Partial defoliation has been shown to affect the water relations and transpiration (gas exchange) of plants. Over one growing season, the water relations in response to partial (∼45%) defoliation were examined in four-year-old Eucalyptus globulus trees in southern Australia. Daily maximum transpiration rates (Emax), maximum canopy conductance (GCmax), and diurnal patterns of tree water-use were measured over a period of 215 days using the heat-pulse technique in adjacent control (non-defoliated) and defoliated trees. Sap-flux measurements were used to estimate canopy conductance and soil-to-leaf hydraulic conductance (KP); leaf water potential (Ψ) and climate data were also collected. Following the removal of the upper canopy layer, defoliated trees exhibited compensatory responses in transpiration rate and canopy conductance of the remaining foliage. Defoliated E. globulus had similar predawn but higher midday Ψl, transpiration rates (E), canopy conductance (GC) and KP compared to the non-defoliated controls, possibly in response to increased water supply per unit leaf area demonstrated by higher midday Ψl. Higher E in defoliated E. globulus trees was the result of higher GC in the morning and early afternoon. This paper also incorporates the cumulative effect of defoliation, in a phenomenological model of maximum canopy conductance of E. globulus. These results contribute to a mechanistic understanding of plant responses to defoliation, in particular the often observed up-regulation of photosynthesis that also occurs in response to defoliation. 相似文献
The soybean cyst nematode (SCN, Heterodera glycines Ichinohe) is a major pest of soybeans (Glycine max L. Merrill) in the central and southern United States. Soybean cyst nematode causes stunted top growth, root pruning and symptoms of mineral element deficiency in soybeans. The objective of this study was to determine the effect of two selections of SCN (I selected on PI209332 and IV selected on PI 89772) on macronutrient uptake, translocation, and tissue concentrations of soybean and to determine the elemental composition of cysts isolated from roots. Soybeans were grown in plastic tubes in the greenhouse where the middle one‐third of the Hodge fine sand (Typic Udipsamment) contained 0, 25,000, or 50,000 SCN eggs. After 35 days, plants were harvested and tissue nutrient element concentrations were determined. Plants infested with both SCN selections were smaller and had much less root volume than controls. Dry weight of each plant tissue decreased as SCN population was increased. Root concentration of potassium (K) and magnesium (Mg) was decreased, whereas root calcium (Ca) and phosphorus (P) concentrations were increased with SCN treatments. Leaf Mg and Ca concentrations increased with SCN treatment. Magnesium uptake per unit root volume was decreased, but Mg translocation (% of total plant content in aerial portion) was increased with SCN treatment. Calcium uptake per unit of root volume was increased, but translocation was unchanged by SCN treatment. The Ca and P concentration of cysts isolated from the soybean roots was high. This high concentration of Ca in cysts is interesting based on the greater root Ca concentration and uptake per unit of root volume in SCN infested plants. Since total uptake and root concentrations of both K and Mg were decreased by SCN treatment, infested soybeans might require very high levels of K and Mg fertilization. These results indicate that K and Mg fertility should be followed closely in SCM‐infested soybean fields. 相似文献
Chemical vine desiccation is an important management practice for late season potatoes (Solanum tuberosum L.) in Michigan. A number of desiccants are registered; however, most Michigan growers apply dinoseb (2-sec- butyl-4,6-dinitrophenol). Greenhouse experiments were initiated to evaluate the potential of ammonium salts and ethephon (2-chloroethyl)phosphonic acid) to increase the efficacy of the chemical harvest aids dinoseb and endothall (7-oxabicyclo[2,2,1]heptane-2,3-dicarboxylic acid) on potato vines. Temperature and potato vine position were evaluated to determine their influence on vine desiccation. All treatments with endothall applied at 0.6 kg/ha resulted in unsatisfactory potato vine desiccation. Ethephon and ammonium sulfate increased efficacy of dinoseb. High temperature both before and after treatment contributed to greater dinoseb efficacy. The horizontal placing of potato vines resulted in the desired desiccation rating of 9.0 or greater using the combination of dinoseb at 2.8 kg/ha, plus ammonium sulfate at 9 kg/ha plus 2.4 L/ha X-77 surfactant.3相似文献
