Strong Growth Response Research Articles

Developing alternatives to adaptive silviculture: Thinning and tree growth resistance to drought in a Pinus species on an elevated gradient in Southern Spain

Forest plantations are more vulnerable to the stress induced by biotic and abiotic factors than are naturally regenerated forests. These effects can be aggravated by a lack of management in large reforestation areas, and thinning could, therefore, help trees to reduce dieback and tree mortality related to drought. We address this question using a dendrochronology and modelling approach to improve the understanding of the growth response of high-density planted pine forests to thinning in drought-prone areas of Southern Spain. An experimental trial was, therefore, carried out with three species (Pinus halepensis, P. nigra, and P. sylvestris) and three thinning treatments (unthinned, moderate, and heavy thinning), after which growth-climate relationships and drought vulnerability indices were assessed. Three separate generalized linear mixed-effects models (GLMM), one for each species and location, were fitted using BAI as the response variable, and post-thinning growth trajectories and drought vulnerability indices were also simulated. Ten-year basal area showed strong growth responses following the thinning treatment (BAI10, 72% for P. halepensis and 50% for P. sylvestris as regards heavy thinning and 51% for P. nigra as regards moderate thinning), with different responses to precipitation and temperature according to species and thinning intensity. The significant effects of thinning on drought vulnerability indices indicated that the thinning treatments had a positive effect, irrespective of the pine species, although this was more evident in the case of P. sylvestris (recovery F = 28.10, p < 0.001, and resilience F = 35.21, p < 0.001 respectively) and P. halepensis (recovery F = 10.97, p < 0.001 and resilience F = 16.91, p < 0.001). The models also showed that climatic effect was greater for P. nigra than for P. sylvestris. The simulation also provides information on the long-term effectiveness of thinning; in P. sylvestris the effect of thinning tended to be attenuated after 20 years, but this was not the case of P. nigra and P. halepensis. High values of modelled resilience were found after thinning, with a time to recovery of between two and four years after drought depending on thinning intensity. Our findings showed the advantages of thinning for growth under different climatic constraints, particularly drought. This work is a new contribution that demonstrates the urgent need for forest managers to take steps in order to help drought-vulnerable Mediterranean pine plantations to adapt to the risks posed by climate change.

Fire-caused mortality within tree neighborhoods increases growth of Pinus lambertiana more than growth of Abies concolor

Global increases in large-tree mortality and multiple disturbances such as fire, drought, and pestilence increase the importance of understanding how large-tree growth responds to changes in competitive neighborhoods. We used 34,175 spatially mapped trees within 25.6 ha that burned at low to moderate severity in 2013 to investigate how changes to tree neighborhoods affected growth of 3,652 surviving trees of two species, Abies concolor (white fir) and Pinus lambertiana (sugar pine). Using diameter measurements taken in 2014 and 2019, we estimated post-fire radial growth of each surviving tree. We modeled annual basal area increment as a function of diameter and extracted residuals to yield relative growth rate (RGR). We used a multi-model approach and AIC to compare the species-specific effects on RGR of all post-fire tree mortality within a neighborhood radius versus mortality broken down by cause. To represent density reduction around each surviving tree, we computed crowding metrics for neighborhood radii up to 20 m for all tree mortality combined and for each mortality cause. The best-fit model included terms for density reduction within 10 m of the surviving tree due to 1) fire or mechanical damage and 2) bark beetle mortality, as well as their interactions with species and diameter. Density reduction due to fire or mechanical damage had a positive effect on RGR that was nearly twice as strong for P. lambertiana as A. concolor. Tree diameter interacted with density reduction for just P. lambertiana. Small-diameter (10-cm) P. lambertiana had a fourfold larger increase in basal area increment than large-diameter (60-cm) P. lambertiana as density reduction due to fire or mechanical damage ranged from 0 to 100 %. The strong growth response of medium-diameter P. lambertiana to density reductions could eventually increase the abundance of large-diameter (≥60 cm) P. lambertiana. In conjunction with mortality rates, which were lower for large-diameter P. lambertiana (0.97 %) than A. concolor (3.31 %), this could increase the relative abundance of large-diameter P. lambertiana from 51.2 % in 2020 to 62.6 % by 2050. Changes to competitive neighborhoods can have species-specific effects on large-tree growth, an important consideration for long-term management of fire-prone forests.

