Term Growth Response Research Articles

Screening and Identification of Aluminium Toxicity Tolerant Lentil (Lens culinaris Medik.) RILs based on Root Growth Studies and Organic Acid Exudation under Hydroponics

Background: Aluminium (Al) stress is among the prime limitations of crop production including Lentil, in acidic soils as Al solubilizes into phytotoxic forms at low pH causing root growth inhibition, minimizing plant-vigor and yield. The current study was performed to identify the Al tolerant RILs based on root-regrowth studies, short term growth culture and organic acid exudation in reaction to Al toxicity under hydroponics. Methods: The study involved screening for Al toxicity tolerance in recombinant inbred lines (RILs) population of lentil through root re-growth studies, short term growth response method under hydroponics treated with toxic concentration of Al (148 µM), organic acid exudation using HPLC and correlation analysis among the traits. Result: ANOVA for root and shoot traits revealed presence of highly significant genotypic differences for all the traits. High GCV along with high H2bs and GA% were observed for the traits revealing the influence of additive genes and suggested reliable selection of these traits for Al toxicity tolerance. Citric acid was exudated in highest amount in all the genotypes and was positively and significantly correlated with RRG. Based on the hydroponics study and organic acid exudation, RILs identified as tolerant were LRIL-10, LRIL-37, LRIL-68, LRIL-96, LRIL-97, LRIL-113, LRIL-125, LRIL-133, LRIL-143, LRIL-144 and LRIL-148. With further evaluation, these RILs may serve as important Al toxicity tolerant varieties suitable for acidic soil conditions. Also, these lines may serve as donors of Al toxicity loci and mapping of Al tolerance genes.

Biodegradation of low-density polyethylene (LDPE) through application of indigenous strain Alcaligenes faecalis ISJ128.

The resiliency of plastic products against microbial degradation in natural environment often creates devastating changes for humans, plants, and animals on the earth's surface. Biodegradation of plastics using indigenous bacteria may serve as a critical approach to overcome this resulting environmental stress. In the present work, a polyethylene degrading bacterium Alcaligenes faecalis strain ISJ128 (Accession No. MK968769) was isolated from partially degraded polyethylene film buried in the soil at plastic waste disposal site. The biodegradation studies were conducted by employing various methods such as hydrophobicity assessment of the strain ISJ128, measurement of viability and total protein content of bacterial biofilm attached to the polyethylene surface. The proliferation of bacterial cells on polyethylene film, as indicated by high growth response in terms of protein content (85.50µgmL-1) and viability (1010CFUmL-1), proposed reasonable suitability of our strain A. faecalis ISJ128 toward polyethylene degradation. The results of biodegradation assay revealed significant degradation (10.40%) of polyethylene film within a short period of time (i.e., 60days), whereas no signs of degradation were seen in control PE film. A. faecalis strain ISJ128 also demonstrated a removal rate of 0.0018day-1 along with half-life of 462days. The scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy studies not only displayed changes on polyethylene surface but also altered level of intensity of functional groups and an increase in the carbonyl indexes justifying the degradation of polyethylene film due to bacterial activity. In addition, the secondary structure prediction (M fold software) of 16SrDNA proved the stable nature of the bacterial strain, thereby reflecting the profound scope of A. faecalis strain ISJ128 as a potential degrader for the eco-friendly disposal of polyethylene waste. Schematic representation of methodology.

A digital sensor to measure real-time leaf movements and detect abiotic stress in plants.

Plant and plant organ movements are the result of a complex integration of endogenous growth and developmental responses, partially controlled by the circadian clock, and external environmental cues. Monitoring of plant motion is typically done by image-based phenotyping techniques with the aid of computer vision algorithms. Here we present a method to measure leaf movements using a digital inertial measurement unit (IMU) sensor. The lightweight sensor is easily attachable to a leaf or plant organ and records angular traits in real-time for two dimensions (pitch and roll) with high resolution (measured sensor oscillations of 0.36 ± 0.53° for pitch and 0.50 ± 0.65° for roll). We were able to record simple movements such as petiole bending, as well as complex lamina motions, in several crops, ranging from tomato to banana. We also assessed growth responses in terms of lettuce rosette expansion and maize seedling stem movements. The IMU sensors are capable of detecting small changes of nutations (i.e. bending movements) in leaves of different ages and in different plant species. In addition, the sensor system can also monitor stress-induced leaf movements. We observed that unfavorable environmental conditions evoke certain leaf movements, such as drastic epinastic responses, as well as subtle fading of the amplitude of nutations. In summary, the presented digital sensor system enables continuous detection of a variety of leaf motions with high precision, and is a low-cost tool in the field of plant phenotyping, with potential applications in early stress detection.

