Relative humidity is a key factor in the acclimation of the stomatal response to CO2

Abstract Modeling stomatal control is critical for predicting forest responses to the changing environment and hence the global water and carbon cycles. A trait-based stomatal control model that optimizes carbon gain while avoiding hydraulic risk has been shown to perform well in response to drought. However, the model’s performance against changes in atmospheric CO2, which is rising rapidly due to human emissions, has yet to be evaluated. The present study tested the gain–risk model’s ability to predict the stomatal response to CO2 concentration with potted water birch (Betula occidentalis Hook.) saplings in a growth chamber. The model’s performance in predicting stomatal response to changes in atmospheric relative humidity and soil moisture was also assessed. The gain–risk model predicted the photosynthetic assimilation, transpiration rate and leaf xylem pressure under different CO2 concentrations, having a mean absolute percentage error (MAPE) of 25%. The model also predicted the responses to relative humidity and soil drought with a MAPE of 21.9% and 41.9%, respectively. Overall, the gain–risk model had an MAPE of 26.8% compared with the 37.5% MAPE obtained by a standard empirical model of stomatal conductance. Importantly, unlike empirical models, the optimization model relies on measurable physiological traits as inputs and performs well in predicting responses to novel environmental conditions without empirical corrections. Incorporating the optimization model in larger scale models has the potential for improving the simulation of water and carbon cycles.

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New representation of water activity based on a single solute specific constant to parameterize the hygroscopic growth of aerosols in atmospheric models

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-5429-2012 ◽

2012 ◽

Vol 12 (12) ◽

pp. 5429-5446 ◽

Cited By ~ 8

Author(s):

S. Metzger ◽

B. Steil ◽

L. Xu ◽

J. E. Penner ◽

J. Lelieveld

Keyword(s):

Relative Humidity ◽

Water Activity ◽

Atmospheric Chemistry ◽

Reference Model ◽

Climate Modeling ◽

Cloud Condensation Nuclei ◽

Hygroscopic Growth ◽

Wide Range ◽

Kohler Theory ◽

Key Factor

Abstract. Water activity is a key factor in aerosol thermodynamics and hygroscopic growth. We introduce a new representation of water activity (aw), which is empirically related to the solute molality (μs) through a single solute specific constant, νi. Our approach is widely applicable, considers the Kelvin effect and covers ideal solutions at high relative humidity (RH), including cloud condensation nuclei (CCN) activation. It also encompasses concentrated solutions with high ionic strength at low RH such as the relative humidity of deliquescence (RHD). The constant νi can thus be used to parameterize the aerosol hygroscopic growth over a wide range of particle sizes, from nanometer nucleation mode to micrometer coarse mode particles. In contrast to other aw-representations, our νi factor corrects the solute molality both linearly and in exponent form x · ax. We present four representations of our basic aw-parameterization at different levels of complexity for different aw-ranges, e.g. up to 0.95, 0.98 or 1. νi is constant over the selected aw-range, and in its most comprehensive form, the parameterization describes the entire aw range (0–1). In this work we focus on single solute solutions. νi can be pre-determined with a root-finding method from our water activity representation using an aw−μs data pair, e.g. at solute saturation using RHD and solubility measurements. Our aw and supersaturation (Köhler-theory) results compare well with the thermodynamic reference model E-AIM for the key compounds NaCl and (NH4)2SO4 relevant for CCN modeling and calibration studies. Envisaged applications include regional and global atmospheric chemistry and climate modeling.

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Stomatal response to decreased relative humidity constrains the acceleration of terrestrial evapotranspiration

Environmental Research Letters ◽

10.1088/1748-9326/ab9967 ◽

2020 ◽

Vol 15 (9) ◽

pp. 094066

Author(s):

Mingzhong Xiao ◽

Zhongbo Yu ◽

Dongdong Kong ◽

Xihui Gu ◽

Ivan Mammarella ◽

...

Keyword(s):

Relative Humidity ◽

Stomatal Response

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Relative Humidity of Blended Cement Pastes in Sealed during Hydration

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.539.60 ◽

2013 ◽

Vol 539 ◽

pp. 60-63

Author(s):

Dan Jin ◽

Wu Yao ◽

Yi Chen

Keyword(s):

Relative Humidity ◽

Blended Cement ◽

Mineral Admixture ◽

Mineral Admixtures ◽

Cement Pastes ◽

Cement Ratio ◽

Water To Cement Ratio ◽

Cement Based Materials ◽

Different Ages ◽

Key Factor

As an important part of cement-based materials，water plays an important role during hydration and self-desiccation so the measurement of relative humidity or internal moisture in the research of cement-based materials is vital. In this paper, the measurement samples are blended cement pastes in sealed with different water to cement ratios and different kind of mineral admixtures. The measurement was taken at different ages during hydration to investigate the changes of relative humidity. The result showed that the water to cement ratio was the key factor of affecting the change of relative humidity, and the effect of mineral admixture kind was not very obvious in this experiment.

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Strong effect of relative humidity on dryland lichens under climate change

10.5194/egusphere-egu21-12245 ◽

2021 ◽

Author(s):

Philipp Porada ◽

Selina Baldauf ◽

Jose Raggio ◽

Fernando Maestre ◽

Britta Tietjen

Keyword(s):

Climate Change ◽

Relative Humidity ◽

Experimental Studies ◽

Early Morning ◽

Ecosystem Functions ◽

Lichen Cover ◽

Key Factor ◽

Underlying Mechanisms ◽

Experimental Findings

Manipulative experiments typically show a decrease in dryland biocrust cover and altered species composition under climate change. Biocrust-forming lichens, such as the globally distributed Diploschistes diacapsis, are particularly affected and show a decrease in cover with simulated climate change. However, the underlying mechanisms are not fully understood, and long-term interacting effects of different drivers are largely unknown due to the short-term nature of the experimental studies conducted so far. We addressed this gap and successfully parameterised a process-based model for D. diacapsis to quantify how changing atmospheric CO2 , temperature, rainfall amount and relative humidity affect its photosynthetic activity and cover. We also mimicked a long-term manipulative climate change experiment to understand the mechanisms underlying observed patterns in the field. The model reproduced observed experimental findings: warming reduced lichen cover, whereas less rainfall had no effect on lichen performance. This warming effect was caused by the associated decrease in relative humidity and non-rainfall water inputs, which are major water sources for biocrust-forming lichens. Warming alone, however, increased cover because higher temperatures promoted photosynthesis during early morning hours with high lichen activity. When combined, climate variables showed non-additive effects on lichen cover, and effects of increased CO2 levelled off with decreasing levels of relative humidity. Our results show that a decrease in relative humidity, rather than an increase in temperature, may be the key factor for the survival of the lichen D. diacapsis under climate change and that effects of increased CO2 levels might be offset by a reduction in non-rainfall water inputs in the future. Because of a global trend towards warmer and drier air and the widespread global distribution of D. diacapsis, this will affect lichen-dominated dryland biocrust communities and their role in regulating ecosystem functions worldwide.

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The Stomatal Response to Reduced Relative Humidity Requires Guard Cell-Autonomous ABA Synthesis

Current Biology ◽

10.1016/j.cub.2012.11.022 ◽

2013 ◽

Vol 23 (1) ◽

pp. 53-57 ◽

Cited By ~ 240

Author(s):

Hubert Bauer ◽

Peter Ache ◽

Silke Lautner ◽

Joerg Fromm ◽

Wolfram Hartung ◽

...

Keyword(s):

Relative Humidity ◽

Guard Cell ◽

Stomatal Response ◽

Aba Synthesis

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