Hydraulic architecture of lianas in a semiarid climate: efficiency or safety?

Abstract

Xylem anatomical traits can provide insights regarding the mechanisms affecting the distribution of vascular plants across environmental gradients. In this study, we aimed to investigate the hypothesis that lianas occurring in semiarid environments have characteristics that maximize the xylem resistance to tension-induced cavitation along the root--stem-branch continuum. To gather information regarding the hydraulic architecture of the lianas, we analyzed several anatomical traits of wood: cross-sectional area occupied by the parenchyma (A P ), fibers (A F ), and vessels (A V ); average vessel diameter (d); wood density (WD); pit diameter in the vessel wall (d pit ); pit density (N pit ), and potential hydraulic conductivity (Kp) in branches, stems, and roots of three congeneric species of lianas that occur in two vegetation types of the semiarid regions of Brazil. We found that lianas in these semiarid environments possess a number of the following xylem traits that may allow resistance to tension-induced cavitation:1) lower vessel diameter, lower Kp, and higher hydraulic safety in roots and branches; 2) Dimorphic vessels, ensuring both hydraulic efficiency and safety; and 3) small diameter of pits (potentially associated with a decrease in the membrane area of the vessel pits). This suite of traits may provide insight into mechanisms allowing lianas to occur in semiarid environments.

Are hydraulic patterns of lianas different from trees? New insights from Hedera helix

“…In contrast, the main stem was less embolism resistant, as its Ψ LC50 was up to 1.5 MPa less negative compared with branches from the same height (Table 2). The higher hydraulic efficiency and lower safety in the main stem compared with branches corresponds to patterns reported for lianas from semi-arid regions (Carvalho et al , 2015) and several angiosperm and gymnosperm trees (Zimmermann, 1978; Domec et al , 2006; Beikircher and Mayr, 2008; Johnson et al , 2016). Due to the small cross-sectional area of the main stem, high k s is apparently essential for temperate lianas to prevent a strong drop of Ψ during transpiration, and limited embolism resistance is probably the consequence of a trade-off between safety and efficiency (i.e.…”

“…Van der Sande et al , 2013; Chen et al , 2017). The k s measured for H. helix (up to 18.67 m 2 s –1 MPa –1 × 10 –4 in branches and up to 31.14 m 2 s –1 MPa –1 × 10 –4 in the main stem; Table 2) was higher than mean values reported for temperate angiosperm trees, but lower than k s values in vines and most tropical lianas (Gartner et al , 1990; Carvalho et al , 2015; Chen et al , 2017). This is not surprising, as extremely wide vessels (>100 µm), which were found in many tropical lianas and vines (e.g.…”

Higher water and nutrient use efficiencies in savanna than in rainforest lianas result in no difference in photosynthesis

“…Our results, therefore, suggest that lianas utilize different ecological strategies in different habitats. Consistent with previous results that lianas tend to have narrower vessels, lower hydraulic conductivity and higher cavitation resistance in dry forests than that in mesic forests ( Carvalho et al. 2015 , Carvalho et al.…”

Why is liana abundance low in semiarid climates?

“…Through anatomical data, Carvalho et al . () demonstrated that the three species of lianas analysed show high potential hydraulic conductivity ( K p ), with F. caudigera being the most efficient species (16.1 ± 3.3 kg m −1 MPa −1 s −1 ), followed by F. chica (6.79 ± 2.7 kg m −1 MPa −1 s −1 ) and F. dispar (5.2 ± 1.6 kg m −1 MPa −1 s −1 ). The K p shows that lianas maintain an efficient hydraulic system, and the high values of P 50 that we found indicate a low resistance to cavitation.…”