| 英文摘要: | Living organisms maintain a balance of chemical elements for optimal growth and reproduction, which plays an important role in global biogeochemical cycles1, 2, 3, 4, 5. Human domination of Earth’s ecosystems has led to drastic global changes6, 7, 8, but it is unclear how these affect the stoichiometric coupling of nutrients in terrestrial plants, the most important food source on Earth. Here we use meta-analyses of 1,418 published studies to show that the ratio of terrestrial plant nitrogen (N) to phosphorus (P) decreases with elevated concentrations of CO2, increasing rainfall, and P fertilization, but increases with warming, drought, and N fertilization. Our analyses also reveal that multiple global change treatments generally result in overall additive effects of single-factor treatments and that the responses of plant nutrients and their stoichiometry are similar in direction, but often greater in controlled than in natural environments. Our results suggest a decoupling of the P biogeochemical cycle from N in terrestrial plants under global changes6, 7, 8, which in turn may diminish the provision of ecosystem services1, 5, 9. From cellular metabolism to ecosystem structure and nutrient cycling, C, N and P are biologically coupled through their effects on the biochemical reactions that control primary production, respiration and decomposition in terrestrial ecosystems1, 2, 3, 4, 5, 8, 10, 11, 12. In the biosphere, living organisms, the major part of biogeochemical cycles, require elements in strict proportions to catalyse metabolic reactions and synthesize essential compounds with specific ratios of C:N:P (refs 1, 2). The biological control—that is, the conserved elemental stoichiometry of organisms—couples biogeochemical cycles to one another3. However, owing to different degrees of control by biological and geochemical processes, biogeochemical C, N and P cycles could be unbalanced or decoupled under rapid global changes2, 8, 13. For example, an increase in aridity with climate changes can reduce soil C and N, but increase soil P in global drylands13, indicating that the coupling between biogeochemical cycles is fragile in drylands in the face of rapid climate change. The decoupling of the biogeochemical cycles of C, N and P may also lead to nutrient decoupling in plants that form the base of food chains5, 8 and consequently can negatively influence the trophic structures and the services of terrestrial ecosystems14. Global changes have drastically affected the biogeochemical cycles of carbon and nutrient elements of Earth’s ecosystems6, 15. The simultaneous changes in global-scale biogeochemical cycles (for example, elevated CO2 concentration [CO2], atmospheric N deposition, and N and P fertilization) and in climates (increasing temperature and altered rainfall) are anticipated to have stoichiometric consequences worldwide (Fig. 1). For example, elevated [CO2] can increase plant C fixation, but stimulated plant photosynthesis, growth and overall production may lead to decreases of plant nutrient concentrations—that is, the ‘dilution effect’16, 17. Warming tends to increase soil microbial activity, but may induce warming-associated droughts, both of which affect plant photosynthesis and plant stoichiometry. The same is true for changes in precipitation that affect plant stoichiometry via soil water availability.
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