Interspecific and intraspecific variation in tree seedling survival: effects of allocation to roots versus carbohydrate reserves

We examined interspecific and intraspecific variation in tree seedling survival as a function of allocation to carbohydrate reserves and structural root biomass. We predicted that allocation to carbohydrate reserves would vary as a function of the phenology of shoot growth, because of a hypothesized tradeoff between aboveground growth and carbohydrate storage. Intraspecific variation in levels of carbohydrate reserves was induced through experimental defoliation of naturally occurring, 2-year-old seedlings of four northeastern tree species –Acer rubrum, A. saccharum, Quercus rubra, and Prunus serotina– with shoot growth strategies that ranged from highly determinate to indeterminate. Allocation to root structural biomass varied among species and as a function of light, but did not respond to the defoliation treatments. Allocation to carbohydrate reserves varied among species, and the two species with the most determinate shoot growth patterns had the highest total mass of carbohydrate reserves, but not the highest concentrations. Both the total mass and concentrations of carbohydrate reserves were significantly reduced by defoliation. Seedling survival during the year following the defoliation treatments did not vary among species, but did vary dramatically in response to defoliation. In general, there was an approximately linear relationship between carbohydrate reserves and subsequent survival, but no clear relationship between allocation to root structural biomass and subsequent survival. Because of the disproportionate amounts of reserves stored in roots, we would have erroneously concluded that allocation to roots was significantly and positively related to seedling survival if we had failed to distinguish between reserves and structural biomass in roots. Received: 14 December 1999 / Accepted: 2 June 1999     

Effect of mycorrhizae on seedlings of six endemic Mimosa L. species (Leguminosae–Mimosoideae) from the semi-arid Tehuacán–Cuicatlán Valley, Mexico

Mimosa is an important genus of legumes in arid and semi-arid ecosystems of the world, but scarce information is available about its interaction with microbial symbionts. In Mexico, there are no reports on the responsive of endemic Mimosa species to arbuscular mycorrhizal (AM) fungal colonization. In this study, the AM association with seedlings of six endemic Mimosa species, M. adenantheroides, M. calcicola, M. lacerata, M. luisana, M. polyantha and M. texana var. filipes, is reported. Field conditions were simulated in the greenhouse. Seeds were collected from plants and soil from the localities where the species occur within the semi-arid Tehuacán–Cuicatlán Valley, Mexico. Four treatments were applied: (1) control, (2) benomyl, (3) phosphorus, and (4) benomyl plus phosphorus. Mycorrhizal seedlings of five species, M. adenantheroides, M. lacerata, M. luisana, M. polyantha and M. texana var. filipes, showed a higher shoot and total dry weight than non-mycorrhizal seedlings. The only species that did not show any difference between mycorrhizal and non-mycorrhizal seedling performance was M. calcicola. M. luisana, M. polyantha and M. texana var. filipes had a higher root/shoot ratio; in general, benomyl treatments promoted seedling biomass allocation to the root, while control, phosphorus and benomyl plus phosphorus treatments decrease root/shoot ratio. Shoot P content was significantly higher in mycorrhizal than in non-mycorrhizal plants, although no significant differences were found for M. adenantheroides in all treatments. Benomyl and benomyl plus phosphorus treatments reduced AM colonization in all the species under study. Benomyl significantly reduced the number of N₂-fixing root nodules, while the phosphorus treatment generally stimulated nodulation. The species M. lacerata, M. luisana, M. polyantha and M. texana var. filipes had a high mycorrhizal dependency index indicating that plant growth was strongly increased by arbuscular mycorrhiza activity. Our results indicate that the response of all Mimosa species to mycorrhization was highly variable. To our knowledge, this is the first report about the effect of AM fungi and phosphorus on Mimosa species, which may be useful in biodiversity and soil conservation programs.     

