Vertical Root Distribution Research Articles

Intercropping effects on root distribution of eight novel winter faba bean genotypes mixed with winter wheat

The spatial root distribution of plant species is generally altered by intra- and interspecific competition. The assessment of species specific root distribution in intercrops was limited so far because of the difficulties to identify roots on a species level. We investigated horizontal and vertical root distribution of eight winter faba bean genotypes (Vicia faba L.) and one winter wheat cultivar (Triticum aestivum L.) grown in sole stands and in 50/50 substitutive row intercrops.Root samples were taken within and between rows with a root auger down to 60 cm soil depth in May 2015 and May 2016 at a field site in central Germany. We used Fourier transform infrared (FTIR) spectroscopy for root species identification. Vertical root distribution was described by the equation y = 1 - βd according to Gale and Grigal (1987).Horizontal root distribution did not differ between bean and wheat and between sole stands and intercrops averaged across the eight bean genotypes: Bean and wheat root biomass was on average 65% lower between rows than within rows in sole stands and in intercrops. Both species proliferated into the soil space between the rows and into the intercropping partner’s row to a similar extent. Bean developed 36% of its root biomass in 0–10 cm soil depth, while wheat had 51%. Bean and wheat had shallower roots within their own row in intercrops (βbean = 0.933; βwheat = 0.858) compared to their own row in sole stands (βbean = 0.945; βwheat = 0.902). In the intercrops both species occupied deeper soil layers within their partner’s row (βbean = 0.947; βwheat = 0.960) compared to their own row (βbean = 0.933; βwheat = 0.858). This change in vertical root distribution was more pronounced for wheat than for bean. Bean genotypes grown in sole stands did not differ in their horizontal and vertical root distribution. However, there were significant differences between bean genotypes within wheat rows in the intercrops: bean genotype Vf6 had the largest horizontal spread but the most shallow root growth within the wheat row, while Vf5 showed the lowest horizontal spread and the highest root fractions in deep soil layers within the wheat row. The alteration of the vertical root distribution of both species in intercrops, compared to the sole crops, could lead to a better resource utilization and an intercrop advantage.

A water acquisition strategy may regulate the biomass and distribution of winter forage species in cold Asian rangeland

AbstractAboveground biomass is often restricted by water availability; therefore, water acquisition strategies have important roles in determining biomass volume and distribution under arid conditions. In cold Asian rangelands, the large tussock grass Achnatherum splendens is the most important forage for maintaining livestock under severe winter conditions. However, A. splendens distribution is restricted to the middle of the slopes of ephemeral streams, making it difficult to manage winter foraging. To understand the mechanisms behind the specific distribution and maintenance of a large A. splendens biomass under arid conditions, we established four typical vegetative plots along a riverside slope with different A. splendens density levels and elevations: river bottom with no A. splendens, riverbank with a large A. splendens community, upper slope with an isolated A. splendens community, and flat plain with no A. splendens. We measured the soil pH and electric conductivity (EC) of the plots and investigated the vertical biomass and root distribution of A. splendens. We also investigated the water source for the A. splendens communities using isotope techniques. The soil pH was not different among plots, while the soil EC was significantly higher in the river bottom because of salt accumulation. However, low soil EC levels were found under the A. splendens communities. In the ground below the A. splendens communities, plant stems were buried deeply. The belowground biomass and buried stem depths decreased at the sites of the isolated A. splendens communities in the upper slope. The aboveground biomass of A. splendens increased as the stem burial depths and, therefore, the adventitious roots depths increased. The water source of A. splendens was estimated to be at a depth of more than 30 cm. Thus, A. splendens prefers a habitat with a low level of soil salinity and a high level of water availability, which may increase with the sand burial depth because of the increasing accessibility of a substantial water source in the deeper soil layer. Sand burial may affect the water acquisition strategy and maintenance of large biomasses of tussock grass species that act as important winter forage in cold Asian rangelands.

Variation of Fine Roots Distribution in Apple (Malus pumila M.)–Crop Intercropping Systems on the Loess Plateau of China

