Relative Soil Water Content Research Articles

Critical effects on the photosynthetic efficiency and stem sap flow of poplar in the Yellow River Delta in response to soil water

To explore the critical relationships of photosynthetic efficiency and stem sap flow to soil moisture, two-year-old poplar saplings were selected and a packaged stem sap flow gauge, based on the stem-heat balance method, and a CIRAS-2 portable photosynthesis system were used. The results show that photosynthetic rates (Pn), transpiration rates (Tr), instantaneous water use efficiency (WUE) and the stem sap flow increased initially and then decreased with decreasing soil water, but their critical values were different. The turning point of relative soil water content (Wr) from stomatal limitation to nonstomatal limitation of Pn was 42%, and the water compensation point of Pn was 13%. Water saturation points of Pn and Tr were 64% and 56%, respectively, and the WUE was 71%. With increasing soil water, the apparent quantum yield (AQY), light saturation point (LSP) and maximum net photosynthetic rate (Pnmax) increased first and then decreased, while the light compensation point (LCP) decreased first and then increased. When Wr was 64%, LCP reached a lower value of 30.7 µmol m−2 s−1, and AQY a higher value of 0.044, indicating that poplar had a strong ability to utilize weak light. When Wr was 74%, LSP reached its highest point at 1138.3 µmol∙m−2 s−1, indicating that poplar had the widest light ecological amplitude and the highest light utilization efficiency. Stem sap flow and daily sap flow reached the highest value (1679.7 g d−1) at Wr values of 56% and 64%, respectively, and then declined with increasing or decreasing Wr, indicating that soil moisture significantly affected the transpiration water-consumption of poplar. Soil water was divided into six threshold grades by critical values to maintain photosynthetic efficiency at different levels, and a Wr of 64–71% was classified to be at the level of high productivity and high efficiency. In this range, poplar had high photosynthetic capacity and efficient physiological characteristics for water consumption. The saplings had characteristics of water tolerance and were not drought resistant. Full attention should be given to the soil water environment in the Yellow River Delta when planting Populus.

Effect of Nitrogen Rates on Wheat Photosynthesis, Anatomical Parameters and Photoassimilate Partitioning in North China Plain

Evaluating the effects of nitrogen (N) on photosynthesis characteristics and photoassimilate partitioning via vascular bundles (VB) under water-saving irrigation is crucial to maximum grain yield of environment-friendly wheat production in the North China Plain (NCP). Field experiments were conducted with four N application rates 0 (N0), 180 (N180), 240 (N240), and 300 (N300) kg N ha−1 under 70% and 65% relative soil water content (RSWC) at jointing and anthesis, respectively. Results showed that, compared with N0, N180 significantly improved the photosynthetic parameters and chlorophyll fluorescence of flag leaf after anthesis. N application improved the anatomical parameters both in the flag leaf and the stem. Total transverse area of VB in the flag leaf and in the stem internode below the ear under N180 was 17.95–23.70% and 37.91–43.90% larger than those of N0, respectively, due to the increased numbers and transverse area of VB. Furthermore, N180 had higher dry matter assimilation after anthesis (DMA) and its contribution to the grain. N180 increased grain yield by 14.23–23.24% compared with N0, and N supply exceeding 180 kg N ha−1 did not further increase yield. Moreover positively correlations were showed among photosynthesis characteristics after anthesis, total transverse area of VB in the flag leaf and in the stem internode below the ear, DMA and grain yield. In summary, the recommended N application rate was 180 kg N ha−1 under RSWC-based supplemental irrigation that can produce grain yield over 7500 kg ha−1 for at least 2 years in the NCP.

Physio-chemical changes of Cassia occidentalis under drought stress

Drought stress is a prime hindrance for Cassia occidentalis, a medicinal plant of potential importance. This experiment was accomplished to interpret the effect of drought stress on C. occidentalis employing four water supply levels (100ml, 200ml, 300ml and control) with soil relative water content ranging from 12% to 65%. The present study was carried out in pot experiments in complete randomized design with three replicates and the results were analysed on the basis of data recorded on growth, physiological and biochemical parameters. The parameters studied were number of leaf, leaf area index, biomass accumulation, NR activity, chlorophyll content and protein accumulation. The result showed a significant decrease in all parameters with the decrease in water supply, however mild level of stress (300ml; 36% SRWC) enhanced the growth. Our study concluded that the experimental plants were able to tolerate a limited water stress (up to 36% SRWC) but excessive drought (100ml) strikingly diminished the physio-biochemical activity and therefore hindered the plant growth.

