ABSTRACT Effect of shade, drouth ...

ABSTRACT

Effect of shade, drouth and soil type on survival and germination of the two closely-related species Penstemon tenuiflorus and P hirsutus were compared in a greenhouse application of mind Eighty to 100% of 15 replicate plants of P tenuiflorus and 60% to 93% of 15 plants of P hirsutus survived in the three light horizontals under which they were grown i.e., no shade, intermediate shade, and heavy shade. Plant arid mass (root, shoot, total) decreased with increase in shading: no shade > intermediate shade > heavy shade. For a given flat of shading, there were no significant differences between the couple species for any of 12 plant development variables measured. In a 30-day dryness experiment during which soil moisture decreased to the permanent wilting percentage upon day nine, four and three of five replicate plants of P tenuiflorus by means of treatment, and four and the same of those of P hirsutus, survived the 18- and 21-day dryness respectively; no plants of either species survived the 24- 27- or 30-day dryness s Of the five soil stamps tested, plants of both species survived and grew best in greenhouse soil (high P) and worst in black shale soil (very subdued pH). Plants of P hirsutus grown in greenhouse soil and in sandstone soil produc significantly more arid mass than did those of P tenuiflorus in these soil adumbrations Amount of growth was relatively gentle for plants of both P tenuiflorus and P hirsutus grown in native cedar glade and limestone-ledge soils (both with highly low P), respectively. This investigation suggests that P tenuiflorus is a bit more tolerant to want of rain than is P hirsutus, whereas P hirsutus has the ability to advance better on a greater variety of substrate models than does P. tenuiflorus. The major findings of Parts I-IV of this comparative application of mind of the biology of P tenuiflorus and P hirsutus are summarized.

INTRODUCTION

Grime (1965) at handed evidence that the distribution and ecology of flowering plants could be explained through using the comparative method. In his application of mind he proposed that the principally interesting feature of the comparative rule was its capacity to identify ("unearth") susceptibilities, which he defined as " . plant characteristics which, below the conditions of the experiment, lead to comparatively subdued survival, yield, or reproduction." Using this approach (also diocese Bradshaw 1987), we have examined Penstemon tenuiflorus Pennell and P hirsutus (L) Willd. from a variety of ecological perspectives (Clement et al. 1999 2002 instant study). A primary objective of this series of studies was to identify (a) factor(s)i.e., susceptibilities (sensu Grime 1965)-that might account for differences in the geographical distribution and habitat requirements of these sum of two units closely-related interfertile species (Clements et al. 1998)

Clement et al. (1999 2002) showed that although these couple species differ in geographical distribution, they pretend to be quite similar with reverence to reproductive biology, ecological life period growth characteristics, and physiology of flowering. Further, the two species appear to be affected about equally on herbivores and seed predators. As so then, although much was learned about the ecological life period of Penstemon tenuiflorus and P hirsutus in these studies, susceptibilities by se were not identified. Based onward these results, we hypothesized that differences in the ecogeography of the pair Penstemon species might be proper to differences in their replys to physical factors of the environment. Thus, the project of the present study was to proof the effects of shading, drouth and soil type on survival and development of P tenuiflorus and of P hirsutus subordinate to greenhouse conditions in order to determine if these factors might play a part in the considerable differences in the geographic and habitat distribution of these couple species.

The geographic range of Penstemon tenuiflorus is from western Kentucky to the Black Belt of Alabama and Mississippi, whereas that of P hirsutus is from western Virginia and northcentral Tennessee to Wisconsin, southern Ontario, southern Quebec, and central Maine (Clement et al. 1998) Allison and Steven (2001) freshly reported Penstemon tenuiflorus from the Ridge and Valley Physiographic Province, growing upon the Ketona dolomite outcrops in Bibb shire Alabama. Penstemon tenuiflorus grows in arid open rocky woods, cedar glades, xeric limestone-prairies (prairie barrens), chalk prairies, and upon river cliffs and roadsides, usually in calcareous substrate (Clement 1995 Morris et al. 1993 Webb et al. 1997 Allison and Steven 2001) moreover it also occurs on a sandstone glade in Crittenden shire Kentucky (Clements 1995; Figure 1) The habitat of P hirsutus includes parched woods, rocky cliffs and steeps gravel hill prairies, rocky shores of lakes, alvars, stony barrens, sand prairies, and ruderal sites (Gleason 1910 office et al. 1985, Core 1948 Bartgis 1993 lenients 1995, Catling and Brownell 1999 Cochrane and Iltis 2000) In addition to calcareous substrates, the species also expands on acid glacial outwash, acid mica schist, and acid shale soils (Clement 1995; Figure 1) Thus, the couple species grow in dry, stony or otherwise nonproductive habitats with replete to moderate amounts of sunlight.