Gold W G, Caldwell M M
Department of Range Science and the Ecology Center, Utah State University, 84322-5230, Logan, UT, USA.
Oecologia. 1990 Jan;82(1):12-17. doi: 10.1007/BF00318527.
The spatial pattern of foliage removal from a tussock grass can influence regrowth through effects on daily carbon gain (CER). This field study examined the extent to which tussock photosynthetic responses to different defoliation patterns were associated with changes in whole-canopy attributes (e.g., foliage age structure, canopy light microclimate). During the spring growing season, 60% of the green foliage area was removed from individual Agropyron desertorum tussocks with scissors in different spatial patterns. These patterns represented extremes of defoliation patterns that might be inflicted by natural herbivores. Tussock photosynthesis (per unit foliage area) at high light (2000 μmol photons m s between 400 and 700 nm; P) increased following clipping with all defoliation patterns. The increases in P were greater when leaves were removed from low in the tussock (older leaves) than if leaves high in the canopy (younger leaves) were removed. These relative changes of P among clipping patterns paralleled the responses of CER and regrowth from an earlier study. Furthermore, the changes in P corresponded with increases in the proportion of foliage within the tussocks that was directly illuminated at midday. The greater photosynthesis of tussocks after lower-leaf removal was directly related to a higher proportion of younger foliage and a smaller fraction of foliage shaded within the tussock. In a dense canopy, such as these grass tussocks, the influence of defoliation on whole-canopy attributes may be of primary importance to whole-plant photosynthetic responses.
从草丛禾本科植物去除叶片的空间模式可通过对每日碳同化量（CER）的影响来影响其再生。本田间研究考察了草丛禾本科植物对不同去叶模式的光合响应程度与全冠层属性变化（如叶片年龄结构、冠层光微气候）之间的关联。在春季生长季节，用剪刀以不同空间模式从单株沙生冰草草丛中去除60%的绿叶面积。这些模式代表了可能由自然食草动物造成的去叶模式的极端情况。在高光强（400至700纳米波长范围内2000微摩尔光子·平方米·秒；P）下，所有去叶模式修剪后草丛光合作用（单位叶面积）均增加。从草丛下部（老叶）去除叶片时P的增加幅度大于从冠层上部（幼叶）去除叶片时。这些修剪模式间P的相对变化与早期研究中CER和再生的响应情况相似。此外，P的变化与中午时分草丛中直接受光照的叶片比例增加相对应。去除下部叶片后草丛光合作用增强直接与幼叶比例较高以及草丛内遮荫叶片比例较小有关。在像这些草丛禾本科植物这样的密集冠层中，去叶对全冠层属性的影响可能对整株植物的光合响应至关重要。
