Relative Growth Response Research Articles

Sodium alginate-g-polyacrylamide hydrogel for water retention and plant growth promotion in water-deficient soils

Natural polymer-based hydrogels are preferred as soil water retention agents due to their inherent biocompatibility and biodegradability. Generally, these natural polymers are chemically modified by graft polymerization of vinyl monomers to improve their water absorption and retention properties. Among the polysaccharides used to prepare natural hydrogels, those based on sodium alginate (Alg) stand out for their high-water absorption and retention capacity, as well as for their ability to promote plant growth. The main objective of this study was to develop a biodegradable alginate-based hydrogel as a water retainer to promote plant growth under water deficit conditions. The synthesis was achieved by grafting poly(acrylamide) (PAM) onto Alg backbone, using bisacrylamide as chemical crosslinker and different ratios of alginate:acrylamide (Ac). In addition, Eucalyptus nitens seedlings were used as a model plant to evaluate the effect of alginate-g-polyacrylamide (Alg:PAM) hydrogel application to the growing medium on plant survival, growth, and physiological responses under both well-watered and water-deficient soil conditions. The maximum degree of swelling (65 g/g) was obtained for the hydrogel prepared. The pseudo-second order model described the water uptake kinetics of the hydrogel. The degradability of Alg:PAM hydrogel reached up to 85 % in 5 weeks in soil and occurs by breaking the glycosidic bonds of the alginate. The E. nitens seedlings cultivated with different doses of Alg:PAM hydrogel (4:1 Alg:Ac) showed higher values of height and root diameter relative growth, survival and photosynthetic responses in comparison to non-treated plants. The results indicate that Alg:PAM hydrogel (4:1 Alg:Ac) has promising applications in forestry as a water retention and seedling growth promoter under water deficient conditions.

Mungbean (Vigna radiata) Growth and Yield Response in Relation to Water Stress and Elevated Day/Night Temperature Conditions

Information regarding the relative importance of elevated day/night-time temperatures combined with water stress on mungbean yield is limited. This study aimed to investigate the yield response of mungbean cultivars to different water stress and temperature regimes under controlled glasshouse conditions. Two mungbean cultivars, Celera II-AU and Jade-AU, were grown and evaluated under four temperature regimes with and without water stress, each replicated 10 times in a randomized complete block design. The four temperature regimes were as follows: (i) HTHT: Plants were consistently exposed to high day/high night temperatures (35/25 °C). (ii) LTHT: Plants experienced ambient day/ambient night temperatures (25/15 °C) for the first 35 days, followed by the HTHT environment. (iii) LTLT: Plants were maintained at ambient day/ambient night temperatures (25/15 °C) throughout the experiment. (iv) HTLT: Plants were subjected to high day/high night temperatures (35/25 °C) for the initial 35 days, followed by the LTLT environment. Under water stress conditions, mungbean yield declined significantly in the HTHT environment by 57% for Jade-AU and 76% for Celera II-AU compared to the LTLT environment. The highest seed yield (10.2 g plant−1 for Jade-AU and 11.4 g plant−1 for Celera II-AU) for both cultivars was observed when grown without water stress in the LTLT environment. However, yield decreased substantially when plants experienced combined heat and water stress during the reproductive stage (HTHT and LTHT environments). Without water stress, mungbean yield under the HTHT environment decreased by 30% for Jade-AU and 60% for Celera II-AU compared to the LTLT environment. Surprisingly, no significant difference in response to water stress was observed between the two cultivars. Furthermore, when grown under no-water stress and HTHT environments, the yield of Celera II-AU was reduced by 37% compared to Jade-AU. Similarly, a comparable response was seen between cultivars under no-water stress and LTHT environment. The results indicated that water and heat stress negatively affected mungbean seed yield. Moreover, it was observed that Jade-AU outperformed Celera II-AU regarding seed yield under heat-stress conditions. In conclusion, this study suggests that adjusting sowing time and selecting suitable heat-tolerant cultivars, such as Jade-AU, could enhance mungbean yield under heat and water stress conditions. The results demonstrate substantial impacts on mungbean productivity from changing climatic and water stress conditions and these findings can be utilized for improving mungbean productivity in dryland regions.