Phytoremediation of potentially toxic elements and rare earth elements by perennial plants in floating wetlands

The impact of urbanization, industrialization, agriculture, mining, and stormwater runoff on ecosystems has resulted in significant water pollution concerns worldwide. Significant attention has been paid to the removal of potentially toxic elements (PTE) and metalloids (e.g., arsenic (As), selenium (Se) and lead (Pb)) by various plant species. However, little research has been published on the simultaneous accumulation of cadmium (Cd), chromium (Cr), and nutrient removal, by floating treatment wetlands (FTW), from stormwater runoff, and the accumulation and recovery of rare earth elements (REE) through energy biomass cultivation. This research bridges knowledge gaps in the remediation of REE using short-rotation willow (Salix spp.) and simulated stormwater remediation of Cd and Cr with Phragmites australis and Iris pseudacorus. In this context, three different microcosm experiments were conducted with perennial plants (P. australis and I. pseudacorus) in FTW. Stem growth, dry biomass, root length, chlorophyll content index (CCI), anatomical plant tissue changes, Cd accumulation and N and P removal from simulated stormwater were investigated over a 50-days period under different Cd doses (0, 1, 2 and 4 mg L−1). In addition, the effects of Cr dose (0, 500, 1000 and 2000 μg L−1) on the growth and anatomy of P. australis and I. pseudacorus, as well as on the accumulation of Cr in plant biomass and N and P removal were studied in FTW over a 50-day period. In addition, the effects of REE doses on stem growth, dry biomass, root length and their accumulation in biomass were investigated in two Salix species (S. myrsinifolia and S. schwerinii) and two cultivars (Klara and Karin) in FTW over a 28-day period. The REE treatments contained a single-dose of lanthanum (La: 50 mg L−1), multi-solute of six-REE (La: 11.50 mg L−1 + yttrium (Y: 11 mg L−1) + neodymium (Nd: 10.50 mg L−1) + dysprosium (Dy: 10) + cerium (Ce: 12 mg L−1) + terbium (Tb: 11.50 mg L−1)) and control (without REE). Moreover, REE recovery from biomass ash after combustion was investigated. In this study, P. australis and I. pseudacorus growth parameters were not hampered by Cd stress, their roots accumulated more Cd than the shoots and were capable of lowering N and P concentrations. The impact of Cr was more evident on plant growth under the low- and medium doses (500 and 1000 μg Cr L−1). However, anatomical changes were observed under the high dose (2000 μg Cr L−1, respectively). Both species were able to remove a substantial (98−99%) concentration of N and P within a 10-day period of increased Cr loading. The greatest amount of Cr was retained in P. australis and I. pseudacorus roots. Salix species and cultivars did not show REE toxicity symptoms and displayed a strong growth response compared to the control. All Salix accumulated REE in their biomass, although the greatest amounts of accumulated REE were found in the roots of the Klara and Karin cultivars. The substantial deposition of Cd and Cr in the roots of P. australis and I. pseudacorus, and REE in the Salix roots show their phytostabilization potential. Approximately 80% of the REE was retained in the Salix ash following combustion of the biomass at 1000 °C. The findings in this research reveal that these perennial plants could be suitable candidates to control the runoff from Cd, Cr and REE affected waterbodies into freshwater resources through immobilization aligned with efficient biomass production.

Effects of two different thinning methods on the diameter and basal area increments of silver lime (Tilia tomentosa Moench) target trees in Fruška Gora (Serbia)

This paper analyses the cumulative effects of selective thinning and thinning from below on diameter and basal area increments of target trees after 25/26 years in 52, 69- and 86-year-old silver lime (Tilia tomentosa Moench) stands. Two target tree collectives were analysed: (1) elite trees selected between 1993–1994 from permanent sampling plots (selective thinning method), and (2) a ‘comparable collective’ of target trees selected in 2019 (25/26 years later) according to the same criteria as the elite trees, in the same stands thinned from below. Elite trees that were selectively thinned had: higher diameter, basal area and volume per tree, higher diameter and basal area increment for a given time period, and lower slenderness coefficients compared to the target trees that were thinned from below at 52 and 69 yr. While diameter increment decreases with age, and differences between elite trees of different ages are clearly delineated, diameter increments of trees thinned from below are not significantly different at 52 and 69 yr. In addition, basal area increment of trees is highest at 69 yr with selective thinning. When thinning from below, there were no significant differences in basal area increments between trees at 69 and 86 yr. Silver lime shows a strong growth response after selective thinning at ages 25/26 and 44 yr. However, our results show that this response is less pronounced when selective thinning begins at 61 yr.

