil moisture condition. Our results highlight that the NEE in steppe and cultivated grassland have negative responses to warming; after reclamation, the natural meadow would subject to loose more C in warmer condition. Therefore, under future warmer condition, the overextension of cultivated grassland should be avoided and scientific planning of cultivated grassland should be achieved.

Effects of increased levels of atmospheric CO2 and high temperatures on rice growth and quality.

The increased atmospheric temperatures resulting from the increased concentration of atmospheric carbon dioxide (CO2) have had a profound influence on global rice production. China serves as an important area for producing and consuming rice. Therefore, exploring the effects of the simultaneously rising levels of atmospheric CO2 and temperatures on rice growth and quality in the future is very important. The present study was designed to measure the most important aspects of variation for rice-related physiological, ecological and quality indices in different growing periods under a simultaneous increase of CO2 and temperature, through simulation experiments in climate-controlled growth chambers, with southern rice as the study object. The results indicated that the ecological indices, rice phenology, and leaf area would decrease under a simultaneous increase of CO2 and temperature. For the physiological indices, Malondialdehyde (MDA) levels increased significantly in the seedling period. However, it showed the trend of increase and subsequent decrease in the heading and filling periods. In addition, the decomposition of soluble protein (SP) and soluble sugar (SS) accelerated in filling period. The rice quality index of the Head Rice Rate showed the decreasing trend and subsequent increase, but the Chalky Rice Rate and Protein Content indices gradually decreased while the Gel Consistency gradually increased.

Long-term effect of biochar application on yield-scaled greenhouse gas emissions in a rice paddy cropping system: A four-year case study in south China.

To evaluate long-term effect of biochar application on yield-scaled greenhouse gas emissions (YSGE) in a paddy rice cropping system, a 4-year field experiment by static chamber - gas chromatograph method was conducted in South China. Principal component analysis and terminal restriction fragment length polymorphism (T-RFLP) and real-time qPCR was used to unravel the microbial mechanisms of biochar addition. Six treatments were included: control (CK), application of 5tha(-1) biochar (BC1), application of 10tha(-1) biochar (BC2), application of 10tha(-1) biochar (BC3), rice straw return at 2400kgha(-1)(RS) and inoculated rice straw return at 2400kgha(-1)(RI). The results indicated that biochar amendment significantly decreased methane (CH4) and gross greenhouse gas (GHG) emissions. This may primarily be ascribed to the stimulated biodiversity and abundance of methanotrophic microbes, increased soil pH and improved aeration by reducing bulk density after biochar incorporation. Compared with CK, RS and RI, 26.18%, 70.02%, 66.47% of CH4 flux and 26.14%, 70.16%, 66.46% of gross GHG emissions were reduced by biochar (mean of three biochar treatments), respectively. Furthermore, biochar significantly increased harvest index of double rice production (p<0.05). In comparison with CK, RS and RI, 29.14%, 68.04%, 62.28% of YSGE was reduced by biochar, respectively, and the highest biochar addition rate (20tha(-1)) contributed most to the mitigation of GHG emissions (36.24% decrease compared to CK) and improvement of rice yield (7.65% increase compared to CK). Results of our study suggested that long-term application of biochar should be the potential way to mitigate GHGs emissions and simultaneously improve rice productivity in the paddy rice system.

Climatic change controls productivity variation in global grasslands.

Detection and identification of the impacts of climate change on ecosystems have been core issues in climate change research in recent years. In this study, we compared average annual values of the normalized difference vegetation index (NDVI) with theoretical net primary productivity (NPP) values based on temperature and precipitation to determine the effect of historic climate change on global grassland productivity from 1982 to 2011. Comparison of trends in actual productivity (NDVI) with climate-induced potential productivity showed that the trends in average productivity in nearly 40% of global grassland areas have been significantly affected by climate change. The contribution of climate change to variability in grassland productivity was 15.2-71.2% during 1982-2011. Climate change contributed significantly to long-term trends in grassland productivity mainly in North America, central Eurasia, central Africa, and Oceania; these regions will be more sensitive to future climate change impacts. The impacts of climate change on variability in grassland productivity were greater in the Western Hemisphere than the Eastern Hemisphere. Confirmation of the observed trends requires long-term controlled experiments and multi-model ensembles to reduce uncertainties and explain mechanisms.