PSAT104 Predicting Response to Growth Hormone Therapy with Pituitary Volume and The Growth Hormone Stimulation Test

Abstract Background Patients with diminished growth hormone (GH) secretion are candidates for GH therapy (GHT). The GH stimulation test (GHST) is considered the gold standard for the diagnosis of GH deficiency (GHD), yet its efficacy has been questioned. In this study we explore the GHST and PV's ability to define GHD and determine their individual ability to predict GHT outcomes. Subjects and Methods A database at a Pediatric Endocrinology center was queried for patients aged 6-18 yrs who underwent a GHST, MRI, and GHT between 1/2018 - 1/2021. Patients with a first follow up (FU) between 3 and 9 months were included; of these patients, second FUs were included if they occurred between 9 and 15 months. Patients with relevant comorbidities, those with GHST peak ≥ 10.0 ng/mL, and nonadherent patients were excluded. MRIs were acquired on a Philips 1.5 or 3.0 T scanner (2mm slices) and PV was calculated using the ellipsoid formula (LxWxH/2). PV and height were converted to SDS. Response to treatment was defined as change in height SDS over the assessed time interval. A multiple linear regression was utilized to analyze the response to GHT relative to peak GH and PV, with initial height and age at stimulation included as covariates. The relationship between peak GH and PV SDS was analyzed with a Pearson correlation Results The first FU ranged between 3.1 and 8.9 months, and the second FU ranged between 9.0 and 14.9 months. 145 patients had one FU, and 83 patients had two FUs. Peak GH and PV SDS were not correlated (r=0.03). Patients who were relatively shorter for their age and gender at stimulation had higher growth rates in the first interval, but not in the second interval. Both PV and peak GH provided information about response to GHT. PV SDS negatively predicted the relative growth response to treatment in the first interval (slope=-0.03, p=0.048). However, PV only explained 3.7% of variation in growth. PV SDS was not a useful predictor of response in the second interval (slope=-0.01, p=0.693). Peak GH was a predictor of response to GHT in the first interval only after accounting for age at stimulation and initial height (slope=-0.01, p=0.032; r2=0.01). Peak GH was a predictor of response in the second interval (slope=-0.02, p=0.040), explaining 5.1% of the variation in growth. Conclusion Since peak GH and PV were not correlated, they likely reflect different physiological processes. PV and peak GH both provide information about response to GHT, so they should both be utilized to determine eligibility for GHT. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.

The growth response and hepatosomatic index of milkfish (<i>Chanos chanos</i> Forsskal) fed with diet various levels carbohydrates in fermented of cow rumen liquid

One effort to reduce the role of protein as an energy source in feed is to maximize the use of feed carbohydrates as an energy source and engineering optimization of feed utilization can be done by adding exogenous digestive enzymes to feed. This study aims to determine the level of carbohydrates in the feed after being given cow rumen liquid which gives the best growth response and hepatosomatic index in milkfish. This study was designed using a completely randomized design (CRD) consisting of 4 treatments and 3 replications, Thus, there are 12 experimental units. The treatments were feeding with different levels of carbohydrate feed, namely 27,81; 39,50; 46,97 and 56,75% mixed with 80 mL of rumen liquid per 100 g of feed. Feed was given to juvenile milkfish measuring 7.19±0,036 g which was kept in a recirculating aquarium with a density of 15 fish/45 L of brackish water. The provision of various levels of carbohydrates in the feed had an effect (α<0.05) on relative growth and survival but had no effect (α>0.05) on the hepatosomatic index of milkfish. Statistically, the best relative growth response and survival were found in fish fed with a carbohydrate-level feed treatment of 27,81; 39,50; 46,97%.

Relative growth response of some barley genotypes to deficient and adequate phosphorus levels

A pot experiment was conducted to study genotypes variation for P Uptake and utilization efficiency in four barley genotypes (Tramilo, Rahan, B12-3 and M97( to P applied at adequate and deficient levels (0 and 100 ppm P resp). Phosphorus level and variety interaction was significant for almost all the parameters studied. Substantial differences were observed among genotypes for accumulation of shoot and root dry weight , total biomass and relative reduction in shoot biomass due to phosphorus stress.
 Phosphorus stress factor ranged between 27.7% to 43.1% that is 2 folds differences in relative reduction in shoot dry weight due phosphorus stress factor among genotypes. Phosphorus utilization efficiency was almost doubled in the genotypes that were grown with no phosphorus supply compared to these grown with 100 ppm P supply. P concentration and uptake in genotypes were significantly different at deficient and adequate phosphorus levels.

