Modeling tree root diameter and biomass by ground-penetrating radar

Roots play a key role in ecosystem functioning as they transfer water and nutrients from soil to plants. Traditional methods for measuring roots are labor-intensive and destructive in nature, which limits quantitative and repeatable assessments in long- term research. Ground-penetrating radar （GPR） provides a non-destructive method to measure plant roots. Based on the superiority of GPR with 2 GHz frequency, we developed a new, practical method to estimate root biomass. First, average root matter density was measured by collecting a small number of root samples. Second, under controlled, experimental conditions in a sandy area, a root diameter estimation model base on GPR was developed from which root diameter was estimated. Third, root volume was calculated using the estimated root diameter and assuming the shape of roots to be cylindrical. Finally, root biomass was estimated by averaging root matter density and root volume. Results of this study suggest the following： （1） the density of coarse roots with diameters greater than 0.5 cm is relatively uniform; （2） a new wave shape parameter, AT, extracted from profile data of 2 GHz frequency antenna is independent of root depth, thus enabling the construction of a root diameter estimation model with high accuracy; and （3） results of a field experiment demonstrated the GPR-based method to be feasible and effective in estimating biomass of coarse roots. These findings are helpful for improving GPR-based root diameter and biomass estimation models and suggest the potential of GPR data in studying root systems.

Vertical root distribution characters of Robinia pseudoacacia on the Loess Plateau in China

On the Loess Plateau, water is the main limiting factors for vegetation growth. Root distribution characters have special ecological meaning as it reflected the utilizations of trees to the environments. Even-aged stands ofRobinia pseudoacacia on slope lands facing south and north were selected as sampling plots for root distribution investigation. Investigatiing results showed that indicated that on all sites, root biomass decreased with depth, and the distribution depth of fine root was deeper than that of coarser root. The results of variance analysis indicated that there were great differences in root biomass among different diameter classes, and coarser root was the main sources of variance, and the root biomass, especially fine root (?<3mm) biomass on northern exposition sites was bigger than that on southern exposition sites. Analysis of the vertical root distribution parameters, root extinction coefficient, β indicated that the value of β on northern exposition was more than 0.982, while the value of β on southern exposition was less than 0.982, which indicated that the vertical root distribution depth ofRobinia pseudoacacia on southern exposition was deeper than that on southern exposition. And the distribution depth of fine roots (Φ<1mm) was deeper than that of thicker roots(Φ<3mm), which was in favor of the uptake of water and nutrients from deeper layers, helped the trees to adapt the arid environment, and promoted the growth of the upper parts of the tree. Keywords Root diameter classes - Variance analysis - Root extinction coefficient - Vertical distribution characters - Site conditions - Loess Plateau CLC number S792.27.01 Document code A Foundation Item: This research was supported by National Natural Science Foundation of China (30371150 and 40371075).Biography: LI Peng (1974-) male, post: Ph. D. in Northwest Scientific & Technological University of Agriculture and Forestry, Yangling 712100, Shaanxi Province, P. R. China. Tel: 029-82312651.Responsible editor: Chai Ruihal

Cell Production and Expansion in the Primary Root of Maize in Response to Low-Nitrogen Stress

Maize plants respond to low-nitrogen stress by enhancing root elongation. The underlying physiological mechanism remains unknown. Seedlings of maize （Zea mays L., cv. Zhengdan 958） were grown in hydroponics with the control （4 mmol L-1） or low-nitrogen （40 μmol L-1） for 12 d, supplied as nitrate. Low nitrogen enhanced root elongation rate by 4.1-fold, accompanied by increases in cell production rate by 2.2-fold, maximal elemental elongation rate （by 2.5-fold）, the length of elongation zone （by 1.5-fold）, and ifnal cell length by 1.8-fold. On low nitrogen, the higher cell production rate resulted from a higher cell division rate and in fact the number of dividing cells was reduced. Consequently, the residence time of a cell in the division zone tended to be shorter under low nitrogen. In addition, low nitrogen increased root diameter, an increase that occurred speciifcally in the cortex and was accompanied by an increase in cell number. It is concluded that roots elongates in response to low-nitrogen stress by accelerating cell production and expansion.

