Larger Root System Research Articles

Root growth inhibition by low temperature explains differences in sugar accumulation between spring and winter wheat

Exposure to low temperatures is associated with an increased concentration of carbohydrate (mainly sugar) in tissues of cool temperate species. Within a species, carbohydrate concentration is usually much higher in winter cultivars than in spring ones, frequently correlates well with winter survival, and is also related to the expression of several genes. It has been proposed that either a smaller reduction in carbon assimilation, or greater growth inhibition by cold in winter cultivars, might explain this differential increase in carbohydrate concentration. However, little experimental support for these hypotheses is available. In this work, carbon assimilation and growth, as related to the cold-induced increase in carbohydrate concentration, are analysed in contrasting wheat (Triticum aestivum L.) genotypes. No significant differences in the degree of cold-induced reduction of carbon assimilation between cultivar types were found. Also, shoot growth was similarly inhibited by cold in both winter and spring cultivars. However, root growth rates were lower in cold-treated winter cultivars than in spring ones, which led to much larger root systems in the latter. A simple method for quantitatively estimating the contribution of cold-induced changes in carbon fixation and growth to changes in carbohydrate concentration was developed. This analytical framework suggests that the degree of root growth inhibition by cold was the main factor in determining differences in carbohydrate content between cultivars.

Mycorrhizal Infection Reduces Shortterm Aluminum Uptake and Increases Root Cation Exchange Capacity of Highbush Blueberry Plants

Aluminum (Al) uptake by and root cation exchange capacity (CEC) of mycorrhizal (M) and nonmycorrhizal (NM) blueberry (Vaccinium corymbosum L.) plants were studied. Root CEC was higher in M plants than in NM plants, but total and root Al contents were higher in NM plants. Leaf Al content was higher in NM than in M plants after 1 and 5 hours of exposure. The aurintriboxylic acid stain for Al indicated the presence of Al in the M symbiont. Despite a larger root system and higher root CEC, regression analysis indicated roots of M plants absorbed less Al in the first 5 hours, suggesting that Al sequestration in the M symbiont is responsible for reduced total Al uptake. Differences in dry matter partitioning between M and NM plants were also observed.

Influência da combinação de fósforo e calcário no rendimento de milho

A presença de Al em níveis tóxicos no solo inibe o crescimento das raízes com reflexos negativos na absorção de água e de alguns nutrientes, especialmente do P. Sendo assim, a adição de grandes quantidades de fertilizantes fosfatados deverá tornar a absorção de P menos dependente da existência de um amplo sistema radicular e com isto diminuir a resposta das culturas à calagem. O presente trabalho objetivou avaliar o rendimento de milho de acordo com a aplicação de quantidades crescentes de P e de calcário. O experimento foi desenvolvido em Lages (SC), de 1994 a 1998, num Latossolo Bruno argiloso com pH 4,7, Al trocável = 39 mmol c kg-1, 1 mg kg-1 de P, que requeriam 9,0 t ha-1 de calcário para elevar o pH a 6,0. Combinaram-se três doses de calcário (0, 4,5 e 9,0 t ha-1) com quatro de P, no delineamento de parcelas subdivididas. As quantidades de P2O5 foram, respectivamente, de 60, 120, 180 e 240 kg ha-1, na primeira safra; de 40, 80, 120 e 160 kg ha-1, na segunda e na quarta, e de 30, 60, 90, e 120 kg ha-1, na terceira safra, perfazendo uma média de 42, 85, 127 e 170 kg ha-1 por cultivo, respectivamente. O efeito benéfico da calagem aumentou com o passar dos anos, de inexistente, no primeiro cultivo, para incrementos de até 39% no rendimento de milho. Na maioria das safras, a produtividade aumentou somente até pH 5,4, quando foi aplicada metade da dose de calcário recomendada pelo método SMP para elevar o pH até 6,0. Nos tratamentos que receberam as duas maiores doses de P2O5 (127 e 170 kg-1 ha-1 por cultivo), (média de 85 kg ha-1 por cultivo), a calagem não influiu no rendimento de milho. A adubação fosfatada aumentou a produtividade de milho em todas as safras, porém em magnitudes que decresceram com a elevação do pH. Os maiores rendimentos foram obtidos com a dose recomendada em duas delas, porém, em outras duas, a quantidade necessária foi 50% maior.

