A. Fangmeier et al., CO2 enrichment enhances flag leaf senescence in barley due to greater grain nitrogen sink capacity, ENVIR EXP B, 44(2), 2000, pp. 151-164
Senescence is a highly regulated process which is under genetic control. In
monocarpic plants, the onset of fruit development is the most important fa
ctor initiating the senescence process. During senescence, a large fraction
of plant nutrients is reallocated away from vegetative tissues into genera
tive tissues. Senescence may therefore be regarded as a highly effective sa
lvage mechanism to save nutrients for the offspring. CO2 enrichment, beside
s increasing growth and yield of C-3 plants, has often been shown to accele
rate leaf senescence. C-3 plants grown under elevated CO2 experience altera
tions in their nutrient relations. In particular their tissue nitrogen conc
entrations are always lower after exposure to elevated CO2. We used a monoc
arpic C-3 crop - spring barley (Hordeum vulgare cv. Alexis) - grown in open
-top field chambers to test the effects of CO2 enrichment on growth and yie
ld, on nitrogen acquisition and redistribution, and on the senescence proce
ss in flag leaves, at two applications of nitrogen fertilizer. CO2 enrichme
nt (650 vs. 366 mu mol mol(-1)) caused an increase both in biomass and in g
rain yield by 38% (average of the two fertilizer applications) which was du
e to increased tillering. Total nitrogen uptake of the crops was not affect
ed by CO2 treatment but responded solely to the N supply. Nitrogen concentr
ations in grains and straw were significantly lower (-33 and -24%) in plant
s grown at elevated CO2. Phenological development was not altered by CO2 un
til anthesis. However, progress of flag leaf senescence as assessed by chlo
rophyll content, protein content and content of large and small subunit of
RubisCO and of cytochrome b559 was enhanced under elevated CO2 concentratio
ns by similar to 4 days. We postulate that CO2 enhanced flag leaf senescenc
e in barley crops by increasing the nitrogen sink capacity of the grains. (
C) 2000 Elsevier Science B.V. All rights reserved.