Understanding different hydraulic strategies between lianas and trees using a mechanistic model

Background/Question/Methods Neotropical ecosystems are experiencing increases in liana abundance and biomass but the reasons of this increase remain obscure. One of the proposed hypotheses is the superior ability of lianas to cope with drought conditions. This hypothesis is supported by observations that lianas grow more rapidly during the dry season, described as the dry season growth advantage. However, a mechanistic understanding for this dry season growth advantage is currently lacking. In this study, we use a mechanistic physiological model, integrating field measurements, to elucidate the different hydraulic strategies of lianas and trees. Results/Conclusions We compare the sapflow dynamics and drought strategies of both tropical lianas and tropical trees, during both wet and dry seasons, in Paracou, French Guiana. By parameterizing a plant hydraulic transport model that includes root uptake, water storage and dynamic stomatal conductance optimization, we are able to integrate and mechanistically understand the differences in sapflow dynamics between trees and lianas. This model was subsequently benchmarked with the sapflow datasets and used in theoretical impact assessment and climate scenario testing. Preliminary results highlight longer daytime sapflow activity for lianas overall, however dry season dynamics show a faster total daily sapflow decline with decreasing soil water availability for the lianas compared to trees. Lianas also appear to be more responsive to rainfall events, while monitored trees showed longer time delays and required larger rainfall amounts before sapflow increased. Our findings provide insight into the depths of dry-season root activity, and suggest lianas are more active in the upper soil layers while trees extract water from deeper, less drought impacted soil layers during the dry period. This results are in agreement with stable water isotopes studies conducted at the site.