Global warming amplifies nitrogen over phosphorus limitation in aquatic ecosystems: A multi-trophic meta-analysis

Nitrogen (N) and phosphorus (P) availability fundamentally regulate the
structure and function of aquatic ecosystems. While global-scale patterns
of relative nutrient limitation have been increasingly documented, their
responses to climate warming remain poorly quantified. To address this, we
integrated a global meta-analysis of nutrient enrichment experiments
(spanning 510 sites and multiple trophic levels) with large-scale datasets
of water chemistry from 3,403 lakes and 13,032 marine sites. Meta-analysis
showed that primary producers have the strongest responses to nutrient
enrichment, especially NP co-addition, with effects attenuating at higher
trophic levels. Increasing temperature amplifies the response of primary
producers to nutrient enrichment, but not for consumers, indicating that
warming disrupts energy flow to higher trophic levels. Furthermore,
relative N limitation of primary producers intensifies with increasing
temperature and decreasing latitude in both freshwater and marine
ecosystems. Global field observation of water chemistry supports such a
pattern as water N:P mass ratios decrease with increasing temperature
across lake and marine ecosystems. Our findings provide robust empirical
evidence that the relative nutrient limitation of primary producers
exhibits a strong latitudinal gradient and climate warming could
fundamentally enhance nitrogen over phosphorus limitation in aquatic
ecosystems, which have critical implications for ecosystem functioning and
management in a warmer world.