Basal Diameter Growth Research Articles

Enhancing temperature resilience in dioecious Salix myrtillacea: The role of acetic acid in eco-physiological and microbial adaptations

The effects of climate change on dioecious plants are of growing concern. Dioecious plants have sex-specific eco-physiological responses. This study investigated the response of Salix myrtillacea, a dioecious wood-producing plant with industrial potential, to high (35°C) and low (15°C) temperature stresses. The efficacy of exogenously applied acetic acid (AA) in enhancing sex-specific temperature stress tolerance was also investigated. The research found that female willows showed greater resilience to both temperature extremes than males. The average stress intensity indices for height and basal diameter growth rate were 19.20 % and 10.87 % higher in males than in females, respectively. This was also evidenced by greater physiological adaptations (antioxidant enzyme activity, hormone accumulation) and nutrient assimilation. Compared with high temperature, willows showed better adaptation to low temperature, resulting in a significant stress reduction. In addition, the application of AA significantly reduced stress in both sexes, while distinct sex-specific differences were observed in the composition of the rhizosphere microbial community. The application of AA particularly influenced certain microbial phyla. For example, it increased the relative abundance of Bacteroidetes by 46.11 % and Chloroflexi by 42.16 %, while decreased Acidobacteria by 29.28 %. This supported carbon uptake and storage to improve stress tolerance in females under high temperature stress. Conversely, males showed a stronger association with fungi to maintain stability. In conclusion, the application of AA significantly improved the temperature stress resistance of dioecious willows. There were pronounced improvements in growth, physiological adaptations, and microbial interactions. These effects were particularly evident in female plants. These findings highlight the potential of AA in tailoring climate resilience strategies for dioecious species.

Biochar Addition Increased Soil Carbon Storage but Did Not Exacerbate Soil Carbon Emission in Young Subtropical Plantation Forest

Forests play a crucial role in mitigating global warming, contributing approximately 46% of the global terrestrial carbon sink. However, it remains uncertain whether the addition of biochar to forests enhances the ecosystem’s carbon sink capacity. This study aims to address this scientific question by investigating whether biochar application increases carbon storage, potentially leading to an overall rise in carbon emissions by influencing soil respiration and identifying the underlying mechanisms. A controlled experiment was conducted in a young plantation forest that had grown for three years, where soil CO2 efflux rate and physicochemical properties, photosynthesis, and plant growth traits were measured across varying biochar addition rates (0, 5, and 10 t/ha) over five seasons. Then, statistical methods including one-way ANOVA, regression analysis, and structural equation modeling (SEM) were employed to assess differences in biological and abiotic factors among biochar addition gradients and understand the influencing mechanisms of soil CO2 efflux change. The findings revealed that biochar addition significantly increased the contents of soil organic carbon (SOC) and microbial biomass carbon (MBC), consequently promoting photosynthesis and plant growth (p < 0.05). Biochar addition accounted for 73.8% of the variation in soil CO2 efflux by affecting soil physicochemical properties, photosynthesis, and plant basal diameter growth. However, the net effect of biochar addition on soil CO2 efflux was found to be low. The positive effects of biochar addition on soil CO2 efflux via factors such as soil bulk density, total nitrogen (TN), MBC, and photosynthesis were counteracted by its negative impact through soil total phosphorus (TP), water content, pH, SOC, and plant basal diameter growth. Overall, our findings indicate that there was no significant increase in soil CO2 efflux in the short term (totaling 16 months) over the biochar addition gradient. However, we observed a substantial increase in soil carbon storage and an enhancement in the soil’s capacity to act as a carbon sink. Therefore, adding biochar to forests may be a feasible strategy to increase carbon sinks and mitigate global climate change.

Effects of fertilizer application on the growth of Stranvaesia davidiana D. seedlings.

