• Despite the importance of nonstructural carbohydrates (NSC) for growth and survival in woody plants, we know little about whole-tree NSC storage. The conventional theory suggests that NSC reserves ...will increase over the growing season and decrease over the dormant season. Here, we compare storage in five temperate tree species to determine the size and seasonal fluctuation of whole-tree total NSC pools as well as the contribution of individual organs.
• NSC concentrations in the branches, stemwood, and roots of 24 trees were measured across 12 months. We then scaled up concentrations to the whole-tree and ecosystem levels using allometric equations and forest stand inventory data.
• While whole-tree total NSC pools followed the conventional theory, sugar pools peaked in the dormant season and starch pools in the growing season. Seasonal depletion of total NSCs was minimal at the whole-tree level, but substantial at the organ level, particularly in branches. Surprisingly, roots were not the major storage organ as branches stored comparable amounts of starch throughout the year, and root reserves were not used to support springtime growth.
• Scaling up NSC concentrations to the ecosystem level, we find that commonly used, process-based ecosystem and land surface models all overpredict NSC storage.
Vegetation phenology controls the seasonality of many ecosystem processes, as well as numerous biosphere-atmosphere feedbacks. Phenology is also highly sensitive to climate change and variability. ...Here we present a series of datasets, together consisting of almost 750 years of observations, characterizing vegetation phenology in diverse ecosystems across North America. Our data are derived from conventional, visible-wavelength, automated digital camera imagery collected through the PhenoCam network. For each archived image, we extracted RGB (red, green, blue) colour channel information, with means and other statistics calculated across a region-of-interest (ROI) delineating a specific vegetation type. From the high-frequency (typically, 30 min) imagery, we derived time series characterizing vegetation colour, including "canopy greenness", processed to 1- and 3-day intervals. For ecosystems with one or more annual cycles of vegetation activity, we provide estimates, with uncertainties, for the start of the "greenness rising" and end of the "greenness falling" stages. The database can be used for phenological model validation and development, evaluation of satellite remote sensing data products, benchmarking earth system models, and studies of climate change impacts on terrestrial ecosystems.
This paper describes the operational methods to achieve and measure both deep-soil heating (0-3m) and whole-ecosystem warming (WEW) appropriate to the scale of tall-stature, high-carbon, boreal ...forest peatlands. The methods were developed to allow scientists to provide a plausible set of ecosystem-warming scenarios within which immediate and longer-term (1 decade) responses of organisms (microbes to trees) and ecosystem functions (carbon, water and nutrient cycles) could be measured. Elevated CO2 was also incorporated to test how temperature responses may be modified by atmospheric CO2 effects on carbon cycle processes. The WEW approach was successful in sustaining a wide range of aboveground and belowground temperature treatments (+0, +2.25, +4.5, +6.75 and +9°C) in large 115m2 open-topped enclosures with elevated CO2 treatments (+0 to +500ppm). Air warming across the entire 10 enclosure study required ∼ 90% of the total energy for WEW ranging from 64283 mega Joules (MJ)d-1 during the warm season to 80102MJd-1 during cold months. Soil warming across the study required only 1.3 to 1.9% of the energy used ranging from 954 to 1782MJd-1 of energy in the warm and cold seasons, respectively. The residual energy was consumed by measurement and communication systems. Sustained temperature and elevated CO2 treatments were only constrained by occasional high external winds. This paper contrasts the in situ WEW method with closely related field-warming approaches using both aboveground (air or infrared heating) and belowground-warming methods. It also includes a full discussion of confounding factors that need to be considered carefully in the interpretation of experimental results. The WEW method combining aboveground and deep-soil heating approaches enables observations of future temperature conditions not available in the current observational record, and therefore provides a plausible glimpse of future environmental conditions.
•A security monitoring camera is used to measure broadband spectral properties.•This is an inexpensive approach to 4-channel (red, green, blue, NIR) imaging.•These data can be used to calculate an ...NDVI-type index, “camera NDVI”.•Our method is applied to long-term monitoring of vegetation phenology in the field.•Compared to RGB imagery, new information is obtained by inclusion of the NIR band.
Sensor-based monitoring of vegetation phenology is being widely used to quantify phenological responses to climate variability and change. Digital repeat photography, in particular, can characterize the seasonality of canopy greenness. However, these data cannot be directly compared to satellite vegetation indices (e.g. NDVI, the normalized difference vegetation index) that require information about vegetation properties at near-infrared (NIR) wavelengths. Here, we develop a new method, using an inexpensive, NIR-enabled camera originally designed for security monitoring, to calculate a “camera NDVI” from sequential visible and visible+NIR photographs. We use a lab experiment for proof-of-concept, and then test the method using a year of data from an ongoing field campaign in a mixed temperate forest. Our analysis shows that the seasonal cycle of camera NDVI is almost identical to that of NDVI measured using narrow-band radiometric instruments, or as observed from space by the MODIS platform. This camera NDVI thus provides different information about the state of the canopy than can be obtained using only visible-wavelength imagery. In addition to phenological monitoring, our method should be useful for a variety of applications, including continuous monitoring of plant stress and quantifying vegetation responses to manipulative treatments in large field experiments.