Untangling the influence of soil moisture on root pullout property of alfafa plant

Root pullout property of plants was of key importance to the soil reinforcement and the improvement of slope stability. To investigate the influence of soil moisture on root pullout resistance and failure modes in soil reinforcement process, we conducted pullout tests on alfalfa(Medicago sativa L.) roots at five levels(40, 30, 20, 10 and 6 kPa) of soil matric suction, corresponding to respectively 7.84%, 9.66%, 13.02%, 19.35% and 27.06% gravimetric soil moisture contents. Results showed that the maximal root pullout force of M. sativa decreased in a power function with increasing soil moisture content from 7.84% to 27.06%. Root slippage rate increased and breakage rate decreased with increasing soil moisture content. At 9.66% soil moisture content, root slippage rate and breakage rate was 56.41% and 43.58%, respectively. The threshold value of soil moisture content was about 9.00% for alfalfa roots in the loess soil. The maximal pullout force of M. sativa increased with root diameter in a power function. The threshold value of root diameter was 1.15 mm, because root slipping force was greater than root breaking force when diameter >1.15 mm, while diameter ≤1.15 mm, root slipping force tended to be less than root breaking force. No significant difference in pullout forces was observed between slipping roots and breaking roots when they had similar diameters. More easily obtained root tensile force(strength) is suggested to be used in root reinforcement models under the condition that the effect of root diameter is excluded as the pullout force of breaking roots measured in pullout tests is similar to the root tensile force obtained by tensile tests.

The inf luence of soil drying- and tillage-induced penetration resistance on maize root growth in a clayey soil

Soil drying may induce a number of stresses on crops. This paper investigated maize（Zea mays L.） root growth as affected by drought and soil penetration resistance（PR）, which was caused by soil drying and tillage in a clayey red soil. Compared with conventional tillage（C） and deep tillage（D）, soil compaction（P） and no-till（N） significantly increased soil PR in the 0-15 cm layer. The PR increased dramatically as the soil drying increased, particularly in soil with a high bulk density. Increased soil PR reduced the maize root mass density distribution not only in the vertical profile（0-20 cm） but also in the horizontal layer at the same distance（0-5, 5-10, 10-15 cm） from the maize plant. With an increase in soil PR in pots, the maize root length, root surface area and root volume significantly decreased. Specifically, the maize root length declined exponentially from 309 to 64 cm per plant with an increase in soil PR from 491 to 3 370 k Pa; the roots almost stopped elongating when the soil PR was larger than 2 200 k Pa. It appeared that fine roots（〈2.5 mm in diameter） thickened when the soil PR increased, resulting in a larger average root diameter. The average root diameter increased linearly with soil PR, regardless of soil irrigation or drought. The results suggest that differences in soil PR caused by soil drying is most likely responsible for inconsistent root responses to water stress in different soils.

Root Plate Growth in Sunflower and Its Relevance to Sclerotinia Basal Stalk Rot

Sclerotinia basal stalk rot (BSR) of sunflower (Helianthus annuus L.) is a fungal disease of the roots that causes symptoms of wilt and a basal stem lesion. Evaluating root plate growth could improve our understanding of BSR. Separate studies were conducted to determine the effect of sunflower growth stage or genotype on root plate diameter in North American environments. Root plate diameter of cultivated hybrids at reproductive growth stages was 3 to 4 times larger than vegetative stages. Cultivated hybrids had larger root plate diameter than interspecific lines. These results have implications for artificial inoculation methods that evaluate genotypes for BSR resistance in the field or greenhouse. Disease escapes can occur if field-grown plants are inoculated too far from the root plate and/or too early at vegetative growth stages. Side-dressing mycelium-infested cereal grain closer (i.e., 10 cm) to plants at reproductive growth stages (i.e., R1 - R4) can increase disease pressure and reduce disease escapes. These guidelines for the field can be used to validate results from artificial inoculations in the greenhouse.

Growth performance and scale insect infestation of Shorea leprosula in a common garden experimental plot

Many tree planting programmes have long been initiated to increase forest cover to mitigate the effects of global climate change.Successful planting requires careful planning at the project level,including using suitable species with favourable traits.However,there is a paucity of improvement data for tropical tree species.An experimental common garden of Shorea leprosula was established to study traits related to growth performance which are key factors in planting success.Seedlings of S.leprosula were collected from nine geographical forest reserves.To study the effects of genetic variation,seedlings were planted in a common environment following a randomized complete block design.From performance data collected 2017‒2019,one population showed the highest coefficient for relative height growth,significantly higher than most of the other populations.Interestingly,this population from Beserah also exhibited the lowest coefficient for scale insect infestation.This study provides preliminary results on growth performance and susceptibility to scale insect infestation in S.leprosula and the first common garden experiment site conducted on dipterocarp species.It lays a foundation for future genome-wide studies.

