Leaf turgor loss point at full hydration for 41 native and introduced tree and shrub species from Central Europe Free

Abstract

The last years, Central European forests have suffered from drought as a direct consequence of climate change. All these forests have a long management history and it lies in the landowner’s responsibility to replant damaged forests. Hence, landowners and the government are searching currently for species suitable to replant in areas affected by tree die-offs. It is a matter of fact that good knowledge of drought resistance of species is a critical measure for the current replanting efforts. We determined a widely recognized trait for leaf drought tolerance (leaf water potential at turgor loss point at full hydration, π_tlp) in 41 woody species native or introduced in Central Europe. The osmometric rapid assessment method was used to measure the leaf osmotic potential at full hydration (π_osm) of sun-exposed leaves and converted to π_tlp. Mean π_tlp of the native species was −2.33 ± 0.33 MPa. The less negative π_tlp was found in the introduced species Aesculus hypocastania and was at −1.70 ± 0.11 MPa. The most negative π_tlp, and thus the potentially highest drought tolerance, were found in the introduced species Pseudotsuga menzesii and was at −3.02 ± 0.14 MPa. High or less negative π_tlp is associated with lower drought tolerance, whereas low or more negative π_tlp stands for higher resistance to drought stress. For example, the two native species Illex aquifolium and Alnus glustinosa are species naturally associated with moist habitats and are characterized by the least negative π_tlp of −1.75 ± 0.02 and −1.76 ± 0.03 MPa, respectively.

摘要

过去几年，中欧的森林遭受了由气候变化引起的直接后果—干旱。所有这些森林都有着悠久的经营历史，重新种植受损森林的责 任落到了土地所有者的身上。因此，土地所有者和政府正在寻找适合在树木灭绝地区重新种植的树种。事实上，很好的了解物种的抗旱性 对当前树木的重新种植非常关键。我们在41种原产于或引进于中欧的木本树种中确定了一个被广泛认可的叶片耐旱特性(在充分水合作用 下膨压损失点的叶片水势，即π_tlp)。采用渗透快速评价法测定了暴露于阳光下的叶片在充分水合作用下的渗透势(π_osm)，并将其转化为π_tlp。 本地种的平均π_tlp为−2.33 ± 0.33 MPa。引进树种Aesculus hypocastania的π_tlp为−1.70 ± 0.11 MPa。引进树种Pseudotsuga menzesii的π_tlp值 为−3.02 ± 0.14 MPa，耐旱性最强。绝对值较低的负值πtlp表示抗旱性较低，绝对值较高的负值π_tlp表示抗旱性较高。例如，两种本地物种 Illex aquifolium和Alnus glustinosa是潮湿生境的自然伴生物种，其π_tlp值分别为−1.75 ± 0.02 MPa和−1.76 ± 0.03 MPa。

INTRODUCTION

Global climate change threatens worldwide forests due to increasing drought and heat stress (Allen et al. 2010; Anderegg et al. 2013) and accelerating forest die-off in response has been reported for many forest ecosystems and climate zones (Cobb et al. 2017). In particular, the heavily managed species-poor forests in Central Europe have been struck by the very dry condition in the last years causing large forest die-off (Kunert 2020). The two conifer tree species, Norway spruce and Scots pine are of high economic importance for the forestry sector. However, both species are most likely unsuitable to be cultivated on the same large scale under the current climate change scenario as in the past. The search for suitable species and planting designs to create more resistant and resilient forests is still ongoing.

Trait-based approaches to identify species potential drought tolerance are currently receiving high attention. In particular, hydraulic traits such as the turgor loss point at full hydration (π_tlp) seem to have a strong predictive power (see e.g. Maréchaux et al. 2016, 2018). Even if π_tlp can be determined with the osmometric methods (Bartlett et al. 2012), measuring campaigns to asses larger numbers of woody species with the same method and within a specific area are still rare. With this data paper, we want to provide a database of π_tlp values for a significant number of tree and shrub species from Central Europe plus some introduced species that are potentially considered to be cultivated in the future in forest management systems in the region.

