Abstract
Microclimate in the tropical montane cloud forest (TMCF) is variable on both spatial and temporal scales and can lead to large fluctuations in both leaf-level transpiration and whole plant water use. While variation in transpiration has been found in TMCFs, the influence of different microclimatic drivers on plant water relations in this ecosystem has been relatively understudied. Within the TMCF, epiphytes may be particularly affected by natural variation in microclimate due to their partial or complete disassociation from soil resources. In this study, we examined the effects of seasonal microclimate on whole plant water balance in epiphytes in both an observational and a manipulative experiment. We also evaluated the effects of different microclimatic drivers using three hierarchical linear (mixed) models. On average, 31 % of total positive sap flow was recovered via foliar water uptake (FWU) over the course of the study. We found that precipitation was the greatest driver of foliar water uptake and nighttime sap flow in our study species and that both VPD and precipitation were important drivers to daytime sap flow. We also found that despite adaptations to withstand seasonal drought, an extended dry period caused severe desiccation in most plants despite a large reduction in leaf-level and whole plant transpiration. Our results indicate that the epiphytes studied rely on FWU to maintain positive water balance in the dry season and that increases in dry periods in the TMCF may be detrimental to these common members of the epiphyte community.
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Acknowledgments
The authors thank the Monteverde Cloud Forest Reserve for the use of laboratory facilities, access to the park and logistical support. We also thank the Monteverde Institute, especially Maricella Solis, for logistical support and help in obtaining research permits. Sarah McGraw aided greatly in the construction of sap flow sensors and in training undergraduate researchers at Franklin and Marshall College. Lynx Guimond provided assistance in the field. Willow Zuchowski and Bill Haber provided assistance in species identification. Erica Hample created Fig. 1. Ram Oren, Janet Fisher, Jaime Blair, Z. Carter Berry and two anonymous reviewers provided valuable suggestions to improve the manuscript. Financial support for this research was provided by Franklin and Marshall College.
Author contribution statement
SGG formulated the ideas resulting in the research. AD, AG and SGG conducted the fieldwork. AD, and SGG conducted the non-modeling statistical analyses. DD conducted modeling analyses and contributed text regarding those analyses. AD and SGG wrote the manuscript. All authors edited the manuscript.
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Communicated by Ram Oren.
This work is the first to describe the importance of different microclimatic drivers on patterns of sap flow in epiphytes. In addition, the manipulative experiment provides important information regarding the vulnerability of this important plant community to long periods of drought. Our results highlight the importance of habitat moisture in driving sap flow in this community as well as the reliance of these species on cloud water interception for positive water balance.
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Darby, A., Draguljić, D., Glunk, A. et al. Habitat moisture is an important driver of patterns of sap flow and water balance in tropical montane cloud forest epiphytes. Oecologia 182, 357–371 (2016). https://doi.org/10.1007/s00442-016-3659-5
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DOI: https://doi.org/10.1007/s00442-016-3659-5