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Twentieth-century land management has altered the structure and composition of mixed-conifer forests and decreased their resilience to fire, drought, and insects in many parts of the Interior West. These forests occur across a wide range of environmental settings and historical disturbance regimes, so their response to land management is likely to vary across landscapes and among ecoregions. However, this variation has not been well characterized and hampers the development of appropriate management and restoration plans. We identified mixed-conifer types in central Oregon based on historical structure and composition, and successional trajectories following recent changes in land use, and evaluated how these types were distributed across environmental gradients. We used field data from 171 sites sampled across a range of environmental settings in two subregions: the eastern Cascades and the Ochoco Mountains. We identified four forest types in the eastern Cascades and four analogous types with lower densities in the Ochoco Mountains. All types historically contained ponderosa pine, but differed in the historical and modern proportions of shade-tolerant vs. shade-intolerant tree species. The Persistent Ponderosa Pine and Recent Douglas-fir types occupied relatively hot-dry environments compared to Recent Grand Fir and Persistent Shade Tolerant sites, which occupied warm-moist and cold-wet environments, respectively. Twentieth-century selective harvesting halved the density of large trees, with some variation among forest types. In contrast, the density of small trees doubled or tripled early in the 20th century, probably due to land-use change and a relatively cool, wet climate. Contrary to the common perception that dry ponderosa pine forests are the most highly departed from historical conditions, we found a greater departure in the modern composition of small trees in warm-moist environments than in either hot-dry or cold-wet environments. Furthermore, shade-tolerant trees began infilling earlier in cold-wet than in hot-dry environments and also in topographically shaded sites in the Ochoco Mountains. Our new classification could be used to prioritize management that seeks to restore structure and composition or create resilience in mixed-conifer forests of the region.

Eukaryotic algae have recently emerged as hosts for metabolic engineering efforts to generate heterologous isoprenoids. Isoprenoid metabolic architectures, flux, subcellular localization, and transport dynamics have not yet been fully elucidated in algal hosts. In this study, we investigated the accessibility of different isoprenoid precursor pools for C.sub.15 sesquiterpenoid generation in the cytoplasm and chloroplast of Chlamydomonas reinhardtii using the Abies grandis bisabolene synthase (AgBS) as a reporter. The abundance of the C.sub.15 sesquiterpene precursor farnesyl pyrophosphate (FPP) was not increased in the cytosol by co-expression and fusion of AgBS with different FPP synthases (FPPSs), indicating limited C.sub.5 precursor availability in the cytoplasm. However, FPP was shown to be available in the plastid stroma, where bisabolene titers could be improved several-fold by FPPSs. Sesquiterpene production was greatest when AgBS-FPPS fusions were directed to the plastid and could further be improved by increasing the gene dosage. During scale-up cultivation with different carbon sources and light regimes, specific sesquiterpene productivities from the plastid were highest with CO.sub.2 as the only carbon source and light:dark illumination cycles. Potential prenyl unit transporters are proposed based on bioinformatic analyses, which may be in part responsible for our observations. Our findings indicate that the algal chloroplast can be harnessed in addition to the cytosol to exploit the full potential of algae as green cell factories for non-native sesquiterpenoid generation. Identification of a prenyl transporter may be leveraged for further extending this capacity.

Aims The aim of this study was to investigate the mechanisms by which nitrogen (N) and phosphorous (P) additions affect plant C:N:P stoichiometry via changes in AMF communities in a Chinese fir plantation. Methods Experimental plots in a 10-year-old Chinese fir plantation were treated with N addition (LN, 30 kg•ha −1 •yr −1 , and HN, 60 kg•ha −1 •yr −1 ) and P addition (LP, 20 mg•kg −1 , and HP, 40 mg•kg −1 ) for 2 years starting from 2017. Soil properties, leaf C:N:P stoichiometry, and changes in AMF community composition and diversity were measured. Results N or P addition increased soil N availability, decreased P availability, and increased N:P in the leaves and soil. Changes in soil pH induced by N and P additions affected the colonization rate and spore density of AMF. AMF colonization rate was increased by N or P addition, and AMF diversity was increased by LN addition. N and P additions altered AMF species composition, and the dominant genus of the AMF in the soil was Glomus in all treatments . The interaction of N and P treatments had no significant effect on AMF diversity. AMF colonization rate and diversity, rather than its composition, affected leaf C:N:P stoichiometry. Conclusion N and P additions affected colonization rate and diversity of AMF though changes in soil pH, which drove leaf C:N:P stoichiometry, and potentially affected forest productivity via the fungi-soil-plant system.

