Recovery of trees from drought depends on belowground sink control

Abstract

Climate projections predict higher precipitation variability with more frequent dry extremes(1). CO2 assimilation of forests decreases during drought, either by stomatal closure(2) or by direct environmental control of sink tissue activities(3). Ultimately, drought effects on forests depend on the ability of forests to recover, but the mechanisms controlling ecosystem resilience are uncertain(4). Here, we have investigated the effects of drought and drought release on the carbon balances in beech trees by combining CO2 flux measurements, metabolomics and (13)CO2 pulse labelling. During drought, net photosynthesis (AN), soil respiration (RS) and the allocation of recent assimilates below ground were reduced. Carbohydrates accumulated in metabolically resting roots but not in leaves, indicating sink control of the tree carbon balance. After drought release, RS recovered faster than AN and CO2 fluxes exceeded those in continuously watered trees for months. This stimulation was related to greater assimilate allocation to and metabolization in the rhizosphere. These findings show that trees prioritize the investment of assimilates below ground, probably to regain root functions after drought. We propose that root restoration plays a key role in ecosystem resilience to drought, in that the increased sink activity controls the recovery of carbon balances.

Legacies of La Niña: North American monsoon can rescue trees from winter drought

“…Increased sensitivity to 3-4 years prior precipitation across species suggests increased reliance on older, less-frequently accessed pools of stored carbohydrates Peltier et al, 2016;Richardson et al, 2013) or deeper water sources (Rempe & Dietrich, 2018) during La Niña periods. Decreases in living root biomass or increases in rhizosphere investment could also underlie drought legacies (Hagedorn et al, 2016). Decreases in living root biomass or increases in rhizosphere investment could also underlie drought legacies (Hagedorn et al, 2016).…”

Day length regulates seasonal patterns of stomatal conductance in Quercus species

“…Additionally, we used one further dataset of our own that measured 5‐year‐old saplings of Quercus pubescens in Birmensdorf, Switzerland, grown in open top chambers. The general set‐up of the chamber—lysimeter system—is described by Hagedorn et al (). We fitted the model separately for angiosperms and gymnosperms using Equations and with “nlme” (Pinheiro et al, ).…”

Biogeochemical Modelling vs. Tree-Ring Measurements - Comparison of Growth Dynamic Estimates at Two Distinct Oak Forests in Croatia

“…According to new findings (e.g. [54]), this logic might not be completely applicable to forests, which can partly explain why the extreme event in a given year might have pronounced effect on plant growth in the forthcoming year(s). These issues are limiting the model to properly predict plant's response to drought stress.…”

“…In stress conditions carbon allocation ratios (i.e. proportions of assimilates allocated to different plant pools/organs, as well as mobilization of reserves) change in order for the plant to successfully overcome stress [54]. The shortcoming of fixed carbon allocation ratios, currently implemented in the BBGCMuSo model, might become increasingly pronounced in the case of extreme events.…”

“…new fine root C : new leaf C 0.95 [52] new fruit C : new leaf C 0.14 [52] new woody stem C : new leaf C 1.42 [52] new coarse root C : new woody stem C 0.26 [54] Meteorological data were analysed for the same period as for growth dynamics, from 2000 to 2014. For each location mean annual (October-September) and seasonal (April-September) air temperature (°C) and precipitation (mm) anomalies were calculated as follows: T = Ti -Tp P = Pi -Pp where T is air temperature anomaly, Ti is mean annual (OctSep) or seasonal (Apr-Sep) air temperature in year i , Tp is mean annual/seasonal air temperature of the investigated period (2000-2014), P is precipitation anomaly, Pi is annual/ seasonal precipitation sum, and Pp is the mean of annual/ seasonal precipitation sums during the investigated period.…”