Long-term effects of defoliation on quaking aspen in relation to genotype and nutrient availability: plant growth,phytochemistry and insect performance

This research tested the long-term effects of defoliation on aspen chemistry and growth in relation to genotype and nutrient availability. We grew saplings of four aspen genotypes in a common garden under two conditions of nutrient availability, and subsequently subjected them to two levels of artificial defoliation. Artificial defoliation suppressed plant growth, and saplings of the four genotypes did not show evidence of genetic variation in tolerance to defoliation. Phenolic glycoside concentrations did not respond to defoliation, but were influenced by genotype and nutrient availability. Condensed tannins responded to defoliation and varied among genotypes. Although defoliation affected condensed tannins, plant quality was not altered in a manner important for gypsy moth performance. Regression analyses suggested that phenolic glycoside concentrations accounted for most of the variation in insect performance. The lack of a strong response important for herbivores was surprising given the severity of the defoliation treatment (nearly 100% of leaf area was removed). In this study, plant genotype was of primary importance, nutrient availability was of secondary importance and long-term induced responses were unimportant as determinants of insect performance.     

Influence of elevated ozone and limited nitrogen availability on conifer seedlings in an open-air fumigation system: effects on growth, nutrient content, mycorrhiza, needle ultrastructure, starch and secondary compounds

Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies Karst.) seedlings were exposed to realistically elevated O₃ levels in open‐air experiments over three growing seasons. The total O₃ exposure doses were 1.2 × (1991), 1.5 × (1992) and 1.7 × (1993) ambient levels. During the 1992 and 1993 growing seasons pine and spruce seedlings received two different levels of nitrogen supply. Effects on growth, mycorrhiza formation, needle ultrastructure, primary and secondary compounds were studied. Ozone exposure had only slight effects on biomass production, growth height and nutrient content of studied conifers. Higher nitrogen availability improved growth of the seedlings and resulted in higher concentration of nitrogen in needles. In Scots pine O₃ exposure did not have effects on quantity of total mycorrhizas and short roots, while higher nitrogen availability decreased quantity of mycorrhizas and short roots. In both tree species O₃ exposure induced O₃‐related ultrastructural symptoms, e.g. granulation and dark staining of the chloroplast stroma in the needle mesophyll cells, at both nitrogen availability levels. Ozone exposure and nitrogen availability did not have significant effects on starch concentrations in either tree species. Concentrations of some individual terpenes were higher in O₃‐exposed needles, while concentrations of individual and total resin acids, total phenolics and catechins were not affected by O₃ exposure. Nitrogen availability did not have substantial effects on concentrations of monoterpenes. By contrast, concentrations of some individual and total resin acids were lower in pine needles and higher in spruce needles with higher nitrogen availability, while phenolic concentration in spruce needles decreased at higher nitrogen availability. The results suggest that realistically elevated levels of O₃ in the field can have some negative effects on the mesophyll ultrastructure of conifer needles, but carbon allocation to root and shoot growth and secondary metabolites are not affected substantially.     

Genetic architecture of plastic methyl jasmonate responses in Arabidopsis thaliana

The ability of a single genotype to generate different phenotypes in disparate environments is termed phenotypic plasticity, which reflects the interaction of genotype and environment on developmental processes. However, there is controversy over the definition of plasticity genes. The gene regulation model states that plasticity loci influence trait changes between environments without altering the means within a given environment. Alternatively, the allelic sensitivity model argues that plasticity evolves due to selection of phenotypic values expressed within particular environments; hence plasticity must be controlled by loci expressed within these environments. To identify genetic loci controlling phenotypic plasticity and address this controversy, we analyzed the plasticity of glucosinolate accumulation under methyl jasmonate (MeJa) treatment in Arabidopsis thaliana. We found genetic variation influencing multiple MeJa signal transduction pathways. Analysis of MeJa responses in the Landsberg erecta x Columbia recombinant inbred lines identified a number of quantitative trait loci (QTL) that regulate plastic MeJa responses. All significant plasticity QTL also impacted the mean trait value in at least one of the two "control" or "MeJa" environments, supporting the allelic sensitivity model. Additionally, we present an analysis of MeJa and salicylic acid cross-talk in glucosinolate regulation and describe the implications for glucosinolate physiology and functional understanding of Arabidopsis MeJa signal transduction.     

