Guangdong Provincial Key Laboratory of Applied Botany & Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China.
Guangdong Forestry Survey and Planning Institute, Guangzhou, China.
Glob Chang Biol. 2024 Feb;30(2):e17192. doi: 10.1111/gcb.17192.
Obtaining a holistic understanding of the impacts of atmospheric nitrogen deposition on multiple ecosystem services of forest is essential for developing comprehensive and sustainable strategies, particularly in heavy N deposition regions such as subtropical China. However, such impacts remain incompletely understood, with most previous studies focus on individual ecosystem function or service via understory N addition experiments. To address this knowledge gap, we quantified the effects of over-canopy and understory N additions on multiple ecosystem services based on a 7-year large-scale field experiment in a typical subtropical forest. Our results showed continued over-canopy N addition with 50 kg ha year over a period of 4-7 years significantly increased plant nutrient retention, but did not affect the services of soil nutrient accumulation, water yield, C sequestration (in plants and soil), or oxygen release. There were trade-offs between the soil and plant on providing the services of nutrient accumulation/retention and C sequestration under over-canopy N addition. However, without uptake and retention of tree canopy, the trade-off between soil and plant were more weaken under the understory N addition with 50 kg ha year , and their relationships were even synergetic under the understory N addition with 25 kg ha year . The results suggest that understory N addition cannot accurately simulate the effects of atmospheric N deposition on multiple services, along with mutual relationships. Interestingly, the services of plant N, P retention, and C sequestration exhibited a synergetic increase under the over-canopy N addition but a decrease under the understory N addition. Our results also found tree layer plays a primary role in providing plant nutrient retention service and is sensitive to atmospheric N deposition. Further studies are needed to investigate the generalized effects of forest canopy processes on alleviating the threaten of global change factors in different forest ecosystems.
获得对大气氮沉降对森林多种生态系统服务影响的整体理解，对于制定全面和可持续的策略至关重要，特别是在像中国亚热带这样的重氮沉降地区。然而，这些影响仍未被完全理解，大多数先前的研究都通过林下添加氮的实验来关注单个生态系统功能或服务。为了弥补这一知识空白，我们基于一个典型亚热带森林的 7 年大规模野外实验，量化了林冠和林下添加氮对多种生态系统服务的影响。我们的研究结果表明，在 4-7 年内持续进行林冠添加，每年添加 50 公斤/公顷的氮，显著增加了植物养分保持，但不影响土壤养分积累、水分产量、碳固存（植物和土壤）或氧气释放等服务。在林冠添加下，土壤和植物在提供养分积累/保持和碳固存服务方面存在权衡。然而，没有树冠的吸收和保持，在林下添加 50 公斤/公顷的氮下，这种权衡关系更为弱化，而在林下添加 25 公斤/公顷的氮下，它们的关系甚至是协同的。研究结果表明，林下添加氮不能准确模拟大气氮沉降对多种服务及其相互关系的影响。有趣的是，在林冠添加氮下，植物氮、磷保持和碳固存的服务表现出协同增加，而在林下添加氮下则减少。我们的研究结果还发现，树木层在提供植物养分保持服务方面起着主要作用，并且对大气氮沉降敏感。需要进一步的研究来调查森林冠层过程在不同森林生态系统中缓解全球变化因素威胁的普遍影响。
