The influence of increasing atmospheric CO₂, temperature, and vapor pressure deficit on seawater‐induced tree mortality

Abstract

Increasing seawater exposure is killing coastal trees globally, with expectations of accelerating mortality with rising sea levels. However, the impact of concomitant changes in atmospheric CO 2 concentration, temperature, and vapor pressure deficit (VPD) on seawater-induced tree mortality is uncertain.We examined the mechanisms of seawater-induced mortality under varying climate scenarios using a photosynthetic gain and hydraulic cost optimization model validated against observations in a mature stand of Sitka spruce (Picea sitchensis) trees in the Pacific Northwest, USA, that were dying from recent seawater exposure.The simulations matched well with observations of photosynthesis, transpiration, nonstructural carbohydrates concentrations, leaf water potential, the percentage loss of xylem conductivity, and stand-level mortality rates. The simulations suggest that seawater-induced mortality could decrease by c. 16.7% with increasing atmospheric CO 2 levels due to reduced risk of carbon starvation. Conversely, rising VPD could increase mortality by c. 5.6% because of increasing risk of hydraulic failure.Across all scenarios, seawater-induced mortality was driven by hydraulic failure in the first 2 yr after seawater exposure began, with carbon starvation becoming more important in subsequent years. Changing CO 2 and climate appear unlikely to have a significant impact on coastal tree mortality under rising sea levels.

The effects of previous summer drought and fertilization on winter non-structural carbon reserves and spring leaf development of downy oak saplings

“…Under the extreme drought in the present study, fertilization did not change the timing of spring leaf phenology but increased the survival rate of plants ( Table 3 , Figure 4 ), despite of very low post-winter shoot NSC concentrations in W0/F+ (~3% in W0/F+ vs. ~7% in W0/F0, P < 0.05). Previous studies proposed that hydraulic failure and carbon starvation are two possible physiological mechanisms for drought-induced tree mortality or growth decline ( Mcdowell et al., 2008 ; Li et al., 2022 ), decreased NSC accompanied by decreased mortality with fertilization in the present study suggest that drought-induced mortality was driven by hydraulic failure, rather than carbon starvation, especially under high nutrient availability. But high nutrient availability might have promoted the mobilization and utilization of carbohydrates during winter ( Wong et al., 2009 ; Galvez et al., 2013 ; Schönbeck et al., 2020 ).…”

“…In the past decades, severe droughts and heatwaves have caused tree mortality and forest dieback across various biomes ( Allen et al., 2010 ; Young et al., 2017 ), leading to profound changes in the structure and functioning of forest ecosystems on both global and local scale ( Zhao and Running, 2010 ; Choat et al., 2018 ; Hartmann et al., 2018 ; Li et al., 2022 ). Natural drought events associated with increasing air temperature have been predicted to occur more frequently and to be of greater intensity in the future ( IPCC, 2021 ), but it is still unclear whether and how trees tolerate and adapt to frequent droughts ( Mcdowell et al., 2008 ; Allen et al., 2010 ; Mitchell et al., 2013 ; Adams et al., 2017 ; Choat et al., 2018 ).…”

Modeling the mechanisms of conifer mortality under seawater exposure

“…3) of shoreline forests are all lower than those of upland forests at the three sites. The simulated reduction in leaf GPP and E T agree with the findings of other modeling studies (Li et al ., 2022; Yoshikai et al ., 2022) and field observations (Duberstein et al ., 2020; Pan et al ., 2020) of coastal forests. Our model also shows soil salinity can lower leaf water potential, Ψ leaf , by as much as 2 MPa (Fig.…”

Litter quality modifies soil organic carbon mineralization in an ecological restoration area

“…Revegetation is widely implemented to curb desertification and reduce soil erosion (Le Houérou, 2000; Li et al, 2014). It not only alters vegetation cover (Zhang et al, 2015), soil properties (Li et al, 2007), and microbial community structure (Liu et al, 2017) but also affects the accumulation of soil organic carbon (SOC) and stock by affecting the SOC mineralization (Yang et al, 2014; Zhang et al, 2019; Li et al, 2022a). The mechanism that underlies a reduced carbon sequestration rate after 50 years of revegetation has not been effectively explained (Yang et al, 2014), and the effect of litter on SOC mineralization may be an important driver.…”

“…The SOC mineralization rates are modified by biotic and abiotic factors, such as revegetation, litter quality (chemical stoichiometry, i.e., C, N, P, and C:N ratio), temperature, and soil moisture (Nemani et al, 2003;Vanhala et al, 2008;Tian et al, 2016;Wang et al, 2016;Li et al, 2020;. The restoration of mobile dune vegetation significantly changes the composition of plant species, as well as the quantity and quality of litter (Li et al, 2007;Li et al, 2022b). However, the impacts and mechanisms of litter quality and compositional changes on SOC mineralization and C loss remain unclear.…”