Reallocation of nitrogen and phosphorus from roots drives regrowth of grasses and sedges after defoliation under deficit irrigation and nitrogen enrichment

Reallocation of nutrients from roots to shoots is essential for plant regrowth in grasslands, particularly nutrient-poor conditions. However, the response root nutrient reallocation changes nitrogen (N) and water availability remains largely unknown. Using a novel 15N 32P labelling technique, we quantified contribution N phosphorus (P) shoot either or direct soil uptake perennial grasses exposed high-frequency deficit irrigation (HFDI) addition. Without addition, HFDI showed no impact on P, likely due unaffected greater diffusion barrier offsetting increased accumulation plant-available P. With rather than P uptake, because increasing instead under combined The decreased both with possibly exhaustion reserves that were re-allocated above-ground. contributed 48%–97% 58%–79% required during first 2 weeks regrowth. Synthesis. Our results highlight importance buffer against maintain N:P ratio