THESIS
2020
xvii, 175 pages : illustrations (some color) ; 30 cm
Abstract
Understanding how marine phytoplankton and their primary consumer (i.e.,
microzooplankton) will respond to projected climate warming is critical for enhancing our
ability to predict the response of marine ecosystems to climate changes over the next century.
There is still poor understanding of thermal responses of phytoplankton and
microzooplankton at community levels and how adaptation and resource availability affect
their thermal sensitivities. To gain more in-depth insights into the response of marine
plankton to warming, we conducted a series of experiments and evaluated the temperature
sensitivity of plankton through activation energy (E
a) based on the framework of Metabolic
Theory of Ecology (MTE). We first estimated the E
a of phytoplankton growth rate and
microzooplankt...[
Read more ]
Understanding how marine phytoplankton and their primary consumer (i.e.,
microzooplankton) will respond to projected climate warming is critical for enhancing our
ability to predict the response of marine ecosystems to climate changes over the next century.
There is still poor understanding of thermal responses of phytoplankton and
microzooplankton at community levels and how adaptation and resource availability affect
their thermal sensitivities. To gain more in-depth insights into the response of marine
plankton to warming, we conducted a series of experiments and evaluated the temperature
sensitivity of plankton through activation energy (E
a) based on the framework of Metabolic
Theory of Ecology (MTE). We first estimated the E
a of phytoplankton growth rate and
microzooplankton grazing rate in subtropical coastal waters. We found that phytoplankton
growth has a lower E
a (0.36 eV, 95% CI = 0.28-0.44 eV) than microzooplankton grazing
(0.53 eV, 95% CI= 0.47-0.59 eV). This result is consistent with previous studies which states
that the temperature sensitivity of autotrophic rates is lower than heterotrophic rates.
However, we attribute this difference to the differential proximities of optimal temperature
(T
opt in nonlinear thermal reaction curve), as we also found T
opt of phytoplankton growth rate
is lower than that of microzooplankton and closer to environmental temperature.
Subsequently, with the finding of T
opt of phytoplankton community, we further examined the thermal response of phytoplankton at a relatively long-term scale (one year). We found the
maximal growth rate of the phytoplankton community increased with T
opt In contrast, E
a of
maximal growth rate (0.47 eV, 95% CI: 0.25 - 0.69) was significantly lower than that at a
short-term scale (1.65 eV, 95% CI: 1.29 - 2.02), which indicates that seasonal adaptation
could compensate the acute short-term thermal response of the phytoplankton community.
Next, we investigated how resource availability affects the thermal response of phytoplankton
by conducting temperature and nutrient modulated experiments in the oligotrophic subtropical
northwest Pacific. We found that nutrient limitation reduces the temperature sensitivity of
Synechococcus growth rate, which is likely due to the temperature-dependent nature of the
half-saturation constants of Synechococcus growth. In contrast, Prochlorococcus growth rate
is never limited by in situ nutrient concentrations even under warming conditions. Finally, we
attempted to quantify the effect of prey concentration and temperature on microzooplankton
based on the framework of MTE. E
a for microzooplankton grazing rate was 0.51 eV, which
supports the predicted value of MTE and demonstrates the effect of temperature on
microzooplankton. We conclude that our findings in this thesis provide quantitative insights
into the thermal response of marine plankton and are conducive to better inclusion of plankton
in biogeochemical or ecosystem models, which, therefore, aids predictions of the impact of
warming on marine ecosystems.
Post a Comment