Hyperspectral reflectance can potentially be used to non-destructively estimate a diverse suite of plant physiochemical functional traits by applying chemometric approaches to leverage absorption features related to chemical compounds and physiological processes associated with these traits. This approach has considerable implications in advancing plant physiological and chemical ecology. For complex functional traits, however, there is a lack of well-defined absorption features and features may be unevenly distributed across the reflectance spectrum, suggesting that the influence of wavelength ranges on the performance of chemometric models is potentially important for accurately estimating foliar functional traits. Here, we investigate the influence of spectral ranges on the performance of models estimating six tree functional traits: CO2 assimilation rate, specific leaf area, leaf water content and concentrations of foliar nitrogen, sugars and gallic acid. Using data collected from multiple different experiments, we quantified plant functional trait responses using standard reference measurements and paired them with proximal leaf-level hyperspectral reflectance measurements spanning the wavelength range of 400-2400 nm. A total of 100 different wavelength range combinations were evaluated using partial least squares regression to determine the influence of wavelength range on model performance. We found that the influence of starting or ending wavelength on model performance was trait specific and better model outcomes were achieved when the starting and ending wavelengths encompassed absorption features associated with the specific leaf trait modelled. Interestingly, we found that including shortwave-infrared wavelength ranges (1300-2500 nm) improved performance for all trait models. Collectively, our findings underscore the importance of optimal spectral range selection in enhancing the accuracy of chemometric models for specific foliar trait estimates. An emergent outcome of this work is that the approach can be used to (1) identify the important spectral features of traits that currently lack known absorption features or have multiple or weak absorption features, (2) expand the current suite of plant functional traits that can be estimated using spectroscopy and (3) ultimately advance the integration of a spectral biology approach in ecological research.

Niche complementarity is suggested to be a main driver of productivity overyielding in diverse environments due to enhanced resource use efficiency and reduced competition. Here, we combined multiple different approaches to demonstrate that niche overlap is the most likely cause to explain a lack of overyielding of three tree species when grown in different species combinations. First, in an experimental planting we found no relationship between productivity and species diversity for leaf, wood, or root production (no slope was significantly different from zero), suggesting a lack of niche differences among species. Second, data extracted from the United States Department of Agriculture Forest Inventory and Analysis revealed that the species do not significantly co-occur in natural stands (p = 0.4065) as would be expected if coexistence was common across their entire range. Third, we compared trait differences among our species and found that they are not significantly different in multi-dimensional trait space (p = 0.1724). By combining multiple analytical approaches, we provide evidence of potential niche overlap that precludes coexistence and a positive diversity–productivity relationship between these three tree species.

Despite decades of research and practice restoring forests on surface coal mines, success is still variable, and failures often occur. To better understand how variation in site factors and management affects the success of restoration of coal mines, we conducted a survey of tree performance for mine sites in the Illinois Basin across Indiana, USA, reclaimed between 2008 and 2018. We explored the impacts of climate and soil conditions on the survival and growth of planted trees, as well as the cover of associated vegetation. Average overall survival (21%) was relatively low compared to typical unmined sites. Organic matter had one of the most consistent and largest effects on most oak species, with the highest performance between 3 and 5%. Soil phosphorus content was the most important factor determining whether a planting totally failed and affected the growth of White oak ( Quercus alba ) and Swamp white oak ( Q. bicolor ), though its effect on White oak was nonlinear. Rainfall in the year of planting had large positive effects on the survival and growth of Persimmon ( Diospyros virginiana ), and Black walnut ( Juglans nigra ) and temperature in the year of planting had large positive effects on the growth of Bur oak ( Q. macrocarpa ) and Persimmon. Planting a diverse mix of species is the best option both for approximating natural conditions, and for avoiding problems from the failure of individual species. While conditions vary, successful forest restoration on former coal mines can occur; this study reveals some of the most important factors affecting such success.