Blue Oak Mini-plug Transplants: How They Compare to Standard Bareroot and Container Stock

Blue oak (<i>Quercus douglasii</i> Hook &amp; Arn. [Fagaceae]) is a widely distributed California oak that is regenerating poorly in portions of its range. Recent concern over habitat loss in blue oak woodlands has prompted efforts to regenerate this species artificially. Our study examined whether a relatively new stock type called mini-plug transplants would perform better in the field than conventional bareroot and container plants. Our results suggest that thought it is possible to produce blue oak mini-plug seedlings with large fibrous root systems, field performance was similar to other stock types that can currently be produced more economically.

Effects of seasonal drought on gap and understorey seedlings in a Bolivian moist forest

In tropical moist forests, length of the dry period may have a profound influence on leaf dynamics, plant growth and survival. To evaluate the role of light and water availability on seedling performance, a 1-y experiment was carried out in a tropical moist forest in the Bolivian Amazon in which seedlings of three tree species (Brosimum lactescens, Cedrela odorata and Schizolobium amazonicum) were planted in gaps and the understorey. Variation in length of the dry period was simulated by subjecting part of the seedlings to a water treatment at the end of the dry period. Gaps and understorey had a similar soil moisture content, which varied between 39% in the wet season and 16% in the dry season. Height and leaf growth rates were higher in gap compared to understorey plants, and in the wet compared to the dry season. A high growth during the wet season provided gap plants with a decisive size advantage over understorey plants during the dry season. Their larger root system allowed gap plants to explore a larger surface area and deeper soil layers for water. Consequently, gap plants of Cedrela experienced a shorter deciduous period (22 d) compared to understorey plants (61 d). Watering at the end of the dry season cued the flushing of new leaves by Cedrela, although it did not lead to a higher plant growth.

A Sampling Method for Measurement of Large Root Systems with Scanner‐Based Image Analysis

Measurement of relatively small (&lt;100 m total length, &lt;6 g fresh wt.) root systems has been simplified by image analysis, but measuring larger root systems remains time‐consuming and inaccurate. Reliability of root estimation can be improved through identification of effective sampling methods. We devised a system for the collection of homogeneous root subsamples by air‐stirring in water. We optimized the subsampling technique and used a scanner‐based image analysis system to measure total root length, mean root diameter, and root surface area of three maize (Zea mays L.) genotypes with contrasting root morphologies: leafy reduced stature (LRS), leafy normal stature (LNS), and Pioneer 3905 (P3905), a commercial hybrid. Root length was determined for 957 subsamples. Confidence intervals were generated by software using the bootstrap resampling approach for optimizing sample size. Confidence intervals for mean estimates of each sample size were defined by ordering the evaluation function values from the smallest to the largest in a set of 5000 iterations. The lower and upper bounds of confidence intervals were also calculated using the standard procedure. This system allowed collection of homogeneous subsamples. Calculations showed that ∼10% of total root volume should be analyzed for estimation of the entire root system to be accurate within 10%. Although unreplicated, these data suggest that maize genotypes with the leafy trait have greater root lengths (1.75 km for LRS, 2.37 km for LNS, and 0.49 km for conventional commercial hybrid P3905) and a greater proportion of fine roots than the nonleafy type.

Physiological responses of black spruce layers and planted seedlings to nutrient addition.

We investigated effects of nutrient addition on several physiological characteristics of 60-cm-tall black spruce (Picea mariana Mill. B.S.P.) layers (i.e., rooted branches of overstory trees) and 20-cm-tall planted seedlings on a clear-cut, N-limited boreal site. After two growing seasons, current-year and one-year-old needles of fertilized trees (layers and seedlings combined) had higher net photosynthetic rates (A(n)) and maximum capacity of Rubisco for CO(2) fixation (V(max)) than unfertilized trees. One-year-old needles of fertilized trees had higher stomatal conductance (g(s)), higher water-use efficiency, and lower intercellular to ambient CO(2) ratio than unfertilized trees. Additionally, fertilized trees had higher predawn and midday shoot water potentials than unfertilized trees. Stomatal conductance of 1-year-old needles was 23% higher in seedlings than in layers, but there were no significant differences in g(s) of current-year needles between the regeneration types. For both needle age-classes, A(n) and V(max) of layers were 25 and 40% higher, respectively, than the corresponding values for seedlings. The higher values of A(n), V(max) and foliar N concentration of layers compared with seedlings after two growing seasons may be associated with the larger root systems of the layers compared with the transplanted seedlings.

