Trees In Autumn Research Articles

Effects of Tree Leaf Color on Human Physical and Mental Recovery from a Looking-Up Perspective

Numerous studies have demonstrated the benefits of understory spaces and plants on human well-being, but most spatial research has focused on a horizontal perspective. Additionally, there is a lack of research on the effects of plant color on human recovery, especially with respect to color proportions. This study classifies the leaf colors of trees in autumn, which are observed from a looking-up perspective, into green, red, and yellow. On this basis, we created monochromatic, two-color, and three-color groups with varying color proportions to assess their recovery effects and preferences. A total of 30 participants participated in this experiment, and their physiological, psychological, and preference-related indicators were evaluated. The results revealed that the following. (1) The two-color groups had the greatest reduction effect on systolic blood pressure. Monochromatic groups were most effective at reducing diastolic blood pressure. The three-color groups had the greatest effect on lowering the pulse rate. (2) EEG responses varied by color type. (3) The three-color groups had the best recovery effects on the psychological measures. (4) The three-color groups were most favored by participants, with a red–yellow–green ratio of 0.2/0.4/0.4 being the most preferred. These findings demonstrate the differing recovery potentials of various leaf color proportions from a looking-up perspective. This study can provide valuable references for the planning and design of urban forest parks, supplementing the theoretical foundation and research framework for evaluating and creating environments that meet people’s restorative needs.

Alternative uses for urban autumn tree leaves: A case study in profitability and greenhouse gas emissions for the city of Berlin

Autumn tree leaves collect as waste on many city streets every year. In the city of Berlin, they are usually collected and transported for composting as their final treatment, which emits greenhouse gases (GHG) into the atmosphere. This study assesses alternative end uses of autumn tree leaves in order explore the potential of reducing GHG emissions while producing electric energy from residual biomass. It uses a combination of partial life-cycle assessments and net present value (NPV) to explore the different net GHG emissions and economic benefits of using autumn tree leaves for the following scenarios: anaerobic digestion (biogas), gasification, and co-firing. Assuming the use of 36,000 tonnes of leaves per year, co-firing in existing power plants shows the highest NPV, of between 10.3 million and 12.1 million euros for a 10-year lifetime, in line with the phase-out of coal combustion in Germany. It also results in the lowest net GHG emissions, with savings of between 252,000 and 144,000 tonnes of CO2eq. Gasification in new plants resulted in similar NPVs, estimated at between 9.80 and 9.86 million euros over a 20-year investment horizon, but lower emissions savings of 178,000 to 127,000 tonnes of CO2eq. Biogas production showed high emissions savings of 204,000 to 203,000 tonnes of CO2eq, but a much lower NPV of between 2.3 and 2.5 million euros. Composting was the only scenario with positive net GHG emissions. The amount of energy retrieved from the conversion technologies and the electrical tariff applied were the main drivers of these results. Other aspects that can shape the results include the availability of infrastructure and transport distances. The results are highly sensitive in both cases to the dryness of the leaves, while electricity tariffs influenced the economic performance considerably.

A NAC transcription factor, PpNAC1, regulates the expression of PpMYB10.1 to promote anthocyanin biosynthesis in the leaves of peach trees in autumn