Growth and biomass allocation of shrub and grass seedlings in response to predicted changes in precipitation seasonality

Anthropogenic emissions contribute to an annual 0.5% increase in atmospheric CO₂. As global CO₂ levels increase, regional precipitation patterns will likely be altered. Our primary objective was to determine whether a reduction in summer precipitation or an increase in winter/spring precipitation, predicted by global climate change models, will favor the establishment of C₄ grasses or C₃ shrubs in southern savannas. Our secondary objective was to determine how defoliation and microsite light availability interact with altered precipitation regimes to influence grass and shrub seedling growth and biomass allocation patterns. Seedlings of 3 shrub species (Prosopis glandulosa var. glandulosa, Acacia berlandieri, and A. greggii var. wrightii) and 3 grass species (Aristida purpurea var. wrightii, Setaria texana, and Stipa leucotricha) were watered based on probable changes in precipitation in a CO₂ enriched atmosphere (0.6, 0.8, and 1.0 current ambient summer precipitation and 1.0, 1.15, and 1.30 current winter/spring precipitation). Seedlings were defoliated at 3 levels (non-defoliated, single defoliation, and repeated defoliation) within 2 levels of microsite light availability (100 and 50% ambient). Defoliation significantly reduced total shrub and grass seedling biomass. Reducing light availability decreased shrub seedling root:shoot ratio, but total biomass was not significantly affected. Grass seedling biomass and root:shoot ratio decreased when light availability was reduced. Changing the seasonality of precipitation by reducing summer rainfall or increasing winter/spring rainfall did not significantly influence growth or biomass allocation of grass and shrub seedlings in a semiarid savanna. Microsite variations in defoliation intensity and light availability influence seedling growth and biomass allocation more than changing seasonality of precipitation. Shrub and grass seedling establishment and growth on semiarid rangelands are already limited by summer precipitation, so a further reduction as proposed by climate change models will have a limited impact on seedling dynamics.     

Influence of mineral nutrient availability on growth of tree seedlings from the tropical deciduous forest

The effects of different nutrient availabilities on growth and biomass partitioning in seedlings from the tropical deciduous forest in Mexico were compared. The tree species studied were Heliocarpus pallidus, a species associated with disturbed parts of the forest, and Caesalpinia eriotachys, Jacquinia pungens and Recchia mexicana, species from mature, undisturbed habitats. The tropical deciduous tree seedlings were grown in pure silica sand for 50 days inside growth chambers under four nutrient regimes; 5, 20, 100 and 200% Long Ashton nutrient solutions. Data showed contrasting responses among species to different nutrient availabilities. Except Jacquinia pungens, all species had increased growth and productivity as nutrient level increased from 5 to 100%; however, no significant differences in these parameters were detected between 100 and 200% in all species. Compared with mature forest species, pioneer species showed higher variations in biomass production, relative growth rate and net assimilation rate. In contrast to mature forest species, root/ shoot ratios in Heliocarpus pallidus were greater and thus showed higher biomass allocation to roots when nutrient supply was limited. This response suggests higher phenotypic plasticity in pioneer species. Species from mature parts of the forest (Caesalpinia eriostachys, Recchia mexicana) showed less dependency on nutrient supply than pioneer species. These responses appear to support observations from studies with temperate plants investigating growth responses to soil fertility.     

Seedling morphological characteristics and seasonal growth of indigenous tree species transplanted into four plantations in South China

The successful transplantation of indigenous tree seedlings into established plantations requires an understanding of the conditions required by the seedlings. We evaluated seedling morphological characteristics and seasonal growth of three indigenous tree species (Castanopsis chinensis, Michelia chapensis, and Psychotria rubra) that were transplanted into four plantations (eucalyptus, mixed-native, mixed-legume, mixed-conifer) in South China; in each plantation, two treatments (understory vegetation and litter retained or removed) were applied before the seedlings were transplanted. Seedling leaf morphological characteristics and biomass allocation were determined at the end of the experiment, and seedling relative growth rate as indicated by change in height (RGRh) was determined during the experiment. Whether understory vegetation and litter were removed or retained, RGRh tended to be higher in the wet season than in the dry season. Leaf morphological characteristics and biomass allocation were significantly affected by species identity. The effect of the understory vegetation and litter treatments on seedling morphological characteristics such as specific leaf area, leaf area ratio, and root weight to total biomass ratio depended on species identity. Redundancy analysis showed that the three transplanted indigenous species differed in their responses to light conditions according to their tolerance to shade, and also differed in their responses to soil physical and chemical properties. Based on seedling seasonal growth patterns and morphological responses, we suggest that forest managers attempting to introduce seedlings of indigenous tree species should artificially supply water to increase seedling growth in the dry season. Also, the introduced tree species should be selected depending on the nature of the plantation; for example, C. chinensis and M. chapensis seedlings can be transplanted into mixed-legume plantations. Additionally, fertilizer with potassium and nitrogen should be used to improve seedling performance.     

