Nitrogen and phosphorus additions alter foliar nutrient concentrations of dominant grass species and regulate primary productivity in an Inner Mongolian meadow steppe

Authors: XIAO, H. - Beijing University Of Agriculture; LI, P. - Beijing University Of Agriculture; Monaco, Thomas; LIU, Y. - Beijing University Of Agriculture; RONG, Y. - Beijing University Of Agriculture

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2023
Publication Date: 12/4/2023
Citation: Xiao, H., Li, P., Monaco, T.A., Liu, Y., Rong, Y. 2023. Nitrogen and phosphorus additions alter foliar nutrient concentrations of dominant grass species and regulate primary productivity in an Inner Mongolian meadow steppe. Science of the Total Environment. https://doi.org/10.1016/j.scitotenv.2023.168791.
DOI: https://doi.org/10.1016/j.scitotenv.2023.168791

Interpretive Summary: Nutrient stoichiometry is a valuable tool to interpret how essential nutrients regulate ecosystem productivity and. As excess nutrients from human inputs have drastically altered ecosystems and agricultural systems, there is a tremendous need to understand how critical areas, like grasslands, will shift under future climate scenarios and how land managers may offset undesirable outcomes. In this experiment, we focused on nitrogen (N) and phosphorus (P), which are the primary limiting nutrients in grassland ecosystems. Because interactions between these essential nutrients are difficult to interpret, our design studied all possible combinations of 5 N-levels and 3 P-levels over a three-year period in a meadow-steppe ecosystem in Inner Mongolia that had not received prior fertilizer applications. Stoichiometry, particularly the N:P ratio of vegetation revealed that productivity in this system is N-limited and that offsetting N-limitation increased N:P ratios to the point where P became limiting. Furthermore, P-addition exasperated N-limitation by reducing the N:P. We also showed that four dominant grass and forb species were primarily responsible for these shifts in ecosystem stoichiometry. Results suggest that N addition from human activities can have cascading effects on grassland ecosystems that are not easily remedied without a thorough understanding of the interactions between N and P. Managing species dominance may also be a way of offsetting anticipated nutrient limitations under future climate scenarios.

Technical Abstract: Excessive nitrogen (N) input may shift grassland productivity from N to phosphorus (P) limitation; therefore, understanding the dynamics of N:P ratios in ecosystems is crucial for managing productivity. However, the influence of variable soil N and P availability on tissue nutrient concentrations and stoichiometric ratios and their roles in regulating plant productivity remain unclear. To address this issue, we applied fifteen fertilization treatments consisting of factorial combinations of N (0, 1.55, 4.65,13.95, 27.9 g N m-2 yr-1) and P (0, 5.24 ,10.48 g P m-2 yr-1) for three years in a meadow steppe ecosystem in Inner Mongolia. We examined plant and soil concentrations and stoichiometric ratios of C (carbon), N, and P, and their associations with plant productivity. Results revealed soil N and P availability strongly regulated C, N, and P concentrations in plants. Community N:P ratios for shoots (i.e., combined species) (12.89 ± 0.98) did not exceed 14 within the control treatment, indicating that plant growth was primarily N-limited in this ecosystem. Consequently, N addition increased N:P ratios, shifting the community from N- to P-limited whereas P addition reduced N:P ratios, further aggravating plant growth due to greater N limitation. Mean leaf-N concentrations for dominant grass and forb species (Leymus chinensis, Stipa baicalensis, Artemisia tanacetifolia, Potentilla acaulis; 19.17 ± 0.74 to 23.87 ± 1.02) exceeded community values (9.36 ± 0.58-19.42 ± 0.87). For grasses, leaf-N concentrations also showed high association with aboveground net primary productivity, while leaf-P concentrations were associated with belowground net primary productivity. These results indicate that leaf-nutrient concentrations of dominant grasses were the best indicators of community productivity and by assessing these critical values, grassland managers can potentially improve productivity and sustainable utilization for grazing and haying in these critical grassland ecosystems by actively altering nutrient concentrations of dominant plants.