Poplar Plantations Research Articles

Estimating canopy and stand structure in hybrid poplar plantations from multispectral UAV imagery

Estimating canopy and stand structure in hybrid poplar plantations from multispectral UAV imagery

Two Male Poplar Clones (Populus × euramericana ‘Siyang-1’ and Populus deltoides ‘Nanlin 3804’) Exhibit Distinctly Different Physiological Responses to Soil Water Deficit

Poplar is a globally important industrial tree species due to its fast growth and abundant applications. However, poplars require sufficient water during the growing season, and drought usually limits their production. Drought caused by climate change poses a serious threat to widely planted poplar plantations, making it crucial to clarify and improve the drought resistance of poplars. We employed two male poplar clones, namely, Siyang-1 (Populus × euramericana ‘Siyang-1’) and NL3804 (Populus deltoides ‘Nanlin 3804’), to investigate the growth and physiological responses of these clones to soil drought stress within 25 days. Under drought treatment, both clones experienced a significant reduction in height growth and biomass accumulation, with Siyang-1 exhibiting a more substantial decrease. Under drought treatment, Siyang-1 allocated more assimilates to roots than NL3804. Compared with Siyang-1, NL3804 wilted earlier and had a significantly higher wilting coefficient (p < 0.05). Siyang-1 had higher peroxidase (POD) activity in leaves under drought stress, while NL3804 had a greater increase in membrane permeability. Drought stress increased P absorption and decreased K absorption in both clones but had no significant effect on N absorption. The translocation of limited N and K resources into the stems and roots, as well as the increased uptake of P by the roots, can contribute to defending against drought for poplars. Siyang-1 enhances its drought resistance by modulating its nutrient status and slowing its growth rate, whereas NL3804 accumulates more biomass in the drought stage but perishes sooner, due to imbalances in water and antioxidant systems.

Eco-Efficiency of Pellet Production from Dedicated Poplar Plantations

Biomass, due to its neutrality in terms of greenhouse gas emissions into the atmosphere during its life cycle, is considered an interesting renewable source for energy production as an alternative to the use of more polluting fossil fuels. Among the different wood fuels, pellets are convenient for use in dedicated stoves, and pellet heating systems have a high energy efficiency. The aim of this work was to estimate the economic and global warming potential (GWP100a) generated along the thermal energy supply chain of wood pellets, starting from the production of raw biomass from dedicated poplar cultivations and ending with the use of pellets in stoves by the end-user to produce thermal energy and ash. The Eco-Efficiency Indicator (EEI) was used to link the economic and environmental performance for eight proposed scenarios, obtained by combining different levels of mechanisation for poplar harvesting and wood biomass management before arrival at the pellet plant. For the thermal energy produced by the poplar wood pellet, the GWP100a ranged from 1.5 × 10−2 to 2.1 × 10−2 kg CO2−eq MJ−1 for three-year-old plantations and from 1.9 × 10−2 to 2.4 × 10−2 kg CO2−eq MJ−1, for six-year-old plantations. In terms of eco-efficiency of the baseline scenario (EEIb), the most favourable scenarios remain those linked to the use of biomass from three-year-old poplar plantations, with EEIb values ranging from 0.31 to 0.60 € kgCO2−eq−1, compared to from 0.29 to 0.36 € kgCO2−eq−1 for pellets obtained from biomass produced from six-year-old poplar plantations. In terms of the Global Eco-Efficiency Indicator (EEIg), which also takes into account the positive effect on the reduction of greenhouse gases due to the storage of carbon in the soil by the plantations and the reduction of emissions from avoided fossil fuels, the most favourable scenarios remain those linked to the use of biomass from three-year-old poplar plantations, with EEIg values that vary in the range of 0.60 ÷ 1.04 € kgCO2−eq−1, compared to 0.55 ÷ 0.62 € kg CO2−eq−1 for thermal energy obtained using biomass from six-year-old poplar plantations.