Trees may exhibit long-lasting morpho-physiological acclimation in response to drought (i.e. drought memory) throughout their extensive life cycles. This acclimation might be particularly crucial for seedlings and saplings due to their limited access to water. We studied the development of drought stress memory in seedlings of black walnut (Juglans nigra L.), western larch (Larix occidentalis Nutt.), and Douglas-fir ((Pseudotsuga menziesii var. menziesii (Mirb.) Franco) in response to controlled drought exposure during their germination year (drought priming). We evaluated the effects of drought priming under a second-year drought, focusing on changes in water uptake capacity and transpiration demand, biomass allocation to new roots and foliage, root architecture, and photosynthesis. Drought priming led to significant morpho-physiological responses in the new leaves and roots developed during the subsequent growing season drought. Western larch showed increased biomass allocation to roots, higher specific root length and root tips, and enhanced water uptake, while Douglas-fir exhibited earlier bud break, greater net photosynthesis, and increased foliage growth. In contrast, black walnut seedlings displayed no notable changes in biomass allocation or physiology. Our results also show that biomass allocation to new roots plays a crucial role in enhancing water uptake capacity and gas exchange during seedling establishment. These findings underscore the importance of drought memory for stress resistance in trees, influencing the capacity of forests to regenerate and respond to recurrent droughts and climate change. The formation and expression of drought memory, however, varied across species, highlighting the complexity of adaptive responses across different forest ecosystems.

Abstract Sewage sludge (SS) application to forest plantation soils as a fertilizer and/or soil amendment is increasingly adopted in plantation forest management. However, the potential risks of SS-derived heavy metals (HMs) remain a concern. Many factors, including woodland slope may affect the risks, but the understanding of this issue is limited. This research evaluated the HMs migration via surface runoff, interflow, and sediments when SS was applied in woodlands of varying slopes. We conducted indoor rainfall simulations and natural rainfall experiments to clarify the effect of slope on the migration of HMs via runoff (including surface and interflow) and sediments. In the simulated rainfall experiment, HMs lost via sediments increased by 9.79–27.28% when the slope increased from 5° to 25°. However, in the natural rainfall experiment, when the slope of forested land increased from 7° to 23°, HMs lost via surface runoff increased by 2.38% to 6.13%. These results indciate that the surface runoff water on a high slope (25°) posed high water quality pollution risks. The migration of HMs via surface runoff water or interflow increased as the steepness of the slope increased. The total migration of Cu, Zn, Pb, Ni, Cr and Cd via sediment greatly exceeded that via surface runoff and interflow. Particles ≤ 0.05 mm contributed the most to the ecological risks posed by sediments. Cd was the main source of potential ecological risks in sediments under both experimental conditions.

In many temperate regions of the world, conifer species have been planted to stabilize soils and promote site recovery on former hardwood sites that were cleared for agriculture. In many areas of eastern North America, these conifer plantings consisted of introduced (non-native) Pinus species planted on abandoned agricultural land once dominated by mesophytic hardwood species. These plantings constitute a shift in overstory composition away from native hardwood species with nutrient-rich litter that decomposes more quickly towards Pinus species with recalcitrant litter that may alter soil chemistry and nutrient availability. To examine how edaphic conditions associated with long-term introduced Pinus species occupancy are related to forest regeneration and herbaceous-layer diversity and composition, we sampled a total of 97 plots in planted Pinus echinata and Pinus strobus stands and naturally regenerated hardwood stands growing on two ecological landtype phases (ELTPs) of southern Indiana, USA forests, Fagus-Acer saccharum/Arisaema Mesic Ridges, and Acer saccharinum/Boehmeria Bottomlands. We collected vegetation data and analyzed soil samples to examine herbaceous-layer species distribution across gradients using non-metric multidimensional scaling (NMS) ordination. Two-way ANOVA was used to examine differences in individual species and species functional groups across stand types (P. echinata, P. strobus, and native hardwoods) and ELTPs. Our results show that differences in soil chemistry resulting from Pinus spp. occupancy were associated with differences in the composition and distribution of herbaceous-layer species in ordination space. Species across stand types and ELTPs were distributed across dominant gradients related to litter depth, cation exchange capacity, cation content, and soil aluminum concentration. Hardwood sites had significantly greater herbaceous-layer cover (139.6 +/- 8.0 %) than P. echinata (48.5 +/- 6.2 %) or P. strobus sites (81.7 +/- 7.7 %), as well as greater herbaceous-layer species richness and diversity (mean species richness was 46.9 +/- 2.1 on hardwood stands vs. 33.3 +/- 1.6 and 36.4 +/- 2.0 on P. echinata and P. strobus stands, respectively). Pinus echinata stands contained a greater density of woody regeneration, including Quercus spp. (201 +/- 48 saplings ha(- 1)) and Fagus grandifolia stems (415 +/- 82 saplings ha(- 1)), both of which occurred in greater density than Acer saccharum (163 +/- 93 saplings ha(- 1)) and A. rubrum (70 +/- 64 saplings ha(- 1)). Our results suggest that pine occupancy has created divergent successional trajectories in comparison to hardwood stands. These differing trajectories may offer both challenges and opportunities for restoration efforts. For example, the greater abundance of Quercus reproduction under P. echinata on ridges, combined with less productive soils, may allow Quercus stems to be promoted into the canopy with less competition from mesophytic competitors.

