Root tensile strength and root distribution of typical Mediterranean plant species and their contribution to soil shear strength

In Mediterranean environments, gully erosion is responsible for large soil losses. It has since long been recognized that slopes under vegetation are much more resistant to soil erosion processes compared to bare soils and improve slope stability. Planting or preserving vegetation in areas vulnerable to erosion is therefore considered to be a very effective soil erosion control measure. Re-vegetation strategies for erosion control rely in most cases on the effects of the above-ground biomass in reducing water erosion rates, whereas the role of the below-ground biomass is often neglected or underestimated. While the above-ground biomass can temporally disappear in semi-arid environments, roots may still be present underground and play an important role in protecting the topsoil from being eroded. In order to evaluate the potential of plant species growing in Mediterranean environments to prevent shallow mass movements on gully or terrace walls, the root reinforcement effect of 25 typical Mediterranean matorral species (i.e. shrubs, grasses herbs, small trees) was assessed, using the simple perpendicular model of Wu et al. (Can Geotech J 16:19–33, 1979). As little information is available on Mediterranean plant root characteristics, root distribution data were collected in SE-Spain and root tensile strength tests were conducted in the laboratory. The power root tensile strength–root diameter relationships depend on plant species. The results show that the shrubs Salsola genistoides Juss. Ex Poir. and Atriplex halimus L. have the strongest roots, followed by the grass Brachypodium retusum (Pers.) Beauv. The shrubs Nerium oleander L. and the grass Avenula bromoides (Gouan) H. Scholz have the weakest roots in tension. Root area ratio for the 0–0.1 m topsoil ranges from 0.08% for the grass Piptatherum miliaceum (L.) Coss to 0.8% for the tree Tamarix canariensis Willd. The rush Juncus acutus L. provides the maximum soil reinforcement to the topsoil by its roots (i.e. 304 kPa). Grasses also increase soil shear strength significantly (up to 244 kPa in the 0–0.1 m topsoil for Brachypodium retusum (Pers.) Beauv.). The shrubs Retama sphaerocarpa (L.) Boiss. and Anthyllis cytisoides L. are increasing soil shear strength to a large extent as well (up to 134 and 160 kPa respectively in the 0–0.10 m topsoil). Whereas grasses and the rush Juncus acutus L. increase soil shear strength in the topsoil (0–0.10 m) to a large extent, the shrubs Anthyllis cytisoides (L.), Retama sphaerocarpa (L.) Boiss., Salsola genistoides Juss. Ex Poir. and Atriplex halimus L. strongly reinforce the soil to a greater depth (0–0.5 m). As other studies reported that Wu’s model overestimates root cohesion values, reported root cohesion values in this study are maximum values. Nevertheless, the calculated cohesion values are used to rank species according to their potential to reinforce the soil.     

A comparison of fine root distribution and water consumption of mature Caragana korshinkii Kom grown in two soils in a semiarid region, China

Water is a key limiting factor for vegetation restoration in the semi-arid areas of China. Caragana korshinkii Kom is a shrub that is widely planted in this region to control soil erosion and land desertification. The objective of this study was to investigate the fine root distribution of mature C. korshinkii and its water consumption, when grown in either silt loam or sandy soils, in order to understand differences between the water cycles of two such soils found in the transition zone between fertile loess hills and desert of the Northern Loess Plateau. Fine root distributions were measured using the trench-profile method. Soil water dynamics were monitored with a neutron probe during two growing seasons. The results showed that fine root area density (FRAD) declined with increasing soil depth in both soils, with 70.7% and 96.6% of the total fine roots being concentrated in the upper 1-m layer of the silt loam and sandy soils, respectively. Water consumption by C. korshinkii in the silt loam was close to that in the sandy soil. Most water consumption in both soil types was from the upper 1-m layer. Little variation in plant available water (PAW) occurred in the 3–6 m soil layer during the whole study period. However, in this layer, the PAW was significantly lower in the silt loam soil than in the sandy soil. Total actual evapotranspiration (ET_a) was slightly higher from the sandy soil plots than from those of the silt loam soil during both growing seasons. Our study indicated that mature C. korshinkii effectively uses about the same amount of water from either the silt loam or sandy soils, but that more soil water at depth was extracted from silt loam soil than from sandy soil.     

