Time lags between crown and basal sap flows in tropical lianas and co-occurring trees

Abstract

Water storage in the stems of woody plants contributes to their responses to short-term water shortages. To estimate the contribution of water storage to the daily water budget of trees, time lags of sap flow between different positions of trunk are used as a proxy of stem water storage. In lianas, another large group of woody species, it has rarely been studied whether stored water functions in their daily water use, despite their increasing roles in the carbon and water dynamics of tropical forests caused by their increasing abundance. We hypothesized that lianas would exhibit large time lags due to their extremely long stems, wide vessels and large volume of parenchyma in the stem. We examined time lags in sap flow, diel changes of stem volumetric water content (VWC) and biophysical properties of sapwood of 19 lianas and 26 co-occurring trees from 27 species in 4 forests (karst, tropical seasonal, flood plain and savanna) during a wet season. The plants varied in height/length from <5 to >60 m. The results showed that lianas had significantly higher saturated water content (SWC) and much lower wood density than trees. Seven of 19 liana individuals had no time lags; in contrast, only 3 of 26 tree individuals had no time lags. In general, lianas had shorter time lags than trees in our data set, but this difference was not significant for our most conservative analyses. Across trees and lianas, time lag duration increased with diurnal maximum changeable VWC but was independent of the body size, path length, wood density and SWC. The results suggest that in most lianas, internal stem water storage contributes little to daily water budget, while trees may rely more on stored water in the stem.

Physiological regulation and efficient xylem water transport regulate diurnal water and carbon balances of tropical lianas

“…; Chen et al . , ). Tropical trees differ in the size of their internal water storage, with some large trees providing substantial amounts of water to the transpiration stream; for example, a study of canopy trees in Panama found that the amount of water withdrawn from stem water storage and used to replace transpirational water losses range from 4 kg day −1 to 54 kg day −1 daily, depending on the main stem size, representing 9–15% of a tree's total daily water loss (Goldstein et al .…”

“…Stomatal regulation may be particularly important for lianas compared with their host trees, because lianas have a higher proportion of exposed leaves at the top of the canopy, where transpirational demand is higher (Putz ), and their internal stem water storage is comparatively small (Chen et al . ).…”

“…embolism) in the vascular system; stomatal regulation thus represents an especially important adaptation for canopy plants, which frequently experience high transpirational demands. Stomatal regulation may be particularly important for lianas compared with their host trees, because lianas have a higher proportion of exposed leaves at the top of the canopy, where transpirational demand is higher (Putz 1983), and their internal stem water storage is comparatively small (Chen et al 2016a).…”

Wood density, growth and mortality relationships of lianas on environmental gradients in fragmented forests of montane landscapes

“…Studies have shown that wood density of lianas is, on average, lower than that of trees (Chen et al., ; Zhu & Cao, ), being comparable to wood density of tree species of secondary forest (Putz, ). Wood density was found to be negatively related to water conductance in lianas (Chen et al., ), as was recorded for trees. Kitajima, Cordero, and Wright () found that mortality was greater at lower wood densities for saplings of trees and of lianas in a Neotropical lowland community.…”

“…Cavitation of the vasculature system can be countered by small‐diameter vessels with thick walls (Hacke, Sperry, Pockman, Davis, & McCulloh, ), resulting in greater wood density. While there are extensive global databases of wood density of trees (Chave et al., ; Zanne et al., ), for lianas, data are restricted to a few local studies (Chen et al., ; Kusumoto, Enoki, & Kubota, ; Putz, ; Zhu & Cao, ), even though lianas can contribute up to 25% of stems and species numbers in tropical forests (Schnitzer & Bongers, ).…”