Photosynthetic responses of young cashew plants to varying environmental conditions
Pereira de Souza R., Vasconcelos Ribeiro R., Caruso Machado E., Ferraz de Oliveira R., Gomes da Silveira J. A. (2005)
Rogéria Pereira de SouzaI; Rafael Vasconcelos RibeiroI; Eduardo Caruso MachadoI; Ricardo Ferraz de OliveiraII; Joaquim Albenísio Gomes da SilveiraIII
IInstituto Agronômico, Centro de Pesquisa e Desenvolvimento em Ecofisiologia e Biofísica, Caixa Postal 28, CEP 13001-970 Campinas, SP, Brazil. E-mail: email@example.com, firstname.lastname@example.org, email@example.com
IIUniversidade de São Paulo, Escola Superior de Agricultura Luiz de Queiroz, Dep. de Ciências Biológicas, Caixa Postal 9, CEP 13400-970 Piracicaba, SP, Brazil. E-mail: firstname.lastname@example.org
IIIUniversidade Federal do Ceará, Dep. de Bioquímica e Biologia Molecular, Caixa Postal 6020, CEP 60451-970 Fortaleza, CE, Brazil. E-mail: email@example.com
in Pesq. agropec. bras. vol.40 no.8 Brasília Aug. 2005 –
The aim of this study was to characterize gas exchange responses of young cashew plants to varying photosynthetic photon flux density (PPFD), temperature, vapor-pressure deficit (VPD), and intercellular CO2concentration (Ci), under controlled conditions.
Daily courses of gas exchange and chlorophyll a fluorescence parameters were measured under natural conditions. Maximum CO2 assimilation rates, under optimal controlled conditions, were about 13 mmol m-2 s-1 , with light saturation around 1,000 mmol m-2 s -1.
Leaf temperatures between 25ºC and 35ºC were optimal for photosynthesis. Stomata showed sensitivity to CO2, and a closing response with increasing Ci. Increasing VPD had a small effect on CO2 assimilation rates, with a small decrease above 2.5 kPa. Stomata, however, were strongly affected by VPD, exhibiting gradual closure above 1.5 kPa.
The reduced stomatal conductances at high VPD were efficient in restricting water losses by transpiration, demonstrating the species adaptability to dry environments. Under natural irradiance, CO2 assimilation rates were saturated in early morning, following thereafter the PPFD changes. Transient Fv/Fm decreases were registered around 11h, indicating the occurrence of photoinhibition.
Decreases of excitation capture efficiency, decreases of effective quantum yield of photosystem II, and increases in non-photochemical quenching were consistent with the occurrence of photoprotection under excessive irradiance levels.