Soil Root Length Density Research Articles

Interactive Effects of Nitrogen and Drip Irrigation Rates on Root Development of Corn (Zea Mays L.) and Residual Soil Moisture

Deficiencies in water and nitrogen (N) can lead to poor crop growth and production. This study was carried out during 2012–2014 to determine (1) the effect of drip irrigation regimes and N fertilizer rates on root length density (RLD) of corn (Zea mays L. cv. Single cross 704) and soil moisture dynamics and (2) the relationship between root development and water availability. The experiment was arranged into a split-plot design with three irrigation regimes as the main factor (I1 = 60, I2 = 80, and I3 = 100% evapotranspiration [ETc]) and five levels of N fertilizer (N1 = 0, N2 = 50, N3 = 100, N4 = 150 and N5 = 200 kg/ha) as the subfactor. The combination I1N4 produced the highest grain yield and yield components while I3N5 gave the lowest performance. The highest RLD was recorded at full irrigation water requirement and it increased with increasing N rate, but not in a linear trend, as higher N rates showed less effect. Nitrogen application under drip irrigation increased the RLD in soil depending on irrigation level. Soil moisture was optimized at full irrigation water requirement and 150 kg/ha N.

Changes in root morphological traits in soybean co-inoculated with Bradyrhizobium spp. and Azospirillum brasilense or treated with A. brasilense exudates

We assessed the effects of co-inoculation with Azospirillum brasilense or the application of its exudates via seeds or leaf spray on root morphological traits and nodulation, as well as on shoot development and grain yield of soybean inoculated with Bradyrhizobium. Two experiments were performed in sterile substrate under greenhouse, and two were performed at field conditions in sandy soils in a crop season with episodes of drought. The treatments in the greenhouse experiments comprised the non-inoculated control, sole inoculation with Bradyrhizobium, co-inoculation of Bradyrhizobium and A. brasilense, and inoculation of Bradyrhizobium with the application of Azospirillum exudates via seeds or leaf spray. Field treatments included non-inoculated controls without and with N-fertilizer and inoculation of Bradyrhizobium and co-inoculation with A. brasilense. Plants were assessed for root weight, total and specific lengths, volume, diameter, tissue density, branches number, root-hair length and incidence, nodule number and dry weight, shoot dry weight and N content, and grain yield. Co-inoculation of Bradyrhizobium and A. brasilense and seed application of A. brasilense exudates increased the number of root branches and nodules compared with the sole inoculation of Bradyrhizobium. However, leaf spray application of exudates was less effective. Co-inoculation also increased specific root length, root length density in soil, root-hair incidence and length, and total N content in shoot, altogether resulting in increases in grain yield. Co-inoculation of soybean with Bradyrhizobium and A. brasilense improved several root morphological traits, increasing the plant capacity to overcome moderate drought stress episodes in sandy soils, allowing to reach higher yields.

Evolutionary Patterns and Biogeochemical Significance of Angiosperm Root Traits

On the basis of a synthesis of recent progress in belowground ecology, we advance and discuss a hypothesis that relates root trait evolution to the increased dominance of angiosperms into dry upland habitats and the decline of atmospheric CO2 concentration that began in the Cretaceous. Our hypothesis is built from examining patterns of fine root adaptations during the Cretaceous, when angiosperms dramatically diversified in association with arbuscular and ectomycorrhizal root-fungal symbionts. We then explore the potential effects of root adaptations and mycorrhizas on the geochemical carbon cycle. On the basis of phylogenetic analyses of root traits among extant plant species, we suggest that angiosperm taxa, which diversified since the early Cretaceous, evolved thinner roots with greater root length per unit of biomass invested (i.e., specific root length [SRL]) than earlier diverging taxa. We suggest that these changes in root morphology were facilitated by a decline in atmospheric CO2, which likely caused water to become more limiting and nutrients more bound to organic matter. Under these conditions, we suggest that thin roots with long SRL would have allowed plants to more efficiently forage for soil water and nutrients. This assertion is supported by the observation that SRL correlates with greater root length density in soil and increased root capacity to take up water. Simulations indicate that the evolution of angiosperm root systems with greater SRL and ectomycorrhizas during the Cretaceous and Cenozoic substantially increased mineral weathering rates, with a fourfold increase in SRL, equivalent to a quadrupling of atmospheric CO2 concentration. The hypothesis presented here raises the possibility that plant hydraulic status and nutrient balance together shaped whole-plant growth strategies, with important consequences for the evolution of the biosphere.

Root Observations Using A Video Recording System In Mini‐Rhizotrons1

AbstractTo understand the development of a crop, information is needed concerning the dynamics of root growth and water uptake. An extendible, 13 mm diam borescope, a low light, monochrome video camera, and a video tape recorder were combined into a system for in situ root observation through 51 mm inside diam clear acrylic tubes installed at an angle 30° from vertical. The viewing area was illuminated by two fiber optic light guides and a variable intensity light source. The observation tubes could also be used as access for a neutron probe to measure water uptake and root growth at the same point. Sector intersections rather than line intersections were counted and used to convert observations from the mini‐rhizotrons to root length densities. A comparison of root length densities determined through mini‐rhizotrons, installed in four orientations with respect to plant rows, with those determined by soil sampling indicates there was a linear relationship between the two techniques. When only depths greater than 20 cm were used the correlation was higher than when all depths were included. Results indicated that no installation orientation was clearly the best when only the depths greater than 20 cm were included. Because of the variability of the results from individual mini‐rhizotrons the results from several tubes had to be averaged before there was a satisfactory correlation with the bulk soil root length density.