Red leaves in autumn are characteristic of a very early-maturing ripening variety of peach (Prunus persica). Analysis of the genetic factors and molecular mechanisms associated with the red-leaf phenotype can help breed peach very early maturing peach varieties. This study investigated the mechanisms underlying the red- and green-leaf phenotypes in autumn. Red compounds accumulated in the older but not younger leaves in the extremely early-maturing peach variety, ‘99-30-33’, and the leaves of the medium-maturing variety, ‘Zhongtao5 (CP5)’. Metabolic analysis showed that cyanidin-3-O-glucoside was the most abundant anthocyanin in the red leaves. The segregation of the progenies obtained from crossing revealed that the red leaves are a unique hereditary phenomenon not in line with Mendel’s law. BSA-seq and RNA-seq analyses suggest that PpNAC1 was essential for enhancing anthocyanin biosynthesis and was highly upregulated in red than in green leaves. Similar to PpNAC1, the anthocyanin activator, PpMYB10.1, was the only gene highly expressed in red leaves. Moreover, the functional genes involved in anthocyanin biosynthesis, such as Prunus persica Flavonoid 3'-hydroxylase (PpF3'H), Prunus persicaDihydroflavonol reductase (PpDFR), Prunus persica Leucoantho-cyanidin dioxygenase (Pp LDOX), Prunus persica Glutathione S-transferase (PpGST), and Prunus persica UDP-glucose, flavonoid-3-O-glucosyltransferase (PpUFGT), were upregulated in the older red leaves of 99-30-33 but downregulated in the younger 99-30-33 and green CP5 leaves. Yeast one-hybrid and dual-luciferase assays further confirmed that PpNAC1, which refers to 'Prunus persica NAC (NAM、A TAF1/2、CUC1/2)' bound to the promoter of PpMYB10.1, PpMYB10.1 stands for 'Prunus persica MYB (v-myb avian myeloblastosis viral) 10.1' and activated its expression along with those of PpGST and PpUFGT. These results provide insights into the mechanisms responsible for the development of red color in peach leaves in autumn.

Morwa biała (Morus alba L.) w ujęciu naukowym i kulturowym. Od jedwabnictwa do papieru

White mulberry (Morus alba L.) in scientific and cultural terms. From silk to paper Sericulture dates back to ancient China. Today it is defined as a branch of agriculture dealing with the cultivation of mulberry for the purpose of silkworm farming and the production of silk. Due to the fact that the mulberry silkworm larvae eat white mulberry leaves, it is a plant inextricably linked with silkworm farming and, consequently the production of silk. Although white mulberry is mainly associated with the cultivation of mulberry silkworms, thanks to its numerous and unique properties, it is a plant that can be used in various branches of the economy, as well as a research object of interest to scientists representing various fields of science. Thanks to the content of many bioactive substances, micro- and macroelements and vitamins, it has been used in herbal medicine, pharmacology and medicine. The richness of bioactive compounds makes it also an attractive raw material for the food and cosmetic industry. At the same time, due to its high energy value, mulberry belongs to the group of energy crops. Both the unique properties of mulberry and the traditions associated with its cultivation have made it a plant appreciated not only by science, but also left its mark in culture, as it has accompanied people for centuries. It is not surprising, therefore, that mulberry was recorded in poems, folk proverbs and on painting canvases, including the most famous brush by Vincent van Gogh – “Mulberry Tree in Autumn”. On the other hand, the processing of mulberry silkworm cocoons into high-quality yarns, and ultimately into delicate but durable fabrics, had a significant impact on the development of art. Both in terms of the so-called applied arts, but also those referred to as beaux-arts. And although the definitions of art have changed throughout history – regardless of period or era – silk was invariably appreciated by artists and craftsmen. Thanks to its properties, quality and aesthetics, silk fiber offers a wide range of possibilities for use in papermaking, which is also important in the cultural context.

‘Seasons of myths and hollow joylessness’

A few years ago I called one of my updates for this magazine ‘Season of myths and mellow fruitfulness’ with apologies to Keats. At the time I was writing about the myths that had built up around the Early Years Foundation Stage Profile. Sadly these persist, with many more being added. As I am actually writing this looking at some lovely Autumn trees, I am going to use the same quote slightly differently to address some myths that are currently increasingly common. So the Keats variation for this month is ‘Seasons of myths and hollow joylessness’. Again with apologies to Keats.

