Relative Growth Rate Of Seedlings Research Articles

Seedling dynamics differ between canopy species and understory species in a tropical seasonal rainforest, SW China

We used 11 years of census data from 450 seedling quadrats established in a 20-ha forest dynamics plot to study seedling dynamics in tree species of a tropical seasonal rainforest in Xishuangbanna, southwestern China. We found that overall seedling recruitment rate and relative growth rate were higher in the rainy season than in the dry season. Both the recruitment rate of seedlings from canopy tree species (two species) and the relative growth rate of seedlings from understory species (nine species) were higher in the rainy season than in the dry season. However, in the rainy season, the recruitment rate of seedlings was higher for canopy tree species than for understory tree species. In addition, relative growth rate of seedlings was higher in the canopy species than in understory seedlings in the dry season. We also observed that, in both rainy and dry seasons, mortality rate of seedlings was higher for canopy species than for understory species. Overall, canopy tree species appear to have evolved a flexible strategy to adapt to the seasonal changes of a monsoon climate. In contrast, understory tree species seem to have adopted a conservative strategy. Specifically, these species mainly release seedlings in the rainy season and maintain relatively stable populations with a lower mortality rate and recruitment rate in both dry and rainy seasons. Our study suggests that canopy and understory seedling populations growing in forest understory may respond to future climate change scenarios with distinct regeneration strategies.

Supplemental light quality affects optimal seeding density of microgreens

AbstractHigher seeding densities can negatively affect the yield of microgreens. We quantified the effects of supplemental light quality and seeding density on the yield of microgreens. Seeds of red beet (Beta vulgaris L. ssp. esculenta) were grown in a greenhouse and provided with a narrow‐spectrum (or “purple”) and broad‐spectrum (or “white”) supplemental lighting at nighttime. Purple spectrum contained 90% red, 0% green, 10% blue, and 0% far‐red (R90: G0: B10: FR0) light, and white spectrum had 35% red, 42% green, 23% blue, and 0% far‐red light (R35: G42: B23: FR0). Each light quality treatment contained seeding densities of 50, 150, 300, and 450 g m−2. We measured fresh weight (FW) and dry weight (DW) on days 8, 10, 12, and 14 after sowing, relative growth rate (RGR), canopy area (CA), and chlorophyll (chl)a, chlb, betacyanin, and betaxanthin pigments. The optimal seeding density in the white treatment was 300 g m−2, whereas FW increased even at the seeding density of 450 g·m−2 in the purple treatment. The RGR of seedlings decreased with increasing seeding density but was higher by 27.8% in the purple than white treatment. The slope of the relationship between DW and CA (related to photosynthetic efficiency) was higher for the purple than white treatment (0.012 vs. 0.008 g cm−2). The ratio of chla to chlb (related to photosynthetic reaction center activity) increased by 15% in the purple than white treatment. Therefore, higher optimal density in the purple than white light quality treatment is likely due to increased photosynthetic efficiency of seedlings.

Comparative growth and physiological performance of American chestnuts, oaks, hickories, and sugar maple across a silvicultural gradient in overstory retention

The development of a blight-tolerant transgenic American chestnut (Castanea dentata (Marsh.) Borkh.) would provide the potential for reintroducing this species into forests it historically dominated. However, we lack a silvicultural understanding of the environmental conditions most favorable to the growth and survival of American chestnut relative to species with which it historically co-existed. We examined effects of shelterwoods with variable residual densities on the growth and physiology of blight-tolerant chestnut seedlings relative to sugar maple (Acer saccharum Marsh.), and several oak (Quercus spp.) and hickory (Carya spp.) species across a broad range of light availabilities (gap light index; GLI; of 4–50%). To assess the hypothesis that American chestnuts are more physiologically plastic and responsive to light than oaks and hickories, we measured seedling relative diameter and height growth rates and photosynthetic light-response curves across a GLI gradient. The diameter and height growth of chestnut increased with GLI, while oaks and hickories did not. All species varied aspects of their photosynthetic physiology across the GLI gradient in an approximately equivalent manner; the dark respiration rate and light compensation point increased equivalently across species in response to increases in light availability. A multivariate analysis identified three major axes of variation across ten measured traits, largely reflecting differences in species averages and phenotypic plasticity across the GLI gradient. American chestnut seedlings were spread across these multivariate dimensions more than other species, consistent with the hypothesis of higher phenotypic plasticity in this focal species. These results suggest that low residual shelterwood densities may better promote the establishment of underplanted chestnut seedlings relative to associated tree species provided it does not result in detrimental increases in the productivity of competing understory species.

