Low Root Growth Research Articles

Variation in the Root System Architecture of Peach × (Peach × Almond) Backcrosses.

The spatial arrangement and growth pattern of root systems, defined by the root system architecture (RSA), influences plant productivity and adaptation to soil environments, playing an important role in sustainable horticulture. Florida's peach production area covers contrasting soil types, making it necessary to identify rootstocks that exhibit soil-type-specific advantageous root traits. In this sense, the wide genetic diversity of the Prunus genus allows the breeding of rootstock genotypes with contrasting root traits. The evaluation of root traits expressed in young seedlings and plantlets facilitates the early selection of desirable phenotypes in rootstock breeding. Plantlets from three peach × (peach × almond) backcross populations were vegetatively propagated and grown in rhizoboxes. These backcross populations were identified as BC1251, BC1256, and BC1260 and studied in a completely randomized design. Scanned images of the entire root systems of the plantlets were analyzed for total root length distribution by diameter classes, root dry weight by depth horizons, root morphological components, structural root parameters, and root spreading angles. The BC1260 progeny presented a shallower root system and lower root growth. Backcross BC1251 progeny exhibited a more vigorous and deeper root system at narrower root angles, potentially allowing it to explore and exploit water and nutrients in deep sandy entisols from the Florida central ridge.

Effect of selenium and soil pH on cadmium phytoextraction by Urochloa decumbens grown in Oxisol

It has been speculated that selenium (Se) supply can affect cadmium (Cd) ‘availability’ and increase the Cd tolerance of plants used for phytoextraction, in a pH-dependent process. Thus, we evaluated the interaction Cd-Se and the effects of soil pH in this interaction on plant availability of Cd and phytoextraction efficiency of Urochloa decumbens cv. Basilisk grown in Oxisol. Two soil concentrations of Cd (0.93 and 3.6 mg kg-1) and Se (<0.2 and 1 mg kg-1) and two soil pH (0.01 mol L-1 CaCl2) conditions (4.1 and 5.7) were considered. At both pH, Se supply increased the exchangeable fraction of Cd and decreased the residual Cd fraction. At pH 4.1, the growth of U. decumbens was impaired by Se addition, regardless of Cd exposure. The lower root growth and tillering of U. decumbens exposed to Cd disappeared at pH 5.7 due to uptake of low Se concentrations. Thus, the toxic or beneficial effects of Se on growth of U. decumbens used for Cd phytoextraction depend on the amount of Se assimilated. The Cd phytoextraction efficiency of U. decumbens was not improved by Se supply, regardless of soil pH. Therefore, we cannot recommend the application of Se to increase Cd phytoextraction by this grass.

