Title: Does plant ecosystem thermoregulation occur? An extratropical assessment at different spatial and temporal scales
Summary
To what degree plant ecosystems thermoregulate their canopy temperature (Tc) is critical to assess ecosystems' metabolisms and resilience with climate change, but remains controversial, with opinions from no to moderate thermoregulation capability.
With global datasets ofTc, air temperature (Ta), and other environmental and biotic variables from FLUXNET and satellites, we tested the ‘limited homeothermy’ hypothesis (indicated byTc&Taregression slope < 1 orTc < Taaround midday) across global extratropics, including temporal and spatial dimensions.
Across daily to weekly and monthly timescales, over 80% of sites/ecosystems have slopes ≥1 orTc > Taaround midday, rejecting the above hypothesis. For those sites unsupporting the hypothesis, theirTc–Tadifference (ΔT) exhibits considerable seasonality that shows negative, partial correlations with leaf area index, implying a certain degree of thermoregulation capability. Spatially, site‐mean ΔTexhibits larger variations than the slope indicator, suggesting ΔTis a more sensitive indicator for detecting thermoregulatory differences across biomes. Furthermore, this large spatial‐wide ΔTvariation (0–6°C) is primarily explained by environmental variables (38%) and secondarily by biotic factors (15%).
These results demonstrate diverse thermoregulation patterns across global extratropics, with most ecosystems negating the ‘limited homeothermy’ hypothesis, but their thermoregulation still occurs, implying that slope < 1 orTc < Taare not necessary conditions for plant thermoregulation.
Leaf energy balance may influence plant performance and community composition. While biophysical theory can link leaf energy balance to many traits and environment variables, predicting leaf temperature and key driver traits with incomplete parameterizations remains challenging. Predicting thermal offsets (δ,Tleaf − Tairdifference) or thermal coupling strengths (β,Tleafvs.Tairslope) is challenging.
We ask: (a) whether environmental gradients predict variation in energy balance traits (absorptance, leaf angle, stomatal distribution, maximum stomatal conductance, leaf area, leaf height); (b) whether commonly measured leaf functional traits (dry matter content, mass per area, nitrogen fraction, δ13C, height above ground) predict energy balance traits; and (c) how traits and environmental variables predictδandβamong species.
We address these questions with diurnal measurements of 41 species co‐occurring along a 1,100 m elevation gradient spanning desert to alpine biomes. We show that (a) energy balance traits are only weakly associated with environmental gradients and (b) are not well predicted by common functional traits. We also show that (c)δandβcan be partially approximated using interactions among site environment and traits, with a much larger role for environment than traits. The heterogeneity in leaf temperature metrics and energy balance traits challenges larger‐scale predictive models of plant performance under environmental change.
A freePlain Language Summarycan be found within the Supporting Information of this article.
Moran, Madeline E.; Aparecido, Luiza M. T.; Koepke, Dan F.; Cooper, Hillary F.; Doughty, Christopher E.; Gehring, Catherine A.; Throop, Heather L.; Whitham, Thomas G.; Allan, Gerard J.; Hultine, Kevin R.(
, New Phytologist)
Summary
Populus fremontiiis among the most dominant, and ecologically important riparian tree species in the western United States and can thrive in hyper‐arid riparian corridors. Yet,P. fremontiiforests have rapidly declined over the last decade, particularly in places where temperatures sometimes exceed 50°C.
We evaluated high temperature tolerance of leaf metabolism, leaf thermoregulation, and leaf hydraulic function in eightP. fremontiipopulations spanning a 5.3°C mean annual temperature gradient in a well‐watered common garden, and at source locations throughout the lower Colorado River Basin.
Two major results emerged. First, despite having an exceptionally highTcrit(the temperature at which Photosystem II is disrupted) relative to other tree taxa, recent heat waves exceededTcrit, requiring evaporative leaf cooling to maintain leaf‐to‐air thermal safety margins. Second, in midsummer, genotypes from the warmest locations maintained lower midday leaf temperatures, a higher midday stomatal conductance, and maintained turgor pressure at lower water potentials than genotypes from more temperate locations.
Taken together, results suggest that under well‐watered conditions,P. fremontiican regulate leaf temperature belowTcritalong the warm edge of its distribution. Nevertheless, reduced Colorado River flows threaten to lower water tables below levels needed for evaporative cooling during episodic heat waves.
