RESUMEN
Isotopic signatures can be used to study sink and source processes of N(2)O, but the success of this approach is limited by insufficient knowledge on the isotope fractionation factors of the various reaction pathways. We investigated isotope enrichment factors of the N(2)O-to-N(2) step of denitrification (epsilon) in two arable soils, a silt-loam Haplic Luvisol and a sandy Gleyic Podzol. In addition to the epsilon of (18)O (epsilon(18O)) and of average (15)N (epsilon(bulk)), the epsilon of the (15)N site preference within the linear N(2)O molecule (epsilon(SP)) was also determined. Soils were anaerobically incubated in gas-tight bottles with N(2)O added to the headspace to induce N(2)O reduction. Pre-treatment included the removal of NO(3) (-) to prevent N(2)O production. Gas samples were collected regularly to determine the dynamics of N(2)O reduction, the time course of the isotopic signatures of residual N(2)O, and the associated isotope enrichment factors. To vary reduction rates and associated fractionation factors, several treatments were established including two levels of initial N(2)O concentration and anaerobic pre-incubation with or without addition of N(2)O. N(2)O reduction rates were affected by the soil type and initial N(2)O concentration. The epsilon(18O) and epsilon(bulk) ranged between -13 and -20 per thousand, and between -5 and -9 per thousand, respectively. Both quantities were more negative in the Gleyic Podzol. The epsilon of the central N position (epsilon(alpha)) was always larger than that of the peripheral N-position (epsilon(beta)), giving epsilon(SP) of -4 to -8 per thousand. The ranges and variation patterns of epsilon were comparable with those from previous static incubation studies with soils. Moreover, we found a relatively constant ratio between epsilon(18O) and epsilon(bulk) which is close to the default ratio of 2.5 that had been previously suggested. The fact that different soils exhibited comparable epsilon under certain conditions suggests that these values could serve to identify N(2)O reduction from the isotopic fingerprints of N(2)O emitted from any soil.
RESUMEN
Two cases of coccidioidomycosis detected in a group of more than 750 renal transplants are presented. The first patient died from unsuspected disseminated coccidioidomycosis 4 1/2 years after primary transplantation and 6 days after retransplantation. In the second patient pulmonary coccidioidomycosis was recognized and treated by lobectomy and amphotericin B before transplantation; subsequent transplantation has provided good renal function without recurrence of infection for 5 years. Experience with six other reported cases of coccidioidomycosis illustrates the high risk of exacerbation and dissemination of preexisting coccidioidal infection in immuno-suppressed transplanted recipients. Nevertheless, this risk can be made acceptable if active coccidioidomycosis is treated vigorously before immunosuppression is started and if the possibility of exacerbation of infection after transplantation is carefully monitored.