Soil methane emissions from plain poplar (Populus spp.) plantations with contrasting soil textures

The forest soil methane (CH4) flux exhibits high spatiotemporal variability. Understanding these variations and their driving factors is crucial for accurately assessing the forest CH4 budget. In this study, we monitored the diurnal and seasonal variations in soil CH4 fluxes in two poplar (Populus spp.) plantations (Sihong and Dongtai) with different soil textures using the static chamber-based method. The results showed that the annual average soil CH4 flux in the Sihong and Dongtai poplar plantations was 4.27 ± 1.37 kg CH4-C ha–1 yr–1 and 1.92 ± 1.07 kg CH4-C ha–1 yr–1, respectively. Both plantations exhibited net CH4 emissions during the growing season, with only weak CH4 absorption (–0.01 to –0.007 mg m–2 h–1) during the non-growing season. Notably, there was a significant difference in soil CH4 flux between the clay loam of the Sihong poplar plantation and the sandy loam of the Dongtai poplar plantation. From August to December 2019 and from July to August and November 2020, the soil CH4 flux in the Sihong poplar plantation was significantly higher than in the Dongtai poplar plantation. Moreover, the soil CH4 flux significantly increased with rising soil temperature and soil water content. Diurnally, the soil CH4 flux followed a unimodal variation pattern at different growing stages of poplars, with peaks occurring at noon and in the afternoon. However, the soil CH4 flux did not exhibit a consistent seasonal pattern across different years, likely due to substantial variations in precipitation and soil water content. Overall, our study emphasizes the need for a comprehensive understanding of the spatiotemporal variations in forest soil CH4 flux with different soil textures. This understanding is vital for developing reasonable forest management strategies and reducing uncertainties in the global CH4 budget.

Elevated CO2 concentration alleviates the negative effect of vapour pressure deficit and soil drought on juvenile poplar growth

Abstract The growth performance of short-rotation woody coppice (SRWC) is strongly influenced by successful establishment in the initial months after planting. Future climates, expected to be warmer due to elevated atmospheric CO2 (eCO2), may bring about more frequent soil droughts alongside increased vapour pressure deficit (eVPD). Hence, this growth chamber experiment aimed to explore the interactive effects of eVPD, eCO2, and soil drought on growth and physiology traits of juvenile hybrid poplars under warmer climates. Our findings with juvenile hybrid poplar J-105 revealed that eVPD resulted in reductions in leaf area (–21%), root (–20%) and stem biomass (–9%), as well as in net assimilation (–15%), stomatal conductance (–26%), and transpiration (–13%). However, these decreases were relatively minor compared to the compensating effect of eCO2, which generally exerted a stronger influence than eVPD. While soil drought emerged as the primary growth-limiting factor in our study, elevated VPD is not expected to pose a significant additional threat to central European SRWC plantations of juvenile hybrid poplars under future conditions of ongoing climate change.

Comparing Four Evapotranspiration Partitioning Methods from Eddy Covariance Considering Turbulent Mixing in a Poplar Plantation

Evapotranspiration is a key link in the water cycle of terrestrial ecosystems, and the partitioning of evapotranspiration is a prerequisite for diagnosing vegetation growth and water use strategies. In this study, we used double-layer eddy covariance (DLEC) measurements within and above the canopy of poplar plantations to divide evapotranspiration into transpiration and evaporation during the growing season. We diagnosed the coupling state of airflows in the canopy vertical layer and found that the daytime coupling state at the half-hourly scale can mask nighttime decoupling. Furthermore, we investigated the daytime and nighttime vertical layer airflow coupling states separately and quantified the effects of coupling states on the DLEC of resolved transpiration. The partitioning results of the DLEC method were taken as the standard after the airflow coupling test. Then, the performance and accuracy of evapotranspiration partitioning for the modified relaxed eddy accumulation (MREA), the conditional eddy covariance (CEC), and the flux variance similarity (FVS) with DLEC were compared. Transpiration calculated from MREA showed the best agreement with DLEC, and the other methods showed different degrees of underestimation (1:1 slope = 0.64–0.83). Evaporation calculated from FVS showed the best agreement with DLEC, while CEC and FVS made an overestimation of more than 26% (1:1 slope = 1.26–1.99), but MREA made an underestimation from 5% to 35% (1:1 slope = 0.65–0.95). The correlation coefficients between DLEC and MREA for transpiration were 0.95–0.97 with RMSEs of 15.52–17.04 W m−2, and those between DLEC and FVS for transpiration were 0.73–0.78 with RMSEs of 10–21.26 W m−2 at the daily half-hourly scale. A detailed comparison of the differences between DLEC and evapotranspiration partitioning methods from high-frequency eddy covariance data under the condition of canopy vertical layer airflow mixing provides knowledge about the consistency of results for evapotranspiration partitioning in poplar plantation forests.