Contrasting climate signals across a Scots pine (Pinus sylvestris L.) tree-ring network in the Middle Volga (European Russia)

Since the late-19th century, the Middle Volga has played a major role in the supplying grains and other agricultural products to European Russia. The study area is located in the south of sub-boreal forest in the north and in the forest-steppe in the south. Due to large seasonal differences in rainfall, agriculture in the region, especially in its southern part, strongly depends on hydroclimate variability. According to climate model forecasts, the frequency and intensity of droughts in the Middle Volga are expected to increase due to ongoing warming. Here we introduce 16 new Scots pine tree ring width (TRW) chronologies (Pinus sylvestris L.) from the region and use a dendroclimatological approach to determine what climatic factors drive radial growth. Our analysis revealed contrasting climate signals across the network of sites with chronologies from the north showing weak correlation with May temperature and precipitation (r = −0.27 and r = 0.28, respectively), while the southern sites demonstrated stronger relationships with climate in the first half of the vegetation season (May to July temperature, r = −0.26 to −0.43; May and July precipitation, r = 0.29–0.35). The northern sites did not demonstrate a strong growth response to the self-calibrated Palmer drought severity index (scPDSI) whereas the southern group was more drought sensitive had a strong drought response and positively correlates with scPDSI for the period from previous July to the current October (r = 0.27–0.56). Based on this strong relationship between southern TRW and scPDSI we reconstruct June-September scPDSI using the most sensitive sites (T04S, T06S, T08S) for the period from 1830 to 2014. The model explains 31% of variance. Our reconstruction shows droughts in 19th century: in 1831–33, 1851, 1853, 1859, 1863–65, 1880, 1891–92, 1897–98 and in 20–21th centuries: in 1906, 1921, 1936, 1939, 1967, 1975, 1996, 2010.

Thinning and Gap Harvest Effects on Soil, Tree and Stand Characteristics in Hybrid Poplar Bioenergy Buffers on Farmland

Linear bioenergy buffers planted with fast-growing trees along field edges are increasingly used to address challenges related to sustainable biomass production, climate change mitigation (i.e., carbon storage and microclimate regulation), water quality protection, and forest habitat connectivity in agricultural landscapes. This study assessed: (1) the extent to which 15 m wide hybrid poplar bioenergy buffers (1666 stems/ha) with closed canopy responded to thinning (diamond pattern of tree removal); (2) the regrowth of poplars from cut stumps following gap harvesting; (3) the effects of harvesting treatments on soil microclimate and nutrient availability; and (4) the spatiotemporal pattern of tree growth in unthinned plots. After three post-thinning years, results showed a strong growth response of seven-year-old hybrid poplar trees to thinning (12% increase in diameter and 30% increase in individual stem volume), accompanied by a slight decline in stand productivity. Gap harvesting was not an effective treatment to regenerate the stand from shoots growing from cut stumps because of the high deer browsing. Overall, thinning had marginal effects on soil nutrients and microclimate, compared with gap harvesting, which increased soil temperature, soil moisture, and the availability of several macro and micronutrients. However, harvest effects on soil nutrients were mostly observed during the first postharvest year, with the exception of soil nitrate, which was lowest in the gap treatment during the second postharvest year. Finally, the spatial pattern observed in tree growth between the buffer rows suggests that other more operational thinning patterns (row or corridor thinning) need to be evaluated in linear buffers.

Deliberation over species change in a monodominant sessile oak stand (Quercetum petraeae Cer. et Jov. 1953., subass. tilietosum) - A case study in ”Djerdap” National Park

Stand structure analysis was conducted before and after natural regeneration (on the same plot) on a site of monodominant sessile oak forest (Quercetum petraeae Cer. et Jov. 1953., subass. tilietosum). In this stage individual old sessile oak trees were still remaining in the stand. Before the regeneration in the 150-yr-old stand in 1992 only sessile oak was rep?resented in the upperstorey. The trees mostly had irregularly developed crowns and reduced growth potential. These were the elements used in planning the regeneration in management plans. Besides the remaining individual old sessile oak trees, silver lime dominates in the young stand in 2017. In the stand structure there is no biological potential of sessile oak trees that could represent the basis for further development because the sessile oak trees are suppressed by silver lime towards the understorey and even the herb layer. Because of the undefined significance of the silver lime in the stand, transient management was prescribed in the man?agement plan so a reconstrucion of the stand should follow in one of the next management periods in order to restore sessile oak on the site as it was suppressed due to an inedequate regeneration procedure. On the basis of the studied stand structure of the young stand, the abandonment of the transient management concept is recommended and introduction of the intensive management approach of slver lime in the current rotation. This was based on the available number of silver lime trees of good quality in the stand, i.e. the aspirants for tending by means of selective thinning and their strong growth response four years after selective thinning. Old sessile oak trees that are still present in the stand are only a simulacrum of the continuity of the current stand with the previous one and they should be removed by means of intensive and rationalized tending of silver lime, and partly integrated in the silver lime stand.

