Facilitating Root Growth Research Articles

Physiological and Transcriptional Characteristics of Banana Seedlings in Response to Nitrogen Deficiency Stress

Nitrogen is a crucial element for the growth and development of plants, directly affecting crop growth and yield. To investigate the physiological and molecular mechanism of nitrogen-deficiency stress, we conducted an investigation into the effects of different nitrogen levels on the growth, photosynthetic characteristics, and gene transcription levels of banana seedlings. Compared with the control group with normal nitrogen levels (NN), the height of plants receiving Reduced-N (NR), Low-N (LN), and N-Free (NF) treatments was decreased by 0.45 cm, 2.5 cm, and 3.25 cm, respectively. Their dry weight was reduced by 1.63 g, 2.99 g, and 2.88 g, respectively. Conversely, the dry weight of the underground plant part in the LN and NF treatment groups exhibited an increase of 0.13 g and 0.16 g, respectively. Regarding photosynthetic characteristics, the Specialty Products Agricultural Division (SPAD) values of the NR, LN, and NF treatments showed reductions of 15.5%, 30.4%, and 35.9%, respectively, compared with those of the control treatments. The values of maximum photosynthetic efficiency (Fv/Fm), actual photosynthetic efficiency (Y(Ⅱ)), and relative electron transfer (ETR) of the banana seedlings decreased to different degrees after NR, LN, and NF treatment, and their values were positively correlated with N levels. Gene transcription analysis showed that N transport-related proteins, including NRT1.7, NRT2.3a, NRT2.3b, and NRT2.5, were significantly up-regulated to increase the nitrogen absorption capacity of plant roots. On the other hand, various transcription factors including GRAS, MYB, and WRKY were notably up-regulated, facilitating root growth and the expanding root absorption area, thereby enhancing nitrogen uptake. Furthermore, genes associated with endogenous hormone metabolic pathways such as gibberellin (GA), strigolactone (SL), and brassinosteroids (BR) were activated in banana plants subjected to low nitrogen stress, enhancing the plant’s ability to adapt to nitrogen-deficient conditions. These findings offer valuable insights into understanding the transcriptional regulatory mechanisms governing banana responses to low nitrogen stress and breeding new varieties with improved nutrient utilization.

Effects of soil physicochemical environment on the plasticity of root growth and land productivity in maize soybean relay strip intercropping system.

Soil is a key foundation of crop root growth. There are interactions between root system and soil in multiple ways. The present study aimed to further explore the response of root distribution and morphology to soil physical and chemical environment under maize (Zea mays L.) soybean (Glycine Max L. Merr.) relay strip intercropping (MS) An experiment was carried out aiming to examine the effects of nitrogen (N) applications and interspecific distances on root system and soil environment in MS. The two N application levels, referred to as no N application (NN) and conventional N application (CN), were paired with different interspecific distances: 30, 45 and 60 cm (MS30, MS45 and MS60) and 100 cm of monoculture maize and soybean (MM/SS100). The results demonstrated that MS45 increased the distribution of soil aggregates (> 2 mm) near the crop roots and maize soil nutrients status, which increased by 20.3% and 15.6%. Meanwhile, MS reduced soil bulk density, increased soil porosity and improved soil oxygen content. Optimization of the soil environment facilitated root growth. The MS45 achieved a better result on root distribution and morphology than the other configuration and also increased land productivity. Relay intercropped soybean with maize in interspecific row spacing of 45 cm, improved soil physicochemical environment, reshaped root architecture and optimized root spatial distribution of crops to achieve greater land productivity. © 2024 Society of Chemical Industry.

