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1. Monitoring cotton water status with microtensiometers

   https://doi.org/10.1007/s00271-024-00930-w  

   Christenson, Clay G; Gohardoust, Mohammad R; Calleja, Sebastian; Thorp, Kelly R; Tuller, Markus; Pauli, Duke (April 2024, Irrigation Science)

   Abstract Stem water potential (Ψ_stem) is a key indicator for assessing plant water status, which is crucial in understanding plant health and productivity. However, existing measurement methods for Ψ_stem, characterized by destructiveness and intermittency, limit its applicability. Microtensiometers, an emerging plant-based sensor, offer continuous monitoring capabilities and have shown success in certain vine and tree species. In this study, we investigate the efficacy of microtensiometers ability to monitor the Ψ_stemof cotton (Gossypium hirsutumL.) under three distinct irrigation treatments in Maricopa, Arizona, an extremely hot, arid environment. We analyze the diurnal dynamics of Ψ_stemacross the irrigation regimes and compare these measurements with midday leaf water potentials (Ψ_leaf) obtained using a dewpoint potentiometer. Our results demonstrate that the microtensiometer-derived Ψ_stemclosely follows known diurnal patterns of Ψ_leaf, tracking with vapor pressure deficit (VPD) and responding to variations in irrigation levels and soil moisture content. Time cross-correlation analysis reveals an 80-minute lag in Ψ_stemresponse to changing VPD under non-water limiting conditions, which shortens under water-limiting conditions. Additionally, we establish a robust linear relationship (R²_adj = 0.82) between Ψ_stemand Ψ_leaf, with this relationship strengthening as water availability decreases. Notably, we observe mean gradients of 1.2 and 0.06 MPa between soil vs. stem and stem vs. leaf water potentials, respectively. Moreover, Ψ_stemdata proves to be more sensitive in distinguishing between irrigation treatments earlier in the growing season compared to Ψ_leaf, leaf temperature and leaf gas exchange parameters. These findings highlight the utility of microtensiometers as valuable tools for monitoring water status in smaller-stemmed row crops such as cotton. 

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2. Using Ly α Absorption to Measure the Intensity and Variability of z  ∼ 2.4 Ultraviolet Background Light

   https://doi.org/10.3847/1538-4357/adc0f9  

   Weiss, Laurel H; Gebhardt, Karl; Davis, Dustin; Mentuch_Cooper, Erin; Lujan_Niemeyer, Maja; Qezlou, Mahdi; Mirza_Khanlari, Mahan; Ciardullo, Robin; Farrow, Daniel; Gawiser, Eric; et al (April 2025, The Astrophysical Journal)

   Abstract We present measurements ofz ∼ 2.4 ultraviolet (UV) background light using Lyαabsorption from galaxies atz ∼ 2–3 in the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) database. Thanks to the wide area of this survey, we also measure the variability of this light across the sky. The data suggest an asymmetric geometry where integrated UV light from background galaxies is absorbed by Hiwithin the halo of a foreground galaxy, in a configuration similar to damped Lyαsystems. Using stacking analyses of over 400,000 HETDEX LAE spectra, we argue that this background absorption is detectable in our data. We also argue that the absorption signal becomes negative due to HETDEX’s sky-subtraction procedure. The amount that the absorption is oversubtracted is representative of thez ∼ 2.4 UV contribution to the overall extragalactic background light (EBL) at Lyα. Using this method, we determine an average intensity (inνJ_νunits) of 12.9 ± 3.7 nW m⁻²sr⁻¹at a median observed wavelength of 4134 Å, or a rest-frame UV background intensity of 508 ± 145 nW m⁻²sr⁻¹atz ∼ 2.4. We find that this flux varies significantly depending on the density of galaxies in the field of observation. Our estimates are consistent with direct measurements of the overall EBL. 

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3. Global response patterns of plant photosynthesis to nitrogen addition: A meta‐analysis

   https://doi.org/10.1111/gcb.15071  

   Liang, Xingyun; Zhang, Tong; Lu, Xiankai; Ellsworth, David S; BassiriRad, Hormoz; You, Chengming; Wang, Dong; He, Pengcheng; Deng, Qi; Liu, Hui; et al (June 2020, Global Change Biology)

