| Effects of atmospheric trace gas on plants receive much attention at home and abroad, involved in plant ecology, plant physiology and plant nutrition. Foreign scientists have done lots of work on changes of trace gas concentrations. However, much of our current knowledge of the effects of NH3 on higher plants is predominantly derived from studies conducted in Europe, and the study subjects mainly focus on forest and grassland vegetation. As a result, few studies on atmospheric NH3 were done in agro-ecosystem. In recent years, more and more scientists have paid much attention to studies of atmospheric trace gas in China but there is seldom information to consult. Thus, it is necessary to test results obtained before. A pot experiment (using corn and winter wheat as indicators) was carried out in Open Top Chambers (OTCs) to study the effects of atmospheric NH3 concentrations on growth and development, photosynthesis characteristics, nutrient distribution, and grain yield of crops with different N efficiency genotypes under different N levels. In this experiment, there were involved in three factors: two NH3 concentrations (elevated NH3, 1000 nL L-1 or EAM; ambient NH3, 10 nL L-1 or AM), two crops (corn: N high efficiency No. 5, NE5 and N low efficiency SD19; winter wheat: N high efficiency Xiaoyan No. 6, XY6 and N low efficiency Changhan No.58, CW58), and two N levels (N deficiency, -N and N sufficiency, +N). The experiment adopted complete design scheme and there were total eight treatments. The experiment were divided into three sub-experiments, experimentâ… (corn planted in nutrition solution) , experimentâ…¡(winter wheat planted in soil) and experimentâ…¢(corn planted in soil), respectively. The main results showed as follows:1. In experimentâ… , experimentâ…¡and experimentâ…¢that elevated NH3 didn't affect total biomass of crops with different N efficiency genotypes under both N levels, but had a significant influence on above-ground biomass (P<0.05), indicating that effects of enriched NH3 on crop growth mainly affected shoots biomass production. Moreover, the effect was related to N levels, i.e. N uptake was repressed at high internal N status and became depressed when N supplies were limited. The results also showed that enhanced atmospheric NH3 had a lower negative influence on above-ground biomass production of N low efficiency genotype compared to N high efficiency genotype under N sufficiency, while NH3 had a significantly higher positive effect on biomass production of N low efficiency genotype than that of N high efficiency under N deficiency (P<0.05). This indicated that low and moderate NH3 concentration could affect crop growth and the influence might be related to crop N efficiency itself and N supply levels in growth medium. In three experiments, atmospheric NH3 enhancement leaded to lower root: shoot ratios (R/S) which was mainly due to shoot growth response. At the same time, changes of R/S also depended on crop species and sampling dates. The results showed that corn absorbed NH3 from air during early growth period and released NH3 to atmosphere during late growth period.2. In experimentâ… , elevated atmospheric NH3 significantly affected each physiology index of two corn genotypes with different N efficiency (P < 0. 05). These physiology indexes included in chlorophyll index value (stand for the relative content of chlorophyll, SPAD value), net photosynthetic rate (Pn), stomatal conductance (Gs), and root: shoot ratios (R/S) etc. The result showed that EAM treatment decreased the SPAD value, Pn and Gs of N high efficiency genotype, NE5 by 7.0%, 14.0% and 6.5%, respectively under N sufficiency compared to AM, and N low efficiency genotype decreased by 7.0%, 14.0% and 6.5%, respectively compared to AM. In contrast to high N level, EAM could significant increase all physiology indexes of both genotypes under low N level. The SPAD value, Pn and Gs of NE5 were increased by 5.7%, 7.1% and 17%, respectively, and SD19 separately increased by 7.0%,11.0% and 22.0%, respectively compared to AM. During three experiments the result also demonstrated that EAM significantly increased leaf SPAD value and pigment contents (Chla and Chlb) of corn/wheat (P < 0. 