Nutrient deprivation improves field performance of woody seedlings in a degraded semi-arid shrubland

The performance of planted seedlings in drylands is affected by seedling morphological and physiological traits. Recent studies support a positive relationship between seedling size and field performance. However, exceptions to this paradigm suggest that this relationship may be dependent on species and degree of stress. To test the hypothesis that small seedlings would be favored under harsh semi-arid conditions over large seedlings, we produced seedlings of five Mediterranean woody species (Pistacia lentiscus, Quercus coccifera, Rhamnus lycioides, Rhamnus alaternus and Tetraclinis articulata) under contrasted fertilization regimes, and evaluated their performance after planting in a semi-arid area. Seedlings were cultivated under full sunlight and received either slow release fertilizer or bi-weekly applications of complete nutrient solution, diluted fertirrigation, or nutrient solutions containing no nitrogen or no phosphorus. Fertilization had a strong effect on nutrient status, above and belowground biomass accumulation, and biomass allocation patterns. Root: shoot ratio was higher in nitrogen- and phosphorus-deficient seedlings than in seedlings receiving complete nutrient solution or slow-release fertilizer. One year after planting, seedling survival was negatively correlated with plant size for all species. The effect of nutritional regime on field survival decreased over the 2 following years. Our results show that nutrient-deprived seedlings are more likely to establish under semi-arid conditions than well-fertilized seedlings, suggesting that morphological and functional characteristics associated with nutrient deficiency may outbalance the scarcity of nutrient reserves in seedling tissues.     

Soil type affects seedling shade response at low light for two Inga species from Costa Rica

Distributions of many humid tropical tree species are associated with specific soil types. This specificity most likely results from processes at the seedling stage, but light rather than nutrient levels is generally considered the dominant limitation for seedling growth in the tropical forest understory. If nutrients are limiting and allocation to belowground resources differs, seedling growth responses to shade should also differ. Here we tested the effects of soil type and light environment on the seedling growth of two canopy tree species in the genus Inga with different soil-type and light-environment affinities as adults. Inga alba is a shade-tolerant soil generalist and I. oestediana is a light-demanding soil specialist. We used four native soils and three light levels (1 and 5% of full sun in shade houses and the forest understory). All growth variables were greatest in 5% full sun, with highest growth rates for the light-demanding soil-type specialist. Soil type significantly affected growth parameters, even at the lower light levels. The specialist grew best on the soils with the most soil phosphorus where adult trees typically occur. Leaf tissue nitrogen:phosphorus ratios suggest increased phosphorus limitation in the low phosphorus soils and with increased light level. Light and soil interacted to significantly affect seedling biomass allocation, growth, and net assimilation rates, indicating that the seedling shade responses were affected by soil type. Seedlings growing on high nutrient soil allocated less to roots and more to photosynthetic tissue. Adult distributions of these two Inga species may be a result of the different growth rates of seedlings in response to the interactive effects of light and soil.     

Performance of germinating tree seedlings below and above treeline in the Swiss Alps

The germination and early survival of tree seedlings is a critical process for the understanding of treeline dynamics with ongoing climate change. Here we analyzed the performance of 0–4 year-old seedlings of seven tree species at three sites above and below the current altitudinal treeline in the Swiss Central Alps near Davos. Starting from sown seeds, we monitored the seedling performance as proportions of living seedlings, seedling shoot height growth, and biomass allocation over 4 years to examine changes along an elevational gradient. We evaluated the relative importance of the environmental factors soil temperature, light conditions, water use efficiency, and nitrogen availability on seedling performance. During the 4 years, the proportions of living seedlings differed only slightly along the elevational gradient even in species currently occurring at lower elevations. Microsite-specific soil temperature and light availability had only little effect on the proportion of living seedlings and seedling biomass across the elevational gradient. Conversely, seedling biomass and biomass allocation correlated well with the foliar stable nitrogen isotope abundance (δ ¹⁵N) that was used as an indicator for nitrogen availability. Collectively, our results suggested that the early establishment of seedlings of a variety of tree species in the treeline ecotone was not limited by current climatic conditions even beyond the species’ actual upper distribution limit. Nitrogen dynamics appeared to be an important environmental co-driver for biomass production and allocation in very young tree seedlings.     

