Water storage capacity is inversely associated with xylem embolism resistance in tropical karst tree species.

Tropical karst habitats are characterized by limited and patchy soil, large rocky outcrops and porous substrates, resulting in high habitat heterogeneity and soil moisture fluctuations. Xylem hydraulic efficiency and safety can determine the drought adaptation and spatial distribution of woody plants growing in karst environments. In this study, we measured sapwood-specific hydraulic conductivity (Ks), vulnerability to embolism, wood density, saturated water content, and vessel and pit anatomical characteristics in the branch stems of 12 evergreen tree species in a tropical karst seasonal rainforest in southwestern China. We aimed to characterize the effects of structural characteristics on hydraulic efficiency and safety. Our results showed that there was no significant correlation between Ks and hydraulic safety across the tropical karst woody species. Ks was correlated with hydraulic vessel diameter (r = 0.80, P < 0.05) and vessel density (r = -0.60, P < 0.05), while the stem water potential at 50 and 88% loss of hydraulic conductivity (P50 and P88) were both significantly correlated with wood density (P < 0.05) and saturated water content (P = 0.052 and P < 0.05, respectively). High stem water storage capacity was associated with low cavitation resistance possibly because of its buffering the moisture fluctuations in karst environments. However, both Ks and P50/P88 were decoupled from the anatomical traits of pit and pit membranes. This may explain the lack of tradeoff between hydraulic safety and efficiency in tropical karst evergreen tree species. Our results suggest that diverse hydraulic trait combination may facilitate species coexistence in karst environments with high spatial heterogeneity.

[Responses of Manglietia glauca growth to soil nutrients and climatic factors].

Tree height and diameter of breast height (DBH) as growth characteristics of Manglietia glauca introduced from Vietnam were measured at many sites in south China and responses of M. glauca growth to soil nutrients and climatic factors were analyzed in this study. Annual average increments of tree height and DBH among different planted sites had significant differences. Annual average increments of tree height and DBH had significant positive correlation with soil total N and P, available N and P, but no significant correlation with soil organic matter, total K, available K, indicating that soil N and P contents could be the main affecting factors for the growth of M. glauca. Annual average increment of tree height had significant difference, but annual average increment of DBH had no significant difference at different altitudes. Annual average increment of tree height increased with the altitude from 150 to 550 m, the maximum was at the altitude of 550 m, and then it decreased. It indicated that the most appropriate altitude for M. glauca introduction is 550 m. Annual average increments of tree height and DBH had significant negative correlation with annual average temperature and > or = 10 degrees C accumulated temperature, and significant positive correlation with annual average precipitation, suggesting that annual mean temperature, > or = 10 degrees C accumulated temperature and annual average precipitation could be the main climatic factors influencing the growth of M. glauca.