| 1. |
- Choudhury, Maidul I., et al.
(författare)
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Charophytes collapse beyond a critical warming and brownification threshold in shallow lake systems
- 2019
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 661, s. 148-154
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Tidskriftsartikel (refereegranskat)abstract
- Charophytes play a critical role for the functioning of shallow lake ecosystems. Although growth of charophytes can be limited by many factors, such as temperature, nutrients and light availability, our understanding about concomitant effects of climate warming and other large-scale environmental perturbations, e.g. increases in humic matter content (‘brownification’) is still limited. Here we conducted an outdoor mesocosm experiment during 71 days with a common charophyte species, Chara vulgaris, along an increasing gradient of temperature and brownification. We hypothesized the growth of C. vulgaris to increase with temperature, but to level off along the combined temperature and brownification gradient when reaching a critical threshold for light limitation via brownification. We show that C. vulgaris increases the relative growth rate (RGR), main and total shoot elongation, as well as number of lateral shoots when temperature and brownification increased by +2 °C and + 100%, respectively above today's levels. However, the RGR, shoot elongation and number of lateral shoots declined at further increment of temperature and brownification. Macrophyte weight-length ratio decreased with increased temperature and brownification, indicating that C. vulgaris allocate more resources or energy for shoot elongation instead of biomass increase at warmer temperatures and higher brownification. Our study shows that C. vulgaris will initially benefit from warming and brownification but will then decline as a future scenario of increased warming and brownification reaches a certain threshold level, in case of our experiment at +4 °C and a 2-fold increase in brownification above today's levels.
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| 2. |
- Hansson, Lars Anders, et al.
(författare)
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Different climate scenarios alter dominance patterns among aquatic primary producers in temperate systems
- 2020
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Ingår i: Limnology and Oceanography. - : WILEY. - 0024-3590 .- 1939-5590. ; 65:10, s. 2328-2336
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Tidskriftsartikel (refereegranskat)abstract
- In a future climate change perspective, the interactions among different life-forms of primary producers will likely be altered, leading to changes in the relative dominance among macrophytes, filamentous, and planktonic algae. In order to improve the possibilities to forecast future ecosystem services and function, we therefore conducted a long-term mesocosm study where primary producers were exposed to different climate scenarios, including both a mean increase in temperature (4 degrees C) and a similar energy input, but delivered as "heat waves" (fluctuations 0-8 degrees C above ambient). We show that in shallow systems, future climate change scenarios will likely lead to higher total macrophyte biomasses, but also to considerable alterations in the macrophyte community composition. The biomass of filamentous algae (Cladophora) showed no significant difference among treatments, although effect size analyses identified a slight increase at heated conditions. We also show that future climate change will not necessarily lead to more phytoplankton blooms, although a considerable alteration in phytoplankton community composition is to be expected, with a dominance of cyanobacteria and Cryptophytes, whereas Chlorophyceae and diatoms will likely play a less pronounced role than at present. In a broader context, we conclude that the total biomass of macrophytes will likely increase in shallow areas, whereas phytoplankton may not show any strong changes in biomass in a future climate change scenario. Instead, the major changes among primary producers will likely be mirrored in a considerably different species composition than at present.
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| 3. |
- Li, Zhongqiang, et al.
(författare)
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Climate warming and heat waves affect reproductive strategies and interactions between submerged macrophytes
- 2017
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013. ; 23:1, s. 108-116
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Tidskriftsartikel (refereegranskat)abstract
- Extreme climatic events, such as heat waves, are predicted to increase in frequency and intensity during the next hundred years, which may accelerate shifts in hydrological regimes and submerged macrophyte composition in freshwater ecosystems. Since macrophytes are profound components of aquatic systems, predicting their response to extreme climatic events is crucial for implementation of climate change adaptation strategies. We therefore performed an experiment in 24 outdoor enclosures (400 L) separating the impact of a 4 °C increase in mean temperature with the same increase, that is the same total amount of energy input, but resembling a climate scenario with extreme variability, oscillating between 0 °C and 8 °C above present conditions. We show that at the moderate nutrient conditions provided in our study, neither an increase in mean temperature nor heat waves lead to a shift from a plant-dominated to an algal-dominated system. Instead, we show that species-specific responses to climate change among submerged macrophytes may critically influence species composition and thereby ecosystem functioning. Our results also imply that more fluctuating temperatures affect the number of flowers produced per plant leading to less sexual reproduction. Our findings therefore suggest that predicted alterations in climate regimes may influence both plant interactions and reproductive strategies, which have the potential to inflict changes in biodiversity, community structure and ecosystem functioning.