Influences of plant spacing on root tensile strength of Schefflera arboricola and soil shear strength

Mechanical root reinforcement depends not only on root biomechanical properties but also on root biomass. Although it is known that plant spacing can affect root growth, it is not clear how it affects root tensile strength. We interpreted a set of field data to study the effects of spacing of Schefflera arboricola on root area ratio (RAR), root tensile strength and their combined effects on soil shear strength (also termed root cohesion). S. arboricola was transplanted into compacted silty sand at a spacing of 0.5 m, 0.8 m and 1.1 m. After 20 months of growth in the field, the root systems were excavated for root tensile testing and post-test trait measurements. Plant spacing affected the growth and tensile strength of roots. More closely spaced plants had higher RAR but lower root tensile strength, especially for roots 0.5–2 mm in diameter. According to the existing root breakage and fibre bundle models used in this study, which calculate root cohesion as the product of RAR and root tensile strength, the effects of plant spacing on root cohesion were minimal for most soil depths apart from 0.4- to 0.5-m depth.

     

Quantifying the effects of root reinforcement of Persian Ironwood (Parrotia persica) on slope stability; a case study: Hillslope of Hyrcanian forests,northern Iran

Forest vegetation is known to enhance the stability of slopes by reinforcing soil and increasing its shear resistance through root system. The effects of root reinforcement depend on the morphological characteristics of the root system, the tensile strength of single roots, and the spatial distribution of the roots in soil. In the present study the results of research carried out in order to evaluate the biotechnical characteristics of the root system of Persian Ironwood (Parrotia persica), in northern Iran are presented. Profile trenching method was used to obtain root area ratio (RAR) values for uphill and downhill sides of the individual trees. For each species, single root specimens were sampled and tested for their tensile strength. It was found that root density generally decreases with depth according to an exponential law. Maximum RAR values were located within the first 0.1 m, with maximum rooting depth at about 0.65 m. RAR values ranged from 0.001% at lower depths to 1.39% near the surface, at upper 0.1 m depth. Significant differences of RAR values, rooting depth and root cohesion between uphill and downhill were observed, however, the differences were not significant for number of roots (ANCOVA). Downhill profiles had higher RAR values, rooting depth and root cohesion. In general, root tensile strength tends to decrease with diameter according to a power law, as observed by other researchers. Downhill roots were significantly stronger in tensile strength than uphill ones. Inter-species variation of tensile strength in downhill roots was also observed. The resulting data were used to evaluate the reinforcing effects in terms of increased shear strength of the soil, using Wu/Waldron Model. The root reinforcement provided by Persian Ironwood is about 46.0 kPa in the upper layers and 0.3 kPa in the deeper horizons. The results of Spearman test revealed a significant correlation between RAR and c_r and that best followed by a power law. The results presented in this paper contribute to expanding the knowledge on biotechnical characteristics of Persian Ironwood on slope reinforcement.     

Modelling root demography in heterogeneous mountain forests and applications for slope stability analysis

Background and aims

Plant roots provide mechanical cohesion (c _r ) to soil on slopes which are prone to shallow landslides. c _r varies in heterogeneous natural forests due to the spatial, inter- and intra-annual dynamics of root demography. Characterizing root initiation density and mortality, as well as how root growth is influenced by abiotic and biotic factors is essential for exploring a root system’s capacity to reinforce soil.

Methods

In this study, root demography data were monitored using field rhizotrons during 1.5 years in two naturally regenerated mixed forests in the French Alps. These forests are composed of trees growing in groups (tree islands) with large gaps between the islands. Three categories of driving variables were measured: (i) spatial factors: altitude (1,400 m, 1,700 m), ecological patch (gap, tree island), soil depth (0.0–1.0 m divided into five layers of 0.2 m); (ii) temporal factors: month (12 months from March 2010 to February 2011), winter (winter of 2009–2010 and 2010–2011); (iii) biological factors: root diameter classes (]0, 1] mm, ]1, 2] mm, ]2, 5] mm (according to the international standard ISO 31–11, ]x, y] denotes a left half-open interval from x (excluded) to y (included)). Two types of two-part models, a Hurdle model (H) and a Zero-inflated model (ZI) were used to fit root data with a high zero population, i.e. if root initiation or mortality was zero during a given time period, or if roots were not present at all points throughout a soil profile.