Restoration of native hardwood forests through tree planting may provide significant ecological and economic benefits, but reforestation in natural forests and afforestation on open field sites is challenging. Conversion of existing plantations of introduced conifers to hardwoods may provide an alternative opportunity for restoration. In the Midwest US, large areas of mature, introduced pine (Pinus spp.) plantations exist that have little economic and ecological value. These stands may provide ideal sites for planting of native hardwood species that have similar site preferences to pine. We sought to determine optimal management strategies for converting pine plantations by manipulating overstory canopy density and understory competition. We underplanted American chestnut (Castanea dentata (Marsh.) Borkh.) and northern red oak (Quercus rubra L.) seedlings in three overstory canopy treatments: control, shelterwood, and clearcut. Understory competition was either controlled or not through two growing seasons. After three growing seasons, oak performed best in the clearcut and chestnut in the shelterwood, reflecting variation in the species’ shade tolerance. Chestnut height and root collar diameter (RCD) were double that of oak, and chestnut leaf N content increased with light availability while oak did not, which can be explained by the species’ different adaptive strategies in biomass allocation. Both species had highest photosynthesis in the clearcut. Chestnut seedlings had significantly higher RCD in weeded clearcut and shelterwood plots, and oak in weeded clearcut plots. Weeding in the uncut control plots was ineffective because shade limited competition. Our results indicate that pine plantations offer suitable habitat for these hardwood species and provide insight regarding their growth strategies. Pine shelterwoods and clearcuts are each viable silvicultural conversion options for chestnut and oak if understory competition is controlled.

Restoration of root hemiparasite trees, such as Hawaiʻi's endemic Santalum species (ʻiliahi), may benefit from underplanting in stands of suitable hosts like the nitrogen‐fixing native tree, Acacia koa (koa). At a pasture site on Hawaiʻi Island previously reforested with koa, we underplanted seedlings of the island‐endemic sandalwood species, Santalum paniculatum , to examine the tradeoff between access to an established root network (distance to the nearest koa tree) under variable overstory shading (8.8–90.1% canopy openness range) during regeneration establishment. We hypothesized that there is an optimal parasite–host spacing and canopy openness that balance parasitic resource transfer with light availability. ʻIliahi seedling survival was 96% with no survival treatment differences. ‘Iliahi seedling growth was positively related to canopy openness but negatively related to the distance to the nearest koa tree, and the slope of these relationships increased over time. Leaf photosynthetic light compensation points, light saturation points, and stomatal density mostly followed similar trends as growth. These results demonstrate that ‘iliahi can be successfully underplanted in an established koa stand, which benefits ‘iliahi plantings and contributes to diversifying initial restoration and reforestation plantings. There appears to be a significant tradeoff in planting distance between benefits from and competition with the host; however, the improvement in growth with increased canopy openness appeared to be much greater than the effect of planting distance. Underplanting into an established host stand with sufficient canopy openness can help restore functionally compatible and abundant ‘iliahi regeneration into forests.

