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| Titel |
Net ecosystem CO2 exchange of an invasive plant infestation: new insights on the effects of phenology and management practices on structure and functioning |
| VerfasserIn |
Oliver Sonnentag, Matteo Detto, Benjamin Runkle, Jaclyn Hatala, Rodrigo Vargas, Maggi Kelly, Dennis Baldocchi |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043751
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| Zusammenfassung |
| The net ecosystem carbon dioxide (CO2) exchange (FC) of invasive plant infestations has
been subject of few studies only. Perennial pepperweed (Lepidium latifolium L.) is an
aggressive invasive plant with severe economic and environmental consequences for infested
ecosystems. A characteristic feature of pepperweed’s phenological cycle is the dense
arrangement of small white flowers during secondary inflorescence. Little is known about
how pepperweed flowering and management practices such as mowing affect canopy
structure and canopy photosynthesis (FA) and autotrophic respiration (FAR) and thus
ecosystem respiration (FER; FC=FER-FA with FER=FAR+heterotrophic respiration
[FHR]). To examine these effects we analyzed three years (2007-2010) of CO2 flux
measurements made with eddy covariance, supporting environmental measurements and
near-surface remote sensing data (canopy-scale reflectance, digital camera imagery)
from a pepperweed-infested pasture in California’s Sacramento-San Joaquin River
Delta. The measurements cover three meteorologically similar summers (1 May –
30 September) that slightly differed in terms of land use practices. In 2007-2010,
the site was subjected to year-round grazing by beef cattle, and in 2008, the site
was additionally mowed in mid-May during flowering. We described structural
changes in canopy development through seasonal changes in surface roughness for
momentum transfer (z0m). Weekly soil CO2 efflux (- FHR) estimates from static
chamber measurements made over bare soil were used to separate FER into FAR
and FHR. We identified the onset of pepperweed’s key phenological phases (i.e.,
germination, early vegetative growth, flowering, seed maturation, senescence, dormancy)
through the integrated analysis of albedo of photosynthetically active radiation
(PAR), a broad-band green normalized difference vegetation index, and a digital
camera-based color index. We used non-linear mixed-effects model analysis to
investigate the combined effects of measurement year and flowering/ mowing on
the variable parameters of the non-linear responses of FA to light and FAR to air
temperature.
We address two specific questions with our research. First, how do year-round grazing
and spring mowing affect the timing (i.e., onset) of pepperweed’s key phenological phases?
Second, we focus on pepperweed flowering, the spectrally most notable phenological phase.
Thus we ask does the onset of flowering trigger changes in structural canopy development
(i.e., z0m) and functioning (i.e., FA; FAR)?
Over the summers (1 May – 30 September) of 2007 and 2009 the site was either almost
neutral with respect to CO2 (-26 g C m-2 period-1 in 2007) or a moderate net CO2 source
(89 g C m-2 period-1 in 2009). In contrast, the pepperweed infestation acted as a net CO2
sink (-162 g C m-2 period-1) over the summer of 2008 when the site was mowed once in
May during flowering to reduce the reproductive success of pepperweed. Preliminary results
show that year-round grazing inhibited the accumulation of dead stalks causing earlier
pepperweed green-up. The onset of flowering had no substantial impact on z0m. In
contrast, the onset of flowering significantly reduced maximum photosynthetic
capacity compared to non-flowering pepperweed, resulting in reduced photosynthetic
CO2 uptake. Similarly, FAR was slightly reduced in response to flowering, most
likely due to the due to the close coupling of growth respiration to FA. In contrast,
mowing early during flowering prevented the decrease in photosynthetic CO2 uptake
and the associated decrease in FAR due to immediate pepperweed regrowth. Our
study highlights the impact of invasive plants’ unique ecophysiological features
and applied management practices on net ecosystem CO2 exchange of infested
ecosystems. |
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