Plant Root Distribution Research Articles

Spatial mapping of root systems reveals diverse strategies of soil exploration and resource contest in grassland plants

Abstract When foraging and competing for below‐ground resources, plants have to coordinate the behaviour of thousands of root tips in a manner similar to that of eusocial animal colonies. While well described in animals, we know little about the spatial behaviour of plants, particularly at the level of individual roots. Here, we employed statistical methods previously used to describe animal ranging behaviour to examine root system overlap and the efficiency of root positioning in eight grassland species grown in monocultures and mixtures along a gradient of neighbour densities. Species varied widely in their ability to distribute roots efficiently, with the majority of species showing significant root aggregation at very fine spatial scales. Extensive root system overlap was observed in species mixtures, indicating a lack of territoriality at the level of whole root systems. However, with increasing density of competitors, several species withdrew roots from the periphery of foraging ranges and increased intraplant root aggregation in the remaining area, which may indicate consolidation of foraging areas under competitive pressure. Several species exhibited responses consistent with resource contest in species mixtures where encounters with competitors’ roots triggered increased root aggregation at the expense of foraging efficiency. Such responses only occurred in mixtures of species with comparable competitive abilities but were absent in asymmetric species combinations. Synthesis. Combining fine‐scale measurement of plant root distributions with spatial statistics yields new insights into plant behavioural strategies with significant potential to impact resource foraging efficiency and productivity.

X‐ray computed tomography imaging of solute movement through ridged and flat plant systems

AbstractThe aim of this investigation was to experimentally compare the movement of a solute through soils with two field‐representative surface geometries: ridge and furrow surfaces versus flat surfaces. X‐ray computed tomography (XCT) imaging was undertaken to trace the movement of a soluble iodinated contrast medium, here used as an XCT‐visible analogue for field‐applied solutes, through soil columns with either a ridge and furrow or flat soil surface geometry. In addition to the soil surface geometry, the experimental treatments included the presence or absence of plants and surface water ponding. Experimental results were compared to existing numerical simulations adapted to represent the present experimental column systems. Similar infiltration patterns were observed in imaging results and the numerical simulations for most treatments. The experimental results suggest that plant roots present a significant localized effect to reduce the infiltration depth of solutes, particularly in planted ridges where the infiltration depth of the contrast medium was minimal. There is variability within the results because the number of replicates was limited to three due to the exploratory nature of the study (testing eight different treatments) and the cost and availability of XCT facilities capable of imaging such physically large samples. Discrepancies between the imaged infiltration depth of the solute and the numerical simulations are attributed to variation in plant root distribution and also spatial soil moisture, as measured using resistive soil moisture sensing. The results of this investigation elucidate the nature of solute movement through soil surface geometries, indicating that plant root water uptake can reduce solute infiltration depth, but surface ponding can negate this. These results suggest that soil surface shape, plant age and the timing of solute application with anticipated rainfall could be important considerations for reducing solute leaching and improving solute application efficiency.Highlights Investigating factors affecting solute infiltration in flat or ridge and furrow soil geometries. X‐ray CT imaging traces soluble contrast media movement in soil columns and is compared to modelling. Plant root water uptake can reduce solute infiltration depth, but surface ponding can negate this. Considering soil surface shape, rain and plant age in solute application could reduce leaching.

Performance of woody and herbaceous plant polyculture in constructed wetland for treating domestic wastewater

Effect of polyculture of woody and herbaceous plant with different ecological niche in constructed wetlands (CWs) on wastewater treatment is unclear. Herein, three kinds of polyculture CWs were constructed to treat domestic wastewater: woody polyculture system (W, Nerium and Hibiscus), herbaceous polyculture system (H, Acorus and Typha), woody and herbaceous polyculture system (WH, Nerium, Hibiscus, Acorus and Typha) and non-planted system (N) as control. The seasonality removal performance of pollutant, activities of urease and phosphatase, microscopic characteristics of roots were measured. Results showed that the average removals of COD, TN and TP in WH were significantly higher than that in the other systems. Interspecies competition existed in WH system, while the difference in terms of biomass gradually diminished. Furthermore, the root lengths, area, volume and tip number were higher compared to the other systems. The correlation between the removal rate of TP and activity of phosphatase in upper and bottom layer of CWs showed the opposite tendency, the distribution of plant roots in polyculture essentially impact TP removal rate in CWs. Our results provide the necessary insights for appropriately selecting different plant types for doing polyculture in CWs.