In arid and semi-arid areas, interspecific below-ground competition is prominent in agroforestry systems. To provide theoretical and technical guidance for the scientific management of apple–crop intercropping systems, a field study was conducted in the Loess Plateau of China to examine the variation of fine roots distribution in apple–crop intercropping systems. The fine roots of apple trees and crops (soybean (Glycine max (L.) Merr) or peanuts (Arachis hypogaea Linn.)) were sampled to 100 cm depth at ten distances from the tree row using the stratified excavation method. The results showed that the vertical distribution of fine roots between intercropped apple trees and intercropped crops were skewed and overlapped. Apple–crop intercropping inhibited the fine roots of apple trees in the 0–60 cm soil depth, but promoted their growth in the 60–100 cm soil depth. However, apple–crop intercropping inhibited the fine roots of intercropped crops in the 0–100 cm soil depth. For the fine roots of each component of the apple–crop intercropping systems, variation in the vertical distribution was much greater than variation in the horizontal distribution. Compared with monocropped systems, apple–crop intercropping caused the fine roots of intercropped apple trees to move to deeper soil, and those of intercropped crops to move to shallower soil. Additionally, apple–crop intercropping slightly inhibited the horizontal extension of the fine-root horizontal barycentre (FRHB) of intercropped apple trees and caused the FRHB of intercropped crops to be slightly biased towards the north of the apple tree row. Variation of the fine roots distribution of each component of the apple–soybean intercropping system was greater than that of the apple–peanut intercropping system. Thus, the interspecific below-ground competition of the apple–peanut intercropping system was weaker than that of the apple–soybean intercropping system. Intense competition occurred in the apple–peanut intercropping system and the apple–soybean intercropping system was in sections whose distance ranged from 0.5–1.3 and 0.5–1.7 m from the tree row, respectively. The interspecific below-ground competition was fiercer on the south side of the apple tree row than on the north side.

Numerical Modeling of Plant Root Controls on Gravel Bed River Morphodynamics

AbstractThe role of vegetation in shaping the geomorphology of rivers and deltas, along with tidal and estuarine environments, is widely recognized. While mutual interactions between flow, plant canopy, and morphodynamics have been extensively investigated, similar studies considering plant roots are limited. Here we present results from a numerical model that quantify the feedbacks of both the aboveground and belowground vegetation on gravel bed river morphodynamics. Plant root biogeomorphic feedbacks, that is, uprooting and root‐enhanced riverbed cohesion, are quantified through the description of the vertical root distribution. By investigating the evolution of the riverbed of a straight gravel channel with a vegetated patch, we show that uprooting is the primary plant root biogeomorphic feedback determining the evolution of the riverbed and the competing influence of the potential flow erosion versus uprooting depth mediates the plant root controls on morphodynamics. These findings broaden our understanding on the role played by plant roots on gravel bed river morphodynamics.

VERTICAL DISTRIBUTION AND SPATIAL PATTERN OF FINE ROOT DENSITY IN COFFEE – BASED AGROFORESTRY SYSTEMS UNDER ORGANIC AND CONVENTIONAL INPUTS

<p>This research shows results on spatial changes of fine roots (<em>d</em> < 2.0 mm) in two <em>Coffea arabica</em>- shade tree associations: coffee shaded by a) <em>Abarema idiopoda </em>(timber and nitrogen fixing tree), and b) <em>Terminalia amazonia </em>(timber tree). These associations were submitted to organic and conventional inputs. In order to identify fine root vertical distribution and using soil cores, coffee and shade tree fine roots were quantified to 50 cm depth. A geostatistical approach was used to quantify the scale of spatial heterogeneity (aggregation patterns) of coffee and shade- tree fine root length density (RLD, cm cm<sup>-3</sup>; 0- 20 cm soil depth). Results about vertical distribution demonstrated that in all the associations the coffee fine roots were concentrated in the upper 20 cm of soil<em>. </em>The significant amount of coffee fine roots in the litter layer demonstrated the importance of including this layer for a real estimation of coffee fine roots in shaded coffee systems. The shade tree fine roots showed marked differences in their vertical distribution and affected the fine root density of coffee plants between 0- 50 cm soil depth; being more abundant when coffee is planted with <em>T. amazonia</em>. The scale of spatial heterogeneity (aggregation patterns) for coffee RLD was longer in the organic plot than in the conventional plot for all of the coffee- tree associations. In the coffee- <em>T. amazonia</em> association, the semivariogram of the coffee RLD under conventional management showed a spatial correlation at a relative short scale (3.5 m); however, in the organic plot, the semivariogram did not show spatial heterogeneity and exhibited a random pattern of coffee RLD at the scale examined. It is concluded that the type of management affects the pattern of spatial aggregation (spatial heterogeneity scale) of <em>C. arabica</em> fine roots. Implying that the ability of coffee roots for the water and nutrient intake change spatially, either vertically or horizontally, depending on the accompanying shade- tree. According to the occupation of the fine roots within the layers of the soil to the depth studied, <em>T. amazonia</em> seems to be the timber species recommended for the establishment of a coffee-based agroforestry system.</p>

Effects of Subsoiling Tillage on Soil Properties, Maize Root Distribution, and Grain Yield on Mollisols of Northeastern China

