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Soil 13 C– 15 N dynamics in an N 2 ‐fixing clover system under long‐term exposure to elevated atmospheric CO 2
Author(s) -
Van Groenigen KeesJan,
Six Johan,
Harris David,
Blum Herbert,
Van Kessel Chris
Publication year - 2003
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/j.1365-2486.2003.00706.x
Subject(s) - trifolium repens , lolium perenne , repens , human fertilization , fertilizer , agronomy , zoology , chemistry , photosynthesis , biology , botany , poaceae
Reduced soil N availability under elevated CO 2 may limit the plant's capacity to increase photosynthesis and thus the potential for increased soil C input. Plant productivity and soil C input should be less constrained by available soil N in an N 2 ‐fixing system. We studied the effects of Trifolium repens (an N 2 ‐fixing legume) and Lolium perenne on soil N and C sequestration in response to 9 years of elevated CO 2 under FACE conditions. 15 N‐labeled fertilizer was applied at a rate of 140 and 560 kg N ha −1 yr −1 and the CO 2 concentration was increased to 60 Pa p CO 2 using 13 C‐depleted CO 2 . The total soil C content was unaffected by elevated CO 2 , species and rate of 15 N fertilization. However, under elevated CO 2 , the total amount of newly sequestered soil C was significantly higher under T. repens than under L. perenne . The fraction of fertilizer‐N ( f N ) of the total soil N pool was significantly lower under T. repens than under L. perenne . The rate of N fertilization, but not elevated CO 2 , had a significant effect on f N values of the total soil N pool. The fractions of newly sequestered C ( f C ) differed strongly among intra‐aggregate soil organic matter fractions, but were unaffected by plant species and the rate of N fertilization. Under elevated CO 2 , the ratio of fertilizer‐N per unit of new C decreased under T. repens compared with L. perenne . The L. perenne system sequestered more 15 N fertilizer than T. repens : 179 vs. 101 kg N ha −1 for the low rate of N fertilization and 393 vs. 319 kg N ha −1 for the high N‐fertilization rate. As the loss of fertilizer‐ 15 N contributed to the 15 N‐isotope dilution under T. repens , the input of fixed N into the soil could not be estimated. Although N 2 fixation was an important source of N in the T. repens system, there was no significant increase in total soil C compared with a non‐N 2 ‐fixing L. perenne system. This suggests that N 2 fixation and the availability of N are not the main factors controlling soil C sequestration in a T. repens system.