Highly local environmental variability promotes intrapopulation divergence of quantitative traits: an example from tropical rain forest trees

Background and Aims

In habitat mosaics, plant populations face environmental heterogeneity over short geographical distances. Such steep environmental gradients can induce ecological divergence. Lowland rainforests of the Guiana Shield are characterized by sharp, short-distance environmental variations related to topography and soil characteristics (from waterlogged bottomlands on hydromorphic soils to well-drained terra firme on ferralitic soils). Continuous plant populations distributed along such gradients are an interesting system to study intrapopulation divergence at highly local scales. This study tested (1) whether conspecific populations growing in different habitats diverge at functional traits, and (2) whether they diverge in the same way as congeneric species having different habitat preferences.

Methods

Phenotypic differentiation was studied within continuous populations occupying different habitats for two congeneric, sympatric, and ecologically divergent tree species (Eperua falcata and E. grandiflora, Fabaceae). Over 3000 seeds collected from three habitats were germinated and grown in a common garden experiment, and 23 morphological, biomass, resource allocation and physiological traits were measured.

Key Results

In both species, seedling populations native of different habitats displayed phenotypic divergence for several traits (including seedling growth, biomass allocation, leaf chemistry, photosynthesis and carbon isotope composition). This may occur through heritable genetic variation or other maternally inherited effects. For a sub-set of traits, the intraspecific divergence associated with environmental variation coincided with interspecific divergence.

Conclusions

The results indicate that mother trees from different habitats transmit divergent trait values to their progeny, and suggest that local environmental variation selects for different trait optima even at a very local spatial scale. Traits for which differentiation within species follows the same pattern as differentiation between species indicate that the same ecological processes underlie intra- and interspecific variation.     

Seedling growth variation in response to sand burial in four <Emphasis Type="Italic">Artemisia</Emphasis> species from different habitats in the semi-arid dune field

We compared seedling growth of four Artemisia species dominated at different habitats to determine whether interspecific seedling growth variation of a same genus in tolerance to burial can be used to explain plant distribution in the sand dune field. Interdune lowland species, Artemisia gmelinii, stabilized dune species, A. frigida, semi-stabilized dune species, A. halodendron, and active dune species, A. wudanica were selected. Seedlings grown for 3 weeks were treated at five burial depths for three burial times in pot experiments. Species from the habitats with little burial had smaller survival rate, dry weight and stem elongation speed than those from the habitats with intensive burial when buried. Furthermore, when buried, the former tended to adjust biomass allocation between shoot and root and produce adventitious buds, while the latter tended to maintain a constant root:shoot ratio and produce adventitious roots. We conclude that (1) seedlings of species with a long evolutionary history of exposure to sand burial (from the active sand dune), show quicker stem growth when buried than do seedlings of species from the habitats with little or no sand burial; (2) seedlings of species which do not change root:shoot ratio might be more tolerant of sand burial than those do; (3) seedlings of species from the habitats with intensive sand burial is prone to produce adventitious roots and seedlings of species from the habitats with little or no sand burial tend to produce adventitious buds when buried.     

Longleaf and loblolly pine seedlings respond differently to soil compaction,water content,and fertilization

Aims

Longleaf pine (Pinus palustris Mill.) is being restored across the U.S. South for a multitude of ecological and economic reasons, but our understanding of longleaf pine’s response to soil physical conditions is poor. On the contrary, our understanding of loblolly pine (Pinus taeda L.) root and shoot growth response to soil conditions is well established.

Methods

We performed a comparative greenhouse study which modeled root length density, total seedling biomass, and the ratio of aboveground:belowground mass as functions of volumetric water content, bulk density and soil fertility (fertilized or not).

Results

Root length density was about 35 % greater in longleaf pine seedlings compared to loblolly pine seedlings, and was reasonably well modeled (R ²?=?0.54) for longleaf pine by bulk density (linear), volumetric water content (quadratic), soil fertility, and the interactions of bulk density, volumetric water content, species, and soil fertility. The aboveground:belowground mass ratio (ABR) increased at both extremes of water content.

Conclusions

This research indicates that young longleaf pine seedling root systems respond more negatively to extremes of soil physical conditions than loblolly pine, and compacted or dry loamy soils should be ameliorated in addition to normal competition control, especially on soils degraded by past management.     

