Nitrogen and CO2 Affect Regrowth and Biomass Partitioning Differently in Forages of Three Functional Groups
- Jack A. Morgan *a,
- R.Howard Skinnerb and
- Jon D. Hansonc
Little work has been done to assess the impact of elevated CO2 on responses of forages to defoliation. This study examines regrowth, biomass partitioning, and labile C and N metabolites in three functional plant-types: a C3 grass [Pascopyrum smithii (Rydb.) A. Love], a C4 grass [Bouteloua gracilis (H.B.K.) Lag.], and a forage legume (Medicago sativa L.). Plants were grown from seed, defoliated twice, and grown in a controlled environment under a factorial arrangement of two CO2 [low CO2 (LC), 355 μmol mol−1, and high CO2 (HC), 700 μmol mol−1] and two N nutrition regimes [low N (LN), watered twice weekly with half-strength Hoagland's containing 0 N, and high N (HN), half-strength Hoagland's containing 14 mM N]. High N enhanced regrowth in all three species, while high CO2 enhanced regrowth only in the two C3 species. In M. sativa, CO2 and N treatments had no significant effect on k, the allometric growth coefficient. In contrast, k was reduced in P. smithii plants grown under LN (0.63) compared with HN (0.99). In B. gracilis, low N also reduced k, but it interacted with CO2 so that k was greatest for plants grown at HN/HC (0.95) and HN/LC (0.89), intermediate at LN/LC (0.58), and least at LN/HC (0.44). These results indicate greater partitioning to below-ground organs (reduced k) when N is limiting, particularly under elevated CO2 Significant correlations were established between k and several measures of plant N status, suggesting that the effects of CO2 on plant biomass partitioning involve N status.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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