Drought, salinity and combined effects on Almond growth and physiological parameters

Almond production is concentrated in semi arid regions where fresh surface water supplies are increasingly scarce and ground waters often salinized. In drought years growers have to restrict fresh water application, either stressing the trees with inadequate water or adding saline water and reducing water stress but causing salt stress. Tree response to combined water and salt stress are critical to management decisions but there is little to no information at this time. We examine the water and salt stress and combined water-salt stress response of two almond cultivars in a two year outdoor experiment with young trees. Water treatments consisted of 100%, 80% and 60% of tree ET and salt treatments of EC= 0.55, 1.20, 2.40 and 3.0 dS m-1), for a total of 120 trees in twelve treatents two cultivars and five replicates. We examined water use, trunk diameter and physiological parameters. All parameters showed significant decline starting at 80% water application and EC 1.2 dS m-1. In terms of growth rather than survival, almond was sensitive to water as well as salt stress. Equations for reduction in trunk growth were developed for treatments with either salinity only or water only stress. We evaluated combined stress using three stress response models: additive stress, dominant stress model and a multiplicative stress model where the predicted growth loss is obtained by multiplying the relative growth response for the individual stresses. Trunk growth under combined water and salt stress treatments was well predicted only when using a multiplicative stress response function.

Tepung limbah fillet ikan nila sebagai alternatif subsitusi tepung ikan komersial dalam formulasi pakan bagi pertumbuhan benih ikan Nila (Oreochromis niloticus)

The research was held on May 7th – 30th 2021 in the Aquaculture Technology Laboratory at the Faculty of Fisheries and Marine of Sam Ratulangi University with the objectives were to determine tilapia fish fillet waste flour’s substitution impact for the growth of the seed and to determine the impact of the tilapia fish fillet waste flour towards the feed’s efficiency. The research lasted for three consecutive weeks. Fish culture container was plastic container with the height of 50 cm and the width of 30 cm for the total of 18 pieces containers. Each container was flowed by 10 liters of water. Fish used had a size of 3 to 5 cm with a weight of 1 gram for each tilapia and stocked as many as 10 fish in each container. The pellets used was flour pellets of tilapia waste fillet with different compositions. Each container was labeled alphabetically: A (0%), B (10%), C (30%), D (30%), E (40%), and F (50%). Frequency of feeding was 3 times a day (08:00 AM, 12:00 AM and 04:00 PM) with a feeding dose of 10%. Water was changed every 4 days. Growth observation was conducted every week using digital scales 0,1 gram. Experimental contrivance was random contrivance exhaustive. Analysis used analysis of diversity. The observed data included relative growth and feed efficiency values. The result showed treatment E gave a better relative growth response and feed efficiency value than other treatments.

Modelling soil nitrogen mineralisation in semi-mature pine stands of South Africa to identify nutritional limitations and to predict potential responses to fertilisation

Estimates of available nitrogen (based on topsoil nitrogen mineralisation rates) in semi-mature stands of Pinus radiata (D Don.) as well as pure species and hybrids of Pinus elliottii (Engelm.) in South Africa display a strong, significant, negative relationship with growth response to applied fertilisers in field experiments. This inexpensive technique can be incorporated in a fertiliser decision support system to minimise wasteful fertiliser applications. South African mid-rotation pine stands respond with high variability to nitrogen fertiliser supplements in the presence of phosphorus. We aimed to find a screening tool for stands that are responsive to fertilisation. The volume growth response relative to control plots (3 years after fertilisation with 200 kg ha−1 N in the presence of 100 kg ha−1 P) was determined across 14 pine fertiliser experiments in South Africa. These values were correlated to soil and other properties for each site and also to estimates of N availability and N mineralisation rates using the Soil Nitrogen Availability Predictor (SNAP) model. The relative volume growth response to fertilisation ranged with a factor from 0.05 to 0.96. No single result from standard soil analyses showed a strong positive or negative correlation with this growth response. However, highly significant negative correlations were observed between an estimate of N availability based on topsoil aerobic nitrogen mineralisation rates and the relative volume growth responses to fertilisation. The estimate of N availability derived from incubation studies may assist us to predict the magnitude of the response to N fertilisation (in the presence of P) with a fair degree of accuracy. The accuracy can be improved if the N availability estimate from aerobic incubation is used with other variables (pH and soil C content) in a multivariate regression to predict relative yield response to fertilisation.

