Variation of magnesium drives plant adaption to heterogeneous environments by regulating efficiency in photosynthesis on a large scale.

Magnesium (Mg) is a vital nutrient for plants, and its role in photosynthesis, enzyme regulation and resistance to environmental stress is becoming increasingly evident. However, there is a paucity of knowledge regarding the characteristics of Mg (content, density and stock) on a large scale, particularly at the community level, which is essential for linking to ecosystem functions. A leaf‐branch‐trunk‐root‐matched database of the Mg content (mg g−1) and biomass density (g m−2) of plant organs across 1972 sampling sites in China was constructed based on field surveys and data compilation. Using machine learning algorithms, we comprehensively explored the spatial patterns and main influencing factors of plant Mg content and density (g m−2). Furthermore, a new index, leaf Mg productivity (LMP), was developed to determine the Mg use efficiency, defined as the ratio of gross primary productivity to leaf Mg density. The Mg contents in the leaves, branches, trunks and roots were 2.80, 0.87, 0.23 and 1.66 mg g−1, respectively. Deserts exhibited higher Mg content, with the primary influencing factors being high temperatures and soil Mg supply. Higher LMP values observed in grasslands and deserts indicate that Mg use is more efficient in these relatively stressful environments, whereas forests require more Mg for unit biomass productivity. This change was driven by the minimum temperature, aridity and soil Mg content. Synthesis. We systematically explored spatial variation in plant community Mg and its correlation with the photosynthetic capacity of plant communities. The aridity and soil Mg content have negative effects on LMP. This suggests that Mg is used more efficiently in photosynthesis under conditions of resource scarcity, indicating that resources become more valuable when they are limited. Photosynthesis in forests is more sensitive to Mg and more Mg is required for biomass production; therefore, Mg is not just a nutrient but a potential bottleneck in optimizing photosynthetic efficiency. Our findings highlight the pivotal role of Mg in photosynthesis and offer a foundation for optimizing ecosystem management through Mg regulation. [ABSTRACT FROM AUTHOR]