Photosynthetic Behavior of Argania spinosa (L.) Skeels Induced under Grazed and Ungrazed Conditions

The endemic Moroccan species Argania spinosa is considered the most grazed tree species in its distribution area. Since grazing exerts an important effect on plant performances, we attempted to explore the impact of grazing on A. spinosa. Thus, we performed a comparative field experiment where seasonal variations of gas exchange, photochemical efficiency, relative water content, photosynthetic pigment content, and stomatal features were assessed in grazed and ungrazed trees. The net photosynthetic rate was increased in grazed trees in spring and autumn, the favorable seasons. Enhancement of photosynthetic performance may be due to the high stomatal conductance registered in grazed trees. This mechanism may compensate for the lost leaf area, in order to recover from grazing stress. In addition, grazed trees exhibit a better photochemical efficiency, use water more economically and show lower oxidative stress. However, results obtained in summer show that the compensation mechanism could be limited by summer drought. Since the key to preserving the future of forests is sustainable forest management, our results suggest that proper grazing management can be a control tool to increase plant performance and improve species resilience.

The potential for biogas production from autumn tree leaves to supply energy and reduce greenhouse gas emissions – A case study from the city of Berlin

Autumn tree leaves are residues that are generated annually and usually composted, but can also be used as a feedstock for biogas production. In this study, three scenarios were analysed to evaluate the utilization of tree leaves from the city of Berlin in Germany: a) composting (business-as-usual scenario); b) biogas production; and c) the pretreatment of leaves before biogas production. For these scenarios, greenhouse gas emissions and energy production potential were calculated using the biological resource utilization impacts (BIORIM) model and considering the location and capacity of existing agricultural biogas plants. A special focus was set on the decay of leaves before their entry into the biogas plant. The overall comparison showed that the biogas-related scenarios had a better performance in terms of greenhouse gas emissions (-140.1 kg of CO2eq per tonne of leaves for biogas and -167.4 kg of CO2eq for pretreatment before biogas) than the business-as-usual scenario (49.0 kg of CO2eq for composting). The pretreated leaves resulted in the lowest net emissions and highest energy production per tonne of feedstock. Measures to reduce the decay of leaves, such as increasing the loading to the biogas plant or ensiling, resulted in lower net emissions and higher energy output. However, further research is needed regarding costs and logistical feasibility for proper implementation. Using tree leaves for biogas production would represent an alternative energy source, which could reduce the share of fossil fuels and electricity imports for the city of Berlin, where about 7.5 metric ton of pretreated leaves would meet the average electrical energy consumption of one person in one year.

The Australasian Cell Death Society (ACDS): celebrating 50 years of Australasian cell death research

The Australasian Cell Death Society (ACDS): celebrating 50 years of Australasian cell death research

Variation in Brant's oak (Quercus brantii Lindl.) leaf traits in response to pollution from a gas refinery in semiarid forests of western Iran.

Air pollution around refineries and factories is one of the major environmental challenges affecting forest ecosystems' health. Although there have been many studies on Iran's forest ecosystems, the physiological and morphological responses of Brant's oak (Quercus brantii Lindl.) leaves to the pollution of the gas refineries in the semiarid forests have not received much attention. We sampled healthy and mature leaves from four oak stands in different seasons (spring, summer, and autumn of 2019) and at various distances from the gas refinery (1,000, 1,500, 2,000, 2,500, and 10,000 m). The results showed that oak trees in different seasons and at different distances from the refinery had different physiological and morphological leaf trait responses to the pollution source. Oak trees with an air pollution tolerance index value of less than 11 were in a sensitive range to air pollution and can be used to biomonitor air pollution around the gas refinery in Zagros forests. Physiological traits in different seasons and at various distances in comparison with morphological traits (persistent reaction responses) were well distinguished from one another and were more affected by pollution. Oak trees in summer and autumn and at distances up to 2,500 m had rapid reaction responses, including oxidative stress indicators such as electrolyte leakage (EL), hydrogen peroxide, and different enzymatic and nonenzymatic antioxidants such as phenol, flavonoids, catalase, and proline. Because of their high sensitivity to atmospheric pollutant stresses, we recommend that these traits be used for rapid and low-cost environmental monitoring of pollution in different seasons and distances from pollution sources in semiarid ecosystems.

Stress Recovery of Campus Street Trees as Visual Stimuli on Graduate Students in Autumn.