Comparative growth response related to hair mineral analysis in dromedary camel calves.

Background:The dromedary camel plays a significant role in supporting the livelihood of pastoral and agropastoral systems, as well as a source of income for the national economy in arid regions.Aim:The current study was executed to check the comparative growth response in relation to hair mineral status in Marecha camel calves reared under an intensive management system and an extensive management system in Thal desert Punjab, Pakistan.Methods:Twelve male and female Camelus dromedarius calves of almost the same weight and age were divided into two groups of 6 each (3 male and 3 female). The calves of the first group were maintained at the Camel Breeding and Research Station, Rakh Mahni, in a semi-open housing system, while the second group was maintained in available housing under field conditions. Calves in the first group were fed concentrate at the rate of 1 kg/head/day along with gram straw (Cicer arientinum) ad libitum, while calves in the second group were allowed to graze/browse for 10 hours daily along with household refusals, including kitchen wastes. Water was provided twice a day. Impressum’s digital weighing scale was used for fortnightly weighing. Data collected on different parameters were subjected to statistical analysis with 2 × 2 factorial arrangements of treatments under a completely randomized design.Results:After the 120-day trial period, the mean body weight and average daily gain of male and female calves were significantly increased (p < 0.05) in IMS as 80.8 ± 2.7, 77.8 ± 2.7 kg and 0.67 ± 0.02, 0.65 ± 0.02 kg/days than EMS as 64.5 ± 2.6, 52.9 ± 2.6 kg and 0.54 ± 0.02, 0.44 ± 0.02 kg/days. Intake of crop residues (p < 0.05) was found to be 6.9 ± 0.45 and 6.4 ± 0.45 kg/days for male and female calves in IMS, respectively, and 3.5 ± 0.23 for male and female calves in EMS, respectively. The conversion index g/kg average daily intake was 97.1, 101.5 and 154.3, 125.7 for male and female calves in IMS and EMS, respectively. Regarding hair mineral status, Ca, Mg, Cu, Zn, Fe, and Mn concentrations were found to be significantly different (p < 0.05) among calf groups in IMS and EMS.Conclusion:This study indicates that wool analysis and management of weight gain in camel calves should be further explored to support increased meat supply in arid regions.

Quantifying climate-growth relationships at the stand level in a mature mixed-species conifer forest.

A range of environmental factors regulate tree growth; however, climate is generally thought to most strongly influence year-to-year variability in growth. Numerous dendrochronological (tree-ring) studies have identified climate factors that influence year-to-year variability in growth for given tree species and location. However, traditional dendrochronology methods have limitations that prevent them from adequately assessing stand-level (as opposed to species-level) growth. We argue that stand-level growth analyses provide a more meaningful assessment of forest response to climate fluctuations, as well as the management options that may be employed to sustain forest productivity. Working in a mature, mixed-species stand at the Howland Research Forest of central Maine, USA, we used two alternatives to traditional dendrochronological analyses by (1) selecting trees for coring using a stratified (by size and species), random sampling method that ensures a representative sample of the stand, and (2) converting ring widths to biomass increments, which once summed, produced a representation of stand-level growth, while maintaining species identities or canopy position if needed. We then tested the relative influence of seasonal climate variables on year-to-year variability in the biomass increment using generalized least squares regression, while accounting for temporal autocorrelation. Our results indicate that stand-level growth responded most strongly to previous summer and current spring climate variables, resulting from a combination of individualistic climate responses occurring at the species- and canopy-position level. Our climate models were better fit to stand-level biomass increment than to species-level or canopy-position summaries. The relative growth responses (i.e., percent change) predicted from the most influential climate variables indicate stand-level growth varies less from to year-to-year than species-level or canopy-position growth responses. By assessing stand-level growth response to climate, we provide an alternative perspective on climate-growth relationships of forests, improving our understanding of forest growth dynamics under a fluctuating climate.

