Growth performance, photosynthetic characteristics and water-use strategies of reintroduced Malania oleifera seedlings across contrasting habitats

Abstract

Habitat conditions are important factors influencing plant reintroduction outcomes, yet the physiological responses of endangered woody species across contrasting reintroduction habitats remain poorly understood. In this study, seedlings of Malania oleifera reintroduced into limestone (karst) and red-soil habitats were investigated, with naturally reintroduced wild seedlings serving as a reference. Photosynthetic light-response and CO 2 -response curves, chlorophyll contents, leaf anatomical traits, morphological characteristics, and water-use efficiency (WUE) were measured to compare physiological and morphological variation among contrasting reintroduction habitats. Seedlings from the limestone reintroduction site exhibited higher maximum net photosynthetic rate ( P max ), light saturation point ( LSP ), and isotope-derived water-use efficiency (WUE) than seedlings from the red-soil reintroduction site, whereas red-soil seedlings showed higher CO 2 -saturated photosynthetic capacity ( A max ). Limestone-grown seedlings also contained higher chlorophyll a and total chlorophyll contents than red-soil seedlings but lower levels than wild seedlings. Leaf anatomical traits also varied among habitats, with wild seedlings exhibiting greater palisade tissue thickness (PT) and higher palisade-to-spongy tissue ratios (PT/ST), whereas limestone- and red-soil-reintroduced seedlings showed similar PT/ST values. Seedlings from the limestone reintroduction site showed greater final plant height and basal stem diameter than those from the red-soil reintroduction site and wild reference habitat, whereas crown width did not differ significantly among habitats. Furthermore, isotope-derived WUE values were higher in seedlings from the limestone reintroduction site than in those from the red-soil site. This difference suggests variation in water-use strategies among habitats, although the underlying mechanisms require further investigation. Thus, seedlings from the three habitats exhibited distinct combinations of photosynthetic, morphological, anatomical, and water-use traits. The observed differences represent habitat-associated variation during the investigated period rather than evidence of universal habitat superiority. Because soil type was confounded with site conditions and the study evaluated seedlings during a single sampling period, long-term monitoring across multiple sites is required to further assess the persistence and reintroduction outcomes of this endangered karst tree species.