Forest thinning utilizing cut-to-length and whole-tree harvesting systems with subsequent underburning were assessed for their impacts on water storage in the extensible tissues of dominant and codominant trees in an uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf.) stand on the east slope of the Sierra Nevada. Prior to the onset of the third growing season following thinning and the second season after burning, manual band dendrometers were installed at breast height on the selected trees and readings of diurnal fluctuation in stem circumference, an indication of bole water status, were taken monthly for one year. Diameter and relative diameter fluctuation were calculated from the circumference measurements. Overall, thinning had a positive influence on stem water recharge capacity, with the most pronounced effects evident in the latter part of the growing season. During this period, bole contraction in thinned stand portions was 49 to 55% greater than in the unthinned control, suggesting that both a greater volume of stored water was available for transpiration and was transpired in trees of the former treatment. There was no clear evidence that harvesting method affected stem water storage and influences of underburning were also absent entirely. Seasonal effects on diurnal changes in stem diameter were prominent, as the extent to which boles contracted generally increased over the course of the growing season, whereas fluctuations were at a minimum during the colder months. The magnitude of stem dimensional flux was found to be negatively correlated with initial tree DBH in one instance, while negative relationships between the former and live crown length as well as percentage were also revealed, albeit infrequently. Changes in bole size were positively correlated with residual basal area in some cases. These results suggest that improvement in water relations can be realized from density management in a dry site forest type with no apparent compromise of this benefit by broadcast underburning. 相似文献
Using a cross-sectional survey, we determined the prevalence and risk factors associated with bovine brucellosis in herds under extensive production system in southwestern Nigeria. Antibodies to Brucella species in serum samples were tested using the Rose Bengal test (RBT) and competitive enzyme-linked immunosorbent assay (cELISA); for milk, the milk ring test (MRT) and indirect-ELISA (i-ELISA) were used. Questionnaire was administered to cattle herdsmen to determine factors predisposing the animals to bovine brucellosis. Data were analyzed using STATA 12. From 513 serum and 635 milk samples tested among 120 herds, overall animal-level prevalence of 10.1% (95% CI 7.5–12.7%) and 20.2% (95% CI 17.1–23.3%) were recorded by RBT and MRT, respectively; while 9.4% (95% CI 6.9–11.9%) and 17.8% (95% CI 14.8–20.8%) were obtained using cELISA and i-ELISA, respectively. In all, from the 120 herds tested, 29.2% and 43.3% were positive by RBT and MRT, respectively. Multivariable logistic regression revealed that herd location (OR?=?8.12, 95% CI 1.68–38.90) and improper disposal of placenta/fetus (OR?=?17.33, 95% CI 4.81–62.33) were predictors for a seropositive herd using RBT; while herd location (OR?=?5.13, 95% CI 1.27–20.28), large herd size (OR?=?2.62, 95% CI 1.15–5.85), and occurrence of abortion for a year or more (OR?=?4.62, 95% CI 1.53–13.71) were predictors of seropositivity to antibodies to Brucella spp. using MRT. We found high prevalence of brucellosis in cattle herds under extensive management system in southwestern Nigeria. Urgent and coordinated control strategies are required to mitigate this problem.
