Seedling Mortality Research Articles

Short‐term survival and growth of 32 native boreal plants on treated oil sands tailings

AbstractThe consolidation of oil sands tailings is a cost‐ and time‐consuming process that requires treatment via active (e.g., centrifugation) and passive (e.g., self‐weight consolidation) methods. The use of plants to dewater tailings is a promising concept and has previously been evaluated using agronomic grass species in greenhouse studies. This greenhouse study evaluated the short‐term survivorship and growth of 32 upland and lowland native plant species (12 forbs, 14 graminoids, and six woody plants) in centrifuged tailings and benchmarked their performance against reclamation soil and undisturbed forest soil. All plant species were propagated from seed and transplanted as seedlings into containers filled with one of the three substrates. After 42 days, the height (woody species only) and total aboveground biomass were determined for all living plants. As expected, the mortality of seedlings in tailings was higher than plants grown in the other two substrates. Graminoid species, regardless of species community type (wetland or upland), had higher survival probabilities and growth compared to forb or woody species across all substrates. Of forbs and woody species evaluated, Geum aleppicum and Populus tremuloides showed the most promise amongst the upland species, and Rumex occidentalis was the wetland equivalent.

Characterization and Pathogenicity of Soilborne Pathogens in Gloriosa superba: Effects of Single- and Multiple-Pathogen Coinfection on Disease Responses.

Glory lily (Gloriosa superba), an ornamental climbing plant, contains the bioactive compound colchicine, attracting attention from the pharmaceutical industry. However, soilborne pathogens have emerged as a serious threat to the cultivation of glory lily, leading to substantial economic losses in the southern parts of India. Among these, the three major pathogens are Macrophomina phaseolina, Fusarium oxysporum, and Agroathelia rolfsii, causing dry root rot (also referred to as charcoal rot), wilt, and stem rot, respectively. Here, we characterized these pathogens using morphological characteristics and phylogenetic analysis of DNA sequences related to the internal transcribed spacer of ribosomal DNA, calmodulin (CAL), and translation elongation factor 1-alpha (TEF-1α). Furthermore, in the pathogenicity tests, the inoculation of M. phaseolina alone resulted in lesions measuring 7.54 ± 0.01 mm on tubers and 90% seedling mortality. This severity was comparable to the simultaneous inoculation of all three pathogens, indicating the prominence of dry root rot among soilborne diseases. This study marks the first detailed investigation of soilborne pathogens combined infection in G. superba, contributing to the understanding of fungal disease complexity in medicinal plants.

BUMDes Strategies for Successful Banana Planting Programs

General Background: Village-Owned Enterprises (BUMDes) are essential for enhancing local economies through agricultural initiatives. Specific Background: In Krembung Village, Sidoarjo Regency, a banana planting program has been implemented to improve productivity and income. Knowledge Gap: However, challenges like high seedling mortality and inadequate practices hinder success. Aims: This study analyzes BUMDes strategies in executing the banana program, focusing on community involvement and resource management. Results: While strength and progress indicators are optimal, the value aspect is suboptimal due to significant seedling losses. Community support for banana cultivation has been strong. Novelty: The research highlights practical challenges and strategic approaches in managing BUMDes agricultural programs. Implications: Findings emphasize the need for better resource allocation and community engagement to enhance agricultural initiatives, providing insights for improving BUMDes operations and promoting sustainable rural development. Highlights: Community Involvement: Strong local support is crucial for the success of the banana planting program. Resource Management: Effective allocation and management of resources are necessary to mitigate seedling mortality. Strategic Approaches: Implementing targeted strategies can enhance agricultural productivity and economic benefits for the village. Keywords: BUMDes, Banana Planting, Community Engagement, Agricultural Productivity, Village Potential

Development of a qPCR Assay for the Detection and Quantification of the Fungal Pathogen Calonectria canadiana on Conifers