Modulation of sunflower growth via regulation of antioxidants, oil content and gas exchange by arbuscular mycorrhizal fungi and quantum dot biochar under chromium stress

Chromium (Cr) toxicity significantly threatens sunflower growth and productivity by interfering with enzymatic activity and generating reactive oxygen species (ROS). Zinc quantum dot biochar (ZQDB) and arbuscular mycorrhizal fungi (AMF) have become popular to resolve this issue. AMF can facilitate root growth, while biochar tends to minimize Cr mobility in soil. The current study aimed to explore AMF and ZQDB combined effects on sunflower plants in response to Cr toxicity. Four treatments were applied, i.e. NoAMF + NoZQDB, AMF + 0.40%ZQDB, AMF + 0.80%ZQDB, and AMF + 1.20%ZQDB, under different stress levels of Cr, i.e. no Cr (control), 150 and 200 mg Cr/kg soil. Results showed that AMF + 1.20%ZQDB was the treatment that caused the greatest improvement in plant height, stem diameter, head diameter, number of leaves per plant, achenes per head, 1000 achenes weight, achene yield, biological yield, transpiration rate, stomatal conductance, chlorophyll content and oleic acid, relative to the condition NoAMF + No ZQDB at 200 mg Cr/kg soil. A significant decline in peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) while improvement in ascorbate peroxidase (APx), oil content, and protein content further supported the effectiveness of AMF + 1.20%ZQDB against Cr toxicity. Our results suggest that the treatment AMF + 1.20%ZQDB can efficiently alleviate Cr stress in sunflowers.

High temperature can improve the performance of invasive plants by facilitating root growth.

The ever-increasing temperatures of the Anthropocene may facilitate plant invasions. To date, studies of temperature effects on alien plants have mainly focused on plant aboveground traits but ignored belowground roots, which may hinder our predictions of plant invasion risks under climate change. The temperature effects on the root growth dynamics of two alien shrubs, invasive Mimosa sepiaria and naturalized Corchorus capsulari, were studied through a 3D transparent growth system under five temperature treatments (18/13°C - 34/29°C), which cover the present and future warming scenario temperature distributions in China. We measured the dynamics of both root depth and width growth in response to temperature treatments across time (84 days). We also investigated the intraspecies and interspecies competitions of the two alien species along the temperature gradient by planting two individuals together. Both M. sepiaria and C. capsularis showed optimum shoot growth in the middle-temperature treatment, whereas M. sepiaria exhibited the fastest root growth under the highest temperature treatment (34/29°C), and the root growth of C. capsularis persistently decreased as temperature increased. Root depth growth was more susceptible than root width to neighbor competition pressure in both species. Compared to C. capsularis, M. sepiaria had relatively stronger intraspecies and interspecies competition advantages with increasing temperature, possibly because high temperature improved root growth. These results suggest that temperature increases can improve the performance of alien plants by facilitating the groth of their underground root widths and depths, which deserves serious concern in future invasion risk management. This article is protected by copyright. All rights reserved.

Effect of cow manure mon the growth of water spinach in gold mine tailing

Gold mining activities produce abundant tailings waste. The negative impacts of tailing pollution on agriculture include soil profile loss, soil compaction, depletion of essential nutrients, organic matter, and soil pH, making it difficult for plants to grow. Cow manure (CM) is a well-known soil amendment to improve soil quality and facilitate root growth. Animal manure fertilizers contain a complete range of macro and micronutrients required by plants. In addition to its ability to enhance soil fertility, CM can also promote plant growth in former mining areas or mineral tailings. The objective of this study was to determine the effect of CM application rates on water spinach plant growth improvement. The experimental design used was a Completely Randomized Block Design (CRBD) with four treatments and six replications. The experimental treatments consisted of a control (without treatment), 10 t ha-1, 20 t ha-1, and 30 t ha-1 of CM. The results of the experiment showed that CM application increased plant height, leaf count, stem diameter, and wet weight of water spinach plants. The application of 10 t ha-1 CM showed the highest growth improvement in terms of plant height, leaf count, stem diameter, and wet weight of plants grown in gold mining tailings compared to other treatments. This experiment highlights the importance of CM for water spinach cultivation in tailing areas.

