Phenotype-specific Drought Strategies in the Invasive Weed Avena fatua

Abstract

Wild oat (Avena fatua L.) is a widespread invasive weed whose performance is strongly influenced by water availability. We compared two lemma-based phenotypes-W (hairy lemma) and B (glabrous lemma)-under four soil-water levels (80-85, 60-70, 50-60, 40-50% field capacity) in a completely randomized pot experiment. We determined organ dry masses and calculated allocation indices (root-to-shoot ratio, R/S; root and leaf mass fractions, RMF and LMF), leaf traits (total leaf area, leaf number, LAR), and growth metrics (RGR, NAR). Drought reduced aboveground biomass in both phenotypes. The W phenotype showed a prioritized allocation to roots under moderate stress, reflected by its R/S peaking at 0.508, while its LAR decreased by 40% under light stress. In contrast, the B phenotype exhibited a more dramatic fluctuation in leaf resource allocation, with its Leaf Mass Fraction (LMF) increasing by nearly 70% under light stress before plummeting under heavier stress. Growth analysis indicated that the Net Assimilation Rate (NAR) of W was relatively stable under light stress, whereas B's NAR dropped sharply by 47%. These results show divergent but predictable allocation and growth adjustments to water limitation and provide a basis for phenotype-aware management of wild oat.