Aboveground Growth Research Articles

Groundcover management changes grapevine root fungal communities and plant-soil feedback

The objective of this study was to determine if vineyard groundcover management can mitigate negative plant-soil feedback caused by soil borne pathogens through changes in root fungal communities. Whole-soil inoculum was collected from a field trial of groundcover identity (exotic grasses, exotic grasses plus legumes, native grasses, and native grasses plus forbs) and irrigation type (drip, sprinkler, and a combination of both) in a modified feedback experiment with grapevine rootstock ‘101–14’ (Vitis riparia x V. rupestris). To see if these groundcovers would differ in their ability to protect vines against negative feedback caused by a soil borne pathogen, we inoculated all pots with the soil-borne root pathogen, Ilyonectria liriodendri (Halleen, Rego & Crous) Chaverri & C. Salgado. After eight months, vines growing with soil trained by exotic grasses had greater above-ground growth response relative to sterilized control than did vines growing with soil trained by native grasses and forbs. These treatments also resulted in compositionally distinct root fungal communities. The intensity of root colonization by arbuscular mycorrhizal fungi did not differ among ground cover treatments. Our results show that soil feedback outcomes for grapevines, including negative effects of black foot pathogens such as Ilyonectria liriodendri, could depend on groundcover vegetation management that alters root-associated fungal communities.

Lyophyllum shimeji confers morphological changes on the roots of Populus nigra and promotes its aboveground growth in vitro

Lyophyllum shimeji confers morphological changes on the roots of Populus nigra and promotes its aboveground growth in vitro

Live long and prosper: plant-soil feedback, lifespan, and landscape abundance covary.

Plant soil feedbacks (PSFs) are thought to be important to plant growth and species coexistence, but most support for these hypotheses is derived from short-term greenhouse experiments. Here we use a seven-year, common garden experiment to measure PSFs for seven native and six nonnative species common to the western United States. We use these long-term, field-based estimates to test correlations between PSF and plant landscape abundance, species origin, functional type, and lifespan. To assess potential PSF mechanisms, we also measured soil microbial community composition, root biomass, nitrogen cycling, bulk density, penetration resistance, and shear strength. Plant abundance on the landscape and plant lifespan were positively correlated with PSFs, though this effect was due to the relationships for native plants. PSFs were correlated with indices of soil microbial community composition. Soil nutrient and physical traits and root biomass differed among species but were not correlated with PSF. While results must be taken with caution because only 13 species were examined, these species represent most of the dominant plant species in the system. Results suggest that native plant abundance is associated with the ability of long-lived plants to create positive plant-soil microbe interactions, while short-lived nonnative plants maintain dominance by avoiding soil-borne antagonists, increasing nitrogen cycling and dedicating resources to aboveground growth and reproduction rather than to belowground growth. Broadly, results suggest that PSFs are correlated with a suite of traits that determine plant abundance.

Rapid root responses of seedlings exposed to a postdrought water pulse.

Mediterranean-type climate ecosystems experience significant variability in precipitation within and across years and may be characterized by periods of extreme drought followed by a brief, high-intensity precipitation pulse. Rapid root growth could be a key factor in effective utilization of precipitation pulses, leading to higher rates of seedling establishment. Changes in root growth rate are rarely studied, however, and patterns in seedling root traits are not well explored. We investigated the influence of an extreme postdrought precipitation event on seedlings that occur in southern California coastal sage scrub. We measured root elongation rate, root tip appearance rate, new leaf appearance rate, and canopy growth rate on 18 mediterranean species from three growth forms. Root elongation rate responded more strongly to the precipitation pulse than did root tip appearance rate and either metric of aboveground growth. The majority of species exhibited a significant change in root growth rate within 1 week of the pulse. Responses varied in rapidity and magnitude across species, however, and were not generally predictable based on growth form. While the majority of species exhibited shifts in belowground growth following the pulse, the direction and magnitude of these morphological responses were highly variable within growth form. Understanding the implications of these different response strategies for plant fitness is a crucial next step to forecasting community dynamics within ecosystems characterized by resource pulses.

