دانلود رایگان مقاله اثرات غلطت ازن بر چرخه نیتروژن خاک میان ارقام گندم

Abstract

Elevated O3 (eO3) has strong effects on natural and managed ecosystems, including decreased plant growth, plant tissue quality, species richness, plant litter inputs, decomposition, and root turnover. However, the effects of eO3 on soil nitrogen (N) cycling are poorly understood. Here, a free -air O3 enrichment experiment was conducted from 2007 to 2012, in which two O3-tolerant wheat cultivars and two O3-sensitive cultivars were grown under ambient O3 (aO3, 40 ppb) and eO3 (60 ppb). We used a 15N pool dilution technique to investigate N transformation rates and N availability in the soils in 2012. Both gross and net N transformation rates were significantly decreased (P < 0.05) by eO3 in soils growing sensitive wheat cultivars, but were unchanged in soils growing tolerant cultivars. Compared with aO3, NH4 + and NO3
concentrations were significantly increased (P < 0.05) by eO3 in soils growing sensitive cultivars but not in soils growing tolerant cultivars. Ammonia monooxygenase activity was significantly increased by eO3 while nitrate reductase activity was significantly decreased. Additionally, redundancy analysis (RDA) suggested that microbial community structure was largely shaped by soil and plant characteristics such as DOC, root C/N ratio, MBC/MBN, shoot/root ratio, root N, soil N and pH. In conclusion, wheat cultivars play an important role in determining the effects of elevated O3 on N transformations. This study provides new insights into our understanding of how changes in microbial diversity and metabolism as mediated by plants will alter N cycling and ecosystem N availability in response to eO3 and suggests that these effects will differ among different plants.

4. Discussion

Understanding the effects of eO3 on soil N cycling is important to predict soil N availability for sustainable agroecosystems under climate change. In this study, we investigated N cycling, plant and soil properties, and soil microbial community structure for four wheat cultivars under aO3 and eO3. We predicted that eO3 would decrease soil microbial activity including N cycling due to lower crop productivity and belowground inputs (Zhu et al., 2011; Simpson et al., 2014). However, we predicted that the effects would depend on the sensitivity of wheat cultivars, with eO3 only decreasing N cycling in sensitive wheat cultivars, but not in tolerant wheat cultivars. Our results were consistent with our predictions, and showed that eO3 significantly decreased N cycling in sensitive wheat cultivars (Y2, Y19) but had no effects on tolerant wheat cultivars (Y15, Y16). Specifically, our results showed that gross ammonifi- cation, gross nitrification and net nitrification were significantly decreased by eO3 in Y2 and Y19 but not in Y15 and Y16. Net ammonification became less negative under eO3 in Y2 and Y19, but not in Y15 and Y16, most likely because nitrification and ammonium immobilization decreased more than gross ammoni- fication. Our results are consistent with the decreases in gross ammonification observed in forest (Holmes et al., 2006), meadow (Kanerva et al., 2007) and cropland ecosystems (Pereira et al., 2011). However, the inhibition of nitrification in the soils with sensitive cultivars may improve N retention as NH4 + is less mobile compared to NO3
that can be leached or removed by surface runoff. As far as we know, our study is the only report of eO3 effects on gross nitrification, which reduced only in the sensitive cultivars. The only previous study that explored responses of N cycling to eO3 for different plant species found no effects of species (Holmes et al., 2003). Further studies should be conducted to explore eO3 effects on N cycling with more plant species with different sensitivity to O3.