1. Plant–microbe competition for available nitrogen (N) has been suggested to be an important mechanism controlling N limitation of plants in a variety of ecosystems. However, spatio-temporal
patterns of competition between plants and microbes for soilNremain unclear.
2. Short-term 15N tracer experiments were conducted during a growing season (July, August and September) in an alpine meadow on the Tibetan Plateau to unravel spatio-temporal patterns of
plant–microbe competition forNH4 + andNO3 ) .
3. Alpine plants were poorer competitors than soil microorganisms for inorganic N in July compared with August and September. Occupation of soil volume by roots and root density (high in
August and September) played a greater role in plant–microbe competition than air temperature or precipitation (high in July).
4. In topsoils (0–5 cm, highest root density), alpine plants effectively competed with soil microorganisms for N and showed a preference for 15NO3 ) , while soil microorganisms that preferentially
took up 15NH4 + out-competed plants below 5 cm soil depth (lower root density). Competition between plants and soil microorganisms for inorganic N strongly depended on root density
(P < 0.0001, R2 = 0.93, exponential decay model).
5. Synthesis. Plant–microbe competition for inorganicN showed a clear spatio-temporal pattern in alpine meadows depending on (i) root density and therefore soil depth, (ii) inorganic N form, and
(iii) different periods during the growing season. These findings have important implications for our understanding of above-ground–below-ground interactions and plant–microbial competition for
available N.
15N recovery by microbial biomass (%of added 15N) from 15NH4 + and 15NO3
) 4 h after 15N injection at different soil depths during the growing season (July, August and September).
Values are means (±1 SE) of five replicates. Asterisks indicate significant differences between the
15Nrecovery bymicrobial biomass from15NH4 + and 15NO3) injections.
Additional Information:
1.Author Information:Xingliang Xu, Hua Ouyang, Andreas Richter, Wolfgang Wanek, Guangmin Cao, Yakov Kuzyakov.
Correspondence: Xingliang Xu, E-mail: xuxingl@hotmail.com
2.Publication History:
Issue published online: 15 FEB 2011
Article first published online: 19 JAN 2011，Journal of Ecology, 99: 563–571. doi: 10.1111/j.1365-2745.2010.01789.x