05). This effect could be attributed to the nitrogen increase in the leaves.3. Elevated atmospheric NH3 didn't remarkably affect leaf Fo value of two N efficiency genotypes corn under both N levels (P>0.05). The other chlorophyll fluorescence, such as Fm and Fv, was significantly affected by NH3 concentration treatments and N levels. The result indicated that compared to AM treatment, EAM significantly decreased leaf Fm and Fv of NE5 under N sufficiency, while both Fm and Fv of SD19 increased significantly (P<0.05). However, effects of NH3 enrichment on Fm and Fv value of both genotypes under N deficiency were in contrast to N sufficiency treatment. Moreover, the increased atmospheric NH3 could reduce the qN and qP value of both N efficiency corn genotypes, which indicated that the protection function of crops on photosynthesis was lower under high atmospheric NH3 compared to normal atmospheric NH3 concentrations.4. In experimentâ…¡, NH3 enrichment significantly increased the plant height, above-ground biomass production and grain yield of N low efficiency genotype, CW58 under N deficiency treatment (P< 0.05). The increased NH3 had a positive influence on these items of N high efficiency genotype, XY6 but the effect was lower. Under sufficient N soil, however, both plant height and grain yield in CW58 significantly increased when atmospheric NH3 concentrations were enhanced, while the corresponding items in XY6 both reduced. In addition, the mean grain yield increase in winter wheat CW58 and decrease in XY6 due to NH3 concentration enrichment were 11.0 % and 26.8 %, respectively in N-sufficient plants. ANOVA showed that the effects of increased NH3 concentration significantly influenced every item investigated of winter wheat grain yield components (P < 0.001).5. Elevated NH3 significantly increased canopy water use efficiency (WUE) and N apparent recovery fraction (Nr) of winter wheat with two N efficiency genotypes and also increased root N-uptake efficiency (NRE) of N low efficiency genotype, CW58 (P<0.05). N use efficiency (NUE) of both genotypes wheat obviously decreased under EAM. Compared to AM, EAM significantly increased the canopy WUE in XY6 and CW58 by 20.6% and 15.9%, respectively under–N treatment. The NUE of XY6 and CW58 in NH3 enrichment was remarkably lower 14.2% and 23.0% than that of ambient NH3 concentration under–N treatment. However, EAM reduced NUE in XY6 and CW58 by 43.6% and 41.2%, respectively compared to AM under +N treatment. There were significant difference between two NH3 concentrations (P<0.01). The result also indicated that under N deficiency, EAM reduced the root matter ratio (RMR) of CW58 by 23.9% significantly compared to AM (P<0.05) while the RMR of XY6 only declined by 1.0% (P>0.05). Moreover, EAM treatment increased the RMR of XY6 by 22.2% significantly compared to AM treatment under N sufficiency, while the RMR of CW58 was significantly reduced by 35.1% (P<0.05).6. Nitrogen content of grain was highest, followed by glumes, then was leaf, rachis and stem, and root was lowest. Nitrogen uptake of grain was highest, followed by leaf ad stem, then was glumes and root, and rachis was lowest. Elevated atmospheric NH3 increased N content of grain in XY6 and CW58 by 45.7% and 37.6%, respectively under sufficiency-N level while the grain N content of XY6 and CW58 increased by 74.8% and 74.6%, respectively under deficiency-N level. Therefore, EAM could increase N uptake of winter wheat compared to AM treatment, but the effect was responsible for the distribution proportion of plant different organs. For N uptake of the whole plant, total N content (TN) under–N treatment was higher than that of +N treatment when atmospheric NH3 was enhanced. This indicated that NH3 enrichment could improve TN contents of crops, and the effect showed stronger on winter wheat growing in–N status.7. From the point of view of effects of elevated NH3 concentration on photosynthesis, chlorophyll fluorescence, root and shoot characteristics, assimilation and nutrient distribution and nutrient efficiency of corn/winter wheat, lower and more realistic NH3 had an influence of N nutrition on crops. The direct of"fertilizer"effects of enriched atmospheric NH3 on plant growth and N assimilation could be used as an additional nitrogen source. However, the effect of extra N input via leaves the influence might be related to crop N efficiency itself (the difference between genotypes) and N supply levels in growth medium. All these results indicated that the absorbed atmospheric NH3 by plants may improve crop nitrogen nutrition growing in low N medium, and there might be more significantly positive effect on low nitrogen efficiency genotype, which was consistent with our hypothesis.
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