C:N stoichiometry, we further show that microbial communities responded in part nonhomeostatically to decreasing resource C:N, in addition to a likely increase in their carbon use efficiency and a decrease in nitrogen use efficiency. While the expected increased allocation to C-and decreased allocation to N-acquiring enzymes was not found, microbial investment in P acquisition (acid phosphatase activity) increased in the nutrient-poor Podzol (but not in the nutrient-rich Gleysol). Enzyme vector analysis showed decreasing C but increasing P limitation of soil microbial communities at both sites. We conclude that simulated N deposition led to physiological adaptations of soil microbial communities across the topsoil profile in two independent experiments, with long-term implications for tree nutrition and SOC sequestration. However, we expect that microbial adaptations are not endless and may reach a tipping point when ecosystems experience nitrogen saturation.
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