Effect of refeeding on growth performance, blood metabolites and physiological parameters of Dorper × Santa Ines lambs previously subjected to feed restriction

Context Weaned lambs raised on pasture-based systems in Brazil are often subjected to periods of forage shortage, limiting their nutrient and energy intake and, hence, their growth. Fast recovery of lamb body weight is important to the efficiency, sustainability and profitability of these sheep production systems. Aim We evaluated the effects of refeeding on growth performance, blood metabolites and physiological parameters of Dorper × Santa Ines lambs after low and moderate feed restriction, to determine whether there was a compensatory growth response. Methods Twenty-four non-castrated male lambs were assigned to a completely randomised design with three treatments and eight replicates. The trial was conducted in a feedlot and divided into two phases: (1) feed restriction for 64 days, and (2) refeeding for 42 days. In Phase 1, the respective treatments provided energy supplies of 0.481, 0.841 and 1.205 MJ metabolisable energy per kg metabolic weight daily, corresponding to 60% (PR60, moderate) and 30% (PR30, low) feed restriction levels and ad libitum intake. In Phase 2, the lambs in PR60 and PR30 treatments were refed ad libitum. Performance and blood measurements were taken in Phase 1 for the ad libitum treatment, and Phase 2 for PR60 and PR30 treatments. Key results Highest initial and final bodyweights of 32.7 and 41.2 kg were recorded in the PR30 treatment during Phase 2, compared with 23.0 and 36.7 kg averaged over PR60 and ad libitum treatments. Average daily gain did not differ among treatments (276 g/day, on average). Dry matter intake was significantly higher in PR30 than the ad libitum treatment (1406 vs 1158 g/day), with PR60 intermediate (1267 g/day). Serum levels of albumin, urea and creatinine indicated that protein metabolism was strongly affected by the PR60 treatment. High metabolic rate and subsequent rapid growth determined high respiratory rate and rectal temperature in the lambs from PR60 and PR30 treatments. Conclusions Moderate feed restriction relative to maintenance level followed by an ad libitum refeeding period in the feedlot leads to a strong compensatory growth response in Dorper × Santa Ines lambs. Implications In periods of low feed availability, keeping weaned lambs under moderate feed restriction is a good strategy to induce an efficient compensatory growth response in the feedlot during the finishing phase.

Stimulation of dissimilatory sulfate reduction in response to sulfate in microcosm incubations from two contrasting temperate peatlands near Ithaca, NY, USA.

Peatlands are responsible for over half of wetland methane emissions, yet major uncertainties remain regarding carbon flow, especially when increased availability of electron acceptors stimulates competing physiologies. We used microcosm incubations to study the effects of sulfate on microorganisms in two temperate peatlands, one bog and one fen. Three different electron donor treatments were used (13C-acetate, 13C-formate and a mixture of 12C short-chain fatty acids) to elucidate the responses of sulfate-reducing bacteria (SRB) and methanogens to sulfate stimulation. Methane production was measured and metagenomic sequencing was performed, with only the heavy DNA fraction sequenced from treatments receiving 13C electron donors. Our data demonstrate stimulation of dissimilatory sulfate reduction in both sites, with contrasting community responses. In McLean Bog (MB), hydrogenotrophic Deltaproteobacteria and acetotrophic Peptococcaceae lineages of SRB were stimulated, as were lineages with unclassified dissimilatory sulfite reductases. In Michigan Hollow Fen (MHF), there was little stimulation of Peptococcaceae populations, and a small stimulation of Deltaproteobacteria SRB populations only in the presence of formate as electron donor. Sulfate stimulated an increase in relative abundance of reads for both oxidative and reductive sulfite reductases, suggesting stimulation of an internal sulfur cycle. Together, these data indicate a stimulation of SRB activity in response to sulfate in both sites, with a stronger growth response in MB than MHF. This study provides valuable insights into microbial community responses to sulfate in temperate peatlands and is an important first step to understanding how SRB and methanogens compete to regulate carbon flow in these systems.