Core Ideas Subsoil tillage (∼30 cm) reduced compaction and increased moisture and N availability on Mollisols. Subsoiling increased the vertical and horizontal distribution of maize roots between rows rather than in row. Grain and dry matter yield were 6.3 and 3.7% greater under subsoiling than conventional tillage. Subsoiling increased maize yield due to improved soil conditions and roots distribution. Soil compaction creates unfavorable soil physical and nutrient conditions, restrains root penetration and distribution, and reduces crop yield. A field experiment was established to assess the effects of tillage treatments on soil properties, root distribution, and grain yield of maize (Zea mays L.) on some Mollisols of Northeastern China. The two treatments included in rotary tillage (RT) and subsoiling tillage (ST). The results showed that soil bulk density, penetration resistance, soil moisture, available nitrogen content, root distribution of maize, and grain yield were significantly affected by tillage systems. Compared with RT, ST had lower soil bulk density and penetration resistance, but greater soil moisture and available nitrogen contents, especially in subsoil layer (i.e., 15‐ to 45‐ cm). The ST practice significantly increased the average root length density by 13.0% than that of RT mainly due to better vertical and horizontal distribution between the rows. Average grain yield and dry matter weight of maize increased by 693 kg ha−1 (6.3%) and 933 kg ha−1 (3.7%), respectively, under ST compared with those under RT. These data show that subsoiling tillage can loosen the soil, fracture the plow pan, increase the availability and infiltration of soil moisture and nitrogen in subsoil layers, improve the vertical and horizontal extension of maize root system in the soil, and increase grain yield on Mollisols of Northeastern China.

Mapping the vertical distribution of maize roots in China in relation to climate and soil texture

Optimizing water and fertilizer management for crops requires an understanding of root distribution. Maize (Zea mays L.) is currently the most widely planted cereal crop in China, yet the vertical distribution of maize roots across different regions remains unknown. The aims of this work were (i) to quantify the effects of climate and soil texture on the vertical distribution of maize roots, and (ii) to show the depth distribution of root biomass in China. We used data of maize root biomass from 11 Chinese ecological stations with discontinuous observations from 2004 to 2014 to fit the regression coefficient β for an asymptotic equation Y = 1 – βᵈ, where d is the soil depth and Y is the proportion of root biomass from the surface to depth d. A statistical model was then developed to quantify the effects of climate and soil texture on the fitted β values. Using the statistical model, we map the depth distribution of maize root biomass in China. Maize root biomass in the 0–100 cm soil depth varied by an order of magnitude at different stations, from 64 to 268 g m⁻². Maize planted in sandy soils and/or maize with high accumulated temperature for development had higher root biomass and deeper rooting systems. The fitted β values ranged from 0.785 to 0.977, which can be modeled by an integration of the accumulated temperature during the maize growing period and the soil clay and sand fractions (R² = 0.66, n = 50, P < 0.001). Up to 82% of maize planting regions in China showed shallower rooting systems where more than 90% and 95% of the root biomass occurred in the top 20 and 30 cm soil layers, respectively. Deeper rooting systems occurred in some temperate arid and temperate semi-arid regions, with less than 80% of the root biomass in the top 20 cm soil. Our findings highlighted the vertical distribution of maize roots, and underlined the spatial variability in the vertical distribution of roots across China’s planting areas of maize.

Timely supplemental irrigation changed nitrogen use of wheat by regulating root vertical distribution

AbstractCrop nitrogen (N) uptake depends on the root absorption area and the soil N availability which are closely related to the soil water status. With the increasing water shortages in the North China Plain, supplemental irrigation (SI) to winter wheat is a promising technique. To clarify the relationships between water and nitrogen use, four SI regimes in Tritcum aestivum L. cv. Jimai 22 were set up: no‐irrigation after emergence (T1), SI at jointing and anthesis (T2), SI at sowing, jointing and anthesis (T3), and SI at pre‐wintering, jointing and anthesis (T4). The results indicate that T2 had higher root length density (RLD) and root surface area density (RAD) in the 0–20, 60–80, and 80–100 cm soil layers, as well as higher post‐anthesis N uptake from soil by 23–26% in 2012–2013 and 162–177% in 2013–2014, compared to T3 and T4. The grain yield under T2 was lower than T3 but was not significantly different from T4, whereas its water use efficiency (WUE) was higher relative to both T3 and T4. There were no significant differences among T2, T3, and T4 in N use efficiency (NUE). The N uptake after jointing and WUE were positively correlated with the RLD and RAD in the 0–20 cm soil layer. The NUE was positively correlated with the RLD and RAD in the 20–40 cm soil layer. These results indicate that timely SI at jointing and anthesis was dependent on a suitable water supply at sowing, which increased the soil water content in the upper soil layer after jointing and improved the absorption area of the roots in both the deep and surface soil layers; this further improved the post‐anthesis N uptake from the soil and the WUE. This approach can be a valuable way to maintain high grain yields and NUE in winter wheat while using less irrigation and achieving higher WUE in the North China Plain.