Interannual Variation of Transpiration and Its Modeling of a Larch Plantation in Semiarid Northwest China

Quantifying the variation of forest transpiration (T) is important not only for understanding the water and energy budget of forest ecosystems but also for the prediction, evaluation, and management of hydrological effects as well as many other ecosystem services of forests under the changes of climate, vegetation, and anthropological impacts. The accurate prediction of T, a key component of water used by forests, requires mechanism-based models describing the T response to environmental and canopy conditions. The daily T of a larch (Larix principis-rupprechtti) plantation was measured through monitoring the sap flow in the growing season (from May to September) of a dry year (2010), a normal year (2012), and a wet year (2014) at a shady slope in the semi-arid area of Liupan Mountains in northwest China. Meanwhile, the meteorological conditions, soil moisture, and forest canopy leaf area index (LAI) were monitored. To get a simple and easily applicable T model, the numerous influencing parameters were grouped into three factors: the atmospheric evapotranspiration demand indicated by the potential evapotranspiration (PET), the soil water supply ability indicated by the relative extractable soil water content (REW), and the vegetation transpiration capacity indicated by the forest canopy LAI. The T model was established as a continuous multiplication of the T response equations to individual factors, which were determined using the upper boundary lines of measured data. The effect of each factor on the T in a dry year (2010) or normal year (2012) was assessed by comparing the measured T in the baseline of the wet year (2014) and the model predicted T, which was calculated through inputting the actual data of the factor (i.e., PET) to be assessed in the dry or normal year and the measured data of other two factors (i.e., REW, LAI) in the baseline of the wet year. The results showed that the mean daily T was 0.92, 1.05, and 1.02 mm; and the maximum daily T was 1.78, 1.92, and 1.89 mm in 2010, 2012, and 2014, respectively. The T response follows a parabolic equation to PET, but a saturated exponential equation to REW and LAI. The T model parameters were calibrated using measured data in 2010 and 2012 (R2 = 0.89, Nash coefficient = 0.88) and validated using measured data in 2014 satisfactorily (R2 = 0.89, Nash coefficient = 0.79). It showed a T limitation in the dry year 2010 for all factors (18.5 mm by PET, 11.5 mm by REW, and 17.8 mm by LAI); while a promotion for PET (1.4 mm) and a limitation for REW (4.2 mm) and LAI (14.3 mm) in the normal year 2012. The daily T model established in this study can be helpful to assess the individual factor impact on T and improve the daily T prediction under changing environmental and canopy conditions.

Quantifying individual and interactive effects of elevated temperature and drought stress on cotton yield and fibre quality

AbstractThe individual effect of high temperatures or water‐deficit stress on cotton has been studied extensively; however, their combined effects were less studied. To that end, an experiment was imposed with a heat‐sensitive (Sumian 15) and a heat‐tolerant (PHY370WR) cultivar in 2016–2018 and two temperature regimes including ambient temperature (AT, 31.0/26.4°C) and elevated temperature (ET, 33.4/28.9°C), and three soil relative water content (SRWC) levels including (75 ± 5)%, (60 ± 5)% and (45 ± 5)% were performed. Results showed that the decline in boll number was the primary driver of yield loss, while the decreases in boll weight minimally impacted yield under drought and combined treatments. Besides, elevated temperature and drought stress performed significant interactions on boll weight (except in 2018) and seed cotton yield (except for Sumian 15 in 2017). Specifically, seed cotton yield was reduced by 23%–35% in Sumian 15 and by 8%–13% in PHY370WR under ET60(ET with SRWC (60 ± 5)%), while the reduction was 44%–54% in Sumian 15 and 37%–43% in PHY370WR under ET45(ET with SRWC (45 ± 5)%), which produced lower yields than any other treatment combination or any single abiotic stress factor. Furthermore, significant interactions between the two stresses were observed in fibre length of Sumian 15 and strength (except for PHY370WR in 2018) and micronaire (except for Sumian 15 in 2017 and for PHY370WR in 2018) of both cultivars. Elevated temperature exacerbated the negative impacts of drought on fibre length but offset them on fibre strength and micronaire. Finally, the economic benefit among different treatments was evaluated. Compared to the control, ET45suffered the biggest economic loss by 2,536.7 USD ha−2in Sumian 15 and by 2,167.8 USD ha−2in PHY370WR, respectively. Quantifying the interactive effects of drought and elevated temperature on cotton yield and fibre quality should allow researchers to better understand the economic implications of these two stresses which often occur concurrently under field conditions.