Human stress recovery response to landscapes is under discussion in Chinese settings. The present study aimed to clarify the stress recovery effects of campus street trees on graduate students in autumn. A total of 150 participants (23.75 ± 1.01 years old) completed the Trier Social Stress Test (TSST) and were then randomly assigned to view one of five virtual environments, including the street trees Sophora japonica, Ginkgo biloba, Platanus acerifolia, Koelreuteria paniculata, and the indoor environment (control). Physiological responses were measured by R-R interval and electroencephalography (EEG). Psychological responses were examined through the state version of the State-Trait Anxiety Inventory (STAI-S) and the Perceived Restorativeness Scale (PRS). Results showed that R-R intervals significantly increased while viewing all street trees. Both alpha and beta brainwave activities while viewing S. japonica and G. biloba were remarkably higher than those while viewing P. acerifolia and K. paniculata. The STAI-S scores significantly decreased, and the positive PRS scores were registered after viewing street trees. We concluded that a brief virtual visual experience of campus street trees in autumn has stress recovery effects on graduate students, and the different levels of stress recovery are associated with different types of street trees.

Digital picture analysis for precision screening of sour cherry progeny for necrotic leaf tissue caused by Blumeriella jaapii

Sour cherry generally holds limited resistance to attack by cherry leaf spot fungus (Blumeriella jaapii) but differences in field performance are found between cultivars and in breeding progeny. Traditionally the degree of attack is estimated visually together with the type of reaction on the leaves. A more precise and less subjective method of evaluation is of interest for screening germplasm. A method of drying leaves, scanning dried leaves and a digital picture analysis protocol was developed to provide exact data on the percentage area of attacked necrotic tissue per leaf and with options of analysing size distribution of single necrotic spots to reveal detailed patterns of infections. The new method was used to characterize leaf attack in autumn on 20 individual leaves from single trees from a sour cherry breeding genepool of over 100 genotypes in a non-sprayed situation with high inoculum present. The percentage of necrotic leaf surface varied highly within the 20 leaves from one genotype, being dependent on the level of inoculum dispersal and air humidity/precipitation over time and space. The mean percentage of attacked leaf surface varied from 0 to almost 35% of total leaf area and the maximum from 0 to 60% necrotic leaf area, indicating the potential large impact on photosynthetic capacity in attacked trees. The distribution of and absolute size of single necrotic spots demonstrated differences in how individual genotypes react to infections, from small spots in tolerant genotypes to large collapsing necrotic spots in very susceptible genotypes. A comparison of attack data with the percentage of remaining leaves on a tree in autumn revealed that some genotypes retain leaves very late even if attacked by leaf spot disease. These trees may maintain a fairly high photosynthetic capacity even if some percentages of the leaf have become necrotic.

Contribution of previous year's leaf N and soil N uptake to current year's leaf growth in sessile oak

Abstract. The origin of N which contributes to the synthesis of N reserves of in situ forest trees in autumn and to the growth of new organs the following spring is currently poorly documented. To characterize the metabolism of various possible N sources (plant N and soil N), six distinct 20-year-old sessile oaks were 15N labelled by spraying 15NH415NO3: (i) on leaves in May, to label the N pool remobilized in the autumn for synthesis of reserves, (ii) on soil in the autumn, to label the N pool taken up from soil and (iii) on soil at the beginning of the following spring, to label the N pool taken up from soil in the spring. The partitioning of 15N in leaves, twigs, phloem, xylem, fine roots, rhizospheric soil and microbial biomass was followed during two growing seasons. Results showed a significant incorporation of 15N into the soil–tree system; more than 30 % of the administered 15N was recovered. Analysis of the partitioning clearly revealed that in autumn, roots' N reserves were formed from foliage 15N (73 %) and to a lesser extent from soil 15N (27 %). The following spring, 15N used for the synthesis of new leaves came first from 15N stored during the previous autumn, mainly from 15N reserves formed from foliage (95 %). Thereafter, when leaves were fully expanded, 15N uptake from the soil during the previous autumn and before budburst contributed to the formation of new leaves (60 %).

Autumn Algorithm-Computation of Hybridization Networks for Realistic Phylogenetic Trees.