Water stress responses of Saba senegalensis provenances during the seedling stage

Saba senegalensis is a multi-purpose liana from sub-Saharan Africa that is under threat from over-exploitation of its fruits and from land degradation and erratic rainfall affecting its regeneration. This research aims to assess survival, growth and dry matter distribution in the responses to water regimes of S. senegalensis seedlings of nine provenances from slightly, moderately and severely dry zones in Burkina Faso. The study parameters were provenance, water regimes and duration of drought stress. A total of 567 seedlings (63 per provenance) were grown using a factorial design. Five months after germination, three water regimes were applied: high, medium and low soil water content, corresponding respectively to 100, 75 and 50% of soil pot capacity. The experiments lasted for 6, 9 and 12 months after water stress began. Survival rates, growth parameters, biomass production, stress tolerance and stress sensitivity indexes were calculated and the data analyzed using a linear mixed model. Drought stress reduced seedling survival and biomass production, while the relative growth rate in collar diameter increased. Concerning the duration of drought stress, the relative growth rate of seedlings in collar diameter decreased and the shoot-to-root ratio increased. After six months under stress, the seedlings had invested more in roots, whereas after nine and twelve months the reverse trend was observed. Furthermore, seedlings from the slightly dry zone produced more biomass when watered under a low soil water content regime, and were more drought-tolerant than those from severely and moderately dry zones. This could indicate that the seedlings originating from these zones are well adapted to growth under severe water stress. For S. senegalensis domestication programs, seedlings originating from the slightly dry zones can be successfully propagated in agroforestry systems where water is a limiting factor.

Responses of tree seedlings to understory filtering by the recalcitrant fern layer in a subtropical forest.

The recalcitrant understory fern layer is an important ecological filter for seedling regeneration, yet how the fern layer influences seedling regeneration dynamics remains unclear. Here we transplanted 576 seedlings of four dominant tree species, Castanopsis fargesii, Lithocarpus glaber, Schima superba and Hovenia acerba, to the treatments of Diplopterygium glaucum retention and removal under an evergreen broad-leaved forest in eastern China. We monitored the survival, growth and biomass data of these seedlings for 28 months, and then used generalized linear mixed models to evaluate the treatment effects on seedling survival, growth, biomass and root-shoot ratio. Our results showed that fern retention significantly inhibited the seedling establishment of all four species. During the seedling development stage, the seedling relative growth rate of L. glaber decreased under fern retention, which was not the case for the other three species. Root-shootratio of C. fargesii and L. glaber increased significantly under fern retention. Our findings provide new evidence of the filtering effect of a recalcitrant fern understory. Notably, we observed that the response of tree seedlings to the recalcitrant fern understory was more sensitive in the establishment stage. Finally, our work highlights that the filtering effect of the recalcitrant fern understory changes depending on the regeneration stages, and that shade-tolerant species, C. fargesii and L. glaber were even more affected by fern disturbed habitats, suggesting that effective management should attempt to curb forest fern outbreaks, thus unblocking forest recruitment.

Uniconazole and Adaptability of Transplantations by Enhancing the Competition Tolerance in a High Sowing Density of Rapeseed Blanket Seedlings

