Physiological responses of Illicium difengpi to simulated persistent and intermittent droughts

Abstract

Global climate change has intensified the impacts of persistent and intermittent droughts on karst plants, especially on endangered and medicinal species, but research in this area remains limited. This study investigated the effects of two types of droughts, i.e., persistent drought–rehydration (PD-R) and cyclic mild/moderate drought–rehydration (CD-R), on Illicium difengpi, an endangered medicine plant native to the karst regions in China, using two-years-old seedlings. Key physiological variables were measured throughout the experimental period. The leaf relative water content and predawn water potential of the species rapidly recovered to the control levels after rehydration. However, photosynthesis-related variables—including net photosynthetic rate (P_n), effective PSII quantum yield (ΦPSII), photochemical quenching coefficient (qP), chlorophyll concentration (Chl a+b), Chl a/b ratio—were positively correlated with soil moisture content (SM) but negatively correlated with drought cycles, leading to increasing decline with increased drought severity and frequency. Consequently, these variables failed to fully recover during the rehydration phase following severe drought or multiple CD-R cycles. Malondialdehyde (MDA) accumulation significantly increased during severe drought and the third CD-R cycle. Catalase (CAT) activity increased progressively with drought intensity under PD-R (60–291 %), while CD-R induced significant increases of 28–68 % (mild) and 44–170 % (moderate). Proline (Pro) and soluble proteins (SP) elevated significantly only under severe persistent drought stress, showing no significant change under CD-R. This study demonstrates that: (i) I. difengpi exhibits strong post-drought water recovery; (ii) drought damage increases with severity and frequency; (iii) CAT plays a key role in antioxidant defense, while Pro and SP primarily respond to severe or multiple drought cycles. These findings provide a preliminary understanding of the physiological response of I. difengpi to persistent and intermittent drought.