Soil N enrichment mediates carbon allocation through respiration in a dominant grass during drought.

Carbon (C) allocation strategy plays a critical role in plant adaptability, which are also important to assess the productivity stability under environmental change. Based on optimal partitioning theory, we asked two questions: (1) How is plant C allocation within tissues affected by nutrient enrichment (N addition)? And (2) does long‐term N addition alter how plants allocate C under drought?To address these questions, we conducted a greenhouse experiment using the widespread perennial C3 grass, Leymus chinensis, under four treatments: 'Watered', 'Dry', 'Watered + N' and 'Dry + N'. 13CO2 pulse labelling was used to trace C transport through the plant–soil system.We found that drought and N addition resulted in additive effects on C allocation. Greater above‐ground biomass under N addition resulted in higher C loss via above‐ground plant respiration, even under drought, which plays a more important role in the adjustment of root:shoot ratio than does the trade‐off between above‐ and below‐ground organs.Compared to the concept of active phenotype adjustment for maximized growth rate in traditional optimal partitioning theory, our results imply that pre‐drought allometry, which changes under long‐term resource addition, also determines how plants respond to drought and their adaptability to changing environmental conditions. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]