To understand the effect of increasing atmospheric temperatures on monoterpene emissions from mature trees, we measured the monoterpene emission rate, monoterpene precursor content, and the SPAD ...value of Acer palmatum, a mature tree grown at three different field sites. The annual mean temperature differed by intervals of 3 °C among the three sites from 10.6 °C to 17.7 °C, depending on the site elevation. The short-term monoterpene emission rate of A. palmatum depended on both the leaf temperature and the light intensity. The growth temperature did not affect the monoterpene emissions in response to short-term variations in temperature and light intensity. The highest standard monoterpene emission rate, Ms, was observed from July to August, but this rate did not differ among the three sites. The Ms showed clear seasonal variation, whereas the monoterpene precursor content did not show them. The trend of the Ms was similar to that of the SPAD, as both values depend on leaf phenology. In A. palmatum, a warming of approximately 3 °C caused the start date of the monoterpene emissions to commence two to three weeks earlier, and end date of the monoterpene emissions to be delayed by two to three weeks. The cumulative temperature method could be used to predict the start and end dates of the monoterpene emissions. To estimate the annual monoterpene emissions, a temperature and light intensity dependent emission model was modified to incorporate the effect of growth temperature on seasonal patterns of Ms. Annual monoterpene emissions were found to increase linearly with annual mean temperature. For each 1 °C of warming, the annual monoterpene emissions from A. palmatum increased by approximately 15%. Our results suggest that the effect of growth temperature on monoterpene emissions should be considered when predicting monoterpene emissions in response to global warming in the foreseeable future.
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•Acer palmatum branch was collected from three different elevations.•Higher ambient air temperature prolonged the monoterpene emission period.•Differences in growth temperature did not affect the maximum emission in summer.•For each 1 °C of warming, annual monoterpene emissions increased by about 15%.•Growth temperature is an important factor that determines monoterpene emissions.
Successful control and prevention of biological invasions depend on identifying traits of non‐native species that promote fitness advantages in competition with native species. Here, we show that, ...among 76 native and non‐native woody plants of deciduous forests of North America, invaders express a unique functional syndrome that combines high metabolic rate with robust leaves of longer lifespan and a greater duration of annual carbon gain, behaviours enabled by seasonally plastic xylem structure and rapid production of thin roots. This trait combination was absent in all native species examined and suggests the success of forest invaders is driven by a novel resource‐use strategy. Furthermore, two traits alone—annual leaf duration and nuclear DNA content—separated native and invasive species with 93% accuracy, supporting the use of functional traits in invader risk assessments. A trait syndrome reflecting both fast growth capacity and understorey persistence may be a key driver of forest invasions.
We show that non‐native, invasive woody plants of North American deciduous forests express a unique functional syndrome combining traits associated with both high growth potential and high shade tolerance. This syndrome was absent in all native species examined and involves an integrated growth strategy reflecting leaf, stem and root traits.
Tree phenology mediates land–atmosphere mass and energy exchange and is a determinant of ecosystem structure and function. In the dry tropics, including African savannas, many trees grow new leaves ...during the dry season – weeks or months before the rains typically start. This syndrome of pre-rain green-up has long been recognized at small scales, but the high spatial and interspecific variability in leaf phenology has precluded regional generalizations.
We used remote sensing data to show that this precocious phenology is ubiquitous across the woodlands and savannas of southern tropical Africa.
In 70% of the study area, green-up preceded rain onset by > 20 d (42% > 40 d). All the main vegetation formations exhibited pre-rain green-up, by as much as 53 ± 18 d (in the wet miombo). Green-up showed low interannual variability (SD between years = 11 d), and high spatial variability (> 100 d).
These results are consistent with a high degree of local phenological adaptation, and an insolation trigger of green-up. Tree–tree competition and niche separation may explain the ubiquity of this precocious phenology. The ubiquity of pre-rain green-up described here challenges existing model representations and suggests resistance (but not necessarily resilience) to the delay in rain onset predicted under climate change.
Tropical dry forests are composed of tree species with different drought coping strategies and encompass heterogeneous site conditions. Actual water use will be controlled by soil moisture ...availability. In a premontane dry forest of southern Ecuador, tree water use patterns of four tree species of different phenologies were studied along an elevational gradient, in which soil moisture availability increases with altitude. Main interest was the influence of variation in soil moisture, vapor pressure deficit, species (representing phenology), elevation, and tree diameter on water use. Special emphasis was put on the stem succulent, deciduous
, as high water use rates and drought coping involving stem succulence was to be expected. Tree water use rates increased linearly with diameter across species at high soil water content. However, when soil moisture declined, sap flux densities of the species responded differently. The stem succulent, deciduous
and other deciduous tree species reduced sap flux sensitively, whereas sap flux densities of the evergreen (broad leaved)
were increasing. This was also reflected in diurnal hysteresis loops of sap flux vs. vapor pressure deficit (VPD) of the air. Under dry soil conditions,
and other deciduous tree species had much smaller areas in the hysteresis loop, whereas the area of
was largely enhanced compared to wet conditions. The evergreen
potentially had access to deeper soil water resources as water use patterns suggest that top soil drought was tolerated. The deciduous species followed a drought avoidance strategy by being leafless in the dry season. The stem succulent deciduous
flushed leaves at the end of the dry season before the rainy season began and also re-flushed early in the dry season after a rain event; however, water use rates at this occasion remained low.
was also ready for fast and strong response in water use when conditions were most favorable during the wet season. The study thus indicates a strong influence of species' drought coping strategy on water use patterns in tropical dry forests.