Increased nitrogen (N) deposition may exacerbate soil phosphorus (P) deficiency, which alters soil greenhouse gas (GHG) emissions by changing soil properties and understory vegetation in subtropical forests. However, the effects of N addition, P addition, and understory vegetation interactions on soil carbon dioxide (CO.sub.2) and nitrous oxide (N.sub.2O) emissions in forest ecosystems and their underlying mechanisms remain unclear. We conducted a continuous N and P addition experiment in a subtropical Chinese fir plantation. The effects of N and P addition on soil CO.sub.2 and N.sub.2O emissions with different understory vegetation were examined using a structural equation model. The addition of N and P did not directly affect soil CO.sub.2 emission of the understory, which was affected by understory species (F = 2.86; p = 0.05). N indirectly and positively affects soil CO.sub.2 emission through plant elements, and directly affect N.sub.2O emission of understory soil. Compared with CK, the addition of N2 promoted the N.sub.2O cumulative emission by 74.3%. N has a direct positive effect on soil N.sub.2O emissions, while P addition indirectly exerts a negative influence on N.sub.2O emissions through its impact on soil properties. Plant elements and soil properties were explained in 26.3% of soil CO.sub.2 emissions, of which 17.6% and 16.0% variations were explained by plant elements and soil properties, respectively. Leaf total N was the most important factor for predicting CO.sub.2 emissions. Our results suggested that soil CO.sub.2 emission was more dependent on plant elements, and soil N.sub.2O emission was directly dependent on N addition rather than plant elements. Thus, different patterns of soil GHG emissions and associated controls following N and P addition provided novel insights into predicting the effects of understory vegetation on climate change mitigation outcomes.

European forests are becoming increasingly threatened by climate change and more frequent droughts. The likely responses of species to climate change will vary, affecting their competitiveness, their existence, and consequently, forest management decisions and measures. We determined the influence of climate on the radial growth of European beech and silver fir along the Carpathians to find similarities between the two species and the main differences. Along the Carpathian Mountains, seven sites with mature fir–beech stands above 800 m above sea level were selected and analyzed. Our study confirmed different responses depending on species and location. A more pronounced response of tree growth to climate was observed on the eastern side of the Carpathians, while it was less expressed or even absent on the southern sites. Both beech and fir show better radial growth with higher precipitation in July and slower growth with higher average and maximum temperatures in June of the current year. Fir demonstrates a positive correlation between radial growth and temperature in winter, while beech demonstrates a negative correlation between radial growth and temperature in summer. In the 1951–1960 decade, the average tree ring widths in fir and beech were largest at the southern sites compared to the other sites, but since 2011, the southern sites have had the lowest increase while northern sites have had the largest. Both species respond differently to climate and are likely to follow different competitive paths in the future.

