Predicted and observed multidecadal variations of tree physiological responses to climate and rising CO2: insights from tree-ring carbon isotopes in temperate forests.

Increasing water-use efficiency (WUE), the ratio of carbon gain to water loss, is a key mechanism that enhances carbon uptake by terrestrial vegetation under rising atmospheric CO2 (ca). Existing theory and empirical evidence suggest a proportional increase of WUE in response to rising ca as plants maintain a relatively constant ratio between the leaf internal (ci) and ambient (ca) partial CO2 pressure (ci/ca). This has been hypothesized as the main driver of the strengthening of the terrestrial carbon sink over the recent decades. However, proportionality may not characterize CO2 effects on WUE on longer time-scales and the role of climate in modulating these effects is uncertain. We evaluated the long-term WUE responses to ca and climate from 1901-2012 CE by reconstructing intrinsic WUE (iWUE, the ratio of photosynthesis to stomatal conductance) using carbon isotopes in tree rings across temperate forests in the northeastern USA. We further replicated iWUE reconstructions at eight additional sites for the 1992-2012 period-overlapping with the common period of the longest flux-tower record at Harvard Forest to evaluate the spatial coherence of recent iWUE variation across the region. Finally, we compared tree-ring based and modelled ci/ca over the 1901-2012 period to examine whether temporal patterns of ci/ca reconstructions are consistent with predictions based on the optimality principle of balancing the costs of water loss and carbon gain.We found that iWUE increased steadily from 1901 to 1975 CE but remained constant thereafter despite continuously rising ca. This finding is consistent with a passive physiological response to ca and coincides with a shift to significantly wetter conditions across the region. Tree physiology was driven by summer moisture at multi-decadal time-scales and did not maintain a constant ci/ca in response to rising ca indicating that a point was reached where rising CO2 had a diminishing effect on tree iWUE. &#160;The ci/ca derived from tree-ring d13C and the predicted values based on the optimality theory model had similar median values over the 1901-2012 CE period, though with a modest agreement (R2adj = 0.22, p < 0.001). The reconstructed and predicted ci/ca trends were not statistically different from 0 when estimated over the 1901-2012 CE period; however, isotope-based reconstruction of the ci/ca trendshowed distinct multidecadal variation while the predicted ci/ca remained nearly constant. Our results challenge the mechanism, magnitude, and persistence of CO2&#8217;s effect on iWUE with significant implications for projections of terrestrial productivity under a changing climate.

Download Full-text

Potential Transient Response of Terrestrial Vegetation and Carbon in Northern North America from Climate Change

Climate ◽

10.3390/cli7090113 ◽

2019 ◽

Vol 7 (9) ◽

pp. 113

Author(s):

Steven A. Flanagan ◽

George C. Hurtt ◽

Justin P. Fisk ◽

Ritvik Sahajpal ◽

Maosheng Zhao ◽

...

Keyword(s):

Climate Change ◽

North America ◽

Time Scales ◽

Transient Response ◽

Landscape Heterogeneity ◽

Carbon Sink ◽

Terrestrial Ecosystems ◽

Ecosystem Model ◽

Terrestrial Vegetation ◽

Equilibrium Response

Terrestrial ecosystems and their vegetation are linked to climate. With the potential of accelerated climate change from anthropogenic forcing, there is a need to further evaluate the transient response of ecosystems, their vegetation, and their influence on the carbon balance, to this change. The equilibrium response of ecosystems to climate change has been estimated in previous studies in global domains. However, research on the transient response of terrestrial vegetation to climate change is often limited to domains at the sub-continent scale. Estimation of the transient response of vegetation requires the use of mechanistic models to predict the consequences of competition, dispersal, landscape heterogeneity, disturbance, and other factors, where it becomes computationally prohibitive at scales larger than sub-continental. Here, we used a pseudo-spatial ecosystem model with a vegetation migration sub-model that reduced computational intensity and predicted the transient response of vegetation and carbon to climate change in northern North America. The ecosystem model was first run with a current climatology at half-degree resolution for 1000 years to establish current vegetation and carbon distribution. From that distribution, climate was changed to a future climatology and the ecosystem model run for an additional 2000 simulation years. A model experimental design with different combinations of vegetation dispersal rates, dispersal modes, and disturbance rates produced 18 potential change scenarios. Results indicated that potential redistribution of terrestrial vegetation from climate change was strongly impacted by dispersal rates, moderately affected by disturbance rates, and marginally impacted by dispersal mode. For carbon, the sensitivities were opposite. A potential transient net carbon sink greater than that predicted by the equilibrium response was estimated on time scales of decades–centuries, but diminished over longer time scales. Continued research should further explore the interactions between competition, dispersal, and disturbance, particularly in regards to vegetation redistribution.

