Drought stress ecophysiology of shrub and grass functional groups on opposing slope aspects of a temperate grassland valley

Abstract

Plant functional groups with contrasting growth strategies co-occur in semiarid ecosystems. In the northern Great Plains, woody shrubs and grasses interact competitively, with shrubs prevalent on mesic hillslopes. To understand topographic influences on physiological drought acclimation, we measured seasonal photosynthetic water use in C3 shrubs ( Artemisia cana Pursh and Rhus trilobata Nutt.) and grasses ( Agropyron cristatum (L.) Gaertn. and Stipa viridula Trin.) on north- and south-facing slopes. Relationships between abiotic controls and photosynthesis were similar on both aspects, indicating an absence of long-term photosynthetic acclimation to xeric, south-facing conditions. Acclimatory differences were observed between functional groups. Soil moisture depletion lowered intercellular:atmospheric CO2 ratio (Ci/Ca) and increased intrinsic water-use efficiency (WUEi = Amax/gs) in shrubs, but not grasses. Consequently, between-slope differences in net photosynthesis (Amax) and stomatal conductance (gs) occurred only in shrubs, with lower values on the south-facing slope. Shrubs also exhibited between-slope differences in the photochemical reflectance index, suggesting drought-related photoprotection. The deuterium:hydrogen ratios of stem water showed that deep water use facilitated late summer growth in shrubs. Consistent with plant distribution, cumulative water use and photosynthesis were higher in shrubs than in grasses on the north-facing slope, but higher in grasses than in shrubs on the south-facing slope. This shows that topographic effects on leaf photosynthetic gas exchange are mediated by physiological acclimation strategy and water source use.

The ecological adaptability of four typical plants during the early successional stage of a tropical rainforest

“…T. maxima and M. floridulus possessed higher WUE than M. candidum Ecological adaptability of typical plants 293 and M. sanguineum, which was similar to the research in the Xilin River Basin, Inner Mongolia, China (Chen et al 2005) and in the northern Chihuahuan Desert grassland (Throop et al 2012). Shrubs generally have deeper root systems than grasses (Letts et al 2010). Because of constant water resources in deeper soil layer, shrubs use a relatively prodigal water use pattern (Gebauer et al 2002;Chen et al 2005;Pochman & Small 2010).…”

“…Plants can keep normal leaf physiological temperature through regulating g s to control E (Larcher 1995). With an increase in T l , g s of M. candidum and M. sanguineum decreased more quickly than that of T. maxima and M. floridulus, indicating that shrubs had stronger adjusting capacity than grasses on stomata (Letts et al 2010). The profligate water use of shrubs is related to their deeper rooting systems (Gebauer et al 2002;Chen et al 2005;Letts et al 2010).…”

“…Compared with shrubs, some studies thought that grasses were profligate (Golluscio & Oesterheld 2007;Letts et al 2010), but others thought that they were conservative (Gebauer et al 2002;Chen et al 2005). Profligate water use of grasses conduced to inhibit shrub growth by reducing soil moisture rapidly within their rooting depth (Golluscio & Oesterheld 2007;Letts et al 2010).…”

“…Compared with shrubs, some studies thought that grasses were profligate (Golluscio & Oesterheld 2007;Letts et al 2010), but others thought that they were conservative (Gebauer et al 2002;Chen et al 2005). Profligate water use of grasses conduced to inhibit shrub growth by reducing soil moisture rapidly within their rooting depth (Golluscio & Oesterheld 2007;Letts et al 2010). However, high efficiency in the use of water is vital for plants to survive in the open environment; especially, most of the tropical rainforests usually experience very high water stress during the dry season (Valladares & Pearcy 1997).…”

“…Smith et al (1993) coined the term "plant functional types", and Gitay and Noble (1997) defined it as "set of species showing similar responses to the environment and similar effects on ecosystem function". There have been some researches on plant functional groups (Wardle et al 1998;Gebauer et al 2002;Reich et al 2003;Hanley et al 2004;Chen et al 2005;Golluscio & Oesterheld 2007;Letts et al 2010;Kamiyama et al 2010). The usual groupings are defined by discrete and measurable biological trait differences (e.g., whether a plant fixes nitrogen or not, has perennial woody tissues or not, and has a given photosynthetic pathway or not) (Reich et al 2003).…”