Cyclic thermal fluctuations can be burden or relief for an ectotherm depending on fluctuations’ average and amplitude

Abstract Predicting the implications of ongoing ocean climate warming demands a better understanding of how short‐term thermal variability impacts marine ectotherms, particularly at beyond‐optimal average conditions during summer heatwaves. Using a globally important model species, the blue mussel Mytilus, in a 5‐week‐long experiment, we (a) assessed growth performance traits under 12 scenarios, consisting of four thermal averages (18.5, 21, 23.5 and 26℃) imposed as constant or daily fluctuating regimes with amplitudes of 2 or 4℃. Additionally, we conducted a short‐term assay using different mussel individuals to (b) test for the species capacity for suppression and recovery of metabolic performance traits (feeding and aerobic respiration) when exposed to a 1‐day thermal fluctuation regime (16.8–30.5℃). Using this high‐resolution data, we (c) generated short‐term thermal metabolic performance curves to predict and explain growth responses observed in the long‐term experiment. We found that daily high‐amplitude thermal cycles (4℃) improved mussel growth when fluctuations were imposed around an extreme average temperature of 26℃, representing end‐of‐century heatwaves. In contrast, thermal cycles negatively affected mussel growth at a less extreme average temperature of 23.5℃, resembling current peak summer temperature scenarios. These results suggest that fluctuations ameliorate heat stress impacts only at critically high average temperatures. The short‐term assay demonstrated that during the warming phase, animals stopped feeding between 24 and 30℃ while gradually suppressing respiration. In the subsequent cooling phase, feeding and respiration partially and fully recovered to pre‐heating rates respectively. Furthermore, nonlinear averaging of short‐term feeding responses (upscaling) well‐predicted longer term growth responses to fluctuations. Our findings suggest that fluctuations can be beneficial to or detrimental for the long‐term performance of ectothermic animals, depending on the fluctuations' average and amplitude. Furthermore, the observed effects can be linked to fluctuation‐mediated metabolic suppression and recovery. In a general framework, we propose various hypothetical scenarios of fluctuation impacts on ectotherm performance considering inter‐ or intra‐species variability in heat sensitivity. Our research highlights the need for studying metabolic performance in relation to cyclic abiotic fluctuations to advance the understanding of climate change impacts on aquatic systems. A free Plain Language Summary can be found within the Supporting Information of this article.

Marginal Calluna populations are more resistant to climate change, but not under high-nitrogen loads

The dominant plant species of European heathlands Calluna vulgaris is considered vulnerable to drought and enhanced nitrogen (N) loads. However, impacts may vary across the distribution range of Calluna heathlands. We tested the hypothesis that Calluna of southern and eastern marginal populations (MP) are more resistant to drought events than plants of central populations (CP), and that this is mainly due to trait differences such as biomass allocation patterns. Furthermore, we hypothesised that N fertilisation can offset differences in drought susceptibility between CP and MP. We conducted a full-factorial 2-year greenhouse experiment with Calluna plants of CP and MP and quantified growth responses in terms of biomass production, allocation and tissue δ13C signatures. Biomass production, shoot–root ratios and tissue δ13C values of 1-year-old plants were higher for CP than for MP, indicating a higher drought susceptibility of CP. These trait differences were not observed for 2-year-old plants. N fertilisation increased shoot–root ratios of 1- and 2-year-old plants and across populations due to a stimulation of the aboveground biomass allocation. As a consequence, population-related differences in drought susceptibility were offset for N-fertilised plants. We concluded that Calluna plants originating from different populations developed adaptive traits to local climates, which determined their drought sensitivity. However, the higher drought resistance of MP can be attenuated by an N-induced increase in shoot–root ratios. This suggests that analyses on plant growth responses to global change should include multi-factor approaches with a focus on different populations throughout a species’ distribution range.

