Defoliation Rates Research Articles

Differential Analysis of Endogenous Hormone Levels and Natural Defoliation Traits During Sugarcane (Saccharum spp.) Maturation

The relationship between natural defoliation rate and endogenous ethylene, indole-3-acetic acid (IAA), and abscisic acid (ABA) levels in four sugarcane cultivars possessing different defoliation traits was investigated. Leaf sheath, leaf scar, and leaf blade samples were collected from the 10th leaf position below the fully expanded leaves during sugarcane maturation stage. Ethylene, IAA, and ABA levels were measured using gas chromatograph, liquid chromatograph, and external standard methods. The results showed that during sugarcane maturation, the highest natural defoliation rate was observed in CYZ03-194, followed by CYZ01-1413, CMT02-467, and CYA99-91. Ethylene production and IAA levels in the leaf scars, leaf sheaths, and leaf blades were the highest during the early-to-mid-maturation stage and decreased afterwards. The ABA levels showed a mono-peak curve change and peaked at the late-to-mid-maturation stage. Ethylene production in leaf scars during the early-to-mid- and mid-maturation stages as well as ABA levels in leaf scars at the late-to-mid-maturation stage significantly differed among the cultivars, with the highest levels in CYZ03-194, followed by CYZ01-1413, CMT02-467, and CYA99-91. On the other hand, the IAA levels in leaf scars and leaf sheaths at the early-to-mid-maturation stage were highest in CYA99-91, followed by CMT02-467, CYZ01-1413, and CYZ03-194. Correlation analysis demonstrated a positive correlation between the natural defoliation rate and ethylene production, ABA level, ethylene/IAA ratios, and ABA/IAA ratios, whereas a negative correlation was observed with IAA level during the early-to-mid- and mid-maturation stages.

Characterization of Natural and Simulated Herbivory on Wild Soybean (Glycine soja Seib. et Zucc.) for Use in Ecological Risk Assessment of Insect Protected Soybean

Insect-protected soybean (Glycine max (L.) Merr.) was developed to protect against foliage feeding by certain Lepidopteran insects. The assessment of potential consequences of transgene introgression from soybean to wild soybean (Glycine soja Seib. et Zucc.) is required as one aspect of the environmental risk assessment (ERA) in Japan. A potential hazard of insect-protected soybean may be hypothesized as transfer of a trait by gene flow to wild soybean and subsequent reduction in foliage feeding by Lepidopteran insects that result in increased weediness of wild soybean in Japan. To assess this potential hazard two studies were conducted. A three-year survey of wild soybean populations in Japan was conducted to establish basic information on foliage damage caused by different herbivores. When assessed across all populations and years within each prefecture, the total foliage from different herbivores was ≤ 30%, with the lowest levels of defoliation (< 2%) caused by Lepidopteran insects. A separate experiment using five levels of simulated defoliation (0%, 10%, 25%, 50% and 100%) was conducted to assess the impact on pod and seed production and time to maturity of wild soybean. The results indicated that there was no decrease in wild soybean plants pod or seed number or time to maturity at defoliation rates up to 50%. The results from these experiments indicate that wild soybean is not limited by lepidopteran feeding and has an ability to compensate for defoliation levels observed in nature. Therefore, the potential hazard to wild soybean from the importation of insect-protected soybean for food and feed into Japan is negligible.

Leaf Pubescence and Defoliation Strategy Influence on Cotton Defoliation and Fiber Quality

Proper defoliation of cotton is critical to maximize both harvest efficiency and fiber quality. Increased levels of leaf grade or trash resulting from inadequate defoliation can lead to decreases in fiber quality and value. Inherent characteristics of cultivars, such as leaf pubescence levels and defoliation practices influence the efficacy of cotton defoliation. This study aimed to determine the impact of leaf pubescence and defoliation strategies on defoliation success and fiber quality in cotton. Treatments included a factorial of four cultivars and two defoliation treatments. Cultivars included two smooth-leaf cultivars and two cultivars with greater leaf pubescence ratings. Defoliation treatments included a standard program and an aggressive program with increased rates of the same defoliant mixture and the addition of a desiccant. There were few instances of a cultivar-by-defoliation strategy interaction, however, both cultivar and defoliation strategy had a significant effect on defoliation ratings. The aggressive defoliation treatment decreased defoliation and increased desiccation in all three locations but did not influence yield or fiber quality. In two of three locations, cultivars with higher leaf pubescence ratings resulted in increased leaf grades and HVI trash ratings compared with the smooth leaf cultivars. The results of this study suggest that the defoliation strategy can impact efficacy of defoliation, whereas leaf pubescence characteristics influence fiber quality parameters.

