Seed Germination and Seedling Growth of Dendrocalumus brandisii in vitro, and the Inhibitory Mechanism of Colchicine

Bamboos seldom bloom and almost no seeds could be harvested, and, hence, few works are focused on germination physiology. Systematic research on the physiological effects of colchicine on germination and seedling growth of bamboo seeds is lacking. In this study, we finely recorded seed germination and seedling growth of Dendrocalamus brandisii in media supplemented with different colchicine concentrations. Physiological effects and mechanisms of colchicine were analyzed. The results showed that D. brandisii seeds were non-dormant, and seed lots achieved their highest germination rates on the 4th day and finished the whole germination period after 21 days. Colchicine inhibited seed germination and seedling growth but did not change its germination pattern. Seed germination and seedling growth decreased constantly with colchicine concentration. Colchicine showed more negative effects on seedling growth than on seed germination and root growth. High concentrations of colchicine retarded the development of plumules and even caused their aberrant development. Under tissue culture conditions, seed germination, and seedling growth relied mainly on the endogenous starch and soluble sugar degradation, in which α-amylase, STP, and SUSY played the key role. Colchicine inhibited seed germination and seedling growth by suppressing the α-amylase, STP, and SUSY activities. Colchicine showed more negative effects on sucrose degradation than on starch degradation during seed germination and seedling growth. This study provides new basic information on the seedling physiology for the genetic breeding of bamboo plants.

Arbuscular mycorrhizal symbiosis facilitates apricot seedling (Prunus sibirica L.) growth and photosynthesis in northwest China

Arbuscular mycorrhizal (AM) fungi can successfully enhance photosynthesis (Pn) and plants growth in agricultural or grassland ecosystems. However, how the symbionts affect species restoration in sunlight-intensive areas remains largely unexplored. Therefore, this study’s objective was to assess the effect of AM fungi on apricot seedling physiology, within a specific time period, in northwest China. In 2010, an experimental field was established in Shaanxi Province, northwest China. The experimental treatments included two AM fungi inoculation levels (0 or 100 g of AM fungal inoculum per seedling), three shade levels (1900, 1100, and 550 µmol m−2 s−1), and three ages (1, 3, and 5 years) of transplantation. We examined growth, Pn, and morphological indicators of apricot (Prunus sibirica L.) seedling performances in 2011, 2013, and 2015. The colonization rate in mycorrhizal seedlings with similar amounts of shade is higher than the corresponding controls. The mycorrhizal seedling biomass is significantly higher than the corresponding non-mycorrhizal seedling biomass. Generally, Pn, stomatal conductance (Gs), transpiration rate (Tr), and water use efficiency are also significantly higher in the mycorrhizal seedlings. Moreover, mycorrhizal seedlings with light shade (LS) have the highest Pn. WUE is increased in non-mycorrhizal seedlings because of the reduction in Tr, while Tr is increased in mycorrhizal seedlings with shade. There is a significant increase in the N, P, and K fractions detected in roots compared with shoots. This means that LS had apparent benefits for mycorrhizal seedlings. Our results also indicate that AM fungi, combined with LS, exert a positive effect on apricot behavior.

Impact of a Soil Conditioner Integrated into Fertilization Scheme on Orange and Lemon Seedling Physiological Performances

Growers in Florida face unique challenges regarding maintaining proper citrus nutrition. Poor draining soils with low fertility, low C.E.C., and high rates of leaching are common in this region. In response to these challenges, interest has grown in products labeled as soil conditioners. Using a completely randomized experimental design, this greenhouse study tested the effects of 5 different combinations of a traditional fertilizer (TF) and a new soil conditioner (SC) on lemon and orange seedling physiology. Eight-month-old ‘Bearss’ lemon and ‘Valencia’ sweet orange grafted on sour orange rootstocks were employed, and five repetitions were used for each treatment. Plant biomass (dry weight), height, stem diameter, chlorophyll content, stomatal conductance and nutrient uptake were analyzed after 120 days of treatment. The results show that SC has a positive impact upon both chlorophyll levels and stomatal conductance values in both orange and lemon seedlings. However, based on dry weight growth data, we can only conclude that the SC was effective for orange seedlings at 50% TF and 0.5% SC. Based on this short 120-day evaluation, the SC achieved positive growth promotion for orange (50% TF) but not for lemon seedlings.