Evaluation of sweet potato genotypes against salinity

Ten sweet potato lines/varieties were studied for growth response under NaCl salt stress condition. The rooting ability, in terms of root number, root length and root volume was studied. Growth in terms of root and shoot dry weight was also studied. A variation was recorded among the eight varieties and two lines in different doses of NaCl for growth responses in terms of rooting ability. The genotypes BARI SP-9, showed rooting ability up to 20 dS-m among the 10 genotypes. The genotypes BARI SP-2, BARI SP-3, BARI SP-7, BARI SP-9 and line SP-613 showed increase in root number upto 6 dS-m as compared to control. Accumulation of Na+ increased with a concomitant decrease in K+. Sweet potato plantlet transport less amount of Na+ and more amount of K+ to the shoot. Genotypes BARI SP-7 and BARI SP-9 showed better performance upto15dS-m.Bangladesh J. Agril. Res. 40(2): 249-257 June 2015

Optimum N and P rates for greenhouse production of vegetative coleus using constant liquid feed

ABSTRACTMany new coleus (C. hybridus cv.) cultivars are vegetatively propagated and require different fertilization practices from seed propagated cultivars. Two experiments were conducted to evaluate growth responses of Henna, Indian Summer, Mint Mocha, New Orleans Red, Red Head, and Trusty Rusty to 0, 70, 140, 280 and 420 mg·L−1 nitrogen (N), and Henna, Mint Mocha, Red Head, and Trusty Rusty to 0, 6.2, 12.4, 24.8, or 49.6 mg·L−1 phosphorus (P) to determine optimum constant liquid feed rates to produce marketable size plants from rooted cuttings. Positive growth responses in terms of biomass were found with increasing N rates but not P rates. For medium-sized cultivars such as Henna, Indian Summer, and New Orleans Red, quadratic responses were found in aboveground biomass, and N at 280 mg·L−1 resulted in similar plant size and dry weight as those fertilized at 140 and 420 mg·L−1 N. For large-sized cultivars such as Mint Mocha, Red Head and Trusty Rusty, plant dry weight responded linearly within the N range tested and were greatest at 420 mg·L−1. However, plant visual quality was negatively affected by N rates at 280 and 420 mg·L−1 in that, leaf color became less intense at these high N rates. Plants fertilized at 70 mg·L−1 were smaller than those fertilized at 140 mg·L−1, however, they received similar visual quality ratings because of more intense leaf color. Therefore, N at 70 to 140 mg·L−1 can be used to grow most vegetative coleus for similar marketable quality. Mint Mocha and Henna were the only cultivars responded to P treatments that, 12.4 mg·L−1 P rate resulted in greater biomass than the no-P control. All other cultivars had no response to supplemental P except a linear response in tissue P%. Therefore, supplemental P is not required during the 8 week production period when there is an initial P charge in the substrate. We found that substrate pH decreases with higher P rates, therefore supplemental P fertilizer can be used for adjusting pH. Both N and P rates found optimum in this study are lower than current industry practices (N at 150 to 250 mg·L−1 and P at 24 mg·L−1) and can significantly lower production cost and potential leaching of excessive nutrient into waterway. Nutrient treatments in further study on postharvest performance of vegetative coleus will be selected based on this study.

