Aquatic hyphomycete strains from metal-contaminated and reference streams might respond differently to future increase in temperature

Abstract

Aquatic hyphomycetes, a group of polyphyletic fungi, have been reported in streams contaminated with metals. This tolerance to metal contamination however can result in limited performance and limited ability to cope with additional environmental change. The predicted increase in water temperature, as a consequence of global warming, will have an additional effect on many streams. The sensitivity to temperature of strains of three aquatic hyphomycete species isolated from a metal-contaminated stream and an uncontaminated stream was assessed by determining their radial growth and activity (conidial production, oxygen consumption, mycelial biomass accumulation, fine particulate organic matter [FPOM] production, and microbial induced leaf mass loss) at 13 C (present water temperature in autumn) and at 18 C (predicted water temperature under global warming). Growth and reproductive activity generally were depressed for the strains isolated from the metal-contaminated stream when compared with those isolated from the unpolluted stream. These differences however were not translated into differences in FPOM production and leaf-litter mass loss, indicating that the strains isolated from the contaminated stream can decompose leaf litter similar to those of the reference stream. The 5 C increase in temperature stimulated fungal activity and litter decomposition, irrespective of species and strain. This might have strong effect on aquatic food-web and ecosystem functioning under global warming because increases in litter decomposition might lead to food shortage for higher trophic levels. The sensitivity to temperature depended on the response variable, species and strain. FPOM production was the variable most sensitive to temperature across strains and species and that for which temperature sensitivities differed most between strains. Fungal tolerance to metal contamination affects the extent to which its functions are stimulated by an increase in temperature, constituting an additional cost of metal tolerance.

• climate warming
• fungal activity
• fungal radial growth
• leaf decomposition
• temperature sensitivity

Acknowledgments

Elsa Rodrigues is thanked for the HPLC analysis. The comments provided by Dr Lee Taylor and two anonymous reviewers on a previous version of the manuscript were much appreciated.

This study was partially financed by the IMAR–CMA, the FEDER Funds through the Program Operational Factors of Competitiveness – COMPETE and National Funds through the Portuguese Science and Technology Foundation ( FCT, project PTDC/CLI/67180/2006). Financial support granted by the FCT to VF (postdoctoral fellowship SFRH/BPD/34368/2006, program POPH/FSE) and to ALG (doctoral fellowship SFRH/BD/47089/2008, program POPH/FSE) is gratefully acknowledged.