Summary
Tropical ecosystems have the highest levels of biodiversity, cycle more water and absorb more carbon than any other terrestrial ecosystem on Earth. Consequently, these ecosystems are ...extremely important components of Earth’s climatic system and biogeochemical cycles. Plant hydraulics is an essential discipline to understand and predict the dynamics of tropical vegetation in scenarios of changing water availability. Using published plant hydraulic data we show that the trade‐off between drought avoidance (expressed as deep‐rooting, deciduousness and capacitance) and hydraulic safety (P50 – the water potential when plants lose 50% of their maximum hydraulic conductivity) is a major axis of physiological variation across tropical ecosystems. We also propose a novel and independent axis of hydraulic trait variation linking vulnerability to hydraulic failure (expressed as the hydraulic safety margin (HSM)) and growth, where inherent fast‐growing plants have lower HSM compared to slow‐growing plants. We surmise that soil nutrients are fundamental drivers of tropical community assembly determining the distribution and abundance of the slow‐safe/fast‐risky strategies. We conclude showing that including either the growth‐HSM or the resistance‐avoidance trade‐off in models can make simulated tropical rainforest communities substantially more vulnerable to drought than similar communities without the trade‐off. These results suggest that vegetation models need to represent hydraulic trade‐off axes to accurately project the functioning and distribution of tropical ecosystems.
Foliar water uptake (FWU) is a common water acquisition mechanism for plants inhabiting temperate fog-affected ecosystems, but the prevalence and consequences of this process for the water and carbon ...balance of tropical cloud forest species are unknown.
We performed a series of experiments under field and glasshouse conditions using a combination of methods (sap flow, fluorescent apoplastic tracers and stable isotopes) to trace fog water movement from foliage to belowground components of Drimys brasiliensis. In addition, we measured leaf water potential, leaf gas exchange, leaf water repellency and growth of plants under contrasting soil water availabilities and fog exposure in glasshouse experiments to evaluate FWU effects on the water and carbon balance of D. brasiliensis saplings.
Fog water diffused directly through leaf cuticles and contributed up to 42% of total foliar water content. FWU caused reversals in sap flow in stems and roots of up to 26% of daily maximum transpiration. Fog water transported through the xylem reached belowground pools and enhanced leaf water potential, photosynthesis, stomatal conductance and growth relative to plants sheltered from fog.
Foliar uptake of fog water is an important water acquisition mechanism that can mitigate the deleterious effects of soil water deficits for D. brasiliensis.
Many tropical montane cloud forest (TMCF) trees are capable of foliar water uptake (FWU) during leaf-wetting events. In this study, we tested the hypothesis that maintenance of leaf turgor during ...periods of fog exposure and soil drought is related to species’ FWU capacity.
We conducted several experiments using apoplastic tracers, deuterium labeling and leaf immersion in water to evaluate differences in FWU among three common TMCF tree species. We also measured the effect of regular fog exposure on the leaf water potential of plants subjected to soil drought and used these data to model species’ response to long-term drought.
All species were able to absorb water through their leaf cuticles and/or trichomes, although the capacity to do so differed between species. During the drought experiment, the species with higher FWU capacity maintained leaf turgor for a longer period when exposed to fog, whereas the species with lower FWU exerted tighter stomatal regulation to maintain leaf turgor. Model results suggest that without fog, species with high FWU are more likely to lose turgor during seasonal droughts.
We show that leaf-wetting events are essential for trees with high FWU, which tend to be more anisohydric, maintaining leaf turgor during seasonal droughts.
Faster growth in tropical trees is usually associated with higher mortality rates, but the mechanisms underlying this relationship are poorly understood. In this study, we investigate how tree growth ...patterns are linked with environmental conditions and hydraulic traits, by monitoring the cambial growth of 9 tropical cloud forest tree species coupled with numerical simulations using an optimization model. We find that fast‐growing trees have lower xylem safety margins than slow‐growing trees and this pattern is not necessarily linked to differences in stomatal behaviour or environmental conditions when growth occurs. Instead, fast‐growing trees have xylem vessels that are more vulnerable to cavitation and lower density wood. We propose the growth ‐ xylem vulnerability trade‐off represents a wood hydraulic economics spectrum similar to the classic leaf economic spectrum, and show through numerical simulations that this trade‐off can emerge from the coordination between growth rates, wood density, and xylem vulnerability to cavitation. Our results suggest that vulnerability to hydraulic failure might be related with the growth‐mortality trade‐off in tropical trees, determining important life history differences. These findings are important in furthering our understanding of xylem hydraulic functioning and its implications on plant carbon economy.