ABSTRACTA real‐time PCR TaqMan assay was developed for the detection of Calonectria canadiana, a fungal pathogen responsible for damping off, root rot and seedling blight in conifer forest nurseries in central and eastern North America. While highly significant in Quebec Forest nurseries, coniferous seedling mortality decreased significantly when nurseries transitioned from bare root to container seedling production. However, over the past few years, this pathogen has re‐emerged as a threat and millions of container white spruce seedlings were culled in two nurseries in eastern Quebec. A sensitive detection and quantification assay for C. canadiana was essential to investigate the biological and environmental factors driving this new epidemic. We designed primers and a TaqMan probe targeting the internal transcribed spacer (ITS) of C. canadiana. The resulting Ccan TaqMan assay successfully differentiated C. canadiana from other soil‐borne pathogens of the Nectriaceae encountered in Quebec Forest nurseries. The limit of detection of the assay was established at eight copies of C. canadiana ITS. The Ccan TaqMan assay quickly identified the presence of the pathogen in both symptomatic and asymptomatic white spruce (Picea glauca) seedlings. Furthermore, we demonstrated that the pathogen was more easily detected when DNA was extracted from necrotic needles at the base of the stem rather than from necrotic roots. This molecular tool will greatly aid in understanding the biology and epidemiology of C. canadiana.

Effect of shade management practice on cocoa seedling mortality: micro evidence from the Amansie-West district of Ghana

Effect of shade management practice on cocoa seedling mortality: micro evidence from the Amansie-West district of Ghana

Plant, bacteria and fungi crosstalk: Direct and indirect biocontrol mechanisms of sugarcane rhizoplane Pseudomonas species against Fusarium wilt

In order to identify an effective rhizoplane Pseudomonas species to combat sugarcane wilt pathogen (Fusarium sacchari), twenty Pseudomonas isolates were obtained from the sugarcane rhizoplane of different genotypes. The three-tier confrontation (direct, indirect and remote) tests revealed antagonistic activity of the bacteria, bacterial non-volatile and volatile compounds. In dual culture assay, SRP19 (46.30%) and SRP20 (39.30%) have shown the highest inhibition against F. sacchari. 16S-23S rDNA sequencing identified them as Pseudomonas chlororaphis subsp. aurantiaca (SRP19) and Pseudomonas aeruginosa (SRP20). Exploration of biocontrol mechanisms revealed the potential roles for IAA production, extracellular enzyme secretion (proteases, cellulases and chitinases), HCN synthesis, siderophore production, pyocyanin or fluorescein production and phosphate solubilization. The molecular analysis revealed the presence of genes (phz, prnD, phlD and pltC) involved in the biosynthesis of antimicrobial peptides like phenazines, pyrrolnitrin, 2,4-diacetyl phloroglucinol and pyoleuteorin, involved in suppressing Fusarium. The antagonistic activity was further confirmed under greenhouse conditions by sett treatment with potential antagonistic isolates, which increased germination and reduced the pre-emergent mortality by 60% and post-emergent seedling mortality by 76% in SRP19 treated pots. The study revealed that the isolate Pseudomonas chlororaphis subsp. aurantiaca strain SRP19 can act as PGPR with both plant growth promoting and pathogen suppressing activity that can be used as an effective biocontrol agent against Fusarium wilt of sugarcane.

The rates of starch depletion and hydraulic failure both play a role in drought-induced seedling mortality

Key messageThe elapsed times to deplete starch concentrations and to reach a null hydraulic safety margin were related to tree seedling mortality under experimental drought. Starch concentration showed an accelerated decline across all species during the early stages of dehydration, while the concentrations of soluble sugars and total nonstructural carbohydrates remained stable. Concomitant carbohydrate depletion and hydraulic failure drive seedling mortality under drought.ContextCurrent upsurges of drought events are provoking impacts on tree physiology, resulting in forest mortality. Hydraulic dysfunction and nonstructural carbohydrate (NSC) depletion have been posited as the main mechanisms leading to plant mortality under drought.AimsThis study explores the dynamics of the two mortality-inducing processes during drought stress using an experimental approach with 12 evergreen tree species.MethodsSeedlings were subjected to drought until 100% mortality was observed. Midday (ΨMD) and predawn (ΨPD) water potentials, xylem pressure leading to a 50% loss of hydraulic conductivity (Ψ50), along with NSC concentrations in different organs (leaves, stems, and roots) were measured regularly during drought.ResultsTotal NSC concentrations and soluble sugar pools did not decline during drought. However, starch pools showed strong reductions early during drought stress as ΨPD decreased, and the time leading to starch depletion emerged as a strong mortality predictor. Ψ50 alone did not provide an accurate estimate of mortality, while the elapsed time to reach a null hydraulic safety margin (ΨMD—Ψ50 = 0) was related to seedling mortality.ConclusionAdopting a dynamic approach by estimating the times to consume both starch reserves and hydraulic safety margins is highly relevant to improve predictions of tree mortality under the current context of increasing global drought.