Hemolymph quality as indicator of health status in juvenile Chinese horseshoe crab Tachypleus tridentatus (Xiphosura) under laboratory culture

The growth performance and hemolymph quality of juvenile Chinese horseshoe crabs under four diet treatments: brine shrimp Artemia salina, short-neck clam Ruditapes philippinarum, sandworm Marphysa sanguinea and mixed clam and sandworm were evaluated in a 12-week experiment. The growth responses in terms of final body weight, specific growth rates and percentage of individuals molted under the clam diet were significantly higher than those fed with brine shrimp and sandworm, whereas the mixed clam and sandworm diet was not statistically different from the other three treatments. While the hemolymph properties among these diets were similar, significant declines in hemocyanin concentration, percentage of oxyhemocyanin, and ratio of granular–spherical to granular–flattened states of amebocytes were noted at the end of the study. Such a decrease in hemolymph quality indicated deleterious effects due to prolonged culture on the health status of the juveniles, which might be attributed to captivity-related issues, such as deficiencies of essential diet compositions, movement constraints and absence of tidal rhythms. This was further supported from the finding that the hemolymph quality of the experimental juveniles was significantly poor compared to that of the juveniles collected from the field. Changes of hemolymph constituents could thus be a useful indicator to reflect the health status of juvenile horseshoe crabs under laboratory culture.

Induced Accumulation of Polyphenolics and Flavonoids in Cyanobacteria under Salt Stress Protects Organisms through Enhanced Antioxidant Activity

Induced accumulation of polyphenolics and flavonoids in cyanobacterial strains grown under different salt concentrations is correlated with their growth under stress conditions and enhanced antioxidant activity. Plectonema boryanum, Hapalosiphon intricatus, Anabaena doliolum and Oscillatoria acuta grown for 21 days under different salt concentrations (80, 160, 240, 320 and 400 mM) in BG11 medium showed differential growth responses in terms of biomass, total protein, chlorophyll content, total content of polyphenol, flavonoid and carotenoid, accumulation of phenolic acids (gallic, caffeic, chlorogenic, ferullic and vanillic) and flavonoids (rutin and quercetin). Cyanobacterial extracts showed prominent free radical scavenging antioxidant activity (AOA) in terms of % DPPH discoloration. Highly significant (p < 0.05) and strong correlation was found between TPC and AOA (r = 0.974). Other positive but non-significant (p < 0.05) correlations were observed between AOA and gallic acid (r = 0.893) and AOA and caffeic acid (r = 0.931). Significant and strong correlation was also observed between gallic and caffeic acid (r = 0.973). Positive but lesser magnitude correlations were recorded between TPC and caffeic acid (r = 0.905), TPC and gallic acid (r = 0.920), gallic and vanillic acid (r = 0.916) and caffeic and vanillic acid (r = 0.814). An integrated combination of growth parameters, salt-induced accumulation of phenylpropanoids and stress-derived subsequent antioxidant property of cyanobacterial extracts is thought to provide evidence that secondary metabolic changes can act as the possible alternative mechanism to overcome stress-induced damages in cells.

Essentiality of calcium supplement in the diets of Heterobranchus bidorsalis fingerlings

An 84-day feeding trial was conducted to determine the effect of calcium (Ca) supplemented diets on growth and body mineral composition of Heterobranchus bidorsalis, initial mean weight (5.05 ± 0.31 g). Glass aquaria (70 × 45 × 40 cm) each filled up to 70 L of its volume with Ca -free water were used for the experiment. Eleven practical diets were formulated to contain graded levels of calcium carbonate (CaCO3) at 0 (Control), 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0%, respectively. Each diet was fed twice daily (08:00 and 16:00) to triplicate groups of fish at 15 fish per replicate. Fish fed DVI (2.5% CaCO3) had the best growth response in terms of final mean weight gain (MWG) (16.3 ± 1.30) g; specific growth rate (SGR) (1.15 ± 0.12) and feed conversion ratio (1.43 ± 0.20). Protein efficiency ratio (PER) and net protein utilization (NPU) values were significantly (P > 0.05) highest (3.69 ± 0.10; 3.07 ± 0.15) in fish fed DVII and DVIII, respectively. Highest values of magnesium (Mg) and phosphorus (P) (13.9 ± 0.12; 36.98 ± 0.21) mg/g were recorded in fish fed DVI and DXI, respectively. The feeding trial confirmed that Ca supplementation would be necessary in the diet of H. bidorsalis for maximum growth and body mineralization. Key words: Heterobrachus bidorsalis, calcium supplement, growth performance, body mineral.