高寒草甸植物群落不同根序根系特征对降雨量变化的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 高寒草甸植物群落不同根序根系特征对降雨量变化的响应 DOI: 10.5846/stxb202104261096 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划(2019YFC0507701)；第二次青藏高原综合科学考察研究项目(2019QZKK0302)；国家自然科学基金(U20A2008)；西南民族大学研究生"创新型科研项目"重点项目(CX2019SZ84) Response of plant roots in different diameter classes to changing precipitation in an alpine meadow Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:根系是草原生态系统中最重要的碳库之一,分析高寒草甸植物群落生物量和地下不同径级根系碳分配特征及根系的生长特征对降雨变化的响应,有利于了解全球变化背景下高寒草甸植物根系、土壤碳氮循环及其过程。采用微根管技术原位监测5种降雨处理下(增雨50%:1.5P、自然降雨:1.0P、减雨30%:0.7P、减雨50%:0.5P、减雨90%:0.1P)高寒草甸植物群落和根系属性(现存量、生产量、死亡量、根系寿命和周转速率)的变化特征,结果表明:(1)降雨变化对地上植物群落生物量无显著影响,但0.5P和0.1P显著增加禾本科生物量(P<0.05)。(2)总根系现存量在处理间无显著差异,但随着降雨量减少呈先增加后降低的趋势。土层间不同径级根系现存量差异显著,0-10 cm土层1.5P和0.7P1级根现存量显著增加,2级和3级根现存量显著降低;在10-20 cm土层,1.0P2级根系现存量显著高于其余处理(P<0.05)。(3)总根生产量与死亡量随降雨减少而降低,在0-10 cm土层,1.0P总根生产量和死亡量最高,0.1P显著降低了1级根生产量(P<0.05)。(4)0.1P显著增加10-20 cm土层1级根和总根寿命(P<0.05)。(5)根系周转随降雨量减少呈降低趋势,但无显著差异(P>0.05)。(6)结构方程模型进一步表明:根系现存量和生产量受土层和水分的直接影响,土层和养分对根系周转有负效应。综上所述,降雨量的变化并未显著改变地下总根系生物量,但少量降雨变化(0.7P、1.5P)会降低植物对2、3级根生物量的分配,投入更多资源以促进1级根的生长;而水分下降至轻度水分胁迫(0.1P),植物会减少地下各径级根系生物量的分配,保持低根系生物量消耗和低根系生长来维持其正常的生长状态,完成其正常的生态功能。 Abstract:Root is one of the most important carbon pools in grassland ecosystem. Analyzing the biomass of plant community, the carbon distribution characteristics of roots with different diameters, and the response of root growth characteristics to changing precipitation contributes to understand the carbon and nitrogen cycle and process of roots and soil in an alpine meadow under global change. In this study, we investigated the biomass of plant community and used the minirhizontron technology to investigate changes of root properties (standing crop, production, mortality, life span and turnover) in an alpine meadow, in response to five precipitation gradient, including 90%, 50% and 30% decrease (0.1P, 0.5P, 0.7P), ambient control (1.P) and 50% increase (1.5P). The results showed that: 1) There was no significant effect of precipitation gradient to above-ground biomass, while 0.5P and 0.1P significantly increased the biomass of grass (P<0.05). 2) The total root standing crop was not significant affected by treatments, but increased first and then decreased with precipitation decrease. There were significant differences in response of roots of different diameter classes among soil layers. In 0-10 cm soil layer, the standing crop significantly increased in 1-level roots under 1.5P and 0.7P, however, significantly decreased in 2 and 3-level. In addition, in 10-20 cm soil layer, the standing crop of 2-level roots in 1.0P was significantly higher than that in other treatment (P<0.05). 3) Root production of 1-level roots in the surface layer are significantly reduced under 0.1P, meanwhile, the total production and mortality of 1.0P in the surface layer was significantly higher than that of other treatments (P<0.05). 4) The life span of total roots and 1-level roots in the bottom layer increased under 0.1P (P<0.05). 5) Root turnover decreased with precipitation decrease, but there was no significant difference among treatments. 6) The structural equation model showed that the root standing crop and production were directly affected by the soil layer and water content, besides the root turnover was directly affected by the soil layer and nutrients. In summary, under small range of precipitation change (0.7P, 0.5P), plants would reduce the biomass allocation to fine roots and invest more resources in the growth of 1-level roots; however, under mild water stress (0.1P), the plant would reduce the allocation of underground root biomass in all diameter classes, maintain low biomass consumption and low root growth to maintain its normal growth state, so as to complete its normal ecological function. 参考文献 相似文献 引证文献

Root growth and crop performance of soybean under chemical, physical, and biological changes after subsoiling

AbstractChemical, physical and biological soil attributes can facilitate soybean root growth in greater volume and depth in the soil, which can minimize yield reduction caused by water deficit. Soil management can contribute positively or negatively to these soil attributes. The aim of this work was to evaluate the root growth and crop performance of soybean, in response to chemical, physical and biological changes after subsoiling at different depths. At the R5 phenological stage, trenches were made for sampling and soil collection for chemical, physical and biological analysis and root growth was carried out. At V5, V7, R2 and R5 stages, plants were collected to evaluate height, leaf area and dry mass. At V5, stage number and dry mass of the nodules were evaluated. Subsoiling increased pH and Ca, and decreased Al in the soil, resulted in higher relative density and did not affect in mechanical penetration resistance compared to non‐subsoiled soil. Basal respiration and soybean nodulation were higher in the subsoiled soil. Up to 15 cm depth, there were 87.91% of the total root dry mass and 78.79% of the total root volume. Initial and final plant growth were the same in subsoiled and non‐subsoiled soil. Number of nodules in the subsoiled soil was 28% higher than in the non‐subsoiled soil. Under these study conditions, subsoiling provides lower root growth but benefits grain yield.

Is a non-synonymous SNP in the HvAACT1 coding region associated with acidic soil tolerance in barley?