Possible Factors of Poplar Susceptibility to Large Poplar Borer Infestation

Poplars (Populus spp.) are of significant ecological and economic importance. Long-term breeding efforts were aimed mainly at obtaining fast-growing and productive plants and less considered resistance to pests. This study aimed to identify patterns of susceptibility or resistance to Saperda carcharias (Linnaeus, 1758) (Coleoptera: Cerambycidae) infestation among clones of Populus hybrids and pure species, focusing on the influence of their placement, seasonal development, stem diameter, height increment, and crossing combinations. Among 34 clones of poplar species and hybrids of Ukrainian and foreign selection, in 2019–2023 S. carcharias infested 14 clones every year. Six clones (‘Ivantiivska’, ‘Kytaiska × pyramidalna’, ‘Volosystoplidna’, ‘Novoberlinska-3’, ‘Robusta’, and ‘Lada’) were the most susceptible to the infestation by S. carcharias. The clones of all presented poplar sections and their crossing combinations, except the Tacamahaca and Leucoides cross, were infested. Greater height increment promoted the infestation by S. carcharias. Ambiguous results were obtained regarding the susceptibility of Populus hybrids compared to pure species to S. carcharias infestations. Considering infestation by S. carcharias and plant placement in the site, it can be concluded that the clones ‘Sakrau45-51’, ‘Deltopodibna’, ‘Rosijska’, ‘Slava Ukrayiny’, ‘Lubenska’, ‘Rohanska’, and ‘Nocturne’ are resistant to this pest. Selecting native species clones or creating mixed clone plantations could enhance the resilience of poplar plantations to pest threats.

Impact of Fertilizers Application on Leaf Litter Decomposition and Nutrient Cycling in White Poplar (Populus alba L.) Forest Ecosystem

Fertilizer application plays a crucial role in the decomposition of white poplar leaf litter and cycling of nutrients within forest ecosystems. The impact of various fertilizer additions on white poplar leaf litter and nutrient cycling is poorly understood. In this study, seven treatments were conducted at the following levels: Control (CK), no adding mineral fertilizers, N fertilization (+N), N and P fertilization (+NP), N, P, K fertilization (+NPK), P, K (+PK), manure fertilizer (+MF), and bird fertilizers (+BF) in a white poplar plantation in Qadis district, and used the litterbag techniques to measure litter mass remaining. The main objectives of our study were: (1) to explore the response of white poplar leaf litter decomposition to various fertilizers and accelerate the decomposition process; (2) to examine the relationship between C, N, and P concentration and their stoichiometric characteristic in leaf litter and soil. In this investigation, our results showed that white poplar leaf litter was significantly affected by fertilizers, and the decomposition process was greatly accelerated with + MF, +NPK, and + BF. The decay rate constant k (year −1) shows the decomposition rate of white poplar leaf litter as follows: +MF > +NPK > +BF > +PK > +NP > +N > CK (0.56, 0.53, 0.52, 0.51,0.51,0.5, and 0.46). Soil nutrients N, P and K increased significantly during the decomposition time with + MF, +NPK, and + BF, respectively, while C:N, C:P, and N:P ratios were highest in the white poplar leaf litter, and lowest in soil, we observed significant association between nutrients concentrations in soil and white poplar leaf and their stoichiometric. This current study concluded that adding + MF, +NPK and + BF fertilizers might be the preferred management option as they provided potentially beneficial changes in leaf litter decomposition and increased nutrient concentration. The data obtained will be a valuable reference for fertilization management strategies in forest ecosystems.

Biology of Euwallacea interjectus, an emerging poplar pest, reared on an ambrosia beetle artificial diet and medium of fungal symbiont.

Euwallacea interjectus, a recently discovered pest in poplar plantations, poses a significant economic threat due to its role in causing widespread tree mortality. This pest's cryptic behaviour has hindered research and control efforts, making laboratory rearing a valuable tool for studying its development and biology. We investigated the development period and biological characteristics of E. interjectus using artificial diets and fungal medium. Our findings revealed that the development time for eggs, larvae, and pupae averages approximately 6, 18, and 6 days, respectively. Notably, first and second instar larvae displayed peak moulting periods at 3.45 ± 0.64 SD and 7.92 ± 1.77 SD days, respectively. Furthermore, we measured head capsule widths of postmolt larvae, yielding values of 318.02 ± 7.38 SD μm for first-instar larvae, 403.01 ± 11.08 SD μm for second-instar larvae, and 549.54 ± 20.74 SD μm for third-instar larvae. Our research also uncovered a positive correlation between the number of progeny (eggs, larvae, pupae, and adults) and the mean length of the gallery system. Interestingly, the haplodiploid reproductive strategy did not significantly affect the number of offspring produced by the foundress. Additionally, we observed that foundresses displayed higher fecundity when subjected to nutrient-rich diets as compared to nutrient-poor diets. Our results will deepen our understanding of the biology of E. interjectus and provide criteria for larval instar classification. Additionally, managing nutrient availability within the colony could be considered a viable approach to regulating population size.