Wild plants represent a potential source of urban landscape trees. Stranvaesia davidiana Dcne. is a member of the Stranvaesia Lindl. Genus, which belongs to family Rosaceae Juss. It has great ornamental value. It can contribute to urban color foliage and fruit species. However, the most effective fertilizer application strategy required for its cultivation is unknown. Therefore, we conducted an orthogonal experiment to investigate the fertilizer type and level (pure nitrogen) using ten experimental groups, including an untreated control group. Pot experiments were used to determine the growth indices of seedlings, including plant height, basal diameter, and chlorophyll content post-fertilizer treatment. This study explored the most appropriate fertiler application model for the growth of S. davidiana seedlings. The results revealed that enhanced seedling growth depended on the type and amount of fertilizer used, and their interaction. Fertilizer application increased the plant height by 2.67 cm to 12.26 cm, basal diameter by 0.39 cm to 0.75 cm, and chlorophyll content by 5.66 to 19.86. Among the different types of fertilizer, organic fertilizer increased the plant height by 0.42 cm to 9.59 cm and basal diameter by 0.01 cm to 0.05 cm, compared with the control group. Organic fertilizer had the maximum effect on seedling growth, especially at medium levels. The total growth of basal diameter and chlorophyll content was 1.58 ± 0.04 cm and 39.53 ± 2.37, respectively. Basal diameter is the most critical index in seedling reproduction . The study results suggest that the application of 4.06 g of organic fertilizer per plant was the most effective, and served as a basis for further field trials.

Savanna tree regrowth after defoliation explained by bud activation rather than reserve mobilization

Livestock rearing is increasing in savannas, so the ability of trees to regrow after consumption represents one of the critical aspects of savanna structure and functioning. Here, we identified specific traits—which may explain the mechanisms behind defoliation tolerance—in saplings of two encroacher tree species (Vachellia caven and Vachellia aroma). We carried out common garden and field experiments where manual defoliation treatments simulated the cattle grazing regime employed in the study region. At the end of the experiments, we recorded growth variables and, in the common garden experiment, root reserves concentration. In the common garden, defoliation decreased height and basal diameter growth but did not affect the aerial relative growth rate. Also, defoliation increased the number of branches per plant and decreased root relative growth rate. Starch concentration was higher or similar in defoliated plants than controls, depending on the species. In the field, defoliation decreased both species’ height and basal diameter growth. We found that tree saplings tolerated defoliation, and the mechanisms behind tolerance would be linked mainly to the axillary bud activation and not to storage reserve mobilization. Over time, these plant architectural changes might complicate cattle movement and management in these systems. From a long-term perspective, livestock rearing might retard juvenile recruitment into reproductive-size classes (e.g., adults) by reducing overall tree growth rates.

Natural Bioactive Substances in Fruits of Aronia melanocarpa (Michx.) Elliott Exposed to Combined Light-Type, Chitosan Oligosaccharide, and Spent Mushroom Residue Treatments.

Greenhouse culture is a practical approach to obtain non-wood forest products from berry fruit at a higher efficacy than resource silviculture in natural understory. In this study, three-year old black chokeberry (Aronia melanocarpa (Michx.) Elliott 1821) seedlings were transplanted to a greenhouse where sunlight was complemented by red- (69.4% red, 30.2% green, 0.4% blue) and blue-color (15.3% red, 64.9% green, 19.8% blue) light-emitting diode (LED) illuminations. Half of the planting soils were amended by spent mushroom residue (SMR) (not amendment as the control) and half the seedlings were sprayed by chitosan oligosaccharide (CO) on leaves. All treatments can increase seedling height, but only blue light reinforces the basal diameter growth. Compared to sunlight, exposure to blue light can promote leaf nitrogen and phosphorus concentrations, superoxide dismutase activity, and fruit proanthocyanidin content. The combination with CO addition will further increase chlorophyl a content, acid phosphatase activity, and total phenolics in fruit. SMR amended can induce the steady state uptake of nutrients but failed to impact fruit quality. Overall, we recommend the combination of blue light LED illumination plus CO addition to culture black chokeberry for the purpose to gain natural bioactive compounds.

Field irrigation using magnetized brackish water affects the growth and water consumption of Haloxylon ammodendron seedlings in an arid area.

Freshwater resources in arid areas are scarce, while there are abundant brackish water reserves that have great application potential for the irrigation of desert plants. However, brackish water irrigation will lead to soil salinization, which will inhibit plant growth. Magnetized water is a new technology that makes the use of brackish water feasible. The present study assessed the effects of irrigation using three water types (fresh, brackish, and magnetized brackish water) and five irrigation amounts (W1, 81 mm; W2, 108 mm; W3, 135 mm; W4, 162mm; and W5, 189 mm) on soil salinity and Haloxylon ammodendron seedling growth. Compared with fresh water, brackish water irrigation inhibited the growth of H. ammodendron and reduced water consumption. Irrigation with magnetized brackish water effectively improved the effect of soil salt leaching, promoted the growth and water absorption of H. ammodendron roots, and stimulated the growth of plant height, basal diameter, shoot length, and crown width. Based on the principal component analysis, the first three treatments of H. ammodendron comprehensive growth state were FW4, FW3, and MBW4, respectively. This showed that magnetized brackish water combined with an appropriate irrigation amount was helpful to optimize the growth of H. ammodendron seedlings on the basis of fresh water saving. Therefore, magnetized brackish water irrigation is an effective strategy for ensuring the establishment and growth of H. ammodendron seedlings in arid and water-deficient areas.

