PARENT SESSION
Poster Session #28: Gas Exchange.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC
135
Ecophysiology of a wild platyopuntia exposed to prolonged drought.
Pimienta-Barrios, Eulogio*,1, González del Castillo-Aranda, María Eugenia1, Nobel, Park2, Ramírez-Hernández, Blanca1, 1 Universidad de Guadalajara., Guadalajara, Jalisco, México2 University of California-Los Angeles., Los Angeles, California
ABSTRACT- The effects of reduced annual rainfall over a 7-year period on the daily patterns of gas exchange were analyzed for a wild platyopuntia (Opuntia robusta) growing in rocky soil in the semiarid highlands of central Mexico. We aimed to examine the adaptations that allowed this species to successfully cope with prolonged drought conditions that prevailed in its rocky environment. Net CO2 exchange was measured every 2 h over eight 24-h periods during 2000. Soil water content, cladode relative water content (RWC), air temperature, air relative humidity and daily photosynthetic photon flux were also recorded on measurement dates. In spite of the considerable water loss, revealed by a low cladode RWC (67%), stomata opened at night and net carbon gain was observed for all sampling periods. Daily net CO2 uptake increased from 81 mmol m-2d-1 in the end of the dry spring season to 419 mmol m-2d-1 in the middle of the summer wet season. A significant positive relationship occurred between the rate of instantaneous CO2 uptake and the relative humidity during nighttime (p<0.001). Opuntia robusta sustained a level of succulence that allowed the plants to take up CO2 at night while maintaining a low investment of carbon through the curtailment in the formation of new roots and new cladodes; this is considered to be an avoidance strategy to water scarcity, which in combination with net CO2 uptake responses to temperature and relative humidity at night, and association with arbuscular mycorrhizal fungi, were the most important adaptations of O. robusta to tolerate prolonged drought conditions. Recent work revealed that benlate application reduce both mycorrhizal colonization and daily net CO2 uptake. These adaptations are in addition to the classical physiological and structural modifications of CAM plants.
KEY WORDS: CO2 uptake, drought, Opuntia robusta, rocky soil