Quantity and frequency of irrigation modulate the response to drought in juvenile individuals of Prosopis chilensis and Porlieria chilensis

Background/Question/Methods . Establishment of plants in Mediterranean ecosystems is severely limited by drought. Climate change models predict increases in the frequency and intensity of drought episodes in the Mediterranean zone of Chile. Therefore, knowing the water requirements of the species that inhabit these areas is of high importance, especially for species used in reforestation and ecological restoration projects, where drought is one of the limiting factors for its success. Reforestations made in central Chile usually irrigate the plantations using 12.5 liters of water every two weeks, and they use the same quantity and frequency of irrigation for all the species. The objective of this study was to determine the effect of the quantity and frequency of irrigation in response to drought and posterior rehydration in two species of the sclerophyllous forests, Prosopis chilensis and Porlieria chilensis. An experiment was carried out in the greenhouse, where individuals of both species were grown for three months under three quantities (12.5L, 4.3L, 2.8L) and two irrigation frequencies (every two and three weeks). Then, these individuals were exposed to severe drought (suspension of irrigation for two months), and subsequent recovery period for two months where the irrigation was re-established.

Results/Conclusions . For both species, at the end of the drought period, net photosynthetic CO₂ assimilation rate (A_N) decreased close to zero in the plants irrigated with 12.5L every two and three weeks, while plants irrigated with the lower doses of water (4.3 and 2.8L) presented negative values of A_N. However, in the rehydration period, all plants recovered their A_N values and plants irrigated every three weeks at all the quantities of water presented higher water use efficiency (WUE). Besides, there were no differences in WUE between plants watered with 12.5 and 4.3 L. In Prosopis chilensis, survival of plants was higher in the treatment that received 4.3 and 12.5L every three weeks than those receiving 4.3 and 12.5L every two weeks. While in Porlieria chilensis, plants watered with 4.3L every three weeks showed the highest survival. Thus, both species showed that growing with a smaller amount of water (4.3L) and a more extended frequency of irrigation (three weeks) than the used nowadays in the reforestation projects was beneficial in terms of physiological performance, and survival after the drought event. We conclude that growing with a low quantity and a more extended irrigation frequency increases the resistance of these species to drought.

Financed by Atlas Renewable Energy, CONICYT-PIA CCTE-AFB170008