Positive associations between the cushion plant Azorella monantha (Apiaceae) and alpine plant species in the Chilean Patagonian Andes
Positive associations between the cushion plant Azorella monantha (Apiaceae) and alpine plant species in the Chilean Patagonian Andes
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DOI：
10.1023/a:1026281405115
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发表时间：
2003-01-01
期刊：
影响因子：
1.7
通讯作者：
Arroyo-Kalin, MA
中科院分区：
文献类型：
--
作者：
Arroyo, MTK;Cavieres, LA;Arroyo-Kalin, MA
低矮、紧凑的垫层植物是温带和亚极地高山栖息地中常见的、通常占主导地位的生命形式。垫层生命形式可以改变风的模式、温度和水分的可用性，因此垫层植物可以作为护理植物，促进其他高山植物物种在其表面的建立。有人认为，护士效应应该在压力更大的环境条件下最为明显，正如在阿尔卑斯山海拔升高时所发现的那样。用于检测护士的方法之一是研究物种之间的空间关联，其中一个物种内部或下方的极端聚集被解释为护理的证据。在南美洲南部巴塔哥尼亚高山（南纬50度）的Cerro Diente上，研究了两个海拔高度（海拔700米，对应于树线以上的海拔高度）和900米，对应于垫带带的上限)的Azorella monantha垫层内外的小气候条件（土壤和空气温度），并记录了在不同大小的垫层上生长的所有植物物种和垫层外同等大小的对偶取样区域。在5 cm深度，垫层土壤温度略高于裸地，但在900 m深度显著高于裸地。垫层微生境在700 m和900 m处的地面气温均显著高于地面气温，且在最高海拔处差异更为明显。在700 m处，共有27种植物生长在垫层内，而垫层外只有29种。在海拔900米处，相应的数字分别是34和18。在海拔最高的地方，垫层内生长的物种明显多于垫层外同等面积的物种。其中17种（48.6%）优先在垫层内生长，其中8种仅局限于垫层微生境。而在海拔700 m处，两种微生境的物种丰富度差异不显著，只有1种（3.1%）优先生长在垫层上。就个体物种而言，两个海拔高度的9个物种在700 m的垫层上表现出非优先招募，而在900 m的垫层上则表现出显著的高频率。结果表明，在Cerro Diente上与monantha Azorella的关联存在显著的海拔差异，从900 m高度非常强到700 m高度几乎没有。在恶劣的巴塔哥尼亚高山环境中，在高海拔的垫子上，较温和的空气和土壤温度、避风处以及相对于外部垫子更大的水分可用性是有利于植物在垫子上繁殖的可能因素。
Low growing, compact cushion plants are a common and often dominant life form in temperate and subpolar alpine habitats. The cushion life-form can modify wind patterns, temperature and water availability and thus cushion species could be expected to act as nurse-plants facilitating the establishment of other alpine plant species on their surfaces. It has been suggested that the nurse effect should be most pronounced under more stressful environmental conditions, as found with increasing elevation in the alpine. One of the approaches used to detect the nurses has been the study of spatial associations among species, in which extreme clumping within or beneath one species has been interpreted as evidence of nursing. We characterized microclimatic conditions (soil and air temperature) within and outside cushions of Azorella monantha at two elevations (700 m a.s.l., corresponding to an elevation just above treeline, and 900 m a.s.l., corresponding to the upper limit of the cushion belt zone) on Cerro Diente in the Patagonian alpine of southern South America (50degrees S) and recorded all plant species growing upon cushions of various sizes and for paired sampling areas of equivalent sizes outside cushions. At 5 cm depth, soil temperature was slightly higher under cushions than under bare ground, but only significantly so at 900 m. Air temperature at ground level was significantly higher in the cushion microhabitat at both 700 m and 900 m, with the difference being more exaggerated at the highest elevation. At 700 m, a total of 27 species were recorded growing within cushions as compared to 29 outside cushions. At 900 m the corresponding numbers were 34 and 18. At the highest elevation, significantly more species grow within cushions than for equal areas outside cushions. Here moreover, 17 (48.6%) species grew preferentially within cushions, with eight of the latter being limited to the cushion microhabitat at this elevation. However, at 700 m there was no significant difference in species richness in the two microhabitats, and only one species (3.1%) grew preferentially on cushions. Considering individual species, nine occurring at both elevations showed non-preferential recruitment on cushions at 700 m, but significantly higher frequencies on cushions at 900 m. Results suggest striking altitudinal variation in the association with Azorella monantha on Cerro Diente, ranging from a very strong at 900 m to near absence at 700 m. Milder air and soil temperatures, shelter from wind, and greater water availability within cushions as opposed to outside cushions are discussed as possible factors favoring strong plant recruitment on cushions at higher elevations in the harsh Patagonian alpine environment.