Belowground carbon allocation patterns in a dry Mediterranean ecosystem: A comparison of two models

Total belowground C allocation (TBCA) accounts for a large fraction of gross primary production, it may overtake aboveground net primary production, and contributes to the primary source of detrital C in the mineral soil. Here, we measure soil respiration, water erosion, litterfall and estimate annual changes in C stored in mineral soil, litter and roots, in three representative land uses in a Mediterranean ecosystem (late-successional forest, abandoned agricultural field, rain-fed olive grove), and use two C balance approaches (steady-state and non-steady-state) to estimate TBCA. Both TBCA approaches are compared to assess how different C fluxes (outputs and inputs) affect our estimates of TBCA within each land use. In addition, annual net primary productivity is determined and C allocation patterns are examined for each land use. We hypothesized that changes in C stored in mineral soil, litter and roots will be slight compared to soil respiration, but will still have a significant effect on the estimates of TBCA. Annual net primary productivity was 648 ± 31.5, 541 ± 42.3 and 324 ± 22.3 g C m⁻² yr⁻¹ for forest, abandoned agricultural field and olive grove, respectively. Across land uses, more than 60% of the C was allocated belowground. Soil respiration (F_S) was the largest component in the TBCA approaches across all land uses. Annual C losses through water erosion were negligible compared to F_S (less than 1%) and had little effect on the estimates of TBCA. Annual changes in C stored in the soil, litter layer and roots were low compared to F_S (16, 24 and 10% for forest, abandoned agricultural field and olive grove, respectively), but had a significant effect on the estimates of TBCA. In our sites, an assumption that Δ[C_S + C_R + C_L]/Δt = 0 will underestimate TBCA, particularly in the abandoned agricultural field, where soil C storage may be increasing more rapidly. Therefore, the steady-state model is unsuited to these Mediterranean ecosystems and the full model is recommended.     

Identification of sources of resistance to damping-off and early root/hypocotyl damage from Rhizoctonia solani in common bean (Phaseolus vulgaris L.)

Rhizoctonia solani causes economically important root and hypocotyl diseases in common bean throughout the world. Root health is a vital factor in plant development and root diseases would negatively influence water and nutrient uptake as well as cause direct stand reduction and root rot damage to the crop. An efficient common bean screening method to evaluate damping-off and early root/hypocotyl damage from R. solani was developed and used to identify dry bean lines with levels of resistance to this disease. Two sets of 163 and 111 lines previously evaluated for drought tolerance in Nebraska and Puerto Rico were evaluated for damping-off resistance and early root/hypocotyl damage under greenhouse conditions. Disease severity on plants was identified based on above-ground symptoms, seedling survival and root lesions using a rating scale of 1 (resistant) to 9 (susceptible). In the first set of lines representing commonly grown dry bean cultivars, germplasm and sources of damping-off resistance, the Rhizoctonia mean rating ranged from 1.7 to 3.9; Phaseolus vulgaris lines PI 310668 and PI 533249 had the highest damping-off resistance. In the second set of the best lines from a drought tolerance shuttle breeding program the Rhizoctonia mean rating was between 2.6 and 5.7. The availability of drought tolerant dry bean lines allowed the testing of the hypothesis that there was a correlation between selecting for drought tolerance and R. solani damping-off resistance. No correlation between mean disease rating and drought tolerance was found, but adapted dry bean lines such as NE14-08-176 released as SB-DT1, and NE14-08-225 were identified with moderate damping-off resistance and drought tolerance. Lines with both traits and other attributes will facilitate development of resistant bean cultivars to manage damping-off caused by R. solani.     

供铁水平对不同苹果基因型生长及根系特性的影响

以小金海棠 (MalusxiaojinensisChengetJiang)和山定子 (MalusbaccataL .Borkh)为试材 ,研究供铁水平对其生长及根系特性的影响 ,结果表明 ,在幼苗生长量、新叶叶绿素含量、营养液pH日变化、根系活力、根系ATP酶活性诸方面 ,存在基因型差异。同一供铁水平 ,小金海棠有明显的铁胁迫反应 ,而山定子铁胁迫反应较弱。低铁胁迫处理 ,小金海棠叶片叶绿素含量、根系活力、根系ATP酶活性皆明显高于山定子。根系活力及根系ATP酶活性可用作铁高效基因型植物的筛选指标     

Responses of Root Growth to Moderate Soil Water Deficit in Wheat Seedlings

Abstract

In the field, plants show better root growth in drying soil than in wet soil. However, the root growth enhancement has not been demonstrated clearly in the laboratory. In this study, the root growth response of wheat seedlings to moderate soil water deficits was characterized quantitatively in an environment-controlled chamber. Germinated seeds of wheat were grown for 15 days in the soil with a water potential ranging from field capacity (FC) to approximately –0.08 MPa. Theleaf area decreased with reduction in soil water potential. By contrast, the root surface area increased upon reduction ofthe soil water potential to –0.04 MPa while it decreased significantly in soil with a water potential of –0.08 MPa. The increase in surface area was obvious in the roots with a diameter of 0.2 to 0.4 mm and larger than 0.7 mm. Root weight increased with the reduction of soil water potential to –0.04 MPa. While specific root length decreased significantly with the reduction of water potential to –0.06 MPa, the specific root surface area did not. Assimilatestransported from shoot might be used in roots to increae the surface area mainly by increasing the diameter rather than the length in response to a moderate soil water deficit in wheat seedlings. This might result from the drought tolerance mechanism of osmotic adjustment in roots.     