Spatial variation of plant communities and shoot Cu concentrations of plant species at a timber treatment site

Plant species, spatial variability in plant diversity and vegetation cover were recorded at a French timber treatment site with Cu-contaminated soils (65–2600 mg/kg). Shoot biomass, shoot Cu concentration and accumulation were determined for each plant species found on 168 quadrats with increasing total Cu in soil and soil solution. A total of 91 species occurred on the site including four considered as invasive (Cyperus eragrostis, Phytolacca americana, Senecio inaequidens, and Sporobolus indicus). Species richness, Shannon index, vegetation cover and plant biomass decreased as soil Cu increased. At low soil Cu, members of the Poaceae were most frequent followed by Fabaceae, Rosaceae, and Asteraceae. At high soil Cu, Poaceae were again most frequent. Species known to form Cu-tolerant populations, i.e. Agrostis capillaris, A. stolonifera and Rumex acetosella were present. Shoot Cu concentration and accumulation were higher in plants growing in the most contaminated soils. At 2142 mg Cu/kg soil, shoot Cu accumulation peaked at 6 mg Cu/m² in A. capillaris, and its shoot Cu concentration (364 mg Cu/kg dry weight) exceeded the fodder Cu threshold for domestic livestock. In less Cu-contaminated soils some candidates were identified for sustainable phytoremediation with a potential financial return.     

Soil influence on the performance of 26 native herbaceous plants suitable for sustainable Mediterranean landscaping

Native herbaceous plants have the potential for renaturalizing and recovering derelict soils, such as urban or anthropized soils.Ecological restoration following the establishment of a native wildflower meadow should lead to a reduction in management costs and to the preservation of native plant populations. This study was aimed at determining the ecological characteristics and the cultivation needs of 26 herbaceous species native to Italy and southern Europe in order to identify their landscape potential in low-maintenance conditions. The species were selected on the basis of their adaptation to unproductive soils in semi-natural and rural areas, and on their ornamental value, including their ability to attract insects. Mono-specific plots were set up in three different soils. Seed germination, seedling emergence, flowering dynamics, and plant growth were determined. Dormancy-breaking treatments were effective in improving the germination of most species. The percentage of field establishment and biomass appeared to be affected by the physical and chemical characteristics of the soil. Soil texture slightly affected seedling emergence, whereas soil texture and the C and N levels affected plant growth, the number of flowers and the duration of flowering. Dianthus carthusianorum, Verbascum blattaria, Matricaria chamomilla and Hypochoeris radicata developed a higher biomass per plant in the soils with a low nutrient content, indicating their adaptability to infertile soils. Daucus carota, Papaver rhoeas, Verbascum sinuatum, Coleostephus myconis produced a higher biomass per plant in the most fertile soil, where they appeared to show a higher potential when competing with other species. The ecological characteristics shown by the native plants are extremely important in terms of combining seeds of different species to create and to maintain semi-natural herbaceous communities in low-maintenance landscapes.     

Biomass allocation in old-field annual species grown in elevated CO2 environments: no evidence for optimal partitioning

Increased atmospheric carbon dioxide supply is predicted to alter plant growth and biomass allocation patterns. It is not clear whether changes in biomass allocation reflect optimal partitioning or whether they are a direct effect of increased growth rates. Plasticity in growth and biomass allocation patterns was investigated at two concentrations of CO₂ ([CO₂]) and at limiting and nonlimiting nutrient levels for four fast‐ growing old‐field annual species. Abutilon theophrasti, Amaranthus retroflexus, Chenopodium album, and Polygonum pensylvanicum were grown from seed in controlled growth chamber conditions at current (350 μmol mol^?1, ambient) and future‐ predicted (700 μmol mol^?1, elevated) CO₂ levels. Frequent harvests were used to determine growth and biomass allocation responses of these plants throughout vegetative development. Under nonlimiting nutrient conditions, whole plant growth was increased greatly under elevated [CO₂] for three C3 species and moderately increased for a C4 species (Amaranthus). No significant increases in whole plant growth were observed under limiting nutrient conditions. Plants grown in elevated [CO₂] had lower or unchanged root:shoot ratios, contrary to what would be expected by optimal partitioning theory. These differences disappeared when allometric plots of the same data were analysed, indicating that CO₂‐induced differences in root:shoot allocation were a consequence of accelerated growth and development rates. Allocation to leaf area was unaffected by atmospheric [CO₂] for these species. The general lack of biomass allocation responses to [CO₂] availability is in stark contrast with known responses of these species to light and nutrient gradients. We conclude that biomass allocation responses to elevated atmospheric [CO₂] are not consistent with optimal partitioning predictions.     