The barley HvAACT1 gene codes for a citrate transporter associated with tolerance to acidic soil. In this report, we describe a single nucleotide polymorphism (SNP) in the HvAACT1 coding region that was detected as T-1,198 (in genotypes with lower root growth on acidic soil) or G-1,198 (greater root growth) and resulted in a single amino acid change (L/V-172). Molecular dynamic analysis predicted that HvAACT1 proteins with L or V-172 were stable, although the substitution led to structural changes within the protein. To evaluate the effect of the SNP on tolerance to acidic soil, barley accessions were separated into haplotypes based on the presence of a 1 kb insertion in the HvAACT1 promoter and a 21 bp insertion/deletion. These markers and the SNP-1,198 allowed the identification of five haplotypes. Short-term soil experiments showed no difference in root growth for most of the accessions containing the 21 bp insertion and T or G-1,198. In contrast, genotypes showing both the 21 bp deletion and G-1,198, with one of them having the 1 kb insertion, showed greater root growth. These results indicate that the SNP was not advantageous or deleterious when genotypes from the same haplotype were compared. The occurrence of the SNP was highly correlated with the 21 bp insertion/deletion that, together with the 1 kb insertion, explained most of the barley tolerance to acidic soil.

Seasonality and partitioning of root allocation to rhizosphere soils in a midlatitude forest

AbstractRoot growth, respiration, and exudation are important components of biogeochemical cycles, yet data on the timing and partitioning of C to these processes are rare. As a result, it is unclear how the seasonal timing, or phenology, of root C allocation is affected by the phenology of its component processes: growth of root tissue, respiration, mycorrhizal allocation, and exudation of labile C. The objective of this study was to estimate the phenology and partitioning of C belowground across the growing season in a midlatitude forest located in central Massachusetts. Fine and coarse root production, respiration, and exudation were summed to estimate a monthly total belowground C flux (TBCF) in two hardwood stands dominated by Quercus rubra and Fraxinus americana, respectively, and one conifer stand dominated by Tsuga canadensis. We observed significant stand‐level differences in belowground C flux and the partitioning of C to root growth, mycorrhizal fungi, exudation, and respiration. The deciduous hardwood stands allocated C belowground earlier in the season compared to the conifer‐dominated stand. The deciduous stands also allocated a greater proportion of TBCF to root growth compared to the conifer‐dominated hemlock (T. canadensis) stand. Of the three stands, red oak partitioned the greatest proportion of TBCF (~50%) to root growth, and hemlock the least. Low root growth rates in hemlock may be related to the arrival and spread of the invasive pest, hemlock wooly adelgid (Adelges tsugae), during the study period. Ongoing research in the eastern hemlock stand may yet determine how whole tree allocation and partitioning change as a result of this infestation.

Soil properties and subsoil constraints of urban and peri-urban agriculture within Mahikeng city in the North West Province (South Africa)

PurposeUrban and peri-urban agriculture is becoming increasingly important as a source of income and food for the urban population in South Africa. While most studies on urban agriculture have focused their attention on surface soils, there is dearth of information regarding subsoil properties. This study examined properties of subsoil horizons that may impede root growth and productivity of crops under urban agriculture.Materials and methodsThe properties of topsoil (0–20 cm) and subsoil horizons (20–40 cm) of four profiles from plots within the city of Mahikeng (25° 48′ S and 25° 38′ E) were examined to determine the nature of subsoil constraints that can limit root growth and crop productivity. The plots were selected in an area extending through four residential suburbs of the city, and two plots with a long history of cultivation were purposely selected from each suburb to represent the main cropping systems and soil types. Soil physical (penetrometer resistance, bulk density, hydraulic conductivity), chemical (pH, exchangeable Ca, Mg, K, Na, phosphorus and boron) and biological (root growth, organic carbon, microbial biomass, enzyme activity) properties were measured in the profiles.Results and discussionEven though there was a large variability between profiles, the results revealed high bulk density (mean 2.06 Mg m−3) at the top of the subsoil for all the profiles. The corresponding mean penetrometer resistance was 1.89 MPa implying high mechanical resistance to root growth in this layer. The hydraulic conductivities at saturation were below 12 mm h−1 suggesting low drainage which may result in perched water table and waterlogging leading to depleted oxygen in the root zone. The pH in all the profiles was slightly acid to moderate alkaline (6.1–8.3, in water), and low levels of plant available boron (B) were found in the subsoil layers. Most of the profiles had extreme values of physical properties that would constrain root growth. All the subsoil layers had significantly (p < 0.05) lower root growth, organic carbon, microbial biomass and enzyme activity.ConclusionsIt was concluded that subsoil constraints to root growth appear to be widespread in profiles of soils used for urban and peri-urban agriculture in the city of Mahikeng. Given that studying and ameliorating subsoil constraints is difficult, time-consuming and expensive, it is recommended that periodic deep ploughing and inclusion of plants with roots which are tolerant or resistant to these conditions be considered as part of routine soil management practice in plots used for urban agriculture.