Effects of warming and nitrogen on above- and below-ground herbivory of an exotic invasive plant and its native congener

Warming and atmospheric nitrogen deposition could impact plant community composition by altering competitive interactions, however, the effects of these environmental changes on plant invasions via above- and below-ground herbivory are unknown. Here we report the effects of warming and nitrogen addition on aboveground insect defoliation and belowground root-knot nematode infection of a native plant and an introduced invasive congener. Warming increased belowground nematode infection only, while nitrogen addition increased both nematodes and defoliation. Defoliation rates were similar for the exotic invasive and native species and the increases with nitrogen addition were large (almost doubled) but comparable. However, roots of native plant were more intensively infected (i.e., knot density) than roots of the exotic invasive plant (~4-fold in ambient conditions) and this difference increased under elevated temperature (~30-fold higher) in which total nematode infection were nearly tenfold higher. Compared to the exotic invasive plant, the native plant had a higher proportion of fine roots and specific leaf area, but lower photosynthesis ability irrespective of warming and nitrogen deposition treatments. The nematode preferred fine roots to coarse roots for both plant species. Our study indicates that above- and below-ground herbivory of plants differ in their sensitivity to varying drivers of environmental change, which may alter plant interactions and makes it difficult to predict future community structure. Together with the dramatic response of belowground nematodes to warming, this suggests that future modeling or experimental studies on species’ responses to environmental change should simultaneously consider above- and below-ground communities.

Modelling the interaction between early blight epidemics and host dynamics of tomato

A model describing an early blight epidemic and the growth dynamics of tomato interacting together is developed. The model is formulated as a set of differential equations for the rate of change in the amount of healthy H, diseased Y and defoliated D area in the disease situation, and healthy H DF and defoliated D DF in the disease-free situation. Model parameters were estimated through fitting the model to experimental data obtained from glasshouse experiments which comprised tomato plants inoculated with A. solani at three inoculation times; early (t INOC = 23 days after transplanting (DAT)), intermediate (33 DAT) and late (43 DAT) in experiment 1 and t INOC = 22, 30 and 38 DAT in experiment 2. Defoliation rates were 2.5 times higher for late inoculated (older) plants compared with the early inoculated (younger) plants. Values of the logistic rate parameter for disease increase were about three-fold higher in the late inoculations (0.380, 0.305 day−1) when compared with the early inoculations (0.151, 0.095 day−1). Based on the good fit of the model outputs to observed data with R 2 > 0.995, the model can be considered as offering a good description of the dynamic interaction between the early blight epidemic and growth of tomato.

Relationship between endogenous ethylene production and natural defoliation traits during the maturation of sugarcane

The relationship between endogenous ethylene production and natural defoliation rate was examined in sugarcane cultivars with different natural defoliation traits. Ethylene production was examined at different positions on leaf sheaths and leaf scars at various sugarcane maturation stages using gas chromatography as an external standard method. During the sugarcane maturation process, ethylene production was greatest in the 2nd leaf sheath scar, followed by the 5th and 10th, in that order. It was also greatest during the early maturation stage, followed by the mid-maturation and harvest stages. Ethylene production of the leaf sheaths and leaf scars differed significantly among the sugarcane cultivars. Cultivars that defoliate easily produced significantly more ethylene than those that do not defoliate easily. The natural defoliation rates was greatest in the harvest stage, followed by mid-maturation and early maturation stage. Correlation analysis indicated that ethylene production was positively correlated with natural defoliation rates, particularly during early- and mid-maturation stages.

