Nitrogen partitioning between microbes and plants in the shortgrass
Bontti, E.E., I.C. Burke and W.K. Lauenroth. 2011. Plant and Soil 342:445-457
Abstract
Nitrogen (N) and water additions in the
shortgrass steppe change the dominance of plant
functional types (PFT) that are characterized by
different photosynthetic pathways and phenologies.
We aimed to examine monthly patterns of plant N and
microbial N storage during the growing season, and to
assess whether N fertilization last applied 30 years
ago alters the timing and magnitude of N storage. We
measured plant biomass and N, and microbial
biomass N monthly during the growing season. We
found differences in temporal patterns of plant and
microbial N storage in the control plots, with
microbial storage higher than plant storage in July,
and the opposite trend in September. Unlike the
control plots, the plots fertilized 30 years ago
exhibited overlapping peaks of N storage in plants
and microbes in August. Seasonal trends indicated
that rainfall was an important control over plant and
microbial activity at the beginning of the growing
season, and that temperature limited these activities at
the end of the growing season. PFT affected the
amount of microbial N, which was in general higher
under C3 grasses than other PFTs, independent of
fertilization. Historical resource additions increased
plant biomass and N, but had little effect on microbial
N. These results highlight the complexity of the
microbial response. Changes in climate that influence
precipitation timing will affect the temporal pattern
for microbial biomass N, while management practices
resulting in altered plant community composition will
influence the magnitude of microbial biomass N.
Key Words
Grasslands; nitrogen partitioning; semi-arid ecosystems; shortgrass steppe; nitrogen availability; plant-microbe interactions