Improved Descriptions of Herbaceous Perennial Growth and Residue Creation for RUSLE2

Earlier versions of the Revised Universal Soil Loss Equation, version 2 (RUSLE2) calculated vegetative residue production only during periods of canopy decline or in response to management operations. This resulted in underestimation of residue amounts and overestimation of soil erosion from pasture and hay lands. To solve this problem, new vegetation routines were implemented in RUSLE2. These modifications were designed to better reflect the amount of residue added by perennial vegetation during its growth and to make it is easier to model haying and grazing scenarios. The new routines were based on the assumption that all unharvested aboveground biomass growth will die after its life span is reached, and this biomass will be added to a standing residue pool. Trained specialists can define the characteristics of a vegetation assemblage in terms of total annual potential production under good management, monthly production percentages reflecting expected fertility and irrigation levels, average vegetation lifespan, maximum canopy height, cutting height for optimal yield, and the tendency of the vegetation to thicken at lower heights (form a sod) in response to repeated defoliations. Users will specify actual harvest management and an underlying model predicts plant growth responses in terms of the amount of harvested forage and the amount of above‐ and belowground residues returned to the soil. The USDA‐NRCS is developing extensive databases so that the new version of RUSLE2 will allow erosion estimates to be a factor considered as part of forage and grazing planning.

Lysine restriction during grower phase on growth performance, blood metabolites, carcass traits and pork quality in grower finisher pigs

The effects of lysine restriction during grower phase and realimentation during finisher phase on growth performance, nutrient digestibility, blood metabolites, carcass traits and pork quality were studied. Sixty-four pigs (two castrated males and two females per pen) weighing 34.34±5.22 kg were assigned to four dietary treatments. During grower (35–55 kg), pigs were fed isoenergetic lysine-restricted diets. The different lysine content of diets were 0.950 (NRC recommendation), 0.760, 0.665 and 0.570%, corresponding to lysine restriction of 20, 30 and 40%. Then all pigs were fed with common finisher 1 (55–85 kg) and 2 (85–115 kg) diets. Lysine restriction during the grower phase resulted in poor performance and lower concentration of blood metabolites but improved the nutrient digestibility and efficiency of lysine utilization. Compensatory growth response in terms of improved weight gain and feed efficiency was observed in pigs previously fed lysine-restricted diets during finisher 1, but the concentration of blood urea nitrogen and total protein were lower. No differences in growth performance, digestibility of nutrients and blood metabolites were noted during finisher 2. Lysine restriction of grower diets decreased the dressing percentage (quadratic, P=0.024), and protein content of longissimus muscle (linear P=0.034, and quadratic P=0.009). Thus, it could be concluded that pigs subjected to lysine restriction during grower phase exhibited compensatory growth responses in weight gain and improved efficiency of feed and lysine utilization for weight gain and lean accretion during finisher phase.

Mounding site preparation for forest restoration: Survival and short term growth response in Quercus robur L. seedlings

Mounding site preparation for forest restoration: survival and short term growth response in Quercus robur L. seedlings control of natural vegetation during afforestation and reforestation is necessary to avoid economical losses through growth reduction and mortality in seedlings. The present field experiment, carried out on a ground-water influenced site with planted oak, included three site preparation treatments and undisturbed control (C). The treatments were: repeated herbicide application (H), mounding site preparation (MSP), and mounding site preparation in combination with repeated herbicide application (MSP + H). The mounds were 25 m long, 2 m wide and 20 cm high inverted mounds on humus, and this method is sometimes also called bedding. Seedlings were monitored for 3 years and at the end of the experiment 90% of oak seedlings survived in the various site preparation methods compared with 58% in the undisturbed control. The best growth was obtained when mounding site preparation was combined with repeated herbicide treatment, producing five times greater seedling biomass compared with the control. Mounding site preparation resulted in equal growth of seedlings compared with repeated herbicide application. Interference from vegetation had a strong negative effect on seedling growth while mounding site preparation itself resulted in a positive seedling growth response. We conclude that mounding site preparation is an efficient tool for forest managers in establishing oak stands and is a good alternative to herbicide treatment on certain sites. On the other hand, a relatively large disturbance area and deep soil disturbances may impair recreational values and destroy archaeological remains.