Effects of fertilization and liming on tree growth, vitality and nutrient status in boreal balsam fir stands

Two fertilization trials were carried out in young balsam fir (Abies balsamea (L.) Mill.) stands showing symptoms of tree decline or foliar chlorosis in boreal forests of eastern Laurentian Highlands in Quebec, Canada. In the first trial, trees showed strong decline symptoms; fertilization treatments consisted of combinations of two nutrients among N, K, and Mg, each at two rates. In the second trial, trees showed some needle chlorosis; various doses of N, K, K–Mg, and K-lime fertilizers were applied. In both trials, N fertilization (200kgNha−1) resulted only in a short-term (2–3years) increase in foliar N concentrations and radial growth. Potassium fertilization (100–400kg K2O ha−1), however, led to an increase of at least 33% in both foliar K concentrations and radial growth, which lasted for the duration of the experiments (7–11years). Liming (1–4t dolomitic lime ha−1) increased the pH, exchangeable calcium and exchangeable magnesium in the humus and top mineral soil horizons, but did not influence balsam fir foliar nutrient status or growth. Tree defoliation rate was mainly related to growth decrease and foliar K concentrations. The trials also show that K was the most limiting nutrient for balsam fir growth, and that the poor K nutrient status and vigor of balsam fir trees can be corrected by K fertilization. These results contrast with past fertilization studies that generally reported N as the most limiting nutrient in these boreal ecosystems. Climatic events may have also played a role in triggering the decline of balsam fir in one trial.

Tree damage and population density relationships for the pine processionary moth: Prospects for ecological research and pest management

The pine processionary moth (Thaumetopoea pityocampa, PPM) is one of the most destructive pests in Mediterranean woodlands. Assessment of PPM impact involves the quantification of pest damage at the stand level from visual evaluations by forestry technicians, using different infestation indices. One such index, widely used in national and regional forest monitoring programmes, is an ordinal index that ranges from no infestation (0) to massive defoliation (5). This index now offers an outstanding opportunity to investigate patterns and processes in PPM population dynamics. Its use as a proxy for insect population density requires, however, knowledge on the relationship between stand defoliation and population density-related measures, which is something that has not been explored to date. In this study, we investigated the relationship between the infestation index, quantifying damage at the stand level by the PPM, and fined-grained measures of PPM population size (number of egg batches, number of hatched caterpillars, number of winter tents) within and between generations. We used data from a long-term monitoring programme conducted in three pine woodland stands at Mora de Rubielos, Spain, for a 19-year period. Generalized linear models (GLM) were fitted in order to test the following hypotheses: (1) high values of population density-related variables, on a log basis, will cause high defoliation in the coming winter (within generation); and (2) high defoliation rates will be associated with high stocks of population size at the next generation of PPM (between generations). Our results indicate that, within the same generation, there was a poor relationship between the infestation index and all three fine-grained measures of population size (maximum R2=0.442), possibly as a result of post-sampling larval survival over winter due to climatic factors. Goodness of fit was higher for PPM population density-related measures in the next generation and the infestation index (maximum R2=0.735). Overall, the results suggest that visual evaluation of pest damage by PPM at the stand level provides an accurate proxy for population size at the next generation, and therefore opens the potential to the use of this index to investigate PPM population dynamics where no direct measures of population size exist.

Does plant colour matter? Wax accumulation as an indicator of decline in Juniperus thurifera

The photosynthesis in evergreen trees living in Mediterranean ecosystems is subjected to multiple climatic stresses due to water shortage and high temperatures during the summer and to low temperatures during the winter. Mediterranean perennials deploy different photoprotective mechanisms to prevent damage to the photosynthetic system. Wax accumulation in leaves is a primary response which by enhancing light scattering in the leaf surface reduces incident radiation in the mesophyll. The existence of high variability in wax accumulation levels between coexisting individuals of a species has a visual effect on colour that provides distinguishable green and glaucous phenotypes. We explored this variability in a Mediterranean evergreen tree Juniperus thurifera (L.) to evaluate the impact of epicuticular wax on optical and ecophysiological properties and on the abundance of photoprotective pigments throughout an annual cycle. Because of light attenuation by waxes, we expected that glaucous phenotypes would lower the need for photoprotective pigments. We evaluated the effect of phenotype and season on reflectance, defoliation levels, photochemical efficiency and photoprotective pigment contents in 20 green and 20 glaucous junipers. Contrary to our expectations, the results showed that glaucous trees suffered from a diminution in photochemical efficiency, but there was no reduction in photoprotective pigments. Differences between glaucous and green phenotypes were greater in winter, which is the most stressful season for this species. Glaucous individuals also showed the highest levels of leaf defoliation. The lower photochemical efficiency of glaucous trees, together with higher defoliation rates and equal or greater number of physiological photoprotective mechanisms, suggests that in spite of wax accumulation, glaucous trees suffer from more severe stress than green ones. This result suggests that changes in colouration in Mediterranean evergreens may be a decline indicator.