Influence of ectomycorrhizal inoculation on Pinus wallichiana and Cedrus deodara seedlings under nursery conditions

A study was undertaken to examine the extent of root colonization by four locally isolated ectomycorrhizal （ECM） fungi （Hebeloma theobrominum, Boletus dryophilus, Scleroderma citrinum and Suillus luteus） and their effects on seedling growth in Pinus wallichiana and Cedrus deodara under nursery conditions. Seedlings of the two conifers were inoculated with mycelium of ECM fungi and were grown in pots containing sterilized forest soil for six months. The percentage of ECM colonization of roots was 38%-52% in Pinus wallichiana and 33%-48~ in Cedrus deodara. ECM colonization increased shoot height, needle number, shoot and root biomass and survival of inoculated seedlings. Among the four ECM fungi Hebeloma theobrominum was more effective with Pinus wallichiana and Scleroderma citrinum with Cedrus deodara in promoting seedling survival and overall growth. All the four ECM fungi used enhanced growth of inoculated seedlings and thus can be used in afforestation and regeneration programmes in degraded forests ecosystems.     

Growth responses to arbuscular mycorrhizae by rain forest seedlings vary with light intensity and tree species

Light intensity and root colonization by arbuscular mycorrhizal (AM) fungi are considered important factors affecting the performance of rain forest plants, yet few studies have examined how these two factors interact. Whether AM colonization promoted growth or caused shifts in biomass allocation in seedlings of four species of Australian rain forest tree (Flindersia brayleana, Acmena resa, Cryptocarya mackinnoniana and Cryptocarya angulata), grown in a glasshouse under light conditions that mimicked the shaded understory (3% PAR) and small light gaps (10% PAR), was examined. Seedlings were grown in sterilized field soil and either inoculated with AM fungi or provided sterile inoculum. Four major findings emerged. First, in all species, seedlings grown in small gap light intensities were larger than seedlings grown in understory light intensities. Second, when seedling biomass was included as a covariate, variation in light intensity was associated with significant shifts in biomass allocation. In all species, leaf area ratio was lower at 10% PAR than at 3% PAR, while root-to-shoot ratio showed the opposite pattern in one of the four species (C. mackinonniana). Third, although percentage root length colonized by AM fungi was greater at 10% PAR than 3% PAR in all species, this difference could be accounted for by variation in seedling size in all species except C. angulata. Fourth, growth and biomass allocation responses to AM colonization varied with light intensity and plant species. AM colonization promoted growth in both light regimes only in F. brayleana, while it had no effect on growth in C. mackinnoniana and C. angulata in either light regime and promoted growth only under high light in A. resa. AM colonization had no effect on leaf area ratio or root-to-shoot ratio in any of the species, and significantly altered specific root length in only one of the four species (C. mackinnoniana). These findings suggest that rain forest seedlings are highly variable in their growth responses to AM colonization and that some of this variability is related to the light intensity of the environment. Given that seedlings may spend many years in the shaded understory, these differences among species could have important effects on long-term seedling performance and seedling community dynamics.     

A comparative study on plant growth and root plasticity responses of two Brachiaria forage grasses grown in nutrient solution at low and high phosphorus supply

Brachiaria forage grasses are widely used for livestock production in the tropics. Signalgrass (Brachiaria decumbens cv. Basilisk, CIAT 606) is better adapted to low phosphorus (P) soils than ruzigrass (B. ruziziensis cv. Kennedy, CIAT 654), but the physiological basis of differences in low-P adaptation is unknown. We characterized morphological and physiological responses of signalgrass and ruzigrass to low P supply by growing both grasses for 30 days in nutrient solution with two levels of P supply using the hydroxyapatite pouch system. Ruzigrass produced more biomass at both levels of P supply whilst signalgrass appears to be a slower-growing grass. Both grasses increased biomass allocation to roots and had higher root acid phosphatase and phytase activities at low P supply. At low P supply, ruzigrass showed greater morphological plasticity as its leaf mass density and lateral root fraction increased. For signalgrass, morphological traits that are not responsive to variation in P supply might confer long-term ecological advantages contributing to its superior field persistence: greater shoot tissue mass density (dry matter content) might lower nutrient requirements while maintenance of lateral root growth might be important for nutrient acquisition in patchy soils. Physiological plasticity in nutrient partitioning between root classes was also evident for signalgrass as main roots had higher nutrient concentrations at high P supply. Our results highlight the importance of analyzing morphological and physiological trait profiles and determining the role of phenotypic plasticity to characterize differences in low-P adaptation between Brachiaria genotypes.     

