Responses of Ecological Stoichiometric Characteristics of Carbon, Nitrogen, and Phosphorus to Periodic Submergence in Mega-Reservoir: Growth of Taxodium distichum and Taxodium ascendens

Ecological stoichiometric studies can be useful for managing the deteriorated riparian zones of mega-reservoirs in which nutrients significantly impact the balanced vegetation cover. The present study aims to explore the effects of periodic submergence on the stoichiometric ecological characteristics of carbon (C), nitrogen (N), and phosphorus (P), as well as the growth conditions of two leading conifer species (Taxodium distichum and Taxodium ascendens) in the hydro-fluctuation zone of the Three Gorges Reservoir (TGR) region, China. The stoichiometrical contents of C, N, and P in fine roots, leaves, and branches, and the growth conditions of T. distichum and T. ascendens were measured in July 2019. The results showed that periodic submergence affected the stoichiometric characteristics and growth conditions of these two woody species, and the impact was restrained, but both grew well. The effects of inundation on the C, N, and P ecological stoichiometric characteristics differed in different parts of trees. In general, the C contents showed the following pattern: leaves > branches > fine roots. The N and P content showed the following pattern: leaves > fine roots > branches, while the C/N and C/P ratios showed an opposite trend to that of N and P. The N and P content in all parts of T. distichum (with means of 17.18 and 1.70 g/kg for leaves, 4.80 and 0.57 g/kg for branches, and 6.88 and 1.10 g/kg for fine roots, respectively) and T. ascendens (with means of 14.56 and 1.87 g/kg for leaves, 5.03 and 0.63 g/kg for branches, and 8.17 and 1.66 g/kg for fine roots, respectively) were higher than the national average level (with means of 14.14 and 1.11 g/kg for leaves, 3.04 and 0.31 g/kg for branches, and 4.85 and 0.47 g/kg for fine roots, respectively). Except for N and P contents in the leaves of T. distichum, there was a significant correlation between N and P elements in other parts (p < 0.05). Nevertheless, the N/P ratio (10.15, 8.52, 6.44, and 7.93, 8.12, 5.20 in leaves, branches, and fine roots of T. distichum and T. ascendens, respectively) was lower than the critical ratio of 14. The growth conditions of T. distichum and T. ascendens were significantly negatively correlated with their leaf C contents and significantly positively correlated with their fine root N and P contents. This study showed that T. distichum and T. ascendens could maintain their normal growth needs by properly allocating nutrients between different organs to adapt to the long periodic submergence in the hydro-fluctuation zone of the TGR region.

More-than-human Infrastructure for Just Resilience: Learning from, Working with, and Designing for Bald Cypress Trees (Taxodium distichum) in the Mississippi River Delta

Humans design infrastructure for human needs, with limited regard for the needs of nonhumans such as animals and plants. Humans also often fail to recognise nonhuman lifeforms such as trees as fellow engineers designers, or architects, even though the contribution of trees to ecosystem services is well established and their right to justice ought to be recognised. Studies have shown that flood-control infrastructure near the Mississippi River inadvertently left Southern Louisiana more vulnerable to coastal threats. We examine this characteristic outcome and identify infrastructural injustices in multispecies communities. Based on theories in philosophy and design supported by historical analyses, we defend the proposals to extend 1) the understanding of resilience to include more-than-human communities; and 2) the notion of justice to include non-human stakeholders. The reframing in more-than-human terms is already under way in a variety of disciplines. However, these efforts rarely extend into considerations of practical design and have attracted criticism for insufficient engagement with historical processes and the accumulations of power and responsibility. To illustrate these injustices, we trace the history of bald cypress trees (Taxodium distichum) in the Mississippi River Delta and show how infrastructure impacted the trees. This analysis demonstrates that designs that do not consider the needs of vulnerable stakeholders can cause harm in multispecies communities. In response, we propose that humans can work to improve infrastructural resilience by including humans and nonhumans as collaborators.