Effects of low and high red to far-red light ratio on tomato plant morphology and performance of four arthropod herbivores

Changing the spectral composition of light has numerous advantages for the production and quality of horticultural crops. However, changing the light spectrum to stimulate growth can have negative consequences for plant responses to biotic stress. Especially changes in the ratio between red and far-red light (R:FR) have an important effect on plant-herbivore interactions. A low R:FR is indicative of shading and competition for light and induces strong growth responses which are known as shade avoidance responses, including stem elongation and leaf hyponasty. Exposure to low R:FR also inhibits plant defensive responses against biotic agents and increases the performance of pests and pathogens. In this study we tested whether an increase in R:FR, through the supplementation of red light LEDs can be used to reduce the performance of arthropod herbivores. Tomato plants (Solanum lycopersocum) were exposed to three different R:FR ratios; 0.5 (shading), 1.2 (sunlight) and 5.2 (artificial) and infested with either caterpillars (Manduca sexta), spider mites (Tetranychus urticae), aphids (Myzus persicae) or whiteflies (Trialeurodes vaporariorum). Plants exposed to a low R:FR showed clear stem elongation and leaf hyponasty consistent with the shade-avoidance responses, while plants exposed to high R:FR showed reduced stem length and reduced hyponasty. The performance of all four herbivore species was significantly increased after exposure to low R:FR, although the strength of this effect varied between phloem feeding and tissue feeding herbivores. Increasing the R:FR only reduced the performance of the caterpillars and did not significantly affect the other herbivore species. These results indicate that herbivore species with different feeding strategies respond differently to changes in light quality. These findings have implications for the use of LEDs in greenhouse horticulture.

Efficacy of niclosamide on the intra-abdominal inflammatory environment in endometriosis.

Endometriosis, a common gynecological disease, causes chronic pelvic pain and infertility in women of reproductive age. Due to the limited efficacy of current therapies, a critical need exists to develop new treatments for endometriosis. Inflammatory dysfunction, instigated by abnormal macrophage (MΦ) function, contributes to disease development and progression. However, the fundamental role of the heterogeneous population of peritoneal MΦ and their potential druggable functions is uncertain. Here we report that GATA6-expressing large peritoneal MΦ (LPM) were increased in the peritoneal cavity following lesion induction. This was associated with increased cytokine and chemokine secretion in the peritoneal fluid (PF), as well as MΦ infiltration, vascularization and innervation in endometriosis-like lesions (ELL). Niclosamide, an FDA-approved anti-helminthic drug, was effective in reducing LPM number, but not small peritoneal MΦ (SPM), in the PF. Niclosamide also inhibits aberrant inflammation in the PF, ELL, pelvic organs (uterus and vagina) and dorsal root ganglion (DRG), as well as MΦ infiltration, vascularization and innervation in the ELL. PF from ELL mice stimulated DRG outgrowth in vitro, whereas the PF from niclosamide-treated ELL mice lacked the strong stimulatory nerve growth response. These results suggest LPM induce aberrant inflammation in endometriosis promoting lesion progression and establishment of the inflammatory environment that sensitizes peripheral nociceptors in the lesions and other pelvic organs, leading to increased hyperalgesia. Our findings provide the rationale for targeting LPM and their functions with niclosamide and its efficacy in endometriosis as a new non-hormonal therapy to reduce aberrant inflammation which may ultimately diminish associated pain.

Comparison of Japanese and Indian intestinal microbiota shows diet-dependent interaction between bacteria and fungi

The bacterial species living in the gut mediate many aspects of biological processes such as nutrition and activation of adaptive immunity. In addition, commensal fungi residing in the intestine also influence host health. Although the interaction of bacterium and fungus has been shown, its precise mechanism during colonization of the human intestine remains largely unknown. Here, we show interaction between bacterial and fungal species for utilization of dietary components driving their efficient growth in the intestine. Next generation sequencing of fecal samples from Japanese and Indian adults revealed differential patterns of bacterial and fungal composition. In particular, Indians, who consume more plant polysaccharides than Japanese, harbored increased numbers of Prevotella and Candida. Candida spp. showed strong growth responses to the plant polysaccharide arabinoxylan in vitro. Furthermore, the culture supernatants of Candida spp. grown with arabinoxylan promoted rapid proliferation of Prevotella copri. Arabinose was identified as a potential growth-inducing factor in the Candida culture supernatants. Candida spp. exhibited a growth response to xylose, but not to arabinose, whereas P. copri proliferated in response to both xylose and arabinose. Candida spp., but not P. copri, colonized the intestine of germ-free mice. However, P. copri successfully colonized mouse intestine already harboring Candida. These findings demonstrate a proof of concept that fungal members of gut microbiota can facilitate a colonization of the intestine by their bacterial counterparts, potentially mediated by a dietary metabolite.