Spatial distribution of soil moisture, soil salinity, and root density beneath a cotton field under mulched drip irrigation with brackish and fresh water

Root systems play a vital role in soil-plant interactions. The dynamics and distributions of soil moisture content (SMC), soil salinity, and cotton (Gossypium hirsutum L.) root density under mulched drip irrigation are complex and their interactions are not well understood. The aim of this study is to describe these dynamics and distributions and to evaluate their impacts on cotton above-ground growth and yield during two-year field experiments in a cotton field under mulched drip irrigation with brackish and fresh water. Significant differences were observed for the distributions of SMC, soil salinity, and root length density (RLD) in the root zone for brackish water irrigation treatment (BWT) and fresh water irrigation treatment (FWT). The average SMC and soil salinity in the root zone were higher for BWT than for FWT. The spacing of irrigation lines also had measurable impacts. SMC was less variable when irrigation spacing was small (narrow rows) than beneath wide rows. SMC for BWT and FWT decreased after irrigation due to root water uptake; simultaneously, salt concentration increased, especially in regions where RLD was relatively high. More roots were observed growing in the mulched narrow and wide rows than in the no-mulch zone. Roots were concentrated in the shallowest 30cm. Our study indicated that the average values of the ECe (electrical conductivity of soil saturation extract) in the root zone after BWT irrigation were higher than the published threshold value for optimal cotton yield. The average RLD, shoot dry weight and yield for BWT were observed to be lower than those of FWT as a result of the elevated soil salinity associated with BWT.

Seasonal Cultural Management Practices for Aging Ultradwarf Bermudagrass Greens in the Subtropics: I. Nitrogen and Potassium Fertilization

Bermudagrass cultivars [Cynodon transvaalensis (L.) Pers. × Cynodon dactylon (Burtt‐Davy)] with more decumbent growth habits referred to as “ultradwarfs” have been released for use on golf course greens and tees as an alternative to standard bermudagrass varieties that have been used for >40 yr. Little research information is available on long‐term ultradwarf management requirements in subtropical environments. Therefore, a 4‐yr experiment was conducted in South Florida on a United States Golf Association specified green to determine the effects of nitrogen (N) fertility and N to potassium (K) ratios on quality, growth, and performance of three commercially released ultradwarfs (‘Champion’, ‘TifEagle’, and ‘FloraDwarf’). For all three cultivars, fertilizing at 879 kg N ha−1 yr−1 resulted in acceptable turfgrass quality with mean tissue N and K concentrations of 31 g N kg−1 and 14 g K kg−1, respectively. Over the 4‐yr experiment, leaf tissue N and K were present approximately as a 2:1 ratio, regardless of N rate and N:K ratio applied. As the ultradwarfs aged, fertilizing with 586 kg N ha−1 yr−1 was adequate. It appears that Champion and TifEagle have different mechanisms for increasing aboveground growth and had better quality and growth characteristics than FloraDwarf. This research documented the need for adjusting fertilization as the ultradwarf bermudagrass green ages and for the ultradwarf cultivar maintained.

Seasonal Cultural Management Practices for Aging Subtropic Ultradwarf Bermudagrass Greens: II. Mechanical Practices of Topdressing and Verticut Frequency

To provide optimum playing surfaces, many golf courses have used ultradwarf bermudagrass [Cynodon transvaalensis Burtt Davy × C. dactylon (L.) Pers.] cultivars for greens, although little is known about regionally defined cultural management. A 4‐yr experiment was conducted in southern Florida, on a US Golf Association (USGA)‐specified green to examine the effect of topdressing and vertical mowing frequency on ultradwarf bermudgrass cultivars Champion, TifEagle, and FloraDwarf for primarily quality, growth, tissue N and K, and ball roll distance. Weekly topdressing during the wet season enhanced quality and reduced the presence of disease‐like symptoms. TifEagle increased aboveground growth when topdressed weekly compared with Champion and FloraDwarf. As the green aged, however, topdressing biweekly during dry‐season months became important for maintaining quality. Influence of vertical mowing on all observations and measurements were minimal and not consistent from season to season. Further long‐term research is needed to determine how changing mechanical management on a seasonal basis can optimize ultradwarf bermudgrass for quality, vigor, and performance.

Comparison of Rooting Strategies to Explore Rock Fractures for Shallow Soil-Adapted Tree Species with Contrasting Aboveground Growth Rates: A Greenhouse Microcosm Experiment.