   Abstract A mechanistic understanding of plant photosynthetic response is needed to reliably predict changes in terrestrial carbon (C) gain under conditions of chronically elevated atmospheric nitrogen (N) deposition. Here, using 2,683 observations from 240 journal articles, we conducted a global meta‐analysis to reveal effects of N addition on 14 photosynthesis‐related traits and affecting moderators. We found that across 320 terrestrial plant species, leaf N was enhanced comparably on mass basis (N_mass, +18.4%) and area basis (N_area, +14.3%), with no changes in specific leaf area or leaf mass per area. Total leaf area (TLA) was increased significantly, as indicated by the increases in total leaf biomass (+46.5%), leaf area per plant (+29.7%), and leaf area index (LAI, +24.4%). To a lesser extent than for TLA, N addition significantly enhanced leaf photosynthetic rate per area (A_area, +12.6%), stomatal conductance (g_s, +7.5%), and transpiration rate (E, +10.5%). The responses ofA_areawere positively related with that ofg_s, with no changes in instantaneous water‐use efficiency and only slight increases in long‐term water‐use efficiency (+2.5%) inferred from¹³C composition. The responses of traits depended on biological, experimental, and environmental moderators. As experimental duration and N load increased, the responses of LAI andA_areadiminished while that ofEincreased significantly. The observed patterns of increases in both TLA andEindicate that N deposition will increase the amount of water used by plants. Taken together, N deposition will enhance gross photosynthetic C gain of the terrestrial plants while increasing their water loss to the atmosphere, but the effects on C gain might diminish over time and that on plant water use would be amplified if N deposition persists. 

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4. An Approximate Criterion for Morphological Transformations in Small Vapor Grown Ice Crystals

   https://doi.org/10.1175/JAS-D-23-0131.1  

   Harrington, Jerry Y; Pokrifka, Gwenore F (February 2024, Journal of the Atmospheric Sciences)

   Abstract Observations and measurements show that crystals remain relatively compact at low ice supersaturations, but become increasingly hollowed and complex as the ice supersaturation rises. Prior measurements at temperatures >−25°C indicate that the transition from compact, solid ice to morphologically complex crystals occurs when the excess vapor density exceeds a threshold value of about 0.05 g m⁻³. A comparable threshold is not available at low temperatures. A temperature-dependent criterion for the excess vapor density threshold (Δρ_thr) that defines morphological transformations to complex ice is derived from laboratory measurements of vapor grown ice at temperatures below −40°C. This criterion depends on the difference between the equilibrium vapor density of liquid () and ice (ρ_ei) multiplied by a measurement-determined constant,. The new criterion is consistent with prior laboratory measurements, theoretical estimates, and it reproduces the classical result of about 0.05 g m⁻³above −25°C. Since Δρ_thrdefines the excess vapor density above which crystals transition to a morphologically complex (lower density) growth mode, we can estimate the critical supersaturation (s_crit) for step nucleation during vapor growth. The derived values ofs_critare consistent with previous measurements at temperatures above −20°C. No direct measurements ofs_critare available for temperatures below −40°C; however, our derived values suggest some measurement-based estimates may be too high while estimates from molecular dynamics simulations may be too low. 

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5. Plant functional types and tissue stoichiometry explain nutrient transfer in common arbuscular mycorrhizal networks of temperate grasslands

   https://doi.org/10.1111/1365-2435.14634  

   Dawson, Hilary Rose; Shek, Katherine L; Maxwell, Toby M; Reed, Paul B; Bomfim, Barbara; Bridgham, Scott D; Bohannan, Brendan_J M; Silva, Lucas_C R (October 2024, Functional Ecology)

   Abstract Plants and mycorrhizal fungi form mutualistic relationships that affect how resources flow between organisms and within ecosystems. Common mycorrhizal networks (CMNs) could facilitate preferential transfer of carbon and limiting nutrients, but this remains difficult to predict. Do CMNs favour fungal resource acquisition at the expense of plant resource demands (a fungi‐centric view), or are they passive channels through which plants regulate resource fluxes (a plant‐centric view)?We used stable isotope tracers (¹³CO₂and¹⁵NH₃), plant traits, and mycorrhizal DNA to quantify above‐ and below‐ground carbon and nitrogen transfer between 18 plant species along a 520‐km latitudinal gradient in the Pacific Northwest, USA.Plant functional type and tissue stoichiometry were the most important predictors of interspecific resource transfer. Of ‘donor’ plants, 98% were¹³C‐enriched, but we detected transfer in only 2% of ‘receiver’ plants. However, all donors were¹⁵N‐enriched and we detected transfer in 81% of receivers. Nitrogen was preferentially transferred to annuals (0.26 ± 0.50 mg N per g leaf mass) compared with perennials (0.13 ± 0.30 mg N per g leaf mass). This corresponded with tissue stoichiometry differences.SynthesisOur findings suggest that plants and fungi that are located closer together in space and with stronger demand for resources over time are more likely to receive larger amounts of those limiting resources. Read the freePlain Language Summaryfor this article on the Journal blog. 

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