Results

Root initiation quantity decreased with increasing soil depth, as well as being lower in tree islands. Both soil depth and ecological patch interacted strongly with altitude. Root dynamics were significantly less active with a lower net production and c _r increment in winter and spring than in summer and autumn. Roots which were ]1, 2] mm in diameter contributed the most to c _r compared to other diameter classes, as they had a high production but a low mortality. With regard to model selection, both H and ZI demonstrated similar outcomes and underestimated extreme values of root demography data.

Conclusion

All factors contributed towards explaining the variability of root demography and c _r . We suggest taking into consideration the seasonality of root dynamics when studying root reinforcement.     

Shoot and root physiological responses to localized zones of soil moisture in cultivated and wild lettuce (Lactuca spp.)

Cultivated crisphead lettuce (Lactuca sativa L.) has a shallower root system than its wild relative, Lactuca serriola L. The effects of localized soil water, at depth, on plant water relations, gas exchange and root distribution were examined in the two species using soil columns with the soil hydraulic-ally separated into two layers, at (0–20 cm and 20–81) cm, but permitting root growth between the layers. Three treatments were imposed on 7-week-old plants, and maintained for 4 weeks: (i) watering, both layers to field capacity; (ii) drying the upper layer while watering the lower layer to field capacity, and (iii) drying both layers. Drying only 0–20 cm of soil had no effect on leaf water status, net photosynthesis, stomatal conductance or biomass production in L. serriola compared to a well-watered control, but caused a short-term reduction (10 d) in leaf water status and photosynthesis in L. sativa that reduced final shoot production. The different responses may be explained by differences in root distribution. Just before the treatments commenced, L. serriola had 50% of total root length at 20–80 cm compared to 35% in L. sativa. Allocation of total biomass to roots in L. serriola was approximately double that in L. sativa. The wild species could provide germplasm for cultivated lettuces to extract more soil water from depth, which may improve irrigation efficiency.     

植物根系固坡抗蚀的效应与机理研究进展

植物根系对抵抗坡体浅层滑坡和表土侵蚀起着巨大的作用.植物根系通过增强土体的抗剪强度发挥固坡效应.目前有关植物根系固坡机理的模型较多,普遍接受的是Wu-Waldron模型.该模型表明,植物根系产生的土体抗剪强度的增量与根系的平均抗拉强度和根面积比成正比,应用该模型评价根系固坡效应的2个最重要因素是根系的平均抗拉强度和根面积比.研究发现,土壤抗侵蚀性随着植物根系数量的增加而提高,但未有一致的定量函数关系.植物根系提高土壤抗侵蚀性主要通过直径小于1mm的须根起作用.须根通过增加土壤水稳性团聚体的数量与粒径等作用来提高土壤的稳定性,以抵抗水流分散;须根还能有效地增强土壤渗透性,减少径流,从而达到减少土壤冲刷的目的.     

3-D numerical investigations into the shear strength of the soil–root system of Makino bamboo and its effect on slope stability

This study attempts to quantify the reinforcement effect of the Makino bamboo (Phyllostachys makinoi Hayata) root system on the stability of slopeland through numerical analyses and in situ tests. Based on the field surveys of Makino bamboo root morphology, a three-dimensional (3-D) numerical model of the soil–root system consisting of the reverse T-shape tap root and hair roots was developed and successfully applied to the finite element simulations of in situ pull-out tests. In the simulations, the soil mass was simulated by a soil element with a perfect elastic–plastic (or Mohr–Coulomb) material model whereas the root system was simulated by a ground anchor element with a linear elastic material model. In addition, a mechanical conversion model with simple mathematical form, which enables a direct transformation of the ultimate pull-out resistance into the shear strength increment of soil–root system was proposed. The conversion model offered a convenient way to quantify the reinforcement effect of the Makino bamboo root system required for the 3-D slope stability analyses. The numerical results indicated that the shear strength increment of the Makino bamboo soil–root system ranged from 18.4 to 26.3 kPa and its effect on the slope stability was insignificant when compared with those adverse influence factors such as the steep slope angle (=50–70°), shallow root depth (=0.8–1.0 m) and large growth height (>10 m) of the Makino bamboo forest slopeland. It can be also speculated that the tension cracks widespread over the slope surface due to the wind loading acting on the bamboo stems and the sequential rainwater infiltration is the dominating factor in the collapse failure of slopeland. For a Makino bamboo forest slopeland with medium slope (25° < slope angle β < 40°), the reinforcement effect of the Makino bamboo root system can mobilize its maximum stabilization capacity when compared with those of slopeland with mild (β < 25°) and steep slopes (β > 40°). Conclusively, the contribution of the Makino bamboo root system to the stability of slopeland is not as significant as expected.     