Potassium Dynamics in the Rhizosphere and K Efficiency of Crops

Nutrient efficiency is defined as the ability of plants to obtain higher relative yields at low nutrient supply compared to other species. The size of the root system, the physiology of uptake and the ability of plants to increase K solubility in the rhizosphere are considered as mechanisms of uptake efficiency. In a solution experiment wheat and sugar beet were more K efficient than potato because wheat had a large root system and both species had an efficient uptake physiology. Also in soil wheat was uptake efficient because of a large root system, whereas the efficiency of sugar beet was caused by the ability to increase K solubility. This could be shown by the use of a model to describe K dynamics in the rhizosphere.

Effects of Pruning Liriope Bibs During Division on Subsequent Growth

Abstract Three experiments were conducted to determine if shoot pruning of liriope [Liriope muscari (Decne.) L.H. Bailey ‘Big Blue’, ‘Evergreen Giant’, and ‘Variegata’] at division affected subsequent growth of roots and shoots. Plants were divided into single bibs and shoots were either left unpruned or pruned 5 cm (2 in) above the plant crown. Plants with shoots pruned took longer to develop 25 new root tips and had smaller root masses at the end of the experiment. ‘Big Blue’ plants had 7.5 bibs per container when plants were not pruned and 4.2 bibs per container when plants were pruned. Root system number at division was also evaluated. Plants with larger roots systems (10 or more roots) developed 25 new roots faster, and produced more bibs than plants with smaller root systems (3-5 roots) at division. In experiments 2 and 3, ‘Evergreen Giant’ was similar to ‘Big Blue’ in that plants that were not pruned developed 25 new roots faster and had larger root systems at the end of the experiment than plants that were pruned. Results with ‘Variegata’, known to be a slower growing cultivar, were varied.

Varietal Differences of Root Systems in Tea-Rooted Cutting.

チャ挿し木苗の根系形態を網円筒枠を用いて調査した結果, 地上部の生育はもちろんのこと, 根系形態にも著しい品種間差異が認められた。新梢長や新梢重は, おおいわせ, おくむさしで優れ, さえみどり, かなやみどり, おくみどりで劣った。また, 発根数や根重は, さやまかおり, ふうしゅんで優れ, さえみどり, おくみどり, おくむさしで劣る傾向にあった。根系形態には品種間差異が認められ, その違いは主成分分析の結果から, 「根の空間的分布様相」と「根量特性」に起因していた。根の空間的分布の広い品種には, 山の息吹, めいりょく, さやまかおり, おくひかりが, 狭い品種には, おおいわせ, さえみどり, かなやみどりが認められた。また, ふうしゅんは根量が多く, 根の伸長角度の小さいことが, おくみどりは根の伸長角度の大きいことが特徴的だった。

ESTABLISHMENT OF VEGETATION ON MINED SITES BY MANAGEMENT OF MYCORRHIZAE

Plant ecosystems, including those in the tropical, temperate, boreal, and desert zones, began evolving more than 400 million years ago. Trees and other land plants in these environments were faced with many natural stresses including extreme temperature changes, fluctuating levels of available water, soil infertility, catastrophic fires and storms, poor soil physical conditions and competition. Basically, these plants evolved by genetic selection and developed many physical, chemical, and biological requirements necessary to survive these periodically stressed environments. Survivors were those that could form extensive lateral root systems to occupy soil volumes sufficiently large for them to obtain enough essential mineral elements and water to support their above and below ground growth needs. The most competitive plants in these stressed ecosystems were those with the largest root systems. One major biological requirement that evolved was the association of plants with mycorrhizal fungi. This is still true today for land that has been disturbed by mining, construction, and other activities. Successful vegetation establishment on these lands has been achieved by using the biological tools; native tree seedlings, shrubs, forbs, and grasses inoculated with specific, beneficial mycorrhizal fungi. Trees and shrubs are custom grown in nurseries with selected mycorrhizal fungi, such as Pisolithusmore » tinctorius (Pt) and other fungi, provide significant benefits to the plants through increased water and mineral adsorption, decreased toxin absorption and overall reduction of plant stress. This has resulted in significant increases in plant growth and survival rates, density and sustainable vegetation.« less