Root growth potential, water relations and carbohydrate status of ash alternative species following pre-plant storage

The catastrophic loss of ash (Fraxinus spp.) trees in the midwestern United States due to emerald ash borer has emphasized the need for greater diversity in urban and community forests. However, the availability of some important Fraxinus alternative species may be limited due to difficulties in nursery production. We conducted two trials to examine growth and physiological responses of bare-root tree liners to pre-plant storage and handling. In both trials, bare-root liners were given one of four treatments for three weeks prior to planting: 1) control, 2) cold storage (4°C), 3) sweating (warm, moist storage), or 4) heeled-in (outdoor storage). Subjecting trees to a warm, moist environment before planting (sweating) increased shoot dieback of Celtic occidentalis trees. Root growth potential was very low for Quercus spp. trees and varied by treatment for Celtis occidentalis trees. Taxodium distichum trees had a relatively high root growth potential in all treatments. Stem water potential measured immediately before and after pre-plant treatments indicated that Quercus spp. trees and T. distichum trees were able to rehydrate during sweating while water stress in C. occidentalis trees remained high (stem water potential <−2.0MPa). The results suggest that poor transplanting success reported for Quercus spp. trees may be related to low root growth potential, whereas poor establishment of Celtis occidentalis trees is related to a combination of factors including desiccation, poor root regeneration and poor carbohydrate status. None of the pre-plant treatments reduced shoot dieback compared to control trees that were not stored prior to planting.

Vigour-yield-quality relationships in long-term deficit irrigated winegrapes grown under semiarid conditions

Regulated deficit irrigation (RDI) and partial root-zone drying irrigation (PRD) are two of the most-promising agronomic practices designed to increase water use efficiency (WUE) and berry and wine quality in field-grown wine grapes in Mediterranean semiarid regions. However, many growers have not yet taken advantage of the new irrigation techniques now available, which would enable them to efficiently manage irrigation in wine grapes with the aims of improving quality and making this crop more competitive and profitable. This study focused on finding significant relationships between several WUE indicators (from the leaf to the plant level) and relevant vine vigour, yield and berry quality traits in order to improve deficit irrigation management in wine grapes under semiarid conditions. Sustained deficit irrigation (SDI), RDI and PRD techniques were compared for 7 years (2006–2012), in field-grown Monastrell grapevines grafted onto 1103P in SE Spain. Five treatments were applied: SDI irrigated at 60–40 % ETc (crop evapotranspiration) for the whole season (308–211 mm year−1); a moderate RDI strategy (110–191 mm year−1) under conventional drip irrigation (RDI-1) and under PRD (PRD-1); and a more-severe RDI strategy (90–144 mm year−1) under conventional drip irrigation (RDI-2) and under PRD (PRD-2). The SDI enhanced root system development and vine vigour, improved technological berry quality but lowered WUE and berry polyphenolic content, compared to deficit irrigation (DI). In contrast, PRD and RDI resulted in lower root growth, vine vigour and leaf-plant canopy water use, but improved cluster microclimate and increased WUE and berry polyphenolic content. Among the DI treatments, the PRD-1 strategy was the one which most improved the long-term vine performance. The most-restrictive DI strategies (PRD-2 and RDI-2) did not give a substantial improvement in WUEyield (kg m−3) or berry quality. Significant interactive effects of irrigation volume (high vs. low) and irrigation placement (PRD vs. RDI) indicate distinct PRD effects on long-term yield, WUE and berry quality, depending on the volume of water applied in the wet root zone and the soil total water availability. Significant vigour-quality relationships were established. We identified a range of optimum physiological and agronomical thresholds in order to develop long-term, efficient deficit irrigation strategies in Monastrell vineyards under semiarid conditions.

