We describe a new and easy technique for placing and lifting root meshes to estimate fine root production in forest ecosystems. The method improves upon previously proposed mesh placement techniques by using a sharp stainless steel blade and two thin stainless steel sheets to insert mesh more easily and accurately in the soil, and utilizing a narrow garden spade to lift the soil block containing the mesh. The proposed technique takes significantly less time than the widely used ingrowth core method, causes minimal disturbance to the soil, and requires only simple equipment. The detailed documentation of the method provided herein should improve estimations of fine root production in forest ecosystems.
We investigated mainly root traits of rice (Oryza sativa L.) seedlings grown under four soil conditions (i.e. anaerobic, aerobic, low and high soil density) in thin and long transparent polyvinyl chloride tubes for 21 days. Using 70 rice varieties from four agricultural ecotypes (i.e. japonica upland (JU), japonica lowland (JL), indica upland (IU), and indica lowland (IL)), we examined the effects of genotypes, environment and their interaction on seminal root length (SRL), seminal root thickness (SRT), number of crown roots (NCR), root and shoot dry weight (RDW and SDW) and root/shoot ratio (R/S ratio). The significant effects of genotype, environment and their interaction on all the traits were detected. Rice varieties could be clearly classified into their own ecotypes by a combined principle component analysis (PCA) for NCR, SRT, and SDW. Seventy rice varieties could be separated into upland and lowland varieties based on the scores of the first principle component (PC) and, among upland varieties, JU varieties could be separated from IU varieties based on the scores of the second PC. JU varieties had longer and thicker seminal roots than the other varieties in aerobic soil conditions, indicating that these varieties may be more suitable for aerobic soil conditions from the view point of the seedling establishment.
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.
Quantitative trait locus (QTL) analyses were performed to map the genes controlling adventitious root formation on the soil surface (ARF-SS) under flooding conditions in seedlings of 317 BC3F1 individuals derived from a cross between elite maize Mi29 x teosinte Zea nicaraguensis. An SSR-based linkage map was developed using 94 markers, covering 896.3 cM of the ten chromosomes. The ability of ARF-SS under flooding conditions showed continuous variation in the BC3F1 population. By single point regression and interval mapping analyses, the QTLs for ARF-SS were located on chromosomes 3 (bin 3.04), 7 (bin 7.04) and 8 (bin 8.03). Alleles of Z. nicaraguensis, which has a high ability of ARF-SS, increased the level of ARF-SS for all the QTLs. By comparing chromosome positions of ARF-SS loci to previously reported loci, the region on chromosome 3 was shown to be unique to this teosinte. A possible application of the new QTL to breed flooding tolerant maize is discussed.