School of Biological Sciences, Washington State University, Vancouver, Washington, United States of America.
PLoS One. 2010 Oct 26;5(10):e13598. doi: 10.1371/journal.pone.0013598.
The effect of low nutrient availability on plant-consumer interactions during early succession is poorly understood. The low productivity and complexity of primary successional communities are expected to limit diversity and abundance of arthropods, but few studies have examined arthropod responses to enhanced nutrient supply in this context. We investigated the effects of nitrogen (N) and phosphorus (P) addition on plant productivity and arthropod abundance on 24-yr-old soils at Mount St. Helens volcano.
METHODOLOGY/PRINCIPAL FINDINGS: We measured the relative abundance of eight arthropod orders and five families in plots that received N, P, or no nutrients for 3-5 years. We also measured plant % cover, leaf %N, and plant diversity. Vegetation responded rapidly to N addition but showed a lagged response to P that, combined with evidence of increased N fixation, suggested P-limitation to N availability. After 3 yrs of fertilization, orthopterans (primarily Anabrus simplex (Tettigoniidae) and Melanoplus spp (Acrididae)) showed a striking attraction to P addition plots, while no other taxa responded to fertilization. After 5 yrs of fertilization, orthopteran density in the same plots increased 80%-130% with P addition and 40% with N. Using structural equation modeling, we show that in year 3 orthopteran abundance was associated with a P-mediated increase in plant cover (or correlated increases in resource quality), whereas in year 5 orthopteran density was not related to cover, diversity or plant %N, but rather to unmeasured effects of P, such as its influence on other aspects of resource quality.
CONCLUSIONS/SIGNIFICANCE: The marked surprising response to P by orthopterans, combined with a previous observation of P-limitation in lepidopteran herbivores at these sites, suggests that P-mediated effects of food quantity or quality are critical to insect herbivores in this N-P co-limited primary successional system. Our results also support a previous suggestion that the availability of N in these soils is P-limited.
在早期演替过程中，低养分可用性对植物-消费者相互作用的影响还不太清楚。初级演替群落的低生产力和复杂性预计会限制节肢动物的多样性和丰度，但很少有研究调查过在这种情况下节肢动物对增强养分供应的反应。我们研究了氮（N）和磷（P）添加对 24 岁圣海伦斯火山土壤上植物生产力和节肢动物丰度的影响。
方法/主要发现：我们测量了在接受 N、P 或无养分 3-5 年的样方中 8 个节肢动物目和 5 个科的相对丰度。我们还测量了植物的盖度、叶 %N 和植物多样性。植被对 N 添加的反应迅速，但对 P 的反应滞后，加上证据表明增加了固氮作用，这表明 P 限制了 N 的可用性。在施肥 3 年后，直翅目（主要是 Anabrus simplex（螽蟴科）和 Melanoplus spp（蝗科））对 P 添加样方表现出明显的吸引力，而其他分类群则没有对施肥做出反应。在施肥 5 年后，同一样方中的直翅目密度增加了 80%-130%，P 添加量增加了 40%。使用结构方程模型，我们表明在第 3 年，直翅目丰度与 P 介导的植物盖度增加有关（或与资源质量的相关增加有关），而在第 5 年，直翅目密度与盖度、多样性或植物 %N 无关，而是与 P 的未测量影响有关，例如其对资源质量的其他方面的影响。
结论/意义：直翅目对 P 的显著反应，加上之前在这些地点观察到的鳞翅目食草动物对 P 的限制，表明 P 介导的食物数量或质量的影响对这种 N-P 共同限制的初级演替系统中的昆虫食草动物至关重要。我们的结果也支持了之前的一个观点，即这些土壤中 N 的可用性受到 P 的限制。