Combined effects of border irrigation and super-absorbent polymers on enzyme activity and microbial diversity of poplar rhizosphere soil.

Fast-growing poplar plantations are considered a great benefit to timber production, but water availability is a key factor limiting their growth and development, especially in arid and semi-arid ecosystems. Super-absorbent polymers facilitate more water retention in soil after rain or irrigation, and they are able to release water gradually during plant growth. This study aimed to examine the effects of reduced irrigation (60% and 30% of conventional border irrigation) co-applied with super-absorbent polymers (0, 40 kg/ha) on root exudates, enzyme activities, microbial functional diversity in rhizosphere soil, and volume increments in poplar (Populus euramericana cv. 'Neva'). The results showed that 60% border irrigation co-applied with super-absorbent polymers significantly increased the content of organic acids, amino acids and total sugars in the root exudates, and the activities of invertase, urease, dehydrogenase, and catalase in the rhizosphere soil in comparison to conventional border irrigation without super-absorbent polymers. Meanwhile, this treatment also enhanced the average well-color development, Shannon index, and McIntosh index, but decreased the Simpson index. Additionally, the average volume growth rate and relative water content of leaves reached their maximum using 60% irrigation with super-absorbent polymers, which was significantly higher than other treatments. However, using 30% irrigation with super-absorbent polymers, had a smaller effect on rhizosphere soil and volume growth than 60% irrigation with super-absorbent polymers. Therefore, using an appropriate water-saving irrigation measure (60% conventional border irrigation with super-absorbent polymers) can help to improve enzyme activities and microbial diversity in the rhizosphere soil while promoting the growth of poplar trees.

Beyond biomass production: Enhancing biodiversity while capturing carbon in short rotation coppice poplar plantations

Biodiversity is essential for the functioning of ecosystems and the provision of services. In recent years, the role of plantations in mitigating climate change through carbon sequestration has been highlighted. In the Mediterranean area, high-density poplar plantations in short-rotation with resprouting management (SRC) have been established for biomass purposes on mostly irrigated agricultural land, coexisting with rainfed and irrigated agricultural crops. This study aims to assess the contribution of these plantations to this type of agroforest ecosystem in terms of biodiversity. For this purpose, both flora and fauna diversity were evaluated both within and outside of the plantation. Additionally, the accumulated carbon in the biomass, as well as in the accompanying vegetation within the plantation, was assessed. Different indices were used to evaluate both the intrinsic diversity of the forest plantation and the degree of substitution and complementarity between the different communities of the landscape. Our findings reveal distinct biodiversity patterns in the land-use scenarios sampled. Specifically, we observed significantly higher flora-species richness in SRC plantations than in the adjacent agricultural land, whereas fauna richness showed a similar but slightly higher level in the forested area. A moderate level of complementarity between land uses was found for insects and mammals (around 45 %), contrasting with high complementarity for birds (87 %) and flora (90 %). This suggests substantial turnover and replacement among these ecological environments. Our results indicate that a second rotation (4 year) plantation could accumulate a total of 61.6 Mg C ha−1, and even though adventitious flora represents <2 % of the total carbon accumulated, its importance in providing ecosystem services is considerable. Hence, these findings evidence the fact that SRC poplar plantations can enhance biodiversity in Mediterranean agroforest ecosystems and actively contribute to various provisioning ecosystem services, including carbon sequestration, reflecting a multi-objective approach that extends beyond biomass production.