Phosphate Uptake is Correlated with the Root Length of Celery Plants Following the Association between Arbuscular Mycorrhizal Fungi, Pseudomonas sp. and Biochar with Different Phosphate Fertilization Levels

The interaction between arbuscular mycorrhizal fungi (AM fungi) and Pseudomonas sp. has received considerable attention. The presence of biochar may affect these microorganisms, with subsequent modification of the phosphorus uptake and root morphology, and plant biomass accumulation. This research sought to identify, in the presence or absence of biochar, the effects of the interactions of mycorrhizal fungi and Pseudomonas sp. on the responses of phosphorus (P) and nitrogen (N) uptake and the root length, surface area, and volume of celery plants with low and high P fertilization under different substrate and soil conditions. The results indicate that strong growth responses of celery plants were observed due to the combination of AM fungi, Pseudomonas sp., and biochar with low P fertilization. A strong linear relationship was found between the plant root length and P accumulation in the shoot fraction in the present study. Increased P and N uptake occurred in treatments combining these microorganisms rather than alone, and this increase especially occurred in the presence of biochar. The low availability of P was substantially recovered by the association of these three aspects. The root morphology was greatly influenced by the biochar additives and in combination with AM fungi and Pseudomonas sp. The root colonization rate of AM fungi was increased by the combination of the inoculation of Pseudomonas sp. and biochar rather than AM fungi and/or Pseudomonas sp. These results indicate an accumulating effect of AM fungi, Pseudomonas sp., and biochar exists on the plant growth response and nutrient uptake because of the increasing root length, surface area, and volume, rather than root biomass.

Effects of living mulch on young vine growth and soil in a semi-arid vineyard

Although the use of under-trellis plants as weed control (living mulch) in vineyards has been gaining popularity, its effects on soil quality and especially soil biology have not been well studied. Due to functional trait differences, plants may differ in how they compete with vines, and may also change abiotic and biotic soil properties. A living mulch trial was established in the semi-arid Okanagan valley of British Columbia comparing vine growth as well as soil abiotic and biotic outcomes for four living mulch treatments: buffalo grass (Bouteloua dactyloides), Chewing's fescue (Festuca rubra ssp. commutata), birdsfoot trefoil (Lotus corniculatus), and shepherd's purse (Capsella bursa-pastoris) with two industry standards: herbicide and cultivation. After two seasons, strong vine growth responses were seen that depended on living mulch identity, e.g., reduction in leaf N status with grasses, reduction in leaf water potential with the legume, birdsfoot trefoil. These effects were related to plant-induced changes to soil C:N ratio and soil moisture. Although treatments did not change abundance of the measured fungal guilds in bulk soil, abundance of arbuscular mycorrhizal fungi in vine roots was lowest with birdsfoot trefoil as living mulch. This study may help growers to select living mulch species appropriate for the soil conditions and resource availability of their site.

Growth effects in tropical nickel‐agromining ‘metal crops' in response to nutrient dosing

AbstractAgromining is an emerging technology that utilizes selected ‘metal crops' (= hyperaccumulator plants) to extract valuable target metals from unconventional resources for profit from mineralised soils. Growth characteristics, shoot metal concentrations, and agrominable locations are important considerations in economic agromining. Globally, the greatest potential for nickel (Ni) agromining exists in the tropics. However, the agronomic systems of tropical ‘metal crops' have not been previously tested. Furthermore, it is currently unknown whether nutrient dosing of prospective tropical agromining Ni ‘metal crops’ could possibly cause a shoot Ni‐dilution effect which may ultimately limit economically viable Ni yields. We undertook a pioneering study on Ni uptake and growth responses to nutrient dosing in two promising tropical ‘metal crops' (Phyllanthus rufuschaneyi and Rinorea cf. bengalensis). The experiment consisted of a large randomised block growth trial in large pots over 12 months in Sabah (Malaysia). At 3‐month intervals, the plants were exposed to soluble treatments that altered available concentrations of nitrogen (N), phosphorus (P), and potassium (K). We found strong positive growth responses to N and P additions in P. rufuschaneyi, whereas K additions had negative growth effects. In R. cf. bengalensis, all treatments had positive growth effects. The increases in biomass in response to nutrient dosing did not significantly reduce shoot Ni concentrations in both species, with the exception of N addition in P. rufuschaneyi. This study reveals that Ni uptake and growth responses to nutrient dosing are species‐dependent, primarily influenced by the ecophysiology of the species. Inorganic fertilization could possibly be an important component of the management of local ‘metal crops' to be used in viable commercial agromining in the tropics, but this needs to be tested in the field with different formulations of N, P, and K.