Growth Responses and Nitrogen-15 Absorption of Desert Saltgrass Under Salt Stress

Saltgrass [Distichlis spicata (L.) Greene var. stricta (Gray) Beetle], accession WA-12, collected from a salt playa in Wilcox, AZ, was studied in a greenhouse to evaluate its growth responses in terms of shoot and root lengths, shoot dry-matter yield, and nitrogen (N) (regular and 15N) absorption rates under control and salt (sodium chloride, NaCl) stress conditions. Plants were grown under a control (no salt) and three levels of salt stress (100, 200, and 400 mM NaCl, equivalent to 5850, 11700, and 23400 mg L− 1 sodium chloride, respectively), using Hoagland solution in a hydroponics system. Ammonium sulfate [(15NH4)2SO4], 53% 15N (atom percent 15N) was used to enrich the plants. Plant shoots were harvested weekly, oven-dried at 60°C, and the dry weights measured. At each harvest, both shoot and root lengths were also measured. During the last harvest, plant roots were also harvested and oven-dried, and dry weights were determined and recorded. All harvested plant materials were analyzed for total N and 15N. The results showed that shoot and root lengths decreased under increasing salinity levels. However, both shoot fresh and dry weights significantly increased at 200 mM NaCl salinity relative to the control or to the 400 mM NaCl level. Shoot succulence (fresh weight/dry weight) also increased from the control (no salt) to 200 mM NaCl, then declined. The root dry weights at both 200 mM and 400 mM NaCl salinity levels were significantly higher than under the control. Concentrations of both total-N and 15N in the shoots were higher in NaCl-treated plants relative to those under the control. Shoot total-N and 15N contents were highest in 200 mM NaCl-treated plants relative to those under the control and 400 mM salinity.

Long term growth responses of loblolly pine to optimal nutrient and water resource availability

A factorial combination of four treatments (control (CW), optimal growing season water availability (IW), optimum nutrient availability (FW), and combined optimum water and nutrient availability (FIW)) in four replications were initiated in an 8-year-old Pinus taeda stand growing on a droughty, nutrient-poor, sandy site in Scotland County, NC and maintained for 9 years. Results for the first 4 years after treatment initiation at this study were first reported by Albaugh et al. [For. Sci. 44 (1998) 317]. The site is primarily nutrient limited and all measured stand parameters (height, basal area, leaf area index, live crown length, stem mass accumulation, current annual stem mass increment) were increased with fertilization throughout the study period. Irrigation effects were also positive for these parameters but the increases were much smaller than those found with fertilization. For example, 9 years after treatment initiation, standing stem mass was increased 100 and 25% by fertilization and irrigation, respectively, while current annual increment of stem biomass production was increased 119 and 23% by fertilization and irrigation, respectively. Interestingly, stem density (stems ha −1) was not significantly affected by treatment in any year of the study. Growth efficiency (stem mass increment per unit leaf area index) was 1.9 Mg ha −1 per year per LAI for CW and influenced by treatment with IW, FW, and FIW achieving growth efficiencies of 2.4, 2.7 and 2.9 Mg ha −1 per year per LAI, respectively. Growth efficiency appeared to be relatively stable in the last 4 years of the study. Ring specific gravity was measured in the third, fourth, and fifth years after treatment initiation. An average reduction in ring specific gravity of 7.5% was observed with fertilization while irrigation had little effect on specific gravity in any year measured. The continuation of high growth rates with no observable growth decline in the treated stands throughout the 9-year study may be a function of the age of the stands when treatments were initiated (8 years), the very poor initial nutrient and moisture availability, and/or the application of an ongoing optimum nutrient regime at the site. The fertilized plots are now at or near an age and a size when a commercial harvest would be feasible. For the stand conditions at this site, then, the optimum nutrient availability plots have achieved high productivity throughout the economic life of the stand without measurable declines in stand productivity.