Microbial consortium inoculant and rock mineral fertiliser differentially improved yield and nutrient uptake of industrial hemp (Cannabis sativa L.) varieties

Industrial hemp (Cannabis sativa L.) production is attracting widespread attention in agriculture but is facing cultivation challenges in nutrient-poor sandy soils. The crop has a fibrous deep taproot system known to have a good association with the rhizosphere soil microbiome. However, there are few reports on incorporating microbial inoculants with or without rock mineral fertilisers to facilitate nutrient mineralisation and stimulate growth of industrial hemp. To test whether microbial consortium inoculant with or without fertiliser improves the growth and yield of industrial hemp by increasing root biomass and nutrient uptake, we assessed the impact of microbial inoculant and rock mineral fertiliser in two hemp varieties (Morpeth and Han FNQ). The experiment was conducted in a randomised complete block design with four treatments: control (CTRL), consortium microbial inoculum (MI), rock mineral fertiliser (MF) and combined microbial inoculum and mineral fertiliser (MI+MF). Plants were grown in compost in a controlled-environment phytotron and harvested 30 and 70 days after sowing (DAS). Han FNQ had higher root dry weight, shoot length, leaf chlorophyll, Mn and Zn uptake than Morpeth at 30 DAS, and Han FNQ in the MI+MF treatment also had greater root volume than Morpeth in all treatments at 30 DAS. At 70 DAS, Morpeth had a higher seed yield than Han FNQ and Morpeth in the MI treatment had greater shoot and root dry weight, leaf chlorophyll, root length and volume, and higher uptake of all macro- and micronutrients in shoots and seeds than Han FNQ in all treatments. These findings suggest that the resource stoichiometry and trade-balance model in plant-microbes symbiosis govern the effectiveness of MI on industrial hemp. The application of MF and the initial nutrients abundance in the compost might suppressed MI activity at 30 DAS whereas, the nutrient limiting condition at 70 DAS might triggered MI activity and symbiotic trade of nutrients between plant and microbes which facilitated root growth and nutrient uptake particularly, in the variety Morpeth.

Effects of plastic fragments on plant performance are mediated by soil properties and drought

In recent years, the effects of plastic contamination on soil and plants have received growing attention. Plastic can affect soil water content and thus may interact with the effects of drought on soil and plants. However, the effects of plastic on soil are highly context-dependent, and interactions with drought have been hardly tested. We conducted two greenhouse experiments to test the combined effects of plastic fragments (of varying size and concentration), water availability and soil texture, on soil water content and performance of the plant Arabidopsis thaliana. Plastic fragments had stronger negative effects on soil water content in low water availability, and the shape of this response (linear vs. unimodal) was mediated by soil texture. Conversely, increasing concentration of plastic had positive effects on plant growth. We suggest that plastic fragments introduce fracture points within soil aggregates. This increases number and size of soil pores favoring water loss but also facilitating root growth. Our results suggest complex interactive effects of plastic and drought, that may lead to a decoupling of plant and soil response. These processes should be taken into account in ecological studies and agricultural practices.

Dose-Dependent Application of Straw-Derived Fulvic Acid on Yield and Quality of Tomato Plants Grown in a Greenhouse.

Fulvic acids are organic compounds widely distributed in soils, and the application of fulvic acids is thought to increase crop yield and quality. However, the effects vary among various sources and doses of fulvic acids and environmental and growth conditions of crops. Here, we investigated the effects of bioresource-derived (corn straw) fulvic acids on plant production and quality of tomato plants and soil chemical properties in soil cultures while experiments on seed germination and hydroponics were conducted to explore the underlying mechanism. Base dressing with 2.7 g kg–1 increased the yield of tomato by 35.0% at most as increased fruit number. Fulvic acids increased the concentrations of minerals, such as Ca, Fe, and Zn and the concentrations of citric, malic, and some amino acids in berries of tomato but did not affect the concentrations of soluble sugars and aromatic substances in tomato fruits. Similarly, fulvic acids at 80–160 mg L–1 increased germination rate, growth vigor, and radicle elongation of tomato seeds while it increased plant biomass, concentrations of nutrients, and root length of tomato plants in hydroponics to the greatest extent in general. The increases in yield and quality can be attributed to the improvement in root growth and, thus, increased nutrient uptake. In addition, the base application of fulvic acids improved soil cation exchange capacity and soil organic matter to an extent. In conclusion, base dressing and the addition into solution of fulvic acids at moderate doses facilitate root growth and nutrient uptake and, thus, vegetable production and quality; therefore, fulvic acids can be an effective component for designing new biofertilizers for sustainable agricultural production.

