Different photoprotective responses under drought conditions of two predominant chilean swamp forest species

Myrceugenia exsucca (DC.) O.Berg (Myrtaceae) and Luma chequen (Molina) A. Gray (Myrtaceae) are two predominants species from swamp forests of Chile. These species present differential microhabitat distribution across soil moisture and north-south precipitation gradients, with only L. chequen being commonly found in lower moisture sites. It is hypothesized that L. chequen has greater plasticity than M exsucca in the attributes involved in photoprotection under drought conditions. To test this hypothesis, both species were exposed to short term drought treatment. A group of individuals was maintained irrigated (with Psi(w) of-0.58 and -0.73 MPa for M exsucca and L. chequen, respectively), while another group was exposed to drought treatment with Psi(w) around-1.4 MPa (Psi D-w). High relationship was founded between relative water content (RWC) and water potential (Psi(w)) for M exsucca (r(2)= 0.74) more than for L. chequen (r(2)= 0.46), indicating that M exsucca experienced larger dehydration during the drought treatment. As functional attributes of photosynthetic apparatus, amount of total chlorophyll and chlorophyll a fluorescence parameter levels were studied in both species. The results show that L. chequen reduced total content of chlorophylls and maximum efficiency of PSII (Fv / Fm) related to decrease of energy capture increasing significantly the thermal dissipation (qN). On the other hand, M exsucca does not change these parameters, but significantly reduced the level of photochemical processes (qL), indicating an energy imbalance. The results indicate M exsucca has less plasticity than L. chequen under drought conditions. It is believed that these differences may be crucial in the establishment period and may be influencing the limited distribution of M exsucca in sites with lower water availability.