Resistance and response of <Emphasis Type="Italic">Pinus pinaster</Emphasis> seedlings to <Emphasis Type="Italic">Hylobius abietis</Emphasis> after induction with methyl jasmonate

Experimental induction of plant chemical defences with methyl jasmonate (MeJa) is a valuable tool for understanding the ecology of plant defensive responses. However, few studies have examined whether MeJa-induced defences in conifers are effective against insect herbivores. We studied, in 17 half-sib Pinus pinaster families, (i) the effect of MeJa application on plant growth and on the induction of diterpenoid resin in different sections of the stem; (ii) whether MeJa-induced defences increase the resistance of living pine juveniles against the large pine weevil Hylobius abietis in an in vivo bioassay and (iii) the induction of resin content after weevil wounding. Resin concentration was greater in the upper section of the stem compared with basal sections in both MeJa-induced and non-induced seedlings. Sixty days after MeJa application, treated plants showed 40% greater resin content all along the stem, but reduced height growth compared to control plants. MeJa-induction was effective against the pine weevil, as induced seedlings were 21% less damaged than control plants. Wounding activity by H. abietis produced a strong local defensive response after 48 h, where resin concentration was double that observed in the basal and apical sections not exposed to the insects.     

Genetics and evolution of phenotypic plasticity to nutrient stress in Arabidopsis: drift,constraints or selection?

To better understand the genetic basis and evolution of phenotypic plasticity, we have investigated how the model plant Arabidopsis thaliana (Brassicaceae) responds to nutrient stress. A preliminary experiment showed that two populations that are very closely related genetically tended to respond in a similar fashion to a variety of nutrient stresses. We then asked if there is a general relationship between the degree of genetic differentiation of 16 natural populations of A. thaliana and the similarity in the way they cope with a fundamental nutrient stress, nitrogen limitation. We also grew plants from four mutant lilies known to be affected in nitrogen uptake and metabolism, using their background isogenic line as a control. This last experiment tested whether or not defects in major genes involved in nitrogen bioprocessing affect the intensity or pattern of phenotypic plasticity. We found a high degree of genetic differentiation among populations for the ability to respond to nitrogen stress. However, we detected no significant correlation between the genetic distance among natural populations and the similarity of their response to low nitrogen availability. Since the genetic distances among populations were measured using neutral molecular markers, this suggests that random genetic drift and other non-deterministic evolutionary phenomena were not the driving force shaping differences among populations in the response to stress. On the other hand, several characters were highly correlated in their responses to nitrogen limitation, suggesting either that they were modified by natural selection in a like manner, or that they are influenced by similar genetic constraints (due to either pleiotropy or tight linkage). Finally, the mutants did not differ from the parental wild type strain in their pattern of nitrogen-induced stress response. Therefore, although the genes defective in the mutants are part of the biochemical pathway that uptakes and metabolizes nitrates, we conclude that they are not involved in the control of phenotypic plasticity to nitrogen limitation in this species.     

TDZ induced micropropagation in Cymbidium giganteum Wall. Ex Lindl. and assessment of genetic variation in the regenerated plants

Multiple protocorm-like bodies (PLBs) were induced from pseudostem segments of Cymbidium giganteum using a low concentration (0.909?μM) of TDZ. An exposure time of 8?weeks to TDZ did not adversely affect healthy plantlet development from the induced PLBs when transferred to basal medium. TDZ at higher concentrations, although induced more PLBs, affected subsequent plantlet and root development. Absorption of TDZ was better in a dual phase culture system where a thin layer of the liquid medium overlaid the semi-solid medium. Significant interaction effects of culture phase and TDZ concentrations were seen for the number of shoots, shoot length and root length. Irrespective of the concentration or culture phase, residual effect of TDZ was seen even after 4?weeks of withdrawal from treatment. Comparison of phenotypic characters did not detect any significant variation between the control and TDZ-derived plants. Assessment of molecular variation using 18 RAPD primers detected overall 5.81?% change in the regenerants. Results suggested that seedling-derived pseudostem segments cultured in a dual phase at a low dose of TDZ is most appropriate for inducing healthy plantlets in C. giganteum. Furthermore, a combination of phenotypic and molecular characterization using proper trait/marker and data analysis using a variety of statistical tools provide better insight into genetic fidelity of the regenerants.     