Temporal and spatial variation of infiltration in urban green infrastructure

AbstractInfiltration is the primary mechanism in green stormwater infrastructure (GSI) systems to reduce the runoff volume from urbanized areas. Soil hydraulic conductivity is most important in influencing GSI infiltration rates. Saturated hydraulic conductivity (Ksat) is a critical parameter for GSI design and post‐construction performance. However, Ksat measurement in the field is problematic due to temporal and spatial variability and measurement errors. This review paper focuses on a comparison of methods for in‐situ Ksat measurement and the causes of temporal and spatial variations of Ksat within GSI systems. Automated infiltration testing methods, such as the Modified Philip–Dunne (MPD) and SATURO infiltrometers, show promise for efficient Ksat measurements. Soil Ksat values can change over time and substantially vary throughout a GSI, which can be attributed to multiple factors, including but not limited to temperature changes, soil composition and properties, soil compaction level, plant root morphology and distribution, biological and macrofauna activities in the soil, inflow sediment characteristics, quality of infiltrating water, and measurement errors. There is evidence that infiltration rates in vegetated urban GSI systems are sustained given an appropriate GSI design, reasonable concentration of suspended sediments in the inflow runoff, and routine maintenance procedures. These observations indicate that clogging can be counteracted by processes that tend to increase the soil hydraulic conductivity (e.g., plant root and biological activities). This self‐sustainability underlines that infiltration‐based GSI systems are a reliable long‐term stormwater management solution. Recommendations on how to incorporate the temporal changes of Ksat in GSI design and on obtaining a spatially‐representative Ksat for the GSI design are presented.

Plant growth, root distribution and non-aqueous phase liquid phytoremediation at the pore-scale

The success of phytoremediation is dependent on the exposure of plants to contaminants, which is controlled by root distribution, physicochemical characteristics, and contaminant behavior in the soil environment. Whilst phytoremediation has been successful in remediating hydrocarbons and other organic contaminants, there is little understanding of the impact of non-aqueous phase liquids (NAPLs) on plant behavior, root architecture and the resulting impact of this on phytoremediation. Light NAPLs (LNAPLs) may be present in pore spaces in the capillary zone as a continuous or semi-continuous phase, or as unconnected ganglia which act as individual contaminant sources. Experimental work with ryegrass (Lolium perenne) grown under hydroponic conditions in idealised pore scale models is presented, exploring how plant growth, root distribution and development, and oil removal are affected through direct physical contact with a model LNAPL (mineral oil). In the presence of low levels of LNAPL, a significant decrease in root length was observed, whilst at higher LNAPL levels root lengths increased due to root diversion and spreading, with evidence of root redistribution in the case of LNAPL contamination across multiple adjacent pores. Changes to root morphology were also observed in the presence of LNAPL with plant roots coarse and crooked compared to long, fine and smooth roots in uncontaminated columns. Root and shoot biomass also appear to be impacted by the LNAPL although the effects are complex, affected by both root diversion and thickening. Substantial levels of LNAPL removal were observed, with roots close to LNAPL sources able to remove dissolved-phase contamination, and root growth through LNAPL sources suggest that direct uptake/degradation is possible.