Lime-induced chlorosis of grapevine as affected by rootstock and root infection with arbuscular mycorrhiza and Pseudomonas fluorescens

Grapevine cuttings ( Vitis vinifera L. cv. Pinot blanc, clone VCR 5), grafted on 3309 C, a lime-susceptible rootstock, SO 4, a medium lime-tolerant rootstock and 41 B, a lime-tolerant rootstock, were grown in pots containing unsterilized calcareous soil. Before potting, the roots of the grafted plants were inoculated with a suspension of a mutant of Pseudomonas fluorescens and with the vesicular-arbuscular mycorrhizal (VAM! fungus Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe, in order to investigate the effect of these microorganisms on the severity of lime-induced chlorosis. The most significant findings were: Pseudomonas fluorescens and Glomus mosseae treatments increased Fe and chlorophyll concentrations in the leaves and thus lime tolerance in plants grafted on 3309 C and 41 B; the positive effect of VAM treatment was associated with increased levels of root infection and lower root growth; the bacterial treatment improved the establishment of VAM fungi; fruit quality of the susceptible graft combination raised to the level of untreated Pinot blanc/SO 4 vines due to the root treatments.

Root growth of perennials in vertical growing media for use in green walls

The vertical orientation of green walls causes a risk of uneven water distribution within the growing medium, and thereby stress on the plant roots. Therefore it was studied how the root and top growth of different species were affected by the water holding characteristics of the growing media.Five species of hardy perennials (Campanula poscharskyana ‘Stella’, Fragaria vesca ‘Småland’, Geranium sanguineum ‘Max Frei’, Sesleria heufleriana and Veronica officinalis ‘Allgrün’) were grown in 3 types of growing media (coir and 2 of rockwool) in vertical boxes under greenhouse conditions. Root distribution was registered over 52 days and the activity of individual root systems was studied via 15N uptake and plant parameters were measured. The water holding characteristics of the growing media was determined on a sandbox.From day 21 and throughout the experiment, the plants growing in the coir medium showed stronger root growth compared to the two rockwool media. From day 28 onwards, there was also a difference between the two rockwool media, with a higher root frequency in the less dense medium. This pattern was consistent for all species, even if they showed different root growth dynamics. Fragaria, Geranium and Veronica showed steadily increasing root growth throughout the experiment, whereas Campanula started slow, but showed a strong root growth towards the end of the experiment. Sesleria showed little root growth throughout the experiment. Dry weight and root activity measured as 15N uptake was higher for plants grown in coir than rockwool. The coir medium showed a more gradual water release with increasing tension than either of the rockwool media, corresponding to the water content measured locally in the boxes.The results confirmed that the growing media affect root and aboveground plant growth. This is consistent with the differences in water retention, as the more even vertical water distribution in the coir medium resulted in stronger growth compared to the rockwool media. The five species showed different root growth dynamics and different abilities to grow in the different media, and 15N uptake showed that low root growth in the rockwool media also resulted in low root uptake activity.

Turfgrass Monoculture, Cool-Cool, and Cool-Warm Season Seed Mixture Establishment and Growth Responses

Turfgrass seeds can be sown individually, in mixes, or overseeded to provide green color and uniform surfaces in all the seasons. This investigation was conducted to compare different turfgrass species and their seed mixtures. In this research, the turfgrasses—perennial ryegrass (Lolium perenne L. `Barball'), kentucky bluegrass (Poa pratensis L. `Merion'), common bermudagrass (Cynodon dactylon [L.] Pers.), and strong creeping red fescue (Festuca rubra L. var. rubra `Shadow')—in monoculture or in mixtures of 1:1 (by weight) and a 1:1:1:1 (by weight) and two sport turfgrasses—BAR 11 (Barenbrug Co.) and MM (Mommersteeg Co.)—were used. The seeds were sown in March and October (spring and fall sowing) in 1998 and 1999. The experiments were conducted in a split-split block design with year as main plot, sowing season as subplot, and turfgrass types as subsubplot. The turfgrasses were compared by measuring visual quality, chlorophyll index after winter and summer, rooting depth, verdure and/or root fresh and dry weight, tiller density, and clippings fresh and dry weight. Fall sowing was superior to spring sowing and resulted in greater root growth, clipping yield, and chlorophyll content. Poa+Cynodon seed mixture was the best treatment and had high tiller density, root growth, and chlorophyll content. Lolium and Festuca monocultures, and Poa+Festuca and Cynodon+Festuca seed mixtures were not suitable with regard to low tiller density, sensitivity to high temperatures, low root growth, and low tiller density, respectively. The cool-warm-season seed mixture (Poa+Cynodon) can be used alternatively in overseeding programs in the areas with soil and environmental conditions similar to this research site.

