Abstracts of Projects

1.  Research Background

Nutrient inputs and extreme droughts are increasing in terrestrial ecosystems, changing the global environment in terms of species diversity and the functioning of ecosystems. For example, analyses from the NPK-D Network have shown that first-year fertilization increased, and drought reduced, community productivity most strongly in arid sites (Bondaruk et al., 2025). On the other hand, species diversity responded differently, with fertilization having stronger effects in humid sites, while drought effects were more pronounced in arid sites (Chong’s expected results). Since arid sites are more limited by water and humid sites by nutrients, these diversity patterns support resource competition theory (Tilman, 1982). However, whether these effects intensify, diminish, or remain consistent over time, remains unexplored. We hypothesize that the effects of fertilization on species diversity and productivity remain consistent over time only in humid sites, whereas the effects of drought are consistent only in arid sites.

Small changes in species diversity can be associated with large compositional changes, or not (Spaak et al., 2017). A change in community productivity can be partitioned into that of species losses, species gains and species that persist through time (Bannar-Martin et al., 2018). For instance, results from the Nutrient Network showed that declines in species richness under nutrient addition were driven by increased species loss and reduced species gains, while the increase in biomass was largely attributed to persistent species (Ladouceur et al., 2022). Clarifying how community compositional changes induced by nutrient addition and drought contribute to shifts in aboveground biomass is essential for understanding the relationship between diversity and community productivity, especially in ecosystems facing increasing anthropogenic pressures.

2.  Scientific Questions

This study analyzes data from the global NPK-D network, using multi-year surveys of plant diversity and aboveground biomass to address the following questions:

1. How do the effects of nutrient addition and drought on grassland diversity change temporally across aridity gradients?

2. How do the effects of nutrient addition and drought on grassland productivity change temporally across aridity gradients?

3. What are the relative contributions of species that are lost, gained, or persist to changes in aboveground biomass?

3.  Required Data

4.  References

Bannar-Martin, K. H., Kremer, C. T., Ernest, S. K. M., Leibold, M. A., Auge, H., Chase, J., Declerck, S. A. J., Eisenhauer, N., Harpole, S., Hillebrand, H., Isbell, F., Koffel, T., Larsen, S., Narwani, A., Petermann, J. S., Roscher, C., Cabral, J. S., & Supp, S. R. (2018). Integrating community assembly and biodiversity to better understand ecosystem function: The community assembly and the functioning of ecosystems (CAFE) approach. Ecology Letters, 21(2), 167–180. https://doi.org/10.1111/ele.12895

Bondaruk, V. F., Xu, C., Wilfahrt, P., Yahdjian, L., Yu, Q., Borer, E. T., Jentsch, A., Seabloom, E. W., Smith, M. D., Alberti, J., Oñatibia, G. R., Dieguez, H., Carbognani, M., Kübert, A., Power, S. A., Eisenhauer, N., Isbell, F., Auge, H., Chandregowda, M. H., … Hautier, Y. (2025). Aridity modulates grassland biomass responses to combined drought and nutrient addition. Nature Ecology & Evolution, 1–10. https://doi.org/10.1038/s41559-025-02705-8

Ladouceur, E., Blowes, S. A., Chase, J. M., Clark, A. T., Garbowski, M., Alberti, J., Arnillas, C. A., Bakker, J. D., Barrio, I. C., Bharath, S., Borer, E. T., Brudvig, L. A., Cadotte, M. W., Chen, Q., Collins, S. L., Dickman, C. R., Donohue, I., Du, G., Ebeling, A., … Harpole, W. S. (2022). Linking changes in species composition and biomass in a globally distributed grassland experiment. Ecology Letters, 25(12), 2699–2712. https://doi.org/10.1111/ele.14126

Spaak, J. W., Baert, J. M., Baird, D. J., Eisenhauer, N., Maltby, L., Pomati, F., Radchuk, V., Rohr, J. R., Van den Brink, P. J., & De Laender, F. (2017). Shifts of community composition and population density substantially affect ecosystem function despite invariant richness. Ecology Letters, 20(10), 1315–1324. https://doi.org/10.1111/ele.12828

Tilman, D. (1982). Resource Competition and Community Structure. (MPB-17), Volume 17. Princeton University Press. https://doi.org/10.2307/j.ctvx5wb72

Abstract

Global changes such as extreme drought events and eutrophication are increasingly threatening Earth’s ecosystems. While experiments have shown that nutrient addition and drought each decrease the stability of ecological communities, their combined impact remains unknown, limiting our ability to manage grasslands under global changes. Using a coordinated, multisite, multiyear experiment across 16 grasslands, we found that nutrient addition and drought predominantly had additive negative effects on the temporal stability of aboveground plant biomass. Nutrient addition increased inter-annual biomass variability, whereas drought decreased mean biomass, both leading to reduced stability. Additionally, both drivers reduced community stability by decreasing species richness and disrupting asynchronous dynamics among species. Our results indicate that the combined pressures of nitrogen deposition and climate extremes could further destabilize grassland ecosystems, jeopardizing their capacity to sustainably deliver essential functions and services.