Winter and spring frost events delay leaf-out, hamper growth and increase mortality in European beech seedlings, with weaker effects of subsequent frosts.

The persistence of plant populations depends crucially on successful regeneration. Yet, little is known about the effects of consecutive winter and spring frost events on the regeneration stage of trees from different seed sources, although this will partly determine the success of climate warming-driven poleward range shifts. In a common garden experiment with European beech (Fagus sylvatica) seedlings from winter 2015/2016 to autumn 2017, we studied how simulated successive spring and winter frost events affect leaf-out dates, growth performance, and survival rates of 1- to 2-year-old seedlings from provenances differing in climate at origin. We further investigated the combined effects of successive frost events. The first spring frost after germination led to a mortality rate up to 75%, resulting in reduced seedling numbers but better frost tolerance of the survivors, as reflected in a weaker impact of the following winter frost event in the survivors compared to the non-acclimated control. Final plant height was most strongly reduced by the spring frost in the second year. The winter frost event delayed leaf-out by up to 40 days, leading to severe growth impairment in 2017. Our results indicate partly successful frost acclimation and/or the selection of frost-hardier individuals, because the negative growth effects of consecutive frost events did not add up after exposure to more than one event. Both mechanisms may help to increase the frost tolerance of beech offspring. Nevertheless, mortality after the first spring frost was high, and frost exposure generally caused growth reductions. Thus, achieving higher frost tolerance may not be sufficient for beech seedlings to overcome frost-induced reductions in competitive strength caused by winter frost damage and delayed leaf enfolding.

Seedling development of Schizolobium parahyba var. amazonicum inoculated with Rhizoglomus clarum in different doses of phosphorus

This work aimed to evaluate the growth and phosphorus uptake of Schizolobium parahyba var. amazonicum (Huber ex Ducke) Barneby (pinho-cuiabano) seedlings inoculated with Rhizoglomus clarum (T.H.Nicolson & N.C.Schenck) Sieverd., G.A.Silva & Oehl at different doses of phosphorus. The treatments consisted of five levels of phosphorus (0, 25, 50, 100 and 200 mg dm-³) and inoculation or not with R. clarum. After 45 days of seedling inoculation, we analyzed: height, root fresh and dry matter, shoot fresh and dry matter, number of leaves, survival, stem diameter, root volume, Dickson quality index, mycorrhizal colonization, relative water content, leaf tissue density, phosphorus content, efficiency of phosphorus uptake and efficiency of phosphorus utilization. Inoculation with R. clarum and the lowest doses of phosphorus resulted in lower seedling mortality rates. R. clarum did not increase the phosphorus content, efficiency of phosphorus uptake, efficiency of phosphorus utilization, relative water content and the Dickson quality index of the seedlings, but it was efficient in increasing the shoot fresh and dry matter as well as leaf tissue density. Inoculation with R. clarum and phosphate fertilization had a significant joint effect on seedling height and root fresh matter. Thus, it can be concluded that R. clarum may represent an important sustainable technology for the production of pinho-cuiabano seedlings, increasing seedling growth, even at low levels of phosphate fertilization.

Virtual Reciprocal Garden Assessment of Germination Syndromes for Elymus elymoides ssp. brevifolius and Elymus multisetus

Bottlebrush squirreltail (Elymus elymoides) and big squirreltail (Elymus multisetus) are high-priority species for restoration of millions of hectares of rangeland in the western United States that have been degraded by accelerated wildfire and introduced annual grasses. Previous research has compared potential germination and seedling performance of these species in a common environment and noted significant genetic differentiation in characteristics that are associated with their environments of origin. In this experiment, we used wet-thermal germination models and long-term simulations of seedbed microclimate to conduct a virtual reciprocal-garden analysis of the potential germination response of these species. We confirmed significant species differentiation in germination rate that appears to confer site-specific advantages for initial seedling establishment in their respective habitats of origin. Our results specifically highlight the relative importance of late-fall seeding for the more rapidly germinating E. multisetus in order to avoid early-fall germination and post-germination seedling mortality from freezing conditions in the winter. In contrast, the slower-germinating E. elymoides ssp. brevifolius A is less likely to germinate in the fall and likely avoids inherently harsher winter temperatures in the seedbed. Virtual simulations of this type might lead to identification of complex-trait genetic markers that are associated with intraspecific and interspecific adaptations to specific environments. Identification of these traits could also inform management of plant communities that are under threat from invasive weeds and climate change.

