Integrated physiological, photochemical and anatomical responses reveal divergent drought-response strategies among herbaceous peony cultivars

Abstract

Drought responses involve coordination across organs and functional levels, yet integrated cultivar strategies remain poorly resolved in herbaceous peony. Five cultivars, ‘Fen Guan’ (FG), ‘Jing Wang Fen’ (JWF), ‘San Dian Hong’ (SDH), ‘Cai Xia’ (CX) and ‘Xiao Ou’ (XO), were exposed for 30 d to nominal target regimes of 65% (CK), 45% (mild drought, LD), 25% (moderate drought, MD) and 5% (severe drought, SD) of substrate maximum water-holding capacity. We quantified leaf water and functional traits, pigment and membrane status, antioxidant enzymes and osmolytes, chlorophyll fluorescence, and leaf and root anatomy. Cultivar differences were evaluated using two-factor models, log response ratios, descriptive principal component analysis, an experiment-specific drought trait-integration index (DTI) and bootstrap resampling. SD reduced relative water content and chlorophyll index, increased relative electrolyte conductivity, and generally induced proline and soluble-sugar accumulation, whereas antioxidant activities, PSII energy fluxes and anatomical responses were cultivar dependent. SDH showed the smallest decline in relative water content and comparatively strong maintenance of PSII photochemical performance. FG showed the largest osmolyte response, but this response did not produce the highest integrated performance. CX showed the largest decline in relative water content and the greatest increase in relative electrolyte conductivity. XO combined pigment-NBI maintenance, photosystem stability and root vascular structural adjustment. Its overall DTI was 0.346 (95% CI, 0.239–0.500). XO ranked first in 99.9% of bootstrap resamples among the five cultivars under the present experimental conditions. These results distinguish stress-response magnitude from functional maintenance and identify XO as the leading candidate for subsequent drought-tolerance validation.