Variation in Seed Germination and Seedling Growth in Five Populations of <i>Vitellaria paradoxa</i>C.F. Gaertn. Subsp. <i>Nilotica</i>in Uganda

We studied seed germination and seedling growth performance in an economically and socially important fruit tree species Vitellaria paradoxa C.F. Gaertn. subsp. nilotica (shea tree) in Uganda. The study aimed at determining variations in germination among five shea tree seed provenances and seedling growth performance based on five growth traits (total height, root collar diameter, leaf length, leaf width and leaf petiole length). Five populations were considered from four agroecological zones comprising of 180 candidate “plus” trees. The seed trees consisted of 16 ethnovarieties selected based on their traits for fast growth and high oil yield. A total of 1,204 biological seeds were collected and sown in a tree nursery at Ngetta Zonal Agricultural Research and Development Institute during the month of June 2018 in a randomized incomplete block design with three replications. Significant variation (χ = 708;p < 0.01) was observed in seedling phenotypic traits within and between populations. Regression equation for height growth and leaf size index were given as y = 0.3787 + 12.671x and y = 0.6483 + 15.413x respectively. Root collar diameter was more correlated to leaf size index (0.425) than to height growth (0.30). Clustering of shea tree seedlings based on phenotypic growth traits revealed one aggregated cluster indicating that most of the seedlings from the five populations were similar (Jaccard index 0.92, p < 0.01). However, clustering based on SNP markers revealed three different populations. We recorded higher growth (χ = 708;p < 0.001) in Arua shea population. Red seeded;thin pulped and hairy fruited shea tree ethnovarieties recorded faster growth than the rest. The results reveal useful traits in selection for tree growth and further identified shea tree ethnovarieties that could be selected for fast growth.

Genotype and Planting Density Effects on Rooting Traits and Yield in Cotton （Gossypium hirsutum L,）

Root density distribution of plants is a major Indicator of competition between plants and determines resource capture from the solh This experiment was conducted in 2005 at Anyang, located in the Yellow River region, Henan Province, China. Three cotton （Gossyplum hlrsutum L.） cultivars were chosen： hybrid Btcultlvar CRI46, conventional Btcultlvars CRI44 and CRI45. Six planting densities were designed, ranging from 1.5 to 12.0 plants/m^2. Root parameters such as surface area, diameter and length were analyzed by using the DT-SCAN Image analysis method. The root length density （RLD）, root average diameter and root area Index （RAI）, root surface area per unit land area, were studied. The results showed that RLD and RAI differed between genotypes; hybrid CRI46 had significantly higher （P 〈0.05） RLD and RAI values than conventlonal cultlvars, especially under low planting densities, less than 3.0 plants/m^2. The root area index （RAI） of hybrid CRI46 was 61% higher than of CRI44 and CRI45 at the flowering stage. The RLD and RAI were also significantly different （P = 0.000） between planting densities. The depth distribution of RAI showed that at Increasing planting densities RAI was Increasingly distributed in the soil layers below 50 cm. The RAI of hybrid CRI46 was for all planting densities, obviously higher than other cultivars during the flowering and boll stages. It was concluded that the hybrid had a strong advantage in root maintenance preventing premature senescence of roots. The root diameter of hybrid CRI46 had a genetically higher root diameter at planting densities lower than 6.0 plants/m^2. Good associations were found between yield and RAI In different stages. The optimum planting density ranged from 4.50 plants/m^2 to 6.75 plants/m^2 for conventional cultlvars and around 4.0-5.0 plants/m^2 for hybrids.

Root tensile strength of terrace hedgerow plants in the karst trough valleys of SW China:Relation with root morphology and fiber content

Root tensile strength is commonly affected by root morphology and fiber content,which combinedly affect the effectiveness of terrace hedgerow on controlling soil erosion in sloping farmland.However,the relationships between these root characteristics are still elusive.This study aimed to compare the root tensile strength,root morphologies,and root fiber contents,and quantify their differences among different plant species.Complete root systems of three terrace hedgerow plant species,i.e.,O.bodinieri,V.villosa,and D.lablab L.were sampled for detecting root morphologies and fiber contents at different slope positions on a representative hillslope in karst trough valley.Single root specimens were collected to measure root tensile properties for these three plant species.Results showed that most root morphological parameters were the highest in O.bodinieri,followed by D.lablab L.Three plant species presented the same dominant diameter class as<1.0 mm,and root volumes as<1.50 cm3.Cellulose with contents closing to 50%was the main fiber type,and increased significantly linearly with the increasing root diameter in both O.bodinieri and V.villosa.The highest tensile strength and Young's modulus were found in D.lablab L.,while the best ultimate tensile force and ultimate elongation were displayed in O.bodinieri.Root diameter showed negative power relationships with tensile strength and Young's modulus,a positive power relationship with ultimate tensile force,and a positive linear relationship with ultimate elongation.Our results will deepen the understanding of the terrace hedgerow functions for controlling soil erosion worldwide.