1. Research Background

The relationship between plant diversity and community productivity is a central issue in ecology, generally showing a positive relationship. This highlights the crucial role of plant diversity in maintaining community productivity (Tilman et al., 2001). However, since the Industrial Revolution, nitrogen deposition and agricultural fertilizer use have led to nutrient enrichment, which may result in negative or trade-off relationships between these two metrics (Isbell et al., 2013; Hautier et al., 2015). For example, the Nutrient Network indicates that as the number of added nutrients increases, grassland aboveground productivity increases significantly (Fay et al., 2015). However, this productivity increase is simultaneously accompanied by significant plant diversity loss (Harpole et al., 2016). These findings suggest that multiple nutrient enrichment could cause a trade-off or conflict relationship between productivity enhancement (improved livestock production) and diversity loss (biodiversity preservation), which is a fundamental challenge in grassland management (Bai et al., 2009; Ladouceur et al., 2022). Thus, how to balance between these two aspects is crucial for sustainable grassland management. Despite these above, it remains unclear how the strength and direction of these trade-off relationships change spatially and temporally—such as climate, soil nutrient, local community productivity and experimental duration.

With global climate warming, both intensity and frequency of droughts are expected to increase significantly (Werner et al., 2021). Droughts could lead to species loss, community composition homogenization (Hautier et al., 2018), and altered soil nutrient availability, thereby affecting grassland productivity. Therefore, clarifying how drought influences the trade-off relationships between productivity enhancement and diversity loss will be essential for grassland management.

2. Scientific Questions

This study plans to analyze data from the global NPK-D network, based on long-term diversity and biomass surveys, aiming to address the following questions:

1) whether and how multiple nutrient addition globally causes trade-off relationships between grassland productivity and diversity?

2) How do the strength and direction of these trade-off relationships change spatially and temporally?

3) How do natural water gradient and experimental drought treatment influence these trade-off relationships?

3. Required data：

4. Early Results

Based on the data from the China Network, our results showed that as the number of added nutrients increased, the relationships between grassland productivity and plant diversity shifted from positive to negative ones (Fig. 1). Along spatial environmental gradients, when local community productivity exceeded the threshold of 219.91 g m^-², grassland productivity and diversity had a negative or trade-off relationship (Fig. 2). However, when local productivity was below this threshold, there was a positive relationship between them. This may be due to higher aboveground biomass intensifying light competition, causing shorter plants to lose their competitive advantage for light, which subsequently leads to diversity loss. Furthermore, when annual precipitation exceeded the threshold of 391.15 mm, the relationships between productivity and diversity shifted from negative to positive ones.

Figure 1. Changes in the slopes of the relationships between grassland productivity and diversity with the number of added nutrients in the China Network

Notes：Formula = Richness~slope*ANPP+intercept

Figure 2. Changes in the slopes of the productivity-diversity relationship with local ANPP (a) and annual precipitation (b) under multiple nutrient enrichment in the China Network

Notes: these results are based on partial regression analysis.

5. Reference

Bai Y, Wu J, Clark CM, Naeem S, Pan Q, Huang J, Zhang L, Han X. 2009. Tradeoffs and thresholds in the effects of nitrogen addition on biodiversity and ecosystem functioning: evidence from inner Mongolia Grasslands. Global Change Biology 16(1): 358-372.

Fay PA, Prober SM, Harpole WS, Knops JMH, Bakker JD, Borer ET, Lind EM, MacDougall AS, Seabloom EW, Wragg PD, et al. 2015. Grassland productivity limited by multiple nutrients. Nature Plants 1(7).

Harpole WS, Sullivan LL, Lind EM, Firn J, Adler PB, Borer ET, Chase J, Fay PA, Hautier Y, Hillebrand H, et al. 2016. Addition of multiple limiting resources reduces grassland diversity. Nature 537(7618): 93-96.

Hautier Y, Tilman D, Isbell F, Seabloom EW, Borer ET, Reich PB. 2015. Anthropogenic environmental changes affect ecosystem stability via biodiversity. Science 348(6232): 336-340.

Isbell F, Reich PB, Tilman D, Hobbie SE, Polasky S, Binder S. 2013. Nutrient enrichment, biodiversity loss, and consequent declines in ecosystem productivity. Proceedings of the National Academy of Sciences of the United States of America 110(29): 11911-11916.

Ladouceur E, Blowes SA, Chase JM, Clark AT, Garbowski M, Alberti J, Arnillas CA, Bakker JD, Barrio IC, Bharath S, et al. 2022. Linking changes in species composition and biomass in a globally distributed grassland experiment. Ecology Letters 25(12): 2699-2712.

Tilman D, Reich PB, Knops J, Wedin D, Mielke T, Lehman C. 2001. Diversity and productivity in a long-term grassland experiment. Science 294(5543): 843-845.

Werner C, Meredith LK, Ladd SN, Ingrisch J, Kubert A, van Haren J, Williams J. 2021. Ecosystem fluxes during drought and recovery in an experimental forest. Science, 374(6574), 1514-1518.

Hautier Y, Isbell F, Borer ET, Seabloom EW, Harpole WS, Lind EM, Hector A. 2018. Local loss and spatial homogenization of plant diversity reduce ecosystem multifunctionality. Nature Ecology & Evolution, 2(1), 50-56.