Download Full-text

Different climate sensitivity for radial growth, but uniform for tree-ring stable isotopes along an aridity gradient in Polylepis tarapacana, the world’s highest elevation tree-species

Tree Physiology ◽

10.1093/treephys/tpab021 ◽

2021 ◽

Author(s):

Milagros Rodriguez-Caton ◽

Laia Andreu-Hayles ◽

Mariano S Morales ◽

Valérie Daux ◽

Duncan A Christie ◽

...

Keyword(s):

Stable Isotopes ◽

Carbon Source ◽

Tree Ring ◽

Tree Growth ◽

Carbon Sink ◽

Growing Season ◽

Wood Formation ◽

Aridity Gradient ◽

Leaf Level ◽

Δ13c And Δ18o

Abstract Tree growth is generally considered to be temperature-limited at upper elevation treelines. Yet, climate factors controlling tree growth at semiarid treelines are poorly understood. We explored the influence of climate on stem growth and stable isotopes for Polyepis tarapacana, the world’s highest elevation tree-species found only in the South American Altiplano. We developed tree-ring width index (RWI), oxygen (δ18O) and carbon (δ13C) chronologies for the last 60 years at four P. tarapacana stands located above 4,400 meters in elevation, along a 500-km latitude-aridity gradient. Total annual precipitation decreased from 300 to 200 mm from the northern to the southern sites. We used RWI as a proxy of wood formation (carbon sink) and isotopic tree-ring signatures as proxies of leaf-level gas exchange processes (carbon source). We found distinct climatic conditions regulating carbon-sink processes along the gradient. Current-growing season temperature regulated RWI at wetter-northern sites, while prior-growing season precipitation determined RWI at arid-southern sites. This suggests that the relative importance of temperature to precipitation in regulating tree growth is driven by site-water availability. In contrast, warm and dry growing-seasons resulted in enriched tree-ring δ13C and δ18O at all study sites, suggesting that similar climate conditions control carbon-source processes. Site-level δ13C and δ18O chronologies were significantly and positively related at all sites, with the strongest relationships among the southern-drier stands. This indicates an overall regulation of intercellular carbon dioxide via stomatal conductance for the entire P. tarapacana network, with greater stomatal control when aridity increases. The manuscript also highlights a coupling and decoupling of physiological processes at leaf level versus wood formation depending on their respectively uniform and distinct sensitivity to climate. This study contributes to better understand and predict the response of high-elevation Polylepis woodlands to rapid climate changes and projected drying in the Altiplano.

Download Full-text

A decreasing trend in global soil water storage from 1981 to 2017

10.5194/egusphere-egu21-5756 ◽

2021 ◽

Author(s):

XinRui Luo ◽

Shaoda Li ◽

Wunian Yang ◽

Liang Liu ◽

Xiaolu Tang

Keyword(s):

