CEFE, Univ. Montpellier, CNRS, EPHE, IRD, Univ. Paul Valéry Montpellier 3, Montpellier, France.
Swiss Federal Research Institute WSL, Birmensdorf, Switzerland.
PLoS One. 2020 Jun 5;15(6):e0229807. doi: 10.1371/journal.pone.0229807. eCollection 2020.
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 drought-resistance 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.
在日益加剧的干旱强度、持续时间和频率的威胁下，地中海地区的栓皮栎（Quercus ilex）林分中的树木更新成功率正面临挑战。种子的萌发和生长受到非生物因素（微生境条件）和生物因素（菌根共生体）之间复杂相互作用的调节，这些因素可能减轻气候变化对树木更新的影响。为了更好地理解和预测这些影响，我们在一项长期的降水减少（PR）野外实验中进行了种子萌发实验，在该实验中，我们监测了幼苗的建立和存活率、微生境条件以及菌根（ECM）在幼苗生长的第一年中不同菌丝体探索类型的定殖情况。我们假设：（i）PR 处理相对于具有环境条件的对照处理会降低幼苗的存活率；（ii）水分和光照可用性的微生境条件是预测幼苗存活率的更好指标，而不是 PR 处理；（iii）PR 处理将有利于具有耐旱特性的 ECM 探索类型的发育，例如分化的根状菌索。与我们的第一个假设相反，对照小区的幼苗存活率较低，而对照小区的整体土壤湿度较高。微生境的光照和土壤湿度条件是预测幼苗存活率和生长的更好指标，这证实了我们的第二个假设。此外，与我们的第三个假设一致，我们发现具有较长外生菌丝体的 ECM 在 PR 处理小区中更为丰富，并且与存活率呈正相关，这表明这种 ECM 探索类型在幼苗存活和更新中可能发挥作用。尽管夏季干旱是幼苗死亡的主要原因，但我们的研究表明，春季较干燥的条件可以提高幼苗的存活率，这可能是由于适应干旱的 ECM 物种与不利于根病原体的条件之间的协同作用。
