Elevated CO₂concentration, nitrogen use, and seed production in annual plants

Abstract

Elevated atmospheric CO 2 concentration ([CO 2 ]) stimulates seed mass production in many species, but the extent of stimulation shows large variation among species. We examined (1) whether seed production is enhanced more in species with lower seed nitrogen concentrations, and (2) whether seed production is enhanced by elevated [CO 2 ] when the plant uses more N for seed production. We grew 11 annuals in open top chambers that have different [CO 2 ] conditions (ambient: 370 lmol mol À1 , elevated: 700 lmol mol À1 ). Elevated [CO 2 ] significantly increased seed production in six out of 11 species with a large interspecific variation (0.84-2.12, elevated/ambient [CO 2 ]). Seed nitrogen concentration was not correlated with the enhancement of seed production by elevated [CO 2 ]. The enhancement of seed production was strongly correlated with the enhancement of seed nitrogen per plant caused by increased N acquisition during the reproductive period. In particular, legume species tended to acquire more N and produced more seeds at elevated [CO 2 ] than non-nitrogen fixing species. Elevated [CO 2 ] little affected seed [N] in all species. We conclude that seed production is limited primarily by nitrogen availability and will be enhanced by elevated [CO 2 ] only when the plant is able to increase nitrogen acquisition.

CO2, nitrogen, and diversity differentially affect seed production of prairie plants

“…Regardless, the absence of strong positive seed production responses to elevated CO 2 was surprising, because many studies have found strongly positive effects of elevated CO 2 on seed production (Ackerly and Bazzaz 1995, Farnsworth and Bazzaz 1995, Huxman et al 1999, LaDeau and Clark 2001, Jablonski et al 2002, Thurig et al 2003; but see Grunzweig and Korner 2000, Ramo et al 2007). However, many of these previous studies were performed on annual plants and crop plants, both more likely to show positive responses in seed production to the addition of any limiting resource (Jablonski et al 2002, Miyagi et al 2007). Seed production is directly linked to population growth for annuals, and crop plants have been selected by humans to respond to increased resources with increased seed production (Jablonski et al 2002).…”

“…Elevated CO 2 has been found to 6 E-mail: jhrl@u.washington.edu strongly affect seed production of some species, but results are difficult to extrapolate to natural communities, because most studies focus on crop species (Jablonski et al 2002) or examine the response of single species to elevated CO 2 (e.g., Huxman et al 1999, LaDeau andClark 2001). To our knowledge, fewer than 10 studies have examined the reproductive responses of co-occurring plant species to elevated CO 2 in the field (Navas et al 1997, Grunzweig and Korner 2000, Thurig et al 2003, Morgan et al 2004, Stiling et al 2004, Miyagi et al 2007, Ramo et al 2007, Williams et al 2007; and only two studies have examined reproductive responses of co-occurring species to multiple global change factors in the field (Cleland et al 2006, Ramo et al 2007). Determining how global change alters seed production of co-occurring members of a plant community would lend insight into the factors that constrain seed production, and may simplify efforts to forecast population or community dynamics under global change scenarios.…”

“…Thus, we predicted that seed production responses to elevated CO 2 and nitrogen deposition would be similar within functional groups (Reich et al 2001, Poorter and Navas 2003. Specifically, we hypothesized that seed production of C 4 grasses would respond negatively and C 3 species, especially legumes, positively to elevated CO 2 (Polley et al 2003, Morgan et al 2004, Miyagi et al 2007; but see Owensby et al 1999). We also expected that seed production of N demanding species would increase (C 3 grasses and non-leguminous forbs), while seed production of species most adept at acquiring this limiting soil resource would decrease with nitrogen deposition (perennial C 4 grasses, legumes ;Tilman 1984).…”

Climate Change: Seed Production and Options for Adaptation

“…In their study, legumes exhibited a more pronounced increase in nitrogen acquisition and enhanced seed production with elevated CO 2 than non-leguminous species. Enhanced CO 2 has been reported to enhance nodulation and nitrogen fixation [36][37][38], and thus white clover may have been expected to demonstrate a seed yield increase. However, if soil nitrogen was not limiting, this may have negated any nitrogen fixation response [39].…”

The effects of CO2 and nutrient enrichment on photosynthesis and growth of Poa annua in two consecutive generations

“…In our study, seed weight and germinability of P. annua were both significantly lower for plants grown in conditions of elevated CO 2 , and this might-at least partly-explain the differences observed in CO 2 responsiveness during the succeeding generation. Decreased germination (Farnsworth and Bazzaz 1995;Andalo et al 1996) and seed weight (Wulff and Alexander 1985) have been reported for other plant species growing in elevated CO 2 , although enhanced seed weight has also been reported (Steinger et al 2000;Miyagi et al 2007). Although most studies point to CO 2 -induced effects on seed characteristics as the mechanism through which intergenerational differences occur, it may also be possible that these effects are driven by genetic changes in a plant's response to elevated CO 2 (Ward and Kelly 2004;Lau et al 2008;Leakey et al 2009).…”