Evaluation of bermuda and paspalum grass types for urban landscapes under saline water irrigation

ABSTRACTIn the arid regions, turfgrass cover is an integral part of landscape to protect the soil from erosion, enhance the aesthetic value, and improve the microclimate. The salinity and the scarcity of fresh water of the arid region are the major challenging factors in turfgrass production. Therefore, the need for salt tolerant turfgrass with functional quality is necessary to improve the turf performance. The detrimental effects of salinity include growth suppression, and lowered osmotic potential ultimately leading to firing of the leaf blades. In this context, the study was undertaken to determine the relative salt tolerance and growth response of turfgrass genotypes in order to recommend turfgrass cultivars that can tolerate high salinity irrigation and maintain excellent visual and functional qualities under United Arab Emirates (UAE) condition. The paspalum cultivars maintained the highest succulence percentage compared to the bermudagrass cultivars under enhanced salinity levels. The shoots count, fresh weight (FW), and dry weight (DW) were found highest in paspalum types. The chlorophyll a, chlorophyll b and the total chlorophyll content was found higher in bermuda grass types under high salinity levels. The bermudagrass cultivars showed significantly higher carotenoids, anthocyanins and proline compared to the paspalum types under salt stress condition. In the case of princess 77 and Yukon, an inherently high amount of proline was recorded which confirmed an increase up to 10,000 ppm and drastically declined beyond this concentration. Sea Dwarf paspalum and Sea Isle 2000 maintained uniformity in the proline level at all levels of salinity without significant variation. These findings point to the fact that both paspalum and bermuda types exhibited varied responses to different physiological and biochemical parameters under the saline conditions. Paspalum types have an edge over the bermudagrass in terms of shoot density, which is a potential factor in determining the high-quality turfs. Bermudagrass types can be applied in lower salinity conditions based on the responses as evidenced from the present results.

Survival and development of embryos of &lt;i&gt;Gallus gallus domesticus&lt;/i&gt; treated with inorganic bromide

The range of bromide (Br-) in groundwater sources surveyed in South Africa is 0 - 18.4 mg/L. The research aimed to establish chicken embryo sensitivity to a range of Br- treatments (mg/L) injected into fertilised Ross-308 eggs in three phases: (1) five eggs injected with 10 mg Br-/L; (2) 45 eggs divided into groups and injected with 0, 1 and 5 mg Br-/L; (3) 148 eggs divided into groups injected with 0, 0.01, 0.05, 0.5, and 1 mg Br-/L. Incubation was at standard conditions. Breakout analysis was done at various stages of incubation. The mass of the embryo and of the heart, liver and brain was measured at Day 20. Statistical analysis used Statistical Analyses System® software FREQ procedure to determine the chi-square goodness-of-fit test for percentages of live or dead embryos within and between treatments. The GLM procedure was applied to test for differences in relative organ mass (g) between treatments using F-test. The results showed: (1) 10 mg Br-/L is toxic; (2) Br- is lethal to embryos at concentrations &gt;1 mg/L and toxic at 1 mg/L; and (3) embryo survival was significantly negatively correlated (R2 = -0.92) with increasing Br- concentrations. Concentrations &gt;0.5 mg Br-/L showed greater risk on differential development. Concentrations &gt;0.01 mg Br-/L showed potentially severe effects on developing embryos. The heart showed the greatest relative growth response followed by the brain. The no observed adverse effect level target water quality range (NOAEL-TWQR) in developing chicken embryos was 0 - 0.01 mg/L.Keywords: Bromine, embryo model, halogens, maximum residue level, toxicity, water quality

Variation in urban forest productivity and response to extreme drought across a large metropolitan region

The growth and survival of urban trees and maintenance of urban forest canopy are important considerations in adaptation of urban regions to climate change, especially in relation to increasing frequency of extreme climatic events such as drought. However, urban forest growth and drought response may vary considerably within large urban landscapes across gradients in land use, urbanization, forest composition and structure, and environmental factors. We quantified urban forest growth and resilience and resistance to extreme drought in the greater Chicago metropolitan region based on patterns of annual basal area production from increment core analysis. We evaluated variation in growth and drought response in relation to a broad urban to rural gradient, land-use categories, local-scale environmental predictors, and forest community characteristics. Urban forest growth varied greatly among land-use classes and major genera. Plot-level variation in productivity was predicted most strongly (R2 = 0.53) by total plot-level basal area, canopy height, species composition, soil and ground-cover characteristics, and position within the urban-rural gradient. Urban forest growth was strongly related to regional meteorological drought. In periods of extreme drought conditions growth declined in the year of the drought (i.e., was not resistant to drought effects), but was highly resilient to drought in the subsequent 5 year period. Drought response did not vary consistently across land-use classes or among major genera, and site or community characteristics had little explanatory power in predicting drought response. Improved understanding of factors driving variation in urban forest growth and drought response could help inform adaptation-focused urban forest management strategies.

