Variation in photosynthetic light-use efficiency in a mountainous tropical rain forest in Indonesiaстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 22 февраля 2016 г.
Аннотация:Photosynthetically active radiation (Q)-use efficiency (ε) is an important parameter for deriving carbon fluxes between forest canopies and the atmosphere from meteorological ground and remote sensing data. A common approach is to assume gross primary production (Pg) and net primary production (Pn) are proportional to Q absorbed by vegetation (Q abs) by defining the proportionality constants εpg and εpn (for Pg and Pn, respectively). Although remote sensing and climate monitoring provide Qabs and other meteorological data at the global scale, information on ε is particularly scarce in remote tropical areas. We used a 16-month continuous CO2 flux and meteorological dataset from a mountainous tropical rain forest in central Sulawesi, Indonesia to derive values of εpg and to investigate the relationship between Pg and Qabs. Absorption was estimated with a 1D SVAT model from measured canopy structure and short wave radiation. The half-hourly Pg data showed a saturation response to Qabs. The amount of Qabs required to saturate Pg was reduced when water vapor saturation deficit (D) was high. Light saturation of Pg was still evident when shifting from half-hourly to daily and monthly time scales. Thus, for a majority of observations, Pg was insensitive to changes in Qabs. A large proportion of the observed seasonal variability in Pg could not be attributed to changes in Qabs or D. Values of εpg, varied little around the long-term mean of 0.0179 mol CO2 (mol photon)-1 or 0.99 g C MJ-1 (the standard deviations were ± 0.006 and ± 0.0018 mol CO2 (mol photon)-1 for daily and monthly means, respectively). In both cases, εpg values were more sensitive to Qabs than to daytime D. These findings show that the current ε-approaches fail to predict Pg at our tropical rain forest site for two reasons: (1) they neglect saturation of Pg when Qabs is high; and (2) they do not include factors, other than Qabs and D, that determine seasonality and annual sums of Pg.