As superficial structures, non-glandular trichomes, protect plant organs against multiple biotic and abiotic stresses. The protective and defensive roles of these epidermal appendages are crucial to developing organs and can be attributed to the excellent combination of suitable structural traits and chemical reinforcement in the form of phenolic compounds, primarily flavonoids. Both the formation of trichomes and the accumulation of phenolics are interrelated at the molecular level. During the early stages of development, non-glandular trichomes show strong morphological similarities to glandular ones such as the balloon-like apical cells with numerous phenolics. At later developmental stages, and during secondary wall thickening, phenolics are transferred to the cell walls of the trichomes. Due to the diffuse deposition of phenolics in the cell walls, trichomes provide protection against UV-B radiation by behaving as optical filters, screening out wavelengths that could damage sensitive tissues. Protection from strong visible radiation is also afforded by increased surface light reflectance. Moreover, the mixtures of trichome phenolics represent a superficial chemical barrier that provides protection against biotic stress factors such as herbivores and pathogens. Although the cells of some trichomes die at maturity, they can modulate their quantitative and qualitative characteristics during development, depending on the prevailing conditions of the external biotic or abiotic environment. In fact, the structure and chemical constituents of trichomes may change due to the particular light regime, herbivore damage, wounding, water stress, salinity and the presence of heavy metals. Hence, trichomes represent dynamic protective structures that may greatly affect the outcome of many plant–environment interactions.
Environmental factors play vital roles in successful plantation and cultivation of tree seedlings. This study focuses on problems associated with reforestation under extreme continental climatic conditions. The objectives were to assess relative seedling performance (survival and growth) with respect to plantation age, and to analyze the influence of specific climatic factors during the early stages of Scots pine (Pinus sylvestris L.) plantations. The study was carried out in reforested areas of the Tujyin Nars region of northern Mongolia on six Scots pine plantations ranging from 5 to 10 years. In each of the six plantations, five 900 m2 permanent sample plots were established and survival rates and growth performance measured annually over 7 years. Results show high variation in survival among the plantations (p < 0.001, F = 29.7). Seedling survival in the first year corresponded directly to the number of dry days in May. However, survival rate appeared to stabilize after the second year. The insignificant variation of height categories throughout the observation period indicated low competition among individuals. Two linear mixed-effect models show that height and radial growth were best explained by relative air humidity, which we consider to be a reliable indicator of site-specific water availability. Insufficient amounts and uneven distribution of rainfall pose a major threat during the first year of plantation establishment. Humidity and water availability are decisive factors for a successful seedling plantation. This highlights the impact of drought on forest plantations in northern Mongolia and the importance of developing climate resilient reforestation strategies.
To determine appropriate quantities of water and fertilizer required for early growth of hybrid poplar cuttings, we recorded the growth traits of four clones grown under four factors (irrigation and nitrogen, phosphorus, and potassium fertilizers), each with four levels, using an orthogonal experimental design. A logistic model was used to estimate growth in height. The growth curves for tree height were sigmoid, and the model R 2 values were greater than 0.9, which indicated that the fit was highly significant. ANOVA results for tree height and basal diameter indicated that all sources of variance showed significant differences (p < 0.001). The average tree height and basal diameter for all the four clones under the different treatments ranged from 155.39 to 235.04 cm, and from 13.71 to 17.42 mm, respectively. A highly positive correlation between the extreme k value and tree height was observed, suggesting that the k value was an accurate estimation of tree height. For model parameters, the earliest average time point for the onset of the rapid growth period of poplar clones was 131 d, and the highest average increment in tree height during the rapid growth period was 138.78 cm. The highest average tree height for all clones under each factor was 219, 210.51, 200, and 201 cm when treated with either 1200 mL of water applied every third day, 3 g of nitrogen, 0 g of phosphorus, or 0 g of potassium, respectively. The most suitable treatment for the early growth of hybrid poplar cuttings, as suggested by the developed logistic model, was 1200 mL of water applied every third day and three applications of 1 g nitrogen (in the form of CH4N2O).
We studied the molecular mechanism of the quality traits of wood formation in larch. We used the immature latewood cells of two Japanese larch (Larix kaempferi) clones with significant differences in density and in microfibrillar angle (MFA) as materials to analyze their gene expression profiles. A total of 1735 differentially expressed genes were detected in immature latewood cells of the two clones, among which, 971 were up-regulated and 764 were down-regulated. Digital gene expression profiling analysis revealed that genes encoding transcription factor members NAC66 and R2R3-MYB4, microtubule-associated protein, actin-related protein, cell wall protein members, arabinogalactan protein, Fasciclin-like arabinogalactan protein and glycine-rich protein, and several cell-wall-synthesis genes affected wood density and MFA by regulating latewood formation at transcriptional level. Our study results represent a basis for selection of quality traits and genetic improvement of larch wood.
