Ecophysiological performance of the rare terrestrial orchid Platanthera integrilabia across contrasting habitats

摘要

Platanthera integrilabia is a rare terrestrial orchid species generally associated with semiopen forested wetlands in the southeastern US. It has been suggested that P. integrilabia has restrictive abiotic resource requirements; however, these requirements have not been implicitly studied despite their potential application to species conservation. We investigated the influence of light and soil moisture on P. integrilabia at landscape and local scales and population and organismal levels across and within four occurrences with contrasting canopy openness. We also evaluated the potential for leaf-level physiological responses to light and soil moisture to reflect habitat suitability and influence performance. At landscape scales, light and soil moisture were not associated with P. integrilabia density or individual size. Across sites, measures of photosynthetic light response and water-use efficiency indicated that P. integrilabia can maximize photosynthetic efficiency and energy gain in contrasting light and soil moisture environments. Minimal associations of these measures with abiotic variations within sites suggested that the capacity for adjustments across small spatial and/or temporal scales may be limited. Preservation of existing habitats associated with viable P. integrilabia occurrences is warranted, but the leaf-level ecophysiology of this species indicates that its habitat suitability also could include more open and drier sites. For populations of P. integrilabia experiencing declines in habitats with recent disturbance, we suggest the possibility that well-managed modifications to canopy cover may be beneficial.