Triaxial compression test of soil–root composites to evaluate influence of roots on soil shear strength

In order to evaluate influences of roots on soil shear strength, a triaxial compression test was carried out to study the shear strength of plain soil samples and composites comprised of roots of Robinia pseucdoacacia and soil from the Loess Plateau in Northwest China. Roots were distributed in soil in three forms: vertical, horizontal, and vertical–horizontal (cross). All samples were tested under two different soil water contents. Test results showed that roots have more impacts on the soil cohesion than the friction angle. The presence of roots in soil substantially increased the soil shear strength. Among three root distribution forms, the reinforcing effect of vertical–horizontal (cross) root distribution was the most effective. Increase in soil water content directly induced a decline in soil cohesion of all test samples and resulted in a decrease in shear strength for both plain soil samples and soil–root composites. It was concluded that the triaxial compression test can be effectively used to study influences of roots on soil shear strength.     

子午岭林区浅层滑坡侵蚀与植被的关系——以富县“7·21”特大暴雨为例

以2013年陕北富县"7·21"特大暴雨滑坡侵蚀灾害为对象,通过调查暴雨侵蚀区典型小流域植被条件及滑坡特征,测定滑坡壁不同土层的根系重量、土壤孔隙度、土壤容重等指标,研究子午岭林区暴雨滑坡侵蚀与植被根系的关系。根据不同类型植被根系深度和滑坡侵蚀特征(侵蚀深度、滑动面宽度及长度,滑坡体体积、滑动距离等),可将林区暴雨滑坡侵蚀划分为三类:以草本植被为主的A类滑坡,以灌丛植被为主的B类滑坡,以乔本植被为主的C类滑坡。结果表明,三类滑坡侵蚀的侵蚀深度与其对应植被类型的根系深度相近,且植被及其根系会加剧滑坡侵蚀的发生。在此次暴雨滑坡侵蚀中,滑坡侵蚀强度受植物根系重量、土壤孔隙度、土壤容重等因素的共同影响,但根系重量对滑坡侵蚀强度的影响占主导作用,通过建立二者之间的关系式发现,根系对滑坡侵蚀的贡献率超过80%。不同植被类型的滑坡侵蚀深度不同,且滑坡侵蚀强度也存在差异,表明植被根系不仅具有塑造滑坡侵蚀特征的作用,而且会影响滑坡侵蚀的强弱程度。在强降水基础上,特别是当降水量达到诱发滑坡灾害发生的临界值时,植被及其根系会加剧滑坡侵蚀的发生。在今后工作中,要因地制宜合理配置各类植被,同时结合其它措施,以便提高植被防治水土流失的作用,更好地发挥植被的水土保持效益。     

Functional traits and root morphology of alpine plants

Background and Aims

Vegetation has long been recognized to protect the soil from erosion. Understanding species differences in root morphology and functional traits is an important step to assess which species and species mixtures may provide erosion control. Furthermore, extending classification of plant functional types towards root traits may be a useful procedure in understanding important root functions.

Methods

In this study, pioneer data on traits of alpine plant species, i.e. plant height and shoot biomass, root depth, horizontal root spreading, root length, diameter, tensile strength, plant age and root biomass, from a disturbed site in the Swiss Alps are presented. The applicability of three classifications of plant functional types (PFTs), i.e. life form, growth form and root type, was examined for above- and below-ground plant traits.

Key Results

Plant traits differed considerably among species even of the same life form, e.g. in the case of total root length by more than two orders of magnitude. Within the same root diameter, species differed significantly in tensile strength: some species (Geum reptans and Luzula spicata) had roots more than twice as strong as those of other species. Species of different life forms provided different root functions (e.g. root depth and horizontal root spreading) that may be important for soil physical processes. All classifications of PFTs were helpful to categorize plant traits; however, the PFTs according to root type explained total root length far better than the other PFTs.