Evaluation of Soil Water Content Measurements with Capacitance Probes to Support Irrigation Scheduling in a “Red Beaut” Japanese Plum Orchard

Advances in electromagnetic sensor technologies in recent years have made automated irrigation scheduling a reality through the use of state-of-the-art soil moisture sensing devices. However, correct sensor positioning and interpretation of the measurements are key to the successful implementation of these management systems. The aim of this study is to establish guidelines for soil moisture sensor placement to support irrigation scheduling, taking into account the physiological response of the plant. The experimental work was carried out in Vegas Bajas del Guadiana (Extremadura, Spain) on a drip-irrigated experimental orchard of the early-maturing Japanese plum cultivar “Red Beaut”. Two irrigation treatments were established: control and drying. The control treatment was scheduled to cover crop water needs. In the drying treatment, the fruit trees were irrigated as in control, except in certain periods (preharvest and postharvest) in which irrigation was suspended (drying cycles). Over 3 years (2015–2017), a series of plant parameters were analyzed in relation to the measurements provided by a battery of frequency domain reflectometry probes installed in different positions with respect to tree and dripper: midday stem water potential (Ψstem), sap flow, leaf stomatal conductance, net leaf photosynthesis and daily fraction of intercepted photosynthetically active radiation. After making a comparison of these measurements as indicators of plant water status, Ψstem was found to be the physiological parameter that detected water stress earliest. The drying cycles were very useful to select the probe positions that provided the best information for irrigation management and to establish a threshold in the different phases of the crop below which detrimental effects could be caused to the crop. With respect to the probes located closest to the drippers, a drop in the relative soil water content (RSWC) below 0.2 would not be advisable for “non-stress” scheduling in the preharvest period. When no deficit irrigation strategies are applied in the postharvest period, the criteria are similar to those of preharvest. However, the probes located between the dripper at 0.15 and 0.30 m depth provide information on moderate water stress if the RSWC values falls below 0.2. The severe tree water stress was detected below 0.1 RSWC in probes located at 60 cm depth from this same position.

Nighttime transpiration represents a negligible part of water loss and does not increase the risk of water stress in grapevine.

Nighttime transpiration has been previously reported as a significant source of water loss in many species; however, there is a need to determine if this trait plays a key role in the response to drought. This study aimed to determine the magnitude, regulation and relative contribution to whole plant water‐use, of nighttime stomatal conductance (g night) and transpiration (E night) in grapevine (Vitis vinifera L.). Our results showed that nighttime water loss was relatively low compared to daytime transpiration, and that decreases in soil and plant water potentials were mainly explained by daytime stomatal conductance (g day) and transpiration (E day). Contrary to E day, E night did not respond to VPD and possible effects of an innate circadian regulation were observed. Plants with higher g night also exhibited higher daytime transpiration and carbon assimilation at midday, and total leaf area, suggesting that increased g night may be linked with daytime behaviors that promote productivity. Modeling simulations indicated that g night was not a significant factor in reaching critical hydraulic thresholds under scenarios of either extreme drought, or time to 20% of soil relative water content. Overall, this study suggests that g night is not significant in exacerbating the risk of water stress and hydraulic failure in grapevine.

Photosynthetic characteristics of Tamarix chinensis under different groundwater depths in freshwater habitats