Variation of soil aggregates in response to soil water under short-term natural rainfalls at different land use

The red soils of China, South America, and Africa are highly weathered inherently infertile soils that have high erosion risks and low soil organic carbon levels. In an effort to protect these soils, they are being converted from annual crops to woodlands in China. However, under such a land use change, soil aggregate stability variation (a key factor of soil erosion) to short-term rainfall events is not clear. The objective of this study was to investigate the influence of rainfall type, soil water contents, and vegetation on short-term changes in the aggregate stability of red soils. Surface (0–20 cm) aggregate stability, SWC and dynamics (Δθ) (differences of SWC on the sampling day and prior to the sampling), rainfall, and plant root distribution (0–60 cm) were monitored from 2017 to 2018 under fir (Taxodiaceae), rapeseed (Bassica napus) and Osmanthus fragrans land use. The results demonstrated that the aggregate size distribution and aggregate mean weight diameter were impacted by the soil water content prior to the precipitation and plant species. Plants such as fir, lowered the soil water content which improved short-term aggregate stability. Variation of aggregate under each type of rainfall was attributed to different change of SWC among plants, which was further confirmed by significantly negative relationships between aggregate fractions (< 0.5 mm) and SWC (θ0 and θ0.5, on the sampling time and half day prior to sampling) under all plants. Differences of aggregates as influenced by SWC among plants was also attributed to different plant root distribution and relative root absorption of soil water rate (RASWr) [r between SWC and root percentage (d = 1–3 mm) was 0.99]. The study suggested that plant types should be carefully selected for their ability to protect the soil and the findings will also provide a theoretical basis for land restoration.

Evaluating the potential slope plants using new method for soil reinforcement program

Herbaceous plants are effective in reinforcing soil in the hilly area of northern China. It is a challenge to select dominant herbaceous species for soil reinforcement. In this study, investigation of plant plots, survey of plant root distribution and tests of root tensile strength were carried out in the north hilly area of Taiyuan city, Shanxi Province, North China. Species importance values (SIV) of nine herbaceous plants were calculated using the four parameters: relative frequency, relative density, relative aboveground coverage and relative underground coverage of the plants. SIV of Lolium perenne L. (32%), Vetiveria zizanioides L. (17%) and Paspalum notatum (14%) accounted for >50% of the total SIV of all species. Root area ratio and tensile strength of the three species were measured, and root cohesion was then evaluated using the Wu-Waldron model. According to the relative root cohesion (RRC) index combining with SIV and root cohesion, the dominant order of the three plants for soil reinforcement was: Lolium perenne L. (1.71 MPa) > Vetiveria zizanioides L. (1.12 MPa) > Paspalum notatum (0.74 MPa). This study provides a new method and data basis for guiding soil reinforcement in restoration projects using herbaceous plants.

Imposing and maintaining soil water deficits in drought studies in pots

Pot studies are frequently used to study the influence of water deficits on plants and to screen genotypes for drought-resistance traits. Limited space and the need to screen large numbers of plants in rapid phenotyping platforms has led to the use of small pots for water-deficit studies. This paper reviews the influence of pot size, pot shape, soil medium, and the method of imposing water deficits on the development of soil water deficits, plant growth and function. Small pot size limits plant growth as the small soil volume limits root extension and proliferation. High-frequency deficit irrigation results in uneven distribution of water in the soil with consequent effects on plant growth, root distribution, water and nutrient uptake, and root-shoot interactions. Cycles of slow drying followed by fully rewetting the soil result in a more even distribution of water and roots throughout the pot and responses to water deficits more similar to those in the field. Small shallow pots and high-frequency deficit irrigation are inappropriate for inducing and maintaining water deficits, particularly when studying roots and root-shoot interactions. Large tall pots and cycles of drying and wetting better simulate water deficits encountered in the field and for identifying drought-resistant traits.

Geological Heritage Values of the Yongcheon Cave (Lava Tube Cave), Jeju Island, Korea