Light and Nutrient Dependent Responses in Secondary Metabolites of Plantago lanceolata Offspring Are Due to Phenotypic Plasticity in Experimental Grasslands

A few studies in the past have shown that plant diversity in terms of species richness and functional composition can modify plant defense chemistry. However, it is not yet clear to what extent genetic differentiation of plant chemotypes or phenotypic plasticity in response to diversity-induced variation in growth conditions or a combination of both is responsible for this pattern. We collected seed families of ribwort plantain (Plantago lanceolata) from six-year old experimental grasslands of varying plant diversity (Jena Experiment). The offspring of these seed families was grown under standardized conditions with two levels of light and nutrients. The iridoid glycosides, catalpol and aucubin, and verbascoside, a caffeoyl phenylethanoid glycoside, were measured in roots and shoots. Although offspring of different seed families differed in the tissue concentrations of defensive metabolites, plant diversity in the mothers'' environment did not explain the variation in the measured defensive metabolites of P. lanceolata offspring. However secondary metabolite levels in roots and shoots were strongly affected by light and nutrient availability. Highest concentrations of iridoid glycosides and verbascoside were found under high light conditions, and nutrient availability had positive effects on iridoid glycoside concentrations in plants grown under high light conditions. However, verbascoside concentrations decreased under high levels of nutrients irrespective of light. The data from our greenhouse study show that phenotypic plasticity in response to environmental variation rather than genetic differentiation in response to plant community diversity is responsible for variation in secondary metabolite concentrations of P. lanceolata in the six-year old communities of the grassland biodiversity experiment. Due to its large phenotypic plasticity P. lanceolata has the potential for a fast and efficient adjustment to varying environmental conditions in plant communities of different species richness and functional composition.     

Variation in flowering size and age of a facultative biennial, Aster kantoensis (Compositae), in response to nutrient availability

Although the flowering of facultative biennials is size-dependent, flowering size varies markedly within a single population as well as among populations. In this study, 15 half-sib families of the facultative biennial Aster kantoensis were grown from seeds at three nutrient levels (low, medium, and high). A significant nutrient × family interaction effect was found for bolting size, and among-family variation in bolting size increased with decreasing nutrient level. Growth from bolting to flowering tended to be greatest at the high nutrient level. Such responses of bolting size and growth from bolting to flowering resulted in an increase in flowering size at the high nutrient level and a significant variation in its reaction norm among families. For flowering age, there was a significant interaction of nutrient × family, and its among-family variation increased with decreasing nutrient levels, as was the case with bolting size. These results indicate that genetic variation in phenotypic plasticity of bolting size with nutrient availability was one cause of the variation in flowering size and age in the A. kantoensis population on the floodplain with the spatially heterogeneous nutrient availability. Moreover, responses of growth from bolting to flowering to nutrient availability could enhance the variation in flowering size.     

The effects of calcium in mediating the inducible morphological defenses of a freshwater snail,Physa acuta

Predation risk is known to induce numerous, often adaptive, plastic changes in the morphology, life history, and behavior of prey. However, little is known about how abiotic factors such as environmental nutrient availability affect these responses. In this experiment, a freshwater pulmonate snail (Physa acuta) was used to determine how predator-induced shell morphology was affected by the availability of an abiotic nutrient important for shell growth (calcium). Each snail was reared individually in a factorial experiment consisting of two predator treatments (chemical cues from crayfish present or absent) and three calcium concentrations (20, 45, or 70 mg/L). Calcium induced larger, heavier, and thicker shells, while predator cues induced heavier and thicker shells. Importantly, the magnitude of the predator effect on shell thickness (i.e., the inducible defense) increased with additional calcium availability. Our results demonstrate the importance of nutrient availability in mediating and limiting the amount of adaptive predator-induced plasticity.     

