Methanotrophic bacteria are the only known biological sink for the
greenhouse gas methane. Therefore, methanotrophs play a key function in
carbon cycling, an important biogeochemical process that affects global
climate change. Yet, little is known of their vulnerability and resilience
to disturbances. Driven by the gap of knowledge, this PhD thesis is a
seminal study focusing on the recovery of methanotrophs from disturbances
with respect to population dynamics, diversity and functioning. Two model
disturbances were tested; disturbance-induced mortality and heat shock.
While the former model disturbance represents a non-selective form of
disturbance, the heat shock treatment may select for sub-populations of
thermo-tolerant methanotrophs. Overall, methanotrophs are shown to be
remarkably resilient to induced disturbances, compensating and even
over-compensating for methane uptake during recovery. Type II methanotrophs,
known to be present in high abundance as resting cells, appear to become
more important during disturbances.
Furthermore, the establishment and subsequent development of the
methanotrophic community and activity were studied along a rice paddy
chronosequence. With the influx of anthropogenic influences once a rice
paddy is formed, the methanotrophic community structure is anticipated to
undergo a dramatic change which in turn, may affect the activity. It appears
that the young and ancient rice paddies do not show clear divergence,
suggesting that the methane oxidizing community was soon established after a
rice paddy is formed. However, the selection of the best adapted
sub-population needs time. Accordingly, long term rice agriculture allows
for higher methane uptake, and may select for a methanotroph sub-population
that remains active. The predominant methanotrophs found in the Chinese rice
paddies are type II, mainly Methylocystis species, and type Ib (RPC-1).
However, type Ib seems to be the active dominant sub-population. This and
previous studies suggest specific adaptation of type Ib to rice paddy
environments. Interestingly, novel sequences phylogenetically grouped
between pmoA and amoA were detected.
Overall, paddy soil methanotrophs are not only able to recover from
disturbances, but are apparently showing specific adaptation to rice paddy
environments, demonstrating their resilience in face of perturbation