Yongcheon Cave is a typical lava tube cave, which formed by multiple flows of lava during the Late Quaternary. However, it is also a lime-decorated cave with numerous splendid carbonate speleothems along two parts of the passage. This paper deals with these special unique features of the cave together with their formation processes and the geoheritage significance based on detailed investigation of overlying carbonate sand dunes and speleothems. The cave is about 3360 m long, composed of 2590-m-long main passage and about 370-m-long branch passages. Because the cave contains unexplored passages at the downstream end, it is estimated that the total length can be at least about 400 m longer. The cave contains various microtopographic characteristics such as multiple and various forms of lava coatings on the surface as well as dented features by thermal erosion. They include pahoehoe and aa lavas, rockfalls, lava falls, lava benches, gutters with overflowed lava levees, tube-in-tubes, and lava benches on the floor. Lava flowlines are prominent on the wall, and also, anastomosing branches, lava bridges, and multiple leveled floors are other distinctive morphological features. Carbonate sand dunes were formed by transportation of beach sands nearby and partially overlie two parts of the cave passage. Carbonate sediments are medium sand-sized and are mostly composed of mollusk and coralline red algae fragments up to 60~70% with a minor contribution of benthic foraminifers, echinoderms, bryozoans, and volcanic rock fragments, which may well represent typical temperate carbonate constituents elsewhere. Beach sediments, the source of carbonate dune sands, also show the similar texture and composition. This suggests that the dune sands were transported onto the area by wind along the valleys. Previous age dating results of four carbonate sand dunes including several paleosol layers imply the formation ages of the dunes at each site since the deposition of carbonate sands in shallow seas between 4700 and 6000 years BP due to full deglaciation after Last Glacial Maximum. Carbonate speleothems began to grow in the cave after the deposition of dunes. Detailed mapping of the cave and dune fields strongly suggest that the dune distributions are directly related to the formation of carbonate speleothems. A variety of carbonate speleothems are found in Yongcheon Cave such as soda straws, stalactites, stalagmites, columns, rimstones, flowstones, cave corals, draperies (curtains and bacon sheets), cave pearls, shelfstones, and moonmilks. However, many carbonate speleothems show erratic morphologies that cannot be seen in any limestone caves elsewhere. It is because the formation of erratic speleothems is directly influenced by distribution of plant roots which helped to transport rainwater into the cave and to precipitate calcite mineral. Their unique abundance of carbonate speleothems providing splendid scenic values as well as Jeju’s special geological conditions for their formation is considered to be the outstanding universal value for the World Heritage site.