A minimum hybridization network is a rooted phylogenetic network that displays two given rooted phylogenetic trees using a minimum number of reticulations. Previous mathematical work on their calculation has usually assumed the input trees to be bifurcating, correctly rooted, or that they both contain the same taxa. These assumptions do not hold in biological studies and "realistic" trees have multifurcations, are difficult to root, and rarely contain the same taxa. We present a new algorithm for computing minimum hybridization networks for a given pair of "realistic" rooted phylogenetic trees. We also describe how the algorithm might be used to improve the rooting of the input trees. We introduce the concept of "autumn trees", a nice framework for the formulation of algorithms based on the mathematics of "maximum acyclic agreement forests". While the main computational problem is hard, the run-time depends mainly on how different the given input trees are. In biological studies, where the trees are reasonably similar, our parallel implementation performs well in practice. The algorithm is available in our open source program Dendroscope3, providing a platform for biologists to explore rooted phylogenetic networks. We demonstrate the utility of the algorithm using several previously studied data sets.

Annual layers in river-bed sediment of a stagnant river-mouth area of the Kitagawa Brook, Central Japan

Abstract. The river mouth of Kitagawa Brook is normally stagnant because it is easily closed by sand and gravel transported by littoral currents of Biwa Lake, Japan. A new urban area exists in the basin and sewerage works were constructed in the early 1990s, so contaminated water with a bad odour had flowed into the brook before the sewerage works. To reduce the smell, the river mouth was excavated to narrow the channel in the early 1980s. Thus, river-bed sediment after this excavation only occurs at the river mouth. From the upper 24 cm of a sediment core, we found 19 strata of leaves which were supplied from deciduous trees in autumn. We also found several gravel layers which were supplied from the lake during severe storms. The combination of veins and gravel layers were reconstructed for about 20 years of sediment records with an error of two to three years.

Awards, Announcements, and News

On the September 19th, 2013 edition of CBC radio’s “Q”, the opening essay by guest host Kevin Sylvester (himself a “kid’s book” writer) focused on why “kiddy litter” gets such short shrift in Canada compared to other countries. He notes that Winnipeg-born, Toronto-trained Jon Klassen won 2 Caldecott medals this year for “This is not my hat” and “Extra yarn.” Kevin asks, “where is our ‘Canada Reads’ for kids?” and suggests we go to cbc.ca/books and click on “kids.” Hear Kevin’s 2-minute essay (http://www.cbc.ca/q/popupaudio.html?clipIds=2407373814)or read it here and find out what kid’s books he writes to boot: (http://kevinarts.blogspot.ca/2013/09/my-q-opening-essay.html)Speaking of children’s book awards, you might have heard of the Silver Birch awards from the Ontario Library Association that have been around for 20 years. But did you know there was a whole “forest of reading” intended to recognize Canadian authors and books, “contribute to the financial stability of the Canadian publish industry, and provide a literacy enhancement tool? Other tree awards include the Blue Spruce, Red Maple, White Pine, Evergreen, Golden Oak, Tamarac, and Peuplier. This would be a great time to find out more because the 2014 nominees are out with an award presentation planned for May 14, 2014. https://www.accessola.org/OLAWEB/Forest_of_Reading/Welcome/OLAWEB/Forest_of_Reading/Welcome.aspx or www.accessola.com/forestAnother group working to increase the culture of reading in Canada is the National Reading Campaign. They have a new website and media package here: http://www.nationalreadingcampaign.ca/. They gather lots of interesting information including their National Reading Plan which starts, “Reading is essential to the quality of our lives and to our ability to take our place as citizens in a democracy.” There is “research” section devoted to studies about the benefits of reading. Among the various “facts” highlighted for the website: “Reading is 68% better at reducing stress than listening to music, 100% more effective than drinking a cup of tea, and 700% better than playing video games”If you also create children’s literature, you might be interested in CANSCAIP’s Packaging Your Imagination Conference on November 16, 2013 in Toronto. From their website the “Canadian Society of Children’s Authors, Illustrators & Performers (CANSCAIP) presents a day of workshops focused on writing, illustrating & performing for children. Whether you are a beginner, a seasoned professional or somewhere in-between, PYI gives you the opportunity to improve your craft, expand your network of industry professionals, and meet and learn from some of the biggest names in the industry.” http://www.nationalreadingcampaign.ca/events/canscaips-packaging-your-imagination-conference/Finally, the CCBC (Canadian Children’s Book Centre) is another good way to keep up with what’s going on in the ever-expanding (and hard to keep track of) world of Children’s literature especially in Canada. http://www.bookcentre.ca/Here’s to the autumn trees (and squirrels) reminding us to stock up on great books to curl up with when we’re not out enjoying all that winter has to offer.David Sulz, Communications Editor