Ewe lamb diet selection on plantain (Plantago lanceolata) and on a herb and legume mix, including plantain, chicory (Cichorium intybus), red clover (Trifolium pratense) and white clover (Trifolium repens)

The objective of Experiment 1 was to examine the diet selection and grazing preference of ewe lambs for plantain (Plantago lanceolata), chicory (Cichorium intybus), red clover (Trifolium pratense) and white clover (Trifolium repens). This was examined in a herb and legume sward mix containing plantain, chicory, red clover and white clover between seasons under both hard- and lax-grazing. During early spring, the sward predominately comprised plantain (63%) and chicory (21%) and ewe lambs grazed a greater proportion (P &lt; 0.05) of these species and displayed greater (P &lt; 0.05) grazing preference for plantain and chicory ahead of red and white clover. From late spring onward, ewe lambs had a greater (P &lt; 0.05) defoliation rate and a greater (P &lt; 0.05) grazing preference for red clover than for all other species. This greater selection of red clover was particularly evident in summer and autumn when red clover made a greater (P &lt; 0.05) contribution to the sward composition (8–9%) and the overall sward nutritive value dropped. This supports previous evidence, suggesting that diet selection is intrinsically affected by availability, access and palatability. The objective of Experiment 2 was to determine whether ewe lamb grazing behaviour during late summer was affected by time since a pure plantain sward was previously grazed. Ewe lambs were observed while grazing plantain of varying weeks since previous grazing (3, 6,10 or 16 weeks). Experiment 2 found no difference (P &gt; 0.05) in the average number of ewe lambs grazing each sward of varying weeks since previous grazing. However, ewe lambs grazed the 3-week-old plantain growth to a lower (P &lt; 0.05) post-grazing sward height than the height of the swards of greater number of weeks since previous grazing. Organic matter digestibility and metabolisable energy content did not differ (P &gt; 0.05) among all swards, regardless of weeks since previous grazing. This suggests that the palatability of plantain is not affected by the time since it was last grazed.

Forest Condition in Europe: 2013 technical report of ICP Forests. Report under the UNECE Convention on Long-Range Transboundary Air Pollution (CLRTAP)

Of the 42 countries that have participated in ICP Forests since 1986, 27 countries reported largescale monitoring data from Level I plots and more detailed forest ecosystem related monitoring data from Level II plots for the year 2012. In total, the participating countries provided information on more than 15,000 plots and more than 220,000 trees. Data analyses for this 2013 Technical Report focused on the impact of air pollution on tree crown condition and on sulphate and nitrogen deposition to forests. In addition, the impact on individual trees of factors other than air pollution, e.g., biotic agents, was assessed. Crown condition is the most widely applied indicator for forest health and vitality of European forests. One of its primary parameters is the rate of defoliation, which is assessed as the percentage of needle/leaf loss in the crown compared to a reference tree with full foliage. The mean defoliation of 114,361 sample trees on 6,168 transnational Level I plots in 2012 was 19.7%. Of all trees assessed in 2012 every fourth to fifth tree (22.9%) was scored as damaged, i.e., had a defoliation rate of more than 25%. In general, broadleaved trees showed a higher mean defoliation rate than conifer species (23.6% and 20.2%, respectively). Oak species still seem to be the most vulnerable of all the investigated species. Of the main species groups, deciduous temperate oak species had the highest mean defoliation (26.5%), closely followed by Mediterranean evergreen oak species (25.2%), and deciduous (sub-) temperate oak species (24.6%). A mean defoliation rate of 19.6% was assessed for European beech (Fagus sylvatica). Coniferous species expressed lower defoliation rates on average, with European spruce (Picea abies) reaching 19.2%, followed by Scots pine (Pinus sylvestris) with 19.3%, and Mediterranean lowland pine species with 20.7%. These figures are, however, not directly comparable to those of previous reports because of fluctuations in the plot sample that are primarily due to changes in the annual participation of countries. Therefore, the temporal development of crown condition was calculated separately from the monitoring results for those countries which have submitted data every year without interruption since 1993, 1998, and 2002, respectively. In addition, maps were drawn that depict temporal species trends in defoliation. The presented results suggest that there was no overall improvement of crown condition for the longest analyzed time period from 1993 to 2012. Over the last 20 years the percentage of plots with clearly increasing mean defoliation (17.2%) even exceeded the share of plots with decreasing defoliation (12.5%) but most of the investigated plots showed no statistically significant change in crown condition (70.3%). Compared to the previous year only, the investigated trees showed on average similar rates of defoliation in 2012. More than three out of four plots (78.7%) showed no statistically significant difference in mean defoliation between those two years. Defoliation increased on 13.8% and decreased on only 7.5% of the plots.