The Genetic Architecture of Juvenile Growth Traits in the Conifer Torreya grandis as Revealed by Joint Linkage and Linkage Disequilibrium Mapping.

Despite its high economical and ornamental values, Torreya grandis, a dioecious non-timber coniferous species, has long been an underrepresented species. However, the advent and application of advanced genotyping technologies have stimulated its genetic research, making it possible to gain new insight into the genetic architecture of complex traits that may not be detected for model species. We apply an open-pollination (OP) mapping strategy to conduct a QTL mapping experiment of T. grandis, in which nearly 100 unrelated trees randomly chosen from the species’ natural distribution and their half-sib progeny are simultaneously genotyped. This strategy allows us to simultaneously estimate the recombination fractions and linkage disequilibrium (LD) coefficients between each pair of markers. We reconstruct a high-density linkage map of 4,203 SNPs covering a total distance of 8,393.95 cM and plot pairwise normalized LD values against genetic distances to build up a linkage-LD map. We identify 13 QTLs for stem basal diameter growth and 4 QTLs for stem height growth in juvenile seedlings. From the linkage-LD map, we infer the evolutionary history of T. grandis and each of its QTLs. The slow decay of QTL-related LDs indicates that these QTLs and their harboring genomic regions are evolutionarily relatively young, suggesting that they can better utilized by clonal propagation rather than through seed propagation. Genetic results from the OP sampling strategy could provide useful guidance for genetic studies of other dioecious species.

Complex effects of different types of acid rain on root growth of Quercus acutissima and Cunninghamia lanceolata saplings

BackgroundSoil acidification caused by acid rain (AR) can damage plant roots, which in turn negatively impacts plant health. In response to changing AR types, research efforts to elucidate their specific impacts on plants have become intense.MethodsFor this study, we investigated the effects of simulated sulfuric, nitric, and mixed AR on the root systems of Quercus acutissima Carr. and Cunninghamia lanceolata (Lamb.) Hook. under different acidity levels.ResultsAs the AR S/N ratio and pH decreased, the height growth rate (HGR), basal diameter growth rate (DGR), total root length (TRL) and total root surface area (TRS) of C. lanceolata decreased, whereas the TRL and TRS of Q. acutissima remained the same. When the NO3− concentration in AR was increased, the root activity, superoxide dismutase (SOD) and catalase (CAT) activities of C. lanceolata roots revealed a downward trend; however, the root activity of Q. acutissima and the peroxidase (POD) activity of C. lanceolata roots revealed an upward trend. Further, redundant analysis and structural equation models indicated that AR pH had a greater impact on the HGR of Q. acutissima than that of C. lanceolata, while the impact of the AR S/N ratio on C. lanceolata growth rates was greater than that of Q. acutissima.ConclusionsOur results suggested that the root systems of different tree species had variable responses to AR, and the AR S/N ratio was an important factor affecting plant root growth. This might facilitate new strategies for the cultivation and protection of plantations in the future.

Research on the Effects of Light Intensity and Seeding Density on the Seed Germination and Seedling Growth of <i>Liriodendron chinense</i>

It provides a theoretical basis for the artificial promotion of the reproduction and regeneration of Liriodendron chinense through exploring the effects of light intensity and seeding density on the seed germination and seedling growth of this rare plant. Controlled experiments were conducted by setting different seeding densities and shading intensities to observe and detect the seed germination and seedling growth under different experimental conditions. The data were analyzed by SPSS and the model was fitted to calculate the seed germination rate, seedling emergence rate and seedling growth parameters of Liriodendron chinense, which were used to analyze the effects of seeding density and light intensity on the seed germination and seedling growth of Liriodendron chinense. Light has a significant impact on the seed germination and seedling growth of Liriodendron chinense (P P > 0.05). High density promotes the seedling height (the seedling height showed a rising trend with the increase of seeding density, reaching the highest at 500 seeds/m2. “3-stitch + 300 seeds/m2” combination is an appropriate condition for Liriodendron chinense reproduction since it can realize higher germination rate and better seedling growth potential. The seedling height and basal diameter growth curve of Liriodendron chinense fits well to the Logistic equation (R2 ≥ 0.977). Light has a significant impact on the seed germination and seedling growth of Liriodendron chinense, and appropriate shading treatment can increase the seed germination rate and seedling emergence rate of Liriodendron chinense. Seeding density has little influence on the seed germination rate of Liriodendron chinense, but high density will promote seedling height.