闽江河口芦苇与短叶茳芏空间扩展植物-土壤系统硫含量变化特征

PDF HTML阅读 XML下载 导出引用 引用提醒 闽江河口芦苇与短叶茳芏空间扩展植物-土壤系统硫含量变化特征 DOI: 10.5846/stxb201703060374 作者: 作者单位: 福建师范大学地理研究所,福建师范大学环境科学与工程学院,福建师范大学地理研究所,福建师范大学地理研究所,福建师范大学地理研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 福建省公益类科研院所重点项目（2016R1032-1）；福建省高等学校"新世纪优秀人才计划"项目；福建省"闽江学者奖励计划"项目；大学生创新创业训练计划（201610394011） Variations in total sulfur content in plant-soil systems of Phragmites australis and Cyperus malaccensis in the process of their spatial expansion in the Min River estuary Author: Affiliation: Institute of Geography, Key Laboratory of Humid Subtropical Eco-geographical Process (Fujian Normal University), Ministry of Education, Fujian Normal University,,Institute of Geography, Key Laboratory of Humid Subtropical Eco-geographical Process (Fujian Normal University), Ministry of Education, Fujian Normal University,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:2015年7月，选取闽江河口鳝鱼滩的芦苇湿地、短叶茳芏湿地以及二者交错带湿地为对象，研究了两种植被空间扩展过程中植物-土壤系统全硫（TS）含量的空间变化特征。结果表明，不同湿地表层土壤的TS含量表现为交错带湿地 > 短叶茳芏湿地 > 芦苇湿地，其差异主要与两种植被的空间扩展改变了交错带湿地土壤的质地及有机质等参数，进而对硫的迁移及转化过程产生重要影响有关；交错带不同植被的根系分布及其对土壤硫养分的竞争导致土壤TS含量的水平和垂直变异性均较芦苇或短叶茳芏纯群落发生较大改变，其土壤的TS含量受芦苇根系分布的影响更为明显，含量和储量均在深层土壤中较高。芦苇与短叶茳芏的空间扩展改变了两种植被的株高、密度及生物量分配格局，尽管二者在交错带中的地下生物量分配比均高于纯群落，但芦苇地下空间占据能力要高于短叶茳芏。研究发现，芦苇与短叶茳芏的空间扩展是双向过程，二者在空间扩展中通过不同的硫养分吸收、累积与分配策略适应竞争环境，即交错带湿地中的芦苇通过增加根部对硫养分的累积能力来保持其竞争力，而短叶茳芏则通过拓展地上空间及提高地上器官的硫养分累积能力来抗衡芦苇的空间扩展。 Abstract:To investigate the variation in total sulfur (TS) content in plant-soil systems of Phragmites australis and Cyperus malaccensis in the process of their spatial expansion in Shanyutan of the Min River estuary, the P. australis marsh (PM), C. malaccensis marsh (CM), and their ecotone (P. australis-C. malaccensis marsh, PCM) were studied in July 2015. Results showed that the TS content in soils of different marshes were generally in the order of CM > PCM > PM and the differences among them were primarily related to the alteration of soil texture and organic matter caused by the spatial expansion of P. australis and C. malaccensis, which substantially influenced the S transfer and transformation processes. The horizontal and vertical variation in TS content in the PCM soils was significantly different from those in the PM or CM community, and this difference was caused by the root distribution of different plants in the ecotone and their competition for the S nutrient. The TS content in soils of the PCM was more affected by the root distribution of P. australis, and TS content and stocks were generally higher in deep soil. The spatial expansion greatly altered the height, density, and biomass allocation of the two plants, and although their allocation patterns of belowground biomass in the ecotone were generally higher than those in the pure communities, P. australis exhibited a higher occupancy capacity in belowground space than did C. malaccensis. This study determined that the space expansion of P. australis and C. malaccensis was bi-directional, and could adapt to the competitive environment by using different strategies for S uptake, accumulation, and allocation. P. australis in the ecotone competed primarily by increasing the S accumulation capacity of its roots, whereas C. malaccensis in the ecotone was able to resist the space expansion of P. australis by expanding in the aboveground space and increasing the S accumulation capacity of aboveground organs. 参考文献 相似文献 引证文献

Effects of rainfall and vegetation to soil water input and output processes in the Mu Us Sandy Land, northwest China

Soil water plays a critical role in vegetation growth and restoration in semiarid regions, and has highly spatiotemporal variability. Gaining a comprehensive understanding of the soil water input and output processes is critical to the study of the hydrological cycle. To further unveil and quantify soil water dynamics, we embarked on a research program to quantify hydrological processes under three sites (i.e., shifting dune, shrub-dominated community, and herb-dominated community) with continuously monitored soil water content at 10-min intervals in the Mu Us Sandy Land between April and October 2012. The results indicated that soil water input and output processes were strongly affected by rainfall infiltration and surface characteristics. Rainfall affects the fluctuation of soil water content in deeper layers (60–80cm) by altering rainfall amount and soil texture; vegetation affects the soil water input process by altering the canopy rainfall interception, hydraulic lift, and soil organic matter content and so on. The effects of rainfall on the soil water output process mainly contributed to direct leakage and evaporation. Plant root distribution was a vital factor affecting the soil water output process. In addition, a state of dynamic equilibrium existed between the absorption of soil water and non-rainfall replenishment of soil water content during the output process over a long period of time. With limited soil water input and relatively larger soil water uptake by deeper roots, the soil water varied up to ~80% under the herb-dominated community. Our results imply that the increment of the deeper layer (60–80cm) would enhance shrub expansion in the Mu Us Sandy Land of China.