A time-lapse imaging platform for quantification of soil crack development due to simulated root water uptake

Plants are major drivers of soil structure dynamics. Root growth creates new macropores and provides essential carbon to soil, while root water uptake may induce crack formation around roots. Cracks can facilitate root growth as they provide pathways of least resistance and improve water infiltration and soil aeration. Due to the lack of suitable quantification methods, knowledge on the effects of root water uptake on soil crack formation remains limited. In the current study, we developed a time-lapse imaging platform that allows i) simulating root water uptake through localized soil drying and ii) quantifying the development of two-dimensional crack networks. Customized soil boxes that were 50 mm wide, 55 mm high and 5 mm deep were designed. Artificial roots made of dialysis tubes were inserted into the soil boxes and polyethylene glycol solution was circulated through the tubes. This induced a gradient in osmotic potential at the contact area (150 mm2) between the soil and the dialysis tubes, resulting in controlled soil drying. Drying intensity was varied by using different polyethylene glycol concentrations. Experiments were conducted with three soils that were subjected to three drying intensities for 6.5 days. We developed a time-lapse imaging system to record soil crack formation at two-minute intervals in twelve samples simultaneously. Resulting crack networks were quantified with an automated image analysis pipeline. Across soils and drying intensities, crack network development slowed down after 24–48 h of soil drying. The extent and complexity of crack networks increased with drying intensity and crack networks were larger and more complex in the clay and clay loam soil than in the silt loam soil. Smaller and less complex crack networks were better connected than larger and more complex networks. These results demonstrate that the platform developed in this study is suitable to quantify crack network development in soil due to simulated root water uptake at high temporal resolution and high throughput. Thereby, it can provide information needed to improve our understanding on how plants modify soil structure.

Effects of strip-till with staggered planting on yield formation and shoot-root characteristics of spring maize in irrigation area of Xiliaohe plain

<p indent="0mm">A field research was conducted in the Agricultural High-tech Demonstration Park in Horqin District of Tongliao, Inner Mongolia, using the maize variety Nonghua 101 with two cropping modes, including strip-till with staggered planting (seeding strip tillage, <sc>15 cm</sc> + <sc>45 cm</sc> narrow-double row staggered sowing, TGCW) and conventional tillage with equal row space (rotary tillage with row space of <sc>60 cm,</sc> CK), and three planting densities (67,500 plants hm^–2, 82,500 plants hm^–2, and 97,500 plants hm^–2) in 2017 and 2018 to study the effect of strip-till with staggered planting on regulating spring maize yield formation and coordination characteristics of shoot-root in irrigation areas of Xiliao river plain. The model of that strip-till with staggered planting enhanced maize yield by 13.1% and 13.8% in 2017 and 2018, under the planting density 82,500 plants hm^–2 compared with CK, respectively. The strip-till with staggered planting showed a distinct advantage on the amount and rate of dry matter accumulation after silking, which obviously delayed the senility of leaves in later growth stage, meanwhile, compared with CK, the light transmittance significantly increased in or above panicle layers. The leaf area index, net photosynthetic rate and population photosynthetic potential in the model of strip-till with staggered planting were higher than those in CK in late growth stage. At later growing stage, the strip-till with staggered planting had significantly higher root dry weight than CK in different soil layers, with the highest root ratio in <sc>20–60 cm,</sc> especially under higher planting density. The grain yield against per unit of root weight at silking and root-shoot ratio at maturity had a distinct advantage. In conclusion the strip-till with staggered planting combined with high planting density can increase light transmission rate in above-spike layer in late growing stage, alleviate leaf area decline, increase production capacity, facilitate root growth and increase root ratio in deeper soil layers. Shoot-root coordination under dense planting is one of the main reasons facilitating yield increase of spring maize in irrigation areas of Xiliao river plain.

