Centre for Ecology & Hydrology, Environment Centre Wales, Deiniol Road, Bangor, Gwynedd, LL57 2UW, UK.
Centre for Ecology & Hydrology, Environment Centre Wales, Deiniol Road, Bangor, Gwynedd, LL57 2UW, UK; Centre for Ecology & Hydrology, Bush Estate, Penicuik, Midlothian, EH26 0QB, UK.
Environ Pollut. 2019 Oct;253:821-830. doi: 10.1016/j.envpol.2019.07.088. Epub 2019 Jul 18.
Nitrogen deposition and tropospheric ozone are important drivers of vegetation damage, but their interactive effects are poorly understood. This study assessed whether long-term nitrogen deposition altered sensitivity to ozone in a semi-natural vegetation community. Mesocosms were collected from sand dune grassland in the UK along a nitrogen gradient (5-25 kg N/ha/y, including two plots from a long-term experiment), and fumigated for 2.5 months to simulate medium and high ozone exposure. Ozone damage to leaves was quantified for 20 ozone-sensitive species. Soil solution dissolved organic carbon (DOC) and soil extracellular enzymes were measured to investigate secondary effects on soil processes. Mesocosms from sites receiving the highest N deposition showed the least ozone-related leaf damage, while those from the least N-polluted sites were the most damaged by ozone. This was due to differences in community-level sensitivity, rather than species-level impacts. The N-polluted sites contained fewer ozone-sensitive forbs and sedges, and a higher proportion of comparatively ozone-resistant grasses. This difference in the vegetation composition of mesocosms in relation to N deposition conveyed differential resilience to ozone. Mesocosms in the highest ozone treatment showed elevated soil solution DOC with increasing site N deposition. This suggests that, despite showing relatively little leaf damage, the 'ozone resilient' vegetation community may still sustain physiological damage through reduced capacity to assimilate photosynthate, with its subsequent loss as DOC through the roots into the soil. We conclude that for dune grassland habitats, the regions of highest risk to ozone exposure are those that have received the lowest level of long-term nitrogen deposition. This highlights the importance of considering community- and ecosystem-scale impacts of pollutants in addition to impacts on individual species. It also underscores the need for protection of 'clean' habitats from air pollution and other environmental stressors.
氮沉降和对流层臭氧是导致植被损害的重要因素，但它们的相互作用仍知之甚少。本研究评估了长期氮沉降是否改变了半自然植被群落对臭氧的敏感性。从中英两国沙丘草地采集了沿氮梯度（5-25kgN/ha/y，包括一个长期实验的两个样地）分布的中尺度培养箱，并进行了 2.5 个月的熏气模拟中等和高臭氧暴露。对 20 种臭氧敏感物种的叶片臭氧损伤进行了量化。测量土壤溶液溶解有机碳 (DOC) 和土壤细胞外酶，以研究对土壤过程的次生影响。接受最高氮沉降的样地的中尺度培养箱显示出与臭氧相关的叶片损伤最小，而氮污染最少的样地的臭氧损伤最大。这是由于群落水平敏感性的差异，而不是物种水平的影响。氮污染样地的臭氧敏感草本植物和莎草植物较少，而相对耐臭氧的禾本科植物比例较高。与氮沉降有关的中尺度培养箱中植被组成的这种差异赋予了对臭氧的不同恢复能力。高臭氧处理的中尺度培养箱的土壤溶液 DOC 随样地氮沉降的增加而升高。这表明，尽管“臭氧耐受”植被群落的叶片损伤相对较小，但由于同化光合作用的能力降低，其随后以 DOC 的形式通过根系损失到土壤中，可能仍会遭受生理损伤。我们得出结论，对于沙丘草地生境，臭氧暴露风险最高的地区是那些长期氮沉降水平最低的地区。这突出了在考虑单个物种的影响之外，还需要考虑污染物对群落和生态系统规模的影响。这也强调了需要保护“清洁”生境免受空气污染和其他环境胁迫。