For tree species adapted to shallow soil environments, rooting strategies that efficiently explore rock fractures are important because soil water depletion occurs frequently. However, two questions: (a) to what extent shallow soil-adapted species rely on exploring rock fractures and (b) what outcomes result from drought stress, have rarely been tested. Therefore, based on the expectation that early development of roots into deep soil layers is at the cost of aboveground growth, seedlings of three tree species (Cyclobalanopsis glauca, Delavaya toxocarpa, and Acer cinnamomifolium) with distinct aboveground growth rates were selected from a typical shallow soil region. In a greenhouse experiment that mimics the basic features of shallow soil environments, 1-year-old seedlings were transplanted into simulated microcosms of shallow soil overlaying fractured bedrock. Root biomass allocation and leaf physiological activities, as well as leaf δ13C values were investigated and compared for two treatments: regular irrigation and repeated cycles of drought stress. Our results show that the three species differed in their rooting strategies in the context of encountering rock fractures, however, these strategies were not closely related to the aboveground growth rate. For the slowest-growing seedling, C. glauca, percentages of root mass in the fractures, as well as in the soil layer between soil and bedrock increased significantly under both treatments, indicating a specialized rooting strategy that facilitated the exploration of rock fractures. Early investment in deep root growth was likely critical to the establishment of this drought-vulnerable species. For the intermediate-growing, A. cinnamomifolium, percentages of root mass in the bedrock and interface soil layers were relatively low and exhibited no obvious change under either treatment. This limited need to explore rock fractures was compensated by a conservative water use strategy. For the fast-growing, D. toxocarpa, percentages of root mass in the bedrock and interface layers increased simultaneously under drought conditions, but not under irrigated conditions. This drought-induced rooting plasticity was associated with drought avoidance by this species. Although, root development might have been affected by the simulated microcosm, contrasting results among the three species indicated that efficient use of rock fractures is not a necessary or specialized strategy of shallow-soil adapted species. The establishment and persistence of these species relied on the mutual complementation between their species-specific rooting strategies and drought adaptations.

Trait shifts associated with the subshrub life-history strategy in a tropical savanna.

Over the past 10 million years, tropical savanna environments have selected for small growth forms within woody plant lineages. The result has been the evolution of subshrubs (geoxyles), presumably as an adaptation to frequent fire. To evaluate the traits associated with the shift from tree to subshrub growth forms, we compared seed biomass, germination, survival, resprouting, biomass allocation, and photosynthesis between congeneric trees and subshrubs, and quantified phylogenetic conservatism. Despite large differences in adult morphology between trees and subshrub species, the differences are modest in seedlings, and most of the variation in traits was explained by genus, indicating considerable phylogenic conservatism. Regardless, tree seedlings invested more heavily in aboveground growth, compared to subshrubs, which is consistent with the adult strategy of savanna trees, which depend on a large resistant-fire stem. Subshrub seedlings also invest in greater non-structural carbohydrate reserves, likely as an adaptation to the high fire frequencies typical of tropical savannas. The modest differences as seedlings suggest that selective pressures during early development may not have contributed substantially to the evolution of the subshrub growth form and that the distinct allocation and life history must arise later in life. This is consistent with the interpretation that the subshrub growth form arose as a life-history strategy in which maturity is reached at a small stem size, allowing them to reproduce despite repeated fire-induced topkill. The convergent evolution of subshrubs within multiple tree lineages reaffirms the importance of fire in the origin and diversification of the flora of mesic savannas.

Plant elicitor peptides promote plant defences against nematodes in soybean.