Responses of shoot growth, return flowering, and fruit yield to post-pruning practices and growth regulator application in olive trees

Winter mechanical hedge pruning of olive trees can result in a strong post-pruning shoot growth response and a low return flowering intensity the following year. However, post-pruning practices including tip heading, watersprout thinning, and the application of the growth inhibitor mepiquat chloride (MC) may positively reduce subsequent vegetative growth and promote flowering. Two experiments were carried out with the aim of addressing the following questions: (1) Do these post-pruning practices applied on trees that received simulated mechanical pruning during the winter reduce growth and increase flowering in the spring of the following year?; and (2) What is the optimal MC dose in unpruned trees needed to increase flowering the following spring? In the first experiment, five-year-old olive trees (cv. Arbequina) growing in a fairly low density orchard (208 trees ha−1) were hedge pruned at the end of winter using manual clippers on the east and west sides to simulate mechanical disk pruning, and the post-pruning treatments were applied at the pit hardening stage (early summer). In the second experiment, foliar or soil application of MC was performed at pit hardening in unpruned trees. The results show that tip heading of new shoots led to a large number of lateral shoots that flowered little, or not at all, the following spring. In contrast, the watersprout thinning treatment had sufficient flowering to significantly increase fruit number and yield the following year compared to tip heading. Foliar application of MC (1500 ppm) after winter pruning did not inhibit new shoot growth, return flowering was low, and yield was less than the watersprout thinning treatment. The lack of a post-pruning response to foliar MC was likely related to the dose used (1500 ppm). In the second experiment, a foliar application of MC at 3000 ppm was associated with greater return flowering and yield than an untreated control. In conclusion, thinning of vigorous watersprouts at the pit hardening stage three months after simulated winter mechanical hedge pruning can improve fruit number and yield the next year, especially on a per canopy volume basis. Furthermore, the responses to foliar MC application in unpruned trees suggest that more detailed post-pruning studies with MC application doses in the 2000–3000 ppm range and at additional phenological stages should be performed over several consecutive years to assess whether this practice could be a suitable management tool.

Optimizing Planting Time for Some Selected Commercial Gladiolus Cultivars under Agro-Climatic Conditions of Faisalabad, Pakistan

A field experiment was conducted at Commercial Floriculture Research Area, Institute of Horticultural Sciences, University of Agriculture, Faisalabad, during 2017-18 to evaluate different planting times for quality production of selected gladiolus cultivars. Sixcommercial gladiolus cultivars, viz., Advance, Amsterdam, Essential, Grand Prix, Rose Supreme and White Prosperity were compared by planting at five different planting times from September to November at 15 days interval. Data regarding vegetative growth, flowering and quality parameters were collected. Early sprouting, best vegetative growth and higher quality gladiolus stems were produced when planted in September for all tested cultivars, while among cultivars, ‘Rose Supreme’ proved best for all planting times in the agro-climatic conditions of Faisalabad. Early planting of gladiolus crop in the season with favourably high temperature and longer photoperiod produced strong growth response as compared to late plantings when temperature dropped below 20 °C with photoperiods became shorter. The minimum time to 50% sprouting (7.0 days) along with the highest sprouting percentage (95%), number of leaves per plant (9.6), leaf area (67.6 cm2), plant height (96.4 cm), spike length (73.0 cm), the longest vase life (11.9 d), the best spike quality (8.3) and the greatest number of cormels per clump (30.5) were recorded for September plantation, which gradually decreased with delayed planting. In summary, the best time of planting gladiolus under agro-climatic conditions of Faisalabad, Punjab (Pakistan) is September, which may be adopted by growers for quality stem production.

