Oechel Walter C, Mustafa Jamil
Biology Department, McGill University, H3A 1B1, Montreal, Quebec, Canada.
Oecologia. 1979 Aug;41(3):305-315. doi: 10.1007/BF00377435.
Two concepts of vegetation function and organization are examined in this paper. The first concerns the possible relationship between energy acquisition and species dominance in a given growth form and vegetation type. The second questions whether homeostatic mechanisms operate at sufficient levels to yield similar and positive photosynthetic performance of evergreen shrubs across a marked environmental and geographical gradient in southern California. This gradient runs from the coast at 135 m to 1,435 m in the mountains and on to 1,150 m at the margin of the desert transition.Total photosynthesis in several species was estimated at each site from late spring through summer. Within a common growth form, species success correlated with photosynthetic capacity. The species with the greatest carbon uptake were best represented in the vegetation. This relationship would not be expected to hold either between widely differing growth forms or where other factors exclude or decrease the abundance or productivity of certain of the species.Across the gradient examined, species displayed a marked degree of photosynthetic homeostasis despite marked environmental changes. For example, photosynthetic uptake in Adenostoma fasciculatum varied by only 32% between the greatest and least productive areas despite large differences in precipitation and temperature. In most cases there was a strong correspondence between cover and photosynthesis across the transect studied.From the available data, the transitions from chaparral to coastal sage, montane forests, or desert transition vegetation do not appear to result from sharp suppression of photosynthetic uptake at these borders. Other factors such as those affecting germination and establishment may be responsible for these transitions. However, further investigations are required at the edges of species distribution to adequately describe the pattern that does exist and to ascertain the relationship between energy capture and species success in these areas.
本文探讨了植被功能和组织的两个概念。第一个涉及在给定的生长形式和植被类型中能量获取与物种优势之间的可能关系。第二个问题是，稳态机制是否在足够的水平上发挥作用，以使南加州明显的环境和地理梯度上的常绿灌木具有相似且积极的光合性能。这个梯度从海拔135米的海岸延伸至山区的1435米，再到沙漠过渡边缘的1150米。从春末到夏季，在每个地点估计了几个物种的总光合作用。在共同的生长形式中，物种的成功与光合能力相关。植被中碳吸收量最大的物种占比最高。在差异很大的生长形式之间，或者在其他因素排除或降低某些物种的丰度或生产力的情况下，预计这种关系不会成立。在所研究的梯度范围内，尽管环境变化明显，但物种仍表现出显著程度的光合稳态。例如，尽管降水和温度差异很大，但束花腺桤木在生产力最高和最低的地区之间的光合吸收仅相差32%。在大多数情况下，在所研究的样带中，盖度与光合作用之间存在很强的对应关系。根据现有数据，从灌丛到海岸鼠尾草、山地森林或沙漠过渡植被的转变似乎并非由于这些边界处光合吸收的急剧抑制所致。其他因素，如影响种子萌发和定居的因素，可能是这些转变的原因。然而，需要在物种分布边缘进行进一步调查，以充分描述确实存在的模式，并确定这些地区能量捕获与物种成功之间的关系。