Аутфітосозологічне оцінювання дендроекзотів відділу Pinophyta ботанічного саду Чернівецького національного університету імені Юрія Федьковича

Здійснено інтегральне аутфітосозологічне оцінювання 41 виду деревних інтродуцентів відділу Pinophyta, які ростуть у ботанічному саду Чернівецького національного університету ім. Юрія Федьковича в умовах відкритого ґрунту. Відповідно до значень вирахуваного для кожного виду аутфітосозологічного індексу досліджувані дендроекзоти віднесено до чотирьох аутфітосозологічних класів (II-V); найбільше видів (27) увійшли до ІІІ класу. Для рослин кожного із аутфітосозологічних класів охарактеризовано ознаки, які найістотніше впливають на фітосозологічну цінність видів: категорія раритетності у Червоному списку МСОП, фітогеографічне та історичне значення, регіональна репрезентативність та кількість штучних природоохоронних об'єктів у межах Чернівецької області, де росте той чи інший вид. Зокрема, найчастіше у дендропарках, парках-пам'ятках садово-паркового мистецтва та у складі пам'яток природи Чернівецької області трапляються Thuja occidentalis L. (30 місцезростань), Pinus strobus L. (22), Platycladus orientalis (L.) Franco (19 місцезростань), і в межах 12-14 природоохоронних об'єктів – Pinus nigra J. F. Arnold, Ginkgo biloba L., Chamaecyparis pisifera (Siebold & Zucc.) Endl. Відзначено, що 51,2 % із досліджуваних видів трапляються, окрім ботанічного саду Чернівецького національного університету, також у дендропарках, парках-пам'ятках садово-паркового мистецтва та пам'ятках природи місцевого значення Чернівецької області. Раритетні види деревних інтродуцентів відділу Pinophyta цінні як резерв генетичного матеріалу. Тому особливої охорони потребують ті з них, які перебувають під загрозою зникнення (категорія раритетності у Червоному списку МСОП – CR, EN та VU), а також ті, що увійшли до ІІ аутфітосозологічного класу (Taxodium distichum (L.) Rich., Sequoiadendron giganteum (Lindl.) J. Buchholz, Metasequoia glyptostroboides Hu & W. C. Cheng, Picea koyamae Shiras.), та частина видів, віднесених до ІІІ класу (зокрема, ті з них, які представлені 1-2 особинами лише у ботанічному саду Чернівецького національного університету, і не здатні розмножуватися насіннєвим шляхом). Під час розроблення рекомендацій з ефективної охорони досліджуваних деревних інтродуцентів варто звертати увагу на екологічні вимоги видів, оскільки від цього значною мірою залежить успішність росту і розвитку інтродуцентів.

Contrasting responses of DOM leachates to photodegradation observed in plant species collected along an estuarine salinity gradient

A series of abiotic processes affected by salinity changes involve light-mediated reactions and different degradation pathways of organic compounds, including altered photo-oxidation, photo-degradation, and photolysis of organic matter (OM). Sunlight is known to degrade, oxidize, or mineralize dissolved organic matter (DOM) in waterways, creating large changes in compositional structure of DOM near the water surface and ultimately in the mixed layer. DOM derived from various vegetation types has differing levels of susceptibility to photolytic degradation depending on initial chemical composition and in what matrix degradation takes place (e.g., salinity). The effect of sunlight and salinity on degradation of leached DOM derived from three dominant vegetative species, Avicennia germinans, Juncus romerianus, and Taxodium distichum, along a riverine continuum in northeast Florida was determined. Leachates from these three sources in a deionized or seawater matrix were irradiated in a continuous flow-through photolytic system over the course of 20 h. Avicennia germinans and Juncus roemerinaus DOM readily degraded as indicated by decreases in absorbance across all wavelengths during the irradiation period, while Taxodium distichum DOM was found to increase in absorbance across all wavelengths in the freshwater matrix, but not in seawater. PARAFAC analysis indicated differences in photochemical components and % change of absorbance and fluorescence over time indicate the importance and variability of individual contributions to the DOM pool across an estuarine continuum. This work characterizes the photochemical properties of three individual DOM sources, exhibits the need for further research on this topic, and explores the salinity effect on photo-degradation of DOM from unique plant-derived DOM.