Defoliation ofTerminalia catappaby Larvae ofThagona tibialis(Lepidoptera: Erebidae) in Viçosa, Brazil1

Larvae of Thagona tibialis (Walker) (Lepidoptera: Erebidae) have been reported to defoliate tropical almond plants, Terminalia catappa L. (Combretaceae), in urban areas of Belo Horizonte (2005), Vicosa (2006), Morro Reuter (2007), and Brasilia (2012), Brazil. The origin of T. tibialis is uncertain, but it is now dispersed throughout urban areas of all Brazilian states that have T. catappa. This pest not only has the capacity for high infestation and defoliation rates on T. catappa, but it also can invade houses and cause allergies to humans because of larval hairs and adult scales that are easily dislodged. The objectives of this research were to describe the morphological and ecological characteristics of T. tibialis and to evaluate defoliation of T. catappa by T. tibialis larvae in Vicosa. The specimens collected for this study were a variant of T. tibialis that does not have dark dots on the forewings. Larvae were bluish-white, with orange sub-dorsal stripes and black spots throughout the body. Final instars were approximately 40 mm long. Adults exhibit sexual dimorphism. Females were always white, while males varied from white to light or dark brown. Eggs were round, except for the flattened base and micropyle regions, with the greatest diameters being 0.86 mm long and 0.62 mm wide. Larvae of T. tibialis injured from 3.6% to 98.9% of the leaves on T. catappa trees. From 78.2% to 96.9% of mature leaves and from 3.2% to 21.8% of young leaves were injured, indicating T. tibialis larvae prefer mature leaves of T. catappa.

Combined effects of fragmentation and herbivory on Posidonia oceanica seagrass ecosystems

Summary Fragmentation is a major agent for seagrass meadow decline, yet little is known about how it interacts with processes like herbivory, an important functional driver of seagrass meadows. The interaction with external stressors like fragmentation could exacerbate the effects of internal ecosystem drivers like herbivory, with distinct implications for ecosystem management. We used manipulative field experiments to assess these interactive effects in two Posidonia oceanica seagrass meadows. We monitored replicated plots in small and large patches in two meadows suffering fragmentation with and without herbivores (using exclusion cages) to test whether fragment size and herbivory could act together to alter ecosystem functioning. We measured changes in defoliation rates, primary production, canopy height and nutrient content in all plots after 4 months of herbivore exclusion. Our results show that herbivores increased defoliation rates resulting in reduced primary production, nutrient content and canopy structure (canopy height). Patch size (fragment) on its own also reduced primary production, nutrient content and canopy structure. We also observed significant additive interactions between herbivores and fragmentation on canopy structure and production responses. In addition, small patches showed nutrient limitation but were able to accumulate more carbohydrate reserves, probably due to a higher light availability. This may explain why small patches can persist under significant herbivore pressure. Synthesis. While fragmentation has already been identified as an important external agent of seagrass decline, the combination of fragmentation and herbivory can seriously exacerbate structural losses and affect primary production, profoundly compromising the role of seagrasses as habitat‐forming ecosystems. These interactions between external stressors and internal drivers may result in large unexpected consequences that may flow on to the rest of the ecosystem.

