Annual Roots Research Articles

Mycorrhizal Fungal Partners Remain Constant during a Root Lifecycle of Pleione bulbocodioides (Orchidaceae).

Mycorrhizal mutualisms are vital for orchids through germination to adulthood. Fungal species diversity and community composition vary across seasons and plant development stages and affect plant survival, adaptation, and community maintenance. Knowledge of the temporal turnover of mycorrhizal fungi (OMF) remains poorly understood in the eco-physiologically diverse orchids (especially in epiphytic orchids), although it is important to understand the function and adaptation of mycorrhizae. Some species of Pleione are epiphytic plants with annual roots and may recruit different fungal partners during their root lifecycle. Based on continuous samplings of Pleione bulbocodioides during a whole root lifecycle, we characterized the fungal temporal dynamics using Illumina sequencing of the ITS2 region. Our data showed that the plants of P. bulbocodioides were quickly colonized by OMF at root emergence and had a constant OMF composition throughout one root lifecycle, although the OMF richness declined with root aging after a peak occurrence during root elongation. In contrast, the richness of root-inhabiting fungal endophytes kept increasing with root aging and more drastic turnovers were found in their species compositions. Our findings of OMF temporal turnover contribute to further understanding of mycorrhizal associations and adaptation of Orchidaceae and will benefit orchid resource conservation and utilization.

Transcriptome comparison among three types of annual roots of Malus hupehensis Rehd

Transcriptome comparison among three types of annual roots of <i>Malus hupehensis</i> Rehd

Influence of Heterogeneous Karst Microhabitats on the Root Foraging Ability of Chinese Windmill Palm (Trachycarpus fortunei) Seedlings

Chinese windmill palms (Trachycarpus fortunei) are widely planted in karst bedrock outcrop areas in southwest China because of their high economic and ecological values. The aims of this study were to investigate the foraging ability of Chinese windmill palm seedlings planted in six different types of karst microhabitat and to identify the main environmental factors that influence root foraging ability. We planted three-year-old Chinese windmill palm seedlings in six typical karst microhabitats (i.e., rocky trough, rocky surface, rocky gully, rocky soil surface, rocky pit, and soil surface microhabitats). One year after transplanting, the seedlings were excavated to determine the morphological parameters values of new roots and the nutrient concentrations of new roots and leaves. The root foraging ability of Chinese windmill palm seedlings, defined as new root length and new root surface area, was significantly greater in the rocky trough, rocky soil surface, and soil surface microhabitats than in the rocky gully, rocky surface, and rocky pit microhabitats (p < 0.05). Redundancy analysis revealed that the main positive factor affecting the rooting ability of Chinese windmill palm seedlings was soil thickness. Chinese windmill palm seedlings improved their root absorption efficiency by increasing their root length and root surface area under soil nutrient deficiency conditions. The organic carbon, total nitrogen, and available potassium in soil positively influenced the concentration of N and K in roots. Total potassium in soil negatively influenced the biomass of new annual leaves and concentrations of N, P and K in new annual roots and leaves. Chinese windmill palm seedlings can be grown in the different karst microhabitats, especially in the rocky trough, rocky soil surface, and soil surface microhabitats, and, therefore, it is suitable for use in the regeneration of karst forests.

Transformation from natural to wheat ecosystems enhances fine roots production and soil organic carbon input in an arid region

In arid regions, fine roots turnover contributes directly to soil carbon and nutrient cycling. However, less information is available on how increasing agricultural activities influence those dynamics. Fine roots biomass, production, and turnover rate were measured by sequential soil cores based on the maximum–minimum method in the 0–60 cm soil layer in three agricultural ecosystems and three natural ecosystems. Most (87% in agricultural and 75% in natural ecosystems) fine roots were distributed in the upper 30 cm soil layer. Mean annual fine roots production and turnover were 457% and 464% greater in agricultural than in natural ecosystems. Soil organic carbon input by fine roots decomposition was 91 g m−2 yr−1 in agricultural and 11 g m−2 yr−1 in natural ecosystems. Both fine roots biomass and fine roots production were significantly higher for two winter wheat (Triticum aestivum) ecosystems from May to October, 2010. Soil pH ranged from 8.2 to 9.4. Soil water content in agricultural ecosystems was higher, whereas soil electrical conductivity was lower than that in natural ecosystems. pH, soil bulk density, gravimetric soil water content, and soil electrical conductivity significantly affected fine roots biomass, production, turnover, and decomposition in all ecosystems investigated. The findings increase our understanding of the soil carbon cycle after natural ecosystems are modified into agricultural ecosystems.

