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Furrow irrigation, which can be combined with fertilisation by dissolving solid fertilisers in irrigation water, is the most common practice in vineyards in the Ningxia Hui Autonomous Region, and drip irrigation and fertigation have been employed in some areas. These irrigation methods and their corresponding fertilisation schemes may affect nitrous oxide (N 2 O) emissions from the soil. Therefore, it is important to use a model to simulate differences in N 2 O emissions and identify farmland management methods that limit N 2 O emissions. During the July–August 2012 and July–September 2013 growing seasons, the denitrification and decomposition (DNDC) model was tested against experimental N 2 O emissions data from vineyards in Yuquanying, Yongning, Yinchuan, Ningxia. After model validation, the simulated differences in emissions between furrow irrigation and drip irrigation were 9.86 ± 0.845 and 0.966 ± 0.464 kg ha −1 a −1 in 2012 and 2013, respectively. Thus, the emissions were reduced by approximately 72.5% and 52.4% in 2012 and 2013. In the regional simulation, the Global Warming Potential (GWP) of the annual N 2 O emission reductions reached 27,749,760 ± 5,489,160 kg CO 2 -equivalents after the vineyards in the Ningxia Autonomous Region were converted from furrow irrigation to drip irrigation. In conclusion, the DNDC model, which proved to be a powerful tool for addressing the efficacy of alternative management practices in vineyards, revealed that N 2 O emissions can be reduced by adopting drip irrigation systems rather than traditional furrow irrigation systems. [ABSTRACT FROM AUTHOR]

Stable carbon isotope composition ( δ13C) usually shows a negative relationship with precipitation at a large scale. We hypothesized that sampling method affects foliar δ13C and its response pattern to precipitation. We selected 11 sites along a precipitation gradient in Inner Mongolia and collected leaves of Leymus chinensis with five or six replications repeatedly in each site from 2009 to 2011. Additionally, we collected leaves of L. chinensis separately from two types of grassland (grazed and fenced) in 2011. Foliar δ13C values of all samples were measured. We compared the patterns that foliar δ13C to precipitation among different years or different sample sizes, the differences of foliar δ13C between grazed and fenced grassland. Whether actual annual precipitation ( AAP) or mean annual precipitation ( MAP), it was strongly correlated with foliar δ13C every year. Significant difference was found between the slopes of foliar δ13C to AAP and MAP every year, among the slopes of foliar δ13C to AAP from 2009 to 2011. The more samples used at each site the lower and convergent P-values of the linear regression test between foliar δ13C and precipitation. Furthermore, there was significant lower foliar δ13C value in presence of grazed type than fenced type grassland. These findings provide evidence that there is significant effect of sampling method to foliar δ13C and its response pattern to precipitation of L. chinensis. Our results have valuable implications in methodology for future field sampling studies. [ABSTRACT FROM AUTHOR]

Abstract: We used an eddy covariance technique to measure evapotranspiration and carbon flux over two very different growing seasons for a typical steppe on the Inner Mongolia Plateau, China. The rainfall during the 2004 growing season (344.7mm) was close to the annual average (350.43mm). In contrast, precipitation during the 2005 growing season was significantly lower than average (only 126mm). The wet 2004 growing season had a higher peak evapotranspiration (4mmday−1) than did the dry 2005 growing season (3.3mmday−1). In 2004, latent heat flux was mainly a consumption resource for net radiation, accounting for ∼46% of net radiation. However, sensible heat flux dominated the energy budget over the whole growing season in 2005, accounting for 60% of net radiation. The evaporative rate (LE/R n) dropped by a factor of four from the non-soil stress to soil water limiting conditions. Maximum half-hourly CO2 uptake was −0.68mgm−2 s−1 and maximum ecosystem exchange was 4.3gCO2 m−2 day−1 in 2004. The 2005 drought growing stage had a maximum CO2 exchange value of only −0.22mgm−2 s−1 and a continuous positive integrated-daily CO2 flux over the entire growing season, i.e. the ecosystem became a net carbon source. Soil respiration was temperature dependent when the soil was under non-limiting soil moisture conditions, but this response declined with soil water stress. Water availability and a high vapor pressure deficit severely limited carbon fixing of this ecosystem; thus, during the growing season, the capacity to fix CO2 was closely related to both timing and frequency of rainfall events. [Copyright &y& Elsevier]

