Section 37
Chapter 36,443

Influence of climate variability on seasonal and interannual variations of ecosystem CO2 exchange in flooded and non-flooded rice fields in the Philippines

Ma. Carmelita, R.A.; Hirano, T.; Miyata, A.; Wassmann, R.; Kumar, A.; Padre, A.; Amante, M.

Field Crops Research 134(none)


ISSN/ISBN: 0378-4290
DOI: 10.1016/j.fcr.2012.05.002
Accession: 036442715

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Seasonal rainfall in the Philippines is known to be modulated by ENSO phenomenon, with El Ni o frequently contributing to reduced rainfall and drought while La Ni a resulting in excessive rainfalls, floods and more intense typhoons. The alterations in rainfall patterns can have considerable feedback on solar radiation, air temperature, and soil moisture which can affect the ecosystem CO2 exchange. In this paper, we assessed the effects of the ENSO events (28 mid 21) on the seasonal climate conditions and determined how it affected the gross primary production (GPP), ecosystem respiration (Re), and net ecosystem production (NEP) of two contrasting rice environments: flooded and non-flooded. The 28 dry season (DS) was under a La Ni a event while the 28 wet season (WS) was a neutral one with strong tropical cyclones associated during the wet season. The 29DS was also La Ni a while the 29WS was El Ni o; however, the northern part of the Philippines experienced strong tropical cyclones. The 21DS was under an El Ni o event. The La Ni a in 28DS resulted in about 15% lower solar radiation (SR), .3 C lower air temperature (T a) and 6% higher precipitation compared to the 28-year climate normal patterns. Both flooded and non-flooded rice fields had lower NEP in 28 DS (164 and 14gCm?2, respectively) than in 28 WS (295 and 82gCm?2, respectively) because the climate anomaly resulted in SR driven decrease in GPP. The La Ni a in 29DS even resulted in .2 C lower air temperature and 4% more precipitation than the 28DS La Ni a. This cooler temperature resulted in lower Re in flooded rice fields while the higher precipitation resulted in higher GPP in non-flooded fields since the climate was favorable for the growth of the aerobic rice, the ratoon crops and the weeds. This climate anomaly benefitted both flooded and non-flooded rice fields by increasing NEP (351 and 218gCm?2, respectively). However, NEP decreased in 29WS in both flooded and non-flooded rice fields (225 and 39gCm?2, respectively) due to the devastating effects of the strong tropical cyclones that hit the northern part of the Philippines. On the other hand, the El Ni o event during 21DS resulted in about 6% higher solar radiation, .4 C higher air temperature and 67% lower precipitation than the 28-year climate normal pattern. The NEP of flooded and non-flooded rice fields were closely similar at 187 and 174gCm?2, respectively. This climate anomaly resulted in T a driven increase in Re, as well as vapor pressure deficit (VPD) driven decrease in GPP in flooded rice fields. The GPP and Re in non-flooded rice fields were less sensitive to higher VPD and higher T a, respectively. It appears that the net ecosystem CO2 exchange in non-flooded rice field was less sensitive to an El Ni o event. Flooded and aerobic fields can become weaker or stronger sinks of CO2 during ENSO. GPP of flooded field was more sensitive to increase in VPD than non-flooded field. The GPP in flooded rice was substantially larger than in aerobic rice. Flooded rice field had lower Re than non-flooded field when LAI was below 5 m2 m?2. The Q 1 values of flooded rice field was higher than non-flooded field.

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