Abstract
Key messagePatterns of stem radial variations showed thatCedrus libaniA. Rich. was less limited by summer drought than co-occurringJuniperus excelsaM. Bieb.Cedrus libanirecovered faster from tree water deficit and showed significantly higher radial growth rates and annual stem increments thanJ. excelsa. However, the ability ofJ. excelsato grow more hours per year may indicate a potential benefit in more extreme conditions.ContextKnowledge about species-specific drought responses is needed to manage productive forests in drought prone areas. Under water shortage, trees commonly show stem shrinkage, which is assumed to inhibit growth.AimsWe investigated whether the two co-existing conifers Juniperus excelsa M. Bieb. and Cedrus libani A. Rich. (growing at the Taurus Mountains, SW-Turkey) show differences in water relations and stem growth in order to evaluate their respective drought tolerance.MethodsStem radius changes were hourly monitored over 2 years using high-resolution point dendrometers. Radial stem growth, tree water deficit-induced stem shrinkage, and maximum daily shrinkage were extracted from stem radius change measurements, investigated for their patterns, and related to environmental conditions.ResultsCedrus libani recovered from tree water deficit under higher temperature and vapor pressure deficit than J. excelsa. The number of hours during which stem growth occurred was higher for J. excelsa; however, growth rates and annual increments were significantly lower than in C. libani. Both species showed highest maximum daily shrinkage during the driest months indicating the ability to maintain gas exchange all year round.ConclusionJuniperus excelsa showed a more conservative growth strategy while C. libani was less limited by summer drought and showed more annual stem increment under the conditions investigated.
Highlights
Future climate scenarios predict that the Mediterranean region will be among the more heavily affected parts of the world in terms of increased frequency and intensity of drought events (Ozturk et al 2015)
One way of investigating tree responses to changing environmental conditions is the use of high-precision point dendrometers which allow for monitoring diel stem radius changes (SRC), intra-annual stem growth patterns, and immediate plant water responses (De Swaef et al 2015; Drew and Downes 2009)
We investigated whether the two co-existing conifers (J. excelsa and C. libani) show differences in water relations (TWD and maximum daily shrinkage (MDS)) and stem growth (GRO) in order to evaluate their respective drought tolerance
Summary
Future climate scenarios predict that the Mediterranean region will be among the more heavily affected parts of the world in terms of increased frequency and intensity of drought events (Ozturk et al 2015). TWD quantifies the loss of water from elastic tissues due to an imbalance between water loss (transpiration) and water uptake and reflects the accumulated water deficit over several days lasting drought periods (Dietrich et al 2018). It can be used as an indicator for drought stress (Zweifel et al 2005). The maximum daily shrinkage (MDS) quantifies the stem shrinkage over 1 day only (Deslauriers et al 2007) and is more an indicator for the actual plasticity of a tree to respond to the current environmental conditions in air and soil (Daudet et al 2005; Giovannelli et al 2007). A small MDS indicates either a day with low light or a day with closed stomata and little transpiration and assimilation
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