Maritime forests are coastal ecosystems that stabilize coastlines, recharge aquifers, and provide protection against storm surges. The range of these forests has been decreasing due to threats such as urban expansion, clearing for agriculture, climate change, and an influx of native but competitive loblolly pine (Pinus taeda L.) from pine plantations. To restore maritime forests, southern live oak (Quercus virginiana Mill.) should be established as the dominant canopy species; however, knowledge of how to grow live oak in a restoration setting is limited. We planted southern live oak seedlings into a clearcut experimental site that was formerly a loblolly pine plantation. Our goal was to test how planting density (1, 2, or 3 m), mulch, and fertilization at planting impacted the initial growth of seedlings over the course of four growing seasons. The application of fertilizer had an initial positive effect on seedling diameter (36%) after the first growing season. The application of mulch increased seedling height in years 2 through 4 (25.6% to 22.7%), diameter in years 3 and 4 (20.9% to 19.3%), and crown width in year four (8.5%). Planting density had no consistent effect over the first four years. These results demonstrate the potential benefits of incorporating fertilizer and mulch into restoration prescriptions to promote seedling field establishment. Planting density should continue to be monitored through canopy closure for potential effects of plant facilitation. Integrating silvicultural treatments such as planting density, soil amendments, and vegetation control may inform cost-effective management recommendations for maritime forest restoration.

Field experiments were conducted on a four-year-old leaf-use ginkgo plantation in southern China to assess the impact of nine different fertilization strategies with varying N-P2O5-K2O rates at three growth phases (FBD: March for bud development; FLG: May for leaf growth; FLS: July for leaf strengthening) on leaf-use ginkgo (Ginkgo biloba L.) leaf productivity and ecological economic benefits (EEBs). The results indicated that regardless of timing and rate, fertilizer application led to an increase in leaf area and thickness, resulting in higher ginkgo leaf yield. The highest fresh (215.14 g tree−1) and dry (78.83 g tree−1) yields were observed with 3 g N + 2.5 g P2O5 + 1.5 g K2O tree−1 in FLG. FLS was found to mitigate the decline in SPAD values of leaves during late summer. Furthermore, fertilized ginkgo trees exhibited higher flavonoid concentrations in leaves, enhancing profitability. However, higher fertilizer rates were associated with elevated greenhouse gas emissions, nitrogen losses and ecological costs. Despite these drawbacks, all fertilization treatments resulted in increased net economic income. Specifically, compared to no fertilization, FBD, FLG and FLS treatments boosted net income by 3.5~26.6%, 11.6~60.5% and 5.8~35.4%, respectively. Using the entropy weight TOPSIS method, it was concluded that optimizing the N, P and K fertilization rate and timing (applying 3–2.5–1.5 g tree−1 of N-P2O5-K2O in May) is a beneficial approach to maximize EEBs and industrial benefits in leaf-use ginkgo plantations in southern China. This study provides valuable insights into suitable fertilization patterns and management for leaf-use ginkgo plantations in southern China.

Forest restoration is challenging in arid and semiarid lands. Research has identified ecotechnologies that may alleviate stressful conditions of planted seedlings, but studies are often limited to the first few years of regeneration establishment. Over 20 years, we tested the effects of tree shelters (mesh- and tube-shelters) and competition suppression (two types of synthetic mulch and manual weeding) on soil water content and development of Pinus halepensis on an arid site in southeastern Spain. Competition suppression increased soil water content at shallow depths only using a polyethylene sheet, with no effect on survival. Tree shelters had a much greater effect than competition suppression on tree responses. Survival was mostly affected by shelter type, with lower survival in tube-shelters compared to mesh-shelters and non-protected seedlings; differences began after the first year, but became more pronounced following an intense drought at 3 years. Survival for pines protected by mesh-shelters was significantly higher than for non-protected seedlings beginning at 6 years, and mortality did not stabilize until 15 years. After 20 years, survival ranked in order of mesh-shelters (57.5%), non-sheltered (46%), and tube-shelters (29.5%). Effects of shelter type on growth response over time followed an opposite pattern, with differences declining when pines outgrew the height of the shelter after 3 years. The response of pines to tube-shelters could be explained by the microenvironmal differences among vertical protection and its effects on a shade intolerant species such as Pinus halepensis : survival depletion is provoked probably by a reduction in root growth under the shaded conditions of tubes. On the other side, growth and morphology response could be partially explained by differences in light, but response of pines in mesh also points towards a reduction of wind pressure that precludes stem growth in thickness. Competition suppression had no effect on pine growth. Lack of response to main effects of competition suppression treatments can be attributed to the minimum changes of soil water content to mulching or weeding under arid conditions. Thus, 20 years after planting, tube-shelters and competition suppression treatments were relatively ineffective at improving survival or growth of P. halepensis . Mesh-shelters are recommended as the most effective protection method for restoration under arid site conditions.