Fine root responses to temporal nutrient heterogeneity and competition in seedlings of two tree species with different rooting strategies.

There is little direct evidence for effects of soil heterogeneity and root plasticity on the competitive interactions among plants. In this study, we experimentally examined the impacts of temporal nutrient heterogeneity on root growth and interactions between two plant species with very different rooting strategies: Liquidambar styraciflua (sweet gum), which shows high root plasticity in response to soil nutrient heterogeneity, and Pinus taeda (loblolly pine), a species with less plastic roots. Seedlings of the two species were grown in sandboxes in inter‐ and intraspecific combinations. Nutrients were applied in a patch either in a stable (slow‐release) or in a variable (pulse) manner. Plant aboveground biomass, fine root mass, root allocation between nutrient patch and outside the patch, and root vertical distribution were measured. L. styraciflua grew more aboveground (40% and 27% in stable and variable nutrient treatment, respectively) and fine roots (41% and 8% in stable and variable nutrient treatment, respectively) when competing with P. taeda than when competing with a conspecific individual, but the growth of P. taeda was not changed by competition from L. styraciflua. Temporal variation in patch nutrient level had little effect on the species’ competitive interactions. The more flexible L. styraciflua changed its vertical distribution of fine roots in response to competition from P. taeda, growing more roots in deeper soil layers compared to its roots in conspecific competition, leading to niche differentiation between the species, while the fine root distribution of P. taeda remained unchanged across all treatments. Synthesis. L. styraciflua showed greater flexibility in root growth by changing its root vertical distribution and occupying space of not occupied by P. taeda. This flexibility gave L. styraciflua an advantage in interspecific competition.

侵蚀退化地植被恢复过程中芒萁对土壤可溶性有机碳的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 侵蚀退化地植被恢复过程中芒萁对土壤可溶性有机碳的影响 DOI: 10.5846/stxb201705040824 作者: 作者单位: 福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31370465，U1405231）；"973"计划前期专项课题（2012CB722203） Effects of Dicranopteris dichotoma on soil dissolved organic carbon in severely eroded red soil Author: Affiliation: School of Geographical Science,Fujian Normal University,,,School of Geographical Science,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:林下植被是生态系统的重要组分。通过对比分析红壤侵蚀区植被恢复过程中，林下有无芒萁覆盖地的土壤可溶性有机碳（DOC，Dissolved Organic Carbon）含量及其与地下根系生物量、地上植被淋溶液DOC含量的关系。结果表明：林下植被芒萁覆盖增加了地上叶片和地下根系生物量，土壤DOC含量及储量也显著增加（P < 0.05），芒萁覆盖对表层土壤（0-20cm）DOC的影响大于深层土壤（20-100cm）（P < 0.05）；相关分析结果表明，林下芒萁覆盖地土壤DOC储量与细根生物量的垂直变化呈显著的正相关关系（P < 0.05），且随植被恢复年限的增加相关性显著增加，地下根系的垂直分布直接影响各土层DOC储量。不同植被恢复时期，林下芒萁覆盖地土壤DOC与鲜叶（马尾松+芒萁）和枯落物（马尾松+芒萁）淋溶液DOC均呈显著的正相关关系（P < 0.01），而林下裸露地土壤DOC仅与鲜叶（马尾松）淋溶液DOC呈显著的相关性（P < 0.01），林下芒萁覆盖地相对于裸露地枯落物淋溶液对土壤DOC储量的影响大于鲜叶。植被恢复过程中芒萁覆盖地土壤微生物生物量碳和微生物熵显著高于林下裸露地。因此，在植被恢复进程中，芒萁能够提供更多底物参与土壤物质与养分循环，对土壤DOC的贡献较大，为侵蚀区马尾松林恢复提供了重要的养分再吸收来源；同时芒萁覆盖增加了微生物活性，促进了微生物对土壤DOC的同化作用，提高了微生物碳源的利用率，对土壤有机碳的积累起着重要的作用。 Abstract:Understory, an important component of the forest ecosystem, plays an important role in maintaining forest structure and soil quality. To analyze the relationship between soil dissolved organic carbon (DOC), belowground biomass, and DOC leachates of aboveground biomass, we conducted a comparative experiment of the presence or absence of understory Dicranopteris dichotoma on severely eroded red soil. The results showed that the aboveground and belowground biomass, and the content of soil DOC increased significantly with understory D. dichotoma coverage (P < 0.05); the effect of D. dichotoma on the surface soil (0-20cm) was greater than the deep soil (20-100cm) (P < 0.05). The correlation analysis showed that there was a significant positive correlation between soil DOC storage and fine root biomass (P < 0.05), indicating that the vertical distribution of underground roots directly affects the soil DOC reserves. Moreover, there was a significant positive correlation between soil DOC with fresh leaf (Pinus massoniana and D. dichotoma) and litter (P. massoniana and D. dichotoma) leachates during vegetation restoration (P < 0.01), but there was only a significant correlation with fresh leaf (P. massoniana) leachates in the bare ground (P < 0.05). The effect of the litter leachates on the soil DOC storage was higher than the fresh leaves. The soil microbial biomass carbon and microbial entropy in D. dichotoma-covered land were significantly higher than bare land in the process of vegetation restoration. Therefore, D. dichotoma may provide more substrates to participate in soil material and nutrient cycling, contributing greatly to soil DOC, which further provides important nutrient reabsorption sources for restoration of P. massoniana forest in eroded areas. It is possible that D. dichotoma coverage increases microbial activity and promotes assimilation of soil microorganisms; thereby playing an important role in the accumulation of soil organic carbon by improving utilization of microbial carbon sources. 参考文献 相似文献 引证文献

