Effects of increasing temperature and, CO₂ on quality of litter, shredders, and microorganisms in Amazonian aquatic systems

<div><p>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 <i>Hevea spruceana</i> (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.</p></div

Effects of increasing temperature and, CO₂ on quality of litter, shredders, and microorganisms in Amazonian aquatic systems - Fig 2

<p><b>Survival (%; A) and pupae (%; B) of <i>Phylloicus elektoros</i> (Trichoptera: Calamoceratidae) in treatments with leaf disks of <i>Hevea spruceana</i> under four climate conditions during the experiment in Control, Light, Intermediate and Extreme treatments</b>.</p

Mean values (standard error) and results of abiotic variables under simulated climate conditions during seven days of the experiment.

<p>Mean values (standard error) and results of abiotic variables under simulated climate conditions during seven days of the experiment.</p

Fungal biomass in treatments with leaf disks of <i>Hevea spruceana</i> under four climate conditions during the experiment in Control, Light, Intermediate and Extreme treatments.

<p>First (lower line) and third (higher line) quartile, the median (bold line), upper and lower limits (dashed line) and outliers (circles). Highest values = a; lowest values = b (p < 0.05).</p

Chemical characteristics of <i>Hevea spruceana</i> leaves growing under different conditions of temperature, CO₂ (Carbon dioxide) and humidity availability.

<p>We included paired t-tests for leaf characteristics of plants grown on flooded and non-flooded soils.</p

The relationships between biotic uniqueness and abiotic uniqueness are context dependent across drainage basins worldwide

Context Global change, including land-use change and habitat degradation, has led to a decline in biodiversity, more so in freshwater than in terrestrial ecosystems. However, the research on freshwaters lags behind terrestrial and marine studies, highlighting the need for innovative approaches to comprehend freshwater biodiversity. Objectives We investigated patterns in the relationships between biotic uniqueness and abiotic environmental uniqueness in drainage basins worldwide. Methods We compiled high-quality data on aquatic insects (mayflies, stoneflies, and caddisflies at genus-level) from 42 drainage basins spanning four continents. Within each basin we calculated biotic uniqueness (local contribution to beta diversity, LCBD) of aquatic insect assemblages, and four types of abiotic uniqueness (local contribution to environmental heterogeneity, LCEH), categorized into upstream land cover, chemical soil properties, stream site landscape position, and climate. A mixed-effects meta-regression was performed across basins to examine variations in the strength of the LCBD-LCEH relationship in terms of latitude, human footprint, and major continental regions (the Americas versus Eurasia). Results On average, relationships between LCBD and LCEH were weak. However, the strength and direction of the relationship varied among the drainage basins. Latitude, human footprint index, or continental location did not explain significant variation in the strength of the LCBD-LCEH relationship. Conclusions We detected strong context dependence in the LCBD-LCEH relationship across the drainage basins. Varying environmental conditions and gradient lengths across drainage basins, land-use change, historical contingencies, and stochastic factors may explain these findings. This context dependence underscores the need for basin-specific management practices to protect the biodiversity of riverine systems.</p

The relationships between biotic uniqueness and abiotic uniqueness are context dependent across drainage basins worldwide

Context Global change, including land-use change and habitat degradation, has led to a decline in biodiversity, more so in freshwater than in terrestrial ecosystems. However, the research on freshwaters lags behind terrestrial and marine studies, highlighting the need for innovative approaches to comprehend freshwater biodiversity. Objectives We investigated patterns in the relationships between biotic uniqueness and abiotic environmental uniqueness in drainage basins worldwide. Methods We compiled high-quality data on aquatic insects (mayflies, stoneflies, and caddisflies at genus-level) from 42 drainage basins spanning four continents. Within each basin we calculated biotic uniqueness (local contribution to beta diversity, LCBD) of aquatic insect assemblages, and four types of abiotic uniqueness (local contribution to environmental heterogeneity, LCEH), categorized into upstream land cover, chemical soil properties, stream site landscape position, and climate. A mixed-effects meta-regression was performed across basins to examine variations in the strength of the LCBD-LCEH relationship in terms of latitude, human footprint, and major continental regions (the Americas versus Eurasia). Results On average, relationships between LCBD and LCEH were weak. However, the strength and direction of the relationship varied among the drainage basins. Latitude, human footprint index, or continental location did not explain significant variation in the strength of the LCBD-LCEH relationship. Conclusions We detected strong context dependence in the LCBD-LCEH relationship across the drainage basins. Varying environmental conditions and gradient lengths across drainage basins, land-use change, historical contingencies, and stochastic factors may explain these findings. This context dependence underscores the need for basin-specific management practices to protect the biodiversity of riverine systems.</p