Plant elicitor peptides (Peps) are widely distributed among angiosperms, and have been shown to amplify immune responses in multiple plant families. Here, we characterize three Peps from soybean (Glycine max) and describe their effects on plant defences against two damaging agricultural pests, the root-knot nematode (Meloidogyne incognita) and the soybean cyst nematode (Heterodera glycines). Seed treatments with exogenous GmPep1, GmPep2 or GmPep3 significantly reduced the reproduction of both nematodes. Pep treatment also protected plants from the inhibitory effects of root-knot nematodes on above-ground growth, and up-regulated basal expression levels of nematode-responsive defence genes. GmPep1 induced the expression of its propeptide precursor (GmPROPEP1), a nucleotide-binding site leucine-rich repeat protein (NBS-LRR), a pectin methylesterase inhibitor (PMEI), Respiratory Burst Oxidase Protein D (RBOHD) and the accumulation of reactive oxygen species (ROS) in leaves. In addition, GmPep2 and GmPep3 seed treatments up-regulated RBOHD expression and ROS accumulation in roots and leaves. These results suggest that GmPeps activate plant defences through systemic transcriptional reprogramming and ROS signalling, and that Pep seed treatments represent a potential strategy for nematode management.

Tree seedling responses to multiple environmental stresses: Interactive effects of soil warming, nitrogen fertilization, and plant invasion

Temperate deciduous forest ecosystems in northeastern North America are under increasing biotic and abiotic stresses that can have interactive effects on understory vegetation, and thus impact the next generation of forest canopy trees. We examined seedling responses of the common and increasingly dominant species Acer rubrum (red maple) to the combined effects of soil warming (+5°C), chronic nitrogen fertilization (+50kgNha−1yr−1), and invasion by the phytotoxic plant Alliaria petiolata (garlic mustard), and their interactions. We planted 296 first-year A. rubrum seedlings in a multifactorial field experiment to examine the effects of all combinations of the experimental treatments. Second-year Acer rubrum seedlings demonstrated higher aboveground growth under soil warming conditions. Further, soil warming positively influenced plant-soil feedbacks through higher arbuscular mycorrhizal colonization in fine roots. However, the positive growth responses and mycorrhizal colonization observed under soil warming were moderated by both N fertilization and A. petiolata invasion. Our results highlight the importance of developing management plans that consider how multiple environmental change factors affect tree seedling performance, particularly via the plant-soil interface.

Alfalfa Responses to Gypsum Application Measured Using Undisturbed Soil Columns.

Gypsum is an excellent source of Ca and S, both of which are required for crop growth. Large amounts of by-product gypsum [Flue gas desulfurization gypsum-(FGDG)] are produced from coal combustion in the United States, but only 4% is used for agricultural purposes. The objective of this study was to evaluate the effects of (1) untreated, (2) short-term (4-year annual applications of gypsum totaling 6720 kg ha−1), and (3) long-term (12-year annual applications of gypsum totaling 20,200 kg ha−1) on alfalfa (Medicago sativa L.) growth and nutrient uptake, and gypsum movement through soil. The study was conducted in a greenhouse using undisturbed soil columns of two non-sodic soils (Celina silt loam and Brookston loam). Aboveground growth of alfalfa was not affected by gypsum treatments when compared with untreated (p > 0.05). Total root biomass (0–75 cm) for both soils series was significantly increased by gypsum application (p = 0.04), however, increased root growth was restricted to 0–10 cm depth. Soil and plant analyses indicated no unfavorable environmental impact from of the 4-year and 12-year annual application of FGDG. We concluded that under sufficient water supply, by-product gypsum is a viable source of Ca and S for land application that might benefit alfalfa root growth, but has less effect on aboveground alfalfa biomass production. Undisturbed soil columns were a useful adaptation of the lysimeter method that allowed detailed measurements of alfalfa nutrient uptake, root biomass, and yield and nutrient movement in soil.

Changes in root morphology with yield level of sugar beet

The high yield level sugar beet has reached in the past years might have altered the morphology of the storage root. The study thus aimed at analyzing storage root diameter and length in relation to yield under various environmental conditions. For that purpose, data of various field and pot experiments were included covering a broad range of storage root diameters and yield levels of sugar beet. It turned out that there was a close relationship between storage root diameter and root yield, which was not affected by different environmental conditions (site, year). Furthermore, breeding progress had obviously not changed this relation, as it was not affected by varieties. Results from pot experiments could well be compared with field trial data. In field trials, storage root length did not exceed 25cm independent of yield level, whereas in pot experiments plants formed longer storage roots with higher yield levels. It is discussed that increasing penetration resistance in soil could limit the further expansion of the storage root diameter. A more aboveground growth of the storage root with increasing yield level, however, will make yield estimates based on root diameter more difficult.

