Stem CO2 Efflux as an Indicator of Forests’ Productivity in Relict Juniper Woodlands (Juniperus thurifera L.) of Southern Spain

There are considerable uncertainties about the C cycle in semi-arid ecosystems. Hence, studies that have focused on Juniperus in Mediterranean woodlands are non-existent. This study provides a survey of the effect of the juniper woodland type (young and mature woodlands; joint effect of maturity and forest productivity) on stem respiration. We checked the seasonal variation of stem respiration, evaluating the effects of stem temperature on stem CO2 efflux. For this, we measured the stem CO2 efflux (µmol CO2 m−2 s−1) over the four seasons on 16 junipers using LI-6400 equipment. The results showed that in the more productive site (young woodland), the stem CO2 efflux was higher. This variable followed a clear seasonal trend, being higher during the spring and progressively decreasing in cold periods. In both juniper woodlands, and especially in the older forests, the Q10 coefficients were low (<2), typical of cold forests and slow-growing species. The exponential model also confirmed that the Q10 was significantly higher in young juniper trees. Thus, stem CO2 efflux was an indicator of the growth in this juniper woodland that is well adapted to a semi-arid climate.

A Novel Sensor for In Situ Detection of Freeze-Thaw Characteristics in Plants from Stem Temperature and Water Content Measurements

Freezing is a typical abiotic stress on plants, which can induce physiological damages of plants. A better understanding of plant freeze-thaw characteristics contributes to solving some hot issues in plant physiology, such as cold resistance and cold acclimation. This article presents a novel sensor for in situ detection of freeze-thaw characteristics in plants based on stem temperature and water content. The measuring circuit of stem temperature was designed based on constant current source and platinum resistance. The measuring circuit of stem water content was designed based on standing wave ratio and the dielectric properties of stem tissue. The temperature resolution of the compound sensor is less than 0.1°C. The MAE and RMSE of temperature measurement are approximately 0.57°C and 0.65°C, respectively. The volumetric water content resolution of the compound sensor is less than 0.05%. The MAE and RMSE of volumetric water content measurement are approximately 1.59% and 1.81%, respectively. Moreover, a mathematical model for describing the freeze-thaw characteristics of plant stem was established and solved based on the compound sensor. Then, some freeze-thaw indicators including stem water content, ice content, freezing depth, freezing velocity, thawing depth, and thawing velocity were solved and used to interpret the freeze-thaw rules of plant stem. It can be concluded that the freeze-thaw velocity is closely related to the physicochemical properties of plant stem which also change dynamically in the freeze-thaw cycle.

A taxonomic evaluation of Astrophytum myriostigma var. Nudum (Cactaceae)

The absence of epidermal trichomes has been used as a diagnostic character to distinguish Astrophytum myriostigma var. nudum from other infraspecific taxa. In the Huizache region of San Luis Potosi, Mexico, between the elevations of 1320 m and 1700 m, the local populations of A. myriostigma are polymorphic, comprised of nude, semi-nude, and flecked plants. However, this polymorphism is non-discrete as there is considerable variation and intermediacy among plants. Also, the proportion of nude plants increases gradually with elevation, which suggests clinal variation correlated with altitude. Exclusively nude populations are currently known only from near Santa Rita del Rucio (? 1710 m) and south of Entronque Huizache (? 1750 m). Farther south, flecked plants were recorded at 1726 m elevation at 6 km E of Guadalcazar, and to the north near El Realejo flecked plants occur as high as 1920 m. At localities southeast of the Sierra San Pedro (Sierra Guadalcazar), nude and semi-nude plants are absent or present at relatively low frequencies in local populations. Epidermal trichomes provide shading and reflectance that protects the cactus stem against excessive solar radiation and moderates stem temperature. The majority of nude A. myriostigma growing in exposed locations at the margins of Hechtia colonies were found to suffer from chlorophyll degeneration due to excessive exposure to solar radiation. A comparative morphological study did not find any characters which can be used in combination to diagnose the var. nudum. Given the lack of a suite of discrete, or nearly discrete diagnostic characters, and given that exclusively nude populations do not have a definable geographic distribution we suggest that the nude phenotype should be treated taxonomically as a “form” rather than as a geographical “variety,” or subspecies.

