与8-9月份相比，7月植物的对无机氮的竞争能力明显弱于土壤微生物群落；在表层土壤中，植物对无机氮的竞争能力强于微生物。
Spatio-temporal variations determine plant–microbe competition for inorganic nitrogen in an alpine meadow
Journal of Ecology
Xingliang Xu *, Hua Ouyang , Andreas Richter , Wolfgang Wanek , Guangmin Cao，Yakov Kuzyakov
Summary
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 soil N remain 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 for NH4+ and NO3−.
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 inorganic N 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.
Source：https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2010.01789.x/abstract