Effects of sand burial depth on seed germination and seedling emergence of Cirsium pitcheri

A greenhouse study was conducted to determine the effects of sand burial on seed germination and seedling emergence of Cirsium pitcheri, a threatened species along Lake Huron sand dunes. In October 1996, seeds of C. pitcheri were sorted into three groups (small, medium and large) and artificially buried at 2, 4, 6, 8, 10 and 12 cm depths in plastic pots filled with unsterilized sand from Lake Huron sand dunes. These pots were placed outside in sand boxes for natural stratification. In early February, the pots were brought into the greenhouse for germination of seeds. Data showed that percent seed germination and emergence of seedlings were not related to seed size. However, both variables were negatively correlated with depth. Seedling emergence occurred from a maximum depth of 6 cm with most seedlings emerging from 2 cm depth. Only one seedling emerged from 8 cm depth. Seedlings from large seeds produced longer roots than those of small seeds. Larger root system would probably enhance seedling establishment.

Effect of different forage plants on denitrification potential of Horotiu soil

Denitrification potential (DNP), water‐soluble soil carbon, soil nitrate, and plant weights were measured in lysimeters growing cocksfoot, tall fescue, chicory, Yatsyn ryegrass, or Ruanui ryegrass in a New Zealand soil. The soil‐related parameters were measured in the topsoil and upper‐ and lower‐subsoil zones of the lysimeters. Significantly lower rates of DNP were measured under Ruanui ryegrass than under the other plants and there was a tendency for higher rates of DNP to be associated with bigger root masses. Water‐soluble carbon was higher in the topsoil than in the upper‐ or lower‐subsoil, but soluble carbon did not differ significantly among the cultivars. DNP responded positively to addition of glucose to the soil, demonstrating that soluble carbon rather than the resident populations of denitrifying micro‐organisms were limiting DNP. Lysimeters growing cocksfoot had the lowest soil nitrate levels and the largest root systems but only intermediate rates of DNP. The quality of root residues entering the soil under cocksfoot is probably lower than for the other plants.

AN IMPROVED PROTOCOL FOR SOMATIC EMBRYOGENESIS IN COCONUT (COCOS NUCIFERA L.)

An improved protocol for somatic embryogenesis in coconut (Cocos nucifera L.) has been established. Immature zygotic embryo explants were found to be more likely to undergo somatic embryogenesis than mature ones. However, longitudinally slicing of the mature zygotic embryo did improve their ability to undergo somatic embryogenesis. The slices derived from the mid-embryo region were the most responsive, with outer sections not producing any somatic embryos. To induce somatic embryogenesis on sliced mature explants 2,4-D (125 mu M) and activated charcoal (2.5 g l(-1)) were required. Incubation of cultures under illuminated conditions inhibited the production of somatic embryos. However, maturation of somatic embryos was light insensitive while plantlet regeneration required illumination. Plantlets were successfully produced, but elongation of shoots was inhibited by the production of a large root system. Removal of these early roots and the re-establishment at a later stage by application of NAA (10 mu M) allowed for normal seedling growth to occur. Plantlets were acclimatised (with a 30% survival rate) and grew normally in a glasshouse.