Water sources of dominant sand-binding plants in dry season in southern Horqin Sandy Land, China

It's important to explore the water sources of sand-binding plants and their relationship to reveal the mechanism underling species coexistence and vegetation stability. In the present study, 12 sand-binding species in two typical habitats (fixed dune and dune slack) in southern Horqin Sandy Land were selected. The δD and δ18O values of plant water, rain water, ground water and soil water were determined, and the percentages of soil water at different depths used by plants were calculated with the IsoSource model. Our results showed that the δD and δ18O values of stem water were significantly different among various life forms in both habitats except for those of trees and shrubs in dune slack. From trees to grass, the depth of soil water contributed to main water source of plant became shallower in dune slack: trees and shrubs mainly used soil water in 50-150 cm or 30-50 cm layer, subshrubs mainly used soil water in 10-30 cm layer while grass relied on soil water of 0-10 cm layer. Shrubs mainly used soil water of 0-30 cm layer and subshrubs mainly used soil water around 50 cm at fixed dune. This study indicated that in dry season plants at fixed dune are more dependent on soil water of 0-50 cm layer compared with those in dune slack. The water sources of sand-binding plants are correlated with plant life form and root distribution range, and the later might play a more important role.

Composition and distribution characteristics of stable carbon isotope in typical riparian grassland ecosystem

Plant-soil carbon stable isotope characteristics of riparian herbaceous ecosystem were ana-lyzed by measuring the δ13C value of plant tissues from four typical riparian herbaceous plants, which were Cynodon dactylon, Trifolium repens, Festuca arundinacea and Imperata cylindrical, and that of soil organic carbon (SOC) from different vertical depths along Dongfeng Port River in Qingpu District, Shanghai. The result showed that T. repens and F. arundinacea were C3 plants while C. dactylon and I. cylindrical were C4 plants. There was no significant difference between the δ13C va-lue of stem and leaf, litter and root of the four herbaceous plants. The surface SOC δ13C value of C3 and C4 plants strips showed different trends with soil depth, which could be related to the background SOC δ13C value, soil carbon stable isotope fractionation effect and plant root distribution depth as well. Plant input was the main source of SOC and the δ13C composition of plant organisms had direct effect on the SOC δ13C value. The δ13C value of plant components were significantly correlated with the δ13C value of SOC. The SOC content and δ13C value were significantly correlated in the four herbaceous plants strips. The SOC content and δ13C value showed linear negative correlation in C3 plant strips and linear positive correlation in C4 plant strips.

Rice Root Distribution of Four Rice Varieties to Different Depth of Submergence

Rice ( Oryza sativa L.) is largely cultivated in lowland area that vulnerable to flood occurrence. Root supposed to play an important role on rice tolerance to submergence stress. An experiment which conducted from January to May 2014 in Cikarawang Field Laboratory, Darmaga, Bogor, West Java aimed to study the role of root distribution on rice submergence tolerant. The experiment used Split Plot design replicated three times, with the depth of submergence as main plot and rice variety as subplot. The main plot consisted of water depth of 5 cm (optimum), 50 cm, 60 cm and 80 cm from soil surface. The subplot consisted of four rice varieties, namely Ciherang, Inpari 30 (Ciherang Sub1), Indragiri and Margasari. Each plant was planted in a root box (30 cm x 40 cm x 5 cm) which put into container (67 cm x 47 cm x 42 cm) and placed into the pond with water depth as treatment. Submergence started when the plant was 39 DAS (Days After Seeding) for ten days. Observation conducted after the submergence stopped (49 DAS). Result showed that submergence retarded plant growth, root distribution and increase root damage for all rice varieties with the biggest effect on susceptible varieties.

Vertical Distribution of Pasteuria penetrans Parasitizing Meloidogyne incognita on Pittosporum tobira in Florida

Pasteuria penetrans is considered as the primary agent responsible for soil suppressiveness to root-knot nematodes widely distributed in many agricultural fields. A preliminary survey on a Pittosporum tobira field where the grower had experienced a continuous decline in productivity caused by Meloidogyne incognita showed that the nematode was infected with Pasteuria penetrans. For effective control of the nematode, the bacterium and the host must coexist in the same root zone. The vertical distribution of Pasteuria penetrans and its relationship with the nematode host in the soil was investigated to identify (i) the vertical distribution of P. penetrans endospores in an irrigated P. tobira field and (ii) the relationship among P. penetrans endospore density, M. incognita J2 population density, and host plant root distribution over time. Soil bioassays revealed that endospore density was greater in the upper 18 cm of the top soil compared with the underlying depths. A correlation analysis showed that the endospore density was positively related to the J2 population density and host plant root distribution. Thus, the vertical distribution of P. penetrans was largely dependent on its nematode host which in turn was determined by the distribution of the host plant roots. The Pasteuria was predominant mostly in the upper layers of the soil where their nematode host and the plant host roots are abundant, a factor which may be a critical consideration when using P. penetrans as a nematode biological control agent.

