Drought or Severe Drought? Hemiparasitic Yellow Mistletoe (Loranthus europaeus) Amplifies Drought Stress in Sessile Oak Trees (Quercus petraea) by Altering Water Status and Physiological Responses

Abstract

European oak species have long been considered relatively resistant to different disturbances, including drought. However, several recent studies have reported their decline initiated by complex changes. Therefore, we compared mature sessile oak trees (Quercus petraea (Matt.), Liebl.) infested versus non-infested by hemiparasitic yellow mistletoe (Loranthus europaeus Jacq.) during the relatively dry vegetation season of 2019. We used broad arrays of ecophysiological (maximal assimilation rate Asat, chlorophyll a fluorescence, stomatal conductance gS, leaf morphological traits, mineral nutrition), growth (tree diameter, height, stem increment), and water status indicators (leaf water potential Ψ, leaf transpiration T, water-use efficiency WUE) to identify processes underlying vast oak decline. The presence of mistletoe significantly reduced the Ψ by 1 MPa, and the WUE by 14%. The T and gS of infested oaks were lower by 34% and 38%, respectively, compared to the non-infested oaks, whereas the Asat dropped to 55%. Less pronounced but significant changes were also observed at the level of photosystem II (PSII) photochemistry. Moreover, we identified the differences in C content, which probably reduced stem increment and leaf size of the infested trees. Generally, we can conclude that mistletoe could be a serious threat that jeopardizes the water status and growth of oak stands.

Impact of Natural Hazards on Forest Ecosystems and Their Surrounding Landscape under Climate Change

“…The Special Issue we introduce consists of 11 original research papers [1][2][3][4][5][6][7][8][9][10][11] divided into three groups based on research interests, namely, 1. hydrological and atmospheric aspects of natural hazards in changing climate and environment, 2. ecophysiological and ecological water-related impacts of natural hazards, and 3. methodological approaches in natural hazard evaluation.…”

Protein Profiling of Psittacanthus calyculatus during Mesquite Infection

“…In addition, during the seed-to-seedling transition of any seed, metabolism is maintained by protein catabolism [ 85 ], and photosynthetic transcripts are down-regulated in both parasitic and other plants [ 128 ]. Chlorophyll and nitrogen contents from seedling establishment to adult life stages have been quantified in other Psittacanthus and mistletoe species [ 127 , 129 , 130 , 131 , 132 ]. Protease activity is directly related to protein catabolism, which in consequence impacts in the nitrogen and chlorophyll content in seeds, germination, and seedling development in P. calyculatus , which are development programs previous to seedling establishment [ 82 ].…”

You are what you eat: nutrient and water relations between mistletoes and hosts

“…Mistletoes had lower N concentrations than hosts (a marginal significance of P = 0.090) in our study, which agrees with previous studies showing that mistletoes have similar (Bannister et al ., 2002; Scalon et al ., 2013; Scalon & Wright, 2015) or lower N than their hosts (Kubov et al ., 2020; Richards et al ., 2021). Also, we found that there were no differences in leaf Ca, Mg, and S concentrations between mistletoes and hosts, which is in line with some previous findings (Goldstein et al ., 1989; Bannister et al ., 2002; Scalon et al ., 2013; but see Glatzel, 1983; Lamont, 1983; Gebauer et al ., 2018).…”