Nutrient conservation increases with latitude of origin in European<Emphasis Type="Italic"> Pinus sylvestris</Emphasis> populations

Nutrient availability varies across climatic gradients, yet intraspecific adaptation across such gradients in plant traits related to internal cycling and nutrient resorption remains poorly understood. We examined nutrient resorption among six Scots pine (Pinus sylvestris L.) populations of wide-ranging origin grown under common-garden conditions in Poland. These results were compared with mass-based needle N and P for 195 Scots pine stands throughout the species' European range. At the common site, green needle N (r(2)=0.81, P=0.01) and P (r(2)=0.58, P=0.08) concentration increased with increasing latitude of population origin. Resorption efficiency (the proportion of the leaf nutrient pool resorbed during senescence) of N and P of Scots pine populations increased with the latitude of seed origin (r(2) > or = 0.67, P < or = 0.05). The greater resorption efficiency of more northerly populations led to lower concentrations of N and P in senescent leaves (higher resorption proficiency) than populations originating from low latitudes. The direction of change in these traits indicates potential adaptation of populations from northern, colder habitats to more efficient internal nutrient cycling. For native Scots pine stands, results showed greater nutrient conservation in situ in cold-adapted northern populations, via extended needle longevity (from 2 to 3 years at 50 degrees N to 7 years at 70 degrees N), and greater resorption efficiency and proficiency, with their greater resorption efficiency and proficiency having genotypic roots demonstrated in the common-garden experiment. However, for native Scots pine stands, green needle N decreased with increasing latitude (r(2)=0.83, P=0.0002), and P was stable other than decreasing above 62 degrees N. Hence, the genotypic tendency towards maintenance of higher nutrient concentrations in green foliage and effective nutrient resorption, demonstrated by northern populations in the common garden, did not entirely compensate for presumed nutrient availability limitations along the in situ latitudinal temperature gradient.     

Leaf optical responses to light and soil nutrient availability in temperate deciduous trees

Leaf optical parameters influence light availability at the cellular, leaf, and canopy scale of integration. While recent studies have focused on leaf optical responses to acute plant stress, the effects of changes in plant resources on leaf optics remain poorly characterized. We examined leaf optical and anatomical responses of five temperate deciduous tree species to moderate changes in nutrient and light availability. Spectral reflectance in the visible waveband generally increased at high light, but decreased with increased nutrient availability. Patterns of both spectral reflectance and absorptance were primarily determined by chlorophyll concentration although carotenoid concentration was also influential. While most anatomical features did not explain residual variation in reflectance, cuticle thickness was significantly related to reflectance at complementary angles compared to the angle of incidence. Absorptance did not change with light environment; however, absorption efficiency per unit biomass increased by approximately 40% under low light, due to reduced leaf mass per area. We conclude that changes in resource availability differentially influence leaf optical properties and that such changes are driven primarily by changes in pigment concentrations. The magnitude of leaf optical responses to moderate changes in resource availability was comparable to those of acute stress responses and varied among species.     

Long term effect of liming and fertilization on ectomycorrhizal colonization and tree growth in old Scots pine (Pinus sylvestris L.) stands

In this study, we surveyed the long term effects of liming and fertilizing in old Scots pine stands on the ectomycorrhiza (ECM) colonization, tree growth and needle nutrient concentration 35 years later. Four mature stands of Scots pine on low productive mineral soil were limed in 1959 and 1964 with total doses of limestone ranging from 3 to 15 Mg ha^?1 and fertilized with nitrogen (N) in 1970. Thirty-five years after the first liming treatment, all stands were analysed for tree growth and needle nutrient concentrations and two of the stands were also analysed for ECM colonization. ECM colonization increased significantly with liming from 61.5% in the control plots to 88% in the plot with the highest limestone dose. ECM colonization increased with increasing pH in the humus layer from 62% colonization at pH?=?3.5 to 90% at pH?=?6.5 and decreased with increasing amount of extractable phosphorus (P) in the humus. Liming did not affect the frequencies of different ECM morphotypes or dead short root tips, the fine root biomass or necromass. ECM colonization was uncorrelated with needle nutrient concentrations or tree increment. Liming did not significantly affect tree growth. However, nutrient concentrations of current-year needles were affected by prior liming. Ca concentrations in current-year needles increased from approximately 15 mg g^?1 in control treatments to more than 30 mg g^?1 in limed plots, whereas concentrations of Mn, Al, Fe, and in two stands, B, decreased due to liming. In conclusion, liming with doses up to 15 Mg ha^?1 was detectable in stands 35 years after treatment. The liming significantly increased the ECM colonization of Scots pine fine roots, increased the needle nutrient concentration of Ca and decreased the needle concentrations of Mn, Al, and Fe.     

