Abstract
Climate change may affect the chemical composition of riparian leaf litter and, aquatic organisms and, consequently, leaf breakdown. We evaluated the effects of different scenarios combining increased temperature and carbon dioxide (CO2) on leaf detritus of Hevea spruceana (Benth) Müll. and decomposers (insect shredders and microorganisms). We hypothesized that simulated climate change (warming and elevated CO2) would: i) decrease leaf-litter quality, ii) decrease survival and leaf breakdown by shredders, and iii) increase microbial leaf breakdown and fungal biomass. We performed the experiment in four microcosm chambers that simulated air temperature and CO2 changes in relation to a real-time control tracking current conditions in Manaus, Amazonas, Brazil. The experiment lasted seven days. During the experiment mean air temperature and CO2 concentration ranged from 26.96 ± 0.98ºC and 537.86 ± 18.36 ppmv in the control to 31.75 ± 0.50ºC and 1636.96 ± 17.99 ppmv in the extreme chamber, respectively. However, phosphorus concentration in the leaf litter decreased with warming and elevated CO2. Leaf quality (percentage of carbon, nitrogen, phosphorus, cellulose and lignin) was not influenced by soil flooding. Fungal biomass and microbial leaf breakdown were positively influenced by temperature and CO2 increase and reached their highest values in the intermediate condition. Both total and shredder leaf breakdown, and shredder survival rate were similar among all climatic conditions. Thus, low leaf-litter quality due to climate change and higher leaf breakdown under intermediate conditions may indicate an increase of riparian metabolism due to temperature and CO2 increase, highlighting the risk (e.g., decreased productivity) of global warming for tropical streams.
Highlights
Global temperatures are increasing due to greenhouse-gas emissions from fossil-fuel combustion and from deforestation, and this is an important threat to aquatic systems [1]
In the Amazon Basin, effects of precipitation changes may vary between regions; for example, an increase in rainfall with subsequent flooding is expected in Western Amazonia, and an increased frequency of droughts is expected in the Central and Lower Amazon areas [2]
We did not record significant differences in leaf quality between the leaf litter from plants growing on flooded versus non-flooded soil in the same microcosm
Summary
Global temperatures are increasing due to greenhouse-gas emissions from fossil-fuel combustion and from deforestation, and this is an important threat to aquatic systems [1]. The Intergovernmental Panel on Climate Change (IPCC) estimates under its most-likely scenario without mitigation (RCP8.5) that by the year 2100 average mean temperature is “likely” (66% probability) to increase by 4.8 ̊C over the 1996–2005 average, and that carbon dioxide (CO2) levels will reach ~1000 parts per million by volume (ppmv) [1]. In Amazonia, year 2100 temperatures in the June-August period would be 6-8 ̊C over the 1996–2005 average under the same scenario In the Amazon Basin, effects of precipitation changes may vary between regions; for example, an increase in rainfall with subsequent flooding is expected in Western Amazonia, and an increased frequency of droughts is expected in the Central and Lower Amazon areas [2]. In freshwater environments flooding results in an increase of water velocity, depth, and hydrological connectivity and may positively affect aquatic fauna and the leafbreakdown process [7,8]
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