Maize and wheat root biomass, vertical distribution, and size class as affected by fertilization intensity in two long-term field trials

Root biomass is the most commonly studied root parameter to investigate below ground crop response to environmental conditions and carbon cycling in agroecosystems. Root growth is strongly regulated by site-specific growth conditions and resource availability, but only little is known about the extent to which root biomass, vertical distribution, and size class respond to fertilization intensity as compared to site. We determined coarse (>2mm) and fine (>0.5mm and≤2mm) root biomass of maize and wheat in three soil layers to 0.75m depth in different farming systems (half and full organic, full conventional) and fertilization treatments (zero, manure, full mineral N plus half mineral PK, full mineral NPK) of the Swiss long-term field trials DOK and ZOFE, respectively, and evaluated the effects of fertilization intensity and site on root biomass, vertical distribution, and size class. In DOK, total root biomass was similar in organic and conventional farming systems. In ZOFE, wheat root biomass was 1.7-times higher under full mineral N plus half mineral PK fertilization than under zero or manure fertilization and intermediate under full NPK fertilization. Vertical root distribution and size class were only marginally affected by fertilization intensity on both sites. By contrast, total root biomass of maize and topsoil root biomass of both maize and wheat were higher but subsoil root biomass of wheat and fine root proportions of both maize and wheat were lower in DOK than in ZOFE. We conclude that roots respond more to site than to fertilization intensity and that absolute inputs of root biomass carbon to soil are similar in low- and high-intensity systems. Further, root-shoot ratios were inversely related to fertilization intensity, implying that estimations of below ground carbon inputs to soil from shoot biomass need to be differentiated by fertilization intensity. Deep (below 0.5m) root biomass was 3-times higher for wheat than for maize, suggesting that crop choice is more important than fertilization intensity for carbon sequestration in deep soil.

Vertical distribution of root biomass and soil carbon stocks in forage cropping systems

Forage cropping systems may differentially affect the vertical distribution of roots and soil organic C stock (C-OM). In annual crops sequences (ACS) and perennial pastures (PP), we assessed the association between root biomass, C-OM, C in mineral-associated organic matter (C-MAOM), and C in particulate organic matter (C-POM) and its vertical distribution. Root biomass, C-OM, C-MAOM and C-POM were measured in a Petrocalcic Argiudol at five soil depths up to 100 cm during two years in the south-eastern Pampas of Argentina. The field experiment comprised 28 plots including five perennial pastures and two annual crop sequences. Associations between variables were assessed by regression analysis and non-linear models. Overall, ACS and PP had similar cumulative root biomass. Both, root biomass and soil C stocks exponentially decreased with soil depth. Soil C stocks associated to root biomass tended to stabilize over a threshold value of root biomass for C-MAOM and C-OM. C-POM tended to stabilize over a threshold value only in treatments that included tall fescue. Our results highlights the key role of roots to improve soil C stocks through the design of forage crop rotations that include crops able to increase root inputs to the soil, such as tall fescue.