Peroxidized lipids reduce growth performance of poultry and swine: A meta-analysis

Animal performance is affected by feeding peroxidized lipids. Nevertheless, inaccuracies and limitations of common lipid peroxidation analyses are associated with inconsistent results regarding animals consuming diets with peroxidized lipids. A comprehensive meta-analysis was conducted to determine the effects of feeding dietary peroxidized lipids on growth performance and oxidative status in poultry and swine. A total of 29 publications with 42 poultry and 23 swine observations were analyzed. Concentration of dietary thiobarbituric acid reactive substances (TBARS) and peroxide value (PV), along with ADG, ADFI, G:F, and serum or plasma concentrations of vitamin E and TBARS were obtained from publications when reported. The relative impact of feeding peroxidized lipids was calculated as a percentage of ADG, ADFI, and G:F relative to responses from feeding isocaloric diets containing unperoxidized lipids. Data were analyzed for outliers, general distribution, and correlations among variables. Overall, feeding peroxidized lipids to both species resulted in a 5% reduction in ADG, a 3% reduction in ADFI, and G:F was reduced by 2% compared with feeding unperoxidized lipids. The difference in the average magnitude of reduction in ADG, compared with less average magnitude of reduction in ADFI, suggests that factors other than caloric intake (i.e. oxidative stress) contribute to reduced ADG when feeding peroxidized lipids. Both species fed peroxidized lipids had reduced serum or plasma vitamin E content (52%) and increased TBARS concentration (120%) relative to animals fed unperoxidized lipids, suggesting that feeding peroxidized lipids contributes to increased oxidative stress. Dietary PV was negatively correlated with ADG (r=− 0.81, P<0.01) for poultry, whereas for swine, dietary TBARS was negatively correlated with ADG (r=− 0.58, P=0.04), but there were large prediction errors for poultry (MSE=0.87) and swine (MSE=12.79). In conclusion, these results suggest that feeding peroxidized lipids reduce growth performance of poultry and swine, but the magnitude of reduction varies among experiments due to differences in fatty acid profiles among types of lipid sources, time and temperature of peroxidation conditions, and relative growth responses among studies. More accurate peroxidation measurement methods need to be developed to accurately estimate the negative impacts of feeding peroxidized lipids on animal growth performance.

Phosphorus Stress-Induced Differential Growth, and Phosphorus Acquisition and Use Efficiency by Spring Wheat Cultivars

ABSTRACTPhosphorus (P) is a finite, non-renewable, and natural resource and a vital major nutrient for plant metabolic and developmental processes. However, adverse soil biogeochemical characteristics of alkaline-calcareous soils (especially Aridisols) and highly weathered acid soils (i.e., Ultisols and Oxisols) render orthophosphate (Pi) as the least available major nutrient due to P complexation, sorption, and/or fixation. In such soil environments, plant bioavailable P is only a small fraction of total soil P, seriously limiting crop growth and production. Different plant species, and even cultivars of the same species, may display a suite of growth responses that enable them to solubilize and scavenge soil P either by enhancing external Pi acquisition or reprioritizing internal Pi use under P-stress soil environments. This paper reports relative growth responses, P acquisition and P-use efficiency characteristics by 14 cultivars of spring wheat (Triticum aestivum L.) grown in solution culture with high/low P supply induced by applying soluble NH4H2PO4, sparingly soluble rock phosphate, and Ca3(PO4)2. The wheat cultivars exhibited considerable genetic diversity in biomass accumulation, P concentrations, P contents, factor (PSF) and P efficiency characteristics [i.e., P utilization efficiency (PUE), P efficiency (PE), and PE ratio (PER)]. Plant growth and PE parameters were significantly correlated, while P uptake was linearly related with biomass increase and solution pH decrease. The wheat cultivars with high PUE, PER and P uptake, and low PSF, and plant P concentration were more efficient in utilizing P and, hence, more tolerant under P-stress environment. Biomass and P contents of “P efficient/low-P tolerant” wheat cultivars were superior to “P inefficient/low-P sensitive” cultivars at all P-stress levels. Hence, “P efficient/low-P tolerant” cultivars are the most desirable wheat genotypes for P-stress environments because they are able to scavenge more P from sparingly soluble P sources or soil-bound P forms.