Developing strategies to recover crop productivity after soil compaction—A plant eco-physiological perspective

Soil compaction constitutes a major threat to the fertility of arable soils and food security. The aim of this paper is to highlight the need and opportunities for plant eco-physiological approaches to identify strategies to recover crop yields after soil compaction. Reduced productivity on compacted soil primarily results from decreased root elongation rates and thus limited accessibility to water and nutrients. Hence, strategies to recover productivity after compaction must address plant eco-physiological phenomena that underlie low root system expansion rates. In compacted soil, root growth is decreased due to high soil penetration resistance and due to low oxygen concentration in soil air caused by reduced fluid transport capability. Thus, plant roots are exposed to a multi-stress environment, which needs to be addressed directly when aiming to recover productivity after compaction in the long-term. Here, we discuss possibilities to increase root growth in order to enhance resource accessibility and recover crop productivity on compacted soil. Yield recovery can be achieved through breeding of novel cultivars and targeted soil management approaches. On the one hand, the tolerance of plants to the different soil physical stresses can be enhanced by selecting for specific root traits that facilitate root growth in compacted soil. Soil management approaches that improve specific physical properties of compacted soil on the other hand can facilitate root growth in compacted soil. Since plant roots are major drivers of soil structure dynamics, increasing root growth in compacted soil may not only mitigate crop productivity losses but also recover soil structure.

Effect of conservation agriculture on soil hydro-physical properties, total and particulate organic carbon and root morphology in wheat (Triticum aestivum) under rice (Oryza sativa)-wheat system

Short-term (5 years) effect of conservation agriculture (CA) practice on soil hydro-physical characteristics, soil organic carbon status and root morphology in wheat (triticum aestivum L.) was monitored under rice (Orgza sativa L.)-wheat rotation in a clay loam soil at the Indian Agricultural Research Institute, New Delhi. A small improvement in soil water content and a marginal decrease in bulk density by CA contributed in significant reduction (30-37%)in sub-surface compaction. The CA improved soil structure in the plough layer (0-15 cm) with significant increase in soil organic carbon status (27-38%). A marginal change in pore size distribution was recorded in favour of larger volume of retention pores (11-12%), in expense of macro- or drainable pore space. Steady-state infiltration, which was essentially profile-controlled, was therefore lower in the CA plots. Decrease in sub-surface soil strength and better soil water retention facilitated root growth in wheat in the sub-surface layer under CA. Results implied thatthe CA practice in rice-wheat system, although with a shorter period, led to an overall physical improvement of the most active root zone. This had positive impact on root morphology, which contributed to increase in the crop yield.

Interdependent Nutrient Availability and Steroid Hormone Signals Facilitate Root Growth Plasticity

Plants acquire essential elements from inherently heterogeneous soils, in which phosphate and iron availabilities vary. Consequently, plants have developed adaptive strategies to cope with low iron or phosphate levels, including alternation between root growth enhancement and attenuation. How this adaptive response is achieved remains unclear. Here, we found that low iron accelerates root growth in Arabidopsis thaliana by activating brassinosteroid signaling, whereas low-phosphate-induced high iron accumulation inhibits it. Altered hormone signaling intensity also modulated iron accumulation in the root elongation and differentiation zones, constituting a feedback response between brassinosteroid and iron. Surprisingly, the early effect of low iron levels on root growth depended on the brassinosteroid receptor but was apparently hormone ligand-independent.The brassinosteroid receptor inhibitor BKI1, the transcription factors BES1/BZR1, and theferroxidase LPR1 operate at the base of this feedback loop. Hence, shared brassinosteroid and iron regulatory components link nutrient status toroot morphology, thereby driving the adaptive response.