Linking the ecology of natural oak regeneration to silviculture

The regeneration requirements of oaks ( Quercus spp.) differ among species. Oaks differ in their ability to produce seed, germinate and, as for reproduction, to endure shade, drought, and other stresses. Under the low to moderate shade that characterizes the understories of their natural habitats, the xerophytic oaks depend heavily on their drought tolerance and capacity to die back and resprout repeatedly. Successful regeneration of xerophytic oaks depends largely on the long-term survival and accumulation of oak reproduction, which may span 2 or more decades. Some of this reproduction develops large roots in advance of final harvest, which thereby enhances long-term survival and the potential for rapid shoot growth after overstory removal. In the more nutrient- and moisture-rich ecosystems, seedling populations of indigenous oaks arising from a single cohort typically fall to near extinction within a few years. High mortality rates are related to seedling intolerance to shade and the prevailing low light intensities under the high stand densities and stratified canopies typical of those ecosystems. In the absence of natural disturbance or silvicultural intervention, oak reproduction beneath dense stands in rich ecosystems typically fails to accumulate over time and thus fails to form the large root systems necessary for competitive success after overstory removal. The required timing and intensity of silvicultural operations for regenerating oaks therefore depend on the ecosystem-specific population dynamics of each species. Knowledge of birth, death, and other population processes of oak reproduction within defined classes of ecosystems, as well as knowledge of periodicity in seed production are prerequisites to the development of ecologically sound silvicultural prescriptions and realistic predictive models for regenerating oaks.

Corn Rootworm (Coleoptera: Chrysomelidae) Larval Injury and Root Compensation of 12 Maize Hybrids: an Assessment of the Economic Injury Index

A 4-yr field investigation (1993-1996) to examine the compensatory root regrowth of 12 commonly grown maize hybrids after larval injury by corn rootworms, Diabrotica spp., was conducted at 2 locations in Illinois. Root injury ratings, root volume measurements taken in July and August, and root regrowth parameters were evaluated for their usefulness in predicting yield. Root ratings were as useful as root volumes and root regrowth measurements in predicting yield. Large root systems in July and August generally were positive factors contributing to yield; however, compensatory root regrowth, particularly when soil moisture was adequate, negatively affected yield. Root regrowth after larval injury typically had a positive effect on yield when soil moisture was inadequate. Regression equations described the very dynamic nature of root injury, root volume, and root regrowth and their impact on yield in different growing seasons and at different locations. In addition, profit margins were estimated using a fixed insecticide cost, actual root injury data, and 4 market prices of maize. Results from different growing seasons and locations indicate that root ratings well below 4.0 can contribute to economic losses.

Effect of spacing on growth and biomass distribution in Eucalyptus camaldulensis, E. pellita and E. urophylla plantations in southeastern Brazil

The growth and biomass accumulation in different plant parts (including root systems) of Eucalyptus camaldulensis, E. urophylla and E. pellita planted at three spacings (3×1.5 m, 3×3 m and 4×3 m) and three ages (15, 31 and 41 months) were evaluated in the savannah region of central Minas Gerais state in southeastern Brazil. A series of equations were produced to estimate per-tree biomass from age, spacing, diameter and height, and per-hectare biomass using age, spacing and a tally of tree diameters and heights. Average total productivity at age 41 months was of the order E. urophylla> E. pellita≥ E. camaldulensis. As spacing increased, individual stems increased in diameter and total biomass; however, total biomass production per hectare decreased. Eucalyptus urophylla had 64.8 vs. 42.8, E. pellita 41.3 vs. 28.9 and E. camaldulensis 35.1 vs. 26.9 Mg ha −1 at 3×1.5 vs. 4×3 m spacings, respectively. Increased spacing levels also decreased the relative amount of growth allocated to the bole of the tree for E. urophylla and E. camaldulensis during the time period of this study and increased allocation to the root system, while E pellita showed relatively small changes. Allocation to the bolewood in E. urophylla changed from 46 to 36%, in E. camaldulensis from 37 to 32%, and E. pellita from 31–34% at 3×1.5 vs. 4×3 m spacings, respectively. Allocation to the root system in E. urophylla changed from 23–30%, in E. camaldulensis from 34–45%, and E. pellita from 37–33% at 3×1.5 vs. 4×3 m spacings, respectively. Thought these results show that some of the biomass changes from species, age and spacing differences are related to distribution, not total biomass production, there were significant differences in total biomass accumulation also. Since larger root systems may increase future yields from coppice growth, the effect of differences in allocation to the root system on future productivity needs to be evaluated.