Having nursery rapeseed (Brassica napus L.) seedlings at a high density in a tray is an indispensable step to realizing mechanized transplanting for rapeseed. The reduction in seedling quality caused by high sowing density is one of the key factors affecting transplanting quality and yield. Uniconazole has been considered as a potential plant growth regulator to improve plant growth under diverse unfavorable circumstances. In two sowing densities (400 and 800 seeds per tray), an experiment was carried out between 2021 and 2022 to investigate the effects of uniconazole seed-coating treatments on pre-transplant and post-transplant seedling characteristics. The results demonstrate that uniconazole treatment can effectively reduce the high-density-induced reduction in seedling dry matter and leaf area, stem thinness, and stem and petiole overgrowth. Further evidence that uniconazole can improve seedling quality, enhance yield, and lessen yield loss due to high-density sowing was provided by yield at maturity. However, because of the uncontrolled growth during the late stage in the tray, the relative growth rate of seedlings after transplant in the transplant shock stage revealed that lower doses of uniconazole treatment have a negative effect on the seedling recovery. The results of principal coordinate analysis and partial correlation analysis proved that the yield and net assimilation rate were related to the improvement of seedling high-density tolerance by uniconazole treatment. Consequently, 500–750 mg L−1 uniconazole coating per 100 g of seeds in 5 mL is recommended by this study, considering the potential risk of seedling emergence and growth caused by an overdose of uniconazole treatment.

Study on Coffee (Coffea arabica L.) Seed Emergence and Seedling Growth Rate Response to Different Sizes of Pot and Biochar Based Rooting Media Preparation at a Nursery Condition of Awada South Ethiopia

Therefore, biochar based nursery media preparation is the best option to accelerate the coffee seedling emergence and seedling relative growth rate at a lower ratio of biochar that provides alternative enhancement media options to speed up coffee seedling growth rate.

Effect of Canopy Gaps on Growth and Water Use Efficiency of Seedling of Vulnerable Species, Hopea sangal Korth

Aims: Hopea sangal Korth. is listed as vulnerable species and recently its remnant habitat was rediscovered in the degraded forest near the springs area in East Java. In the forest, the regeneration of the seedling and saplings understory is affected by the heterogeneity in environmental factors especially various light levels due to the canopy gaps. H. sangal is considered a shade-tolerant species, hence the establishment of the seedling in its natural habitat occurs under the closed canopy. This study aimed to understand the Water Use Efficiency (WUE) and Relative Growth Rate (RGR) of Hopea sangal Korth seedling grown in two different levels of tree canopy shades.
 Study Design: This research was using a completely randomized design, with 9 replications.
 Place and Duration of Study: This study was conducted in the Purwodadi Botanic Garden, East Java, between March – July.
 Methodology: We used seedling of H. sangal collected from the field in Pasuruan which were planted in plastic pots and acclimatized to obtain seedling of a similar size. The microclimate was measured weekly using solarimetri and sling psychrometer at 08.00; 10:00; 12:00; 14:00 and 16:00. RGR was measured by harvesting the seedling and whole plant WUE was measured using the gravimetric method.
 Results: We observed the light level during the periodic opening of the canopy gap was significantly different at a specific time (8-12 am), with the highest light intensity at 10.00 of 333.57 µmol photon m-2s-1. The canopy shades differences did not affect the WUE of seedling (P = 0.333), meanwhile, there was a significant difference in the seedling RGR (P = 0.025). The seedling that were grown under a higher gap and received higher light intensity periodically during a day had higher RGR than those under a closed canopy. The WUE has a positive relationship with the RGR of seedling (R2 = 0.5; P < 0.05).
 Conclusions: This study suggested that the H. sangal is one of the shade-tolerant species capable of responding to gap-opening sunlight. The study also showed RGR of the seedling positively correlated with the WUE of plants, indicating that the seedling could use the water supply efficiently to grow rapidly.

Effects of Above- and Below-Ground Interactions of Plants on Growth of Tree Seedlings in Low-Elevation Tropical Rainforests on Hainan Island, China