METADATA CONTENT

Study site description

The botanical material of 32 native species was collected in the forest in the rural district of Fürth in Middle Frankonia, Germany (49°24′36.0″ N 10°49′39.3″ E) (Supplementary Data S1). The forest has a long management history and has been actively managed since the 14th century. Since then the forest was converted from former mixed-species forests with Scots pine, birch and oak into mainly monospecific stands of Scots pine (Pinus sylvestris L.) (Kunert 2020). The forest grows mainly on the less fertile areas leading to a very patchy forest distribution. Roughly 30% of the area is still covered with forest and the remaining 70% is used for agriculture. Due to its high value and fast growth, the main tree species cultivated in the area are Scots pine, followed by Norway spruce (Picea abies (L.) H. Karst.). Those two conifer species are representing more than 80% of the trees in the forested area and less than 20% is covered by broadleaved species like European oak (Quercus robur L.). The invasive black cherry (Prunus serotina Ehrh.) is of increasing importance and takes over rapidly the understory. The region was affected by dramatic forest die-off events in the last 2 years following three very dry summers and heatwaves in 2015, 2016 and 2019 (Klemmt et al. 2018). Spruce was affected by bark beetle outbreaks and pine by a complex combination of fungi (Kunert 2019). The samples of the introduced species were collected from the same abovementioned area or public parks in the adjacent township.

Determination of the turgor loss point at full hydration via osmometry

We determined the turgor loss point at full hydration (π_tlp) by measuring the leaf osmotic potential (π_osm) with a vapor pressure osmometer (VAPRO 5520, Wescor, Logan, UT, USA) (Bartlett et al. 2012) (Supplementary Table S1). Therefore, three tree individuals from the abovementioned species were sampled. Per individual, we collected one fully sun-exposed branch. The campaign took place during the growing season between the 7th and the 18th of July 2019. After cutting the branches from the trees, they were immediately transferred into humid and opaque plastic bags and brought to the laboratory as fast as possible. In the laboratory, all branches were recut underwater and at least two nodes distal to the original cut. After recutting, the branches were placed in buckets with water and covered with plastic bags. The branches were allowed to rehydrate overnight. On the following day, two fully expanded leaves per individual were removed from each branch and further processed. To reduce any damage by storage, the collected samples were processed within 24 h after sampling. Per leaf two discs were cut with a 4-mm-diameter cork borer. We used a different approach for conifer species as suggested by Kunert (2020). From the rehydrated branch of the conifers, we took a couple of needles and aligned the needles next to each other and we cut approximately 4 mm discs from those aligned needles. Both, the leaf discs form broadleaved and conifer species were wrapped in aluminum foil and shock-frozen in liquid nitrogen (LN₂) (Bartlett et al. 2012). We used the standard 10 µl chamber well of the osmometer to perform the osmometric measurements. The frozen discs were punctured with a dissection needle for about 10–15 times before placing them into the chamber of the osmometer. The osmometer was set in the autorepeat mode which performs automatically 10 measurements of the osmotic potential with automatic drying of the well in between measurements. We assumed to have a representative value of the leaf osmotic potential when the increase between measurements of less than 0.01 MPa (5 osmometer readings). The osmotic potential (π_osm) was calculated from the solute concentration value c₀ (in mmol kg⁻¹), using the following equation:

where R is the ideal gas constant and T is the temperature in degrees Kelvin (here 25°C). Leaf water potential at turgor loss point at full hydration (π_tlp) was calculated π_osm by using the calibration equation established by Bartlett et al. (2012):

Supplementary Material

Supplementary material is available at Journal of Plant Ecology online.

Data S1: Meta data TLP Europe.

Table S1: Table with measurement results.

Conflict of interest statement. None declared.

Funding

None declared.

REFERENCES