Effects of elevated CO2 concentration and nitrogen addition on the chemical compositions, construction cost and payback time of subtropical trees in Cd-contaminated mesocosm soil.

Rising atmospheric CO2 concentration ([CO2]) and nitrogen (N) deposition are changing plant growth, physiological characteristics and chemical compositions; however, few studies have explored such impacts in a heavy metal-contaminated environment. In this study, we conducted an open-top chamber experiment to explore the impacts of 2 years of elevated atmospheric [CO2] and N addition on the growth, physiological characteristics and chemical compositions of five subtropical tree species in a cadmium (Cd)-contaminated environment. Results showed that N addition significantly increased concentration of leaf N and protein in five tree species and also decreased payback time (PBT) and leaf carbon:nitrogen ratios and increased tree relative height growth rate (RGR-H) and basal diameter growth rate (RGR-B) in Liquidambar formosana Hance and Syzygium hainanense Chang et Miau. Elevated [CO2] increased leaf maximum photosynthetic rate (Amax) and concentration of total non-structural carbohydrates and shortened PBT to offset the negative effect of Cd contamination on RGR-B in Acacia auriculiformis A. Cunn. ex Benth. The combined effects of elevated [CO2] and N addition did not exceed their separate effects on RGR-H and RGR-B in Castanopsis hystrix Hook. f. & Thomson ex A. DC. and Cinnamomum camphora (L.) presl. The addition of N significantly increased the concentration of leaf Cd by 162.1% and 338.0%, and plant Cd bio-concentration factor by 464% and 861% in C. hystrix and C. camphora, respectively, compared with only Cd addition. Among the five tree species, the decrease in PBT and the increase in Amax, RGR-B and concentrations of leaf protein in response to N and Cd addition under elevated [CO2] were on average 86.7% higher in A. auriculiformis than other species, suggesting that the mitigation of the negative effects of Cd pollution by elevated [CO2] and N addition among five species was species-specific. Overall, we concluded that N addition and elevated [CO2] reduced Cd toxicity and increased the growth rate in A. auriculiformis, S. hainanense and L. formosana, while it maintained the growth rate in C. hystrix and C. camphora by differently increasing photosynthetic rate, altering the leaf chemical compositions and shortening PBT.

Physiological Responses of Robinia pseudoacacia and Quercus acutissima Seedlings to Repeated Drought-Rewatering Under Different Planting Methods.

Changing precipitation patterns have aggravated the existing uneven water distribution, leading to the alternation of drought and rewatering. Based on this variation, we studied species, namely, Robinia pseudoacacia and Quercus acutissima, with different root forms and water regulation strategy to determine physiological responses to repeated drought-rewatering under different planting methods. Growth, physiological, and hydraulic traits were measured using pure and mixed planting seedlings that were subjected to drought, repeated drought-rewatering (i.e., treatments), and well-irrigated seedlings (i.e., control). Drought had negative effects on plant functional traits, such as significantly decreased xylem water potential (Ψmd), net photosynthetic rate (AP), and then height and basal diameter growth were slowed down, while plant species could form stress imprint and adopt compensatory mechanism after repeated drought-rewatering. Mixed planting of the two tree species prolonged the desiccation time during drought, slowed down Ψmd and AP decreasing, and after rewatering, plant functional traits could recover faster than pure planting. Our results demonstrate that repeated drought-rewatering could make plant species form stress imprint and adopt compensatory mechanism, while mixed planting could weaken the inhibition of drought and finally improve the overall drought resistance; this mechanism may provide a theoretical basis for afforestation and vegetation restoration in the warm temperate zone under rising uneven spatiotemporal water distribution.