Understanding the effects of above- and below-ground interactions on seedling growth is pivotal for identifying the key drivers of secondary forest succession. However, it is still unclear whether the effects of above- and below-ground interactions of plants are consistent for seedling growth of deciduous and evergreen species. There are two types of broadleaved forests (i.e., tropical lowland rainforest and tropical deciduous monsoon rainforest) in the low-elevation (<800 m) areas of Hainan Island in China. Here, 32 seedling transplanting plots (1 × 1 m2) were established in the tropical lowland rainforest and the tropical deciduous monsoon rainforest, respectively. Four treatments (each with 16 replicates) were carried out to reduce above- and below-ground interactions of plants in the low-elevation forests: removal of vegetation (R), root trenching (T), removal of vegetation and root trenching (R + T), and no vegetation removal or trenching (as the control) (C). Seedlings of four deciduous species and four evergreen species were planted to observe their performance in the experiments. The relative growth rates (RGR) of the seedlings were measured to distinguish the relative effects of above- and below-ground interactions. The photosynthetically active radiation (PAR) was measured as a proxy for above-ground interaction and the root biomass was used as a proxy for below-ground interaction. The relationships between seedling RGR and PAR/root biomass were examined. Results showed that: (1) R and R+T treatments significantly increased the seedlings RGR, but T treatment had no effect on the RGR; (2) the growth rates of deciduous species were greater than those of the evergreen species; and (3) seedling growth rates were increased with more PAR. Our study suggests that above-ground vegetation removal had a stronger effect than trenching on the growth and assembly of tree seedlings in the low-elevation tropical rainforests.

Effect of biofuel waste, urea, deer browsing, and vegetation control on Pinus banksiana seedling growth on a dry upland site in central Canada

Ash from biofuels and nitrogen fertilizer are increasingly being used as soil amendments. While this can increase tree growth, it can also increase mammalian grazing and competition with vegetation. We applied moderate amounts of ash (1.5 t·ha−1·year−1) and urea (74 kg N·ha−1·year−1) in each of 2 years to a well-drained site in southeastern Manitoba, planted with Pinus banksiana Lamb. Subplots received deer browsing and (or) vegetation control. The ash resulted in an increase in pH in the upper 15 cm of mineral soil from ∼5.7 to 6.6, and the urea created short-term spikes in soil inorganic nitrogen (NH4 and NO3) levels. Urea combined with ash significantly increased seedling relative growth rates in the first 2 years, with seedlings being largest with urea, with or without ash. However, by the fourth year, seedling growth and size did not differ between the amendments. Urea application increased browsing damage to 91%, but only when vegetation was mowed. Browsing guards resulted in seedlings having 1.6 times greater shoot mass by the end of the fourth growing season. These results suggest that on sandy soils in the dry region of central Canada, P. banksiana may get little benefit from ash applications.

Contrasting growth responses to aluminium addition among populations of the aluminium accumulator Melastoma malabathricum.

Aluminium (Al) hyper-accumulation is a common trait expressed by tropical woody plants growing on acidic soils. Studies on Al accumulators have suggested that Al addition may enhance plant growth rates, but the functional significance of this trait and the mechanistic basis of the growth response are uncertain. This study aimed to test the hypothesis that differential growth responses to Al among populations of an Al accumulator species are associated with variation in biomass allocation and nutrient uptake. We conducted two experiments to test differential responses to the presence of Al in the growth medium for seedlings of the Al accumulator shrub Melastoma malabathricum collected from 18 populations across Peninsular Malaysia. Total dry mass and relative growth rate of dry mass were significantly greater for seedlings that had received Al in the growth medium than for control plants that did not receive Al, but growth declined in response to 5.0 mM Al addition. The increase in growth rate in response to Al addition was greater for a fast-growing than a slow-growing population. The increase in growth rate in response to Al addition occurred despite a reduction in dry mass allocation to leaves, at the expense of higher allocation to roots and stems, for plants grown with Al. Foliar concentrations of P, K, Mg and Ca increased in response to Al addition and the first axis of a PCA summarizing foliar nutrient concentrations among populations was correlated positively with seedling relative growth rates. Some populations of the Al hyper-accumulator M. malabathricum express a physiological response to Al addition which leads to a stimulation of growth up to an optimum value of Al in the growth medium, beyond which growth declines. This was associated with enhanced nutrient concentrations in leaves, which suggests that Al accumulation functions to optimize elemental stoichiometry and growth rate.