Effects of fertiliser applications after thinning of Pinus radiata on a high-elevation site in south-eastern Australia

ABSTRACTA trial to assess the effects of fertiliser applied after thinning was established in a ten-year-old Pinus radiata stand growing on a high elevation site in south-eastern Australia. The trial had two components. The first studied the effects of fertilisers applied in a factorial design with two levels of phosphorus (0 and 50 kg P ha–1) and three of nitrogen (0, 150 and 300 kg N ha–1) plus a mixed nutrient treatment to areas thinned to a routine intensity. In the second part, levels of thinning intensity were assessed with and without a fertiliser (N1P1) application. Over the seven years of the study, growth was affected by below average rainfall in four of the years. Significant responses to fertiliser were achieved with all treatments; the best was 150 kg N ha–1 + 50 kg P ha–1 plus trace elements. The volume increment was increased by 28%, however this was not significantly different from the N1P1 alone. The N1P1 fertiliser increased productivity at all thinning levels including the unthinned treatment. Models predicting relative growth response based on foliage nutrient levels gave reasonable predictions, that is, 29% increase in volume periodic increment and this was slightly higher than that achieved. On such low rainfall sites, rather than having multiple thinnings, one option is a relatively heavy thinning at a young age with fertiliser application and then leaving the stand until final harvest. Estate optimisation models provide forest managers with the means to evaluate fertiliser-thinning treatment options against objectives such as maximising the present value of expected future cash flow within production and budget constraints.

Phosphorus Stress Induced Variations in Growth Behavior and P Efficiency among Brassica Cultivars Grown with Sparingly Soluble P Sources

To evaluate phosphorus (P)–stress–induced relative growth responses, P-efficiency characteristics, P remobilization, and redesign in root architectural systems, Brassica cultivars were grown with sparingly soluble rock phosphate and calcium phosphate [Ca3(PO4)2] or with low/high P supply in solution and sand culture experiments. Tested cultivars showed considerable genetic diversity in biomass accumulation, concentration and contents of P, P-stress factor (PSF), and P-efficiency characteristics [P-utilization efficiency (PUE), P efficiency (PE), and P-efficiency ratio (PER)]. Statistically significant correlations were observed between P efficiency and growth parameters. Elongation rates of primary roots decreased but the length of lateral roots and branched zone elongation rates increased under P starvation. Cultivars remobilized P from metabolically inactive to active sites in P-stressed plants that may have helped low-P-tolerant cultivars to establish a better rooting system, which provided basis for enhanced P-use efficiency and tolerance against P stress. Cultivars depicting high P efficiency and low PSF values were more tolerant and are a better choice to grow under P-stress environments.

Response of tree regeneration to experimental gap creation and deer herbivory in north temperate forests

Structural heterogeneity has become a goal of contemporary forest management, yet the effect of incorporating variable sized canopy openings characteristic of older forests on ecosystem services is still largely unknown. Single-tree selection silviculture reduces tree species diversity, and group-selection harvests often produce inconsistent results in maintaining the proportion of species with low or intermediate shade tolerance. It is unclear how much variability is related to inherent growth rate differences among shade tolerance classes, asymmetric competition, sprouting behavior, herbivory, and other factors. We conducted an experiment to control several of these factors. The northern hardwood study area in north-central Wisconsin included 15 replicates of each of 3 sizes of experimental gaps (50m2, 200m2, and 380m2). Ten main plots (80×80m2) were fenced to exclude deer. Vertical height growth of saplings and stump sprouts was monitored for two years pre-treatment and four years post-treatment.Overstory gaps significantly increased height growth rates, but there was no significant difference between rates of the very shade-tolerant Acer saccharum and several midtolerant species in any gap size. Saplings dominated the regeneration layer in small gaps. Stump sprouts were more abundant and grew faster than saplings in large gaps, but after 4years, A. saccharum advance regeneration still predominated in the upper height classes. Deer had limited effects on sapling development or species composition because tall advance regeneration was beyond their reach, but they severely affected the sprout layer. In unfenced plots, the unpalatable Ostrya viriginiana had the tallest sprouts. Overall, midtolerant species made up about 16% of the gap regeneration layer and appear to be increasing their proportion over time. Height growth rates of many saplings and sprouts exceeded 50cm per year, suggesting that successful gap capture would be likely for both shade-tolerance groups under current environmental conditions. The non-significant difference in growth rates between shade-tolerant and midtolerant species across the light gradient could change as more time elapses since gap creation. However, our findings after four years are consistent with other studies in suggesting that there may be no consistent trends in the relative growth responses of shade-tolerant and midtolerant tree species to increased light and gap size.