Groundwater is the major source of water for Tamarix chinensis growth in the Yellow River Delta (YRD) region, and the groundwater depth (GWD) dramatically influences the physiological activities of T. chinensis. The quantitative response of the photosynthetic physiological process of T. chinensis to the GWD in freshwater habitats remains unclear. In this study, the response characteristics of gas exchange parameters in the leaves of three-year-old T. chinensis seedlings were measured and analyzed at a graded series of seven GWDs (0 m, 0.3 m, 0.6 m, 0.9 m, 1.2 m, 1.5 m and 1.8 m). The GWD thresholds corresponding to drastic changes in the photosynthetic efficiency and the GWDs of several levels of photosynthetic productivity and efficiency were also determined. In the freshwater habitats of the YRD, variations in GWD significantly altered the relative soil water content (RSWC) and thus influenced the photosynthetic efficiency of T. chinensis. RSWC at 0 ≤ GWD ≤ 0.9 m and GWD at 1.2 m ≤ GWD ≤ 1.8 m directly influenced the photosynthetic physiology of T. chinensis. When the GWD was 1.2 m, net photosynthetic rate (Pn), apparent quantum efficiency and water use efficiency (WUE) values all peaked. Thus, T. chinensis exhibited a high light and water use efficiency, wide ecological amplitude in terms of light, and high photosynthetic capacity. The optimum GWD for photosynthetic carbon assimilation and WUE in T. chinensis was determined to be 1.2 m. At a deep (≥1.64 m) or shallow (≤0.53 m) GWD, both Pn and WUE in T. chinensis clearly decreased below the corresponding mean values. The main causes for the reduction in Pn in these two GWD ranges (≤0.53 m, ≥1.64 m) were stomatal and nonstomatal limitations, respectively. Additionally, a moderate GWD of 1.09–1.25 m corresponded to the “high-productivity and high-efficiency GWD” range, in which T. chinensis displayed a high photosynthetic yield and WUE. Overall, the photosynthetic capacity of T. chinensis shows characteristics of high tolerance to moderate GWDs from 1.09 m to 1.25 m but intolerance at both shallow (≤0.53 m) and deep (≥1.64 m) GWDs in freshwater habitats.

Potassium (K) application alleviates the negative effect of drought on cotton fiber strength by sustaining higher sucrose content and carbohydrates conversion rate

Potassium (K) application can alleviate the negative effect of drought on fiber strength of cotton, but the involved physiological mechanism is still unclear. To explore this, two cotton varieties, Siza 3 and Simian 3, were planted under three K levels of 0, 150 and 300 kg K2O ha−1. These were exposed to two water regimes consisting of a well-watered level (WW) of 75 ± 5% soil relative water content (RSWC) and a short-term drought stress (DS) of 40 ± 5% SRWC at flowering and boll development stage of cotton. Results revealed that cotton fiber strength of the 7th main-stem fruiting branch (FB7, middle branch) and 3rd main-stem fruiting branch (FB3, lower branch) significantly decreased under drought conditions. The K application significantly increased cotton fiber strength on all FBs under both WW and DS conditions and alleviated the fiber strength decline on FB3 and FB7 under drought. Correspondingly, K application alleviated the DS-caused decrease of sucrose content, cellulose content, sucrose and callose conversion rate, and SuSy and β-1,3-glucanase activities. Correlation analysis also revealed that sucrose content was the most associated to final cotton fiber strength, followed by callose and sucrose conversion rate. Greater increase in enzymes activity, carbohydrate content and conversion rate, and final fiber strength by K application was observed in Siza 3 than in Simian 3 under DS. Summarily, since the carbohydrate content and enzymes activity under DS increased with the increase of K application, the negative effect of DS on fiber strength on FB3 and FB7 gradually reduced. Sustaining higher sucrose content and carbohydrate conversion rate (CCR) would be the strategy for K alleviating the DS-induced decline in fiber strength in cotton.

Plant growth promoting rhizobacteria alleviates drought stress in potato in response to suppressive oxidative stress and antioxidant enzymes activities

Maintenance of plant physiological functions under drought stress is normally considered a positive feature as it indicates sustained plant health and growth. This study was conducted to investigate whether plant growth-promoting rhizobacteria (PGPR) Bacillus subtilis HAS31 has potential to maintain potato growth and yield under drought stress. We analyzed trends of chlorophyll concentration, photosynthesis process, relative water content, osmolytes, antioxidants enzymes and oxidative stress, relative growth rate, tuber and aboveground biomass production in two potato varieties, Santae (drought-tolerant) and PRI-Red (drought-sensitive). Plants of both genotypes were treated with 100 g of HAS31 inoculant at 10 days after germination and exposed to different soil relative water contents (SRWC), including 80 ± 5% (well watered), 60 ± 5% (moderate stress) and 40 ± 5% SRWC (severe stress) for 7 days at tuber initiation stage (30 days after germination). The drought stress reduced plant relative growth rate, biomass production, leaf area, number of leaves and tubers, tuber weight, and final yield. The drought-stressed plants showed decline in chlorophyll contents, membrane stability, leaf relative water contents and photosynthetic rate. Under drought stress, enzymatic activity of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD), contents of total soluble sugars, soluble proteins and proline increased. The application of PGPR reduced the impact of drought and maintained higher growth and physio-chemical traits of the plants. The plants with PGPR application showed higher relative growth rate, dry matter production, leaf area, number of tubers, tuber weight and yield as compared to plants without PGPR. The PGPR-HAS31 treated plants maintained higher photosynthetic process, contents of chlorophyll, soluble proteins, total soluble sugars, and enzymatic activities of CAT, POD and SOD as compared to plants without PGPR. The results of the study suggest that plant growth regulators have ability to sustain growth and yield of potato under drought stress by maintaining physiological functions of the plants.

