THE GROWTH AND DEVELOPMENT OF HETEROPOGON CONTORTUS (TEMPERATURE, MICROSITES).

Abstract

Studies were conducted on Heteropogon contortus at three natural stands and a common nursery in southeast Arizona and under controlled conditions. The objective was to examine H. contortus growth and development and relate it to concurrently measured environmental variables, especially soil temperature. It was hypothesized that response to such environment variables would be sufficiently consistent to serve as an indicator of range site characteristics. Response to temperature of local accessions was examined under controlled conditions to confirm field observations and determine the possibility of ecotypic differences. Common nursery studies examined phenotypic response of local accessions plus others from outside the region, to examine ecotypic response. Major conclusions were that H. contortus distribution pattern varies among sites of different temperature and/or moisture regime. Sites where H. contortus is prominent have definite characteristics, associated with warm microsites at high elevations (southern aspects, increasing slope) and mesic microsites at low elevations (the borders of washes, roadsides or microdepressions). Growth was entirely associated with the current year, with no carry-over of vegetative tillers from previous years. Growth began in spring, but was soon restricted by depleted soil moisture. Major growth, flowering and seedling establishment occurred during summer rains. Growth ceased with the first frost. Seedling survival appeared temperature dependent at high elevations, extreme temperatures perhaps responsible for age structure differences among sites. Overall growth and development and microsite requirements appear sufficiently consistent for H. contortus presence and growth pattern to indicate range site characteristics, especially temperature. The response to temperature of H. contortus is typical of C4 species, the temperature threshold for leaf elongation being approximately 15 C. However, carry-over effects of cold nights together with warm days may reduce elongation. There is little ecotypic difference in response to temperature among local accessions. However, non-local material differs in cold tolerance (both more or less tolerant) and flowering date from local accessions. Some accessions may be more valuable for early-season growth than local accessions if H. contortus establishment is considered.