Irrigation and Nitrogen Regimes Promote the Use of Soil Water and Nitrate Nitrogen from Deep Soil Layers by Regulating Root Growth in Wheat.

Unreasonably high irrigation levels and excessive nitrogen (N) supplementation are common occurrences in the North China Plain that affect winter wheat production. Therefore, a 6-yr-long stationary field experiment was conducted to investigate the effects of irrigation and N regimes on root development and their relationship with soil water and N use in different soil layers. Compared to the non-irrigated treatment (W0), a single irrigation at jointing (W1) significantly increased yield by 3.6–45.6%. With increases in water (W2, a second irrigation at flowering), grain yield was significantly improved by 14.1–45.3% compared to the W1 treatments during the drier growing seasons (2010–2011, 2012–2013, and 2015–2016). However, under sufficient pre-sowing soil moisture conditions, grain yield was not increased, and water use efficiency (WUE) decreased significantly in the W2 treatments during normal precipitation seasons (2011–2012, 2013–2014, and 2014–2015). Irrigating the soil twice inhibited root growth into the deeper soil depth profiles and thus weakened the utilization of soil water and NO3-N from the deep soil layers. N applications increased yield by 19.1–64.5%, with a corresponding increase in WUE of 66.9–83.9% compared to the no-N treatment (N0). However, there was no further increase in grain yield and the WUE response when N rates exceeded 240 and 180 kg N ha−1, respectively. A N application rate of 240 kg ha−1 facilitated root growth in the deep soil layers, which was conducive to utilization of soil water and NO3-N and also in reducing the residual NO3-N. Correlation analysis indicated that the grain yield was significantly positively correlated with soil water storage (SWS) and nitrate nitrogen accumulation (SNA) prior to sowing. Therefore, N rates of 180–240 kg ha−1 with two irrigations can reduce the risk of yield loss that occurs due to reduced precipitation during the wheat growing seasons, while under better soil moisture conditions, a single irrigation at jointing was effective and more economical.

Facilitation of phosphorus uptake in maize plants by mycorrhizosphere bacteria

A major challenge for agriculture is to provide sufficient plant nutrients such as phosphorus (P) to meet the global food demand. The sufficiency of P is a concern because of it’s essential role in plant growth, the finite availability of P-rock for fertilizer production and the poor plant availability of soil P. This study investigated whether biofertilizers and bioenhancers, such as arbuscular mycorrhizal fungi (AMF) and their associated bacteria could enhance growth and P uptake in maize. Plants were grown with or without mycorrhizas in compartmented pots with radioactive P tracers and were inoculated with each of 10 selected bacteria isolated from AMF spores. Root colonization by AMF produced large plant growth responses, while seven bacterial strains further facilitated root growth and P uptake by promoting the development of AMF extraradical mycelium. Among the tested strains, Streptomyces sp. W94 produced the largest increases in uptake and translocation of 33P, while Streptomyces sp. W77 highly enhanced hyphal length specific uptake of 33P. The positive relationship between AMF-mediated P absorption and shoot P content was significantly influenced by the bacteria inoculants and such results emphasize the potential importance of managing both AMF and their microbiota for improving P acquisition by crops.