Nursery cultivation practices can be modified to increase resistance to water stress in forest seedlings following field establishment, which may be increasingly important under climate change. We evaluated the morphological (survival, growth) and physiological (chlorophyll fluorescence, leaf water potential) responses to water stress for three ecologically diverse Quercus species (Q. robur, Q. pubescens, and Q. ilex) with varying traits resulting from the combination of growing media (peat, coir) and fertilization (standard, P-enriched, K-enriched). For all species under water stress, seedlings grown in coir had generally higher growth than those grown in peat. Seedlings fertilized with P performed better, particularly for survival; conversely, K fertilization resulted in inconsistent findings. Such results could be explained by a combination of factors. P fertilization resulted in higher P accumulation in seedlings, while no K accumulation was observed in K fertilized seedlings. As expected, the more drought-sensitive species, Q. robur, showed the worst response, while Q. pubescens had a drought resistance equal or better to Q. ilex despite being classified as intermediate in drought resistance in Mediterranean environments.

Introduced pests (insects and pathogens) have rapidly increased the numbers of at-risk native forest tree species worldwide. Some keystone species have been functionally extirpated, resulting in severe commercial and ecological losses. When efforts to exclude or mitigate pests have failed, researchers have sometimes applied biotechnology tools to incorporate pest resistance in at-risk species to enable their reintroduction. Often erroneously equated solely with genetic engineering, biotechnology also includes traditional and genome informed breeding—and may provide a holistic approach toward applying genomic-based information and interventions to increase tree species’ pest resistance. Traditional tree breeding is responsible for successes to date, but new technologies offer hope to increase the efficiency of such efforts. Remarkable recent progress has been made, and for some at-risk species, novel biotechnological advances put reintroduction within reach. The high costs of reintroduction of at-risk species at necessary scale, however, will initially limit the pursuit to a few species. Successful deployment of pest resistant material may require improved species-specific knowledge and should integrate into and leverage existing reforestation systems, but these operations are sometimes rare where pest threats are greatest. While use of some biotechnologies, such as traditional tree breeding, are commonplace, others such as genetic engineering are controversial and highly regulated, yet may be the only viable means of achieving reintroduction of some at-risk species. Efforts to modify policy toward allowing the use of appropriate biotechnology, especially genetic engineering, have lagged. Provided that risk-benefits are favorable, policy is likely to follow with public opinion; in some countries, society is now increasingly open to using available biotechnologies. Continued engagement using the most recent advances in social science to build public trust, combined with a science-based collaboration among land managers and regulators, will generate the collective momentum needed to motivate policymakers to act rapidly given the speed at which forest health threats unfold and the large areas they affect.

Forests globally are threatened by native and non-native pathogens and pests. Butternut (Juglans cinerea L.) is a hardwood tree species native to North America that currently faces population declines due to butternut canker disease (BCD) by the non-native causal fungus Ophiognomonia clavigignenti-juglandacearum. Developing approaches to detect the presence of BCD in butternut and distinguishing between butternut and hybridized trees will be crucial for accelerating a butternut BCD-resistance breeding program. We found shifts in spectral profiles that were related to disease and species, but that spectral separation of disease presence was similar across species. These findings suggest the capability of foliar hyperspectral data to aid in disease detection in an endangered tree species with significant implications for developing high throughput breeding approaches.

IntroductionPlant species often exhibit significant variation in functional traits in populations along elevational gradients to cope with varying stress conditions. While plant development has been assumed to be most limited by a single resource, growing evidence suggests the potential for interactions of co-limiting resources to impact plant performance. Here, we aimed to determine how light, nitrogen, and water availability influence the growth and physiology of different populations of koa (Acacia koa), a tree species of concern that occurs across a large elevational gradient in tropical Hawaii, United States.MethodsPopulations from three seed sources [low (L), mid (M), and high (H) elevation] were grown in a controlled greenhouse experiment and exposed to co-limiting light, water, and nutrient (nitrogen) conditions. Light response, gas exchange, water status, resource use efficiency, nutrients and shoot non-structural carbohydrate concentrations, and growth and biomass allocation responses were quantified.ResultsWe found that resource co-limitation sometimes interacted to determine responses of the measured parameters. In general, the low elevation (L) koa population was more sensitive to conditions where both moisture and nutrients were limiting, while the high elevation (H) koa population was more sensitive to conditions where either light and moisture or light and nitrogen were co-limiting. The M population performed well overall regardless of resource limitation.DiscussionOur findings lend support to the theory that multiple resources limit growth and physiology of populations rather than the traditional view of a single resource limiting performance. Therefore, the possibility that multiple resource limitations drive population differences should be considered when developing population-based guidelines for forest and tree species restoration.

