Root-shoot Relations Research Articles

Cotton-Based Rotation, Intercropping, and Alternate Intercropping Increase Yields by Improving Root–Shoot Relations

Crop rotation and intercropping are important ways to increase agricultural resource utilization efficiency and crop productivity. Alternate intercropping, or transposition intercropping, is a new intercropping pattern in which two crops are intercropped in a wide strip with planting positions switched annually on the same land. Transposition intercropping combines intercropping and rotation and thus performs better than either practice alone. Compared with traditional intercropping or rotation, it can increase yield and net return by 17–21% and 10–23%, respectively, and the land equivalent ratio (LER) by 20% to 30%. In crop growth and development, a balanced root–shoot relation is essential to obtain satisfactory yields and yield quality. Intercropping, rotation, or the combination can alter the original root–shoot relation by changing the ecology and physiology of both root and shoot to achieve a rebalancing of the relation. The crop yield and yield quality are thus regulated by the root–shoot interactions and the resulting rebalancing. The review examines the effects of above- and belowground interactions and rebalancing of root–shoot relations on crop yields under cotton-based intercropping, rotation, and particularly alternate intercropping with the practices combined. The importance of signaling in regulating the rebalancing of root–shoot relations under intercropping, rotation, and the combination was also explored as a possible focus of future research on intercropping and rotation.

Evidence for scale-dependent root-antation feedback and its role in halting the spread of a pantropical shrub into an endemic sedge.

Vegetation pattern formation is a widespread phenomenon in resource-limited environments, but the driving mechanisms are largely unconfirmed empirically. Combining results of field studies and mathematical modeling, empirical evidence for a generic pattern-formation mechanism is demonstrated with the clonal shrub Guilandina bonduc L. (hereafter Guilandina) on the Brazilian island of Trindade. The mechanism is associated with water conduction by laterally spread roots and root augmentation as the shoot grows-a crucial element in the positive feedback loop that drives spatial patterning. Assuming precipitation-dependent root-shoot relations, the model accounts for the major vegetation landscapes on Trindade Island, substantiating lateral root augmentation as the driving mechanism of Guilandina patterning. Guilandina expands into surrounding communities dominated by the Trindade endemic, Cyperus atlanticus Hemsl. (hereafter Cyperus). It appears to do so by decreasing the water potential in soils below Cyperus through its dense lateral roots, leaving behind a patchy Guilandina-only landscape. We use this system to highlight a novel form of invasion, likely to apply to many other systems where the invasive species is pattern-forming. Depending on the level of water stress, the invasion can take two distinct forms: (i) a complete invasion at low stress that culminates in a patchy Guilandina-only landscape through a spot-replication process, and (ii) an incomplete invasion at high stress that begins but does not spread, forming isolated Guilandina spots of fixed size, surrounded by bare-soil halos, in an otherwise uniform Cyperus grassland. Thus, drier climates may act selectively on pattern-forming invasive species, imposing incomplete invasion and reducing the negative effects on native species.

Mechanisms of Differential Manganese Uptake Efficiency in Winter Cereals at Generative Phase

Plant species as well as cultivars of the same species differ in their Mn efficiency. This paper studied the differential Mn efficiency in relation to Mn dynamics in the rhizosphere and root shoot relations of one durum wheat (cultivar PDW 291), four bread wheat varieties (cv. PBW 509, PBW 636, DBW 17 and PBW 550) and one triticale (cv. TL 2908). The six cultivars were grown in pots under two Mn treatments: (i) 0 mg Mn kg−1 soil (i.e. soil with 1.54 mg kg−1 of DTPA-extractable Mn) and (ii) 50 mg Mn kg−1 soil. Plants were harvested at tillering and 45 days post tillering to record root length (RL), shoot dry weight (SDW), Mn uptake and soil parameters. Under Mn deficiency conditions, PBW 550 produced 47 % of its maximum RL and 58 % of its maximum SDW, whereas PDW 291 produced only 13 and 35 %, respectively. PBW 550 and PDW 291 showed highest and lowest RL/SDW ratio, root surface area and Mn uptake, respectively. Greater Mn concentration difference between bulk soil and root surface in PBW 550 and TL 2908 resulted into 1.4 times higher Mn influx as compared to durum cultivar. It seemed triticale cv. has adaptations to low nutrient availability as indicated by its lowest relative shoot growth rate and highest relative root growth rate.

Evolutionarily Stable Strategy Carbon Allocation to Foliage, Wood, and Fine Roots in Trees Competing for Light and Nitrogen: An Analytically Tractable, Individual-Based Model and Quantitative Comparisons to Data

We present a model that scales from the physiological and structural traits of individual trees competing for light and nitrogen across a gradient of soil nitrogen to their community-level consequences. The model predicts the most competitive (i.e., the evolutionarily stable strategy [ESS]) allocations to foliage, wood, and fine roots for canopy and understory stages of trees growing in old-growth forests. The ESS allocations, revealed as analytical functions of commonly measured physiological parameters, depend not on simple root-shoot relations but rather on diminishing returns of carbon investment that ensure any alternate strategy will underperform an ESS in monoculture because of the competitive environment that the ESS creates. As such, ESS allocations do not maximize nitrogen-limited growth rates in monoculture, highlighting the underappreciated idea that the most competitive strategy is not necessarily the "best," but rather that which creates conditions in which all others are "worse." Data from 152 stands support the model's surprising prediction that the dominant structural trade-off is between fine roots and wood, not foliage, suggesting the "root-shoot" trade-off is more precisely a "root-stem" trade-off for long-lived trees. Assuming other resources are abundant, the model predicts that forests are limited by both nitrogen and light, or nearly so.