Estimating crown defoliation of Scots pine (Pinus sylvestris L.) trees using small format digital aerial images

This study focuses on the possibilities of using small format digital aerial images for the estimation of tree crown condition. The test area was located in the eastern part of Lithuania where Scots pine (Pinus sylvestris L.) trees prevail and was photographed using a Canon EOS-1DsMark II digital camera installed on-board a SkyArrow ultra-light aircraft. The camera lenses were adopted to capture images corresponding to conventional color-infrared photography. In addition, the test area was photographed using a large format digital frame aerial camera (Vexcel UltraCam D) installed on board a Rockwell Turbo Commander 690A high performance commuter aircraft. The ground sampling density of the images taken was around 9-10 cm. Crown defoliation was assessed in the field for more than 500 Scots pine trees located in 46 sample plots representing stands of trees that were either 65 years old or 170 years old. Spearman’s correlations coefficients were used to check for relationships between tree crown defoliation and image characteristics. The defoliation was also predicted using the non-parametric k-Nearest Neighbor method applied on data available from aerial images alone. The results were validated using the “Leave One Out” technique by comparing the obtained data with data from the field assessed defoliation rates. The prediction root mean square errors were calculated using data from the small format aerial images as being 11.5% for the younger trees, whereas those calculated using conventional aerial images were between 9.5 and 9.9%. The differences in predicted root mean square errors disappeared in the older stands and both methods produced errors of between 8.1 and 8.5%. Defoliation class was correctly predicted for approximately 84-88% of the older tree crowns and correctly for 75-85% of the younger tree crowns. These results showed that small format aerial images had the potential to predict defoliation in tree crowns and were comparable with results obtained using conventional aerial images. Their main advantage is that small format images are much cheaper to obtain than conventional images when the areas targeted are thousands of hectares in size.

Etiology of a recent white spruce decline: role of potassium deficiency, past disturbances, and climate change

Along with climate, multiple global or large-scale change agents shape forest ecosystem health. We present a case study where we attempted to elucidate the driving factors causing decline symptoms in white spruce (Picea glauca (Moench) Voss) in young spruce–fir boreal stands. Tree defoliation rate in the studied areas was related to the foliage discoloration intensity of the 2-year old needles and the decreasing stem basal area increment from 1997 to 2008. The onset of this growth decline in 1997 coincided with the occurrence of extremes for four climatic indices. The foliage of affected trees was deficient in K. The relationship between tree decline and K deficiency was tested through a diagnostic fertilization trial using a two-level factorial combination of N, K, and Mg. The trial indicated that K was the single limiting nutrient among the three tested elements. A single K addition increased stem basal area by 43% on average after 11 years. It is hypothesized that the poor K status of trees can be attributed to a series of natural and anthropogenic disturbances along with past forest management activities. Climate change in the region since the last decades also may have contributed to exacerbate K deficiency in such forest ecosystems.

Evaluation of the impacts of herbivory by lace bugs on Chinese privet (Ligustrum sinense) survival and physiology

Biological control of Chinese privet, Ligustrum sinense, is the best long-term option for control of this widespread invasive plant in the southeastern USA. A pre-release efficacy assessment was conducted by testing the effects of damage caused by a lace bug, Leptoypha hospita, on potted privet plants in the laboratory. Inoculating 15 pairs of lace bug adults on plants resulted in a significantly higher defoliation rate and reduced leaf biomass by more than 59% compared to 0 and 3 lace bug pairs. Leaf biomass of plants inoculated with 3 and 9 pairs of lace bug did not differ significantly from control plants. The percentage of the total leaf area affected by lace bug feeding was positively correlated with the density of lace bugs inoculated. This was also evident by the reduced chlorophyll content of leaves exposed to 9 and 15 pairs of lace bugs and their offspring. Our tests showed that one generation of feeding by the lace bug caused significant defoliation as well as reduced photosynthetic activity of remaining leaves. Continuous long term feeding by the lace bug or other potential defoliating insects could result in suppression of Chinese privet populations and possibly reduction to desirable levels.

