Due to symbiotic N-2 fixation, five years of elevated atmospheric pCO(2) had no effect on the N concentration of plant litter in fertile, mixed grassland
Ua. Hartwig et al., Due to symbiotic N-2 fixation, five years of elevated atmospheric pCO(2) had no effect on the N concentration of plant litter in fertile, mixed grassland, PLANT SOIL, 224(1), 2000, pp. 43-50
Experimental findings indicate that, in terrestrial ecosystems, nitrogen cy
cling changes under elevated partial pressure of atmospheric CO2 (pCO(2)).
It was suggested that the concentration of N in plant litter as well as the
amount of litter are responsible for these changes. However, for grassland
ecosystems, there have been no relevant data available to support this hyp
othesis. Data from five years of the Swiss FACE experiment show that, under
fertile soil conditions in a binary plant community consisting of Lolium p
erenne L. and Trifolium repens L., the concentration of litter N does not c
hange under elevated atmospheric pCO(2); this applies to harvest losses, st
ubble, stolons and roots as the sources of litter. This is in strong contra
st to the CO2 response of L. perenne swards without associated legumes; in
this case the above-ground concentration of biomass N decreased substantial
ly. Increased symbiotic N-2 fixation in T. repens nodules and a greater pro
portion of the N-rich T. repens in the community are regarded as the main m
echanisms that buffer the increased C introduction into the ecosystem under
elevated atmospheric pCO(2). Our data also suggest that elevated atmospher
ic pCO(2) results in greater amounts of litter, mainly due to increased roo
t biomass production. This study indicates that, in a fertile grassland eco
system with legumes, the concentration of N in plant litter is not affected
by elevated atmospheric pCO(2) and, thus, cannot explain CO2-induced chang
es in the cycling of N.