Study on Screening of Waterlogging Tolerance Germplasm Resources of Zanthoxylum bungeanum

In order to screen out strong waterlogging tolerance germplasm resources of Zanthoxylum bungeanum, the growth and waterlogging damage of six Z. bungeanum germplasm materials selected by Sichuan academy of botanical engineering in the early stage were comprehensively evaluated through artificial flooding experiment. The results showed that under waterlogging stress, Chuanzhi-3 still maintained a large stress index of plant height and basal diameter growth, and the waterlogging symptoms appeared only after waterlogging stress for 66 h, with a waterlogging index of only 5.56%, and after waterlogging stress for 96 h, the waterlogging index was 55.56%. The average waterlogging index of each treatment was only 9.63%. The waterlogging symptoms of Chuanzhi-3 were much lighter than other materials, and the waterlogging tolerance was the strongest.

Effects of CaO on the Clonal Growth and Root Adaptability of Cypress in Acidic Soils

Cypress (Cupressus funebris Endl.) is a major tree species planted for forestland restoration in low-fertility soil and in areas where rocky desertification has occurred. Calcium (Ca) fertilizer can adjust the pH of soil and has an important effect on the growth of cypress. Soil and water losses are serious in Southern China, and soil acidification is increasing, which results in high calcium loss. However, the adaptability of cypress clones to different concentrations of calcium in acidic soils has not been studied. In this investigation, a potted-plant experiment was set up with three concentrations of calcium oxide (CaO) fertilizer (0, 3, and 6 g·kg−1) added under local soil conditions with 0 and 3 g·kg−1 nitrogen (N), phosphorus (P), and potassium (K) fertilizer. The effects of CaO on the growth, root development, and nutrient uptake and utilization efficiency of cypress clones were analyzed. The growth, root development, and nutrient absorption and utilization of cypress differed when calcium fertilizer was applied to acidic soils with different degrees of fertility. In the soil with 0 g·kg−1 NPK fertilizer, the 3 and 6 g·kg−1 CaO treatments significantly increased the clonal growth of cypress seedling height, basal diameter, and dry-matter weight. In addition, the length, surface area, and volume of the roots less than 2.0 mm of root diameter also significantly increased, indicating that the fine cypress roots were somewhat able to adapt to differing Ca levels under lower fertility conditions. Moreover, the efficiency of N, P, and Ca accumulation was highest in the 3 g·kg−1 CaO treatment. After adding 3 g·kg−1 CaO fertilizer to the soil with 3 g·kg−1 NPK fertilizer, only the root dry-matter weight increased significantly, indicating that root development (including root length, surface area, and volume) in the D1–D3 diameter classes (≤1.5 mm in diameter) was significantly elevated. When CaO application reached 6 g·kg−1, the seedling height, basal diameter, and dry-matter weight of each organ decreased, as did the length, surface area, and volume of the roots in the all diameter classes, indicating that the addition of excessive CaO to fertile soil could inhibit the growth and root development of cypress. In Ca-deficient low-quality acidic soils, adding CaO fertilizer can promote the development of fine roots and the uptake and utilization of N, P, and Ca. The results of this study provide a basis for determining the optimal fertilization strategy when growing cypress in acidic soils in Southern China.

Response of Quercus acutissima foliage to different types of simulated acid rain

The harm of acid rain (AR) to plants foliage is mainly manifested by changing their physiological and biochemical processes, such as chlorosis, nutrient loss, enzyme activity changes, etc., which in turn impacts plant growth. Since the types of AR in China is changing, the response of plants to different types of AR has become a research hotspot. In this research, we investigated the responses of Q. acutissima foliage to simulated AR with different SO42−/NO3−(S/N) ratios and pH through chlorophyll contents, chlorophyll fluorescence characteristics, malondialdehyde content and antioxidant enzyme activities. The results showed that the maximal photochemical efficiency of PSⅡ (Fv/Fm) and superoxide dismutase (SOD) activity of Q. acutissima gradually decreased as the increase of NO3− concentration. With the decrease of AR pH, the inhibitory effect of simulated AR on growth rate and photochemical quenching coefficient (qP) gradually increased, and it also induced the increase of SOD and catalase (CAT) activities. Besides, pure NAR with low acidity (pH = 4.5) significantly increased basal diameter growth rate (DGR), chlorophyll content, peroxidase (POD) activity and qP, while decreased Chla/Chlb, fluorescence efficiency, non-photochemical quenching coefficient (NPQ), malondialdehyde (MDA) content and SOD activity. Correlation analysis indicated that the growth rate, chlorophyll content and fluorescence characteristics of Q. acutissima were highly correlated with foliar antioxidant enzyme activities under simulated AR stress. Our results indicated that different types of simulated AR had discrepant influences on the foliage physiological characteristics and above-ground growth of Q. acutissima, but not always negative, which made the protection of Q. acutissima plantation more complicated.

