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- Effects of water regime during rice-growing season on annual direct N2O emission in [Annual paddy rice–winter wheat rotation constitutes one of the typical cropping systems in southeast China,in which various water regimes are currently practiced during the rice-growing season, including continuous
flooding (F), flooding-midseason drainage-reflooding (F-D-F), and flooding-midseason drainage-reflooding and moisture but without waterlogging (F-D-F-M). We conducted a field experiment in a rice–winter wheat rotation system to gain an insight into the water regime-specific emission factors and background emissions of nitrous oxide (N2O) over the whole annual cycle. While flooding led to an unpronounced N2O emission during the rice-growing season, it incurred substantial N2O emission during the following non-rice season.
During the non-rice season, N2O fluxes were, on average, 2.61 and 2.48 mg N2O–Nm?2 day?1 for the 250kg N ha?1 applied plots preceded by the F and F-D-F water regimes, which are 56% and 49% higher than those by the F-D-F-M water regime, respectively. For the annual rotation system experienced by continuous
flooding during the rice-growing season, the relationship between N2O emission and nitrogen input predicted the emission factor and background emission of N2O to be 0.87% and 1.77 kg N2O–N ha?1, respectively. For the plots experienced by the water regimes of F-D-F and F-D-F-M, the emission factors of N2O averaged 0.97% and 0.85%, with background N2O emissions of 2.00 kg N2O–N ha?1 and 1.61 kg N2O–N ha?1 for the annual rotation system, respectively Annual direct N2O–N emission was estimated to be 98.1 Gg yr?1 in Chinese rice-based cropping systems in the 1990s, consisting of 32.3 Gg during the rice-growing season and 65.8 Gg during the non-rice season, which accounts for 25–35% of the annual total emission from croplands in China.]
- Estimates of synthetic fertilizer N-induced direct nitrous oxide emission from Chinese croplands during 1980–2000 [There is increasing concern that agricultural intensification in China has greatly increased N2O emissions due to rapidly increased fertilizer use. By linking a spatial database of precipitation, synthetic fertilizer N input, cropping rotation and area via GIS, a precipitation-rectified emission factor of N2O for upland croplands and water regime-specific emission factors for irrigated rice paddies were adopted to estimate annual synthetic fertilizer N-induced direct N2O emissions (FIE-N2O) from Chinese croplands during 1980–2000. Annual FIE-N2O was estimated to be 115.7 Gg N2O-N year-1 in the 1980s and 210.5 Gg N2O-N year-1 in the 1990s, with an annual increasing rate of 9.14 Gg N2O-N year-1 over the period 1980–2000. Upland croplands contributed most to the national total of FIE-N2O, accounting for 79% in 1980 and 92% in 2000. Approximately 65% of the FIE-N2O emitted in eastern and southern central China.]
- Expression analysis suggests potential roles of microRNAs for phosphate and arbuscular mycorrhizal signaling in Solanum lycopersicum. [MicroRNAs (miRNAs) have emerged as a class of gene expression regulators that play crucial roles in many biological processes. Recently, several reports have revealed that micoRNAs participate in regulation of symbiotic interaction between plants and nitrogen-fixing rhizobia bacteria. However, the role of miRNAs in another type of plant-microbe interaction, arbuscular mycorrhizal (AM) symbiosis, has not been documented. We carried out an microarray screen and poly(A)-tailed RT-PCR validation for miRNA expression in tomato (Solanum lycopersicum) under varying phosphate (Pi) availability and AM symbiosis conditions. In roots, miRNA158, miRNA862-3p, miRNA319, miRNA394 and miR399 were differentially regulated under three different treatments, Pi sufficient (+P), Pi deficient (-P), and AM symbiosis (+M). In leaves, up to 14 miRNAs were up or down regulated under either or both of the Pi treatments and AM symbiosis, of which miR158, miR319 and miR399 were responsive to the treatments in both roots and leaves. We detected that miR395, miR779.1, miR840 and miR867 in leaves were specifically responsive to AM symbiosis, which is independent of Pi availability, while miR398 in leaves and miR399 in both roots and leaves were Pi starvation induced. Furthermore, miR158 in roots as well as miR837-3p in leaves were responsive to both Pi deprivation and AM colonization. In contrast, miR862-3p in roots was responsive to Pi nutrition, but not to AM symbiosis. Moreover, the group of miRNA consisting miR319 and miR394 in roots and miR158, miR169g*, miR172, miR172b*, miR319, miR771 and miR775 in leaves were up- and down-regulated by Pi starvation, respectively. The data suggests that altered expression of distinct groups of miRNA is an essential component of Pi starvation induced responses and AM symbiosis.]
