Diverging temperature response of tree stem CO2 release under dry and wet season conditions in a tropical montane moist forest

Alexandra Zach,Viviana Horna,Christoph Leuschner

doi:10.1007/s00468-009-0398-9

Abstract

It is commonly presumed that plant respiratory CO2 release increases with increasing temperature. However, we report on very contrasting stem CO2 release (R S)–temperature relationships of trees in a species-rich tropical montane forest of southern Ecuador under dry and wet season conditions. Rates of R S were low and completely uncoupled from the dial temperature regime during the humid season. In contrast, during the dry season, R S was generally higher and temperature sensitivity of R S differed greatly in degree and even in the direction of response, indicating that temperature might not be the only determinant of R S. In order to explain the heterogeneity of R S, we related R S to vapour pressure deficit, wind speed and solar radiation as important abiotic drivers influencing transpiration and photosynthesis. Stepwise multiple regression analyses with these meteorological predictors either were biased by high collinearity of the independent variables or could not enhance the ability to explain the variability of R S. We assume maintenance respiration to dominate under humid conditions unfavourable for energy acquisition of the tree, thus explaining the pronounced uncoupling of R S from atmospheric parameters. In contrast, the drier and hotter climate of the dry season seems to favour R S via enhanced assimilatory substrate delivery and stem respiratory activity as well as elevated xylem sap CO2 imports with increased transpiration. In addition, tree individual differences in the temperature responses of R S may mirror diverging climatic adaptations of co-existing moist forest tree species which have their distribution centre either at higher or lower elevations.

Highlights

Temperature has long been identified as the most important abiotic factor influencing plant respiratory activity due to its well known effect on enzymatic reactions (e.g. Amthor 1989)
We report on very contrasting stem CO2 release (RS)– temperature relationships of trees in a species-rich tropical montane forest of southern Ecuador under dry and wet season conditions
The study was conducted in the Reserva San Francisco (RSF) adjacent to the Podocarpus National Park (PNP) on the eastern slopes of the southern Ecuadorian Andes

Summary

Introduction

Temperature has long been identified as the most important abiotic factor influencing plant respiratory activity due to its well known effect on enzymatic reactions (e.g. Amthor 1989). Temperature has long been identified as the most important abiotic factor influencing plant respiratory activity due to its well known effect on enzymatic reactions A strong relationship between temperature and plant tissue respiration has been exhaustively proved and verified under controlled conditions Edwards and McLaughlin 1978; Negisi 1982; Lavigne 1987; Gunderson et al 2000; Teskey and McGuire 2002). Woody tissue respiration is reported not to be exclusively related to temperature since other sources of CO2 than the respiratory activity of living wood cells (inner bark, cambium, xylem parenchyma) alone can influence the apparent amount of CO2 escaping through the bark. McGuire and Teskey 2004; Teskey et al 2008; Saveyn et al 2008a, b) Stem internal CO2 concentrations can constantly fluctuate, which in turn can affect the amount of CO2 diffusing out of the bark (e.g. McGuire and Teskey 2004; Teskey et al 2008; Saveyn et al 2008a, b)

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