Conclusions

The results of the study illustrate the remarkable differences between root traits of alpine plants, some of which cannot be assessed from simple morphological inspection, e.g. tensile strength. PFT classification based on root traits seems useful to categorize plant traits, even though some patterns are better explained at the individual species level.     

Phosphorus runoff from a phosphorus deficient soil under common bean (Phaseolus vulgaris L.) and soybean (Glycine max L.) genotypes with contrasting root architecture

The selection and breeding of crop genotypes with root traits that improve soil resource extraction is a promising avenue to improved nutrient and water use efficiency in low-input farming systems. Such genotypes may accelerate nutrient extraction (“nutrient mining”), but may also reduce nutrient loss via soil erosion by producing greater shoot biomass and by direct effects of root traits on aggregate formation and water infiltration. Little is known about the effects of root architecture on phosphorus (P) runoff and soil erosion, and the relative importance of root and shoot traits on runoff P loss has not been determined. Four genotypes of common bean (Phaseolus vulgaris L.) and two genotypes of soybean (Glycine max) selected for contrasting root architecture were grown in a low P soil (Aquic Fragiudult, <20 mg kg^?1 Mehlich-3 P, 3% slope) and subjected to rainfall-runoff experiments with and without shoot removal. Plots with intact shoots had significantly lower runoff volumes (1.3–7.6 mm) and total P loads in runoff (0.005–0.32 kg ha^?1) than plots with shoots removed (7.0–16.8 mm; 0.025–1.95 kg ha^?1). Dissolved reactive P leached from plant material did not contribute significantly to P loss in runoff. Total root length acquired from soil cores differed significantly among genotypes. Root length densities in the upper 15 cm of soil mid-way between rows were less than 4.0 cm cm^?3 and variation in root length density was not correlated with runoff or P loss. Root length density also did not affect rainfall infiltration or surface runoff volume. We conclude that for annual dicotyledonous crops such as bean and soybean with relatively low root length densities, root traits have little direct effect on soil erosion.     

先锋种丰富度对边坡植被群落特征及其护坡效益的影响

乡土植物灌木化建植是高速公路边坡防护的重要途径。以成渝高速(G85)永川段为例,以西南地区两种典型的边坡绿化初始配置"慈竹(Neosino calamus affinis)+野牛草(Buchloe dactyloides)"、"棉槐(Amorpha fruticosa)+紫羊茅(Festuca rubra)"为基础,分别与马棘(Indigofera pseudotinctoria Mats.)、黄荆(Vitex negundo)、狗牙根(Cynodon dactylon)、芒(Miscanthus sinensis)等路域优势种以不同方式组合,研究一定立地条件下初始绿化植物(先驱植物)的丰富度对边坡植被群落生长发育、早期演替行为及护坡性能的影响。结果表明:1)先驱植物丰富度可直接影响边坡植被的成坪时间、生物量积累:相同建植条件(边坡条件、播种密度等)下,先锋种种类越多,成坪时间就越短,被积累的生物量也越多;2)先锋种数量与群落的生物多样性水平有关(R20.954):相同演替阶段内,先锋种越多,群落的多样性水平(如物种丰富度、Shannon-Wiener指数、Pielou指数)则越高;3)群落中物种多样性水平与植被的护坡性能密切相关(R20.998):多样性水平越高,植被的蓄水、保土能力越强,边坡内径流系数、土壤侵蚀模数越小。可见,在边坡条件、播种密度等建植条件与建植措施一致的情形下,提高初始绿化植物的物种数可有效改善边坡植被的护坡性能。     

Habitat-specific responses of seed germination and seedling establishment to soil water condition in two Rheum species in the high Sino-Himalayas

Knowledge of how germination and seedling establishment respond to soil water condition is crucial for plant conservation under global warming and land-use changes. We tested the flooding and drought tolerance of two plant species with different occurrences along a soil water gradient by assessing seed germination, seedling survival, seedling growth, and root characteristics. In the high Sino-Himalayas, Rheum alexandrae typically occurs in wetlands, R. nobile in scree or open slope with well-drained soils. Seeds and seedlings of the two species were subjected to different soil water conditions in controlled greenhouse experiments. Seed germination in both species was inhibited by high soil water content; however, seeds of R. alexandrae were more tolerant to flooding, especially to submergence. Seedling survival, biomass accumulation, root diameter, and root porosity of R. alexandrae increased significantly with increased soil water content, but submergence was lethal for seedlings. Seedling survival, biomass accumulation, and root length of R. nobile increased significantly in response to reduced soil water content. These results indicate that in the two species, seed germination and seedling establishment in response to different soil water condition are habitat-specific. Because both species are susceptible to moderate changes in soil water condition, their species-specific requirements with respect to this factor should be a consideration when planning their conservation.     