Potentially toxic elements (PTEs) including Cu, Zn, Pb, Cd and Ni in sewage sludge compost (SSC) are important obstacles to SSC forestry utilization. Synergistic fixation of bulking agent and adsorbent may shed new light on solving the problem for stabilization of PTEs in SSC before forestry disposal. The aim of this study was to investigate whether bulking agent (bagasse) + adsorbent (zeolite) can be integrated into forestry utilization processes of SSC. First, stabilization of PTEs in SSC were compared to those of composted bagasse + sewage sludge (BSC), zeolite + sewage sludge (ZSC) and bagasse + zeolite + sewage sludge (BZSC) after 60 days of composting. Subsequently, the long-term stability of PTEs in different composts-amended soil was monitored in a 2-year field trial on Eucalyptus urophylla forestland. Finally, a 12-month pot experiment was carried out to investigate their effects on the growth of Eucalyptus urophylla seedlings and PTEs absorption. Compared with SSC, addition of bagasse and zeolite significantly decreased total and extractable PTEs concentration and increased residual fractions in compost. In the field experiment, the total and extractable fraction concentrations of PTEs in topsoil after BZSC application were significantly lower than those after SSC and BSC application, and the status kept unchanged during the 2-year trial period. In the pot experiment, we further found that, compared with SSC, BSC and ZSC addition in the cultivated soil, the addition of BZSC promoted significantly greater growth and reduction in PTEs concentrations in Eucalyptus urophylla seedlings. Our results indicate that the combined addition of bagasse and zeolite can stabilize PTEs in SSC for an extended duration, improve plant growth, and therefore enhance the potential of sewage sludge compost utilization in forestry.

Root hemiparasitic trees can photosynthesize yet also acquire resources from host plants, which may benefit the long-term survival and growth of the hemiparasite. Experimental evaluation of planting distance between tree hemiparasites and their hosts can lead to biological insights and contribute to practitioner decision making. On an abandoned pasture site in a historically tropical dry forest in Hawai'i, we studied the effects of two host species and four planting distances on the survival and growth of 'iliahi (Hawaiian sandalwood, Santalum pan-iculatum), an endemic root hemiparasitic tree. Treatments included a control with no host or one of two native host species: 'a'ali'i (Dodonaea viscosa), a fast-growing shrub, or koa (Acacia koa), a fast-growing nitrogen-fixing tree. 'Iliahi and host seedlings were planted at a distance of <0.2, 0.5, 1.0, or 2.0 m from each other. After three years, survival of 'iliahi seedlings was greatest for 'iliahi paired with koa at 1.0 m (88 %) compared to the control with no host (53 %) and when paired with koa at 2.0 m (55 %). Height and ground line diameter of 'iliahi seedlings were greater when paired with koa at closer distances than with 'a'ali'i at any distance or the control with no host. Specifically, 'iliahi growth was greatest when paired with koa at <0.2 m distance. Foliar nitrogen concentration was greater for 'iliahi paired with koa at <0.2, 0.5, and 1.0 m distances, whereas the other foliar nutrient concentrations were typically greater for the 'iliahi control with no host. For sites with few or no pre-established hosts, such as abandoned pastures, 'iliahi growth can be greatly improved by co-planting in proximity to koa. As with other Santalum spp., early and abundant parasitic root connections with a host, especially a nitrogen-fixing host, are likely important for 'iliahi establishment and early growth.