Spatial distribution of soil water, soil temperature, and plant roots in a drip-irrigated intercropping field with plastic mulch

Intercropping and drip irrigation with plastic mulch are two agricultural practices used worldwide. Coupling of these two practices may further increase crop yields and land and water use efficiencies when an optimal spatial distribution of soil water contents (SWC), soil temperatures, and plant roots is achieved. However, this coupling causes the distribution of SWCs, soil temperatures, and plant roots to be more complex than when only one of these agricultural practices are used. The objective of this study thus was to investigate the effects of different irrigation treatments on spatial distributions of SWCs, soil temperatures, and root growth in a drip-irrigated intercropping field with plastic mulch. Three field experiments with different irrigation treatments (high T1, moderate T2, and low T3) were conducted to evaluate the spatial distribution of SWCs, soil temperatures, and plant roots with respect to dripper lines and plant locations. There were significant differences (p < 0.05) in SWCs in the 0–40 cm soil layer for different irrigation treatments and between different locations. The maximum SWC was measured under the plant/mulch for the T1 treatment, while the minimum SWC was measured under the bare soil surface for the T3 treatment. This was mainly due to the location of drippers and mulch. However, no differences in SWCs were measured in the 60 100 cm soil layer. Significant differences in soil temperatures were measured in the 0 5 cm soil layer between different irrigation treatments and different locations. The soil temperature in the subsoil (15 25 cm) under mulch was higher than under the bare surface. The overlaps of two plant root systems in an intercropping field gradually increased and then decreased during the growing season. The roots in the 0 30 cm soil layer accounted for about 60% 70% of all roots. Higher irrigation rates produced higher root length and weight densities in the 0 30 cm soil layer and lower densities in the 30 100 cm soil layers. Spatial distributions of SWCs, soil temperatures, and plant roots in the intercropping field under drip irrigation were significantly influenced by irrigation treatments and plastic mulch. Collected experimental data may contribute to designing an optimal irrigation program for a drip-irrigated intercropping field with plastic mulch.

Interaction Between Plant Roots and Soil Water Flow in Response to Preferential Flow Paths in Northern China

AbstractPreferential flow is expected to provide preferential channels for plant root growth and variations in soil water flow, but few studies were conducted to imply the impacts of these changes, particularly for preferential flow in stony soils. This study aimed to characterize soil water flow and plant root distribution in response to preferential flow paths and quantitatively describe the relation between plant root distribution and soil water flow. Field dye‐tracing experiments centered on experimental plants were conducted to determine the root length density and soil water flow process. Laboratory analyses were performed to characterize changes in the relative concentration of the accumulated effluent and the degree of interaction between plant roots and soil water flow. The amount of fine plant roots with preferential flow paths decreased with increasing soil depth for all experimental plots. The largest plant roots were recorded in the upper soil layers to a depth of 20 cm. The relative concentration of the accumulated effluent increased with time and decreased with soil depth under saturated soil conditions, whereas a distinct early turning point for the relative concentration of the accumulated effluent was observed in the 0–20‐cm soil columns, and the relative concentration of the accumulated effluent initially decreased and then increased with time under unsaturated soil conditions. This study provides quantitative information with which to characterize the interaction between plant roots and soil water flow in response to preferential flow paths in soil–plant–water systems. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Root distributions in a laboratory box evaluated using two different techniques (gravimetric and image processing) and their impact on root water uptake simulated with HYDRUS