We investigate the relationships between tropical cloud forest trees hydraulic traits and their growth patterns. Our results indicate the existence of a growth‐hydraulic safety trade‐off that has several important ecological and physiological implications. This trade‐off can be explained using the fast–slow plant economic theory and represented with a profit optimization model. Our findings are an important contribution to the development of a wood economic spectrum theory for tropical trees
In Brazil, the campos rupestres occur over the Brazilian shield, and are characterized by acidic nutrient‐impoverished soils, which are particularly low in phosphorus (P). Despite recognition of the ...campos rupestres as a global biodiversity hotspot, little is known about the diversity of P‐acquisition strategies and other aspects of plant mineral nutrition in this region. To explore nutrient‐acquisition strategies and assess aspects of plant P nutrition, we measured leaf P and nitrogen (N) concentrations, characterized root morphology and determined the percentage arbuscular mycorrhizal (AM) colonization of 50 dominant species in six communities, representing a gradient of soil P availability. Leaf manganese (Mn) concentration was measured as a proxy for carboxylate‐releasing strategies. Communities on the most P‐impoverished soils had the highest proportion of nonmycorrhizal (NM) species, the lowest percentage of mycorrhizal colonization, and the greatest diversity of root specializations. The large spectrum of leaf P concentration and variation in root morphologies show high functional diversity for nutritional strategies. Higher leaf Mn concentrations were observed in NM compared with AM species, indicating that carboxylate‐releasing P‐mobilizing strategies are likely to be present in NM species. The soils of the campos rupestres are similar to the most P‐impoverished soils in the world. The prevalence of NM strategies indicates a strong global functional convergence in plant mineral nutrition strategies among severely P‐impoverished ecosystems.
BACKGROUND AND AIMS: Foliar water uptake has been reported for different species, including conifers living in drought-prone environments. We conducted three experiments to determine whether leaves ...might absorb mist water and how this affects the water relations of well-watered and water-stressed young plants of Araucaria angustifolia. METHODS: Three independent experiments were conducted using well-watered and water-stressed plants: immersion of shoot in water for the quantification of water uptake, the short-term exposure of plants to deuterium-enriched artificial mist, followed by the evaluation of plant water status and δ²H of xylem and soil water, and the use of the heat ratio method to measure the sap flow in saplings submitted to artificial mist. RESULTS: Foliar water uptake was demonstrated in both groups of plants, but only water-stressed plants showed a significant improvement of shoot water status. Isotope analyses indicated release of mist water in water-stressed plants rhizosphere’s, and measurements of sap flow pointed to flow reversals in saplings exposed to mist, after a soil drought period. CONCLUSIONS: The results confirm the capacity of A. angustifolia for absorbing water deposited in its leaves and demonstrate that leaf-absorbed water can be transported through the xylem to the soil close to the roots and improve plant water status.
Trees from tropical montane cloud forest (TMCF) display very dynamic patterns of water use. They are capable of downwards water transport towards the soil during leaf-wetting events, likely a ...consequence of foliar water uptake (FWU), as well as high rates of night-time transpiration (Enight) during drier nights. These two processes might represent important sources of water losses and gains to the plant, but little is known about the environmental factors controlling these water fluxes. We evaluated how contrasting atmospheric and soil water conditions control diurnal, nocturnal and seasonal dynamics of sap flow in Drimys brasiliensis (Miers), a common Neotropical cloud forest species. We monitored the seasonal variation of soil water content, micrometeorological conditions and sap flow of D. brasiliensis trees in the field during wet and dry seasons. We also conducted a greenhouse experiment exposing D. brasiliensis saplings under contrasting soil water conditions to deuterium-labelled fog water. We found that during the night D. brasiliensis possesses heightened stomatal sensitivity to soil drought and vapour pressure deficit, which reduces night-time water loss. Leaf-wetting events had a strong suppressive effect on tree transpiration (E). Foliar water uptake increased in magnitude with drier soil and during longer leaf-wetting events. The difference between diurnal and nocturnal stomatal behaviour in D. brasiliensis could be attributed to an optimization of carbon gain when leaves are dry, as well as minimization of nocturnal water loss. The leaf-wetting events on the other hand seem important to D. brasiliensis water balance, especially during soil droughts, both by suppressing tree transpiration (E) and as a small additional water supply through FWU. Our results suggest that decreases in leaf-wetting events in TMCF might increase D. brasiliensis water loss and decrease its water gains, which could compromise its ecophysiological performance and survival during dry periods.
Purpose. Justification of the feasibility of using new types of drainage materials, such as Concrete Canvas (CC), under the upper structure of the railway permanent way. Methodology. The tasks were ...solved by a complex research method, including analysis and generalization of literary and patent sources, analytical, experimental studies, using computer and mathematical modeling methods. Tests were conducted with and without the CC layer in a multi-level shear box. After the shear test, the specimens were also tested for load-bearing capacity (E2, according to the Hungarian standard) and particle breakage. The contact surface between the bottom of the ballast and the CC was measured using a precision 3D laser scanner (GOM ATOS) and visualized graphically using AutoCAD software. Findings. Experimental testing of the vertical load during connection and analysis compared with the test results of geocomposite/geogrid structures, internal shear resistance, and other parameters proved the structure’s higher load-bearing capacity with the CC layer. Based on the results, the Concrete Canvas structure provides higher reinforcement than the average geogrid type. Originality. The advantages of using new Concrete Canvas materials in the structure of a railway track have been demonstrated for the first time to provide greater internal shear resistance than the average for geogrids. Practical value. These results may provide primary data for using Concrete Canvas in railway tracks and superstructures in the future.