Thermotolerance evaluation of Taiwan Japonica type rice cultivars at the seedling stage

BackgroundThe subtropical rice varieties grown in Taiwan are mainly Japonica-type rice varieties, which are grown in the southernmost- and lowest-latitude Japonica type rice cultivation area in the world. In Taiwan, seedlings that are planted either by transplanting or direct seeding in the second crop will face the season with the highest temperatures during the year. High-temperature stress severely influences early rice growth and causes yield losses. With global warming deteriorating, this problem is becoming increasingly severe. This study attempted to establish a high-efficiency and time-saving screening tool for rice varieties that exhibit thermotolerance during the early growth stages and further identify good donors with better tolerance for high temperature stress from Taiwan Japonica type rice germplasm.ResultsDuring the initial germination stage, there were significantly different responses to heat stress among the different rice varieties. After the temperature induction response technique (TIR) treatment, the seedling survival rate and relative growth rate of the rice varieties under high temperature stress were significantly improved. In addition, the seedlings of the thermotolerant varieties demonstrated greater thermotolerance performance in the pot experiment as well as cell membrane stability (CMS) and cell activity (2,3,5-triphenyl-tetrazolium chloride; TTC) test results. However, the correlation between the thermotolerance of the seedlings and seeds was low. A phylogenetic dendrogram was plotted and revealed that thermotolerant genes did not concentrate in specific clusters. Furthermore, there was a non-significant correlation between the thermotolerance of the varieties and the years in which they were released.ConclusionsThe temperature induction screening tool established by this study could determine the potential of each variety to adapt to high temperature stress. Additionally, thermotolerance during different growth stages (i.e., the germination, seedling, and grain maturation stages) exhibited low correlations. In this study, the varieties obtained through preliminary screening (i.e., TK14, HC56, TT30, TNG70, and TK8) exhibited outstanding thermotolerance. The screen tools and thermotolerance varieties could be valuable resources for the countries that grow Japonica type rice to apply when breeding thermotolerant varieties in the future.

Ecophysiological responses of Jatropha curcas L. seedlings to simulated acid rain under different soil types

Acid rain is a global environmental problem. Acid rain can affect plants directly by damaging the leaves and indirectly by soil acidifying. Many studies have been conducted to investigate the impacts of acid rain on plant under a single soil type. However, there is little information on the effect of acid rain on plant under different soil types. Jatropha curcas L. is an energy plant widely distributed in acid rain pollution area with various soil types. In this study, we investigated the effects of acid rain (pH2.5, pH3.5, pH4.5, pH5.6) on the growth, physiology, nutrient elements and bacterial community of J. curcas seedlings under different soil types [Red soils (RS), Yellow soils (YS), Yellow-brown soils (YBS), and Purplish soils (PS)]. Acid rain and soil types significantly influence the growth of J. curcas seedlings, and there was a significant interaction between acid rain and soil types. Acid rain (pH 4.5) was beneficial to the growth of J. curcas seedlings, whereas acid rain (pH 2.5 or 3.5) inhibited growth of J. curcas seedlings. The growth of J. curcas seedlings could resist the stress of acid rain by scavenging and detoxification of active oxygen species in leaves. Combined with the increase in relative growth rate of seedlings treated with simulated acid rain at pH 4.5, we inferred that K can stimulate the growth of seedlings. The lower soil pH, cation exchange capacity and base saturation had stronger inhibitory effects on growth of J. curcas seedlings. YBS and PS were beneficial for growth of J. curcas seedlings by higher buffering capacity under acid rain treatments. The phylum Proteobacteria was found to predominate in rhizosphere soils. YBS was favorable to support Proteobacteria growth and reproduction. The redundancy analysis showed that the Cyanobacteria were favorable to growth of J. curcas seedlings.

Seed storage importance and behaviour of a vulnerable species Angsana (Pterocarpus indicus Willd.)

Angsana (Pterocarpus indicus Willd.) is one of woody plant species listed in the IUCN red list for priority in conservation as a vulnerable species. The effective and low-cost methods of seed storage is required to support the ex-situ conservation through seedling recruitments for population improvement. This study used completely randomized factorial design with 2 factors i.e. seed storage methods (room temperature, sealed jar and cold temperature), and storage duration (1,2,3,4 and 5 months). This study used 3 replications for each treatments and 10 seeds for each replication. The result showed that the seed of P. indicus start to germinate in 5-11 days after seeding while leaf emerged in 15-13 days after seeding. Seed viabilities generally were high until 3 months of storage (up to 65%) and start to decline at 4 months of storage at 51%. Storage methods and storage duration significantly influenced the seedling growth, viability, and Relative Growth Rate (RGR). There was an interaction between two factors. The storage at room temperature during a month (1RT) has the highest seedling height. The seeds stored in sealed jar during 5 months (5SJ) showed the highest seedling RGR, while the seeds stored in sealed jar during 3 months (3SJ) has the highest seed viability. For longer term storage, the seed of P. indicus should be stored in sealed jar or at room temperature at 11% moisture content. Both in the rainy and dry season, seedling recruitments were low and sapling stage was rare which showed low seedling establishment. Moreover, based on the phenological information, it is better to store the seed during the rainy season.