Temporal and depth‐dependent variations in soil aggregate‐associated organic carbon in reclaimed coastal poplar plantations

AbstractCoastal reclamation alters the ecological environment of wetlands and influences global carbon cycles. However, variations in soil organic carbon fractions and stability in the soil profile during reclamation, particularly in the subsoil, remain unclear. In this study, soil aggregate‐associated organic carbon and its stability were investigated in soil profiles (0–100 cm) at different reclamation times (0, 24, 44, and 64 years) in coastal poplar plantations in East China. Total soil organic carbon concentrations in the topsoil (0–40 cm) increased with increasing reclamation time but varied little in the subsoil (40–100 cm). In the topsoil, the soil organic carbon concentrations in different aggregate fractions tended to increase with increasing reclamation time, which was enhanced mainly by particulate organic carbon within macro‐aggregates. In the subsoil, soil organic carbon concentrations increased in the micro‐aggregate fraction and decreased in the silt and clay fraction with increasing reclamation time, whereas the opposite changes led to smaller variations in total soil organic carbon. This relative balance was regulated by micro‐aggregate formation via new organic matter input (e.g., root litter) and old mineral‐associated organic carbon depletion. Regardless of the soil horizon, soil aggregate stability increased with reclamation time, whereas the total particulate organic carbon/mineral‐associated organic carbon ratio increased with increasing reclamation time, implying that the soil organic carbon stability decreased, which may be attributed to an increase in the vulnerability of soil organic matter to mineralization as the reclamation progresses. These findings indicate that long‐term plantation development influences aggregate‐associated organic carbon accrual throughout the soil profile in reclaimed coastal land. Thus, effective management is required to improve soil organic carbon accrual in coastal woodland subsoil, which is crucial for increasing soil carbon sequestration.

Chemical Recalcitrance Rather Than Soil Microbial Community Determined Short-Term Biochar Stability in a Poplar Plantation Soil

The stability of biochar is fundamental to its soil carbon (C) sequestration potential. The relative importance of chemical recalcitrance and the soil microbial community on biochar stability is still unclear. To unveil the question, we conducted a 60-day incubation to explore the stability of two rice-straw-derived biochars pyrolyzed at 300 and 500 °C (denoted as BS300 and BS500), as well as the relative contribution of the soil microbial community and biochar chemical recalcitrance to biochar stability in a poplar plantation soil. Biochar-derived cumulative carbon dioxide (CO2) emission was estimated to be 41.3 and 6.80 mg C kg−1, accounting for 0.73 and 0.11% of the amended biochar-derived organic C (OC) in BS300 and BS500 treatments, respectively. The mean retention time (MRT) estimated by double-exponential model fitting was 49.4 years for BS300 and 231 years for BS500. Compared to control, BS300 and BS500 decreased β-D-glucosidase activity by 20.9 and 18.0%, while they decreased phenol oxidase activity by 31.8 and 18.9%, respectively. Furthermore, BS300 increased the soil microbial metabolic quotient (qCO2) by 155%, but BS500 decreased it by 13.4%. In addition, BS300 resulted in a 520% higher biochar-derived hot-water-extractable OC than BS500. Partial least-squares path modeling (PLSPM) showed that the path efficients of biochar’s chemical recalcitrance and microbial qCO2 were 0.52 and 0.25, respectively, and that of the soil microbial activity is neglected. We conclude from this short-term study that chemical recalcitrance imposed a greater effect than soil microbial community on biochar stability.

Economic and environmental assessment of a multifunctional poplar plantation for roundwood and wood chip production in Spain

Aim of study: To analyze the environmental and economic performance of a multifunctional poplar plantation (MPP), which was managed to produce timber for sawn wood and chips for bioenergy. Area of study: The plantation was located in Southern Spain producing roundwood and woodchips (from tops and branches). Material and methods: The life cycle assessment (LCA) methodology was chosen to perform the environmental impact assessment from a cradle-to-gate perspective. Capital goods, including machinery-manufacturing processes, were included. One oven dry tonne (odt) of forest biomass was chosen as functional unit. The economic analysis was performed using present costs and common indicators: net present value (NPV) and internal rate of return (IRR). Main results: The harvest operations are the most environmental impacting subsystem and cultivation the costliest. Chipping was the process contributing the most to the environmental burden. The use of fertilizers, within the cultivation subsystem, had a notable impact on certain midpoint categories. In terms of climate change potential, 1 odt of delivered wood chips generated 64.1 kg CO2-eq. When considering the whole system (including the roundwood fraction), this value was 45.2 kg CO2-eq odt-1. MPP was hardly profitable with land rental and irrigation being the most expensive items. NPV, including harvesting and transport subsystems, was 1,582 € ha-1, while IRR reached 6.3%. Research highlights: Our results allow to identify the costliest operations and those with the greatest impact to improve the system. Finally, these figures can be compared with other crop alternatives such us poplar short rotation coppice (SRC).