Adaptive growth response of exotic Elaeagnus angustifolia L. to indigenous saline soil and its beneficial effects on the soil system in the Yellow River Delta, China

Our manuscript showed that Elaeagnus angustifolia L. can be introduced to the Yellow River Delta of China and planting E. angustifolia was beneficial effects on the soil system. The saline soil of the Yellow River Delta of China is not suitable for the growth of crop and afforestation seedlings due to high salt content, high underground water level, and deficiencies in organic matter, nitrogen and phosphorus, which limits urban road greening around the Yellow River Delta. Elaeagnus angustifolia L. (E. angustifolia) is a member of the Elaeagnaceae family, which is a deciduous shrub or small tree. Due to its good resistance, E. angustifolia has been planted widely in the western region of China, and it has been used for wind breaking, landscaping and sand stabilization. Furthermore, E. angustifolia seedlings were introduced to the Yellow River Delta due to its strong stress and adaptive growth response, which were studied in 2014 and 2015. The results revealed that the seedlings of E. angustifolia grew well with high relative growth rates, big crowns, thick basal diameter, thick diameter at the breast height, and many branches, especially during the second year. Planting E. angustifolia on the Yellow River Delta significantly decreased its salt content, and increased its content of organic matter, nitrogen and phosphorus, as well as the number of fungus, bacteria, salt-tolerant bacteria, actinomycetes and salt-tolerant actinomycetes, especially after planting E. angustifolia for two consecutive years. In conclusion, E. angustifolia seedlings can grow well in the saline soil of the Yellow River Delta with a large biomass. In turn, planting E. angustifolia could improve saline soil properties. Hence, E. angustifolia can be a potential local greening tree species.

A Forest Tent Caterpillar Outbreak Increased Resource Levels and Seedling Growth in a Northern Hardwood Forest.

In closed-canopy forests, gap formation and closure are thought to be major drivers of forest dynamics. Crown defoliation by insects, however, may also influence understory resource levels and thus forest dynamics. We evaluate the effect of a forest tent caterpillar outbreak on understory light availability, soil nutrient levels and tree seedling height growth in six sites with contrasting levels of canopy defoliation in a hardwood forest in northern lower Michigan. We compared resource levels and seedling growth of six hardwood species before, during and in the three years after the outbreak (2008–2012). Canopy openness increased strongly during the forest tent caterpillar outbreak in the four moderately and severely defoliated sites, but not in lightly defoliated sites. Total inorganic soil nitrogen concentrations increased in response to the outbreak in moderately and severely defoliated sites. The increase in total inorganic soil nitrogen was driven by a strong increase in soil nitrate, and tended to become stronger with increasing site defoliation. Seedling height growth increased for all species in the moderately and severely defoliated sites, but not in lightly defoliated sites, either during the outbreak year or in the year after the outbreak. Growth increases did not become stronger with increasing site defoliation, but were strongest in a moderately defoliated site with high soil nutrient levels. Growth increases tended to be strongest for the shade intolerant species Fraxinus americana and Prunus serotina, and the shade tolerant species Ostrya virginiana. The strong growth response of F. americana and P. serotina suggests that recurring forest tent caterpillar outbreaks may facilitate the persistence of shade intolerant species in the understory in the absence of canopy gaps. Overall, our results suggest that recurrent canopy defoliation resulting from cyclical forest insect outbreaks may be an additional driver of dynamics in temperate closed-canopy forests.

Grand Fir Nutrient Management in the Inland Northwestern USA

Grand fir (Abies grandis (Douglas ex D. Don) Lindley) is widely distributed in the moist forests of the Inland Northwest. It has high potential productivity, its growth being nearly equal to western white pine, the most productive species in the region. There are large standing volumes of grand fir in the region. Nutritionally, the species has higher foliage cation concentrations than associated conifers, especially potassium (K) and calcium (Ca). In contrast, it has lower nitrogen (N) foliage concentrations, which creates favorable nutrient balance on N-limited sites. Despite concentration differences, grand fir stores proportionally more nutrients per tree than associated species because of greater crown biomass. Although few fertilization trials have examined grand fir specifically, its response is inferred from its occurrence in many monitored mixed conifer stands. Fertilization trials including grand fir either as a major or minor component show that it has a strong diameter and height growth response ranging from 15% to 50% depending in part on site moisture availability and soil geology. Grand fir tends to have a longer response duration than other inland conifers. When executed concurrently with thinning, fertilization often increases the total response. Late rotation application of N provides solid investment returns in carefully selected stands. Although there are still challenges with the post-fertilization effects on tree mortality, grand fir will continue to be an important species with good economic values and beneficial responses to fertilization and nutrient management.