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| 4. |
- Li, Zhongqiang, et al.
(författare)
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Heat Waves Alter Macrophyte-Derived Detrital Nutrients Release under Future Climate Warming Scenarios
- 2021
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 55:8, s. 5272-5281
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Tidskriftsartikel (refereegranskat)abstract
- In addition to a rise in global air and water mean temperatures, extreme climate events such as heat waves are increasing in frequency, intensity, and duration in many regions of the globe. Developing a mechanistic understanding of the impacts of heat waves on key ecosystem processes and how they differ from just an increase in mean temperatures is therefore of utmost importance for adaptive management against effects of global change. However, little is known about the impact of extreme events on freshwater ecosystem processes, particularly the decomposition of macrophyte detritus. We performed a mesocosm experiment to evaluate the impact of warming and heat waves on macrophyte detrital decomposition, applied as a fixed increment (+4 °C) above ambient and a fluctuating treatment with similar energy input, ranging from 0 to 6 °C above ambient (i.e., simulating heat waves). We showed that both warming and heat waves significantly accelerate dry mass loss of the detritus and carbon (C) release but found no significant differences between the two heated treatments on the effects on detritus dry mass loss and C release amount. This suggests that moderate warming indirectly enhanced macrophyte detritus dry mass loss and C release mainly by the amount of energy input rather than by the way in which warming was provided (i.e., by a fixed increment or in heat waves). However, we found significantly different amounts of nitrogen (N) and phosphorus (P) released between the two warming treatments, and there was an asymmetric response of N and P release patterns to the two warming treatments, possibly due to species-specific responses of decomposers to short-term temperature fluctuations and litter quality. Our results conclude that future climate scenarios can significantly accelerate organic matter decomposition and C, N, and P release from decaying macrophytes, and more importantly, there are asymmetric alterations in macrophyte-derived detrital N and P release dynamic. Therefore, future climate change scenarios could lead to alterations in N/P ratios in the water column via macrophyte decomposition processes and ultimately affect the structure and function of aquatic ecosystems, especially in the plankton community.
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| 5. |
- Urrutia Cordero, Pablo, et al.
(författare)
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Climate warming and heat waves alter harmful cyanobacterial blooms along the benthic-€“pelagic interface
- 2020
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 101:7, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- In addition to a rise in mean air and water temperatures, more frequent and intense extreme climate events (such as heat waves) have been recorded around the globe during the past decades. These environmental changes are projected to intensify further in the future, and we still know little about how they will affect ecological processes driving harmful cyanobacterial bloom formation. Therefore, we conducted a long-term experiment in 400-L shallow freshwater mesocosms, where we evaluated the effects of a constant +4°C increase in mean water temperatures and compared it with a fluctuating warming scenario ranging from 0 to +8°C (i.e., including heat waves) but with the same +4°C long-term elevation in mean water temperatures. We focused on investigating not only warming effects on cyanobacterial pelagic dynamics (phenology and biomass levels), but also on their recruitment from sediments—which are a fundamental part of their life history for which the response to warming remains largely unexplored. Our results demonstrate that (1) a warmer environment not only induces a seasonal advancement and boosts biomass levels of specific cyanobacterial species in the pelagic environment, but also increases their recruitment rates from the sediments, and (2) these species-specific benthic and pelagic processes respond differently depending on whether climate warming is expressed only as an increase in mean water temperatures or, in addition, through an increased warming variability (including heat waves). These results are important because they show, for the first time, that climate warming can affect cyanobacterial dynamics at different life-history stages, all the way from benthic recruitment up to their establishment in the pelagic community. Furthermore, it also highlights that both cyanobacterial benthic recruitment and pelagic biomass dynamics may be different as a result of changes in the variability of warming conditions. We argue that these findings are a critical first step to further our understanding of the relative importance of increased recruitment rates for harmful cyanobacterial bloom formation under different climate change scenarios.