Phenotyping tree resistance to a bark‐chewing insect,the pine weevil Hylobius abietis

Breeding for resistance to forest pests and pathogens is emerging as a promising tool for minimising the impact of the increasing biotic threats that our forests are experiencing as a consequence of global change. Efficient phenotyping protocols of resistance are urgently needed. Here we present the results of two experiments aimed to determine whether the variation in resistance to the pine weevil Hylobius abietis, a harmful pest of European conifers, can be inferred by nondestructive bioassays using excised plant material collected in forest genetic trials. Weevil damage and amount of nonvolatile resin induced by weevil feeding were assessed in young trees and in branches of adult trees using several phenotyping procedures (bioassays using either living trees, excised plant material and cut stem twigs) on four pine species (Pinus pinaster, P. radiata, P. sylvestris and P. pinea). Half of the plants were previously induced with methyl jasmonate (MJ), a treatment that is known to affect resistance to the pine weevil. In Experiment 1, living and excised plants showed parallel results: MJ treatment significantly reduced weevil damage, and saplings responded to weevil damage locally increasing the nonvolatile resin (NVR) in the stems proportionally to the damage suffered. This response was, however, slightly lower in excised than in living saplings. On the contrary, patterns of weevil feeding on stem twigs completely departed from those observed in living and excised seedlings. Moreover, cut stem twigs were unable to respond to weevil feeding increasing NVR according to the weevil damage. In Experiment 2, assessment of weevil damage on excised branches explained around 50% of variation in damage on living branches. This relationship became much more pronounced (R² = 0.81) when explored at the mean treatment level; branch manipulation did not alter the patterns of variation in resistance across pine species or MJ treatments. Irrespective of the assessment procedure, MJ consistently decreased weevil damage in all pine species, with larger reduction in weevil damage in stone and maritime pine than in radiata and Scots pine. Radiata pine was the most resistant while Scots pine was the most susceptible to the pine weevil. Overall, results suggest that using excised plant material is an operative alternative for phenotyping weevil resistance whenever care is taken to maintain the functionality of the excised plant material. This will allow taking advantage of multiple available conifer genetic trials to deepen the ecological genetics of resistance to the pine weevil and to screen for resistance without compromising the long‐term utility of those genetic trials.     

Effects of light and nutrient availability on the growth,allocation, carbon/nitrogen balance,phenolic chemistry,and resistance to herbivory of two freshwater macrophytes

Phenotypic responses of Potamogeton amplifolius and Nuphar advena to different light (7% and 35% of surface irradiance) and nutrient environments were assessed with field manipulation experiments. Higher light and nutrient availability enhanced the growth of P. amplifolius by 154% and 255%, respectively. Additionally, biomass was allocated differently depending on the resource: high light availability resulted in a higher root/shoot ratio, whereas high nutrient availability resulted in a lower root/shoot ratio. Low light availability and high nutrient availability increased the nitrogen content of leaf tissue by 53% and 40% respectively, resulting in a 37% and 31% decrease in the C/N ratio. Root nitrogen content was also increased by low light and high nutrient availability, by 50% (P=0.0807) and 77% respectively, resulting in a 20% and 40% decrease in root C/N ratio. Leaf phenolics were significantly increased 72% by high light and 31% by high nutrient availability, but root phenolic concentrations were not altered significantly. None of these changes in tissue constituents resulted in altered palatability to crayfish. N. advena was killed by the same high nutrient treatment that stimulated growth in P. amplifolius, preventing assessment of phenotypic responses to nutrient availability. However, high light availability increased overall growth by 24%, but this was mainly due to increased growth of the rhizome (increased 100%), resulting in a higher root/shoot ratio. High light tended to increase the production of floating leaves (P=0.09) and significantly decreased the production of submersed leaves. High light availability decreased the nitrogen content by 15% and 25% and increased the phenolic concentration by 88% and 255% in floating and submersed leaves, respectively. These differences in leaf traits did not result in detectable differences in damage by herbivores.     

