Biomass partitioning in a future dry andCO₂enriched climate: Shading aggravates drought effects in Scots pine but not European black pine seedlings

Abstract

Climate change alters both water and CO2 availability for plants, but it is largely unknown how they interact with light to affect tree seedling establishment and early growth. Light availability is often regulated by forest management, thus understanding how these resources co‐limit the regeneration success of tree species and populations with contrasting drought tolerances is essential for adaptive forest management and particularly for assisted migration. We studied biomass partitioning of 3‐year‐old Scots pine (Pinus sylvestris) and European black pine (Pinus nigra) seedlings in response to combined effects of light (22% and 40% shade), soil water availability (moist and dry conditions) and CO2 (ambient and elevated), and examined the responses of seedlings from Central Alpine and Mediterranean origin. Seedlings of nine populations with varying drought tolerances were grown in a common garden in the European Central Alps. Shoot height, vertical root length, shoot and root biomass of the plants were assessed at the end of the third growing season. Under 40% shade and dry conditions, P. sylvestris seedlings severely reduced shoot biomass, resulting in an increased specific shoot height (SSH) compared to seedlings under 22% shade and moist conditions. In contrast, P. nigra seedlings retained a constant shoot biomass under all treatment combinations. Seedlings from drier origin were generally larger, heavier and had longer vertical roots than those from wetter locations. In order to keep up shoot height, seedlings from wetter origins disproportionately increased SSH under shaded conditions compared to populations from drier origin. Synthesis and applications. Under high light availability, Scots pine (Pinus sylvestris) and European black pine (Pinus nigra) seedlings were well adapted to dry conditions. Moderate shading, however, substantially reduced Scots pine but not black pine growth, and potentially amplified the vulnerability of Scots pine seedlings to drought. Optimising light conditions in forests, for example by thinning, may thus enhance early Scots pine regeneration in a drier future climate.

Memory of environmental conditions across generations affects the acclimation potential of scots pine

“…Similar to the results of seed germination success, the offspring growth (leaf area and biomass) and mortality during the initial period (until Week 14 after sowing) was primarily driven by watering. The importance of water supply for Scots pine seed germination and offspring growth or mortality during the initial period has also been reported by other studies (Bachofen, Wohlgemuth, & Moser, ; Castro, ; Moser et al, ). Thus, the environmental legacy to which the mother trees have been exposed to did not influence the early offspring development, which was mainly affected by direct environmental cues.…”

Phenotypic plasticity versus ecotypic differentiation under recurrent summer drought in two drought‐tolerant pine species

“…We observed, indeed, ecotypic variation in frost tolerance in P. nigra seedlings in a previous study on the same experiment, but very low risk of damage from intermittent frost events (Bachofen et al 2016). The higher shoot growth of populations from drier locations can also be explained by a better soil water access due to longer taproots of drought adapted populations, which was shown in a previous study on the same experiment (Bachofen et al 2019). Interestingly, we observed ecotypic differentiation and high phenotypic plasticity at the same level of organisation, in the shoot morphological traits, whereas foliar morphological and anatomical traits exhibited both low plasticity (RDPI < 1) and low ecotypic differentiation (Figs.…”

“…Common garden experiments are powerful for identifying genetic variation among populations (Jankowski et al 2019), and if combined with experimental treatments allow to compare adaptive with plastic responses of functional traits. The overall experiment included manipulations of precipitation, light and CO 2 availability as described in detail in Moser et al (2016) and Bachofen et al (2019). For this study, we only considered the precipitation manipulation and therefore selected a subset of…”

Contrasting Leaf Trait Responses of Conifer and Broadleaved Seedlings to Altered Resource Availability Are Linked to Resource Strategies

“…Another marked difference between the two species group is that SLA of EC was independent of light availability, whereas SLA of DB increased under low PAR combined with high nutrient and water availability. As long as neither nutrients nor water were limiting (P 100 × N hi ), DB thus responded to low PAR according to "optimal partitioning", i.e., with higher investments in the organs capturing the most limiting resource, light [18,19,48]. Interestingly, while plants exposed to water stress have been shown to reduce SLA [45], the precipitation treatment did not affect DB but increased SLA of EC under high light availability due to a reduction in foliar dry weight ( Figure S1).…”

“…For instance, in tree canopies, where water and light availability show large vertical gradients (e.g., [14]), the distribution of nitrogen to different compartments of the photosynthetic machinery is affected by both water and light availability [15][16][17][18]. Moreover, increased light availability may mitigate drought stress of light-demanding tree species by alleviating carbon investment trade-offs between water and light capturing plant parts [19]. Experiments testing the limiting effects of water and nutrient availability are scarce (but see: [13]), and co-limitations of more than two resources are rarely studied (but see: [20,21]).…”