Soil Water ◽

Water Loss ◽

Root Zone ◽

Carbon Sink ◽

Temporal Trends ◽

Water Storage ◽

Terrestrial Ecosystems ◽

Environmental Drivers ◽

Soil Water Storage ◽

Soil Drought

Soil water storage serves as a vital resource of the terrestrial ecosystems, and it can significantly influence water cycle and carbon cycling with the frequent occurrence of soil drought induced by land-atmosphere feedbacks. However, there are high variations and uncertainties of root zone soil water storage. This study applied comparison map profile (CMP), Mann-Kendall test, Theil-Sen estimate and partial correlation analysis to (1) estimate the global root zone (0~1 m) soil water storage, (2) and investigate the spatial and temporal patterns from 1981 to 2017 at the global scale, (3) and their relationships with environmental drivers (precipitation, temperature, potential evaportranspiration) using three soil moisture (SM) products &#8211; ERA-5, GLDAS and MERRA-2. Globally, the average annual soil water storage from 1981 to 2017 varied significantly, ranging from 138.3 (100 Pg a-1, 1 Pg = 1015 g) in GLDAS to 342.6 (100 Pg a-1) in ERA-5. Soil water storage of the three SM products consistently showed a decreasing trend. However, the temporal trend of soil water storage among different climate zones was different, showing a decreasing trend in tropical, temperate and cold zones, but an increasing trend in polar regions. On the other hand, temporal trends in arid regions differed from ERA-5, GLDAS and MERRA-2. Spatially, the SM products differed greatly, particularly for boreal areas with D value higher for 2500 Mg ha-1 a-1 and CC value lower for -0.2 between GLDAS and MERRA-2. Over 1981 to 2017, water storage of more than 50% of the global land area suffered from a decreasing trend, especially in Africa and Northeastern of China. Precipitation was the main dominated driver for variation of soil water storage, and distribution varied in different SM products. In conclusion, a global decreasing trend in soil water storage indicate a water loss from soils, and how the water loss affecting carbon sink in terrestrial ecosystems under ongoing climate change needs further investigation.

Download Full-text

Stable carbon isotopes as powerful tools for studying land-atmosphere flux exchanges and improving land surface models

10.5194/egusphere-egu21-11232 ◽

2021 ◽

Author(s):

Aliénor Lavergne ◽

Laia Andreu-Hayles ◽

Soumaya Belmecheri ◽

Rossella Guerrieri ◽

Heather Graven

Keyword(s):

Carbon Isotopes ◽

Land Surface ◽

Stable Carbon Isotopes ◽

Environmental Changes ◽

Carbon Sink ◽

Stable Carbon ◽

Land Surface Models ◽

Terrestrial Plants ◽

Plant Materials ◽

Surface Models

The stable isotopic compositions of carbon and oxygen in terrestrial plants can provide valuable insights into plant eco-physiological responses to environmental changes at seasonal to annual resolution. Yet, the potential of these datasets to study land-atmosphere interactions remains under-exploited. Here, we present some examples of how stable carbon isotopes (&#948;13C) measured in plant materials (leaves and tree-rings) can be used to explore changes in the magnitude and variability of carbon and water flux exchanges between the vegetation and the atmosphere and to improve land surface models. First, we show that the discrimination against 13C (&#916;13C), calculated as the difference in &#948;13C between the source atmospheric CO2 and the plant material studied, varies strongly between regions and biomes and is useful for better understanding the CO2 fertilisation effect of plant growth. For example, tree-ring &#916;13C records from boreal evergreen forests in North America increased linearly with rising CO2 during the 20th century, suggesting that those forests have actively contributed to the land carbon sink by removing CO2 from the atmosphere at a relatively constant rate. However, such an increase in&#160;&#916;13C with rising CO2 is not observed everywhere. We found that over the same time period, while some forests had a fairly constant &#916;13C, others exhibited a slight decrease in &#916;13C over time, which might indicate a reduction of the capacity of trees to absorb CO2. Using a response function approach, we show that the differences between sites and regions are most likely the result of different evaporative demands and soil water availability conditions experienced by forests. We then discuss how predictions of the coupled carbon and water cycles by vegetation models can be improved by incorporating stable carbon isotopes to constrain the model representation of carbon-water fluxes regulation by leaf stomata. Specifically, we examine and evaluate simulations from the JULES vegetation model at different eddy-covariance forest sites where stable carbon isotopic data and canopy flux measurements are available. Overall, our analyses have strong implications for the understanding of historical changes in the strength of the CO2 fertilisation effect and in the water use efficiency of terrestrial ecosystems across regions.&#160;

Download Full-text

Tracing source and transformation of carbon in an epikarst spring-pond system by dual carbon isotopes (13C14C): Evidence of dissolved CO2 uptake as a carbon sink

Journal of Hydrology ◽

10.1016/j.jhydrol.2020.125766 ◽

2021 ◽

Vol 593 ◽

pp. 125766

Author(s):

Bo Chen ◽

Min Zhao ◽

Hao Yan ◽

Rui Yang ◽

Hong-Chun Li ◽

...