黄土高塬沟壑区草地沟头立壁土壤抗冲性特征

黄土高原植被恢复使沟头立璧土壤侵蚀过程发生显著变化.为明确黄土高塬沟壑区草地沟头立壁土壤抗冲性特征及其影响因素,以裸地为对照,利用室内原状土槽冲刷试验研究了草地沟头立壁O～1m不同土层(0～10、10～20、20 ～ 40、40～ 60、60 ～ 80、80～ 100 cm)土壤理化性质和抗冲性特征.结果 表明:草地和...     

Effects of contrasting soil fertility on root mass, root growth, root decomposition and soil carbon under a New Zealand perennial ryegrass/white clover pasture

The contribution of below ground plant root tissue to soil carbon (C) pools is attracting considerable interest in the context of greenhouse gas mitigation options. A field experiment was conducted on a perennial ryegrass/white clover pasture in the Manawatu, New Zealand, to examine the effect of differing soil nitrogen (N) and phosphorus (P) fertility status on root dynamics. Root standing mass, shoot and root dry matter (DM) accumulation and root tissue decomposition were measured at 6–8 week intervals over one year at moderate (Olsen P?=?24, no added N) and high (Olsen P?=?49, 400 kgN ha^?1y^?1 added N) soil fertility levels. Shoot production was significantly greater in the high fertility treatment (2550 cf. 1890 gDM m^?2y^?1) but differences in root dynamics were confined to two periods in spring and winter. In late spring the pattern was for lower root mass (183 cf. 231 gDM m^?2 between 0–80 mm depth) and higher root production (0.71 cf. 0.52 gDM m^?2 d^?1 between 0–120 mm depth) under higher fertility. In winter the reverse was observed. There is some evidence that the soil type used in the root in-growth cores underestimated root production values for this site by a factor of approx. one third. Short-term differences between the two fertiity treatments in standing root mass and root production did not lead to treatment differences in topsoil C and N changes over four years. This may reflect insufficient separation in the two soil fertility treatments and a low overall root tissue input to soil organic matter.     

Root cohesion of forest species in the Italian Alps

Forests can prevent and/or mitigate hydrogeomorphic hazards in mountainous landscapes. Their effect is particularly relevant in the case of shallow landslides phenomena, where plants decrease the water content of the soil and increase its mechanical strength. Although such an effect is well known, its quantification is a relatively new challenge. The present work estimates the effect of some forest species on hillslope stability in terms of additional root cohesion by means of a model based on the classical Wu and Waldron approach (Wu in Alaska Geotech Rpt No 5 Dpt Civ Eng Ohio State Univ Columbus, USA, 1976; Waldron in Soil Sci Soc Am J 41:843–849, 1977). The model is able to account for root distribution with depth and non-simultaneous root breaking. Samples of European beech (Fagus sylvatica L.), Norway spruce (Picea abies (L.) Karst.), European larch (Larix decidua Mill.), sweet chestnut (Castanea sativa Mill.) and European hop-hornbeam (Ostrya carpinifolia Scop.), were taken from different locations of Lombardy (Northern Italy) to estimate root tensile strength, the Root Area Ratio and the root cohesion distribution in the soil. The results show that, in spite of its dramatic variability within the same species at the same location and among different locations, root cohesion can be coherently interpreted using the proposed method. The values herein obtained are significant for slope stabilisation, are consistent with the results of direct shear tests and back-analysis data, and can be used for the estimation of the stability of forested hillslopes in the Alps.     

Increased plant density of winter wheat can enhance nitrogen–uptake from deep soil

Background and Aims

Increased plant density improves grain yield and nitrogen (N)–use efficiency in winter wheat (Triticum aestivum L.) by increasing the root length density (RLD) in the soil and aboveground N–uptake (AGN) at maturity. However, how the root distribution and N–uptake at different soil depths is affected by plant density is largely unknown.

