Ecosystem responses to external inputs of nutrients and organisms are highly variable. Theory predicts that ecosystem traits will determine the responses to spatial subsidies, but evidence for how vegetation structure can modulate those effects is lacking. We investigated how vegetation structure (i.e., leaf area index [LAI] and vegetation height) influenced the ecosystem and community responses to insect spatial subsidies in a subarctic grassland. Our experiment consisted of a 2 × 2 manipulation where in one treatment we either blocked flying insects over a 2‐yr period in 1‐m² plots near the shore of Lake Mývatn, Iceland, where deposition of aquatic adult midges (Diptera: Chironomidae) to land is high, or left control plots accessible to flying midges. In the second treatment, grassland vegetation was cut (tall vs. short) at the start of each season and then allowed to regrow. We then measured litter decomposition and arthropod composition and density within each plot (n = 6 replicates × 4 treatments). Midge‐exclusion cages reduced midge deposition by 81% relative to the open plots. Vegetation cutting initially reduced LAI and vegetation height by 3× and 1.5×, respectively, but these were not different by the end of the second‐growing season. We found that vegetation structure modulated the effects of midge subsides on litter decomposition, with taller canopies intercepting more insect subsidies than shorter ones, leading to 18% faster litter decomposition. In contrast, the short‐vegetation plots intercepted fewer subsidies and had higher temperatures and sunlight, resulting in no effects of midges on decomposition. However, by the end of the experiment when all vegetation structure characteristics had converged across all plots, we found no differences in decomposition between treatments. The effects of midge subsidies on arthropod composition depended on the vegetation structure, suggesting that arthropods might also be responding to the structural effects on spatial subsidies. Our findings indicate that vegetation structure can modify the abiotic environment and the quantity of subsidies entering a recipient ecosystem as aerial insects, resulting in ecosystem‐ and community‐level responses. Thus, changing vegetation structure via habitat disturbances will likely have important implications for ecosystem functions that rely on spatial subsidies.

中文翻译：

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植被结构调节生态系统和社区对空间补贴的反应

生态系统对养分和生物体外部输入的反应是高度可变的。理论预测，生态系统特征将决定对空间补贴的反应，但是缺乏有关植被结构如何调节这些影响的证据。我们调查了植被结构（即叶面积指数[LAI]和植被高度）如何影响北极北极草原生态系统和群落对昆虫空间补贴的反应。我们的实验由2×2操作组成，在一种处理中，我们要么在1 m ²的2年时间内阻止了飞行中的昆虫冰岛米湖湖岸附近的地块，水生成年mid（双翅目：Chironomidae）在陆地上的沉积量很高，或者左侧控制区易于飞行的mid虫进入。在第二种处理方法中，在每个季节开始时将草地植被砍伐（矮矮），然后让其再生。然后，我们在每个样地中测量了凋落物分解，节肢动物的组成和密度（n = 6次重复×4次治疗）。相对于开阔地块，排除笼使reduced沉积减少了81％。最初，植被砍伐使LAI和植被高度分别降低了3倍和1.5倍，但到第二个生长季结束时，两者没有变化。我们发现，植被结构调节了蚊子塌陷对凋落物分解的影响，较高的树冠比较短的树冠截获更多的昆虫补贴，从而使凋落物的分解速度加快了18％。相比之下，短植被地块的补贴较少，温度和日照较高，因此没有mid虫对分解的影响。但是，到实验结束时，当所有植被的所有植被结构特征都收敛时，我们发现处理之间的分解没有差异。蚊虫补贴对节肢动物组成的影响取决于植被结构，这表明节肢动物可能也对空间补贴的结构效应作出了反应。我们的发现表明，植被结构可以改变非生物环境以及作为空中昆虫进入受体生态系统的补贴的数量，从而导致生态系统和社区层面的反应。因此，通过栖息地干扰改变植被结构可能会对依赖空间补贴的生态系统功能产生重要影响。我们的发现表明，植被结构可以改变非生物环境以及作为空中昆虫进入受体生态系统的补贴的数量，从而导致生态系统和社区层面的反应。因此，通过栖息地干扰改变植被结构可能会对依赖空间补贴的生态系统功能产生重要影响。我们的发现表明，植被结构可以改变非生物环境以及作为空中昆虫进入受体生态系统的补贴的数量，从而导致生态系统和社区层面的反应。因此，通过栖息地干扰改变植被结构可能会对依赖空间补贴的生态系统功能产生重要影响。