Thiourea priming enhances salt tolerance through co-ordinated regulation of microRNAs and hormones in Brassica juncea

Activation of stress tolerance mechanisms demands transcriptional reprogramming. Salt stress, a major threat to plant growth, enhances ROS production and affects transcription through modulation of miRNAs and hormones. The present study delineates salt stress ameliorating action of thiourea (TU, a ROS scavenger) in Brassica juncea and provides mechanistic link between redox, microRNA and hormones. The ameliorative potential of TU towards NaCl stress was related with its ability to decrease ROS accumulation in roots and increase Na+ accumulation in shoots. Small RNA sequencing revealed enrichment of down-regulated miRNAs in NaCl + TU treated roots, indicating transcriptional activation. Ranking analysis identified three key genes including BRX4, CBL10 and PHO1, showing inverse relationship with corresponding miRNA expression, which were responsible for TU mediated stress mitigation. Additionally, ABA level was consistently higher till 24 h in NaCl, while NaCl + TU treated roots showed only transient increase at 4 h suggesting an effective stress management. Jasmonate and auxin levels were also increased, which prioritized defence and facilitated root growth, respectively. Thus, the study highlights redox as one of the “core” components regulating miRNA and hormone levels, and also strengthens the use of TU as a redox priming agent for imparting crop resilience to salt stress.

Abiotic and biotic drivers of biomass change in a Neotropical forest

Summary Tropical forests play an important role in the global carbon cycle, but the drivers of net forest biomass change (i.e. net carbon sequestration) are poorly understood. Here, we evaluate how abiotic factors (soil conditions and disturbance) and biotic factors (forest structure, diversity and community trait composition) shape three important demographic processes (biomass recruitment, growth and mortality) and how these underlie net biomass change. To test this, we evaluated 9 years of biomass dynamics using 48 1‐ha plots in a Bolivian tropical moist forest, and measured for the most abundant species eight functional traits that are important for plant carbon gain and loss. Demographic processes were related to the abiotic and biotic factors using structural equation models. Variation in net biomass change across plots was mostly due to stand‐level mortality, but mortality itself could not be predicted at this scale. Contrary to expectations, we found that species richness and trait composition – which is an indicator for the mass‐ratio theory – had little effect on the demographic processes. Biomass recruitment (i.e. the biomass growth by recruiting trees) increased with higher resource availability (i.e. water and light) and with high species richness, probably because of increased resource use efficiency. Biomass growth of larger, established trees increased with higher sand content, which may facilitate root growth of larger trees to deeper soil layers. In sum, diversity and mass‐ratio are of limited importance for the productivity of this forest. Instead, in this moist tropical forest with a marked dry season, demographic processes are most strongly determined by soil texture, soil water availability and forest structure. Only by simultaneously evaluating multiple abiotic and biotic drivers of demographic processes, better insights can be gained into mechanisms playing a role in the carbon sequestration potential of tropical forests and natural systems in general.

Dynamics of plant nutrient uptake as affected by biopore-associated root growth in arable subsoil

Soil biopores facilitate root growth in arable subsoil, thus improve resource acquisition potential. We aimed at determining the dynamic relationship between soil biopores and performance of two winter crops in field condition considering different biopore size classes, root characteristics and crop growth parameters. Chicory with dominant taproot system and tall fescue with limited taproots were grown for two consecutive years as precrops. Density of soil biopores larger than 2 mm and smaller than 2 mm in diameter was measured at 45 cm of soil depth. Destructive samplings were carried out for investigation on following barley and canola roots. Shoot biomass production, nutrient uptake and final yield of the following crops were determined throughout the growth seasons. Higher shares of large or small-sized bipoores were observed after chicory (23 %) or tall fescue (20 %) precrops, respectively. On average root diameter and root dry mass of following crops were greater by 11 and 15 % after chicory than tall fescue. At anthesis chicory-barley treatment accumulated 10 % more K in comparison to tall fescue-barley treatment. P uptake of canola was greater (7 %) after tall fescue compared with chicory at the stage of fruit development. Our results suggest that the subsoil heterogenization by altered soil biopores hold relevance for plant root growth and overall crop performance. However, the effects depended on biopore size classes, root characteristics and crop species. Development of direct methods that can quantify biopore-root-shoot processes, detailed investigation on drilosphere, root phenotyping for detection of the genetic variation in response to biopore systems have to be followed in the future.

Water relations in tree physiology: where to from here?