Havrilla, Caroline A.; Chaudhary, V. Bala; Ferrenberg, Scott; Antoninka, Anita J.; Belnap, Jayne; Bowker, Matthew A.; Eldridge, David J.; Faist, Akasha M.; Huber‐Sannwald, Elisabeth; Leslie, Alexander D.; et al(
, Journal of Ecology)
Abstract
Understanding the importance of biotic interactions in driving the distribution and abundance of species is a central goal of plant ecology. Early vascular plants likely colonized land occupied by biocrusts — photoautotrophic, surface‐dwelling soil communities comprised of cyanobacteria, bryophytes, lichens and fungi — suggesting biotic interactions between biocrusts and plants have been at play for some 2,000 million years. Today, biocrusts coexist with plants in dryland ecosystems worldwide, and have been shown to both facilitate or inhibit plant species performance depending on ecological context. Yet, the factors that drive the direction and magnitude of these effects remain largely unknown.
We conducted a meta‐analysis of plant responses to biocrusts using a global dataset encompassing 1,004 studies from six continents.
Meta‐analysis revealed there is no simple positive or negative effect of biocrusts on plants. Rather, plant responses differ by biocrust composition and plant species traits and vary across plant ontogeny. Moss‐dominated biocrusts facilitated, while lichen‐dominated biocrusts inhibited overall plant performance. Plant responses also varied among plant functional groups: C4grasses received greater benefits from biocrusts compared to C3grasses, and plants without N‐fixing symbionts responded more positively to biocrusts than plants with N‐fixing symbionts. Biocrusts decreased germination but facilitated growth of non‐native plant species.
Synthesis. Results suggest that interspecific variation in plant responses to biocrusts, contingent on biocrust type, plant traits, and ontogeny can have strong impacts on plant species performance. These findings have important implications for understanding biocrust contributions to plant productivity and community assembly processes in ecosystems worldwide.
Lang, Ashley K.; Pett‐Ridge, Jennifer; McFarlane, Karis J.; Phillips, Richard P.(
, Journal of Ecology)
Abstract
Identifying the primary controls of particulate (POM) and mineral‐associated organic matter (MAOM) content in soils is critical for determining future stocks of soil carbon (C) and nitrogen (N) across the globe. However, drivers of these soil organic matter fractions are likely to vary among ecosystems in response to climate, soil type and the composition of local biological communities.
We tested how soil factors, climate and plant–fungal associations influenced the distribution and concentrations of C and N in MAOM and POM in seven temperate forests in the National Ecological Observatory Network (NEON) across the eastern United States. Samples of upper mineral horizon soil within each forest were collected in plots representing a gradient of dominant tree–mycorrhizal association, allowing us to test how plant and microbial communities influenced POM and MAOM across sites differing in climate and soil conditions.
We found that concentrations of C and N in soil organic matter were primarily driven by soil mineralogy, but the relative abundance of MAOM versus POM C was strongly linked to plot‐level mycorrhizal dominance. Furthermore, the effect of dominant tree mycorrhizal type on the distribution of N among POM and MAOM fractions was sensitive to local climate: in cooler sites, an increasing proportion of ectomycorrhizal‐associated trees was associated with lower proportions of N in MAOM, but in warmer sites, we found the reverse. As an indicator of soil carbon age, we measured radiocarbon in the MAOM fraction but found that within and across sites, Δ14C was unrelated to mycorrhizal dominance, climate, or soil factors, suggesting that additional site‐specific factors may be primary determinants of long‐term SOM persistence.
Synthesis. Our results indicate that while soil mineralogy primarily controls SOM C and N concentrations, the distribution of SOM among density fractions depends on the composition of vegetation and microbial communities, with these effects varying across sites with distinct climates. We also suggest that within biomes, the age of mineral‐associated soil carbon is not clearly linked to the factors that control concentrations of MAOM C and N.
Osburn, Ernest D.; Hoch, Peter J.; Lucas, Jane M.; McBride, Steven G.; Strickland, Michael S.(
, Functional Ecology)
Abstract
Soil biota are increasingly recognized as a primary control on litter decomposition at both local and regional scales, but the precise mechanisms by which biota influence litter decomposition have yet to be identified.
There are multiple hypothesized mechanisms by which biotic communities may influence litter decomposition—for example, decomposer communities may be specially adapted to local litter inputs and therefore decompose litter from their home ecosystem at elevated rates. This mechanism is known as the home‐field advantage (HFA) hypothesis. Alternatively, litter decomposition rates may simply depend upon the range of metabolic functions present within a decomposer community. This mechanism is known as the functional breadth (FB) hypothesis. However, the relative importance of HFA and FB in litter decomposition is unknown, as are the microbial community drivers of HFA and FB. Potential relationships/trade‐offs between microbial HFA and FB are also unknown.
To investigate the roles of HFA and FB in litter decomposition, we collected litter and soil from six different ecosystems across the continental US and conducted a full factorial litter × soil inoculum experiment. We measured litter decomposition (i.e. cumulative CO2‐C respired) over 150 days and used an analytical model to calculate the HFA and FB of each microbial decomposer community.
Our results indicated clear functional differences among decomposer communities, that is, litter sources were decomposed differently by different decomposer communities. These differences were primarily due to differences in FB between different communities, while HFA effects were less evident.