Meloidogyne paranaensis and M. exigua alter coffee physiology

Summary Root-knot nematodes, Meloidogyne spp., cause great losses to coffee crops in Brazil and worldwide. However, little is known about the physiological changes that these pathogens induce in coffee plants. The present work aimed to compare the physiological variables of coffee seedlings (Coffea arabica ‘Catuaí Vermelho IAC 144’) infected with Meloidogyne paranaensis or M. exigua with healthy coffee plants. Nematode-infected plants showed reductions in height and starch content in roots compared to healthy plants. In addition, the infected plants had a reduction in transpiration, stomatal conductance and CO2 concentration. However, only the coffee seedlings infected with M. paranaensis showed reduction in the rate of photosynthesis. Nematode-infected plants had lower leaf contents of P, K, Mn and Fe when compared to healthy plants. However, only coffee seedlings parasitised by M. paranaensis exhibited lower levels of Ca in the leaves. Therefore, M. paranaensis and M. exigua, with emphasis on M. paranaensis, alter the normal coffee seedling physiology.

Endogenous translocation patterns of current photosynthate in post-transplant Quercus rubra seedlings

Variability between individuals can cause error in plant physiology studies when measurements or treatments occur on a chronological basis. Thus, plant growth indices such as the Quercus morphological index (QMI) were developed, enabling distinctions between exogenous treatment effects and endogenous ontological effects. Few studies have examined post-transplant northern red oak (Quercus rubra L.) seedling physiology in relation to the QMI. We used 14CO2 to label current photosynthate of post-transplant northern red oak seedlings during the first flush to assess endogenous patterns of current photosynthate translocation. Carbon translocation patterns relative to QMI growth stages of post-transplant seedlings resembled those described in pre-transplant seedlings, with expanding leaves and shoots retaining the majority of current photosynthate early in the flush, followed by increases in downward translocation to both new and old roots during the lag stage, when active aboveground growth ceased for the flush. Early post-transplant growth of new shoots relied heavily on stored carbohydrates, and old shoots demonstrated negligible sink strength for current photosynthate throughout the experiment. Our findings emphasize the importance of stored carbohydrates for early post-transplant growth and suggest that QMI-based observations regarding carbohydrate translocation patterns of pre-transplant seedlings in this species remain largely valid for post-transplant seedlings.

Effects of fire radiative energy density dose on Pinus contorta and Larix occidentalis seedling physiology and mortality

Climate change is projected to exacerbate the intensity of heat waves and drought, leading to a greater incidence of large and high-intensity wildfires in forested ecosystems. Predicting responses of seedlings to such fires requires a process-based understanding of how the energy released during fires affects plant physiology and mortality. Understanding what fire ‘doses’ cause seedling mortality is important for maintaining grasslands or promoting establishment of desirable plant species. We conducted controlled laboratory combustion experiments on replicates of well-watered nursery-grown seedlings. We evaluated the growth, mortality and physiological response of Larix occidentalis and Pinus contorta seedlings to increasing fire radiative energy density (FRED) doses created using natural fuels with known combustion properties. We observed a general decline in the size and physiological performance of both species that scaled with increasing FRED dose, including decreases in leaf-level photosynthesis, seedling leaf area and diameter at root collar. Greater FRED dose increased the recovery time of chlorophyll fluorescence in the remaining needles. This study provides preliminary data on what level of FRED causes mortality in these two species, which can aid land managers in identifying strategies to maintain (or eliminate) woody seedlings of interest.