Relative Phytoplankton growth responses to physically and chemically dispersed South Louisiana sweet crude oil

We conducted controlled laboratory exposure experiments to assess the toxic effects of water-accommodated fractions (WAFs) of South Louisiana sweet crude oil on five phytoplankton species isolated from the Gulf of Mexico. Experiments were conducted with individual and combinations of the five phytoplankton species to determine growth inhibitions to eight total petroleum hydrocarbon (TPH) equivalent concentrations ranging from 461 to 7,205 ppb. The composition and concentration of crude oil were altered by physical and chemical processes and used to help evaluate crude oil toxicity. The impact of crude oil exposure on phytoplankton growth varied with the concentration of crude oil, species of microalgae, and their community composition. At a concentration of TPH < 1,200 ppb, dinoflagellate species showed significantly better tolerance, while diatom species showed a higher tolerance to crude oil at higher concentrations of TPH. For both groups, the larger species were more tolerant to crude oil than smaller ones. The toxicity potential of crude oil seems to be strongly influenced by the concentration of polycyclic aromatic hydrocarbons (PAHs). The addition of the dispersant, Corexit® EC9500A, increased the amount of crude oil up to 50-fold in the water column, while the physical enhancement (vigorous mixing of water column) did not significantly increase the amount of TPH concentration in the water column. The species response to crude oil was also examined in the five-species community. Each phytoplankton species showed considerably less tolerance to crude oil in the five-species community compared to their individual responses. This study provides baseline information about individual phytoplankton responses to crude oil and dispersed crude oil for subsequent research efforts seeking to understand the impacts of oil on the phytoplankton in the bigger picture.

Climate warming and precipitation redistribution modify tree–grass interactions and tree species establishment in a warm‐temperate savanna

Savanna tree-grass interactions may be particularly sensitive to climate change. Establishment of two tree canopy dominants, post oak (Quercus stellata) and eastern redcedar (Juniperus virginiana), grown with the dominant C4 perennial grass (Schizachyrium scoparium) in southern oak savanna of the United States were evaluated under four climatic scenarios for 6years. Tree-grass interactions were examined with and without warming (+1.5°C) in combination with a long-term mean rainfall treatment and a modified rainfall regime that redistributed 40% of summer rainfall to spring and fall, intensifying summer drought. The aim was to determine: (1) the relative growth response of these species, (2) potential shifts in the balance of tree-grass interactions, and (3) the trajectory of juniper encroachment into savannas, under these anticipated climatic conditions. Precipitation redistribution reduced relative growth rate (RGR) of trees grown with grass. Warming increased growth of J. virginiana and strongly reduced Q. stellata survival. Tiller numbers of S. scoparium plants were unaffected by warming, but the number of reproductive tillers was increasingly suppressed by intensified drought each year. Growth rates of J. virginiana and Q. stellata were suppressed by grass presence early, but in subsequent years were higher when grown with grass. Quercus stellata had overall reduced RGR, but enhanced survival when grown with grass, while survival of J. virginiana remained near 100% in all treatments. Once trees surpassed a threshold height of 1.1m, both tiller number and survival of S. scoparium plants were drastically reduced by the presence of J. virginiana, but not Q. stellata. Juniperus virginiana was the only savanna dominant in which neither survival nor final aboveground mass were adversely affected by the climate scenario of warming and intensified summer drought. These responses indicate that climate warming and altered precipitation patterns will further accelerate juniper encroachment and woody thickening in a warm-temperate oak savanna.