Microplastics and heavy metal pollution frequently co-occur in the marine environment, raising concerns about their potentially harmful impacts on marine fish. This study undertook a comprehensive evaluation of the individual and combined stress effects of polylactide microplastics (PLA-MPs) and chromium (Cr) on marine medaka larvae. Following a 14-day exposure to PLA-MPs (100 μg/L) and Cr (50 μg/L), both individually and in combination, significant increases in heart rate and body length were observed. Notably, the combined exposure to PLA-MPs and Cr caused marked histopathological alterations, including shedding, atrophy, and lysis of the intestinal tissues. Furthermore, both individual and combined exposure induced oxidative stress in fish larvae, leading to changes in various enzyme activity indices. Individual exposure to either PLA-MPs or Cr led to anxious behavior in the larvae, whereas combined exposure not only caused anxious behavior but also altered swimming patterns. These findings suggest that combined exposure to PLA-MPs and Cr can exacerbate the toxic effects on marine medaka larvae.

Previous studies have observed a two-dimensional relationship (i.e., decoupled correlation) between leaf size and leaf economics, as well as a tight correlation between leaf economics and drought tolerance. However, the underlying mechanism maintaining the relationship between leaf size and drought tolerance remains largely unknown. Here, we measured leaf size, water potential at 50% loss of hydraulic conductance, hydraulic safety margin and different orders of vein traits across 28 tree species in a subtropical forest in Southern China. We found that leaf size and drought tolerance were in two independent dimensions (R² = 0.00, P > 0.05). Primary and secondary vein traits (i.e., vein diameter and density) explained the variation of leaf size with R² ranging from 0.37 to 0.70 (all P < 0.01), while minor vein traits accounted for the variation of leaf drought tolerance with R² ranging from 0.30 to 0.43 (all P < 0.01). Our results provide insight into the two-dimensional relationship between leaf size and drought tolerance, and highlights the importance of vein hierarchy in plant leaf functioning.

Minimum leaf conductance (gmin) refers to the residual water loss through plant leaf cuticle and incompletely closed stomata. Despite its importance in plant drought adaptation, the variation in gmin across forest trees and the factors influencing it remain poorly understood. In this study, we quantified the gmin of 39 tree species with contrasting light requirement strategies (light-demanding vs. shade-tolerant) in subtropical forests of southern China and analysed their correlations with leaf anatomical and physiological traits. We found that across the studied species, gmin was negatively correlated with cuticle thickness (R2=0.81), but positively correlated with the fraction of epidermis allocated to stomata (fgc; R2=0.17). Species with higher gmin tended to have greater fgc, which was associated with higher stomatal conductance (gs), elevated photosynthetic rates (A), and shorter leaf lifespans. Interestingly, compared with shade-tolerant species, light-demanding species displayed significantly higher gmin values, which might be attributed to their thinner cuticles and, to a lesser extent, greater fgc. Our results demonstrate that cuticle thickness is the primary driver of gmin variation in subtropical forest tree species. These findings reveal a tight linkage between gmin and leaf structure that is shaped by the contrasting light-requirement strategies of plants, thus highlighting the trade-off between carbon gain and dehydration tolerance at the leaf level.