Complex responses of spring vegetation growth to climate in a moisture-limited alpine meadow.

Since 2000, the phenology has advanced in some years and at some locations on the Qinghai-Tibetan Plateau, whereas it has been delayed in others. To understand the variations in spring vegetation growth in response to climate, we conducted both regional and experimental studies on the central Qinghai-Tibetan Plateau. We used the normalized difference vegetation index to identify correlations between climate and phenological greening, and found that greening correlated negatively with winter-spring time precipitation, but not with temperature. We used open top chambers to induce warming in an alpine meadow ecosystem from 2012 to 2014. Our results showed that in the early growing season, plant growth (represented by the net ecosystem CO2 exchange, NEE) was lower in the warmed plots than in the control plots. Late-season plant growth increased with warming relative to that under control conditions. These data suggest that the response of plant growth to warming is complex and non-intuitive in this system. Our results are consistent with the hypothesis that moisture limitation increases in early spring as temperature increases. The effects of moisture limitation on plant growth with increasing temperatures will have important ramifications for grazers in this system.

Climate change and its impacts on vegetation distribution and net primary productivity of the alpine ecosystem in the Qinghai-Tibetan Plateau.

Changes in climate have caused impacts on ecosystems on all continents scale, and climate change is also projected to be a stressor on most ecosystems even at the rate of low- to medium-range warming scenarios. Alpine ecosystem in the Qinghai-Tibetan Plateau is vulnerable to climate change. To quantify the climate change impacts on alpine ecosystems, we simulated the vegetation distribution and net primary production in the Qinghai-Tibetan Plateau for three future periods (2020s, 2050s and 2080s) using climate projection for RCPs (Representative Concentration Pathways) RCP4.5 and RCP8.5 scenarios. The modified Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ model) was parameter and test to make it applicable to the Qinghai-Tibetan Plateau. Climate projections that were applied to LPJ model in the Qinghai-Tibetan Plateau showed trends toward warmer and wetter conditions. Results based on climate projections indicated changes from 1.3°C to 4.2°C in annual temperature and changes from 2% to 5% in annual precipitation. The main impacts on vegetation distribution was increase in the area of forests and shrubs, decrease in alpine meadows which mainly replaced by shrubs which dominated the eastern plateau, and expanding in alpine steppes to the northwest dominated the western and northern plateau. The NPP was projected to increase by 79% and 134% under the RCP4.5 and RCP8.5. The projected NPP generally increased about 200gC·m(-2)·yr(-1) in most parts of the plateau with a gradual increase from the eastern to the western region of the Qinghai-Tibetan Plateau at the end of this century.

Effects of Warming on CO2 Fluxes in an Alpine Meadow Ecosystem on the Central Qinghai-Tibetan Plateau.

To analyze CO2 fluxes under conditions of climate change in an alpine meadow on the central Qinghai-Tibetan Plateau, we simulated the effect of warming using open top chambers (OTCs) from 2012 to 2014. The OTCs increased soil temperature by 1.62°C (P < 0.05), but decreased soil moisture (1.38%, P < 0.05) during the experiments. The response of ecosystem CO2 fluxes to warming was variable, and dependent on the year. Under conditions of warming, mean gross ecosystem productivity (GEP) during the growing season increased significantly in 2012 and 2014 (P < 0.05); however, ecosystem respiration (ER) increased substantially only in 2012 (P < 0.05). The net ecosystem CO2 exchange (NEE) increased marginally in 2012 (P = 0.056), did not change in 2013(P > 0.05), and increased significantly in 2014 (P = 0.034) under conditions of warming. The GEP was more sensitive to climate variations than was the ER, resulting in a large increase in net carbon uptake under warming in the alpine meadow. Under warming, the 3-year averages of GEP, ER, and NEE increased by 19.6%, 15.1%, and 21.1%, respectively. The seasonal dynamic patterns of GEP and NEE, but not ER, were significantly impacted by warming. Aboveground biomass, particularly the graminoid biomass increased significantly under conditions of warming. Soil moisture, soil temperature, and aboveground biomass were the main factors that affected the variation of the ecosystem CO2 fluxes. The effect of warming on inter- and intra-annual patterns of ecosystem CO2 fluxes and the mechanism of different sensitivities in GEP and ER to warming, require further researched.