Distinct effects of phyllosphere and rhizosphere microbes on invader Ageratina adenophora during its early life stages.

Microbes strongly affect invasive plant growth. However, how phyllosphere and rhizosphere soil microbes distinctively affect seedling mortality and growth of invaders across ontogeny under varying soil nutrient levels remains unclear. In this study, we used the invader Ageratina adenophora to evaluate these effects. We found that higher proportions of potential pathogens were detected in core microbial taxa in leaf litter than rhizosphere soil and thus leaf inoculation had more adverse effects on seed germination and seedling survival than soil inoculation. Microbial inoculation at different growth stages altered the microbial community and functions of seedlings, and earlier inoculation had a more adverse effect on seedling survival and growth. The soil nutrient level did not affect microbe-mediated seedling growth and the relative abundance of the microbial community and functions involved in seedling growth. The effects of some microbial genera on seedling survival are distinct from those on growth. Moreover, the A. adenophora seedling-killing effects of fungal strains isolated from dead seedlings by non-sterile leaf inoculation exhibited significant phylogenetic signals, by which strains of Allophoma and Alternaria generally caused high seedling mortality. Our study stresses the essential role of A. adenophora litter microbes in population establishment by regulating seedling density and growth.

Distinct effects of phyllosphere and rhizosphere microbes on invader Ageratina adenophora during its early life stages

Microbes strongly affect invasive plant growth. However, how phyllosphere and rhizosphere soil microbes distinctively affect seedling mortality and growth of invaders across ontogeny under varying soil nutrient levels remains unclear. In this study, we used the invader Ageratina adenophora to evaluate these effects. We found that higher proportions of potential pathogens were detected in core microbial taxa in leaf litter than rhizosphere soil and thus leaf inoculation had more adverse effects on seed germination and seedling survival than soil inoculation. Microbial inoculation at different growth stages altered the microbial community and functions of seedlings, and earlier inoculation had a more adverse effect on seedling survival and growth. The soil nutrient level did not affect microbe-mediated seedling growth and the relative abundance of the microbial community and functions involved in seedling growth. The effects of some microbial genera on seedling survival are distinct from those on growth. Moreover, the A. adenophora seedling-killing effects of fungal strains isolated from dead seedlings by non-sterile leaf inoculation exhibited significant phylogenetic signals, by which strains of Allophoma and Alternaria generally caused high seedling mortality. Our study stresses the essential role of A. adenophora litter microbes in population establishment by regulating seedling density and growth.

Post-fire resurveys reveal predictability of long-term conifer recruitment in severely burned California dry forests

High severity fire is far outpacing post-fire reforestation capacity across the American West, highlighting the need to better understand when and where natural regeneration is sufficient to meet short- and long-term reforestation goals. The vast majority of available post-fire data represents regeneration in the first few years following a fire, raising the question of how well recovery trajectories can be predicted from early post-fire snapshots. We utilize a unique dataset from seven wildfires and 78 plots surveyed twice following stand-replacing fire in two California ecoregions, the northern Sierra Nevada and Klamath Mountains, to ask (1) how are post-fire vegetation and conifer densities changing over time and (2) how well do relatively early post-fire sampling efforts and biophysical factors (availability of seed source, shrub competition, and microclimate) explain longer-term (12–23 year) conifer recovery in California dry forests. Change in conifer seedling density between survey periods was highly variable. Overall, densities of all conifer species during the first decade after fire provided reliable estimates of longer-term conifer recovery in northern California dry forests, though in different ways for different species. Early post-fire seedling density readily explained longer-term densities for less shade-tolerant species, yellow pine (Pinus ponderosa and Pinus jeffreyi) and Douglas-fir (Pseudotsuga menziesii). In contrast, early seedling density was a poor predictor for shade-tolerant species, predominantly white fir (Abies concolor), with site conditions better explaining longer-term density. In general, the probability of a site experiencing net seedling mortality between surveys was highest in sites with high shrub cover and the probability of net recruitment increased with decreasing heat load, suggesting a continued role of microclimate and competition in forest recovery long after the initial post-fire period. Our results lend support to the use of relatively early post-fire surveys to infer longer-term forest recovery trajectories for forest management planning and can help refine reforestation prioritization tools.