Further characterization of two QTLs that increase phosphorus uptake of rice (Oryza sativa L.) under phosphorus deficiency

Four quantitative trait loci (QTLs) for P uptake were previously identified in a rice population that had been developed from a cross between the indica landrace Kasalath (high P uptake) with the japonica cultivar Nipponbare (low P uptake). For further studies, near isogenic lines (NILs) were developed for a major QTL linked to marker C443 on chromosome 12 and for a minor QTL linked to C498 on chromosome 6. On a highly P-deficient upland soil (aerobic conditions), NIL-C443 had three to four times the P uptake of Nipponbare, whereas the advantage of NIL-C498 was in the range of 60-90%. The superiority of NILs over Nipponbare vanished when grown in the same soil under anaerobic paddy conditions. All genotypes had high P uptake when P was supplied at a rate of 60 kg P ha -1 , regardless of soil conditions. These results confirmed the presence of both QTLs and furthermore implied that QTLs affected absorption mechanisms that specifically increased P uptake in a P deficient upland soil. Additional experiments were conducted to investigate if the effect of QTLs is linked to an increase in root growth or due to more efficient P uptake per unit root size (higher root efficiency). Root size did not differ significantly between genotypes in the plus-P treatment. P deficiency, however, reduced the root surface area of Nipponbare by more than 80% whereas NIL-C443 maintained almost half of its non-stress root surface area. The low root growth of Nipponbare observed under P deficiency was probably the result of insufficient P uptake to sustain plant growth, including root growth. Genotypic differences in the ability to maintain root growth, therefore are likely caused by some mechanism that increases the efficiency of roots to access P forms not readily available. This however, only had an effect in aerobic soil. Potential mechanisms leading to higher P uptake of NILs are discussed.

Benomyl Applied to Roots Improves Second-Year Survival and Growth of Shortleaf Pine

Abstract Benomyl added to a clay-slurry root dip at a low concentration (0.5 % a.i.) increased second-year survival and growth of shortleaf pine (Pinus echinata Mill.) seedlings. The increase was greatest for stored seedlings lifted before December and after January, but results indicated that unstored seedlings and those lifted at the optimum time can benefit from benomyl. Planting seedlings in partially frozen soil did not seriously reduce performance. Seedlings that showed very low root growth potential due to root damage caused by lifting from frozen soil performed well when planted under favorable field conditions. Further study is needed to determine whether the beneficial effect of benomyl is due to: (1) suppression of pathogenic fungi in storage, (2) encouragement of mycorrhizae fungi, or (3) a cytokinin-like effect. Knowledge of the mode of action of benomyl will provide for development of techniques to insure the maximum benefit by using it appropriately. South. J. Appl. For. 19(1):36-41.

Rhizodeposition and turnover of root-derived organic material in barley and wheat under conventional and integrated management

Carbon fluxes in the rhizospherre of barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) were studied under the field conditions with conventional management (CONV) and integrated management (INT) using 14C-CO2 pulse labelling. As estimated by a model rhizodeposition technique, the bulk of the 14C soil/root respiration during a 3 week period after pulse labelling originated from root respiration and only a minor part was due to microbial activity. Root 14C losses during washing from soil considerable (up to 40%) and were corrected for. Most of the carbon transfer to the roots of barley and wheat occurred in the early developmental stages, with a maximum flux around tillering. Over the entire growing season, this amounted to 52% of the above-ground production. Of the annual root growth, about one-half was found to be decayed by the end of the growing period. Compared with CONV, in INT a lower transfer of carbon to the roots, a lower root growth and a lower total rhizodeposition was found. In winter wheat this was mainly due to a lower overall plant production, and not a different C distribution pattern. Total rhizodeposition constituted 29–50% of the carbon translocated below ground and was 1.5–2.1 times the amount of roots left at crop harvest. Microbial respiration of rhizodeposits was higher in CONV than in INT.