Comparative transcriptome analysis reveals the importance of phenylpropanoid biosynthesis for the induced resistance of 84K poplar to anthracnose

BackgroundPoplar anthracnose, which is one of the most important tree diseases, is primarily caused by Colletotrichum gloeosporioides, which has been detected in poplar plantations in China and is responsible for serious economic losses. The characteristics of 84K poplar that have made it one of the typical woody model plants used for investigating stress resistance include its rapid growth, simple reproduction, and adaptability.ResultsIn this study, we found that the resistance of 84K poplar to anthracnose varied considerably depending on how the samples were inoculated of the two seedlings in each tissue culture bottle, one (84K-Cg) was inoculated for 6 days, whereas the 84K-DCg samples were another seedling inoculated at the 6th day and incubated for another 6 days under the same conditions. It was showed that the average anthracnose spot diameter on 84K-Cg and 84K-DCg leaves was 1.23 ± 0.0577 cm and 0.67 ± 0.1154 cm, respectively. Based on the transcriptome sequencing analysis, it was indicated that the upregulated phenylpropanoid biosynthesis-related genes in 84K poplar infected with C. gloeosporioides, including genes encoding PAL, C4H, 4CL, HCT, CCR, COMT, F5H, and CAD, are also involved in other KEGG pathways (i.e., flavonoid biosynthesis and phenylalanine metabolism). The expression levels of these genes were lowest in 84K-Cg and highest in 84K-DCg.ConclusionsIt was found that PAL-related genes may be crucial for the induced resistance of 84K poplar to anthracnose, which enriched in the phenylpropanoid biosynthesis. These results will provide the basis for future research conducted to verify the contribution of phenylpropanoid biosynthesis to induced resistance and explore plant immune resistance-related signals that may regulate plant defense capabilities, which may provide valuable insights relevant to the development of effective and environmentally friendly methods for controlling poplar anthracnose.

Forest Carbon Modeling in Poplar and Black Locust Short Rotation Coppice Plantation in Hungary

Forest carbon dynamic modeling for estimating the carbon stock in short rotation coppice bioenergy plantation in Hungary will be vital for better comprehending the role of black locust (Robinia pseudoacacia) and poplar (Populus sp.) in carbon dioxide sequestration from the atmosphere. The research aims were to estimate the potential carbon stock and describe the carbon distribution of the short rotation coppice bioenergy plantation above and below ground. Various sources were used to acquire parameterization data for developing forest carbon dynamic models. CO2FIX modeling V.3.2 was utilized in the data analysis to estimate the total carbon stock in biomass, soil, harvested wood products, and bioenergy compartments. Modeling has been around for 45 years. In this research, the total carbon stock of black locust and poplar at the end of the simulation period was 64.13 and 131.08 MgC.ha-1, respectively. The average carbon allocation above and below ground for black locust and poplar was 0.76, 19.76, 1.80, and 21.67 MgC.ha-1, respectively. In conclusion, poplar outperformed black locust regarding carbon storage in the short rotation coppice bioenergy plantation. Below ground carbon allocation was much higher than above ground. Therefore, more attention should be paid on below ground allocation through environmentally friendly soil management. Keywords: bioenergy plantation, carbon dynamics, climate change mitigation, CO2FIX model, fast growing species

Characterization of potassium-solubilizing fungi, Mortierella spp., isolated from a poplar plantation rhizosphere soil.

Potassium-solubilizing microorganisms are capable of secreting acidic chemicals that dissolve and release potassium from soil minerals, thus facilitating potassium uptake by plants. In this study, three potassium-dissolving filamentous fungi were isolated from the rhizosphere soil of a poplar plantation in Jiangsu Province, China. Phylogenetic analyses based on ITS, 18S, and 28S showed that these three isolates were most similar to Mortierella. These strains also possessed spherical or ellipsoidal spores, produced sporangia at the hyphal tip, and formed petal-like colonies on PDA media resembling those of Mortierella species. These findings, along with further phenotypic observations, suggest that these isolates were Mortierella species. In addition, the potassium-dissolution experiment showed that strain 2K4 had a relatively high potassium-solubilizing capacity among these isolated fungi. By investigating the influences of different nutrient conditions (carbon source, nitrogen source, and inorganic salt) and initial pH values on the potassium-dissolving ability, the optimal potassium-solubilization conditions of the isolate were determined. When potassium feldspar powder was used as an insoluble potassium source, isolate 2K4 exhibited a significantly better polysaccharide aggregation ability on the formed mycelium-potassium feldspar complex. The composition and content of organic acids secreted by strain 2K4 were further detected, and the potassium-dissolution mechanism of the Mortierella species and its growth promotion effect were discussed, using maize as an example.