Soil and Water Quality Rapidly Responds to the Perennial Grain Kernza Wheatgrass

Perennial grain cropping systems could address a number of contemporary agroecological problems, including soil degradation, NO3 leaching, and soil C loss. Since it is likely that these systems will be rotated with other agronomic crops, a better understanding of how rapidly perennial grain systems improve local ecosystem services is needed. We quantified soil moisture, lysimeter NO3 leaching, soil labile C accrual, and grain yields in the first 2 yr of a perennial grain crop under development [kernza wheatgrass, Thinopyrum intermedium (Host) Barkworth &amp; D.R. Dewey] relative to annual winter wheat (Triticum aestivum L.) under three management systems. Overall, differences between annual and perennial plants were much greater than differences observed due to management. In the second year, perennial kernza reduced soil moisture at lower depths and reduced total NO3 leaching (by 86% or more) relative to annual wheat, indicating that perennial roots actively used more available soil water and captured more applied fertilizer than annual roots. Carbon mineralization rates beneath kernza during the second year were increased 13% compared with annual wheat. First‐year kernza grain yields were 4.5% of annual wheat, but second year yields increased to 33% of wheat with a harvest index of 0.10. Although current yields are modest, the realized ecosystem services associated with this developing crop are promising and are a compelling reason to continue breeding efforts for higher yields and for use as a multipurpose crop (e.g., grain, forage, and biofuel).

Localization and Dynamic Change of Saponin in Vegetative Organs of Polygala tenuifolia

Anatomical, histochemical and phytochemical methods were used to investigate the structure, localization and dynamic changes of total saponin and senegenin of vegetative organs in Polygala tenuifolia Willd. Histochemical localization results showed that saponin accumulated mainly in parenchyma cells of vegetative organs. The phytochemical results also showed that the saponin accumulated in the vegetative organs of P. tenuifolia, with higher content in roots and lower content in the aerial parts that included stems and leaves. The saponin content and dry weight of the vegetative organs of P. tenuifolia had dynamic variance at the developmental stages and all reached the highest level in the post-fruit period. Hence, the roots and aerial parts should be gathered in August to make full use of the plant. As the root is the main medicinal organ of P. tenuifolia, the content of total saponin and senegenin of different aged and different parts of the root were determined. The content of total saponin and senegenin exhibited a sustained decreasing trend with increasing root age; therefore, the annual roots had high quality. The content of total saponin and senegenin in different parts of the root showed obvious variation. The content in the "skin areas" was much higher than that of xylem. The results offer a theoretical basis for determining the appropriate harvesting stage and a reasonable harvest of P. tenuifolia.

Seasonal adaptations of the tuberous roots of Ranunculus asiaticus to desiccation and resurrection by changes in cell structure and protein content

The annual developmental cycle of tuberous roots of Ranunculus asiaticus was studied with respect to structure and content of their cells, to understand how these roots are adapted to desiccation, high temperature and rehydration. Light microscopy, histochemical analysis, and protein analyses by SDS-PAGE were employed at eight stages of annual root development. During growth and maturation of the roots, cortical cells increased in size and their cell walls accumulated pectin materials in a distinct layer to the inside of the primary walls, with pits between adjoining cells. The number of starch granules and protein bodies also increased within the cells. Several discrete proteins accumulated. Following quiescence and rehydration of the roots there was a loss of starch and proteins from the cells, and cell walls decreased in thickness. The resurrection geophyte R. asiaticus possesses desiccation-tolerant annual roots. They store carbon and nitrogen reserves within their cells, and pectin within the walls to support growth of the plant following summer quiescence and rehydration.

THE LIMITING PROPERTIES OF THE CANOVA AND HANSEN TEST UNDER LOCAL ALTERNATIVES

This paper investigates the limiting properties of the Canova and Hansen test, testing for the null hypothesis of no unit root against seasonal unit roots, under a sequence of local alternatives with the model extended to have seasonal dummies and trends or no deterministic term and also only seasonal dummies. We derive the limiting distribution of the test statistic and its characteristic function under local alternatives. We find that the local limiting power is an inverse function of the spectral density at frequency π (π/2) when we test against a negative unit root (annual unit roots). We also theoretically show that the local limiting power of the Canova and Hansen test against a negative unit root (annual unit roots) does not increase when the true process has annual unit roots (a negative unit root) but not a negative unit root (annual unit roots), which has been observed in Monte Carlo simulations in such research as Caner (1998, Journal of Business and Economic Statistics 16, 349–356), Canova and Hansen (1995, Journal of Business and Economic Statistics 13, 237–252), and Hylleberg (1995, Journal of Econometrics 69, 5–25).