Woodland utilization is a promising disposal method for sewage sludge (SS). However, the potential risk of heavy metals (HMs) transport with runoff must be considered. Among the various factors influencing HMs loss, SS application methods (Holing application, HA; Broadcasting and mixing application, BM; Broadcasting application, BA) are likely to cause significant effects by altering soil erosion and soil aggregates. This study aimed to determine how SS application methods affect HMs loss, soil aggregates erosion, and how they are related. Accordingly, the losses of HMs in surface runoff, interflow, and sediment were quantified during six simulated rainfalls. The results demonstrated that all methods reduced surface runoff, but BA was the most effective. Additionally, BA significantly reduced the total sediment yield and the total proportion of the <0.05 mm fraction aggregates. Moreover, BA had the smallest cumulative losses of Pb and Cd through surface runoff and Cu, Pb, and Cd through sediment. Sediment was the most important pathway for HMs loss, through which over 76.56 % of HMs were lost. In BA, the <0.05 mm fraction aggregates had the lowest HMs load, whereas in other treatments had the highest (54.33 %-80.33 %). The potential ecological risk coefficient of Cd was beyond "moderate" in all the pathways of BM and "high" in the interflow of each SS treatment. Nonetheless, when the multi-elements were evaluated collectively, the potential ecological risk index for each SS treatment was categorized as "low". Overall, BA not only reduced soil erosion but also posed no risk of HMs pollution. It should be noted that the loss of Cd in the interflow had a great impact, while the <0.05 mm fraction aggregates played a significant role in the HMs load. Thus, the current study not only provides an effective approach for the environmentally safe disposal of SS but also proposes a scientific method for the application of SS in woodlands.

PurposePoor structure, nutrient deficiency, and acidification are core factors restricting the reclamation of rare earth mining wasteland soil (REMWS). Sewage sludge, bagasse, and molybdenum tailings, all of which need proper disposal, have great potentials in REMWS reclamation. The goal of this study was to explore the remediation effect on rare earth mining wasteland soil with the combined application of sewage sludge compost (SSC), bagasse, and modified molybdenum tailings (MMT).Materials and methodsSSC (T1), SSC + bagasse (T2), and SSC + bagasse + MMT (T3) were applied in REMWS as amendments in a 4-month pot experiment, and their effects on REMWS properties and heavy metals (HMs) toxicity were tested with Eucalyptus urophylla, which grows fast, resists environment stress, and is a promising plant in REMWS reclamation.ResultsThe application of SSC (T1) improved REMWS fertility, but increased Cu, Zn, Cd, and Ni contents in soil and E. urophylla seedlings, and inhibited E. urophylla growth. Bagasse application (T2) alleviated growth inhibition and further addition of bagasse + MMT (T3) significantly improved E. urophylla growth. Moreover, T3 improved soil physical properties, organic carbon content, pH, and reduced soil HMs bioavailability and plant HMs content as compared to T1 and T2. Structural equation modeling results revealed that plant nutrient accumulation increased plant HMs accumulation, the latter inhibited plant nutrient accumulation in turn, and soil pH played a key role in retarding HMs uptake and improving E. urophylla growth and nutrients uptake.ConclusionThese results suggested that the combined application of SSC, bagasse, and MMT is an effective approach for REMWS amelioration and land disposal of solid waste resources.

Natural selection for plant species in heterogeneous environments creates genetic variation for traits such as cold tolerance. While physiological or molecular analyses have been used to evaluate stress tolerance adaptations, combining these approaches may provide deeper insight. Acacia koa (koa) occurs from sea level to 2300 m in Hawai'i, USA. At high elevations, natural koa populations have declined due to deforestation, and freeze tolerance is a limiting factor for tree regeneration. We used physiology and molecular analyses to evaluate cold tolerance of koa populations from low (300-750 m), middle (750-1500 m), and high elevations (1500-2100 m). Half of the seedlings were cold acclimated by exposure to progressively lowered air temperatures for eight weeks (from 25.6/22.2°C to 8/4°C, day/night). Using the whole plant physiology-freezing test and koa C-repeat Binding Factor CBF genes, our results indicated that koa can be cold-acclimated when exposed to low, non-freezing temperatures. Seedlings from high elevations had consistently higher expression of Koa CBF genes associated with cold tolerance, helping to explain variation in cold-hardy phenotypes. Evaluation of the genetic background of 22 koa families across the elevations with low coverage RNA sequencing indicated that high elevation koa had relatively low values of heterozygosity, suggesting that adaptation is more likely to arise in the middle and low elevation sources. This physiology and molecular data for cold tolerance of koa across the elevation gradient of the Hawaiian Islands provides insights into natural selection processes and may help to support guidelines for conservation and seed transfer in forest restoration efforts.