A series of conventional distance-independent and distance-dependent competition indices, a highly flexible distance-dependent crowding index, and two light resource estimation indices were compared to predict individual tree diameter growth of five species of mature trees from natural-origin boreal mixed forests. The crowding index was the superior index for most species and ecosites. However, distance-independent indices, such as basal area of competing trees, were also effective. Distance-dependent light estimation indices, which estimate the fraction of seasonal photosynthetically-active radiation available to each tree, ranked intermediate to low. Determining separate competition indices for each competitor species accounted for more variation than ignoring species or classifying by ecological groups. Species’ competitive ability ranked (most competitive to least): paper birch ≈ white spruce ≈> trembling aspen > lodgepole pine > balsam poplar. Stratification by ecosite further improved model performance. However, the overall impact of competition on mature trees in these forests appears to be small. 相似文献
We have extracted information on the habitats of bigeye (Thunnus obesus), skipjack (Katsuwonus pelamis) and yellowfin (Thunnus albacares) in the Eastern Tropical Pacific Ocean by matching the spatial‐temporal distribution of catch and effort of purse seine and longline fleets collected by the Inter‐American Tropical Tuna Commission with oceanographic conditions and subjecting the matched data to Quotient Analysis and General Additive Models (GAMs). These analyses yielded the following results. The habitats defined by the GAM analysis of young fish differ significantly between two periods, one before and one after the introduction of fish aggregation devices (FADs). This was not true for the older fish caught by longline. We speculate that these changes were caused by the extensive use of FADs. Younger bigeye and yellowfin caught by the purse seine fleet have a different preference of environmental variables compared to older fish caught by longline. This is to be expected since tuna of different age groups have different sizes, metabolic capabilities and swimming skills. Moreover, as revealed by GAMs, the habitats of young fish differ between species to a much larger degree than those of older fish. Our results indicate the fundamental differences between fishing methods, targeted species, and operating region of the two fisheries. Specifically, young bigeye occupy equatorial waters farther from the coast and where the hypoxic layer is deeper, young skipjack occupy more productive waters associated with equatorial and coastal upwelling, and young yellowfin occupy broad areas where waters are underlain by a shallow hypoxic layer. 相似文献
ABSTRACT 1. This study quantified xylanase-induced changes in soluble monosaccharides, xylooligosaccharides (XOS) and volatile fatty acid (VFA) contents of the different sections of the gastrointestinal tract (GIT) and whether these were related to altered bird performance. 2. An in vitro digestion of the wheat-based diet was carried out with the xylanase (Econase XT at 16,000BXU/kg diet) to compare the in vitro and in vivo generation of these XOS and monosaccharides. For the in vivo study, 80 male Ross 508 b roiler chicks were split into two groups fed a wheat-based diet with or without Econase XT (16,000BXU/kg diet) for 21 days. 3. There were no effects of Econase XT inclusion on growth performance characteristics, likely a result of the high-quality wheat diet, the corresponding high performance of the control group (FCR average of 1.45 in controls) and the relatively young age of the birds (from four to 26 days of age). 4. Econase XT supplementation increased the xylotetraose (X4) content in the colon (P = 0.046, enzyme x GIT section interaction) and the xylose contents in the colon and caeca (P < 0.001, enzyme x GIT section interaction). 5. The trend for increased acetate production in the caeca of Econase XT treated birds (P = 0.062) suggested that the XOS generated were subsequently fermented in the caeca, potentially impacting upon the types of microbiota present. 6. The present study suggested that wheat arabinoxylan degradation was enhanced by xylanase supplementation, which may have increased the production of beneficial volatile fatty acids (VFA) in the caeca, and thereby potentially modulated the caecal microbiome, but without affecting bird performance at this early age. 相似文献
Salvia reflexa (lance-leaf sage)-contaminated alfalfa hay was fed to ~500 mixed-breed beef cattle. Within hours of exposure, nearly half of the cattle developed lethargy, anorexia, depression, and recumbency, followed by bellowing, colic, and death. Even though the uneaten contaminated hay was removed the first day, nearly 100 animals died within the first 48 h. Three of these cattle were examined postmortem, and tissues and hay samples were collected for microscopic and chemical analysis. Several days later, a smaller number of the clinically poisoned cattle developed neurologic disease with aberrant behavior, aggression, icterus, blindness, exhaustion, and death. A total of 165 cattle were fatally poisoned. Poisoned cattle had swollen, dark, mottled livers that had a prominent nutmeg-like lobular pattern on cut section. Histologically, there was severe centrilobular-to-panlobular hepatic necrosis with marked hepatocellular swelling, degeneration, and necrosis. The surviving cattle developed liver disease characterized by altered serum biochemical analyses and microscopic hepatocellular degeneration and necrosis. In subsequent biopsies and analysis, these lesions resolved within 6–7 mo. After confirming toxicity of the hay in cattle, goats, and mice, followed by a mouse bioassay–guided chemical fractionation process, Salvia reflexa was identified as the contaminant in the hay responsible for the hepatotoxicity. S. reflexa has not been reported previously to cause fatal hepatotoxicity in livestock in North America, to our knowledge. 相似文献