Stable carbon isotope composition (δ (13)C) usually shows a negative relationship with precipitation at a large scale. We hypothesized that sampling method affects foliar δ (13)C and its response pattern to precipitation. We selected 11 sites along a precipitation gradient in Inner Mongolia and collected leaves of Leymus chinensis with five or six replications repeatedly in each site from 2009 to 2011. Additionally, we collected leaves of L. chinensis separately from two types of grassland (grazed and fenced) in 2011. Foliar δ (13)C values of all samples were measured. We compared the patterns that foliar δ (13)C to precipitation among different years or different sample sizes, the differences of foliar δ (13)C between grazed and fenced grassland. Whether actual annual precipitation (AAP) or mean annual precipitation (MAP), it was strongly correlated with foliar δ (13)C every year. Significant difference was found between the slopes of foliar δ (13)C to AAP and MAP every year, among the slopes of foliar δ (13)C to AAP from 2009 to 2011. The more samples used at each site the lower and convergent P-values of the linear regression test between foliar δ (13)C and precipitation. Furthermore, there was significant lower foliar δ (13)C value in presence of grazed type than fenced type grassland. These findings provide evidence that there is significant effect of sampling method to foliar δ (13)C and its response pattern to precipitation of L. chinensis. Our results have valuable implications in methodology for future field sampling studies.

A decrease in foliar δ (13)C with increasing precipitation is a common tendency in steppe plants. However, the rate of decrease has been reported to differ between different species or populations. We here hypothesized that plant populations in the same habitat of temperate steppes may not differ in foliar δ (13)C response patterns to precipitation, but could differ in the levels of plasticity of foliar δ (13)C across different habitats. In order to test this hypothesis, we conducted controlled watering experiments in northeast China at five sites along a west-east transect at latitude 44°N, which show substantial interannual fluctuations and intra-annual changes in precipitation among them. In 2001, watering treatment (six levels, three replicates) was assigned to 18 plots at each site. The responses of foliar δ (13)C to precipitation (i.e., the sum of watering and rainfall) were determined in populations of several grass species that were common across all sites. Although similar linear regression slopes were observed for populations of different species growing at the same site, significantly different slopes were obtained for populations of the same species growing at different sites. Further, the slope of the line progressively decreased from Site I to Site V for all species in this study. These results suggest habitat-specific differences in plasticity of foliar δ (13)C in temperate steppe grasses. This indicates that species' δ (13)C response to precipitation is conservative at the same site due to their long-term acclimation, but the mechanism responsible behind this needs further investigations.

Plants depend upon both genetic differences and phenotypic plasticity to cope with environmental variation over different timescales. The spatial variation in foliar δ(13)C levels along a moisture gradient represents an overlay of genetic and plastic responses. We hypothesized that such a spatial variation would be more obvious than the variation arising purely from a plastic response to moisture change. Leymus chinensis and Stipa spp. were sampled from Inner Mongolia along a dry-wet transect, and some of these species were transplanted to an area with a moisture gradient. For Stipa spp., the slope of foliar δ(13)C and mean annual precipitation along the transect was significantly steeper than that of foliar δ(13)C and mean annual precipitation after the watering treatment. For L. chinensis, there was a general decreasing trend in foliar δ(13)C under the different (increasing) watering levels; however, its populations showed an irregular relationship between foliar δ(13)C and moisture origin. Therefore, support for our hypothesis was obtained from Stipa spp., but not from L. chinensis.