Decomposition and soil nitrogen availability in chihuahuan desert field microcosms

We examined the relationships between the decomposition of seven litter and root substrates, soil N availability, and populations of soil biota in field microcosm for 13 months. Most of the variation of N loss from the substrates was a function of initial substrate N concentration. Small portions of the variation of substrate mass loss and soil inorganic N were explained by initial substrate N concentration. Most of the variation of substrate mass loss, soil inorganic N. and soil biota populations was explained by differences between the decomposition of roots vs litter and of annual roots vs perennial roots. N loss from roots was more rapid than from litter. Mass of bacteria plus yeast in root microcosms was lower, nematode populations were higher, and the potential N mineralization rate at 9 months was higher than in litter microcosms. These results suggest that organic matter turnover in root microcosms was more rapid than in litter microcosms. Mass loss from annual roots was higher but N loss was lower than from perennial roots. Bacteria plus yeast mass in annual-root microcosms was lower, nematode populations were higher, and soil inorganic N was less than in perennial-root microcosms. The addition of annual roots reduced inorganic N concentrations below that of the unamendcd controls and the other substrate treatments in month 6 and 9 samples indicating that annual-root decomposition led to N immobilization or denitrilication. The addition of litter or perennial-roots increased soil inorganic N concentrations above the unamendcd control in the month 9 samples. The decomposition of N-poor annual plant roots may significantly reduce N availability in desert ecosystems.

Decomposition of roots in a Chihuahuan Desert ecosystem.

Mass losses of tethered buried roots of two woody shrubs and two herbaceous annuals buried in plots irrigated at 25 mm·month-1, 6 mm·week-1 and no irrigation were measured. At the end of 1 year, 10-15% of the mass of the herbaceous annual roots remained and 60% of the mass of woody shrub roots remained. There were no differences in mass loss attributable to added water. Rates of mass losses of roots in the Chihuahuan Desert were equal to or higher than those reported from mesic ecosystems. Roots of woody shrubs had relatively constant C:N ratios through the experiment. There was significant N immobilization in Baileya multiradiata roots. Percent mass loss of grass roots, Erioneuron pulchellum, and herbaceous annual roots, B. multiradiata, in plots with termites was 62% and in plots without termites was 15%. These data suggest that subterranean termites are responsible for most of the mass loss and mineralization of carbon and nitrogen in dead grass and herbaceous roots in the northern Chihuahuan Desert.

Seasonal pattern of biomass allocation in flowering and nonflowering specimens of three Pinguicula species

The seasonal patterns of biomass allocation in flowering and nonflowering specimens of Pinguicula alpina L., P. villosa L., and P. vulgaris L. were compared in a subarctic environment. Pinguicula alpina had a large perennial root system, comprising 50% of the nonreproductive biomass. The other two species had smaller, annual roots, representing 5–10% of their biomass. Nonflowering specimens usually had winter buds about twice as large as flowering specimens, P. vulgaris varied, however, with site in this respect. Flowering P. alpina allocated approximately equal proportions of biomass to reproduction (flower stalk, capsule, and seeds) and over-wintering organs (bud and roots), while P. villosa's investment in reproduction was about five times that invested in the winter bud. For P. vulgaris, no correlation was found between the size of reproductive organs and the size of the bud. The number of seeds produced per capsule varied from 30 in P. villosa to 110–140 in the other two species. Seed weight was lower in P. alpina (15 μg/seed) than in P. vulgaris (24μg) and P. villosa (28μg). Plant biomass and reproductive effort varied between sites for P. vulgaris; however, this variation was apparently not related to differences in nutrient availability between sites.

Effects of simulated grazing on foliage and root production and biomass allocation in an arctic tundra sedge (Eriophorum vaginatum).