Land managers use hazard (susceptibility) and risk rating systems to guide the application of forest management treatments that aim to reduce future damages to forests. Rating systems are typically designed for individual damage agents, but tree mortality often results from multiple agents without a clear proximate cause. In interior Douglas‐fir (DF, Pseudotsuga menziesii var. glauca) forests in the Northern Rocky Mountains, USA, multiple damage agents are commonly associated with DF tree mortality, such as insects, disease, weather, and fire. We investigated how recent DF tree mortality from insects and diseases (excluding fire and harvest) shifted stand structure and composition in DF forests and was influenced by susceptibility (e.g., stand structure and composition, topography, and spatial variability in climate) and risk (biotic agent pressure). Our multi‐scale analysis used 884 plots remeasured after 10 years from the USDA Forest Inventory and Analysis program with support from spatial datasets. Across a large, forested landscape, 60% of the plots had no new DF mortality, and most plots (80%) experienced mortality <10% of DF basal area. However, severe tree mortality, defined as >25% loss of DF basal area, occurred in 6% of plots. Most of the dead DF trees (68%) were smaller diameter (12.7–29 cm at breast height) and mortality rates of smaller trees were significantly greater than those of larger diameter trees (>29 cm), a finding consistent with natural stand development processes. During the remeasurement period, average DF tree size increased in most plots (80%) and <4% of DF‐dominated plots with severe mortality shifted in dominance from DF to another tree species. Greater DF mortality (percentage of initial DF basal area) was associated with lower tree growth rates, larger average tree sizes, greater availability of DF tree hosts for biotic agents, cooler and wetter topo‐climatic locations, and higher Douglas‐fir beetle population pressure. The relative importance of each variable differed west and east of the Continental Divide. By identifying thresholds in susceptibility and risk variables associated with higher DF tree mortality, our results support adaptive forest management for multiple damage agents, when the goal is to reduce tree mortality of a widespread and abundant conifer.

Background and Aims Phosphorus (P) plays a vital role in plant physiology, and the soils of Chinese fir-producing areas are rich in aluminum and iron ions, making phosphorus highly susceptible to fixation. Insufficient phosphorus nutrient supply is a main constraint to the sustainability of Chinese fir plantations. The aim of this study is to ameliorate the problem of soil available phosphorus deficiency in Chinese fir plantations by changing the management mode, introducing local broad-leaved tree species to form multiple layers of different ages, thereby enhancing soil productivity. Methods The properties and phosphorus fractions of the surface soils (0-20 cm), litter and leaf nutrients were determined, and macro-genomic technique was used to explore changes of soil phosphorus cycling (P-cycling) genes. Results (1) The close-to-nature management (CNM) significantly increased soil organic carbon (SOC) and available phosphorus (AP) content and affected litter and plant nutrients. (2) The CNM affected the availability of soil phosphorus. The labile phosphorus (resin-P, NaHCO 3 -Pi) and moderately labile phosphorus (NaOH-Pi) were significantly higher in CNM forests than in Chinese fir plantation. (3) The relative abundances of most of the P-cycling genes differed between the forests, with higher abundances of P-solubilization ( ppa ), P-mineralization ( phnL and opd ) and P-regulatory ( phoB ) genes in CNM forests. Moreover, MBC (microbial biomass carbon), SOC, total nitrogen (TN) and LTP (litter total phosphorus) were the main factors affecting the composition of soil P-cycling genes. Conclusions The CNM affected properties (soil, litter and plant) and improved soil phosphorus availability and the relative abundance of P-cycling genes. This study revealed the regulation mechanism of P-cycling in the CNM of Chinese fir plantation from microbial P-cycling genes perspective, which highlights the importance of P supply and microbial metabolic strategy by CNM of Chinese fir plantation.

Competitive vegetation in forest stands influence seedling growth by changing soil nutrient availability. However, studies on the effects of different weed control methods on seedling growth of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) are rare. We applied three weed control methods, comprising artificial sickle weeding (ASW), woody disc weeding (WDW), and nonwoven cloth weeding (nWCW), to explore their effect on growth of Chinese fir seedlings in a plantation in Jiangxi Province, China. The weed control methods affected the shoot height and root-collar diameter of the seedlings. The contents of sugar, glucose, triglycerides, total cholesterol, and free fatty acids in newly developed leaves were increased after ASW and nWCW treatment, and were consistent with the expression of genes associated with glucokinase, sucrose phosphate synthase, and sucrose synthase. Weeding method influenced soil properties, including pH, moisture, total nitrogen (TN), ammonium-N, nitrate-N, total phosphorus, available phosphorus, and dissolved organic carbon contents. Moisture content was the main factor that influenced the soil bacterial community and leaf nutrition. High-throughput sequencing of the bacterial 16 S rRNA gene revealed that the weeding methods affected bacterial community structure. Specifically, compared with ASW and nWCW, WDW contributed to lower soil bacterial diversity, simpler bacterial interaction, and increase in pathogenic bacteria potential. The weeding methods differ in influence on soil bacterial community structure, soil properties, and plant growth, which are potentially useful to improve the growth of Chinese fir seedlings. ASW and nWCW strategies were recommended to be applied in the practice of weed control on seedling growth of Chinese fir.