Below‐ground complementarity effects in a grassland biodiversity experiment are related to deep‐rooting species

Abstract Below‐ground resource partitioning is often proposed as the underlying mechanism for the positive relationship between plant species richness and productivity. For example, if species have different root distributions, a mixture of plant species may be able to use the available resources more completely than the individual species in a monoculture. However, there is little experimental evidence for differentiation in vertical root distributions among species and its contribution to biodiversity effects. We determined species‐specific root standing biomass over depth using molecular techniques (real‐time qPCR) in a large grassland biodiversity experiment (one to eight plant species mixtures), in 2 years. Species‐specific root biomass data were used to disentangle the effects of positive interactions between species (complementarity effects) and effects due to dominance of productive species (selection effects) on root biomass in mixtures. In a next step, these biodiversity effects were linked to the diversity of rooting depths and the averaged rooting depth of the community. Root biomass increased with species richness. This was mainly due to positive interactions (the complementarity effect), which increased with species richness below‐ground. In contrast, the selection effect decreased with species richness. Although there was considerable variation in vertical root distribution between species in monocultures, the diversity of rooting strategies did not explain the complementarity effect. Rather, the abundance of deep‐rooting species in mixtures (i.e. high community‐weighted mean) was significantly related to the complementarity effect. Comparing the “predicted” root distribution (based on monocultures) to the actual distribution in mixtures, we found that mixtures rooted deeper than expected, but this did not better explain the complementarity effect. Synthesis. This study demonstrates that vertical root distributions of species provide only subtle evidence for resource partitioning. We found no evidence that functional diversity in vertical rooting patterns was important for the complementarity effect, in contrast to our expectation that the enhancement of productivity was due to resource partitioning. Alternatively, we found significant but weak relationships between the complementarity effect and deep‐rooting communities, based on the community‐weighted mean root distribution. This suggests that factors other than below‐ground resource partitioning alone may drive the biodiversity–productivity relationship.

Root vertical distribution is important to improve water use efficiency and grain yield of wheat

The winter wheat (Triticum aestivum L.) production of the North China Plain is threatened by increasing water shortages. Therefore, the invention of effective irrigation techniques is crucial to maintain high yields of winter wheat through improved water use efficiency (WUE). In this study, field experiments were carried out in the North China Plain region in 2012–2013 and 2013–2014. Based on the soil moisture regulation at sowing to ensure the normal emergence of the winter wheat, four supplemental irrigation (SI) regimes were set up: no-irrigation after emergence (T1), SI at jointing and anthesis (T2), SI at sowing, jointing and anthesis (T3), and SI at pre-wintering, jointing and anthesis (T4). The results showed that the root length density (RLD), root surface area density (RAD), and root weight density (RWD) in the 0–0.2m soil layer from T2 increased rapidly after jointing and were significantly higher than those from T3 and T4 at anthesis. Those of T2 in the 0.6–0.8m and 0.8–1.0m soil layers were also significantly higher at anthesis. T2 was significantly higher than T1 in the photosynthetic rate (Pn) and instantaneous water use efficiency (WUEleaf) of flag leaves, post-anthesis dry matter accumulation (DMA), contribution of DMA to grain (CDMA), grain yield and WUE, but lower than T1 in the pre-anthesis dry matter remobilization efficiency (DMRE) and contribution of DMR to grain (CDMR). T2 had significantly lower plant populations and dry matter at jointing, Pn and WUEleaf at 28days after anthesis, DMA and CDMA, but higher dry matter increase rate after jointing, tiller survival rate, DMR, DMRE, CDMR and WUE. The combined effect of these differences enabled T2 to have yield that was not significantly different to T4. In summary, SI at joining and anthesis that was based on suitable soil water content at sowing increased the absorbing area of roots in both deep and surface soil layers; accelerated the dry matter accumulation after jointing; increased the Pn and WUEleaf of flag leaves, DMA and DMR; and finally achieved a high grain yield and higher WUE. However, excessive irrigation reduced the WUE by inhibiting the redistribution of dry matter, although the WUEleaf of flag leaves was still increased.

Dynamic niche partitioning in root water uptake facilitates efficient water use in more diverse grassland plant communities