The effect of land preparation at re-establishment on the productivity of fast growing hardwoods in South Africa

Appropriate land preparation at re-establishment is of major importance to forest managers to ensure maximum survival and vigorous early growth of South African plantation forests. This work revisits a series of trials carried out over the last two decades in an attempt to evaluate the long-term effects of land preparation at re-establishment on the productivity of fast—growing hardwoods (Acacia mearnsii and Eucalyptus spp.). A wide range of land preparation techniques was tested: ploughing, ripping, subsoiling, ridging and complete site preparation (de-stumping, ripping and discing) inter alia. Of the eleven trials originally planted, five reached rotation age (between 9 and 11 years) and, apart from one which was destroyed by a storm at 5 years, the rest, at time of writing, were close to clearfelling. With the exception of one trial where significant growth responses were recorded, and apart from a few significant lower-order interactions, final survival, basal area and volume were not affected by land preparation when compared to a standard pitting operation. Overall, growth responses in terms of basal area and volume to various forms of surface cultivation, ripping, subsoiling and terracing ranged between +21% and—23% for all species tested. Intensive site preparation (e.g. de-stumping, ripping/subsoiling and discing) has generally not resulted in improved growth of E. grandis or A. mearnsii across a range of sites and in some cases even resulted in a reduction in site productivity. Erratic growth responses of Eucalyptus spp. and A. mearnsii to ripping were recorded. Forest management should focus efforts on less intensive and more cost-effective methods of re-establishment such as pitting, shallow ripping to mark a planting line, or surface ploughing unless a known growth limitation exists (such as a root-limiting compacted B horizon overlying a horizon with available water). It is conjectured that the lack of major growth responses to intensive site preparation is due to a combination of the good physical condition of forest soils in the summer-rainfall growing region of South Africa, and beneficial perforation effects of tree roots from previous rotations. The results imply that topsoil disturbance and mixing of soil layers caused by intensive site preparation may pose a threat to long-term site productivity.

Nutritional value and cholesterol-lowering effect of wild lettuce (Laucaea taxaracifolia) leaf as a source of protein

The nutritive value and cholesterol-lowering effect of wild lettuce (Launaea taxaracifolia) leaf when fed as a source of protein was assessed by using male albino rats (Rattus norvegicus) as an index of evaluation. The rats were fed on both methionine supplemented and unsupplemented wild lettuce leaf diets and elicited significant plasma hypocholesterolemic response (p < 0.05) at all levels of inclusions. There were no significant differenc-es in the cholesterol levels as determined in some visceral organs namely liver, kidney and heart of animals fed on the wild lettuce diets (p > 0.05). Total lipid levels determined in the liver, kidney and heart of the animals fed on both wild lettuce leaf protein diets and casein-based diets (as control) were comparatively similar. However, lipid levels in the plasma of the animals maintained on the wild lettuce diets were significantly higher than those fed on the casein diets (p < 0.05). Total plasma protein was not affected by feeding animals with wild lettuce leaf. However, the rats fed with the lettuce leaf diets (both methionine supplemented and unsupplemented) gai-ned comparatively lower growth response in terms of weight gain, protein efficiency ratio (PER) and feed effici-ency ratio (FER) when compared with animals on the respective control diets (p < 0.05). (Journal of Applied Science and Technology: 2001 6(1-2): 94-100)

Effects of temperature, irradiance, salinity and inorganic nitrogen concentration on coral zooxanthellae in culture

SUMMARY: Effects of temperature, irradiation, salinity and inorganic nitrogen concentration on two cultured strains of zooxanthellae isolated from the corals Pocillopora damicornis (strain P) and Montipora verrucosa (strain M) were studied. Each strain showed different growth responses in terms of temperature and light intensity. A maximum growth rate of strain P, 1.2 per day, was observed at 32°C under all light intensities examined (5–40 μEm−2s−1). However, its photosystem 2 activity (FRI) was higher at 28°C than at 32°C under most light intensities. In contrast, the growth rate of strain M was affected more by light intensity and was almost invariably affected at all temperatures examined (24–36°C). Both algal strains had a comparable growth rate and FRI at salinities from 20 to 35 PSU under moderate temperature and irradiant conditions. High temperature and low irradiation reduced the algal tolerance against low salinity. The gross photosynthesis per cell was not affected by the ammonium enrichment more than 5 μM per day although the cellular chlorophyll a content and cell density increased in proportion with the ammonium enrichment up to 20 μM per day. A potential response of zooxanthellae to the multiple environmental stresses was shown from these results.