Background and aims Competitive vegetation in forest stands influence seedling growth by changing soil nutrient availability. However, studies on the effects of different weed control methods on seedling growth of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) are rare. Methods We applied three weed control methods, comprising artificial sickle weeding (ASW), woody disc weeding (WDW), and nonwoven cloth weeding (nWCW), to explore their effect on growth of Chinese fir seedlings in a plantation in Jiangxi Province, China. Results The weed control methods affected the shoot height and root-collar diameter of the seedlings. The contents of sugar, glucose, triglycerides, total cholesterol, and free fatty acids in newly developed leaves were increased after ASW and nWCW treatment, and were consistent with the expression of genes associated with glucokinase, sucrose phosphate synthase, and sucrose synthase. Weeding method influenced soil properties, including pH, moisture, total nitrogen (TN), ammonium-N, nitrate-N, total phosphorus, available phosphorus, and dissolved organic carbon contents. Moisture content was the main factor that influenced the soil bacterial community and leaf nutrition. High-throughput sequencing of the bacterial 16 S rRNA gene revealed that the weeding methods affected bacterial community structure. Specifically, compared with ASW and nWCW, WDW contributed to lower soil bacterial diversity, simpler bacterial interaction, and increase in pathogenic bacteria potential. Conclusions The weeding methods differ in influence on soil bacterial community structure, soil properties, and plant growth, which are potentially useful to improve the growth of Chinese fir seedlings. ASW and nWCW strategies were recommended to be applied in the practice of weed control on seedling growth of Chinese fir.

Aims Long-term nitrogen (N) fertilization has been shown to profoundly affect the soil microorganisms and strongly result in several imbalances in element concentrations. The objective of this study was to examine links among the soil microorganisms, enzyme activities, and soil carbon (C), N, and phosphorus (P) stoichiometry in a subtropical Chinese fir ( Cunninghamia lanceolata (Lamb.) Hook) plantation after continuous N fertilization for 13 years. Methods This study was performed in 25-year-old fir plantation along a fertilization gradient (0, 60, 120, and 240 kg N ha −1  yr. −1 ), designated as N0, N1, N2, and N3, respectively. Soil microbial properties, including the microbial community composition, as revealed by phospholipid fatty acids (PLFAs), and soil enzyme activities (i.e., sucrase, urease and catalase) were measured, and soil elemental stoichiometry was calculated based on soil C, N, and P concentrations. A redundancy analysis (RDA) was conducted to determine the relationship between soil C:N:P stoichiometry and soil microbial properties. Results Compared with the control (N0), N fertilization decreased the total PLFAs (−12.20%), bacteria (−14.33%), fungi (−12.97%), and actinomycetes (−17.11%) on average. Sucrase, urease and catalase activities were enhanced by low and middle levels of N (N1 and N2), but not with high level of N (N3). Long-term N fertilization decreased soil pH, C to N ratio (C/N), and C to P ratio (C/P), while increased soil C, N and N to P ratio (N/P). The RDA identified the first two axes of soil stoichiometry variation that explained 20.4% of the variation at the soil depth of 0–20 cm, 28.6% at 20–40 cm and 49.9% at 40–60 cm in PLFAs biomarkers and enzymes, respectively. Significant correlations between soil stoichiometry (soil N/P and C/P ratio) and soil microbial properties were found in this study. Conclusions These observations suggested that long-term N fertilization influenced soil microbial community composition and enzyme activities by changing the soil C/P and N/P ratios. Future studies are needed to consider the coupling relationships between soil microbial community composition, enzyme activities and elemental stoichiometry in different ecosystems under future climatic change.