Abstract Efficient extraction of soil water is essential for the productivity of plant communities. However, research on the complementary use of resources in mixed plant communities, and especially the impact of plant species richness on root water uptake, is limited. So far, these investigations have been hindered by a lack of methods allowing for the estimation of root water uptake profiles. The overarching aim of our study was to determine whether diverse grassland plant communities in general exploit soil water more deeply and whether this shift occurs all the time or only during times of enhanced water demand. Root water uptake was derived by analysing the diurnal decrease in soil water content separately at each measurement depth, thus yielding root water uptake profiles for 12 experimental grasslands communities with two different levels of species richness (4 and 16 sown species). Additional measurements of leaf water potential, stomatal conductance, and root traits were used to identify differences in water relations between plant functional groups. Although the vertical root distribution did not differ between diversity levels, root water uptake shifted towards deeper layers (30 and 60 cm) in more diverse plots during periods of high vapour pressure deficit. Our results indicate that the more diverse communities were able to adjust their root water uptake, resulting in increased water uptake per root area compared to less diverse communities (52% at 20 cm, 118% at 30 cm, and 570% at 60 cm depth) and a more even distribution of water uptake over depth. Tall herbs, which had lower leaf water potential and higher stomatal conductance in more diverse mixtures, contributed disproportionately to dynamic niche partitioning in root water uptake. This study underpins the role of diversity in stabilizing ecosystem function and mitigating drought stress effects during future climate change scenarios. Furthermore, the results provide evidence that root water uptake is not solely controlled by root length density distribution in communities with high plant diversity but also by spatial shifts in water acquisition. A plain language summary is available for this article.

Vertical root distribution of individual species in a mountain grassland community: Does it respond to neighbours?

Abstract Vertical differentiation in root placement is one of the potential mechanisms of plant niche differentiation. It can be due to the remarkable plasticity of roots in response to nutrients and neighbours, but most data on it come from pot or garden experiments. The roles of vertical differentiation and of plasticity in it in the field are thus not well known. We examined species‐specific root vertical distribution in a montane grassland using quantitative real‐time PCR. We asked whether individual species differ in their rooting depths, whether such differences are associated with above‐ground functional traits (such as height or specific leaf area), and whether they respond to the presence of a competitor. This response was assessed by comparison of species‐specific vertical profiles between control plots and plots where the dominant species, Festuca rubra, had been removed. Vertical profiles of individual species varied considerably, from species with most root biomass concentrated in the uppermost (&lt;2 cm) soil layer, through species with uniform vertical distribution, to a species with roots predominantly below 8 cm (Nardus stricta). Species at the fast end of the plant economy spectrum were more likely to place their roots in the uppermost layers. Grassland species, thus, exploit different parts of the below‐ground resources in spite of their short stature, minor differences in height above‐ground and shallow soil. While below‐ground and above‐ground biomasses of most species were higher in the removal plots, species rooting patterns did not change in response to the removal. The interspecific differences in vertical profiles were thus due to species' innate differences, not to plastic responses to the presence of the dominant species. Synthesis. The findings imply that vertical root differentiation in the field is strong and can contribute to niche differentiation. However, the role of root plasticity in natural systems may be considerably weaker than in artificial systems with few species and strong nutrient gradients. This absence of the plastic response in the field is likely to be due to a fairly homogeneous distribution of nutrients in the soil and to the predominantly symmetric nature of below‐ground competition.

Trophic and non‐trophic interactions influence the mechanisms underlying biodiversity–ecosystem functioning relationships under different abiotic conditions

Plant diversity effects on ecosystem functioning usually have been studied from a plant perspective. However, the mechanisms underlying biodiversity–ecosystem functioning relationships may also depend on positive or negative interactions between plants and other biotic and abiotic factors, which remain poorly understood. Here we assessed whether plant–herbivore and/or plant–detritivore interactions modify the biodiversity–ecosystem functioning relationship and the mechanisms underlying biodiversity effects, including complementarity and selection effects, biomass allocation, vertical distribution of roots, and plant survival using a microcosm experiment. We also evaluated to what extent trophic and non‐trophic interactions are affected by abiotic conditions by studying drought effects. Our results show that biotic and abiotic conditions influence the shape of the biodiversity–ecosystem function relationship, varying from hump‐shaped to linear. For instance, total biomass increased linearly with plant richness in the presence of detritivores, but not in the absence of detritivores. Moreover, detritivore effects on belowground plant productivity were highly context dependent, varying in the presence of herbivores. Plant interactions with soil biota, especially with herbivores, influenced the mechanisms underlying diversity effects. Herbivores increased plant complementarity and modified biomass allocation and vertical distribution of roots. Furthermore, biotic–abiotic interactions influenced plant productivity differently across plant functional groups. Our findings emphasize the importance of complex biotic interactions underlying biodiversity effects, and that these biotic interactions may change with abiotic conditions. Despite minor changes in productivity in the short‐term, soil biota‐induced changes in plant–plant interactions and plant survival are likely to have significant long‐term consequences for ecosystem functioning. Considering the context‐dependency of multichannel interactions may contribute to reconciling differences among observed patterns in biodiversity studies. Further, abiotic conditions modified the effects of biotic interactions, suggesting that changes in environmental conditions may not only affect ecosystems directly, but also change the biotic composition of and dynamics within ecosystems.