Abstract Knowledge of the distribution of plant roots in a soil profile (i.e. root density) is needed when simulating root water uptake from soil. Therefore, this study focused on evaluating barley and wheat root densities in a sand-vermiculite substrate. Barley and wheat were planted in a flat laboratory box under greenhouse conditions. The box was always divided into two parts, where a single plant row and rows cross section (respectively) was simulated. Roots were excavated at the end of the experiment and root densities were assessed using root zone image processing and by weighing. For this purpose, the entire area (width of 40 and height of 50 cm) of each scenario was divided into 80 segments (area of 5×5 cm). Root density in each segment was expressed as a root percentage of the entire root cluster. Vertical root distributions (i.e. root density with respect to depth) were also calculated as a sum of root densities in each 5 cm layer. Resulting vertical root densities, measured evaporation from the water table (used as the potential root water uptake), and the Feddes stress response function model were used for simulating substrate water regime and actual root water uptake for all scenarios using HYDRUS-1D. All scenarios were also simulated using HYDRUS-2D. One scenario (areal root density of barley sown in a single row, obtained using image analysis) is presented in this paper (because most scenarios showed root water uptakes similar to results of 1D scenarios). The application of two root detecting techniques resulted in noticeably different root density distributions. Differences were mainly attributed to the fact that fine roots of high density (located mostly at the deeper part of the box) had lower weights in comparison to the weight of few large roots (at the box top). Thus, at the deeper part, higher root density (with respect to the entire root zone) was obtained using the image analysis in comparison to that from the gravimetric analysis. Conversely, lower root density was obtained using the image analysis at the upper part in comparison to that from the gravimetric analysis. On the other hand, fine roots overlapped each other and therefore were not visible in the image, which resulted in lower root density values from image analysis. Root water uptakes simulated with HYDRUS-1D using diverse root densities obtained for each cereal declined differently from the potential root water uptake values depending on water scarcity at depths of higher root density. Usually, an earlier downtrend associated with gradual root water up-take decreases and vice versa. Similar root water uptakes were simulated for the presented scenario using the HYDRUS-1D and HYDRUS-2D models. The impact of the horizontal root density distribution on root water uptake was, in this case, less important than the impact of the vertical root distribution resulting from different techniques and sowing scenarios.

The signature of randomness in riparian plant root distributions

AbstractKnown as “the hidden half”, plant roots are fundamental contributors to the riparian ecosystem functioning. Roots show an extraordinary architectural complexity that recalls their remarkable ability to adapt to environmental heterogeneity, resources availability, and climate. In fluvial environments, phreatophytes and hydrophytes cope with flow and sediment processes, and hydrotropism and aerotropism are the main drivers for root growth. In this work, we show how the vertical root density distribution in riparian plants is the result of how plants respond to the random fluctuations of river flows. A root data set from field and controlled outdoor experiments is used in combination with a physically based analytical model to demonstrate that the root vertical density distribution can be ascribed to the interplay of randomness and determinism in a simple mathematical form. The shape of the distribution reflects the profitability of plant roots to grow in different soil layers depending on the soil moisture availability. For the first time, this model helps understanding in an analytical manner the adaptation strategy of plant roots to different scenarios, paving the way for the comprehension of the effects of future changes in climate and environmental conditions.

Application of the method of spatial point pattern analysis to the horizontal spatial distribution of preferential flow paths

Preferential flow significantly influences hydrological processes in forests. The occurrence and development of this flow is directly affected by its spatial distribution. To determine whether or not point pattern analysis method can be used to examine the horizontal spatial distribution of preferential flow paths, experiments were conducted with dye tracer permeation to observe flow processes. Results indicated that an increase in penetration water volume exerted only a specific effect on preferential flow paths of large class in the topmost soil. Moreover, such paths showed distinct clumped patterns at the 25-cm scale under both high permeation water volume and low permeation water volume treatments. Nonetheless, the distribution pattern became uniform as scale range increased. The significance of the correlation between the spatial distribution of preferential flow paths and plant roots decreased from the top soil layer to the bottom. These findings suggest that soil depth and water permeation volume are important to the horizontal spatial distribution of preferential flow paths. Moreover, point pattern analysis method is suitable for investigating the horizontal spatial distribution of preferential flow paths and determining the correlation between the spatial distribution of preferential flow paths and plant roots.