PS 22-7 - Global response patterns of terrestrial plant biomass allocation to nitrogen addition: A meta-analysis

Background/Question/Methods

Modification of biomass allocation is one of the main means of maximizing plant growth rate, survival, and adaptability under different biotic and abiotic pressures. To maintain the necessary physiological activities and to achieve regular growth, the plant must balance the distribution of biomass among leaves, branches, stems, and roots. Nitrogen (N) is an essential nutrient for plant growth and ecosystem productivity both in terrestrial and marine ecosystems. Nitrogen deposition is one of the most widespread drivers of global change. As a fundamental component of the terrestrial ecosystem, plant growth may be sensitive to enhanced N deposition. However, it is not clear whether functional traits and environmental factors drive the response of plant biomass allocation to N addition due to the lack of empirical support for simple linear relationships predicted by existing theories. Understanding the response of terrestrial plant biomass allocation to N addition can help explain changes in terrestrial ecosystem productivity, functions, and services. Therefore, in this study, using meta-analysis, we compiled a global dataset of 2,707 filed experimental observations from 38 countries encompassing most of the dominant plant species in terrestrial ecosystems to identify the global patterns of biomass accumulation and allocation response to reactive N addition.

Results/Conclusions

We found that N addition increased the terrestrial plant biomass by 55.6% (95% CI: 51.4–59.8%). According to the growth forms of plants, N addition enhanced herbaceous plant biomass and woody plant biomass by 60.1% (50–77.4%) and 53.8% (48.2–59.5%), respectively. By biological realms of plants, N addition increased the biomass of seed plants by 20.9% (33.2–47.2%) but had no effects on spore plants. Besides, N addition increased stem mass fraction, shoot mass fraction, and leaf mass fraction by 13.8% (95% CI: 4.0–23.6%), 12.9% (4.3–21.5%), 13.4% (4.4–22.4%), respectively. In contrast, plant root-shoot ratio and root mass fraction showed a negative response to N addition, which decreased 27% (−4.0 to −23.6%) and 14.7% (−17.8 to −11.6%) on average. More importantly, plant reproductive mass fraction decreased by 3.4% (−6.1 to −0.8%) on average in response to N addition. Our meta-analysis suggested that N addition alters the biomass allocation strategy of terrestrial plants, with N addition leading more biomass to be allocated to aboveground than belowground tissues and more biomass seemed to be allocated to vegetative organs than to reproductive organs.