Limited Root Growth Research Articles

RELAÇÕES ENTRE PRODUTIVIDADE DE SORGO FORRAGEIRO E ATRIBUTOS FÍSICOS E TEOR DE MATÉRIA ORGÂNICA DE UM LATOSSOLO DO CERRADO

The soil physical attributes and organic matter influence plant growth and development by limiting root growth and crop yield. Aiming to study the spatial and linear correlations among forage sorghum yield and soil physical properties and organic matter, an experiment was carried out in a Distroferric Red Latosol, in Selvíria, Mato Grosso do Sul State, Brazil, in the 2005 crop season. Thus, the forage sorghum fresh and dry matter yield, microporosity, macroporosity, total porosity, soil bulk density, and organic matter content were analyzed, at three depths (0.00-0.10 m, 0.10-0.20 m, and 0.20-0.30 m). The samples were collected in a geostatistical grid, with a total of 124 points, in an area of 4,000 m2. The sorghum fresh and dry matter yield showed high variability, while, for the soil properties, it was low. The plant attributes, macroporosity (in the first layers), microporosity, total porosity, and bulk density, in the first and third layers, followed well-defined spatial standards, reaching from 17.9 m to 84.2 m, while the other attributes showed pure nugget effect. The simple linear correlation among the plant attributes was high and positive, while among the plant and soil attributes it was low and significant, with positive interactions for macroporosity and total porosity, as well as negative for soil bulk density, in the first layer. The bulk density in the soil surface layer was an excellent indicator of soil physical quality, for the estimation of dry matter yield.KEY-WORDS: Spacial variability; macroporosity, microporosity, total porosity; bulk density.

Physical properties of a rhodic haplustox under two sugarcane harvesting systems

This study had the purpose of evaluating the effects of two management types of sugarcane: harvesting of burnt cane (BCH) and mechanized harvesting of unburnt green cane (MCH), on some soil physical properties of a dystrophic Rhodic Haplustox. The data were then compared with results for the same soil type under native forest. A completely randomized design was used, with three treatments and 20 replications. The following characteristics were determined: organic matter, aggregate stability, soil bulk density, and porosity at depths of 0-0.20 m and soil penetration resistance. After 15 years of cultivation, there were some alterations in the soil under cane burnt before harvesting, evidenced by a drop in the weighted average diameter of stable aggregates in water and increased soil bulk density. Significant changes were also detected in total porosity and pore distribution under both harvesting systems. Critical values for penetration resistance were observed in the area under mechanized sugar cane harvesting, with a value of 4.5 MPa in the 40-55 cm layer. This value is considered high and could indicate compaction and restriction of root growth. Soil properties under the green cane (unburned) management system were closest to those of the soil under native forest.

Acidity and Aluminum Speciation as Affected by Surface Liming in Tropical No‐Till Soils

Aluminum toxicity is one of the major soil factors limiting root growth in acidic soils. Because of the increase in organic matter content in the upper few centimeters of soils under no‐till systems (NTS), most Al in soil solution may be complexed to dissolved organic C (DOC), thus decreasing its bioavailability. The aim of this study was to evaluate the effects of surface liming on Al speciation in soil solution in Brazilian sites under NTS. Field experiments were performed in two regions with contrasting climates and levels of soil acidity: Rondonopolis, Mato Grosso State, on a Rhodic Haplustox, and Ponta Grossa, Paraná State, on a Typic Hapludox. The treatments consisted of a control and three lime rates, surface applied to raise the base saturation to 50, 70, and 90%. Soil solution was obtained at soil water equilibrium (1:1 w/w soil/water ratio). The effects of surface liming on soil chemical attributes and on the composition of the soil solution were dependent on weather conditions, time under NTS, and soil weathering. Most Al in soil solution was complexed to DOC, representing about 70 to 80% of the total Al at pH <5.0, and about 30 to 40% at pH >5.0. Under pH 5.5, the results were closely correlated with the solubility line for amorphous Al. Organic complexes may control Al3+ release into soil solution at pH <5.5. Results suggest that in areas under NTS for a long period of time, Al toxicity might decrease due to its complexation to high‐molecular‐weight organic compounds.