[Observation for CH4 and N2O emissions under different rates of nitrogen and phosphate fertilization in double rice fields].

Two non-CO2 greenhouse gas emissions (methane and nitrous oxide) and related environmental factors were measured within rice growing season under five treatments including non-fertilization (CK), balanced fertilization (BF), decreased nitrogen and phosphate 1 (DNP1), decreased nitrogen and phosphate 2 (DNP2) and increased nitrogen and phosphate 1 (INP) in double rice fields of red clay soil in 2009, using the method of static chamber-gas chromatograph techniques. The results showed that the average CH4 emission fluxes for treatments of BF, DNP1, DNP2 and INP were 4.57, 5.42, 4.70 and 4.65 mg x (m2 x h)(-1) during early rice growing period, which increased by 39%, 49%, 41% and 40% compared with non-fertilizer treatment, respectively. The average CH4 emission fluxes in late rice growing season was higher than preseason's. Compared to CK, CH4 emission increased by 11%, 1%, 26% and - 4% in treatments of BF, DNP1, DNP2 and INP within late rice growing season. Applying nitrogen and phosphate enhanced CH4 emission in turning green period for early and late rice. No significant difference was observed between the CH4 emissions of five treatments during early and late rice growing season (p > 0.05). N2O emission was very little during mid-seasonal drainage period. In contrast, N2O emission peaks were observed in period of alternation of wetting and drying after mid-seasonal drainage in this experiment. N2O emission was, on average, equivalent to 0.18% of the nitrogen applied in double rice growing season. Statistically, air temperature, soil Eh and soil moisture (water-filled pore space, WFPS) at 0-10cm depth significantly affected the fluctuations of the seasonal CH4 flux, but no significant correlationship has been found between N2O flux and related environmental factors. CH4 was the dominated greenhouse gas in double rice fields which contributed approximately 90% for the integrated global warming potential of CH4 and N2O released during the rice growing season. Therefore, the mitigation options should focus on how to reduce CH4 emission in local area. The result indicates that BF is a recommended fertilization method for early rice production, and a optimum fertilization for late season can increase rates of nitrogen and phosphate fertilizers on the basis of BF treatment slightly by considering total global warming potential and grain yield. The rates of BF treatment were 150-90-90 kg x hm(-2) N-P2O5-K2O for early rice, and 180-90-135 kg x hm(-2) N-P2O5-K2O for late rice, respectively.

[Grassland net primary productivity and its spatiotemporal distribution in northern Tibet: a study with CASA model].

Based on the remote sensing data, meteorological data and other related data from 1981 to 2004, the grassland net primary productivity (NPP) and its spatiotemporal distribution in Northern Tibet were analyzed by CASA (Carnegie-Ames-Stanford Approach) model. The results indicated that in the study area, the spatial distribution of grassland NPP was affected by the local water and heat conditions, and represented a horizontal zonality. From southeast to northwest, the grassland NPP reduced from 230 g C x m(-2) x a(-1) to near 0 g C x m(-2) x a(-1). The overall level of grassland NPP in Northern Tibet was rather low, with the multi-years average value of total NPP being 21.3 x 10(12) g C x a(-1) and the mean value of NPP being 48.1 g C x m(-2) x a(-1), which were obviously lower than those in Qinghai-Tibetan Plateau and other grassland areas of China. The mean values of NPP on flat land (slope gradient <1 degree) and south slope were relatively lower. On the main alpine grasslands in Northern Tibet, the NPP from July to September occupied 64.0%-70.0% of the whole year. From 1981 to 2004, the grassland NPP within the whole Northern Tibet had a greater annual fluctuation, and tended to further reduce.