Impact in quarantine of the galling weevil Lepidapion argentatum on shoot growth of French broom (Genista monspessulana), an invasive weed in the western U.S.

ABSTRACTIn weed biocontrol, there is a need for pre-release efficacy assessments for potential agents. Genista monspessulana ((L.) L. A. S. Johnson (Fabaceae), French broom) is an invasive perennial shrub in the western U.S. The galling weevil Lepidapion argentatum Gerstaecker is a potential biocontrol agent. The impact of increasing weevil density on galling damage, plant height, width, leaf damage, and relative growth rate (RGR) was assessed in greenhouse experiments on two to three-month-old seedlings infested with either one or three weevils. Infestation by three female weevils caused 48% more galls producing 27% more larvae than did infestation with one female while causing only 1% leaf damage and no difference in total leaf area. Infestation with multiple weevils caused a 55% and 29% decrease in plant height and canopy width respectively, while single-weevil infestation decreased height by 32% and width to the same degree as for multiple weevils. The RGR of seedlings infested with three weevils was three times slower than the controls, while growth was reduced 2-fold by single-weevil infestation. Reductions in plant size and growth rate induced by weevil galling could reduce plant competitive survival to reproduction and also plant population dispersal as seedlings. Our results suggest that L. argentatum has the potential to cause impact to French broom seedlings if released in the invasive range.

Relative Growth Rate and Its Components in Invasive Species Heracleum sosnowskyi and Congeneric Native Species H. sibiricum

We studied the relative growth rate of seedlings and aboveground and underground organs, as well as functional traits of leaves and absorbing roots in the invasive species Heracleum sosnowskyi and congeneric native species H. sibiricum. The plants were grown in laboratory conditions and the functional plant traits of 21- and 35-day-old seedlings were analyzed. The relative growth rate (RGR) of H. sosnowskyi differed from that of H. sibiricum by 2.5 times, but the growth of plants in height and in area of leaves was similar. Plant biomass and total leaf area were twice as high in 35-day-old seedlings of invasive species. Structural features of the leaves in 35-day-old H. sosnowskyi seedlings were a lower leaf thickness and a higher leaf density. The invasive species had a lower root mass ratio, but the roots were more branched with a greater ratio of absorbing roots and a better development of the root hairs. As a result, H. sosnowskyi had a higher growth rate of absorbing roots (by 2 times) and a larger absorbing surface in relation to the total root surface. We concluded that the structural and functional traits of the leaves and roots provided a 2 times higher net assimilation rate (NAR) and 2.5 times larger RGR in the invasive species H. sosnowskyi.

Effects of sand burial and overstory tree age on seedling establishment in coastal Pinus thunbergii forests in the northern Shandong Peninsula, China

Coastal Pinus thunbergii (Japanese black pine) forests in the northern Shandong Peninsula of China recently experienced widespread natural regeneration failure. This study identifies critical factors that affect natural regeneration of P. thunbergii. Seeds from trees of various ages (13–32 years) were used to investigate the effects of age and burial depth in sand on germination and seedling establishment. Results show that seed density in 2–5 cm soil decreased with increased distance from the shoreline. Sand burial decreased seed germination but did not affect the relative growth rate of seedlings at depths from 0.5 to 3 cm. Germination, leaf mass ratio, and relative growth rates were higher with seedlings originating from older trees, all of which enhanced seedling resistance to sand burial. Tree age and seed burial were found to be determining factors for natural regeneration of the coastal P. thunbergii forest. Silvicultural treatments that promote quality of seed sources and mitigation of sand burial can be used in the future to improve the regeneration of these coastal forests.

