Microhabitat and ectomycorrhizal effects on the establishment, growth and survival of Quercus ilex L. seedlings under drought

Abstract

The success of tree recruitment in Mediterranean holm oak (Quercus ilex) forests is threatened by the increasing intensity, duration and frequency of drought periods. Seedling germination and growth are modulated by complex interactions between abiotic (microhabitat conditions) and biotic factors (mycorrhiza association) that may mitigate the impacts of climate change on tree recruitment. To better understand and anticipate these effects, we conducted a germination experiment in a long-term precipitation reduction (PR) field experiment where we monitored seedling establishment and survival, micro-habitat conditions and ectomycorrhizal (ECM) colonization by different mycelia exploration types during the first year of seedling growth. We hypothesized that (i) the PR treatment decreases seedling survival relative to the control with ambient conditions, (ii) microhabitat conditions of water and light availability are better predictors of seedling survival than the PR treatment, (iii) the PR treatment will favour the development of ECM exploration types with droughtresistance traits such as differentiated rhizomorphs. Contrary to our first hypothesis, seedling survival was lower in control plots with overall higher soil moisture. Micro-habitat light and soil moisture conditions were better predictors of seedling survival and growth than the plot-level PR treatment, confirming our second hypothesis. Furthermore, in line with our third hypothesis, we found that ECM with longer extramatrical mycelia were more abundant in the PR treatment plots and were positively correlated to survival, which suggests a potential role of this ECM exploration type in seedling survival and recruitment. Although summer drought was the main cause of seedling mortality, our study indicates that drier conditions in spring can increase seedling survival, presumably through a synergistic effect of drought adapted ECM species and less favourable conditions for root pathogens.

Hydraulic‐stomatal coordination in tree seedlings: tight correlation across environments and ontogeny in Acer pseudoplatanus

“…Seedlings represent a demographic bottleneck for natural regeneration, and are exceptional in many aspects of their structure and function. Several studies point to extensive mortality rates in the first year, with peaks shortly after germination and/or during summer drought (Johnson & Smith, 2005;Johnson et al, 2011;Reinhardt et al, 2015;Augustine & Reinhardt, 2019;Garcia de Jalon et al, 2020;Miller et al, 2020), due at least in part to limited photosynthetic carbon gain and drought stress (e.g. Germino et al, 2002;Fenner & Thompson, 2005;Reinhardt et al, 2015;Brodersen et al, 2019).…”

Chemical plasticity in the fine root construct of Quercus spp. varies with root order and drought

“…Beniwal et al, 2010;Sebastiana et al, 2019), although the experimental findings on drought effects can be quite mixed (Lehto & Zwiazek, 2011). Water stress did increase oak EcM colonization in some studies (Dixon et al, 1980;Garcia de Jalon et al, 2020), although the opposite was also reported (poplar; Beniwal et al, 2010). As previous studies suggested, the actual response can be highly specific to the combination of fungi species, hosts and experimental conditions.…”

The effects of drought and inter-plant competition on the ectomycorrhizal interaction between fungi and Aleppo pine seedlings

“…Mediterranean forests are prone to relatively frequent environmental changes (Petit et al, 2005). The effects of these changes, which are often the result of fires (Glassman et al, 2016) or droughts (García de Jalón et al, 2020), might be mitigated by the ectomycorrhizal fungal community that had evolved in these habitats. Aleppo pine (Pinus halepensis Miller) is the most common forest tree species around the Mediterranean (Ne'eman & Osem, 2021) and is well adapted to local conditions (Klein et al, 2011;Voltas et al, 2018;Patsiou et al, 2020).…”