Growth, Nitrogen Uptake and Flow in Maize Plants Affected by Root Growth Restriction

The objective of the present study was to investigate the influence of a reduced maize root-system size on root growth and nitrogen (N) uptake and flow within plants. Restriction of shoot-borne root growth caused a strong decrease in the absorption of root: shoot dry weight ratio and a reduction in shoot growth. On the other hand, compensatory growth and an increased N uptake rate in the remaining roots were observed. Despite the limited long-distance transport pathway in the mesocotyl with restriction of shoot-borne root growth, N cycling within these plants was higher than those in control plants, implying that xylem and phloem flow velocities via the mesocotyl were considerably higher than in plants with an intact root system. The removal of the seminal roots in addition to restricting shoot-borne root development did not affect whole plant growth and N uptake, except for the stronger compensatory growth of the primary roots. Our results suggest that an adequate N supply to maize plant is maintained by compensatory growth of the remaining roots, increased N uptake rate and flow velocities within the xylem and phloem via the mesocotyl, and reduction in the shoot growth rate.

A Novel Plant Leucine-Rich Repeat Receptor Kinase Regulates the Response ofMedicago truncatulaRoots to Salt Stress

In plants, a diverse group of cell surface receptor-like protein kinases (RLKs) plays a fundamental role in sensing external signals to regulate gene expression. Roots explore the soil environment to optimize their growth via complex signaling cascades, mainly analyzed in Arabidopsis thaliana. However, legume roots have significant physiological differences, notably their capacity to establish symbiotic interactions. These major agricultural crops are affected by environmental stresses such as salinity. Here, we report the identification of a leucine-rich repeat RLK gene, Srlk, from the legume Medicago truncatula. Srlk is rapidly induced by salt stress in roots, and RNA interference (RNAi) assays specifically targeting Srlk yielded transgenic roots whose growth was less inhibited by the presence of salt in the medium. Promoter-beta-glucuronidase fusions indicate that this gene is expressed in epidermal root tissues in response to salt stress. Two Srlk-TILLING mutants also failed to limit root growth in response to salt stress and accumulated fewer sodium ions than controls. Furthermore, early salt-regulated genes are downregulated in Srlk-RNAi roots and in the TILLING mutant lines when submitted to salt stress. We propose a role for Srlk in the regulation of the adaptation of M. truncatula roots to salt stress.

Impact of soil compaction on root architecture, leaf water status, gas exchange and growth of maize and triticale seedlings

Triticale and maize, with different structure of the root system and type of photosynthesis were examined to know changes in shoot physiology and root architecture in response to varying degree of soil compaction. In the root-box, effects of different levels of soil compaction (1.30, 1.47 and 1.58 Mg m -3 ) on a shoot and root dry matter, leaf number and area, number and length of seminal, seminal adventitious, nodal and lateral roots, leaf water potential (ψ), maximum quantum yield of PS II (Fv/Fm) and gas exchange were studied. Severe soil compaction treatments decreased leaf number, leaf area and dry matter of shoots and roots, while increasing shoot-to-root dry matter ratio. In addition, high level of soil compaction strongly affected the length of seminal and seminal adventitious roots, and the number and length of lateral roots developed on the seminal root. Along with the restriction of root growth, significant influences were observed in ψ, Fv/Fm and gas exchange. High soil compaction treatments resulted in decreased ψ, Fv/Fm, and photosynthetic rate, transpiration rate and stomatal conductance for both triticale and maize. Maize whose root growth was more heavily restricted by the soil compaction compared to triticale showed greater damages in physiological characteristics in leaves, while the impact on triticale was relatively small. The results indicated that damages in photosynthesis, water relation and shoot growth by soil compaction would be closely related to sensitivity of root systems architecture to high mechanical impedance of soil.

Potato Yield and Quality Response to Subsoil Tillage and Compaction

Compacted soils have been found in intensively cultivated vegetable crop regions of Central Wisconsin, resulting in the wide scale use of subsoil tillage by growers. The goal of this project was to assess potato (Solanum tuberosum L.) yield and quality response to soil compaction and subsoil tillage. Potato quality factors evaluated were marketable yield, tuber size distribution, internal quality, and sugar concentration. A controlled small plot experiment and several field scale experiments located in collaborating grower fields were conducted to assess potato and soil responses to subsoil tillage. Cone index profiles showed the potential for limited root growth below the compacted soil layer with values >2.0 MPa. Subsoil tillage reduced cone index values to <1.0 MPa below 33 cm in 2 of 3 yr. Total and U.S. no. 1 yields were not influenced by subsoil tillage. Likewise, no consistent differences were seen in the size distributions of U.S. no. 1 tubers across treatments, but subsoil tillage tended to decrease proportion of tubers 113 to 170 g. Subsoil tillage did not affect tuber glucose or sucrose concentrations at harvest or following storage for 120 d. Internal tuber defects were not affected by either compaction or subsoil tillage. The lack of consistent effects of subsoil tillage on potato yield raises questions regarding the validity of this practice. The recommendation that potato growers use subsoil tillage may be linked to increased tuber size distribution or factors other than yield such as water, nutrient, or disease management.