Variation in the morphological structure of the crown of Norway spruce in North Estonian alkalised soil

Characterisation of tree crown structure provides critical information to assess a variety of ecological conditions for multiple purposes and applications. The aim of investigation was to elucidate the influence of the alkaline soil on the formation of the crown of Norway spruce (Picea abies (L.) Karst.). The seven sample plots (0.05ha) with 75–90-year-old spruce stands of Oxalis–Myrtillus site type were selected at different distances from a cement plant influenced over 40years by alkaline dust pollution. The studies were conducted 13years after dust pollution had practically stopped. High pH values (6.1–7.8), large concentrations of dominant dust components (Ca, Mg, K) and a lower level of N and organic matter in the upper layers of soil within about 6km from the emission source compared to the unpolluted control area 30.4km from the source (pH 3.3) were found. Disbalance in mineral composition in needles and shoots was established, deficite in N and excess in Ca and K concentrations were brought about a great differentiation in growth and biomass formation between unpolluted and polluted trees. On the most polluted area the average height of trees and living crown, the length and dry mass of shoots and needles were lower, and average life span of needles were shorter than in unpolluted area, indicating an increased defoliation rate of the crown.

Grazing patterns on signalgrass pasture according to location of cattle feces

This study was conducted to evaluate the defoliation patterns on B. decumbens cv. Basilisk (signalgrass) tiller as a function of influence of feces deposited naturally by cattle. The signalgrass was managed with an average height of 25 cm, under continuous stocking and variable stocking rate. Interval and intensity of defoliation, grazing efficiency and forage loss were evaluated in two sites on pasture - one close and the other distant from feces. The completely randomized block design with three replications was adopted. The defoliation rate of the pasture site close to feces was 40% lower than at that distant from feces. This response pattern was similar to defoliation intensity of leaf blade. The leaf blade of the tiller close to feces also achieved lower de foliation (1.64) than that in the tiller distant from feces (3.97). The relative number of grazed leaf per tiller in the tillers distant from feces was approximately 185% higher than those close to feces. The grazing efficiency was lower in the local close to feces compared with that distant, unlike forage loss. The natural deposition of feces by cattle modifies the grazing and use patterns of B. decumbens under continuous stocking.

Response of spruce stands in national parks of southern Poland to air pollution in 1998–2005

The purpose of this study was to describe changes in the deposition of air pollutants and the response of spruce trees in the period of 1998–2005. The investigation was carried out in twelve sites, mainly national parks. Air pollution level, that is, SO2, NO2, and O3 concentrations in the air, as well as throughfall and soil solution chemical composition was analysed. The reaction of trees was described based on a stand health parameter, that is, defoliation. A decrease in the concentration of SO2 and NO2 in the investigated period was observed. In most of the analysed sites, ozone concentrations in the growing season exceeded the level regarded as harmful to plants. Annual loads of nitrogen and sulphur reaching the forest soil exceeded 10 kg/ha. The data collected for the analysed period confirmed that the health status of forests at the investigated sites did not show a general tendency towards improvement. Also, no dependency between the air pollution level and defoliation rate was found.

Response of the photosynthetic apparatus to a flowering-inductive period by water stress in Citrus

The photosynthetic responses to a flowering-inductive water-stress period and recovery were studied and compared in two Citrus species. Under greenhouse conditions, Fino lemon and Owari satsuma trees were subjected to moderate (−2 MPa at predawn) and severe (−3 MPa) water stress levels and were re-watered after 60 days. Vegetative growth was inhibited during the stress assays, and strong defoliation levels were reported, especially in Fino lemon. In both species, bud sprouting was induced after re-watering. Flowers and vegetative shoots developed in Owari satsuma after a drought period, and the development was independent of the stress level. In Fino lemon, vegetative shoots and flowers were primarily formed after moderate and severe stress, respectively. The photosynthetic rate and stomatal conductance were reduced by water stress, and a marked increase in water-use efficiency at the moderate water deficit level was observed. Nevertheless, the photosynthetic apparatus was not damaged, since the maximum quantum yield, photosynthetic pigment concentrations and Rubisco level and activity did not change. Furthermore, the measured malonyldialdehyde (MDA) and peroxidase activity indicated that oxidative stress was not specifically triggered by water stress in our study. Therefore, the gas exchange, fluorescence and biochemical parameters suggested that diffusional limitations to photosynthesis predominated in both of the studied Citrus species, and explained the rapid recovery of the photosynthetic parameters after rehydration. The net CO2 fixation rate and stomatal conductance were recovered within 24 h in Fino lemon, whereas 3 days were required in Owari satsuma. This suggests the presence of some metabolic limitations in the latter species. Furthermore, the sensibility of the defoliation rates, the accumulation of proline and the stomatal behaviour in response to water stress indicated a higher drought tolerance of Fino lemon, according to its better acclimation to hot climates.