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| 6. |
- Urrutia Cordero, Pablo, et al.
(författare)
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Phytoplankton diversity loss along a gradient of future warming and brownification in freshwater mesocosms
- 2017
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 62:11, s. 1869-1878
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Tidskriftsartikel (refereegranskat)abstract
- 1. Globally, freshwater ecosystems are warming at unprecedented rates and northern temperate lakes are simultaneously experiencing increased runoff of humic substances (brownification), with little known consequences for future conservation of biodiversity and ecosystem functioning.2. We employed an outdoor mesocosm experiment during spring and summer to investigate the combined effects of gradually increasing warming and brownification perturbations on the phytoplankton community structure (biodiversity and composition) and functioning (biomass).3. While we did not observe overall significant treatment effects on total phytoplankton biomasses, we show that predicted increases in warming and brownification can reduce biodiversity considerably, occasionally up to 90% of Shannon diversity estimates. Our results demonstrate that the loss of biodiversity is driven by the dominance of mixotrophic algae (Dinobryon and Cryptomonas), whereas several other phytoplankton taxa may be temporarily displaced from the community, including Cyclotella, Desmodesmus, Monoraphidium, Tetraedron, Nitzschia and Golenkinia.4. The observed loss of biodiversity coincided with an increase in bacterial production providing resources for potential mixotrophs along the gradient of warming and brownification. This coupling between bacterial production and mixotrophs was likely a major cause behind the competitive displacement of obligate phototrophs and supports evidence for the importance of consumer-prey dynamics in shaping environmental impacts on phytoplankton communities.5. We conclude that warming and brownification are likely to cause a profound loss of biodiversity by indirectly affecting competitive interactions among phytoplankton taxa. Importantly, our results did not show an abrupt loss of biodiversity; instead the reduction in taxa richness levelled off after exceeding a threshold of warming and brownification. These results exemplify the complex nonlinear responses of biodiversity to environmental perturbations and provide further insights for predicting biodiversity patterns to the future warming and brownification of freshwaters.
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| 7. |
- Zhang, Huan, et al.
(författare)
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Life-history traits buffer against heat wave effects on predator-prey dynamics in zooplankton
- 2018
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Ingår i: Global Change Biology. - : WILEY. - 1354-1013 .- 1365-2486. ; 24:10, s. 4747-4757
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Tidskriftsartikel (refereegranskat)abstract
- In addition to an increase in mean temperature, extreme climatic events, such as heat waves, are predicted to increase in frequency and intensity with climate change, which are likely to affect organism interactions, seasonal succession, and resting stage recruitment patterns in terrestrial as well as in aquatic ecosystems. For example, freshwater zooplankton with different life-history strategies, such as sexual or parthenogenetic reproduction, may respond differently to increased mean temperatures and rapid temperature fluctuations. Therefore, we conducted a long-term (18months) mesocosm experiment where we evaluated the effects of increased mean temperature (4 degrees C) and an identical energy input but delivered through temperature fluctuations, i.e., as heat waves. We show that different rotifer prey species have specific temperature requirements and use limited and species-specific temperature windows for recruiting from the sediment. On the contrary, co-occurring predatory cyclopoid copepods recruit from adult or subadult resting stages and are therefore able to respond to short-term temperature fluctuations. Hence, these different life-history strategies affect the interactions between cyclopoid copepods and rotifers by reducing the risk of a temporal mismatch in predator-prey dynamics in a climate change scenario. Thus, we conclude that predatory cyclopoid copepods with long generation time are likely to benefit from heat waves since they rapidly wake up even at short temperature elevations and thereby suppress fast reproducing prey populations, such as rotifers. In a broader perspective, our findings suggest that differences in life-history traits will affect predator-prey interactions, and thereby alter community dynamics, in a future climate change scenario.
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