Rice ROOT ARCHITECTURE ASSOCIATED1 Binds the Proteasome Subunit RPT4 and Is Degraded in a D-Box and Proteasome-Dependent Manner

Root growth is mainly determined by cell division and subsequent elongation in the root apical area. Components regulating cell division in root meristematic cells are largely unknown. Previous studies have identified rice (Oryza sativa) ROOT ARCHITECTURE ASSOCIATED1 (OsRAA1) as a regulator in root development. Yet, the function of OsRAA1 at the cellular and molecular levels is unclear. Here, we show that OsRAA1-overexpressed transgenic rice showed reduced primary root growth, increased numbers of cells in metaphase, and reduced numbers of cells in anaphase, which suggests that OsRAA1 is responsible for limiting root growth by inhibiting the onset of anaphase. The expression of OsRAA1 in fission yeast also induced metaphase arrest, which is consistent with the fact that OsRAA1 functions through a conserved mechanism of cell cycle regulation. Moreover, a colocalization assay has shown that OsRAA1 is expressed predominantly at spindles during cell division. Yeast two-hybrid and pull-down assays, as well as a bimolecular fluorescence complementation assay, all have revealed that OsRAA1 interacts with a rice homolog of REGULATORY PARTICLE TRIPLE-A ATPASE4, a component that is involved in the ubiquitin pathway. Treating transgenic rice with specific inhibitors of the 26S proteasome blocked the degradation of OsRAA1 and increased the number of cells in metaphase. Mutation of a putative ubiquitination-targeting D-box (RGSLDLISL) in OsRAA1 interrupted the destruction of OsRAA1 in transgenic yeast. These results suggest that ubiquitination and proteasomic proteolysis are involved in OsRAA1 degradation, which is essential for the onset of anaphase, and that OsRAA1 may modulate root development mediated by the ubiquitin-proteasome pathway as a novel regulatory factor of the cell cycle.

Organic N and particulate organic matter fractions in organic and conventional farming systems with a history of manure application

Indicators of soil fertility are needed for the effective management of organic farming systems. Sustainable management hinges upon our gaining an improved understanding of C and N dynamics. The influence of cropping systems and amendments applied in the Lakeland Wisconsin Integrated Cropping Systems Trial on total hydrolyzable organic N (THN) fractions and particulate organic matter (POM) was investigated after a decade in a conventional cash grain system (Conv) of continuous maize amended with inorganic fertilizer, an organic cash-grain system (Org-CG) that relied on legume N, and an organic animal-based system (Org-AN) that included alfalfa and manure additions. Maize yields had consistently ranked Org-CG Org-CG > Conv. Amino sugar-N (AS-N) contents, which reflect microbially derived N, did not differ among systems and concentrations were quite high (346.5 mg AS-N/kg soil in the 0–50 cm depth). This, and soil variability were attributed to the sites’ history of manure application. The amount (1.3 g POM-C/kg soil) and proportion (≈7.5% of total SOC) of POM-C were quite low and did not differ among systems. Failure to accumulate SOC or POM in these soils, even under organic management, is attributed to rapid C decay and/or limited root growth. An N rate study was added the fall before samples were taken and N addition did increase yield in the Conv and Org-CG systems despite evidence of soil N surplus. This suggests that either amino N is unavailable to plants or that root N acquisition is limited by other constraints. Low POM-C contents accompanied by high AS-N and AA-N levels reveal an imbalance in these soils which are likely to be C limited. Based on this, we conclude excess N has prevented use of organic practices from enhancing soil quality at this site.

First Report of Wilt and Stem Canker of Poinsettia (Euphorbia pulcherrima) Caused by Phytophthora nicotianae in Puerto Rico.