Grab to fill the gap: key factors influencing Reynoutria japonica germination and seedling establishment in the secondary distribution range

Reynoutria japonica (Japanese knotweed) is a highly invasive female plant that primarily reproduces through vegetative regeneration during secondary distribution. Despite producing a substantial number of viable hybrid seeds, the occurrence of seedlings and young plants in the wild remains rare; the reasons for this rarity are unclear. Environmental intolerance and chromosomal anomalies during hybridisation can impede seedling development. This study evaluates the combined impact of these factors by examining substrate, temperature, and light effects on germination, as well as assessing seedling genome sizes and viability. Seeds were cultivated in both natural and controlled environments to manage external influences. Flow cytometry was employed to evaluate chromosomal arrangements. The final germination was notably high at 99%, and 68% of seedlings thrived under controlled conditions, emphasising hybrid seedling viability regardless of highly polyploid levels ranging from pentaploid to aneuploid (2C DNA genome size from 5.17 to 11.95 pg). Thus, it is evident that seeds can germinate and produce vital seedlings despite various chromosomal sets. Even fluctuating temperatures and type of substrate do not limit seed germination. However, these results were obtained under laboratory conditions, with seeds and seedlings receiving regular irrigation. A significant seedling mortality rate (99%) was observed in the field experiment, and the final germination was also low there (15%). Observations suggest that water stress might be the cause of this mortality. Further research on water stress is necessary because it could be the primary factor limiting the successful generative spread of the knotweeds.

Effect of drought and pine weevil damage on mechanically protected Norway spruce seedlings

Pine weevils (Hylobius abietis L.) pose a significant threat to conifer seedlings by feeding on the bark, thus damaging or killing seedlings. Historically, insecticides were used to suppress such damage, but were slowly phased out in Sweden due to environmental and health concerns. This study aimed to assess field performance of an alternative protection method: mechanical coating applied to the stem of planted Norway spruce (Picea abies) seedlings. Field trials were conducted on 14 sites in south Sweden, using four different types of mechanical protection (Cambiguard, Conniflex, Ekovax, Hylonox), standard insecticide (Merit Forest), and ambient control. Seven sites were established in the drought year of 2018 and seven more in 2019. This allowed for additional investigation of the effect of drought on seedling establishment and possible interaction with pine weevil damage. Seedlings were surveyed for survival and height after the first, second and fourth growing season. Results show drought as the main source of damage for seedlings planted in 2018, with no significant effect of insecticide or mechanical protection on survival of seedlings. However, mechanical protections performed equally well as insecticide and positively increased survival by 30 %, compared to untreated, four growing seasons after planting for seedlings planted in 2019. Seedling height was not significantly affected by planting year or any of the treatments, suggesting no adverse effects of coating application. However, a synergistic effect between pine weevil damage and drought was observed, where even low levels of pine weevil damage resulted in high mortality for seedlings planted in 2018, compared to those planted in 2019. Additionally, for seedlings planted in 2019, damage to the top of the stem did not result in significant mortality, until high damage levels were reached (40 % and above). The opposite was found for seedlings planted in a 2018 drought year, where both damage to the top and the bottom of the stem followed a linear response. In conclusion, we show that investigated mechanical protection methods can be considered a viable replacement for insecticides, but our results also highlight the importance of considering multiple environmental stressors such as drought and pest damage on seedling establishment.