Comparison of cadmium accumulation in upright and leaning poplar trees

Poplar 69 (Populus deltoides Bartr. cv. ‘Lux’ (I-69/55)) was chosen for a pot experiment to study the growth and the extraction of Cd from soil to various parts of the one-year-old trees growing in upright and artificial leaning (45°) patterns under different Cd stress. The results indicated considerable tolerance of both upright poplar (UP) and leaning poplar (LP) to Cd stress in the soil, though with significant inhibition from Cd application. LP demonstrated significantly lower height and basal diameter growth than UP. Cd concentrations in different parts of both UP and LP increased with the increase of Cd in the soil and it followed a general order as Bark > Leaf > Root > Stem. Different parts of poplar had average bio-concentration factor (BCF) ranges between 0.08 to 2.36, and average translocation factor (TF) between 0.67 to 7.92, indicating a big difference of phytoextraction ability among the parts, among the treatments, and between LP and UP. Average Cd concentration, BCF, and TF for each part of LP were higher than that of UP, but the difference was not significant. Significantly higher Cd concentration was found in the tension zone of stem wood than that in the opposite zone for LP.

Performance of white oak (Quercus alba) and three pine species in novel multi-cropped plantations in eastern Tennessee, USA

Loblolly pine (Pinus taeda L.), shortleaf pine (Pinus echinata Mill.), and eastern white pine (Pinus strobus L.) seedlings were multi-cropped with standard and large-diameter white oak (Quercus alba L.) seedlings to test for neutral or positive effects of multi-cropping. The study was established in 2014 in three complete blocks within recent clearcuts in eastern Tennessee, USA. Each block consisted of six multi-cropped treatments and four monocultures randomly assigned to ten 14.63 × 21.95 m plots. Within each block, monocultures of white oak and each pine species were planted in four control plots. Multi-cropped treatments included loblolly pine planted with white oak at a 0.31 m spacing, loblolly pine planted with white oak in alternating rows at a 1.74 m spacing, shortleaf pine planted with white oak at a 0.31 m spacing, shortleaf pine planted with white oak at a 1.74 m spacing, eastern white pine planted with white oak at a 0.31 m spacing, and eastern white pine planted with white oak at a 1.74 m spacing. Each plot with white oak received 20 standard (~0.127 cm in basal diameter) and 20 large-diameter (~0.632 cm in basal diameter) white oak seedlings that were randomly assigned to planting locations. Initial height, basal diameter, and early survival were recorded for each seedling just after planting. Height growth, basal diameter growth, survival, herbivory, and insect damage were recorded in early December 2014, 2015, 2016, 2017, 2018, and 2019. In 2019, percent survival among treatments did not differ significantly for white oak (p = 0.152), loblolly pine (p = 0.396), shortleaf pine (p = 0.246), or eastern white pine (p = 0.065). In addition, mean height growth and mean basal diameter growth did not differ significantly among treatments for white oak (p = 0.698 and 0.437, respectively), loblolly pine (p = 0.630 and 0.762, respectively), shortleaf pine (p = 0.324 and 0.251, respectively), or eastern white pine (p = 0.623 and 0.823, respectively). Survival was greater for large-diameter white oak seedlings than standard seedlings (p < 0.001). Mean height and mean basal diameter growth in large-diameter white oak seedlings were significantly greater than in standard seedlings ((p < 0.001) and (p < 0.001), respectively). Although these plantings are in the early stages of development, the lack of significant differences in seedling performance among treatments suggests species compatibility and no net negative impact of multi-cropping white oak with the three pine species.