Keyword(s):

Carbon Isotopes ◽

Carbon Sink ◽

Co2 Uptake ◽

Pond System

Download Full-text

Is Amphistomy an Adaptation to High Light? Optimality Models of Stomatal Traits along Light Gradients

Integrative and Comparative Biology ◽

10.1093/icb/icz085 ◽

2019 ◽

Vol 59 (3) ◽

pp. 571-584 ◽

Cited By ~ 6

Author(s):

Christopher D Muir

Keyword(s):

Energy Budget ◽

Water Loss ◽

R Package ◽

High Light ◽

Carbon Gain ◽

Marginal Effect ◽

Costs And Benefits ◽

Leaf Surfaces ◽

Stomatal Traits ◽

Optimality Models

AbstractStomata regulate the supply of CO2 for photosynthesis and the rate of water loss out of the leaf. The presence of stomata on both leaf surfaces, termed amphistomy, increases photosynthetic rate, is common in plants from high light habitats, and rare otherwise. In this study I use optimality models based on leaf energy budget and photosynthetic models to ask why amphistomy is common in high light habitats. I developed an R package leafoptimizer to solve for stomatal traits that optimally balance carbon gain with water loss in a given environment. The model predicts that amphistomy is common in high light because its marginal effect on carbon gain is greater than in the shade, but only if the costs of amphistomy are also lower under high light than in the shade. More generally, covariation between costs and benefits may explain why stomatal and other traits form discrete phenotypic clusters.

Download Full-text

Inferring non-steady-state terrestrial vegetation carbon turnover times from multi-decadal space-borne observations on global scale

10.5194/egusphere-egu2020-17717 ◽

2020 ◽

Author(s):

Naixin Fan ◽

Simon Besnard ◽

Maurizio Santoro ◽

Oliver Cartus ◽

Nuno Carvalhais

Keyword(s):

Climate Change ◽

Steady State ◽

Carbon Fixation ◽

Carbon Sink ◽

Gross Primary Production ◽

Terrestrial Ecosystems ◽

Global Scale ◽

Turnover Time ◽

Terrestrial Vegetation ◽

Time Step

The global biomass is determined by the vegetation turnover times (&#964;) and carbon fixation through photosynthesis. Vegetation turnover time is a central parameter that not only partially determines the terrestrial carbon sink but also the response of terrestrial vegetation to the future changes in climate. However, the change of magnitude, spatial patterns and uncertainties in &#964; as well as the sensitivity of these processes to climate change is not well understood due to lack of observations on global scale. In this study, we explore a new dataset of annual above-ground biomass (AGB) change from 1993 to 2018 from spaceborne scatterometer observations. Using the long-term, spatial-explicit global dynamic dataset, we investigated how &#964; change over almost three decades including the uncertainties. Previous estimations of &#964; under steady-state assumption can now be challenged acknowledging that terrestrial ecosystems are, for the most of cases, not in balance. In this study, we explore this new dataset to derive global maps of &#964; in non-steady-state for different periods of time. We used a non-steady-state carbon model in which the change of AGB is a function of Gross Primary Production (GPP) and &#964; (&#916;AGB = &#945;*GPP-AGB/ &#964;). The parameter &#945; represents the percentage of incorporation of carbon from GPP to biomass. By exploring the AGB change in 5 to 10 years of time step, we were able to infer &#964; and &#945; from the observations of AGB and GPP change by solving the linear equation. We show how &#964; changes after potential disturbances in the early 2000s in comparison to the previous decade. We also show the spatial distributions of &#945; from the change of AGB. By accessing the change in biomass, &#964; and &#945; as well as their associated uncertainties, we provide a comprehensive diagnostic on the vegetation dynamics and the potential response of biomass to disturbance and to climate change.&#160; &#160;

Download Full-text

A short overview on linking annual tree ring carbon isotopes to historical changes in atmospheric environment

Forest Science and Technology ◽

10.1080/21580103.2012.672017 ◽

2012 ◽

Vol 8 (2) ◽

pp. 61-66 ◽

Cited By ~ 2

Author(s):

Woo-Jung Choi ◽

Kye-Han Lee

Keyword(s):

Carbon Isotopes ◽

Tree Ring ◽

Atmospheric Environment ◽

Historical Changes ◽

Ring Carbon ◽

Short Overview

Download Full-text

Tree-ring width and δ13C records of industrial stress and recovery in Pennsylvania and New Jersey forests: Implications for CO2 uptake by temperate forests

Chemical Geology ◽

10.1016/j.chemgeo.2010.02.026 ◽

2010 ◽

Vol 273 (3-4) ◽

pp. 250-257 ◽

Cited By ~ 7

Author(s):

Long Li ◽

Zicheng Yu ◽

Gray E. Bebout ◽

Tom Stretton ◽

Andrew Allen ◽

...