We look back over 50 years of research into the water relations of trees, with the objective of assessing the maturity of the topic in terms of the idea of a paradigm, put forward by Kuhn in 1962. Our brief review indicates that the physical processes underlying the calculation of transpiration are well understood and accepted, and knowledge of those processes can be applied if information about the leaf area of trees, and stomatal conductance, is available. Considerable progress has been made in understanding the factors governing stomatal responses to environment, with insights into how the hydraulic conducting system of trees determines the maximum aperture of stomata. Knowledge about the maximum stomatal conductance values likely to be reached by different species, and recognition that stomatal responses to increasing atmospheric vapor pressure deficits are in fact responses to water loss from leaves, provides the basis for linking these responses to information about hydraulic conductance through soil–root–stem–branch systems. Improved understanding in these areas is being incorporated into modern models of stomatal conductance and responses to environmental conditions. There have been significant advances in understanding hydraulic pathways, including cavitation and its implications. A few studies suggest that the major resistances to water flux within trees are not in the stem but in the branches. This insight may have implications for productivity: it may be advantageous to select trees with the genetic propensity to produce short branches in stands with open canopies. Studies on the storage of water in stems have provided improved understanding of fluxes from sapwood at different levels. Water stored in the stems of large trees may provide up to 20–30% daily sap flow, but this water is likely to be replaced by inflows at night. In dry conditions transpiration by large trees may be maintained from stored water for up to a week, but flows from storage may be more important in refilling cavitated xylem elements and hence ensuring that the overall hydraulic conductivity of stems is not reduced. Hydraulic redistribution of water in the soil may make a contribution to facilitating root growth in dry soils and modifying resource availability. We conclude that the field of tree water relations is mature, in the sense that the concepts underlying models describing processes and system responses to change are well-tested and accepted and there are few, if any, serious anomalies emerging. Models are essentially formal statements about the way we think systems work. They are always subject to further testing, refinement and improvements. Gaps in knowledge appear within the framework of accepted concepts and mechanisms research is needed to fill those gaps. The models currently available can be used to scale estimates of transpiration from leaf to landscape levels and predict species responses to drought. The focus in tree water relations has shifted to examine the climatic thresholds at which drought, high temperatures and vapor pressure deficits cause mortality. Tree death may be caused by hydraulic collapse following irreversible cavitation or extremely low water potentials, but recent research indicates that the relative sensitivity of stomatal conductance and whole-plant hydraulic conductance plays a major role in determining plant responses to drought.

Overexpression of a Hevea brasiliensis ErbB-3 Binding protein 1 Gene Increases Drought Tolerance and Organ Size in Arabidopsis.

Rubber trees are economically important tropical tree species and the major source of natural rubber, which is an essential industrial material. This tropical perennial tree is susceptible to cold stress and other abiotic stresses, especially in the marginal northern tropics. Recent years, the genome sequencing and RNA-seq projects produced huge amount of sequence data, which greatly facilitated the functional genomics study. However, the characterization of individual functional gene is in urgent demands, especially for those involved in stress resistance. Here we identified and characterized the rubber tree gene ErbB-3 binding protein 1, which undergoes changes in expression in response to cold, drought stress and ABA treatment. HbEBP1 overexpression (OE) in Arabidopsis increased organ size, facilitated root growth and increased adult leaf number by delaying the vegetative-to-reproductive transition. In addition, HbEBP1 OE enhanced the resistance of the Arabidopsis plants to freezing and drought stress, demonstrating that this gene participates in the regulation of abiotic stress resistance. RD29a, RD22 and CYCD3;1 expression was also greatly enhanced by HbEBP1 OE, which explains its regulatory roles in organ size and stress resistance. The regulation of drought stress resistance is a novel function identified in plant EBP1 genes, which expands our understanding of the roles of EBP1 gene in response to the environment. Our results provide information that may lead to the use of HbEBP1 in genetically engineered crops to increase both biomass and abiotic stress resistance.