- Increased competitive ability and herbivory tolerance in the invasive plant Sapium sebiferum [The evolution of increased competitive ability (EICA) hypothesis predicts that release from natural enemies in the introduced range favors exotic plants evolving to have greater competitive ability and lower herbivore resistance than conspecifics from the native range. We tested the EICA hypothesis in a common garden experiment with Sapium sebiferum in which seedlings from native (China) and invasive (USA) populations were grown in all pairwise combinations in the native range (China) in the presence of herbivores. When paired seedlings were from the same continent, shoot mass and leaf damage per seedling were significantly greater for plants from invasive populations than those from native populations. Despite more damage from herbivores, plants from invasive populations still outperformed those from native populations when they were grown together. Increased competitive ability and higher herbivory damage of invasive populations relative to native populations of S. sebiferum support the EICA hypothesis. Regression of biomass against percent leaf damage showed that plants from invasive populations tolerated herbivory more effectively than those from native populations. The results of this study suggest that S. sebiferum has become a faster-growing, less herbivore-resistant and more herbivore-tolerant plant in the introduced range. This implies that increased competitive ability of exotic plants may be associated with evolutionary changes in both resistance and tolerance to herbivory in the introduced range. Understanding these evolutionary changes has important implications for biological control strategies targeted at problematic invaders.]
- Plasticity of Sapium sebiferum seedling growth to light and water resources: inter- and intraspecific comparisons [Two main hypotheses have been posed to explain the role of phenotypic plasticity in the invasive success of exotic plants: (1) invasive species may be more plastic than resident species in the introduced range, and (2) invasive populations of an exotic species may be more plastic relative to native populations due to evolutionary changes after introduction. To test the first hypothesis, we conducted a greenhouse pot experiment in which seedlings of invasive Sapium sebiferum competed against native Schizachyrium scoparium grasses under different light and water conditions. To test the second hypothesis, we performed an additional greenhouse pot experiment in which seedlings from native and invasive populations of S. sebiferum were grown under environmental treatments analogous to those in the first greenhouse experiment. Compared to native S. scoparium grasses, or to S. sebiferum seedlings from native populations, growth rates of S. sebiferum seedlings from invasive populations were generally higher. When they were competing with S. scoparium grasses, the greater response of S. sebiferum to light and water conditions reflected different patterns: S. sebiferum seedlings were better able to respond with increased growth in unflooded soils, whereas S. sebiferum had more robust growth in the shaded conditions. No difference in responses to change in water conditions, but a significant difference in responses to variation in light conditions was found between two population types of S. sebiferum. The results of this study suggest that relative to S. scoparium, the greater plasticity of S. sebiferum to variation in light conditions is evolved in the introduced range, while that to variation in water conditions reflects an innate property.]
- Decreased resistance and increased tolerance to native herbivores of the invasive plant Sapium sebiferum [Release from natural enemies may favor invasive plants evolving traits associated with reduced herbivore-resistance and faster-growth in introduced ranges. Given a genetic trade-off between resistance and tolerance, invasive plants could also become more tolerant to herbivory than conspecifics in the native range. We conducted a field common garden study in the native range of Sapium sebiferum using seeds from native Chinese populations and invasive North American populations to compare their growth and herbivory resistance. We also performed a cage-pot experiment to compare their resistance and tolerance to Bikasha collaris beetles that are specialist feeders on S. sebiferum trees in China. Results of the common garden study showed that Sapium seedlings of invasive populations relative to native populations were more frequently attacked by native herbivores. Growth and leaf damage were significantly higher for invasive populations than for native populations. Growth of invasive populations was not significantly affected by insecticide spray, but insecticide spray benefited that of native populations. In the bioassay trial, beetles preferentially consumed leaf tissue of invasive populations compared to native populations when beetles had a choice between them. Regression of percent leaf damage on biomass showed that invasive populations tolerated herbivory more effectively than native populations. Our results suggest that S. sebiferum from the introduced range had lower resistance but higher tolerance to specialist herbivores. Both defense strategies could have evolved as a response to the escape from natural enemies in the introduced range.]
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