中科院华南植物园科学家近期研究发现，原始林比次生林和人工林更加脆弱。有关研究成果日前在线发表于《环境科学与技术》杂志。

针对氮沉降全球化的背景，华南植物园生态系统管理研究组副研究员鲁显楷、博士生毛庆功、研究员莫江明等人选取中国南方典型的三种森林生态系统：原始（或成熟林）、次生林和人工林，探讨了不同土地利用历史的生态系统土壤缓冲能力对长期氮沉降的响应。

研究发现，原始林的土壤缓冲能力高于曾受到严重毁林干扰的次生林和人工林，但长期高氮沉降仅降低了原始林的土壤缓冲能力，对次生林和人工林没有明显影响。进一步研究发现，土地利用历史导致的生态系统氮状态不同是上述分歧响应的重要原因。然而，相对“氮限制”的次生林和人工林则属于恢复中的生态系统，仍可吸收大量沉降的氮，从而减缓了氮沉降诱发的元素流失。

上述发现挑战了有关生态系统稳定性的传统观点；该观点认为，原始林通常具有更加保守的元素地球化学循环模式，在应对外界干扰时，比近期干扰林具有更大的弹性。因此，在未来全球变化加剧背景下，从生物多样性保护的角度出发，与其他低氮状态林型相比，人们应更关注“富氮的”原始林/成熟林，因为元素的流失难以逆转。（来源：中国科学报 李洁尉 周飞）

Divergent Responses of Soil Buffering Capacity to Long-Term N Deposition in Three Typical Tropical Forests with Different Land-Use History

Abstract  Elevated anthropogenic nitrogen (N) deposition has become an important driver of soil acidification at both regional and global scales. It remains unclear, however, how long-term N deposition affects soil buffering capacity in tropical forest ecosystems and in ecosystems of contrasting land-use history. Here, we expand on a long-term N deposition experiment in three tropical forests that vary in land-use history (primary, secondary, and planted forests) in Southern China, with N addition as NH4NO3 of 0, 50, 100, and 150 kg N ha–1 yr–1, respectively. Results showed that all three forests were acid-sensitive ecosystems with poor soil buffering capacity, while the primary forest had higher base saturation and cation exchange capacity than others. However, long-term N addition significantly accelerated soil acidification and decreased soil buffering capacity in the primary forest, but not in the degraded secondary and planted forests. We suggest that ecosystem N status, influenced by different land-use history, is primarily responsible for these divergent responses. N-rich primary forests may be more sensitive to external N inputs than others with low N status, and should be given more attention under global changes in the future, because lack of nutrient cations is irreversible.

原文链接：http://pubs.acs.org/doi/ipdf/10.1021/es5047233