Biomass Production of the Poplar Clone OP42 During the Second Rotation Plantation–The Effects of Four Thinning Treatments

Poplar (Populus species and their hybrids) plantations can produce large amounts of biomass on agricultural land during the first rotation. However, there is limited knowledge regarding plantation re-establishment through re-sprouting (second rotation) after harvest, stand management options for such plantations, and biomass production during rotation length up to 20 years. In this study, we analysed biomass production responses to thinning treatments in an 18-year-old second rotation poplar plantation in Southern Sweden. The first rotation plantation was established with clone OP42 (Populus maximowiczii A. Henry × P. trichocarpa Torr. and Gray). The thinning experiment was conducted seven years after the first rotation harvest, comprising four treatments: unthinned – 6000 stems ha−1, light thinning – 3000 stems ha−1, medium thinning – 1100 stems ha−1, and heavy thinning – 550 stems ha−1. Eleven years after thinning, standing volume/biomass reached 484 m3 ha−1 (162 Mg DM ha−1) in the unthinned and medium thinning plots, 443 m3 ha−1 (148 Mg DM ha−1) in lightly and 338 m3 ha−1 (113 Mg DM ha−1) in heavily thinned plots. The mean annual increment was not different among the unthinned, light, and medium thinnings, 26 m3 ha−1 yr−1 (9 Mg DM ha−1 yr−1). The total production, including living, dead and removed trees, was highest following the medium thinning, 695 m3 ha−1 (233 Mg DM ha−1). Gradual self-thinning in the unthinned and lightly thinned plots was increased by a drought period. Overall, this study suggests that the second rotation of poplar plantations has high biomass production and provides an alternative to planting after harvest.

Comparison between Different Mechanization Systems: Economic Sustainability of Harvesting Poplar Plantations in Italy

After a period of significant development, poplar cultivation in Italy has been in rapid decline since the 1980s. Because of its marked ductility, poplar is valuable for both wood furniture and energy production. Production could be increased through mechanization, because innovative machinery and equipment can reduce the exposure of forest workers to common risk factors, ensure greater and better productivity, increase the efficiency of operations, and reduce costs. There are various systems for the mechanization of poplar production (from traditional to advanced and pushed mechanization). We describe the range of possibilities (in terms of both the techniques adopted and the machines used) for planting, harvesting, and chopping poplar. Based on our analysis of operating costs, we conclude that mechanized poplar production could reduce the average cost per ton of wood chips (EUR/t) by 23% and the average gross cost per hectare of wood chips produced (EUR/ha) by 37%.

Screening old and modern wheat varieties for shading tolerance within a specialized poplar plantation for agroforestry farming systems implementation

AbstractThe sustainability of silvoarable agroforestry systems largely depends on the choice of suitable crop species and varieties for minimizing competitive interactions in the interaction zone with trees. Up to date crop intraspecific variability has been poorly investigated, and mainly in pot trials under artificial shading. Given this framework, a trial was conducted in field conditions in NE Italy to study the response of 10 common wheat varieties cultivated in the 6-m narrow inter-row of a specialized 4-year old poplar plantation (AF, agroforestry) vs. full sun conditions (C, controls). Here it was demonstrated that large genetic variability exists in wheat, as grain yield reductions under shading ranged between 31 and 75% (average − 57%) depending on variety choice. Better tolerance was highlighted in old varieties (− 44% of yield in AF vs. C), that was associated to greater plasticity in delaying leaf senescence, and increased both leaf area index and SPAD (index of chlorophyll content), while achieving the highest grain protein contents (&gt; 17.3% DW). However, under shading modern wheat varieties still remained the highest yielding, particularly in bread-making varieties (469 g m−2 on average), thanks to larger improvement of the leaf-to-culm biomass ratio and better harvest index. We conclude that there is large scope for identifying wheat varieties suitable for agroforestry systems, while breeding programs can select for specific morpho-physiological adaptation traits to low irradiance.