Growth and nutritional response of Pinus pinaster after a large pine weevil (Hylobius abietis) attack

Hylobius abietis is an important pest of coniferous plantations in Europe, to which high mortality, stem deformities, and growth loss are typically attributed. In pine trees, as in other long-lived organisms, there is uncertainty regarding the long-term costs of short-term resistance against invading organisms. We examined the nutritional status of Pinus pinaster after a 2-year long H. abietis attack, measuring needle and phloem N and P concentrations, and the impact of the damage on subsequent growth, survival, and stem deformities over a period of 5 years. The study sites were a P. pinaster family × fertilization trial, and a neighbouring twin trial with similar climate and soil characteristics that was not attacked. Growth losses after the H. abietis attack were important (up to 40%), but restricted to the first years after the attack. Five years after the attack, the annual height increment of pines in the attacked stand was not related to the initial damage suffered, and plants showed regular stems, normal leader dominance, and regular height after 5 years. These findings suggest strong compensatory growth in P. pinaster and indicate relatively high tolerance to the large pine weevil. Needle nutrient concentrations in the healthy stand were, as expected, significantly greater in experimentally fertilized plants, and they were linearly related to those in phloem showing equilibrated stoichiometry both for nitrogen (r = 0.86; P < 0.01; N = 25) and phosphorus (r = 0.84; P < 0.01; N = 25). However, at the attacked stand, nutrient concentrations in the needles did not follow the experimentally manipulated nutrient availability in soils, and phosphorus concentration in the needles was unexpectedly not related to those in the phloem. The pine seedlings attacked by H. abietis showed altered potential of allocating nutrients to their tissues according to the nutrient availability existing in the soil, as well as altered stoichiometry in N and P concentrations among phloem and leaves. Maritime pine seems to be tolerant to the pine weevil attack, at least in the conditions of this study, where pine weevil damage caused a deep alteration of nutrient allocation and nutritional status. Further research is needed to elucidate to what extent altered nutrient allocation may be part of an induced response to the attack or just derived from the vascular injury caused by the weevil wounding in the phloem.     

Water Supply Changes N and P Conservation in a Perennial Grass Leymus chinensis

Changes in precipitation can influence soil water and nutrient availability, and thus affect plant nutrient conservation strategies. Better understanding of how nutrient conservation changes with variations in water availability is crucial for predicting the potential influence of global climate change on plant nutrient-use strategy. Here, green-leaf nitrogen (N) and phosphorus (P) concentrations, N- and P-resorption proficiency (the terminal N and P concentration in senescent leaves, NRP and PRP, respectively), and N- and P-resorption efficiency (the proportional N and P withdrawn from senescent leaves prior to abscission, NRE and PRE, respectively) of Leymus chinensis (Trin.) Tzvel., a typical perennial grass species in northern China, were examined along a water supply gradient to explore how plant nutrient conservation responds to water change. Increasing water supply at low levels (< 9000 mL/year) increased NRP, PRP and PRE, but decreased green-leaf N concentration. It did not significantly affect green-leaf P concentration or NRE. By contrast, all N and P conservation indicators were not significantly influenced at high water supply levels (> 9000 mL/year). These results indicated that changes in water availability at low levels could affect leaf-level nutrient characteristics, especially for the species in semiarid ecosystems. Therefore, global changes in precipitation may pose effects on plant nutrient economy, and thus on nutrient cycling in the plant-soil systems.     