N deposition affects allelopathic potential of Amaranthus retroflexus with different distribution regions.

This study aims to determine the allelopathic potential of Amaranthus retroflexus (Ar) with different climatic zones on seed germination and growth of A. tricolor (At) treated with a gradient N addition. Ar leaf extracts only displayed significantly allelopathic potential on the underground growth of Ar but not the aboveground growth of At. The allelopathic potential of Ar leaf extracts on root length of At were enhanced under N addition and there may be a N-concentration-dependent relationship. The effects of the extracts of Ar leaves that collected from Zhenjiang on seed germination and growth of At may be higher than that collected from Jinan especially on root length of At under medium N addition. This reason may be the contained higher concentration of secondary metabolites for the leaves of plants that growths in high latitudes compare with that growth in low latitudes. This phenomenon may also partly be attributed to the fact that Ar originated in America and/or south-eastern Asia which have higher similarity climate conditions as Zhenjiang rather than Jinan. The allelopathic potential of Ar on seed germination and growth of acceptor species may play an important role in its successful invasion especially in the distribution region with low latitudes.

Growth and yield response of glasshouse- and field-grown sweetpotato to nitrogen supply

Nitrogen (N) is an essential element for producing optimum crop yields, but negative responses to high N supply are commonly reported in sweetpotato (Ipomoea batatas) production. This study assessed contrasting responses of sweetpotato yield as a result of N application rates of 0, 30, 60, 90, 130, 160 and 230 kg ha−1 in a glasshouse trial, and rates of 0, 50, 100, 150, 200 and 250 kg ha−1, equivalent to 160, 210, 260, 310, 360 and 410 kg ha−1 when soil N supply is included. The glasshouse-grown sweetpotato produced a maximum number and dry-biomass of storage roots, aboveground biomass and leaf area at 130 kg N ha−1, while leaf N concentration peaked at 90 kg N ha−1. Further increasing N application to 230 kg ha−1 did not result in significant change in any of these attributes. In field-grown sweetpotato, leaf and storage root N concentrations increased with increasing N supply. Although N supply had no effect on the number of storage roots, total yield peaked at 260 kg ha−1. Further increase of N supply reduced the total yield by up to 14% of the maximum yield. With increasing N supply, the glasshouse-grown sweetpotato yield linearly increased with leaf area; the arrangement of the trial permitting light interception to exceed the pot surface area. The yield reduction in field-grown plants was attributed to excess growth of aboveground parts, beyond that needed for efficient light capture. Respirational demand of the aboveground growth occurred at the expense of storage root yields.

Effects of soilless substrates on seedling quality and the growth of transplanted super japonica rice

This study was conducted to investigate the effects of soilless substrates of hydroponically grown long-mat seedlings (HLMS) on seedling quality and field growth characteristics of transplanted super japonica rice. A widely grown conventional super japonica rice cultivar (Wuyunjing 23) was selected as the test material. The effect of HLMS on seedling quality, mechanical transplantation quality, field growth characteristics, yield, and benefit-cost ratio were compared with seedlings grown in organic substrates and traditional nutritive soil, which was selected as the control. Root number, root twisting power and root activity of seedlings cultivated by HLMS were decreased compared to that of the organic substrates and control. However, seedling root length as well as aboveground growth were increased compared to the organic substrates and control seedlings. In the HLMS, the content of gibberellin acid (GA3) decreased while abscisic acid (ABA) content increased compared to that of the organic substrates and control seedlings. During the early stages after transplanting, the re-greening of HLMS was delayed compared to that of the organic substrates and control seedlings. Nevertheless, there were no significant differences in tiller dynamics and crop yield among the HLMS, organic substrates and control treatments. The effects of HLMS on seedling production were similar to those of the organic substrates and traditional nutritive soil in the present study, suggesting that HLMS have the potential to replace traditional nutritive soil in seedling production without decreasing crop yield. Finally, it is important to reduce organic substrates and topsoil dependence during rice seedling production and worthwhile to consider HLMS popularization and its application on a larger scale.