南方红豆杉水浸提液对喜树种子发芽和幼苗生长的化感作用

化感作用是影响人工混交林种间关系的重要因素之一。已有研究表明：喜树南方红豆杉混交对喜树生长有明显促进作用，并从混交改善混交林地微气候角度解释了这种促进作用，但未从种间化感作用角度探讨这种作用。为了探究南方红豆杉是否对喜树具有潜在的化感促进作用，从而更全面了解喜树南方红豆杉混交林种间关系，考察了不同浓度（25、50 g/L和100 g/L）的南方红豆杉（Taxus chinensis var.mairei）鲜叶、凋落叶、枝和根水浸提液对喜树（Camptotheca acuminata）种子发芽和幼苗生长的影响。结果表明：（1）南方红豆杉凋落叶浸提液对喜树种子发芽和幼苗生长无显著影响（P>0.05），而鲜叶、枝和根浸提液对喜树发芽和幼苗生长均具有不同程度的促进作用（P<0.05），且作用强度大体与浓度呈正相关；（2）100 g/L的南方红豆杉鲜叶、枝和根浸提液浸泡的喜树种子，其发芽率比对照组分别提高8.1%、14.9%和25.6%；（3）南方红豆杉鲜叶浸提液只有在高浓度（100 g/L）时，对喜树幼苗基径生长具有促进作用（P<0.05），而对其株高、全株干重和净光合速率无显著影响；南方红豆杉根和枝浸提液对喜树幼苗株高、基茎、干重和净光合速率均具有促进作用（P<0.05），与对照组相比，100 g/L的根和枝浸提液浇灌喜树幼苗，可以使喜树幼苗株高分别提高14.2%和8.4%，基径分别提高19.0%和15.3%，干重分别提高23.1%和15.9%，净光合速率分别提高11.6%和6.1%。研究结果表明，在喜树南方红豆杉混交林中，南方红豆杉对喜树的正向化感作用可能是促进喜树生长的重要因素之一。;Allelopathy is one of the important factors that affect the interspecific relationship of artificial mixed forest. Previous studies have shown that Taxus chinensis var. mairei has a significant promoting effect on the growth of Camptotheca acuminata in the mixed forest of T. chinensis var. mairei and C. acuminata, which was explained from the perspective of improving the microclimate of mixed forest land, but not from the perspective of interspecific allelopathy. In order to explore whether T. chinensis var. mairei has potential allelopathy promoting effect on C. acuminata, so as to understand more comprehensively the interspecific relationship of T. chinensis var. mairei and C. acuminata mixed forest, the effects of water extracts from fresh leaves, litter leaves, branches and roots of T. chinensis var. mairei with different concentrations (25 g/L, 50 g/L, and 100 g/L) on seed germination and seedling growth of C. acuminata were studied in this study. The results showed that (1) the litter extract of T. chinensis var. mairei had no significant effect on seed germination and seedling growth of C. acuminata (P>0.05), but the fresh leaves, branches and roots extracts had the promoting effects on C. acuminata germination and seedling growth in different degrees (P<0.05), and the intensity was positively correlated with the concentration of extracts. (2) The germination percentage of C. acuminata seeds soaked in 100 g/L extracts of fresh leaves, branches and roots from T. chinensis var. mairei was 8.1%, 14.9% and 25.6% higher than that of the control group, respectively. (3) The fresh leaves extract of T. chinensis var. mairei could promote the basal diameter growth of C. acuminata seedlings at high concentration (100 g/L) (P<0.05), but had no significant effect on plant height, total dry weight and net photosynthetic rate regardless of extracts concentration. The root and branch extracts of T. chinensis var. mairei had the promoting effects on plant height, basal stem, dry weight and net photosynthetic rate of C. acuminata seedlings (P<0.05). Compared with the control group, 100 g/L of root and branch extracts could increase the height of C. acuminata seedlings by 14.2% and 8.4%, the basal diameter by 19.0% and 15.3%, the dry weight by 23.1% and 15.9%, and the net photosynthetic rate by 11.6% and 6.1%, respectively. The results showed that the positive allelopathy of T. chinensis var. mairei to C. acuminata may be one of the important factors to promote the growth of C. acuminata in the mixed forest of the two trees.