Inhibitory effect of leachate from Helianthus annuus on germination and growth of Kharif crops and weeds

Allelopathic potential of sunflower (Helianthus annuus L.) fresh plant tissues aqueous extraction in bioassay, rhizosphere soil in pot experiment and phytotoxicity of decomposed sunflower plant biomass in bioassay against Vigna radiata, Pennisetum glaucum, Trianthema portulacastrum and Parthenium hysterophorum was investigated. In bioassay aqueous extracts of fresh sunflower plant tissue inhibited the germination, seedling growth (shoot and root) and dry matter accumulation of test plant species. In pot study sunflower rhizosphere soil inhibited growth attributes (plant height, population, number of branches) and yield attributes (grain yield, biomass yield) of selected crops and weeds. Phytotoxicity of decomposed sunflower biomass showed inhibitory effect on selected plant species. The fresh plant tissues was greatest inhibitory to test plants and followed by that of the decomposed biomass extracts in all bioassays. Significant reductions in the root and shoot growth were observed as the extract concentration was increased. The concentrations of extract fraction of fresh sunflower was determined, since nine compounds i.e. ferulic, p-coumaric, syringic, chlorogenic acid, isochlorogenic acid, neochlorogenic acid, vanillic acid, p-hydroxybenzoic acid, caffeoylquinic acid, found to be main growth inhibitors in sunflower plant tissue. These results suggested that sunflower plants may possess allelopathic potential, and the plant tissues may be potentially useful for weed management.     

Phenotypic plasticity of four Chenopodiaceae species with contrasting saline–sodic tolerance in response to increased salinity–sodicity

It is unknown whether phenotypic plasticity in fitness‐related traits is associated with salinity–sodicity tolerance. This study compared growth and allocation phenotypic plasticity in two species with low salinity–sodicity tolerance (Chenopodium acuminatum and C. stenophyllum) and two species with high salinity–sodicity tolerance (Suaeda glauca and S. salsa) in a pot experiment in the Songnen grassland, China. While the species with low tolerance had higher growth and allocation plasticity than the highly tolerant species, the highly tolerant species only adjusted their growth traits and maintained higher fitness (e.g., plant height and total biomass) in response to increased soil salinity–sodicity, with low biomass allocation plasticity. Most plasticity is “apparent” plasticity (ontogenetic change), and only a few traits, for example, plant height:stem diameter ratio and root:shoot biomass ratio, represent “real” plasticity (real change in response to the environment). Our results show that phenotypic plasticity was negatively correlated with saline–sodic tolerance and could be used as an index of species sensitivity to soil salinity–sodicity.     

Simulated hurricane‐induced changes in light and nutrient regimes change seedling performance in Everglades forest‐dominant species

Wind damage from cyclones can devastate the forest canopy, altering environmental conditions in the understory that affect seedling growth and plant community regeneration. To investigate the impact of hurricane‐induced increases in light and soil nutrients as a result of canopy defoliation, we conducted a two‐way factorial light and nutrient manipulation in a shadehouse experiment. We measured seedling growth of the dominant canopy species in the four Everglades forest communities: pine rocklands (Pinus elliottii var densa), cypress domes (Taxodium distichum), hardwood hammocks, and tree islands (Quercus virginiana and Bursera simaruba). Light levels were full sun and 50% shade, and nutrient levels coupled with an additional set of individuals that were subjected to a treatment mimicking the sudden effects of canopy opening from hurricane‐induced defoliation and the corresponding nutrient pulse. Seedlings were measured weekly for height growth and photosynthesis, with seedlings being harvested after 16 weeks for biomass, leaf area, and leaf tissue N and ¹³C isotope ratio. Growth rates and biomass accumulation responded more to differences in soil nutrients than differences in light availability, with largest individuals being in the high nutrient treatments. For B. simaruba and P. elliottii, the highest photosynthetic rates occurred in the high light, high nutrient treatment, while T. distichum and Q. virginiana photosynthetic rates were highest in low light, high nutrient treatment. Tissue biomass allocation patterns remained similar across treatments, except for Q. virginiana, which altered above‐ and belowground biomass allocation to increase capture of limiting soil and light resources. In response to the hurricane simulation treatment, height growth increased rapidly for Q. virginiana and B. simaruba, with nonsignificant increases for the other two species. We show here that ultimately, hurricane‐adapted, tropical species may be more likely to recolonize the forest canopy following a large‐scale hurricane disturbance.