Plant phenolics: Recent advances on their biosynthesis, genetics, and ecophysiology

Land-adapted plants appeared between about 480 and 360 million years ago in the mid-Palaeozoic era, originating from charophycean green algae. The successful adaptation to land of these prototypes of amphibious plants - when they emerged from an aquatic environment onto the land - was achieved largely by massive formation of "phenolic UV light screens". In the course of evolution, plants have developed the ability to produce an enormous number of phenolic secondary metabolites, which are not required in the primary processes of growth and development but are of vital importance for their interaction with the environment, for their reproductive strategy and for their defense mechanisms. From a biosynthetic point of view, beside methylation catalyzed by O-methyltransferases, acylation and glycosylation of secondary metabolites, including phenylpropanoids and various derived phenolic compounds, are fundamental chemical modifications. Such modified metabolites have altered polarity, volatility, chemical stability in cells but also in solution, ability for interaction with other compounds (co-pigmentation) and biological activity. The control of the production of plant phenolics involves a matrix of potentially overlapping regulatory signals. These include developmental signals, such as during lignification of new growth or the production of anthocyanins during fruit and flower development, and environmental signals for protection against abiotic and biotic stresses. For some of the key compounds, such as the flavonoids, there is now an excellent understanding of the nature of those signals and how the signal transduction pathway connects through to the activation of the phenolic biosynthetic genes. Within the plant environment, different microorganisms can coexist that can establish various interactions with the host plant and that are often the basis for the synthesis of specific phenolic metabolites in response to these interactions. In the rhizosphere, increasing evidence suggests that root specific chemicals (exudates) might initiate and manipulate biological and physical interactions between roots and soil organisms. These interactions include signal traffic between roots of competing plants, roots and soil microbes, and one-way signals that relate the nature of chemical and physical soil properties to the roots. Plant phenolics can also modulate essential physiological processes such as transcriptional regulation and signal transduction. Some interesting effects of plant phenolics are also the ones associated with the growth hormone auxin. An additional role for flavonoids in functional pollen development has been observed. Finally, anthocyanins represent a class of flavonoids that provide the orange, red and blue/purple colors to many plant tissues. According to the coevolution theory, red is a signal of the status of the tree to insects that migrate to (or move among) the trees in autumn.

The levels of hormone and carbohydrate in autumn and non-autumn flowering tree peonies

Mornya, P. M. P. and Cheng, F. 2011. The levels of hormone and carbohydrate in autumn and non-autumn flowering tree peonies. Can. J. Plant Sci. 91: 991-998. This study analyzed the levels of gibberellic acid (GA3), indole-3-acetic acid (IAA), cytokinin (CTK) and abscisic acid (ABA) hormones using high-performance liquid chromatography, along with the levels of sucrose, reducing sugar and starch carbohydrates by spectrophotometer during induction, initiation and differentiation stages of bud development in autumn (AFP) and non-autumn (NAFP) flowering tree peony cultivars exhibiting variations in flowering pattern. The experimental design was a randomized complete block with three replications. The variation in flowering pattern between AFP and NAFP was largely influenced by differences in GA3, IAA and CTK levels at different bud developmental stages. The flower formation cycle was completed earlier in AFP than in NAFP, hence flowering was twice annually. Cytokinin, particularly N6-(▵2-isopentenyl)-adenosin...