Keyword(s):

New Jersey ◽

Tree Ring ◽

Temperate Forests ◽

Ring Width ◽

Co2 Uptake ◽

Tree Ring Width

Download Full-text

TREE RING RECONSTRUCTION OF MODERN RADIOCARBON DIOXIDE VARIABILITY OVER THE SOUTHERN OCEAN

10.26686/wgtn.14703831 ◽

2021 ◽

Author(s):

Rachel Corran

Keyword(s):

Southern Ocean ◽

Southern Hemisphere ◽

Tree Ring ◽

Deep Water ◽

Latitudinal Gradient ◽

Carbon Sink ◽

Carbon Uptake ◽

Co2 Uptake ◽

Anthropogenic Carbon ◽

Ocean Carbon

The Southern Ocean is the largest ocean carbon sink region. However, its trend of increasing carbon uptake has shown variability over recent decades. It is important to understand the underlying mechanisms of anthropogenic carbon uptake such that the future response of the Southern Ocean carbon sink under climate forcing can be predicted. The carbon uptake of the Southern Ocean is characterised by the balance of outgassing of CO2 from carbon-rich deep water and sequestration of anthropogenic carbon into surface waters. Atmospheric radiocarbon dioxide (Del14CO2) in the Southern Hemisphere is sensitive to the release of CO2 from the upwelling of ‘old’ 14C-depleted carbon-rich deep water at high southern latitudes, but is insensitive to CO2 uptake into the ocean. Thus Del14CO2 has the potential to be used as a tracer of the upwelling observed, thereby isolating the outgassing carbon component. The Southern Ocean Region has limited atmospheric Del14CO2 measurements, with sparse long-term sampling sites and few shipboard flask measurements. Therefore in this PhD project I exploit annual growth tree rings, which record the Del14C content of atmospheric CO2, to reconstruct Del14CO2 back in time. Within tree ring sample pretreatment for 14C measurement I automate the organic solvent wash method at the Rafter Radiocarbon Laboratory. I present new annual-resolution reconstructions of atmospheric Del14CO2 from tree rings, from coastal sites in New Zealand and Chile, spanning a latitudinal range of 44 S to 55 S, for the period of interest, 1985 – 2015. Data quality analysis using a range of replicate 14C measurements conducted within this project leads to assignment of apx 1.9 ‰ uncertainties for all results, in line with atmospheric measurements. In this project I also develop a harmonised dataset of atmospheric Del14CO2 measurements in the Southern Hemisphere for this period from different research groups, including the new tree ring Del14CO2 records alongside existing data. The harmonised atmospheric Del14CO2 dataset has a wide range of applications, but specifically here allows investigation of temporal and spatial variability of atmospheric Del14CO2 over the Southern Ocean over recent decades, thereby also considering the role of upwelling in recent Southern Ocean carbon sink variability. Backward trajectories are produced for the tree ring sites from an atmospheric transport model, to help inform interpretation of results. Over recent decades a latitudinal gradient of 3.7 ‰ is observed between 41 S and 53 S in the New Zealand sector, with a smaller gradient of 1.6 ‰ between 48 S and 55S in the Chile sector. This is consistent with other studies, with the spatial variability of atmospheric Del14CO2 attributed to air-sea 14C disequilibrium associated with carbon outgassing from 14C-depleted carbon-rich deep water upwelling at around 60 S, driving a latitudinal gradient of atmospheric Del14CO2 in the Southern Hemisphere, with longitudinal variability also observed. A stronger atmospheric Del14CO2 latitudinal gradient is observed in the 1980s/1990s relative to later 1990s/2000s. Stronger atmospheric Del14CO2 latitudinal gradients observed in 1980s/1990s suggest stronger deep water upwelling thereby greater associated outgassing of 14C-depleted CO2. These Del14CO2-based observations are consistent with modelling studies that predict changes in deep-water upwelling have controlled decadal variability in CO2 uptake, and are consistent with observation-based studies of decadal changes in rate of CO2 uptake of the Southern Ocean. The results presented in this thesis present the first observation-based confirmation that decadal changes in the strength of deep-water upwelling can explain decadal changes in the rate of CO2 uptake.

Download Full-text