Poinsettias are grown extensively in greenhouses in Puerto Rico, a five million dollar industry during the winter season of 2005. More than 2,000 'Freedom' plants from an ornamental nursery near Aibonito exhibited severe wilt and dieback symptoms. The disease was found in 5 of 12 surveyed greenhouses where severity ranged from 50 to 100% and occurred regardless of the use of metalaxyl and mefenoxam. Symptoms during the growth phase included stunted plants, thin stems, chlorotic leaves, and brown roots. During flower bract development, symptoms consisted of leaf wilting often in sectors, stem canker, and purple-to-black lesions that extended from the stem to the petioles followed by soft rot. Isolations from symptomatic stem and root tissue were made on corn meal agar (CMA) (17 g/liter) amended with pimaricin (10 mg/liter), ampicillin (250 mg/liter), rifampicin (10 mg/liter), pentachloronitrobenzene (100 mg/liter), and hymexazol (50 mg/liter) (PARPH) (1). Pure cultures were obtained by hyphal-tip transfers onto CMA-PARPH. Colonies grown on acidified potato dextrose agar (APDA) at 25°C were arachnoid with abundant aerial mycelium and sporangia. Sporangia formed singly or in a loose sympodium on long sporangiophores and were papillate, mostly persistent, or caducous with short pedicel. The shape of sporangia varied from ellipsoidal to elongated ovoid, with a length/breath ratio of 16.5 × 14.2 μm. Large, spherical, terminal, and intercalary chlamydospores readily formed in APDA and PARPH. The isolate was identified as Phytophthora nicotianae on the basis of morphological and molecular characteristics. Molecular identification by sequence analysis of the internal transcribed spacer rDNA region confirmed the identity of the isolate P210.1 as P. nicotianae (GenBank Accession No. DQ485412). Pathogenicity tests were conducted with isolates P210.1 and IG grown on APDA for 7 days at 24°C. Isolates were then covered with sterile water for 48 h to induce sporangia and zoospore production at 24°C and continuous light. A suspension of 10 ml of approximately 120 sporangia ml-1 were added to pots containing 2.2 kg of a 1:1 mixture of field soil and soilless media (Promix) composed of peat moss vermiculite and perlite. One healthy poinsettia rooted stem and one 2-month-old plant were transplanted individually into the inoculated soil and pots were flooded with sterile water for 24 h. A noninoculated control was included, each isolate and control were replicated five times. First symptoms (7 to 10 days after inoculation) included brown, limited root growth and lower stem discoloration. Plants (30- to 45-day-old) show a decline in vigor and rapid death of branches that are similar symptoms to those observed on infected poinsettias in commercial greenhouses. P. nicotianae was reisolated from infected root, crown, and stem tissue on PARPH media. A strict sanitation program was recommended to prevent recontamination. To our knowledge, this is the first report of P. nicotianae on poinsettia in Puerto Rico. Reference: D. J. Mitchell and M. E. Kannwischer-Mitchel, Phytophthora. Page:31 in: Methods for Research on Soilborne Phytopathogenic Fungi. L. L. Singleton et al., eds. The American Phytopathological Society, St. Paul, MN, 1993.

Fine root distribution of trees and understory in mature stands of maritime pine (Pinus pinaster) on dry and humid sites

Maritime pine (Pinus pinaster) is the main tree cropping species in the Landes of Gascogne forest range in south western France. Soils are nutrient poor, sandy podzosols and site fertility is determined essentially by organic matter content and depth of water table, which is known to limit root growth. We hypothesised, with an ultimate goal of constructing a nutrient uptake model applicable to this region, that the organic top horizons together with the depth of the water table should be the most important parameters related to fine root distribution and presence of associated mycorrhiza. To test this hypothesis, we compared two adult Pinus pinaster stands, contrasting in depth of water table and soil fertility and evaluated fine roots (diameter ≤2 mm) of understory species and fine roots and ectomycorrhizal morphotypes of Pinus pinaster down to 1.2 m, using a soil corer approach. Total fine root biomass of Pinus pinaster was not significantly different between both sites (3.6 and 4.5 t ha−1 for the humid, respectively, dry site), but root distribution was significantly shallower and root diameter increased more with depth at the humid site, presumably due to more adverse soil conditions as related to the presence of a hardpan, higher amount of aluminium oxides and / or anoxia. Fine roots of Pinus pinaster represented only about 30% of total fine root biomass and 15% of total fine root length, suggesting that the understory species cannot be ignored with regards to competition for mineral nutrients and water. A comparison of the ectomycorrhizal morphotypes showed that the humid site could be characterised by a very large proportion of contact exploration types, thought to be more relevant in accessing organic nutrient sources, whereas the dry site had a significantly higher proportion of both long-distance and short-distance exploration types, the latter of which was thought to be more resistant to short-term drought periods. These results partly confirm our hypothesis on root distribution as related to the presence of soil mineral nutrients (i.e. in organic matter), point out the potential role of understory plant species and ectomycorrhizal symbiosis and are a valuable step in building a site-specific nutrient uptake model.