Innovative fertilizers with added plant extracts in the cultivation of Valeriana officinalis and Raphanus sativus and in the control of Botrytis and powdery mildew

Research objective: The main objective of this article is to report the results obtained from the use of innovative fertilisers with added plant extracts in agriculture. In particular, this article will deal with two important topics: i) study of the effect of innovative fertilisers on the biomass of vegetable plants; ii) possible control on mortality due to diseases such as Botrytis and powdery mildew. The information reported in this research work can support the design of cultivation systems in which agricultural sustainability is fundamental due to the presence of plant extracts as an alternative to synthetic plant protection products. Materials and Methods: The plants were grown in pots under controlled conditions; 30 seedlings per thesis, divided into 3 replications of 10 plants each, were planted in early January 2024. The plants used in the trial were Valeriana officinalis L. and Raphanus sativus. The five experimental groups in cultivation were: i) group control, irrigated with water and previously fertilised substrate; ii) group with Aktigen, irrigated with water and previously fertilised substrate, (3 ml per plant once a week); iii) group with Lifegen, irrigated with water and previously fertilised substrate, (3 ml per plant once a week); iv) group with QI-gen, irrigated with water and previously fertilised substrate, (3 ml per plant once a week); v) Group with Ecklonia maxima (EK): (peat 70% + pumice 20%), irrigated with water and previously fertilised substrate, (3 ml per plant once a week). On 5 May 2024, plant height, number of leaves, primary root length (mm), biomass of the aerial and root system, and number of dead plants (Botrytis and powdery mildew) were recorded. Results and Discussion: The experiment showed that the use of innovative fertilisers enriched with plant extracts can indeed significantly improve the vegetative and root growth of Valeriana officinalis L. and Raphanus sativus. All treatments showed a significant improvement over the untreated control and the commercial Ecklonia maxima treatment for the agronomic parameters analysed, but the Qi-gen treatment was significantly the best for increasing vegetative and root biomass. Improvements were also found in plant height, leaf number and root length. The trial also revealed the significant effect on Botrytis control of the product Aktigen and on powdery mildew of the product Lifegen, in fact they reduced the mortality of Valeriana officinalis and Raphanus sativus seedlings. Conclusions: A number of scientific studies have shown that the application of biofertilizers can improve plant growth, productivity, quality, and tolerance to biotic and abiotic stresses. Because of their multiple properties, they have become increasingly important as advanced agricultural techniques in global agriculture. This type of product, which includes natural substances, will contribute significantly to ecologically and economically sustainable agricultural production systems in the coming years, as well as serving as the foundation for large-scale sustainable agriculture in the future.

Evaluation of Endophytic Microorganisms (Trichoderma hazianum and Bacillus subtilus) as Biofungicides against Bayoud Disease (Fusarium oxysporum f. sp. albedinis) on Date Palm (Phoenix dactylifera L.)

Backgraound: Date palm disease named Bayoud, is the major constraint caused by the soil fungus Fusarium oxysporum f. sp. albedinis (Foa) in Algeria. This work has the objective to in vivo biocontrol on bayoud disease incidence on three date palm varieties (Deglet-Nour, Feggous and H-mira), using two antagonistic microorganisms, one fungus (Trichoderma harzianum) and one bacterium (Bacillus subtilus). Methods: Foa strains obtained from isolation of the spines carrying the typical symptoms of Bayoud disease. Two strains used T. harzianum and B. subtilus, are isolated from rhizosphere soils of the date palm. Using the greenhouse screening test, the in vivo biocontrol test is carried out on 3-4 month-old date palm seedlings at the rate of 5 ml of inoculum suspension. Result: A significant (P less than 0.01), difference of date palm seedlings reactions against Foa isolate and antagonistic microorganisms was observed. All three date palm varieties present a high susceptibility against Foa until the total mortality of date palm seedlings. The biocontrol test showed that two antagonists showed different reaction, with the complete resistance of three varieties treated by T. harzianum, while, the antagonist B. subtilus protect just two varieties (Deglet-Nour and H-mira) and can’t protect Feggous variety when showed the susceptibility reaction by presentation of typical symptoms of bayoud disease. We can apply of these antagonistic microorganisms to protect our groves contaminated by Bayoud disease and contain just susceptible commercial cultivars of date palm.