Pine wilt disease (PWD) is a devastating disease affecting the growth of Pinus massoniana, often leading to withering and death. To reveal the changes involved during disease progression, we investigated the mRNA expression profile of P. massoniana infested by Bursaphelenchus xylophilus. The infestation resulted in the downregulation of genes involved in interactions with pathogenic pathways such as disease resistance gene, CC-NBS-LRR resistance-like protein, and the gene encoding a putative nematode resistance protein. Increased infestation pressure (number of nematodes inoculated) caused a continuous decline in the gene expression of stem samples. An infestation of P. massoniana also resulted in a pathway enrichment of genes involved in phenylpropanoid metabolism and flavonoid biosynthesis, which in turn reduced the levels of total phenols and total flavonoids. A downregulation of auxin responsive family protein was observed in infested samples, which resulted in a suppression of plant growth. Thus, upon B. xylophilus infestation, a downregulation of genes associated with the recognition of pathogens, PWD resistance, and growth regulation was observed in P. massoniana, together with a decrease in the levels of phytoalexin-like secondary substances, all of which resulted in withering and ultimately death of P. massoniana.
Light is the most common limiting factor in forest plant communities, influencing species composition, stand structure, and stand productivity in closed canopy stands. Stand vertical light structure is relatively simple under a closed canopy because most light is captured by overstory trees. However, wind disturbance events create canopy openings from local to landscape scales that increase understory light intensity and vertical light structural complexity. We studied the effects of an EF-1 tornado on horizontal and vertical (i.e. three-dimensional) light structure within a Quercus stand to determine how light structure changed with increasing disturbance severity. We used a two-tiered method to collect photosynthetic photon flux density at 4.67 m and 1.37 m above the forest floor to construct three-dimensional light structure across a canopy disturbance severity gradient to see if light intensity varied with increasing tornado damage. Results indicate that increased canopy disturbance closer to the tornado track increased light penetration and light structure heterogeneity at lower forest strata. Increased light intensity correlated with increased sapling density that was more randomly distributed across the plot and had shifted light capture higher in the stand structure. Light penetration through the overstory was most strongly correlated with decreased stem density in the two most important tree species (based on relative dominance and relative density) in the stand, Quercus alba L. (r = − 0.31) and Ostrya virginiana (Mill.) K. Koch (r = − 0.27, p < 0.01), and indicated that understory light penetration was most affected by these two species. As managers are increasingly interested in patterning silvicultural entries on natural disturbances, they must understand residual stand and light structures that occur after natural disturbance events. By providing spatial light data that quantifies light structure post-disturbance, managers can use these results to improve planning required for long-term management. The study also provides comparisons with anthropogenic disturbances to the midstory that may offer useful comparisons to natural analogs for future silvicultural consideration.
Glomalin-related soil protein (GRSP) sequesters large amounts of carbon and plays important roles in maintaining terrestrial soil ecosystem functions and ecological restoration; however, little is known about GRSP variation in 1-m soil profiles and its association with stand characteristics, soil properties, and climatic conditions, hindering GRSP-related degraded soil improvement and GRSP evaluation. In this study, we sampled soils from 1-m profiles from poplar (Populus spp.) shelterbelts in Northeast China. GRSP contents were 1.8–2.0 times higher in the upper 40 cm soil layers than at 40–100 cm. GRSP-related soil organic carbon (SOC) sequestration in deeper soil layers was ~ 1.2 times higher than in surface layers. The amounts of GRSP-related nutrients were similar throughout the soil profile. A redundancy analysis showed that in both surface and deeper layers, soil properties (pH, electrical conductivity, water, SOC, and soil nutrients) explained the majority of the GRSP variation (59.5–84.2%); the second-most-important factor in GRSP regulation was climatic conditions (temperature, precipitation, and altitude), while specific shelterbelt characteristics had negligible effects (< 5%). Soil depth and climate indirectly affected GRSP features via soil properties, as manifested by structural equation model analysis. Our findings demonstrate that GRSP is important for carbon storage in deep soils, regardless of shelterbelt characteristics. Future glomalin assessments should consider these vertical patterns and possible regulating mechanisms that are related to soil properties and climatic changes.
The fluxes of masses and the nutrients Ca, Mg, K, N, P and S were determined in the litterfall of two adjacent forest ecosystems of Hungarian oak (Quercus frainetto L.) and European beech (Fagus sylvatica L.) in a mountainous area of northeastern Greece in 2010–2015. The foliar litterfall for both species reached about 70% of the total litterfall, and was significantly higher from the other two fractions (woody and rest litterfall). The fluxes of masses and nutrients were compared between ecosystems for each fraction separately. Only one significant statistical difference was found, that of K in the woody litterfall. In addition, the stocks of masses and nutrients were calculated in the forest floors and mineral soils of the two ecosystems. Likewise, the stocks of nutrients in the forest floors and mineral soils were compared between ecosystems. In the L horizon of the forest floors, statistical differences, as a result of species effect, were found for the stocks of Ca and N. In the FH horizons, the masses and all the nutrient stocks differed significantly, as the beech plot had much higher quantities of organic matter and nutrients. These higher quantities were probably due to low soil temperatures (microclimate) and high acidity in the beech plot (species effect) that slowed down decomposition. In the mineral soils, the propagation of random error derived from random errors of the individual soil layers was an important factor in the statistical comparisons. Because of the soil acidity in the beech plot, the stocks of exchangeable base cations were significantly higher in the oak plot, whereas the other nutrient stocks did not differ.