Enhanced photosynthesis and flower production in a sagebrush morphotype associated with animal burrows

Abstract

Two morphotypes of the evergreen shrub Artemisia tridentata Nutt. ssp. wyomingensis occur in the Shirley Basin of central Wyoming ͑USA͒, one of which was associated exclusively with Mima-like mounds generated by animal burrowing activity. Measured on a particularly dry year according to a 34-year precipitation record, plants growing on mounds ͑M͒ versus inter-mound locations ͑IM͒ were taller with greater leaf biomass and leaf area per unit ground area, and had over 90% of all inflorescences. As a result, the landscape consists of a patchy distribution of reproductive islands ͑~20-40 m -2 in size͒ separated by a mean distance of~30 m. In addition, greater photosynthesis per unit leaf area occurred for M plants when ephemeral leaves dominated total leaf area in spring and early summer, as well as during short time periods ͑ Ͻ 3 days͒ following sporadic rainfall events in summer when only perennial leaves were present. As a result, estimated total annual carbon gain was 41% greater for M plants from May to mid-June, but was not significantly different from IM plants for the remainder of the season, resulting in a total summer carbon gain that was 14% greater in M plants. Stomatal and nonstomatal conductances to CO 2 uptake were also greater for the ephemeral leaves of M plants, along with lower internal CO 2 concentrations ͑193 Ϯ 4 l l -1 vs. 209 Ϯ 8 l l -1 , respectively͒. M plants also maintained higher xylem water potentials throughout most of the growth season ͑-1.1 Ϯ 0.1 SD MPa in May, declining to Ϫ 4.4 Ϯ 0.3 SD MPa in August͒, along with higher water use efficiencies ͑photosynthesis/transpiration͒. M and IM soils did not differ significantly in total organic or nitrate contents, although leaf nitrogen content was higher in M plants when photosynthesis was also greater. Photosynthesis in M plants also responded more positively to afternoon showers greater than about 7 mm compared to IM plants. Thus, improved water and nutrient relations was associated with enhanced photosynthetic carbon gain in M plants, enabling greater flower production. Moreover, morphotypic plasticity coupled with the effects of animal burrows may have substantially increased sexual reproductive success in A. t. wyomingensis.

Antioxidant Capacity Of Wyoming Big Sagebrush (Artemisia tridentataSSP.Wyomingensis) Varies Spatially and is Not Related to the Presence of a Sagebrush Dietary Specialist

“…This finding may be due to the difference in resources and growth strategies between plants on- and off-mounds. For example, on-mound plants are taller, with larger biomass and greater photosynthesis per unit leaf area, than are off-mound plants (Hill et al 2005). The investment in growth by an individual plant or in a specific leaf type may come with a trade-off of lower investment in chemical defenses (Endara and Coley 2011) and therefore polyphenols (Siemens et al 2012).…”

“…Plants growing on-mound are generally taller, with greater leaf biomass and leaf area per unit ground area, and have greater flower production compared to plants growing off-mound (Hill et al 2005). To compare anti -oxidant capacity between morphotypes within a population of Wyoming sagebrush at the Camas Prairie site, we collected leaves of sage -brush from paired plants on and off mounds ( n = 26) that were not occupied by pygmy rabbits.…”