Urban tree growth and their dependency on infiltration rates in structural soil and structural cells

Expanding tree canopies can be difficult to achieve in built environments because urban land is costly and urban soil inhospitable to vegetation so engineered planting systems offer a potentially valuable tool for achieving sustainable urban forests. Tree water uptake, performance and root distribution were assessed in systems of structural soil and structural cell. Structural soil relies on stone and soil, it is highly porous and designed to support tree root growth and possess pavement strength. The structural cell is made up of rigid structural units with 90% void space which is to be filled with soil. To evaluate tree performance under the conditions of fill and drain regimes in structural soil and structural cell, these two systems were subjected to three simulated infiltration rates. This study was conducted in April 2015 to April 2016 in the tropical equatorial environment of South East Asia. Infiltration rate affected both biomass accumulation and rooting depth. Species and substrate effect was significant for biomass and rooting characteristics but less prominent for transpiration. Biomass was greater for trees in structural cells, and Pouteria obovata was particularly sensitive to prolonged inundation. Rooting depth was always higher in the rapid infiltration indicating the negative effects inundation had on this parameter. Root system in the structural cell was deeper while those in the structural soil were wider. Samanea saman had better adapted to the drain and fill regimes, and this was despite Pouteria obovata being a coastal species and was expected to be flood tolerant. Species and substrate effect was weak (R² ranging from 0.20 to 0.28) but moderate drainage consistently led to higher transpiration. We conclude that structural soil and structural cell are potential solutions and provide a tool to overcome suboptimal urban growing conditions. The application of these solutions will allow for seamless integration of greenery with urban infrastructure.     

土壤耕层深度和施肥深度对桔梗根部主要农艺性状的影响

[目的]探索优质高产的桔梗栽培方法。[方法]在15、20、30、40cm的耕深和不施肥、全层施肥、深层施肥（30～40cm）的3个施肥深度条件下,调查桔梗根的主要农艺性状。[结果]在耕深试验中,30cm耕深条件下的主根长最长、根粗最粗、单根鲜重最重,但侧根数也最多;施肥效果为深层施肥的效果好于全层施肥和不施肥。[结论]试验结果对山区、半山区桔梗栽培体系的建立有一定的参考价值。     

Effect of thinning flower buds on fruit and seed traits and root yield of Panax ginseng C.A. Meyer

Panax ginseng C.A. Meyer, commonly known as ginseng, is a perennial herb. Agricultural practices have an influence on growth and yield of P. ginseng plants. Effect of thinning flower buds (treatment A (TA) the outermost whorl of flower buds in the umbels was retained while all other buds were excised; treatment B (TB) the two outer whorls of flower buds in the umbels) on fruit traits, which include number of fruits per plant, single fruit: double fruit ratio, fruit weigh (FW) per square meter, weight of 100 fruits, vertical length of fruit (VLF), horizontal diameter of the fruit (HFD) and thickness of the fruit (TF), seed traits, which include number of seeds per square meter, weight of 1000 seeds, number of different seed grading categories (extremely large seeds (ELS), large seeds (LS), medium-sized seeds (MS), small seeds (SS)) per square meter, vertical length of the seed (VLS), horizontal diameter of the seed (HSD), thickness of the seed (TS), and the root yield and total ginsenosides content of root of four- and five-year-old cultivated P. ginseng was studied in Fusong region of north-eastern China. The results showed that the FW and VLF, the weight of 1000 seeds, number of ELS per square meter, VLS and HDS of ELS, HDS and TS of MS and root yield were increased significantly by TA and TB (p < 0.05), whereas the number of MS and SS were significantly reduced (p < 0.05) in four- and five-year-old plants. The number of ELS and LS in TB and control were higher than that of in TA, and not significant was observed between TB and control. The root yield in TB was significantly higher than that in control of five-year-old plants. Number of the seeds per square meter of five-year-old plants was higher than that of four-year-old plants. The results indicated that the method of thinning flower buds, which was the two outer whorls of flower buds in the umbels, on five-year-old cultivated P. ginseng plants was a favourable method to promote the production of high-quality seeds and maximise the root yield.     

土壤湿度对香料烟根系发育和根系活力的影响

研究了香料烟两个主要栽培类型， Ｂａｓｍ ａ（芳香型）和 Ｓａｍ ｓｕｎ（吃味型），在不同土壤湿度条件下的根系发育和根系活力，结果表明土壤适度干旱处理（土壤相对含水量６０％ ）两类型的根系干重、吸收面积和活跃吸收面积的测定值均高于其他处理。在土壤相对含水量６０％ ～８０％ 的处理条件下， Ｓａｍ ｓｕｎ 类型上述项目测定值均高于 Ｂａｓｍ ａ 类型；而土壤相对含水量在４５％ ～３５％ 的条件下， Ｂａｓｍ ａ 类型的项目测定值高于 Ｓａｍ ｓｕｎ 类型。     

土壤转换对二年生平邑甜茶根系发生与功能的影响

以2年生平邑茶为试材研究表明：土壤转换后，根系的发生与功能有所改变，由粘壤土转入沙壤土的根系吸收表面积、分泌H^ 速率和吸收NO3^-速率比由沙壤土转入粘壤土的高，但均比未处理植株低；前者新根量大，生长势强，分布广，后者的吸收根大量死亡。。     

Evolution of Root Characters of Soybean Varieties Developed in Different Years

It was studied that the evolution of root characteristics among 42 soybean varieties developed in Heilongjiang and Jilin Province in different years. The results showed that there were differences on the root characteristics among soybean varieties. From 1950s to 1990s, root fresh weight, root volume, root surface, root dry weight, lateral root length of main root characters tendedly increased with the variable development years. The root system of the varieties in 1990s was relatively well developed compared with that in the other years. The evolutionary trend of the root system of soybean varieties was increasing in root weight, root volume, root surface and length of lateral root.