Seedling dynamics differ between canopy species and understory species in a tropical seasonal rainforest, SW China

We used 11 years of census data from 450 seedling quadrats established in a 20-ha forest dynamics plot to study seedling dynamics in tree species of a tropical seasonal rainforest in Xishuangbanna, southwestern China. We found that overall seedling recruitment rate and relative growth rate were higher in the rainy season than in the dry season. Both the recruitment rate of seedlings from canopy tree species (two species) and the relative growth rate of seedlings from understory species (nine species) were higher in the rainy season than in the dry season. However, in the rainy season, the recruitment rate of seedlings was higher for canopy tree species than for understory tree species. In addition, relative growth rate of seedlings was higher in the canopy species than in understory seedlings in the dry season. We also observed that, in both rainy and dry seasons, mortality rate of seedlings was higher for canopy species than for understory species. Overall, canopy tree species appear to have evolved a flexible strategy to adapt to the seasonal changes of a monsoon climate. In contrast, understory tree species seem to have adopted a conservative strategy. Specifically, these species mainly release seedlings in the rainy season and maintain relatively stable populations with a lower mortality rate and recruitment rate in both dry and rainy seasons. Our study suggests that canopy and understory seedling populations growing in forest understory may respond to future climate change scenarios with distinct regeneration strategies.

Mitigative translocation of Singleton Mint Bush (Prostanthera cineolifera) on the NSW North Coast: Effects of soil texture, horticultural practice and bushfire on the translocation outcome

SummaryTranslocation of the threatened species Singelton Mint Bush (Prostanthera cineolifera R.T.Baker & H.G.Sm.) was carried out for a highway project on the New South Wales North Coast to mitigate development impact on this species. The translocation aimed to augment an existing population with propagated plants to compensate for cleared plants and conduct field research to better understand the effects of soil properties, horticultural practices and a wildfire on translocation results. A novel soil seedbank and fire method applied ex‐situ was used to propagate plants for introduction. After an initial attempt at site‐wide introduction resulted in widespread mortality of seedlings from a wilt disease, three plot‐based experiments were carried out to examine how disease incidence was related to spatial variation in soil properties and horticultural practices. The experiments showed that relatively subtle changes in the clay and sand content of soil strongly affected susceptibility of Singelton Mint Bush seedlings to wilt disease; 12 month old seedlings performed much better than 6 month old seedlings; plants propagated from seed performed better than cuttings, and most of the recipient site represented unsuitable habitat for Singelton Mint Bush. Sufficient Singelton Mint Bush seedlings were established after 3 years, but after a bushfire, the translocated cohort recruited poorly from seed, so that after 6 years, <10% of the total Singelton Mint Bush population in the recipient site was of translocated origin and >90% of in‐situ (pre‐translocation) origin. Lessons learnt from the translocation project were that: (i) microhabitat is as important as macrohabitat in selecting a translocation recipient site; (ii) short‐term survival may not be a reliable indicator of a self‐sustaining population; (iii) translocation incorporating designed experiments can greatly improve understanding of how certain factors influence species performance and (iv) horticultural practices can be as important as ecology in determining the translocation outcome.

Lethal combination for seedlings: extreme heat drives mortality of drought-exposed high-elevation pine seedlings.

Hotter drought- and biotically-driven tree mortality are expected to increase with climate change in much of the western United States, and species persistence will depend upon ongoing establishment under novel conditions or migration to track ecological niche requirements. High-elevation tree species may be particularly vulnerable to increasing water stress as snowpack declines, increasing the potential for adult mortality and simultaneous regeneration failures. Seedling survival will be determined by ecophysiological limitations in response to changing water availability and temperature. We exposed seedlings from populations of Pinus longaeva, Pinus flexilis, and Pinus albicaulis to severe drought and concurrent temperature stress in common gardens testing timing of drought onset under two different temperature regimes. We monitored seedling functional traits, physiological function, and survival. The combined stressors of water limitation and extreme heat led to conservative water use strategies and declines in physiological function, with these joint stressors ultimately exceeding species' tolerances and leading to complete episodic mortality across all species. Growing conditions were the primary determinant of seedling trait expression, with seedlings exhibiting more drought-resistant traits such as lower specific leaf area in the hottest, driest treatment conditions. Water stress-induced stomatal closure was also widely apparent. Under adequate soil moisture, seedlings endured prolonged exposure to high air and surface temperatures, suggesting broad margins for survival. The critical interaction between soil moisture and temperature suggests that rising temperatures will exacerbate growing season moisture stress. Our results highlight the importance of local conditions over population- and species-level influences in shaping strategies for stress tolerance and resistance to desiccation at this early life stage. By quantifying some of the physiological consequences of drought and heat that lead to seedling mortality, we can better understand the future effects of global change on the composition and distribution of high-elevation conifer forests.