Root Distribution of Different Grapevine Rootstocks on a Relatively Saline Soil

Distribution of roots of Chenin blanc grafted onto 10 different rootstocks on a relatively saline, sandy clayloam with a varying electrical resistance was investigated. Root distribution was similar for all cultivars in that the majority of roots were found in the shallower soil layers (<600 mm), where electrical resistance was relatively high. Restriction of root growth in the deeper soil layers appeared to enhance growth of particularly the finer roots, closer to the soil surface. Root number varied with rootstock cultivar, the highest root numbers being found with 216/3 Castel and 1103 Paulsen and the lowest with US 16-13-23 and Ramsey. Above-ground growth and root density of the rootstocks were found to be in balance.

Reduced growth due to belowground sink limitation is not fully explained by reduced photosynthesis.

Sink limitation is known to reduce plant growth, but it is not known how plant carbon (C) balance is affected, limiting our ability to predict growth under sink-limited conditions. We manipulated soil volume to impose sink limitation of growth in Eucalyptus tereticornis Sm. seedlings. Seedlings were grown in the field in containers of different sizes and planted flush to the soil alongside freely rooted (Free) seedlings. Container volume negatively affected aboveground growth throughout the experiment, and light saturated rates of leaf photosynthesis were consistently lower in seedlings in containers (-26%) compared with Free seedlings. Significant reductions in photosynthetic capacity in containerized seedlings were related to both reduced leaf nitrogen content and starch accumulation, indicating direct effects of sink limitation on photosynthetic downregulation. After 120 days, harvested biomass of Free seedlings was on average 84% higher than seedlings in containers, but biomass distribution in leaves, stems and roots was not different. However, the reduction in net leaf photosynthesis over the growth period was insufficient to explain the reduction in growth, so that we also observed an apparent reduction in whole-plant C-use efficiency (CUE) between Free seedlings and seedlings in containers. Our results show that sink limitation affects plant growth through feedbacks to both photosynthesis and CUE. Mass balance approaches to predicting plant growth under sink-limited conditions need to incorporate both of these feedbacks.

Vegetative propagation capacity of invasive alligator weed through small stolon fragments under different treatments

The ability to propagate via small diaspores is crucial for the invasion of a clone plant that does not reproduce sexually in its introduced range. We investigated the effects of node and internode adjacent mode, fragment type, burial orientation and position of the node in relation to the soil surface on the sprouting and growth of alligator weed (Alternanthera philoxeroides (Martius) Griseb.). All the factors had effects and interaction effects on the sprouting rate and growth. As a whole fragment in all treatments, the fragments with basal node buried upward on the soil surface, exhibited the best above-ground growth and root growth. The one-node fragment with basal node buried downward above the soil surface and upward under the soil surface significantly decreased the above-ground growth and root growth compared to that of the two-node fragment. Therefore, the one-node fragments were more affected by environmental conditions than the two-node fragments. The results indicated that reducing the number of nodes of a fragment and burying the node under the soil or orienting it downward above the soil surface could be applied to control the invasion of alligator weed.

Four years of experimental warming do not modify the interaction between subalpine shrub species.

Climate warming can lead to changes in alpine plant species interactions through modifications in environmental conditions, which may ultimately cause drastic changes in plant communities. We explored the effects of 4years of experimental warming with open-top chambers (OTC) on Vaccinium myrtillus performance and its interaction with neighbouring shrubs at the Pyrenean treeline ecotone. We examined the effects of warming on height, above-ground (AG) and below-ground (BG) biomass and the C and N concentration and isotope composition of V. myrtillus growing in pure stands or in stands mixed with Vaccinium uliginosum or Rhododendron ferrugineum. We also analysed variations in soil N concentrations, rhizosphere C/N ratios and the functional diversity of the microbial community, and evaluated whether warming altered the biomass, C and N concentration and isotope composition of V. uliginosum in mixed plots. Our results showed that warming induced positive changes in the AG growth of V. myrtillus but not BG, while V. uliginosum did not respond to warming. Vaccinium myrtillus performance did not differ between stand types under increased temperatures, suggesting that warming did not induce shifts in the interaction between V. myrtillus and its neighbouring species. These findings contrast with previous studies in which species interactions changed when temperature was modified. Our results show that species interactions can be less responsive to warming in natural plant communities than in removal experiments, highlighting the need for studies involving the natural assembly of plant species and communities when exploring the effect of environmental changes on plant-plant interactions.