Root Function in Nutrient Uptake and Soil Water Effect on NO 3−-N and NH 4+-N Migration

Root function in uptake of nutrients and the effect of soil water on the transfer and distribution of NO 3 −-N in arable soil were studied using summer maize ( Zea mays L. var. Shandan 9) as a testing crop. Results showed that root growth and water supply had a significant effect on NO 3 −-N transfer and made NO 3 −-N distributed evenly from bulk soil to rhizosphere soil. Under a natural condition with irrigation, the difference of NO 3 −-N concentration at different distance points from a maize plant was smaller, while obvious difference of NO 3 −-N concentration was observed under conditions of limited root growth space without irrigation. Whether root growth space was restricted or not, the content of soil NO 3 −-N decreased gradually from 10 to 0 cm from the plant, being opposite to the root absorbing area in soils. When root-grown space was limited, changes of NO 3 −-N concentration at different distances from a plant were similar to that of water content in tendency. Results showed that NO 3 −-N could be transferred as solute to plant root systems with water uptake by plants. However, the transfer and distribution of NH 4 +-N were not influenced by root growth and soil water supply, being different to NO 3 −-N.

Identification of dominant mutations that confer increased aluminium tolerance through mutagenesis of the Al-sensitive Arabidopsis mutant, als3-1

Aluminium (Al) toxicity is a global agricultural problem that occurs in acid soil environments and severely limits root growth and crop productivity. The isolation and characterization of a gene, ALS3, which is absolutely required by Arabidopsis seedlings for growth in an Al-toxic environment was reported previously. Since the als3-1 loss-of-function mutant has extreme root growth inhibition even in the presence of very low levels of Al, it was an excellent candidate for using a mutagenesis approach to identify suppressor mutations that would increase either Al resistance or tolerance in Arabidopsis roots. EMS-mutagenized als3-1 seedlings were screened for mutants that could sustain root growth in an Al-containing environment that is highly toxic to als3-1 but not Col-0 wt. This approach resulted in identification of 12 strong suppressor mutants that reversed the als3-1 phenotype and grew as well or better than Col-0 wt in the presence of high levels of Al. Subsequent analysis of three representative suppressor mutants revealed that the phenotype of each probably arises from dominant gain-of-function mutations at the same locus. Detailed analysis of one of these, alt1-1 (Al tolerant), suggests that this mutation positively impacts Al resistance in a manner dependent on pH adjustment rather than enhanced Al exclusion. Identification of these suppressor mutations, should not only further elucidate the biochemical and molecular mechanisms underlying Al toxicity and tolerance but also will develop a collection of mutations that may be useful for engineering crop plants that can grow and thrive in Al-toxic environments.

Physiological and genetic analyses of aluminium tolerance in rice, focusing on root growth during germination

Aluminium (Al) ion limits root growth of plants in acidic soils, and rice exhibits the highest level of Al-tolerance among graminous crops. To elucidate Al-tolerance mechanisms in rice, response to Al was compared between rice ( Oryza sativa L., cv. Nipponbare) and wheat ( Triticum aestivum L., cv. ET8), focusing on seminal root growth at seedling stage and germination stage. At seedling stage, rice and wheat were similarly sensitive to Al in both dose- and time-dependent manner during a 24-h Al exposure. On the contrary, at germination stage, rice was more tolerant to Al than wheat, and wheat roots displayed the loss of plasma membrane integrity more extensively than rice. A rice mutant exhibiting Al hypersensitivity at germination stage was obtained by screening 42,840 R 2 progeny derived from the regenerated R 0 plants of Nipponbare and thereafter confirmation of the mutant phenotype in R 3 progeny. At germination stage, root growth of the mutant was strongly inhibited in the presence of Al but not in the absence of Al. However, at seedling stage, root growth of the mutant and wild type was similarly tolerant to Al. Taken together, we conclude that rice possesses Al-tolerant function that is under genetic control and specifically operates for root growth at germination stage, making rice more tolerant to Al than wheat.