Variation in natural selection for growth and phlorotannins in the brown alga Fucus vesiculosus

Directional selection for plant traits associated with resistance to herbivory tends to eliminate genetic variation in such traits. On the other hand, balancing selection arising from trade-offs between resistance and growth or spatially variable selection acts against the elimination of genetic variation. We explore both the amount of genetic variation and variability of natural selection for growth and concentration of phenolic secondary compounds, phlorotannins, in the brown alga Fucus vesiculosus. We measured variation in selection at two growing depths and two levels of nutrient availability in algae that had faced two kinds of past growing environments. Genetic variation was low for growth but high for phlorotannins. The form and strength of selection for both focal traits depended on the past growing environment of the algae. We found strong directional selection for growth rate in algae previously subjected to higher ultraviolet radiation, but not in algae previously subjected to higher nutrient availability. Stabilizing selection for growth occurred especially in the deep growing environment. Selection for phlorotannins was generally weak, but in some past-environment-current-environment combinations we detected either directional selection against phlorotannins or stabilizing selection. Thus, phlorotannins are not selectively neutral but affect the fitness of F. vesiculosus. In particular, there may be a fitness cost of producing phlorotannins, but the realization of such a cost varies from one environment to another. Genetic correlations between selective environments were high for growth but nonexistent for phlorotannins, emphasizing the high phenotypic plasticity of phlorotannin production. The highly heterogeneous selection, including directional, stabilizing, and spatially variable selection as well as temporal change in selection due to responses to past environmental conditions, probably maintains a high amount of genetic variation in phlorotannins. Such variation provides the potential for rapid evolutionary response of phlorotannins under directional selection.     

Potential ecosystem-level effects of genetic variation among populations of Metrosideros polymorpha from a soil fertility gradient in Hawaii

This study assessed intrinsic differences in tissue quality and growth rate among populations of Metrosideros polymorpha native to sites with a range of soil fertilities. We collected seedlings from three Hawaiian mesic forests that were either phosphorus-limited, nitrogen-limited, or relatively fertile. These individuals were grown in a common garden under a factorial high/low, N/P fertilization regime for 1.5 years and then harvested to determine genetic divergence; aboveground growth rate; and lignin, N, and P concentrations in leaves and roots. Allozyme analyses indicated that the three groups had genetically diverged to some degree (genetic distance = 0.036-0.053 among populations). Relative growth rate did not differ significantly among the populations. Senescent leaves from the fertile-site population had the highest N concentrations (due to low N resorption) and had lower lignin concentrations than plants from the N-limited site. Across treatments, P concentrations in senescent leaves were highest in plants from the fertile and P-limited site. Root tissue quality did not generally differ significantly among populations. Since decomposition rate of senescent leaves in this system is related positively to N concentration and negatively to lignin concentration, senescent leaves from the fertile-site population may have a genetic tendency toward faster decay than the others. The intrinsic qualities of the three populations may provide positive feedbacks on nutrient cycling at each site-nutrient availability may be raised to some degree at the fertile site, and reduced at the N- or P-limited sites. Our results suggest that even a small degree of genetic differentiation among groups can influence traits related to nutrient cycling.     

Responses of Pinus clausa, Pinus serotina and Pinus taeda seedlings to anaerobic solution culture. II. Changes in tissue nutrient concentration and net acquisition

Fifteen or 30 days of anaerobic growth conditions significantly reduced shoot and root nitrogen, potassium, phosphorus, iron and manganese concentrations in seedlings of pond pine ( Pinus serotina Michx.), sand pine [ P. clausa (Engelm.) Sarg.] and drought-hardy and wet-site loblolly pine ( P. taeda L.) grown in a culture system using non-circulating, continuously flowing solution. Calcium and shoot magnesium levels were least affected by anaerobic growth conditions – largely reflecting the passive nature of their uptake. Shoot and root nutrient content (mg nutrient pot^-1) followed similar trends, with wet-site loblolly and pond pine seedlings least affected by anaerobic solution culture. Shoot biomass of wet-site loblolly and pond pine seedlings was not affected by anaerobiosis, suggesting an increase in shoot nutrient utilization efficiency. Root biomass was significantly reduced by 15 or 30 days of anaerobiosis, with sand pine exhibiting the largest reduction in root dry weight (57%).
These results suggest that anaerobiosis interferes with net nutrient acquisition, even under the high nutrient conditions provided by solution culture. Sand pine suffered the largest reductions in shoot and root biomass and nutrient concentrations, showing earlier symptoms of waterlogging injury and nutrient stress than drought-hardy loblolly pine seedlings. Whether net nutrient acquisition decreased because of the reduction in root surface area available for absorption and/or reduced uptake efficiency cannot be ascertained from these data.