Dry Grasslands Defy the Fertilizer Effect: Aridity Decides How Nutrients Destabilize Ecosystems

One of the largest coordinated nutrient experiments ever mounted across the grasslands of Eurasia has delivered a result that could reshape how scientists think about ecosystem stability in a changing world. A team led by Xiaoan Zuo of the Chinese Academy of Sciences, working with colleagues from institutions across China, the Netherlands, Israel and the United States, has shown that the consequences of pumping extra resources into grasslands depend dramatically on how dry the landscape is and on the spatial scale at which ecologists make their measurements. The study, published in Nature Communications, reveals that the much-documented destabilizing effect of nutrient enrichment is not a universal law of ecology but a conditional one, governed by water.

The research addresses a long-standing puzzle in ecosystem science. For decades, experiments in grasslands around the world have shown that adding limiting resources, typically nitrogen, phosphorus and other nutrients, tends to reduce plant diversity and make the productivity of a community less stable from year to year. The classic explanation is that when the constraint of nutrient scarcity is lifted, a handful of fast-growing species monopolize the available light and space, crowding out competitors and leaving the community dominated by one or a few species whose fortunes swing with every fluctuation in weather. Yet the new findings demonstrate that this familiar story, while true in moist grasslands, weakens progressively as conditions become more arid, until in the driest sites the effects of resource addition are barely detectable.

The scale of the undertaking is what gives the result its power. The team established experimental plots across a vast aridity gradient spanning Eurasian grasslands, from relatively mesic sites to dry steppes and desert grasslands, and manipulated the number of added resources at each location. Rather than adding a single nutrient, the experiment varied how many different resources were supplied simultaneously, including water and multiple nutrients, allowing the researchers to ask a question that single-factor experiments cannot answer: what happens when several limitations are relieved at once? This design mirrors reality, because atmospheric nitrogen deposition, rising carbon dioxide and altered precipitation patterns are all changing resource availability concurrently in the world’s grasslands.

The central finding concerns the distinction between two levels of stability. At the scale of an individual plot, adding more resources had no measurable effect on the stability of plant productivity, meaning the year-to-year variability of biomass production within a single community did not change appreciably. But when the researchers aggregated their measurements to larger spatial scales, combining many local communities into a regional picture, a clear and troubling signal emerged: productivity stability declined as the number of added resources increased. An ecosystem can therefore appear robust at the scale of a single field yet become progressively less reliable at the scale of a landscape or region, a scale dependence that has profound implications for how stability is assessed and predicted.

The mechanism behind this scale-dependent destabilization lies in a phenomenon ecologists call spatial asynchrony. When different patches of a landscape fluctuate out of phase, one patch thriving in a wet year while another suffers, their opposing swings cancel each other out, and the total productivity of the region remains comparatively steady. This portfolio effect, analogous to financial diversification, is one of nature’s most important buffers against volatility. The experiment showed that increasing the number of added resources eroded this buffer. Resource enrichment reduced local plant species richness and, crucially, reduced the asynchrony of biomass dynamics among local communities. Once neighboring patches began rising and falling in unison, their fluctuations no longer canceled, and large-scale productivity became less stable.

The loss of asynchrony is tightly linked to the loss of diversity. Species-rich communities tend to respond differently to the same environmental conditions, because different species have different tolerances to drought, different phenologies and different growth strategies. This response diversity is what keeps patches out of phase. When nutrient additions whittle the community down to a smaller set of species with similar ecological strategies, the remaining plants tend to respond to weather in the same way at the same time, synchronizing the system. The new study confirms this chain of causation at an unprecedented geographic breadth, showing that the diversity loss and the asynchrony loss travel together along the aridity gradient.

And here is where aridity enters as the decisive moderator. The negative effects of multiple resource addition on species richness, on spatial asynchrony and on large-scale stability all weakened as aridity increased. In moist grasslands, where water is plentiful and nutrients are the primary constraint on growth, relieving nutrient limitation unleashed strong competitive exclusion and the associated cascade of diversity loss and synchronization. In arid grasslands, water remains the overriding bottleneck no matter how many nutrients are supplied, so additional resources simply cannot be fully exploited. The plants of drylands are adapted to scarcity and pulse-driven growth, and the competitive hierarchies that nutrient enrichment reorganizes in wetter systems are held in check by the unrelenting constraint of water. The result is that dry grasslands proved remarkably resistant to the destabilizing influence of enrichment.

The study also uncovered a subtler interaction: increasing aridity weakened the contribution that spatial asynchrony itself makes to large-scale stability. In other words, even where asynchrony persists in dry systems, it does less work smoothing out regional productivity than it does in moist ones. Arid ecosystems are governed by pulses of rainfall that can strike multiple patches simultaneously, imposing a degree of regional coherence on biomass dynamics regardless of species composition. This means the insurance provided by asynchronous dynamics is itself climate-dependent, thinning out precisely in the regions where livelihoods, from pastoralism to dryland agriculture, may be most vulnerable to swings in forage and crop production.

The implications for global change policy are considerable. Nitrogen deposition continues to rise across much of Asia and Europe, and many grassland regions face simultaneous changes in water availability and nutrient loading. If the destabilizing effects of enrichment are strongest in relatively moist grasslands, then those ecosystems, often the most productive and heavily managed, should be prioritized for nutrient management, including controls on fertilizer runoff and atmospheric deposition. Conversely, the findings caution against assuming that dryland restoration or fertilization schemes will behave like their mesic counterparts; adding resources to arid grasslands may deliver far smaller productivity gains and far less ecological disruption than standard models predict, but also fewer of the benefits that enrichment is meant to provide.

For the science of ecological forecasting, the message is methodological as much as substantive. Stability measured at one scale cannot be extrapolated to another, and the direction and strength of human impacts on ecosystems cannot be extrapolated across climate gradients. The Eurasian grassland experiment demonstrates that biodiversity, asynchrony and stability form a connected chain whose links are forged differently in wet and dry worlds. As climate change redraws the map of aridity, the sensitivity of the world’s grasslands to nutrient enrichment will shift with it, and the regions that cross moisture thresholds may find their ecosystems responding to fertilization in ways that today’s wet-site experiments never anticipated. Understanding where along the dryness spectrum the tipping points lie is now an urgent task for ecologists charged with safeguarding the productivity of the vast rangelands that feed hundreds of millions of people.

Subject of Research: Scale-dependent effects of multiple resource addition on grassland biodiversity and productivity stability along aridity gradients

Article Title: Aridity regulates scale-dependent effects of multiple resource additions on productivity stability in Eurasian grasslands

Article References: Zuo, X., Song, Z., van der Plas, F., Wang, S., Collins, S. L., Smith, M. D., Sternberg, M., Liang, M., Wu, H., He, Y., Diao, H., Dong, K., Liu, J., Peng, D., Wei, C., Cao, D., An, H., Liu, S., Zhang, F., … Hautier, Y. (2026). Aridity regulates scale-dependent effects of multiple resource additions on productivity stability in Eurasian grasslands. Nature Communications. https://doi.org/10.1038/s41467-026-78043-5

Image Credits: AI Generated

DOI: 10.1038/s41467-026-78043-5

Keywords: grassland ecology, aridity, productivity stability, spatial asynchrony, biodiversity, nutrient enrichment, eutrophication, spatial scale, Eurasian steppe, ecosystem stability, nitrogen deposition, climate change