Promotive Effect of Priming with 5-Aminolevulinic Acid on Seed Germination Capacity, Seedling Growth and Antioxidant EnzymeActivity in Rice Subjected to Accelerated Ageing Treatment

:Seed deterioration by ageing caused by natural and artificial treatments lowers germinability and viability. Seed priming is a technique used to relieve seed deterioration from ageing. We evaluated the effect of seed priming with 5-aminolevulinic acid (ALA) at various concentrations on the seed germination capacity, seedling growth, antioxidant enzyme activities, and lipid peroxidation in the rice seedling cultivar Pathum Thani 1 with or without exposure to artificial ageing treatment. Seeds were subjected to accelerated ageing treatment by exposure to high relative humidity and high temperature conditions for 84 hr (aged seeds). The shoot length was significantly reduced and the injury index and H2O2 formation were increased in the seedlings emerged from the aged seeds. Priming of the aged seeds with 0.5 μg mL–1 ALA significantly enhanced the seed germination capacity and seedling relative growth rate to values higher than those obtained by priming with water (hydropriming). However, there was no significant difference in superoxide dismutase, peroxidase and ascorbate peroxidase activity as compared with hydropriming. In the seeds not given ageing treatment priming with ALA significantly increased the superoxide dismutase and peroxidase activities in the seedlings by 144% and 282%, respectively, as compared with the hydropriming treatment. Seed priming with ALA at 0.2 μg mL–1 significantly increased the relative growth rate of seedling and lowered seedling water content as compared with the values without priming or with hydropriming. Seed priming with ALA was confirmed to enhance rice seed germination capacity, seedling growth, and antioxidant enzyme activity in rice seedlings.

Trade-offs in seedling growth and survival within and across tropical forest microhabitats.

For niche differences to maintain coexistence of sympatric species, each species must grow and/or survive better than each of the others in at least one set of conditions (i.e., performance trade-offs). However, the extent of niche differentiation in tropical forests remains highly debated. We present the first test of performance trade-offs for wild seedlings in a tropical forest. We measured seedling relative growth rate (RGR) and survival of four common native woody species across 18 light, substrate, and topography microhabitats over 2.5 years within Hawaiian montane wet forest, an ideal location due to its low species diversity and strong species habitat associations. All six species pairs exhibited significant performance trade-offs across microhabitats and for RGR versus survival within microhabitats. We also found some evidence of performance equivalence, with species pairs having similar performance in 26% of comparisons across microhabitats. Across species, survival under low light was generally positively associated with RGR under high light. When averaged over all species, topography (slope, aspect, and elevation) explained most of the variation in RGR attributable to microhabitat variables (51–53%) followed by substrate type (35–37%) and light (11–12%). However, the relative effects of microhabitat differed among species and RGR metric (i.e., RGR for height, biomass, or leaf area). These findings indicate that performance trade-offs among species during regeneration are common in low-diversity tropical forest, although other mechanisms may better explain the coexistence of species with small performance differences.

Effect of Watering Regimes and Water Quantity on the Early Seedling Growth of Picralimanitida (Stapf)

Competing land use pattern has necessitated planting of useful forest trees on marginal lands with varying water status. A study was conducted on the effect of watering regimes and water quantity on seedlings growth of P. nitida. Seedlings were raised from seeds, transplanted in polythene bags and subjected to watering at full capacity daily, once in 3 days, 5 days; 20 ml daily, 3 days, 5 days; 15 ml daily, 3 days, 5 days; 10 ml daily, 3 days, 5 days; and flooding. The growth traits assessed were plant height, collar diameter, number of leaves; shoot, root and leaf dry weights as well as leaf area. The effect of watering regime and water quantity were significant (P ? 0.05) on quantitative morphological parameters of seedlings. Total dry weight and root dry weight were lower in both water-stressed and waterlogging than well-watered conditions, but the lowest values were obtained under flooding. However, specific leaf area (SLA) and leaf area ratio (LAR) were higher in water-stressed conditions than well-watered conditions. Relative growth rate of seedlings is related more to the net assimilation rate values than LAR and SLA. Also, root/shoot ratio was highest under daily full capacity watering. Thus, daily watering at full capacity with water availability or 15-20 ml of water per seedling during scarcity is recommended for raising P. nitida seedlings.