Methods for Calibration of Specimen Temperature During In Situ Transmission Electron Microscopy Experiments

One of the biggest challenges for in situ heating transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) is the ability to measure the local temperature of the specimen accurately. Despite technological improvements in the construction of TEM/STEM heating holders, the problem of being able to measure the real sample temperature is still the subject of considerable discussion. In this study, we review the present literature on methodologies for temperature calibration. We analyze calibration methods that require the use of a thermometric material in addition to the specimen under study, as well as methods that can be performed directly on the specimen of interest without the need for a previous calibration. Finally, an overview of the most important characteristics of all the treated techniques, including temperature ranges and uncertainties, is provided in order to provide an accessory database to consult before an in situ TEM/STEM temperature calibration experiment.

Role of Bark Color on Stem Temperature and Carbohydrate Management during Dormancy Break in Persian Walnut

Temperature is assumed to be the principal regulatory signal that determines the end of dormancy and resumption of growth. Indirect evidence that stem temperature interferes with phenology comes from the common orchard practice of painting stems to protect them from disease. This work studies the effects of application of white paint to the stems of persian walnut (Juglans regia) trees on winter stem temperature, carbohydrate content, and spring phenology. Painting bark resulted in the delay of budbreak by several days, higher nonstructural carbohydrate (NSC) concentrations in the bark and wood of painted extension shoots and changes in the spatial gradients of NSC during budbreak. The demands of maintenance respiration exceeded mobilization from local carbon pools during bud development suggesting a potential role of carbohydrate transport during spring budbreak in persian walnut. Painting provides an exciting perspective for mitigating effects of milder winter in orchards. The effect of reducing diurnal and spatial temperature variability limits early budbreak, NSC depletion associated with intense maintenance respiration, freeze–thaw cycles and frost dehardening.

Improved precision of hydraulic conductance measurements using a Cochard rotor in two different centrifuges

An improved way ofcalculating hydraulic conductance (K) in a Cochard cavitron is described. UsuallyK is determined by measuring how fast water levels equilibrate between two reservoirs while a stem spins in a centrifuge. A regression of log meniscus position versus time was used to calculate K and this regression method was compared to the old technique that takes the average of discrete values. Results of a hybrid Populus 84K shows that the relative error of the new approach is significantly lower than the old technique by 4~5 times. The new computational method results in a relative error less than 0.5% or 0.3% from 8 or 12 points of measurement, respectively. The improved precision of K measurement also requires accurate assessment of stem temperature because temperature changes K by 2.4% oC-1. A computational algorithm for estimating stem temperature stability in a cavitron rotor was derived. This algorithm provides information on how long it takes stem temperature to be known to within an error of ±0.1oC.

Infrared Camera Measurements Reveal Diurnal Variation in the Effect of Mechanically Induced Internal Voids on Stem Temperatures of Small Trees Passively Heated by the Sun

The relationship between stem temperature measured by an infrared (IR) camera and a tree’s internal condition was proposed as a basis for diagnosing potentially hazardous defects in the landscape. Before practical application, this diagnostic technique needs clarification to guide expectations of its resolution and precision. In this study, cylindrical voids of varying size were created in 5 cm diameter stems of Dracaena fragrans and Syzygium grande by mechanically removing tissue from specimens in an outdoor nursery, and the surface temperature of these plants was measured twice daily at 0830h and 1830h using an IR camera. The collected IR images were analyzed using a concurrent mixed methods approach with qualitative image evaluation and quantitative temperature analysis where the temperature distributions of stems containing internal voids were compared to those without defects. For both species, there was no difference in stem temperatures, as observed in IR images, among any experimental plants at 0830h, but an anomalous temperature reduction was exclusively apparent at 1830h near the 3.8 cm void, occupying 76% stem cross-sectional area. There was also a larger decrease in the linear temperature trend (0.34°C–0.51°C) near this void margin compared with other treatments, although this was more pronounced in the monocot species than eudicot. The remaining treatments did not exhibit stem temperatures visibly different from the control. Under experimental conditions, the technique identified relatively large internal defects, but the reduced heat capacity of stems containing such defects is only apparent in the evening after being passively heated by the sun.