Effects of small aggregates of mature tree retention on adjacent planted coastal Douglas-fir growth and survival

Long-term retention of mature trees at the time of harvesting, called variable retention, has increased significantly since the 1990s as a silvicultural practice for maintaining stand-level biodiversity. A common approach is aggregated retention where groups of trees are left to increase structural diversity and provide forest influence over the adjacent harvested area. Despite the increased global application of aggregated retention, the growth and survival of adjacent trees has received less research effort than biodiversity studies. This knowledge gap was addressed with a study of small (0.01 to 0.58 ha, mean 0.3 ha) retained mature tree aggregates in harvested areas on southeast Vancouver Island, British Columbia, Canada. Coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco.) seedlings were planted in ~10-m-wide belt transects (three planting rows), extending up to 10 m into and 50 m away from aggregate edges in four cardinal directions. Nitrogen fertilizer was applied at planting to some transects. Basal diameter, height and survival of the planted Douglas-fir were measured for an average of 11 years. We used nonlinear mixed-effects models to assess the relationships of planted-tree basal diameter and height growth to distance from aggregate edge, edge orientation, planted-tree age, fertilization and aggregate characteristics (basal area and height). We extended planting into the aggregates to model tree response on both sides of edges. Modeled growth rates were slower for 10-year-old planted trees under the aggregate canopy and along the edges of the harvested area compared to growth at about 10 m and greater distance from aggregate edges; i.e. trees achieved 90% of their potential height and diameter by about 10 m from the aggregate canopy. Impacts were greatest on north-facing edges and least on south-facing edges, although differences were very small. We examined planted-tree survival by proximity to aggregate edges using a Cox proportional hazards model. Survival was lower directly beneath the aggregate canopy and up to approximately 5 m into the harvested area and was also slightly lower adjacent to south-facing edges. Fertilized trees showed a minor increase in survival versus unfertilized trees. Structural characteristics of aggregates had only a minimal impact on planted-tree growth and survival. This study helps provide a better understanding of the relationships among planted-tree growth and survival and edge effects for implementation of aggregated retention.

Response of Ziziphus mucronata and Acacia nilotica saplings to increasing clipping intensity in a southern African savanna

Many woody plants respond to intense clipping through an increase in growth parameters and nutritive value. However, optimal clipping intensities that result in peak plant growth and nutritive value have not been determined. We studied the response of Ziziphus mucronata and Acacia nilotica saplings to four clipping intensities. Parts of the main stem and each lateral branch were removed to simulate 0%, 30%, 60%, and 90% clipping intensity. After four months of resprouting five sapling growth parameters were determined viz. height, basal stem diameter, length of the longest shoot, root length, and number of new shoots. In addition, foliar crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), total phenolic (TP), and condensed tannin (CT) concentrations were determined. Shoot clipping did not stimulate sapling height and basal diameter growth, while shoot length responded to an increase in clipping intensity with a weak hump-shape in both species. Ziziphus mucronata increased root growth in response to increasing clipping intensity, while A. nilotica showed no clear trend. The largest number of new shoots was produced at 60% and 30% clipping intensities for Z. mucronata and A. nilotica respectively. Ziziphus mucronata produced more new shoots than A. nilotica. The most severe (90%) clipping intensity produced the highest CP and lowest NDF content in the two species, reduced TP and CT content in A. nilotica, but not in Z. mucronata. We conclude that an increase in clipping intensity produced varying responses in sapling growth parameters and nutritive values in Z. mucronata and A. nilotica.

Early indications of success rehabilitating an underperforming teak (Tectona grandis) plantation in Panama through enrichment planting

Enrichment planting can be an effective strategy for increasing the ecological and economic value of timber plantations, but success depends on appropriate matching of under- and overstory species and site conditions. This case study in the Panama Canal Watershed explores the viability of enrichment planting for rehabilitating underperforming teak (Tectonia grandis) plantations, which are common in the area. Two high-value timber species native to the neotropics, Dalbergia retusa and Terminalia amazonia, were underplanted in an established teak plantation at the Agua Salud research site in the province of Colon, Panama. Seedling survival, basal diameter, height, total biomass and relative growth rate were assessed for the two years following planting. In contrast with the widespread belief that teak is a poor nurse tree, both species achieved promising early growth with low mortality in plantation understory conditions. Neither understory light availability nor combined above- and below-ground effects of crowding pressure from teak strongly predicted growth of either species. D. retusa, thought to be more shade-tolerant, performed equally across a range of intermediate light levels whereas T. amazonia, thought to be more heliotropic, performed best at the highest light levels, though light relationships explained little variation in seedling growth. These early findings support the suitability of either species for use in enrichment plantings in established, underperforming teak plantations in the Panama Canal Watershed. Longer-term research is needed to evaluate the potential of enrichment planting to increase profitability and ecosystem services such as carbon sequestration and water resource management in these plantations.