Biology of M argarodes vredendalensis De Klerk (Coccoidea: Margarodiae) in South Africa

Various aspects of the biology of Margarodes vredendalensis De Klerk, a vine infesting species, were studied. Under laboratory conditions adult females emerged during January and February, and only 10-16% of the cysts developed into females annually. Although cysts were detached from their host plant, females emerged during four successive years from the same population. Adult females did not migrate to the soil surface for mating, and reproduced parthenogenetically. The average oviposition period of females was 18 days, and their average lifespan 40 days. An average of 507 eggs per female were oviposited, the highest number being produced during the first 9 days. The effects of temperature, relative humidity and soil moisture on oviposition, as well as on incubation of the eggs, are reported on. Cysts in the field were found to a depth of 1,2 m in the soil, the highest number occurring at a depth of 46-60 cm. The vertical distribution of cysts was directly related to the vertical distribution of roots. Significant negative correlations were also found between the vertical distribution of cysts and soil moisture, as well as the percentage clay of the soil.

SPATIAL AND VERTICAL DISTRIBUTION OF LITTER AND BELOWGROUND CARBON IN A BRAZILIAN CERRADO VEGETATION

ABSTRACT Forest ecosystems contribute significantly to store greenhouse gases. This paper aimed to investigate the spatial and vertical distribution of litter, roots, and soil carbon. We obtained biomass and carbon of compartments (litter, roots, and soil) in a vegetation from Cerrado biome, state of Minas Gerais, Brazil. The materials were collected in 7 0.5 m² sub-plots randomly allocated in the vegetation. Root and soil samples were taken from five soil layers across the 0-100 cm depth. Roots were classified into three diameter classes: fine (&lt;5 mm), medium (5-10 mm), and coarse (&gt;10 mm) roots. The carbon stock was mapped through geostatistical analysis. The results indicated averages of soil carbon stock of 208.5 Mg.ha-1 (94.6% of the total carbon), root carbon of 6.8 Mg.ha-1 (3.1%), and litter of 5 Mg.ha-1 (2.3%). The root carbon was majority stored in coarse roots (83%), followed by fine (10%), and medium roots (7%). The largest portion of fine roots concentrated in the 0-10 cm soil depth, whereas medium and coarse roots were majority in the 10-20 cm depth. The largest portion of soil (53%) and root (85%) carbon were stored in superficial soil layers (above 40 cm). As conclusion, the carbon spatial distribution follows a reasonable trend among the compartments. There is a vertical relation of which the deeper the soil layer, the lower the soil and root carbon stock. Excepting the shallowest layer, coarse roots held the largest portion of carbon across the evaluated soil layers.

Above‐ and below‐ground responses of four tundra plant functional types to deep soil heating and surface soil fertilization

Summary Climate warming is faster in the Arctic than the global average. Nutrient availability in the tundra soil is expected to increase by climate warming through (i) accelerated nutrient mobilization in the surface soil layers, and (ii) increased thawing depths during the growing season which increases accessibility of nutrients in the deeper soil layers. Both processes may initiate shifts in tundra vegetation composition. It is important to understand the effects of these two processes on tundra plant functional types. We manipulated soil thawing depth and nutrient availability at a Northeast‐Siberian tundra site to investigate their effects on above‐ and below‐ground responses of four plant functional types (grasses, sedges, deciduous shrubs and evergreen shrubs). Seasonal thawing was accelerated with heating cables at c. 15 cm depth without warming the surface soil, whereas nutrient availability was increased in the surface soil by adding slow‐release NPK fertilizer at c. 5 cm depth. A combination of these two treatments was also included. This is the first field experiment specifically investigating the effects of accelerated thawing in tundra ecosystems. Deep soil heating increased the above‐ground biomass of sedges, the deepest rooted plant functional type in our study, but did not affect biomass of the other plant functional types. In contrast, fertilization increased above‐ground biomass of the two dwarf shrub functional types, both of which had very shallow root systems. Grasses showed the strongest response to fertilization, both above‐ and below‐ground. Grasses were deep‐rooted, and they showed the highest plasticity in terms of vertical root distribution, as grass root distribution shifted to deep and surface soil in response to deep soil heating and surface soil fertilization respectively. Synthesis. Our results indicate that increased thawing depth can only benefit deep‐rooted sedges, while the shallow‐rooted dwarf shrubs, as well as flexible‐rooted grasses, take advantage of increased nutrient availability in the upper soil layers. Our results suggest that grasses have the highest root plasticity, which enables them to be more competitive in rapidly changing environments. We conclude that root vertical distribution strategies are important for vegetation responses to climate‐induced increases in soil nutrient availability in Arctic tundra, and that future shifts in vegetation composition will depend on the balance between changes in thawing depth and nutrient availability in the surface soil.