Abiotic versus biotic controls on soil nitrogen cycling in drylands along a 3200 km transect
Nitrogen (N) cycling in drylands under changing climate is not well understood. Our understanding of N cycling over larger scales to date relies heavily on the measurement of bulk soil N, and the information about internal soil N transformations remains limited. The <sup>15</sup>N natura...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-03-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/14/989/2017/bg-14-989-2017.pdf |
| Summary: | Nitrogen (N) cycling in drylands under changing climate is not well
understood. Our understanding of N cycling over larger scales to date relies
heavily on the measurement of bulk soil N, and the information about internal
soil N transformations remains limited. The <sup>15</sup>N natural abundance
(<i>δ</i><sup>15</sup>N) of ammonium and nitrate can serve as a proxy record for the
N processes in soils. To better understand the patterns and mechanisms of N
cycling in drylands, we collected soils along a 3200 km transect at about
100 km intervals in northern China, with mean annual precipitation (MAP)
ranging from 36 to 436 mm. We analyzed N pools and <i>δ</i><sup>15</sup>N of
ammonium, dual isotopes (<sup>15</sup>N and <sup>18</sup>O) of nitrate, and the microbial
gene abundance associated with soil N transformations. We found that N status
and its driving factors were different above and below a MAP threshold of
100 mm. In the arid zone with MAP below 100 mm, soil inorganic N
accumulated, with a large fraction being of atmospheric origin, and ammonia
volatilization was strong in soils with high pH. In addition, the abundance
of microbial genes associated with soil N transformations was low. In the
semiarid zone with MAP above 100 mm, soil inorganic N concentrations were
low and were controlled mainly by biological processes (e.g., plant uptake and
denitrification). The preference for soil ammonium over nitrate by the
dominant plant species may enhance the possibility of soil nitrate losses
via denitrification. Overall, our study suggests that a shift from abiotic
to biotic controls on soil N biogeochemistry under global climate changes
would greatly affect N losses, soil N availability, and other N
transformation processes in these drylands in China. |
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| ISSN: | 1726-4170 1726-4189 |