Methods

A 2–year field study using the winter wheat cultivar Tainong 18 was conducted by injecting ¹⁵?N–labeled urea into soil at depths of 0.2, 0.6, and 1.0 m under four plant densities of 135 m^?2, 270 m^?2,405 m^?2, and 540 m^?2.

Results

We observed significant RLD and ¹⁵?N–uptake increases at each soil depth as the plant density increased from 135 to 405 m^?2. ¹⁵?N–uptake increased with plant density as the soil depth increased, although the corresponding RLD value fell with depth. The ¹⁵?N–uptake at each soil depth was positively related to the RLD at the same depth. The total AGN was positively related to RLD in deep soil, especially at 0.8–1.2 m.

Conclusions

Increasing the plant density from 135 m^?2 to the optimum increases AGN primarily by increasing the RLD in deep soil and therefore increasing the plant density of winter wheat can be used to efficiently recover N leached to deep soil. Moreover, the total root numbers per unit area and RLD still increased at supraoptimal density while shoot number and N uptake stagnated.     

华北山区典型人工林土壤水势动态和水分运移规律

大规模植树造林工程有效缓解了我国北方水土流失等问题,但伴随植被生长和降水格局变化,水循环过程发生明显改变。土壤水分运动是水循环的关键过程,研究变化环境下人工林植被土壤水分运移规律,对植被生态恢复具有重要意义。基于2014-2018年多时间尺度（半小时、天、月和年）华北山区崇陵流域典型人工侧柏林和荒草土壤剖面水势监测数据,阐明不同植被覆盖下土水势动态变化规律,提出土壤水分运移和植被水分利用模式。研究结果表明：侧柏林土壤水势日变幅显著低于荒草植被,但土水势日变幅随土壤深度增加而减小的速率90 a侧柏依次大于60 a侧柏和荒草;月、年尺度侧柏林不同深度土水势变化对降水的响应大于荒草地,其中60 a侧柏林年均土水势与年降雨量显著线性相关（P<0.05）。由水势梯度和零通量面多年平均变化可知,90 a侧柏林0-50 cm土壤水呈下渗趋势,根系水力提升促使50-100 cm土壤水向上蒸散;60 a侧柏林0-20 cm、70-100 cm以及枯水年30-70 cm土壤水均以蒸散为主,根系可同时吸收利用表层和深层土壤水分;荒草地0-20 cm土壤水分蒸发强烈,且为根系主要吸水深度,20-100 cm土壤水稳定下渗。相比60 a侧柏林和荒草,90 a侧柏林的土壤调蓄能力增强,与荒草互被可减少植被间水分竞争,充分利用土壤水,从而减少流域内地表径流和土壤侵蚀量。     

喀斯特坡地2种地埂篱根-土复合体抗剪和抗冲性能综合评价

分析喀斯特地区不同地埂篱根系的形态和力学特性,量化其根-土复合体抗剪和抗冲性能的强弱,探寻该地区地埂篱根系固土抗蚀性能的评价因子,为喀斯特坡地水土流失治理中植被恢复措施的科学应用提供参考。选取重庆酉阳龙潭槽谷为研究区,分上、中、下坡分别布设拉巴豆和光叶苕子2种地埂篱,采用根系扫描仪和电子万能试验机测定其根系形态和力学参数,应变控制式直剪仪测定复合体抗剪强度,原状土冲刷水槽法测定复合体抗冲指数。结果表明：(1)抗剪复合体中,拉巴豆平均根长密度和根表面积密度分别高出光叶苕子59.32%和16.86%;抗冲复合体中,拉巴豆平均根长密度、根表面积密度和根体积密度较之光叶苕子高出30.48%、57.78%、92.98%;拉巴豆根系极限抗拉力和抗拉强度均显著高于光叶苕子。(2)2种地埂篱根系均能增强土壤的抗剪和抗冲性能,其中拉巴豆和光叶苕子复合体粘聚力较之对照土体分别增强了113.06%—124.37%和51.56%—87.12%,抗冲指数最高达到对照土体的2.81倍和2.45倍。(3)不同坡位,下坡2种植物的根长密度显著高于上、中坡;拉巴豆根系抗拉特性在下坡表现最优,光叶苕子在上坡表现更好;拉巴...