Amazonian evergreen forests show distinct canopy phenology and photosynthetic seasonality but the climatic triggers are not well understood. This imposes a challenge for modeling leaf phenology and ...photosynthesis seasonality in land surface models (LSMs) across Amazonian evergreen forest biome. On continental scale, we tested two climatic triggers suggested by site observations, vapor pressure deficit (VPD), and short‐wave incoming radiation (SW) for defining leaf shedding and incorporated VPD‐ and SW‐triggered new canopy phenology modules in the ORCHIDEE LSM (hereafter VPD‐AP and SW‐AP versions). Our results show that both VPD and SW are plausible precursors of large scale litterfall seasonality across the basin by comparing against in situ data from 14 sites. Specially, both VPD‐AP and SW‐AP correctly capture the increases in litterfall during the early dry season, followed by a flush of new leaves with increasing photosynthetic rates during the later dry season. The VPD‐AP version performs better than the SW‐AP version in capturing a dry‐season increase of photosynthesis across the wet Amazonia areas where mean annual precipitation exceeds 2,000 mm yr−1, consistent with previous satellite data analysis. Both VPD‐AP and SW‐AP model versions perform well in northern, central and southern Amazon regions where the SW seasonality is unimodal, but miss the seasonality of satellite GPP proxies in the eastern region off the coast of Guyana shield where SW seasonality is bimodal. Our findings imply that atmospheric dryness and sunlight availability likely explain the seasonality of leaf shedding and leaf flush processes, respectively, and consequently control canopy photosynthesis in Amazonian evergreen forests.
Key Points
The new canopy phenology module captures the large‐scale spatial and seasonal patterns of Amazonian forest photosynthesis
Vapor pressure deficits and sunlight explain seasonality of Amazonian forest phenology and photosynthesis
This study for the first time integrates site‐level process knowledge to match diagnostic evidence at large scale across Amazonian forests
Current remote sensing studies of phenology have been limited to coarse spatial or temporal resolution and often lack a direct link to field measurements. To address this gap, we compared remote ...sensing methodologies using Landsat Thematic Mapper (TM) imagery to extensive field measurements in a mixed northern hardwood forest. Five vegetation indices, five mathematical fits to model a continuous temporal response, and a suite of threshold estimates for “start of spring/season” (SOS) assessments were compared to field measurements of bud burst stage and hemispherical photo derived canopy structural metrics (transparency, leaf area index, greenness). Results indicated that a four-parameter logistic model based on at least five spring coverages of the Enhanced Vegetation Index (EVI) and a SOS threshold of 0.3 was most closely related to field metrics and most accurate in predicting the date of full leaf out. Plot level SOS was predicted with a mean absolute error of 11days for all species and elevation combinations, but improved to 9days for hardwood dominated plots and 7days for sugar maple dominated plots. Mean absolute error was improved to 8days when forest type (mixed, conifer hardwood) was used to refine predictions. The consistency of prediction errors across forest types indicates that while overall accuracy across pixels may be low, inter-annual comparisons of changes in phenology on a pixel basis may provide accurate assessments of changes in phenology over time. This was confirmed by application to seven years of independent phenology data predicted with 12days of mean absolute error. However, image availability will be a limiting factor in areas of frequent cloud cover.
•Vegetation indices are most closely correlated with visual phenology rankings.•A 4-term logistic fit using an EVI threshold of 0.3 predicts SOS most accurately.•The presence of conifers and mixed hardwood species reduces SOS accuracy.•SOS prediction can vary up to 9days based on image availability.
Midday depressions in stomatal conductance (gₛ) and photosynthesis are common in plants. The aim of this study was to understand the hydraulic determinants of midday gₛ, the coordination between leaf ...and stem hydraulics and whether regulation of midday gₛ differed between deciduous and evergreen broadleaf tree species in a subtropical cloud forest of Southwest (SW) China. We investigated leaf and stem hydraulics, midday leaf and stem water potentials, as well as midday gₛ of co‐occurring deciduous and evergreen tree species. Midday gₛ was correlated positively with midday stem water potential across both groups of species, but not with midday leaf water potential. Species with higher stem hydraulic conductivity and greater daily reliance on stem hydraulic capacitance were able to maintain higher stem water potential and higher gₛ at midday. Deciduous species exhibited significantly higher stem hydraulic conductivity, greater reliance on stem capacitance, higher stem water potential and gₛ at midday than evergreen species. Our results suggest that midday gₛ is more associated with midday stem than with leaf water status, and that the functional significance of stomatal regulation in these broadleaf tree species is probably for preventing stem xylem dysfunction.
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