Purpose. To prove that the GCCM (geosynthetic cementitious composite mat) – type Concrete Canvas (CC) – is an adequate supplementary layer on the top of the subgrade. As its drainage function is ...known, this article tries to prove the reinforcement possibility. This layer is relatively thin; nevertheless, it can behave like the geogrids. It is the main path to finding out the opportunity of the interlocking effect and its impact on the railway ballast’s inner shear resistance. Methodology. The laboratory measurements were performed in a multi-level shear box, which allows simulating the multi-level shift of the ballast layer. The tests were planned with and without the CC layer. After shearing, the samples were also tested for load-bearing capacity (E2; according to the Hungarian Standard) and particle breakage. On the other hand, the contact surface between the lowest part of the ballast and CC was also measured by a sophisticated 3D laser scanner (GOM ATOS) and graphically by AutoCAD software. Findings. After the results of the laboratory experiments are analyzed, the following parameters are calculated and determined: 1) the reinforcement ratio as the tangent of the inner shear resistance curves in the 5–15 mm horizontal shearing interval as well as the area under graphs by integration in the 0–40 mm interval; 2) the change in load-bearing capacity of the layer-structure with and without CC; 3) the amount of the cement particles; 4) the amount of the broken particles; 5) contact surface between the lowest layer of ballast and CC; 6) flatness of CC sheets after shearing. Based on the results, the Concrete Canvas provides significant reinforcement to the railway ballast. Originality. Any other type of measurement with Concrete Canvas in a multi-level shear box is unknown. The topic is unique. Practical value. In the future, these results may provide baseline data to verify the suitability of the Concrete Canvas in the railway sub- or superstructure for various types of transport.
Purpose. The authors’ aim is to summarize the results of relevant international publications and, based on these, to give a comprehensive review about the modern ballasted tracks’ substructure. ...Methodology. This article is a start of a PhD research, which means it was proceeded by a secondary research. At first, the substructure and its protection layers were summarized, after that the geosynthetic cementious composite mat materials, especially the Concrete Canvas are discussed. Findings. The experiences of the geosynthetics’ and other protection layers’ functions, show that a possible using of the GCCM (geosynthetic cementious composite mat) under the ballast can be a good solution for renewing short sections in the railway tracks. Originality. One of the authors – namely Balázs Eller – is a PhD student at Szechenyi Istvan University in Gyor (Hungary). His research topic is the reinforcement possibilities of railway substructure with the usage of special (mainly cement-bonded) layers. This article was written to collect and summarize the up to date knowledge related to modern ballasted railway tracks’ substructure to be able to determine the following research ways and possibilities at this topic. The research plan will be sentenced in the near future, as well as the required laboratory and field tests will be prepared. Practical value. As expectation, after having executed the related research, the advantages and disadvantages of GCCM layers in the railway substructure will be able to defined, as well as factual deterioration process can be determined related to the ballasted tracks and their geometrical stability.
Мета. Основна мета цього дослідження – узагальнити результати відповідних міжнародних публікацій і на їх основі дати вичерпний огляд нижньої будови сучасних залізничних колій з баластним шаром. Методика. Ця стаття є початком аспірантського дослідження; відповідно існує друга частина дослідження. Спочатку автори підводять підсумки досліджень про нижню будову колії та її захисні шари, після чого аналізують матеріали геосинтетичного цементного складеного мата, особливо – бетонне полотно. Результати. Досвід використання функцій геосинтетичних та інших захисних шарів показує, що можливе використання геосинтетичного цементного складеного мата (ГЦСМ) під баластним шаром може стати хорошим рішенням для поновлення коротких ділянок залізничних колій. Наукова новизна. Один з авторів, а саме Балаш Еллер, є аспірантом в Університеті Іштвана Сечені у Дьєрі (Угорщина). Тема його дослідження – можливість зміцнення нижньої будови залізничної колії з використанням спеціальних (переважно цементних) шарів. Ця стаття була написана для збору та узагальнення нових знань про нижню будову сучасних баластних шарів залізничних колій, щоб можна було визначити наступні шляхи та можливості дослідження цієї теми. План досліджень буде сформульовано найближчим часом, також будуть підготовлені необхідні лабораторні та польові випробування. Практична значимість. Як і очікувалося, після проведення відповідних досліджень можна буде визначити переваги й недоліки використання шарів ГЦСМ у нижній будові залізничних колій, а також визначити фактичний процес зносу, пов’язаний із баластними коліями та їх геометричною стабільністю.
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