Effects of soil temperature on shoot and root growth and nutrient uptake of 5-year-old Norway spruce seedlings

Soil temperature is a main factor limiting root growth in the boreal forest. To simulate the possible soil-warming effect of future climate change, 5-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were subjected to three simulated growing seasons in controlled environment rooms. The seedlings were acclimated to a soil temperature of 16 degrees C during the first (GS I) and third growing seasons (GS III), but were assigned to random soil-temperature treatments of 9, 13, 18 and 21 degrees C during the second growing season (GS II). In GS II, shoot diameter growth was lowest in the 21 degrees C treatment and root growth was lowest in the 9 degrees C treatment. In GS III, shoot height and root length growth improved in seedlings that had been kept at 9 degrees C during GS II, indicating compensatory growth in response to increased soil temperature. The temporary decrease in soil temperature had no long-lasting significant effect on seedling biomass or total nutrient uptake. At the end of GS III, fine roots of seedlings exposed to a soil temperature of 21 degrees C in GS II were distributed more evenly between the organic and mineral soil layers than roots of seedlings in the other treatments. During GS II and GS III, root growth started earlier than shoot growth, decreased during the rapid shoot elongation phase and increased again as shoot growth decreased.

Growth and potassium uptake by Maize (Zea mays L.) in three soils differing in clay contents

Soil texture affects nutrient availability in soil hence affects plant growth. Soils high in clay contents retain more K+, and generally plants grown on these soils do not respond to applied K+. A pot experiment was conducted to evaluate growth response and K+uptake by maize plants grown on three different textured soils. There were four K+ levels 0, 50, 100 and 150 mg K+/kg soil. Ten seeds of hybrid maize (cv. Magic) were sown in each pot which was replicated four times. Crop was harvested after seven weeks. Root and shoot dry matter was recorded and samples were analysed for K+ concentration. Soil texture significantly (p< 0.05) affected biomass production by maize plants. Shoot dry matter produced was maximum in plants grown in sandy soil. Root growth was minimum in soil high in clay contents compared to plant grown in sandy soil. Root to shoot dry matter ratio correlated negatively with clay contents (r = 0.91) showing limited root growth in soils high in clay contents. It also influenced total dry matter (TDM) as indicated by its positive correlation (r = 0.83). Potassium application did not affected plant growth in soil high in clay content, however, K+ uptake was increased with an increase in K+level in soils low in clay contents. Total dry matter was significantly correlated (r = 0.83) with root K+uptake, but correlation with shoot K+uptake was not significant.

THE EFFECTS OF PROGRESSIVE ROOT REMOVAL PRIOR TO PLANTING ON SHOOT AND ROOT GROWTH OF BETULA PENDULA Roth

Summary Root loss during transplanting of bare rooted nursery stock is thought to limit water uptake during establishment. An initial investigation into the effects on growth under well watered conditions of progressive removal of root material from dormant trees of Betula pendula Roth, was set up in spring 1994. Trees with roots ≤1 mm removed (40% removal by mass) and with roots ≤ 5 mm removed (84% removal by mass) were compared to controls. Some limited measurements of water relations were also made. Shoot and root growth were increasingly limited by progressive root removal. Root regrowth was apparently proportional to the amount of old root material left behind after transplanting. In addition, the most severe treatment (roots ≤ 5 mm were removed) limited root growth in favour of shoot growth. Direct measurements of water relations proved to be difficult and inconclusive, however, increases in stem diameter, an indirect measurement of changes in water relations, indicated that progressive root removal subtly increased water stress in the trees. Alternative hypotheses for the observed of changes in growth based on limitations in sugar physiology and hormone imbalance are also discussed.