NITROGEN SOURCE AND MANGANESE APPLICATION EFFECTS ON MANGANESE DYNAMICS IN THE RHIZOSPHERE OF WHEAT CULTIVARS GROWN ON MANGANESE-DEFICIENT SOILS

To study the effect of two different nitrogen (N) sources and manganese application on root-shoot relations and manganese (Mn) dynamics in the rhizosphere of two wheat cultivars, a screen house experiment was conducted using manganese-deficient soil. Significantly higher root length (RL), root surface area, shoot dry weight (SDW), root length density, and manganese uptake were recorded in calcium nitrate supplied plants of cultivar ‘WH 542’ when applied with calcium nitrate along with manganese rather than ammonium sulfate. Cultivar ‘PD W274’ produced 72% of the maximum RL and 77% of the maximum SDW under similar conditions. Results indicated that cultivar ‘WH 542’ was more manganese efficient than ‘PD W274’ and calcium nitrate was a better source of nitrogen than ammonium sulfate. However, maximum shoot manganese content was recorded in ammonium sulfate supplied plants, which was due to depletion of manganese at root surface to a lower value, causing higher concentration gradient and hence higher manganese influx to root.

Growth characteristics of root-shoot relations of three birch seedlings raised under different water regimes

Growth characteristics of root-shoot relations of three birch seedlings raised under different water regimes

Shading and root–shoot relations in saplings of silver birch, pedunculate oak and beech

Silver birch ( Betula pendula Roth), pedunculate oak ( Quercus robur L.) and beech ( Fagus sylvatica L.) can regenerate successfully under a canopy of Scots pine ( Pinus sylvestris L.). Shading reduces plant growth and modifies plant form, two related aspects. This study focuses on the effects of shading on root–shoot relations of these species. Saplings were grown for 2 years under full light (light availability of 100%) and shaded conditions (light availability of 30%) and then harvested and their root system excavated. Shading had no effect on the biomass distribution within the root system. Shading reduced the root–shoot ratio of the species studied. Only for silver birch the fine root biomass–leaf biomass ratio decreased by shading, indicating a reduced partitioning to the fine roots in comparison to the leaves. Shading reduced the fine root length–leaf area ratio of the three species studied. However the magnitude of reduction differed between the species; small in pedunculate oak, intermediate in beech and large in silver birch. For pedunculate oak and beech this effect must be primarily attributed to an increase in specific leaf area under shaded conditions, while for silver birch this effect can be attributed to both the morphological adjustment in the leaves and the increased partitioning to the leaves. As the capacity of leaves and fine roots to acquire resources has to balance we postulate that under the experimental conditions an increase the efficiency of carbon uptake relative to the efficiency of nutrient uptake is the dominant acclimation of pedunculate oak. The response of silver birch indicates that the dominant acclimation to shading is based on a shift in a biomass partitioning between the leaves and the fine roots. Beech holds an intermediate position, as there is evidence for an increase in the efficiency of carbon uptake relative to the efficiency of nutrient uptake and an increase of leaf area relative to fine root length.

Modelling root growth of wheat as the linkage between crop and soil

The simulation of crop - soil systems with a model requires an appropriate description of the root dynamics. An empirical root growth model that simulates root-shoot relations, root distribution and a dynamic response to environmental conditions is presented. The root model extends an existing crop model and links it to a soil model to calculate dry matter accumulation, water and nitrogen dynamics of a wheat crop. Simulated roots are distributed over soil layers according to carbon supply from the shoots by using a 'top down principle'. This principle favours the top layers for root growth by first providing all available carbon to the first layer. Under unfavourable soil conditions in that layer, carbon is given to the next deeper soil layer. This procedure is repeated until a separately calculated rooting depth is reached. At that depth all available carbon is used for root growth regardless of current soil conditions. Under most simulated conditions the 'top down principle ' results in a negative exponential function of a monotone decrease of root distribution with soil depth. However, it can also account for larger root densities deeper in the profile when water or nitrogen deficiency occurs in soil. In addition to soil water and soil nitrogen supply the root model considers soil compaction, aeration and root distribution history for root growth simulation. The new model, consisting of an existing crop and soil model and linked through a new developed root model, was calibrated and tested using two independent field experiments. A sensitivity analysis was carried out by varying parameters, initial soil conditions and hypothetic weather patterns as part of the validation process. Root length density distribution (r2(1:1)=0.65), shoot, grain and total root biomass (r2(1:1)=0.87) were predicted satisfactorily, thus providing a useful tool for specific simulation studies on that site.

ROOT-SHOOT RELATIONS AS AFFECTED BY PGR APPLICATION AND ROOT MANIPULATION

ROOT-SHOOT RELATIONS AS AFFECTED BY PGR APPLICATION AND ROOT MANIPULATION