Assessment of photosynthetic activity of nursery-grown Piceaglauca seedlings using an integrating fluorometer to monitor variable chlorophyll fluorescence

Photosynthetic activity of intact nursery-grown white spruce (Piceaglauca (Moench) Voss) seedlings was assessed by measuring CO2 exchange (apparent photosynthesis) and normalized, integrated variable chlorophyll fluorescence emission. Agreement between fluorescence and apparent photosynthesis indicated that photosynthetic inactivation of seedlings from selected seedlots began in mid-August and approached completion in late October. Inactivation occurred somewhat earlier in northern seedlot seedlings than in those from a more southerly provenance. Seedlings tested in late October showed significant photosynthetic inactivation, as indicated by both fluorescence and apparent photosynthesis. These seedlings also had passed the −18 °C frost hardiness test currently used in British Columbia as an indicator for safe lifting. On removal from −2 °C storage, seedlings lifted and stored according to nursery practises showed fluorescence emission indicative of photosynthetic reactivation and also had high root growth capacity scores. Low root growth capacity scores were associated with delayed or incomplete photosynthetic reactivation. These results show that fluorescence assessment provides information about the physiological status of white spruce seedlings. Variable fluorescence assays are nondestructive and can be made and interpreted within minutes. As an indicator of shoot metabolic activity, fluorescence assessment provides information useful in selecting lifting dates and in evaluating the effects of dark cold storage on white spruce seedlings.

Root growth and phosphorus uptake in relation to the size and strength of soil aggregates. I. Experimental studies

Cotton and sunflower were grown in pots containing aggregates of 6 different sizes in the range of 1–19 mm. The penetrometer pressures of individual aggregates from each pot were measured with a 1-mm diameter blunt (total cone angle 60°) probe, driven at 3 mm min −1. Root lengths within aggregates, in voids and along the surface of aggregates were measured after 15 days of growth. Root hair lengths were also measured. At this time, plant tops were harvested and phosphorus concentrations in the tops were determined. Maximum penetrometer pressure was significantly higher with large than with small aggregates. Total root length and the proportion of the total length growing within aggregates was greater with small aggregates, while mean root hair length was greater with large aggregates. Dry weight and phosphorus content of plant tops was higher in beds of small aggregates than in beds of large aggregates. The lower root growth and phosphorus uptake in beds of large compared with small aggregates is attributed to greater mechanical impedance to root penetration and lower availability of phosphorus.

Early growth of planted spruce

Observations were made on the growth of white spruce (Piceaglauca (Moench) Voss) and Engelmann spruce (P. engelmanni Parry), each planted at a single location in the interior of British Columbia. In both species bareroot stock (either 2 + 0 seedlings or 2 + 1 transplants) with a low root growth capacity made only limited height growth during the first two seasons after planting. In the first season, many short stem units were formed, whereas in the second season, stem units were much longer but many fewer. The length of needles formed after planting by the bareroot trees was, in the first season, only about half that of needles formed the previous year in the nursery. Needle length increased slightly in the 2nd year. Container-grown trees (1 + 0 seedlings from 336-mL containers), which had a high root growth capacity, made relatively good height growth in the first season when they formed long needles and stem units. Height growth by these seedlings was much less in the second season, however, as were needle length and stem unit number, but not stem unit length. Application of slow release N,P, and K fertilizer at planting improved shoot growth by bareroot trees more in the second season than the first. In contrast, the container-grown stock made a large shoot growth response to fertilization in both the first and the second seasons. The results are consistent with the hypothesis that, as root establishment proceeds, shoot growth tends to be limited by the supply, first of water, then of mineral nutrients. This implies that the early growth of planted spruce can be maximized by using stock with a high root growth capacity, or other adaptations to drought, and applying slow release fertilizer at planting. Observations on the white spruce revealed an acceleration in shoot growth by both stock types during the third season. This followed the establishment, by the end of the second season, of root systems several metres in diameter. A large difference in height: diameter ratio, observed at the time of planting, between the container-grown and bareroot white spruce disappeared entirely in the course of the first three growing seasons.