Nitrogen and carbon storage in alpine plants

Abstract

Alpine plants offer unique opportunities to study the processes and economics of nutrient storage. The short alpine growing season forces rapid completion of plant growth cycles, which in turn causes competition between vegetative and reproductive growth sinks during the early part of the growing season. Mobilization of stored nitrogen and carbon reserves facilitates competing sinks and permits successful completion of reproduction before the onset of winter stress. We discuss the theoretical framework for assessing the costs and benefits of nutrient storage in alpine plants in order to lay the foundation for interpretation of observations. A principal point that has emerged from past theoretical treatments is the distinction between reserve storage, defined as storage that occurs with a cost to growth, and resource accumulation, defined as storage that occurs when resource supply exceeds demand, and thus when there is no cost to growth. We then discuss two case studies, one already published and one not yet published, pertaining to the storage and utilization of nitrogen and carbon compounds in alpine plants from Niwot Ridge, Colorado. In the first case, we tested the hypothesis that the seasonal accumulation of amino acids in the rhizome of N-fertilized plants of Bistorta bistortoides provides an advantage to the plant by not imposing a cost to growth at the time of accumulation, but providing a benefit to growth when the accumulated N is remobilized. We show that, as predicted, there is no cost during N accumulation but, not as predicted, there is no benefit to future growth. In the presence of N accumulation, reliance on stored N for growth increases, but reliance on current-season, soil-derived N decreases; thus the utilization of available N in this species is a 'zero sum' process. Inherent meristematic constraints to growth cause negative feedback that limits the utilization of accumulated N and precludes long-term advantages to this form of storage. In the second case study, we discuss new results showing high concentrations of cyclic polyol (cyclitol) compounds in the leaves of many alpine species dominant in the dry fellfield habitat. In Artemisia scopulorum, cyclitols were induced as the growing season progressed, and reached highest concentrations during the dry, late-summer months. Leaf cyclitol concentrations were high in all four species of the Caryophyllaceae that we examined and appeared to be constitutive components of the leaf carbohydrate pool as concentrations were high through the entire growing season. We observed correlations among seedling abundance, seeding survivorship and the presence of high leaf cyclitol concentrations. We propose that the primary function of cyclitols in the leaves of alpine, fellfield herbs is to promote drought tolerance through osmotic protection, and enhance fitness by improving seedling survival. We considered the possibility that cyclitols also function as carbon storage compounds that are remobilized at the end of the growing season and used to support growth...

Changes in soluble carbohydrates in polar Caryophyllaceae and Poaceae plants in response to chilling

“…Myo-inositol forms isomers, such as D-chiro-inositol, and methyl derivatives, including D-pinitol and D-ononitol. Whereas myo-inositol is commonly found in the cells of various organisms, its isomers and methyl derivatives were detected only in selected plant species, which could have chemotaxonomic implications (Monson et al 2006). The analyses of the content and composition of SCs in the tissues of Cerastium alpinum and Colobanthus quitensis revealed high cyclitols level with a predominance of D-pinitol.…”

“…High cyclitols concentration accounting for around 50 % of total SCs were observed in four plant species of the family Caryophyllaceae which are commonly found in the alpine zone of the Rocky Mountains (Colorado, USA). Cyclitol levels remain constant throughout the entire growing season, and they are regarded as a constant component of SCs which induce tolerance to drought through osmotic protection (Monson et al 2006).…”

Polyols as biomarkers and bioindicators for 21st century plant breeding

“…Polyols have been isolated from plant tissues up to 8.9% leaf DW (Richter and Popp 1992;Streeter et al 2001;Monson et al 2006;Merchant et al 2007) up to 90% of phloem sap carbon (Moing et al 1997) and often more than 50% of the carbon in the xylem sap (Richter and Popp 1992;Popp and Smirnoff 1995;Popp et al 1997). The synthesis of polyols follows strong taxonomical (Bieleski and Briggs 2005;Merchant et al 2007) and ecotypic (Pfundner 1993) patterns and these concentrations fluctuate in response to environmental cues (Vernon and Bohnert 1992;Wanek and Richter 1997;Streeter et al 2001;Merchant et al 2006b).…”

“…The synthesis and accumulation of polyols is common to many plant tissues with discrete patterns identified among both plant taxa (Plouvier 1963;Lewis and Smith 1967;Bieleski 1982) and environments (Merchant et al 2006a;Monson et al 2006). Several functions of polyols in plant tissues have been identified, however, despite their close association with primary metabolism they are often overlooked in plant research.…”

Reproductive response to nitrogen and phosphorus fertilization along the Hawaiian archipelago’s natural soil fertility gradient

“…The allocation of nutrients to plant reproductive structures, such as inflorescences, fruit, and seeds, varies greatly in terms of quantity (e.g., number of reproductive structures produced) and quality (e.g., nutrient concentration of reproductive structures produced), due to the resource availability in an environment (Chapin 1980;Bloom et al 1985;Chapin et al 1990; Monson et al 2006). Fertilization Abstract Nitrogen (N) and phosphorus (P) are the most important nutrients involved in plant reproduction and typically the most limiting in terrestrial ecosystems.…”