We observed a positive relationship between HFA and the disturbance‐sensitive bacterial phylum Verruomicrobia, suggesting that HFA may be an important mechanism in undisturbed environments. We also observed a negative relationship between bacterial r versus K strategists and FB, suggesting an important link between microbial life‐history strategies and litter decomposition functions.
Microbial FB and HFA exhibited a strong unimodal relationship, where high HFA was observed at intermediate FB values, while low HFA was associated with both low and high FB. This suggests that adaptation of decomposers to local plant inputs (i.e. high HFA) constrains FB, which requires broad rather than specialized functionality. Furthermore, this relationship suggests that HFA effects will not be apparent when communities exhibit high FB and therefore decompose all litters well and also when FB is low and communities decompose all litters poorly. Overall, our study provides new insights into the mechanisms by which microbial communities influence the decomposition of leaf litter.
Read the freePlain Language Summaryfor this article on the Journal blog.
Guo, Zhengfei, Still, Christopher J., Lee, Calvin K. F., Ryu, Youngryel, Blonder, Benjamin, Wang, Jing, Bonebrake, Timothy C., Hughes, Alice, Li, Yan, Yeung, Henry C. H., Zhang, Kun, Law, Ying Ki, Lin, Ziyu, and Wu, Jin. Does plant ecosystem thermoregulation occur? An extratropical assessment at different spatial and temporal scales. New Phytologist 238.3 Web. doi:10.1111/nph.18632.
Guo, Zhengfei, Still, Christopher J., Lee, Calvin K. F., Ryu, Youngryel, Blonder, Benjamin, Wang, Jing, Bonebrake, Timothy C., Hughes, Alice, Li, Yan, Yeung, Henry C. H., Zhang, Kun, Law, Ying Ki, Lin, Ziyu, & Wu, Jin. Does plant ecosystem thermoregulation occur? An extratropical assessment at different spatial and temporal scales. New Phytologist, 238 (3). https://doi.org/10.1111/nph.18632
Guo, Zhengfei, Still, Christopher J., Lee, Calvin K. F., Ryu, Youngryel, Blonder, Benjamin, Wang, Jing, Bonebrake, Timothy C., Hughes, Alice, Li, Yan, Yeung, Henry C. H., Zhang, Kun, Law, Ying Ki, Lin, Ziyu, and Wu, Jin.
"Does plant ecosystem thermoregulation occur? An extratropical assessment at different spatial and temporal scales". New Phytologist 238 (3). Country unknown/Code not available: Wiley-Blackwell. https://doi.org/10.1111/nph.18632.https://par.nsf.gov/biblio/10404597.
@article{osti_10404597,
place = {Country unknown/Code not available},
title = {Does plant ecosystem thermoregulation occur? An extratropical assessment at different spatial and temporal scales},
url = {https://par.nsf.gov/biblio/10404597},
DOI = {10.1111/nph.18632},
abstractNote = {Summary To what degree plant ecosystems thermoregulate their canopy temperature (Tc) is critical to assess ecosystems' metabolisms and resilience with climate change, but remains controversial, with opinions from no to moderate thermoregulation capability.With global datasets ofTc, air temperature (Ta), and other environmental and biotic variables from FLUXNET and satellites, we tested the ‘limited homeothermy’ hypothesis (indicated byTc&Taregression slope < 1 orTc < Taaround midday) across global extratropics, including temporal and spatial dimensions.Across daily to weekly and monthly timescales, over 80% of sites/ecosystems have slopes ≥1 orTc > Taaround midday, rejecting the above hypothesis. For those sites unsupporting the hypothesis, theirTc–Tadifference (ΔT) exhibits considerable seasonality that shows negative, partial correlations with leaf area index, implying a certain degree of thermoregulation capability. Spatially, site‐mean ΔTexhibits larger variations than the slope indicator, suggesting ΔTis a more sensitive indicator for detecting thermoregulatory differences across biomes. Furthermore, this large spatial‐wide ΔTvariation (0–6°C) is primarily explained by environmental variables (38%) and secondarily by biotic factors (15%).These results demonstrate diverse thermoregulation patterns across global extratropics, with most ecosystems negating the ‘limited homeothermy’ hypothesis, but their thermoregulation still occurs, implying that slope < 1 orTc < Taare not necessary conditions for plant thermoregulation.},
journal = {New Phytologist},
volume = {238},
number = {3},
publisher = {Wiley-Blackwell},
author = {Guo, Zhengfei and Still, Christopher J. and Lee, Calvin K. F. and Ryu, Youngryel and Blonder, Benjamin and Wang, Jing and Bonebrake, Timothy C. and Hughes, Alice and Li, Yan and Yeung, Henry C. H. and Zhang, Kun and Law, Ying Ki and Lin, Ziyu and Wu, Jin},
}
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