Additive, dominant, and epistatic effects for maize grain yield in acid and non-acid soils

Acid soils severely reduce maize (Zea mays L.) yield in the tropics. Breeding for tolerance to soil acidity provides a permanent, environmentally friendly, and inexpensive solution to the problem. This study was carried out to determine the relative importance of additive, dominant, and epistatic effects on maize grain-yields in different tropical genotypes. Divergent selection in three populations (SA4, SA5, and SA7) provided inbred lines tolerant or sensitive to acid soils. The tolerant and sensitive lines from each population were used to obtain the F1, F2, F3, back-crosses, second back-crosses, and selfed back-cross generations. In addition, the tolerant lines from SA4 and SA5 were crossed with a sensitive line from the Tuxpeno Sequia population, from which the same generations were also derived. All generations from each of the five sets of crosses were evaluated in three acid-soil environments and one non-acid-soil environment. A generation-mean analysis was performed on each set for yield. The sequential sum of squares associated with additive, dominance, and digenic epistatic effects were used to estimate the relative importance of each genetic effect. Epistasis was not important in any set in the non-acid-soil environment, with dominance accounting for 80.76% of the total variation among generation means across sets. In acid-soil environments, epistasis was more important. The relative importance of digenic epistasis was greater in those evaluations with large experimental errors. The tolerant line from population SA5 was prone to severe root lodging, suggesting a very poor root system. Apparently, the tolerance to soil acidity in this line is not associated with a large root system.

CLIMATIC CONDITIONS AND TROPICAL MONTANE FOREST PRODUCTIVITY: THE FOG HAS NOT LIFTED YET

Tropical montane cloud forests (TMCF) differ from lowland moist forests in structure (low stature, small and tough leaves, low diversity) and functioning (low productivity, low nutrient-cycling rates). To explain these differences, a variety of hypoth- eses have been proposed, most of which are related directly or indirectly to climate, but none of these provides a satisfactory explanation for all typical TMCF traits. The single climatic factor shared by all TMCF, the frequent occurrence of low cloud, has multiple effects, but not all are well understood. In this paper we describe and analyze the climatic and soil-moisture conditions prevailing in TMCF as reported in the literature. TMCF evapo- transpiration is limited by both climatic conditions and canopy conductance. TMCF pro- ductivity is low, but our understanding of these forest's carbon balance is incomplete. Leaf photosynthetic capacity is not particularly low, but canopy photosynthesis probably is, due to persistent cloudiness (low radiation) and a low leaf-area index (LAI). We suggest that the low LAI of TMCF is controlled by light climate and by leaf structure and longevity. TMCF productivity is probably further limited by a substantial investment of carbon in the growth and functioning of a relatively large root system, which is itself a consequence of unfavorable soil conditions.

Growth Responses of Drought Resistant Rice Cultivars to Soil Compaction under Irrigated and Succeeding Non-irrigated Conditions during the Vegetative Stage

We investigated whether drought resistant rice cultivars exhibit higher dry-matter production under wet and dry compacted soil conditions in the vegetative stage and determined the dominant factors governing resistance to soil compaction. Three rice cultivars, a drought-sensitive Nipponbare, and drought-resistant Senshou and Dular, were grown in pots at four soil bulk densities (SBD) ranging from 1300 to 1600 dry soil kg m−3. Root and shoot dry matter productions was slightly smaller in Nipponbare over the 29 days after sowing under irrigated conditions than in the other cultivars at all SBDs. Senshou and Dular also maintained a higher dry matter production, both in relative and absolute values, than Nipponbare under the condition of withheld irrigation from days 29 — 39 after sowing. The higher stomatal conductance and leaf water potential of these two cultivars were supported by a larger root system which was mostly accompanied by lower top-root ratios in the irrigated and compacted soils. The higher plant growth rate under the non-irrigated condition might have been a result of both the higher water absorption rate and water use efficiency, which in turn were supported by the larger root biomass. We conclude that the ability of rice to rapidly develop a root system in the early vegetative phase under compacted soils facilitates plant production under subsequent soil desiccated conditions.