Acacia tree density strongly affects N and P fluxes in savanna
Acacia tree density strongly affects N and P fluxes in savanna
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金合欢树密度强烈影响稀树草原的氮和磷通量
DOI：
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发表时间：
2015
期刊：
影响因子：
4
通讯作者：
H. Olde Venterink
中科院分区：
文献类型：
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作者：
Judith Sitters;P. Edwards;W. Suter;H. Olde Venterink
热带稀树草原生态系统中养分循环的研究很少考虑通量如何受到树木密度和食草动物养分再分配的局部变化的影响。研究了热带稀树草原生态系统中桑给巴尔相思树密度对氮素固定输入、火烧输出以及N、P通过食草动物归还的影响。我们发现，N输入和P输出都随着密度的增加固氮树，N效应是由于树密度，而不是固定率的差异。然而，总氮输出量由于火灾并不随树木密度，因为从草本层的损失减少，从乔木层的损失增加。与此相反，总P输出增加树木密度，因为从乔木层的P损失超过那些从草本层。我们认为，在固定氮的树木密度的变化，再加上火灾的影响，可能会导致显着的差异，在当地的N和P平衡稀树草原植被。在某种程度上，这些差异可能是均衡的趋势，浏览草食动物转移营养物质从金合欢-草为主的地区。我们的结论是侵占固氮树木和灌木生态系统的属性，如N和P的动态有重要的后果。
Studies of nutrient cycling in savanna ecosystems rarely consider how fluxes are affected by local variations in tree density and nutrient redistribution by herbivores. We studied how the density of Acacia zanzibarica trees in a humid savanna ecosystem affected the input of nitrogen (N) through N2-fixation and N and phosphorus (P) outputs through fire and also internal pathways of N and P return through herbivores. We found that N inputs and P outputs both increased with increasing density of N2-fixing trees, the N effect being due to tree density rather than to differences in the rate of N2-fixation. However, total N outputs due to fire did not vary with tree density because losses from the herb layer decreased as losses from the tree layer increased. In contrast, total P outputs did increase with tree density because P losses from the tree layer exceeded those from the herb layer. We suggest that variation in the density of N2-fixing trees coupled with the effects of fire can cause substantial differences in the local N and P balances in savanna vegetation. To some extent, these differences may be evened out by the tendency for browsing herbivores to transfer nutrients from Acacia- to grass-dominated areas. We conclude that encroachment by N2-fixing trees and shrubs has important consequences for ecosystem properties such as N and P dynamics.