Effect of High pH on Foliar Chlorosis and Growth of Five Betula Species

Abstract The relative alkalinity tolerances of yellow birch, sweet birch, river birch, paper birch, and Japanese white birch were evaluated by comparing foliar chlorosis and growth of seedlings irrigated for 56 days with either a pH 6.0 nutrient solution (control) or K2CO3-amended solutions adjusted to pH 7.3 or 8.3. Both visual ratings and SPAD-502 chlorophyll meter measurements were effective methods of quantifying the severity of alkalinity-induced foliar chlorosis. Eight weeks of the pH 8.3 treatment was more effective than 4 weeks of the same treatment or 4 or 8 weeks of the pH 7.3 treatment for detecting differences in alkalinity tolerance among the species. Treatment for 8 weeks with either pH 7.3 or 8.3 solutions increased foliar chlorosis of sweet, river, paper, and Japanese white birch seedlings relative to the control treatment, whereas yellow birch seedlings exhibited mild chlorosis only in the pH 8.3 treatment. Based upon severity of chlorosis, yellow birch was most tolerant of soil alkalinity, sweet birch was least tolerant, and river, paper and Japanese white birch were intermediate in tolerance. Stem relative growth rates and shoot and root cumulative dry mass values did not consistently corroborate the relative alkalinity tolerances of the birch species indicated by the chlorosis and chlorophyll data, possibly because of container restriction of root growth of the more rapidly growing species. Results of this study indicate that yellow birch may be valuable for developing new birch cultivars adapted to alkaline soils.

Crescimento radicular e nutrição da soja cultivada no sistema plantio direto em resposta ao calcário e gesso na superfície

A deficiência de cálcio e a toxidez de alumínio têm sido os fatores de acidez mais limitantes ao crescimento de raízes. Com o objetivo de avaliar o crescimento radicular e a absorção de nutrientes pela soja, cv. EMBRAPA 58, e seus reflexos sobre a produção de grãos, considerando as doses de calcário e gesso na superfície, em sistema plantio direto, foi realizado um experimento em um Latossolo Vermelho distrófico textura média, em Ponta Grossa (PR). O delineamento experimental empregado foi o de blocos ao acaso em parcela subdividida, com três repetições. Foram utilizadas quatro doses de calcário dolomítico, com 84% de PRNT: 0, 2, 4 e 6 t ha-1, e quatro doses de gesso agrícola: 0, 4, 8 e 12 t ha-1. A calagem foi realizada em julho e a aplicação de gesso em novembro de 1993. O crescimento radicular da soja não foi afetado pelas condições de acidez, em solo com 15, 12 e 8 mmol c dm-3 de Ca trocável e 28, 32 e 40% de saturação por Al, respectivamente, nas profundidades de 0-10, 10-20 e 20-40 cm. Houve aumento da absorção, pela cultura da soja, de todos os macronutrientes com a calagem, e de Ca e S com a aplicação de gesso. Somente a calagem aumentou a produção de soja, em decorrência de maior disponibilidade e absorção de Mg e de redução dos teores foliares de Zn e Mn.

Densidade radicular do milho considerando os atributos de um solo com horizonte B textural

A absorção de água e nutrientes pelas plantas depende de vários fatores, principalmente do volume de solo explorado pelas raízes. Determinados fatores e, ou, processos ocorridos no solo podem limitar o crescimento das raízes. Este estudo objetivou: (a) quantificar as relações entre densidade radicular da cultura do milho e alguns atributos de um Argissolo Vermelho distrófico arênico e identificar quais desses atributos restringem o crescimento de raízes no horizonte Bt e a produtividade do milho; (b) monitorar a variação temporal de água no solo para avaliar a extração de água do horizonte Bt. O estudo foi realizado com milho no sistema plantio direto, no ano agrícola de 93/94, em um Argissolo Vermelho distrófico arênico, localizado na área experimental do Departamento de Solos da Universidade Federal de Santa Maria. Foram analisados a microporosidade, macroporosidade, porosidade total, densidade do solo, espaço aéreo, textura, concreções, resistência à penetração, cálcio + magnésio, saturação por alumínio, densidade radicular e produtividade do milho. Observando os perfis culturais e a densidade radicular, percebeu-se que o horizonte Bt restringiu o crescimento radicular, principalmente nos perfis com horizonte A raso, quando comparados aos perfis com horizonte A profundo. A densidade do solo e a resistência à penetração não restringiram o crescimento radicular nas condições estudadas; já a presença de concreções e a elevada saturação por alumínio trocável foram as variáveis que mais restringiram o crescimento radicular. Não foi observada redução da umidade volumétrica do horizonte Bt durante o ciclo de crescimento do milho, mesmo em prolongado período de déficit hídrico, indicando que a água presente neste horizonte não foi absorvida pela cultura, considerando a baixa densidade radicular neste horizonte. A produtividade de grãos de milho foi reduzida em 23% nos perfis com horizonte A raso, comparado aos perfis com horizonte A profundo, provavelmente por causa da restrição ao crescimento radicular.