Autumnal N storage determines the spring growth, N uptake and N internal cycling of young peach trees

Although N storage determines early spring growth in trees, the usefulness of autumn N supply remains unclear as N uptake decreases in autumn, but could be restored earlier in spring to compensate for low N cycling. We intended here to evaluate the effects of autumn N supply on N uptake, storage and cycling, and spring growth. Four levels of N fertilisation were applied to 1-year-old peach trees, between the end of shoot growth and leaf fall. In spring, N supply was 15N labelled. Organ dry weights and concentrations of 14N, 15N, starch and soluble sugars were evaluated after the first growth flush. Bud development had previously been described in the same trees by Jordan et al. (Trees-Struct Func 23:235–245, 2009). Fertilisation promoted autumn N uptake, spring N uptake and growth up to a threshold level, since no differences were evidenced between the three highest N treatments. The variability in tree 14N contents was related to the number of phytomers per tree in autumn, i.e. to tree size. In spring, the depletion of the perennial structures was independent of treatment, indicating a complete mobilisation of the N stores. Spring growth was related to the amounts of cycling N, and spring N uptake was in turn proportioned to shoot and fruit growth. The lower N uptake of the N limited trees was not due to a C shortage since these trees displayed the highest starch concentrations. We conclude that a moderate autumn fertilisation improved spring growth and fruit production (Jordan et al. in Trees-Struct Func 23:235–245, 2009) and that a deficit of N storage could not be compensated for by an increase in spring N uptake.

Hydration Status of South African Forestry Workers Harvesting Trees in Autumn and Winter

To determine both the prevalence and severity of dehydration of forestry workers harvesting trees in autumn and winter. Two cross-sectional observational studies were conducted on convenience samples of 103 and 79 workers in autumn and winter, respectively. The prevalence of dehydration pre- and post-shift was determined using urine specific gravity (U(SG)), and the severity of dehydration by the percent loss of body weight across the shift. Pre-shift, 43% in autumn and 47% in winter were dehydrated (U(SG) > 1.020 g ml(-1)) on arrival at work. There was a significant increase (P ≤ 0.001) in the prevalence of dehydration post-shift as 64% (P ≤ 0.001) in autumn and 63% (P = 0.043) in winter were dehydrated. In each area, ±22% had dehydrated by ≥2% loss of body weight. Pre-shift, 23% in autumn and 13% in winter were overhydrated (U(SG) < 1.013 g ml⁻¹). Post-shift, 4% in autumn and 2% in winter were overhydrated. An excessive consumption of hypotonic fluid (water) in combination with a reduced salt intake to prevent hypertension exposed an important minority to the risk of potentially fatal dilutional hyponatremia. Neither dehydration nor hyperhydration was related to season, gender, or job category. During average shifts, the South African forestry workers, regardless of season, gender, or job category, experienced dehydration of a magnitude that compromised both their safety and productivity.

EFFECTS OF CONTROLLED-RELEASE FERTILIZER VERSUS FERTIGATION ON CITRUS THOMPSON NAVEL VEGETATIVE GROWTH, YIELD AND NITROGEN STATUS

A field experiment on a commercial citrus orchard was carried out with mature trees of Thompson navel orange [Citrus sinensis (L.) Osb.], grafted on sour orange rootstock [Citrus aurantium (L.) Osb.]). Trees received the same amount of nutrients but in one plot of half an hectare the trees were fertilized with a controlled release fertilizer (17N-12P-18K +2Mg) applied at a depth of 10 cm in the beginning of the spring tree flush growth (first week of April) and again at the beginning of autumn tree flush growth (end of August) with another slow release fertilizer (13N-5P-27K +2Mg). On a second plot with the same area, trees were supplied with N, P, K and Mg by fertigation distributed during all the growth season. The yield and foliar nitrogen concentration in September were similar in both treatments. In contrast, the vegetative growth in the spring, summer and autumn flushes and The SPAD readings from May to November were greater in trees supplied with controlled-release fertilizer than with fertigation.