Tree allocation dynamics beyond heat and hot drought stress reveal changes in carbon storage, belowground translocation and growth

Abstract

Heatwaves combined with drought affect tree functioning with as yet undetermined legacy effects on carbon (C) and nitrogen (N) allocation.We continuously monitored shoot and root gas exchange, δ 13 CO 2 of respiration and stem growth in well-watered and drought-treated Pinus sylvestris (Scots pine) seedlings exposed to increasing daytime temperatures (max. 42°C) and evaporative demand. Following stress release, we used 13 CO 2 canopy pulse-labeling, supplemented by soil-applied 15 N, to determine allocation to plant compartments, respiration and soil microbial biomass (SMB) over 2.5 wk.Previously heat-treated seedlings rapidly translocated 13 C along the long-distance transport path, to root respiration (R root ; 7.1 h) and SMB (3 d). Furthermore, 13 C accumulated in branch cellulose, suggesting secondary growth enhancement. However, in recovering drought-heat seedlings, the mean residence time of 13 C in needles increased, whereas C translocation to R root was delayed (13.8 h) and 13 C incorporated into starch rather than cellulose. Concurrently, we observed stress-induced low N uptake and aboveground allocation.C and N allocation during early recovery were affected by stress type and impact. Although C uptake increased quickly in both treatments, drought-heat in combination reduced the above-belowground coupling and starch accumulated in leaves at the expense of growth. Accordingly, C allocation during recovery depends on phloem translocation capacity.

Memory Effects of Water Deprivation in European Beech (Fagus sylvatica L.) and Silver Fir (Abies alba Mill.) Seedlings Grown in Mixed Cultivation

“…C and N metabolism closely interact with each other in plant growth, productivity, and stress resistance [84,85]. Compared to C dynamics, information on post-stress responses of N contents and partitioning in trees is extremely scarce, despite this knowledge being of particular importance for predicting the resilience of forests under climate change conditions [31,86]. The total N contents observed in this study were in the range previously found in European beech and fir [33,53,[87][88][89].…”

Increasing temperature and vapour pressure deficit lead to hydraulic damages in the absence of soil drought

“…As a result, T and VPD have been identified as increasingly important drivers of plant hydraulic conductivity losses (Olson et al, 2020 ), growth reduction (Trotsiuk et al, 2021 ), plant mortality (Adams et al, 2009 ; Allen et al, 2015 ) and reduced ecosystem productivity (Ciais et al, 2005 ). Many studies focus on plant responses to a combination of soil drought and either high T (‘hot droughts') (Allen et al, 2015 ; Cochard, 2019 ; Grossiord et al, 2018 ; Rehschuh et al, 2021 ), or high VPD (Anderegg & Meinzer, 2015 ; Eamus et al, 2013 ; Fontes et al, 2018 ). For example, high VPD combined with soil drought leads to extreme xylem tensions and embolisms (Tardieu & Simonneau, 1998 ).…”

Dynamics of initial carbon allocation after drought release in mature Norway spruce—Increased belowground allocation of current photoassimilates covers only half of the carbon used for fine‐root growth

“…Because the frequency of drought events is predicted to increase in the future (IPCC, 2021), recovery from these events is an important aspect of tree survival, which has attracted less attention compared with direct drought effects (Ruehr et al, 2019). On the one hand, drought release can increase aboveground C sink activity for repair processes such as growth of new xylem and embolism refilling (Brodersen & McElrone, 2013; Ruehr et al, 2019; Zang et al, 2014) or C storage to prepare for future droughts (Galiano et al, 2017; Rehschuh et al, 2021). On the other hand, drought release can stimulate belowground C sinks such as root production, mycorrhizal and microbial activity, and associated soil respiration (Brunner et al, 2019; Gao et al, 2021; Hagedorn et al, 2016; Joseph et al, 2020; Werner et al, 2021).…”