Response of two riparian woody plants to Phytophthora species and drought

Abstract

Disease combined with drought poses an important threat to plant survival, often compromising success in the restoration of riparian forests. Thus, understanding how biotic and abiotic stressors may affect plant survival and growth performance can greatly increase the success of ecosystem management strategies. The purpose of this study was to understand how two plant species, often used together in restoration of riparian ecosystems but with different ecological preferences, would respond to infection by each of two Phytophthoraspecies in Mediterranean-climate regions, in the absence or presence of a simulated drought. Saplings of the drought resistant species Frangula californica, and of the riparian species Alnus rhombifoliawere each inoculated in a greenhouse experiment with one of two Phytophthoraspecies and exposed to two watering regimes. Saplings were allocated to six treatments, combining three levels of pathogen inoculation (no inoculation, inoculation with Phytophthora cactorumand inoculation with Phytophthora crassamura), and two watering regimes (well-watered and drought). The response of A. rhombifoliaand F. californicasaplings was assessed through the observation of health metrics and morphological parameters. Results showed that both P. cactorumand P. crassamuraare important pathogens of A. rhombifoliaand F. californica. As expected, drought conditions were the main cause of decline and mortality in A. rhombifoliasaplings, while water availability was a facilitator of P. cactoruminfection in F. californicasaplings. We observed two seemingly contrasting results in A. rhombifoliasaplings: infection by Phytophthoraspp. decreased survival in well-watered plants, while the opposite was recorded for saplings under drought conditions whose survival increased in Phytophthora-inoculated treatments. Saplings of F. californicawere able to cope with drought conditions, even when infected by Phytophthoraspecies and water availability increased root infection and decreased sapling survival. We conclude that the continued use of F. californicaand A. rhombifoliain sites infested by Phytophthoraspecies can be beneficial in restoration, if appropriate management actions are adopted. Such actions include avoiding the planting of F. californicasaplings in areas subjected to water accumulation, and ensuring that A. rhombifoliais planted in areas where drought stress is minimal and where Phytophthoraspecies are possibly absent. We also emphasize the importance of ensuring that plant stock used in revegetation projects is not infected by Phytophthoraspecies, and that biotic and abiotic risks are assessed prior to restoration actions.

Citation

Gomes Marques, I.; Solla, A.; David, T.S.; Rodríguez-González, P.M.; Garbelotto, M. 2022. Response of two riparian woody plants to Phytophthora species and drought. Forest Ecology and Management. 518(6): 120281. https://doi.org/10.1016/j.foreco.2022.120281.