Eriophorum vaginatum is a tussock-forming member of the Cyperaceae, widespread in the arctic tundra, and a common food item for grazing herbivores on the Alaskan North Slope. Populations of this sedge at Atkasook, Alaska, were subjected to a variety of simulated grazing experiments to determine tiller responses to frequent and intensive defoliation.The intial, short-term response of Eriphorum to defoliation was an increase in leaf production at the expense of belowground structures. Multiple defoliations, however, resulted in proportionately greater reductions in leaf weight than leaf area. Leaf blades of defoliated plants weighed 0.71 mg/cm of length, compared to an average weight/length ratio of 0.91 mg/cm in control plants. Declines in leaf production were accompanied by weight losses in stem base and sheath components and a curtailment of root growth. Root initiation was reduced by 28 and 63%, respectively, after one and two seasons of multiple defoliations, and the depth of penetration of these annual roots was reduced substantially. Total root biomass was reduced 24% in the least severe defoliation treatment and 85% in the most severe treatment. The allocation of dry matter into new tillers on defoliated plants, relative to new tiller production of control plants, was reduced by 75% after two seasons of defoliation, although equivalent numbers of tillers were initiated. The reduced biomass of daughter tillers was restored to levels observed in control plants during the season of rest following the season of multiple defoliation. Sexual reproduction was significantly depressed in the most severe defoliation treatment and stimulated by the least severe treatment. Defoliation treatments of intermediate severity had no significant impact on flower initiation.Over 80% of the tillers subjected to complete defoliation at 10-day intervals for one entire growing season survived, overwintered and initiated growth the following season. Recovery from multiple defoliations was partially achieved by the stimulated growth and extended longevity of older leaves on the tiller, although one season of rest was not enough to fully replenish weight losses of storage organs. Tillers were capable of withstanding more defoliation events when clipping was initiated early in the growing season. Biomass of storage organs of tillers subjected to multiple defoliations imposed at 10-day intervals for two entire growing seasons was 34% above the estimated minimum biomass necessary for tiller survival. The data suggest that Eriophorum tillers can survive 100% leaf removal at 10-day intervals for 50 to 75% of their estimated three to four year lifespan.

The development of the endoder mis andPhi layer of apple roots

Suberin lamellae and a tertiary cellulose wall in endodermal cells are deposited much closer to the tip of apple roots than of annual roots. Casparian strips and lignified thickenings differentiate in the anticlinal walls of all endodermal andphi layer cells respectively, 4–5 mm from the root tip. 16 mm from the root tip and only in the endodermis opposite the phloem poles, suberin lamellae are laid down on the inner surface of the cell walls, followed 35 mm from the root tip by an additional cellulosic layer. Coincidentally with this last development, the suberin and cellulose layers detach from the outer tangential walls and the cytoplasm fragments. 85 mm from the root tip the xylem pole endodermis (50% of the endodermis) develops similarly, but does not collapse. 100–150 mm from the root tip, the surface colour of the root changes from white to brown, a phellogen develops from the pericycle and sloughing of the cortex begins. A few secondary xylem elements are visible at this stage. Plasmodesmata traverse the suberin and cellulose layers of the endodermis, but their greater frequency in the outer tangential and radial walls of thephi layer when compared with the endodermis suggests that this layer may regulate the inflow of water and nutrients to the stele.

Concurrent changes in plant weight and soil water regimes in herbaceous communities in Central Australia

AbstractTwo studies of arid zone plant communities are described. In the first, the perennial grass Eragrostis eriopoda was sampled over 8 months for dry weight and water stress of tops, and water content and tension of soil to a depth of 150 cm. In the second, lasting 2 years, pure Eragrostis and pure Aristida con‐torta (annual) communities were sampled for dry weight of tops and roots and soil water content. Plots of naturally occurring mixtures of Eragrostis and Aristida were also studied.During periods of prolonged high soil water content, perennial communities greatly out‐yielded annuals (1200 and 260gm‐2 respectively). During prolonged droughts all communities yielded less than 100 gm‐2.Perennial root systems were larger than for annuals. The weight of annual roots varied little with season as distinct from perennials which varied greatly. Maximum weight of annual roots occurred in the top 10 cm of soil; the zone of maximum rooting by perennials was 10–30 cm. Water loss from annual, perennial and bare plots was similar and extended throughout the measured profile. Two gradients of soil water tension of opposite signs developed during prolonged drought. The greater was due to evapo‐transpiration and the lesser developed below the zone of recharge.On average. Eragrostis grew 4.6 times faster than the annuals which enjoyed a marginally more favourable water regime. In a mixture which had received one heavy simulated grazing the presence of annuals reduced the growth of Eragrostis by 68%, suggesting that the invasion of Eragrostis by annuals would seriously reduce productivity.

The colonization of host-root and soil by Rhizobia—I. Species and strain differences in the field

Growing-season populations of rhizobia associated with annual host-plant roots and nearby soil were examined in a field soil showing a nodulation problem in the second year after establishment. Rhizobium lupini reached higher populations at a faster rate than R. trifolii. A sharp drop in the population of R. trifolii associated with subterranean clover roots early in the growing season was followed by a recovery to high numbers. No such phenomenon occurred with R. lupini. The numbers of rhizobia under patches of non-nodulated plants in second-year stands were very low, usually <5/g soil, whereas the numbers under healthy plants in problem stands were similar to those under established stands. Differences in the colonization of both root and soil by R. trifolii in the first year were reflected in the second-year nodulation.