Understanding and predicting the relationship between leaf temperature (
) and air temperature (
) is essential for projecting responses to a warming climate, as studies suggest that many forests are ...near thermal thresholds for carbon uptake. Based on leaf measurements, the limited leaf homeothermy hypothesis argues that daytime
is maintained near photosynthetic temperature optima and below damaging temperature thresholds. Specifically, leaves should cool below
at higher temperatures (i.e., > ∼25-30°C) leading to slopes <1 in
/
relationships and substantial carbon uptake when leaves are cooler than air. This hypothesis implies that climate warming will be mitigated by a compensatory leaf cooling response. A key uncertainty is understanding whether such thermoregulatory behavior occurs in natural forest canopies. We present an unprecedented set of growing season canopy-level leaf temperature (
) data measured with thermal imaging at multiple well-instrumented forest sites in North and Central America. Our data do not support the limited homeothermy hypothesis: canopy leaves are warmer than air during most of the day and only cool below air in mid to late afternoon, leading to
/
slopes >1 and hysteretic behavior. We find that the majority of ecosystem photosynthesis occurs when canopy leaves are warmer than air. Using energy balance and physiological modeling, we show that key leaf traits influence leaf-air coupling and ultimately the
/
relationship. Canopy structure also plays an important role in
dynamics. Future climate warming is likely to lead to even greater
, with attendant impacts on forest carbon cycling and mortality risk.
•Continuous measurement of forest canopy temperature is reported.•Measurement errors are characterized and best practices are suggested.•Canopy temperature deviation from air temperature varies by ...species and conditions.•Thermal cameras offer new datasets for understanding vegetation energy balances.
Leaf temperature is an elementary driver of plant physiology, ecology and ecosystem productivity. Individual leaf temperature may deviate strongly from air temperature, and may vary throughout the canopy. Measurements of leaf temperature, conducted at a high spatial and temporal resolution, can improve our understanding of leaf water loss, stomatal conductance, photosynthetic rates, phenology, and atmosphere-ecosystem exchanges. However, continuous high-resolution measurement of leaf temperature outside of a controlled environment is difficult and rarely done. Here, thermal infrared cameras are used to measure leaf temperatures. We describe two long-term field measurement sites: one in a temperature deciduous forest, and the other in a subalpine conifer forest. The considerations and constraints for deploying such cameras are discussed and the temperature errors are typically +/–1°C or smaller (σ=0.60°C, 2σ=1.20°C). Lastly, we compare leaf temperature by species and height at hourly to multi-seasonal timescales and show that on average, leaf temperature is warmer than air temperature in a temperate forest. Leaf temperature can be uniform or heterogeneous across a scene, depending on canopy structure, leaf habit, and meteorology. With this data, we verify that leaf temperature follows classic expectations, yet exhibits noteworthy departures that require additional study and theoretical consideration.
Summary
Leaf optical properties impact leaf energy balance and thus leaf temperature. The effect of leaf development on mid‐infrared (MIR) reflectance, and hence thermal emissivity, has not been ...investigated in detail.
We measured a suite of morphological characteristics, as well as directional‐hemispherical reflectance from ultraviolet to thermal infrared wavelengths (250 nm to 20 µm) of leaves from five temperate deciduous tree species over the 8 wk following spring leaf emergence.
By contrast to reflectance at shorter wavelengths, the shape and magnitude of MIR reflectance spectra changed markedly with development. MIR spectral differences among species became more pronounced and unique as leaves matured. Comparison of reflectance spectra of intact vs dried and ground leaves points to cuticular development – and not internal structural or biochemical changes – as the main driving factor. Accompanying the observed spectral changes was a drop in thermal emissivity from about 0.99 to 0.95 over the 8 wk following leaf emergence.
Emissivity changes were not large enough to substantially influence leaf temperature, but they could potentially lead to a bias in radiometrically measured temperatures of up to 3 K. Our results also pointed to the potential for using MIR spectroscopy to better understand species‐level differences in cuticular development and composition.
We present a new microfluidic method to coalesce pairs of surfactant-stabilized water-in-fluorocarbon oil droplets. We achieve this through the local addition of a poor solvent for the surfactant, ...perfluorobutanol, which induces cohesion between droplet interfaces causing them to merge. The efficiency of this technique is comparable to existing techniques providing an alternative method to coalesce pairs of droplets.
Nonstructural carbohydrates (NSCs) play a critical role in plant physiology and metabolism, yet we know little about their distribution within individual organs such as the stem. This leaves many ...open questions about whether reserves deep in the stem are metabolically active and available to support functional processes. To gain insight into the availability of reserves, we measured radial patterns of NSCs over the course of a year in the stemwood of temperate trees with contrasting wood anatomy (ring porous vs diffuse porous). In a subset of trees, we estimated the mean age of soluble sugars within and between different organs using the radiocarbon (14C) bomb spike approach. First, we found that NSC concentrations were the highest and most seasonally dynamic in the outermost stemwood segments for both ring-porous and diffuse-porous trees. However, while the seasonal fluctuation of NSCs was dampened in deeper stemwood segments for ring-porous trees, it remained high for diffuse-porous trees. These NSC dynamics align with differences in the proportion of functional sapwood and the arrangement of vessels between ring-porous and diffuse-porous trees. Second, radial patterns of 14C in the stemwood showed that sugars became older when moving toward the pith. The same pattern was found in the coarse roots. Finally, when taken together, our results highlight how the radial distribution and age of NSCs relate to wood anatomy and suggest that while deeper, and likely older, reserves in the stemwood fluctuated across the seasons, the deepest reserves at the center of the stem were not used to support tree metabolism under usual environmental conditions.
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