Regenerating temperate forest mesocosms in elevated CO2: belowground growth and nitrogen cycling.

The response of temperate forest ecosystems to elevated atmospheric CO2 concentrations is important because these ecosystems represent a significant component of the global carbon cycle. Two important but not well understood processes which elevated CO2 may substantially alter in these systems are regeneration and nitrogen cycling. If elevated CO2 leads to changes in species composition in regenerating forest communities then the structure and function of these ecosystems may be affected. In most temperate forests, nitrogen appears to be a limiting nutrient. If elevated CO2 leads to reductions in nitrogen cycling through increased sequestration of nitrogen in plant biomass or reductions in mineralization rates, long-term forest productivity may be constrained. To study these processes, we established mesocosms of regenerating forest communities in controlled environments maintained at either ambient (375 ppm) or elevated (700 ppm) CO2 concentrations. Mesocosms were constructed from intact monoliths of organic forest soil. We maintained these mesocosms for 2 years without any external inputs of nitrogen and allowed the plants naturally present as seeds and rhizomes to regenerate. We used 15N pool dilution techniques to quantify nitrogen fluxes within the mesocosms at the end of the 2 years. Elevated atmospheric CO2 concentration significantly affected a number of plant and soil processes in the experimental regenerating forest mesocosms. These changes included increases in total plant biomass production, plant C/N ratios, ectomycorrhizal colonization of tree fine roots, changes in tree fine root architecture, and decreases in plant NH4+ uptake rates, gross NH4+ mineralization rates, and gross NH4+ consumption rates. In addition, there was a shift in the relative biomass contribution of the two dominant regenerating tree species; the proportion of total biomass contributed by white birch (Betula papyrifera) decreased and the proportion of total biomass contributed by yellow birch (B. alleghaniensis) increased. However, elevated CO2 had no significant effect on the total amount of nitrogen in plant and soil microbial biomass. In this study we observed a suite of effects due to elevated CO2, some of which could lead to increases in potential long term growth responses to elevated CO2, other to decreases. The reduced plant NH4+ uptake rates we observed are consistent with reduced NH4+ availability due to reduced gross mineralization rates. Reduced NH4+ mineralization rates are consistent with the increases in C/N ratios we observed for leaf and fine root material. Together, these data suggest the positive increases in plant root architectural parameters and mycorrhizal colonization may not be as important as the potential negative effects of reduced nitrogen availability through decreased decomposition rates in a future atmosphere with elevated CO2.

Response of Spirulina platensis (= Arthrospira fusiformis) from Lake Chitu, Ethiopia, to salinity stress from sodium salts

Spirulina platensis (=Arthrospira fusiformis) was isolated from Lake Chitu, a soda crater lake in the Ethiopian Rift Valley, where it formsa dense and almost unialgal population. Growth experiments were run in turbidostats under constant light, to assess growth response and tolerance to salinity, as well as to the component anions. Salinity was tested over the range 13–88 g L-1 using additions of NaHCO3, NaCl or Na2SO4. A maximum specific growth rate (µmax d-1) of 2.14 was achieved at the lowest salinity, but quantum yield (Φ%) was highest between 33 to 51 g L-1. Increasing salinity of the medium reduced the specific growth rate (µ) to a minimum of 0.33 d-1, and Φ to < 0.5%. Growth response in terms of µ and Φ was best in HCO 3 - , less in Cl-, and least in SO 4 2- series. Cultures showed obvious differences in cellular morphology, pigment, nitrogen and phosphorus contents in response to treatment with the different anions. Results indicate that the species has a wide range of tolerance to salinity from NaHCO3. Some degree of tolerance is also shown to high concentrations of Cl- and SO 4 2 , but with an overall lower performance of cells in terms of growth rate, light utilization efficiency, and nutrient status to cells grown in high HCO 3 - concentrations and the same levels of salinity and light.