Non-stomatal processes reduce gross primary productivity in temperate forest ecosystems during severe edaphic drought.

Severe drought events are known to cause important reductions of gross primary productivity (GPP) in forest ecosystems. However, it is still unclear whether this reduction originates from stomatal closure (Stomatal Origin Limitation) and/or non-stomatal limitations (Non-SOL). In this study, we investigated the impact of edaphic drought in 2018 on GPP and its origin (SOL, NSOL) using a dataset of 10 European forest ecosystem flux towers. In all stations where GPP reductions were observed during the drought, these were largely explained by declines in the maximum apparent canopy scale carboxylation rate VCMAX,APP (NSOL) when the soil relative extractable water content dropped below around 0.4. Concurrently, we found that the stomatal slope parameter (G1, related to SOL) of the Medlyn et al. unified optimization model linking vegetation conductance and GPP remained relatively constant. These results strengthen the increasing evidence that NSOL should be included in stomatal conductance/photosynthesis models to faithfully simulate both GPP and water fluxes in forest ecosystems during severe drought. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.

Analysis of floodplain forest sensitivity to drought.

Floodplain forests are very complex, productive ecosystems, capable of storing huge amounts of soil carbon. With the increasing occurrence of extreme events, they are today among the most threatened ecosystems. Our study's main goal was to assess the productivity of a floodplain forest located at Lanžhot in the Czech Republic from two perspectives: carbon uptake (using an eddy covariance method) and stem radius variations (using dendrometers). We aimed to determine which conditions allow for high ecosystem production and what role drought plays in reducing such production potential. Additionally, we were interested to determine the relative soil water content threshold indicating the onset and duration of this event. We hypothesized that summer drought in 2018 had the most significant negative effects on the overall annual carbon and water budgets. In contrast with our original hypothesis, we found that an exceptionally warm spring in 2018 caused a positive gross primary production (GPP) and evapotranspiration (ET) anomaly that consequently led in 2018 to the highest seasonal total GPP and ET from all of the investigated years (2015–2018). The results showed ring-porous species to be the most drought resistant. Relative soil water content threshold of approximately 0.45 was determined as indicating the onset of drought stress.This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’.

Dynamics of soil penetration resistance in water-controlled environments

In water-controlled environments, because rainfall is one of the primary hydroclimatic forcings, its variability can affect the dynamics of soil water content and other related processes such as soil penetration resistance (PR), plant growth, and food production. The objective of this study was to simulate the relative soil water content (s) and PR year-round considering semi-arid rainfall conditions for different soil classes. An experiment was conducted to obtain relative soil water content (s) and PR data in sandy soil and this information was combined with a data set of four soils from a similar experiment conducted on different soil texture classes. The relative soil water content and PR were simulated at a daily timescale using a stochastic soil water balance model for the five soils. The parameters of the PR-s model can be estimated from the soil texture and bulk density. Under rainfed conditions, there is a short window for tillage (plowing and cultivation) of sandy soils compared with clay soils. During the majority of a typical hydrological year, the PR reaches high values (greater than 5.0 MPa) imposing a moderate to high physical limitation for root growth in sandy soils. In the same soils, limiting PR is reached at s levels very close to the field capacity during the drying process. This indicates that an extra input of water through irrigation may be required during the establishment of crops with a well-developed root system in order to prevent impairments to root growth. The daily PR values modeled over the course of a hydrological year followed a beta distribution with shape parameters (α and β) which were strongly correlated with the frequency of rainfall events during the wet season (λwet). The modeling framework presented here for simulating relative soil water content and soil penetration resistance can be applied to agricultural systems in order to prevent physical limitations on crop growth and to plan tillage management schedules.

Soil water availability threshold indicator was determined by using plant physiological responses under drought conditions

Soil water shortage is a critical limiting factor that threaten the growth of vegetation and their sustainability in semi-arid areas. Grasses directly respond to the soil water availability (SWA), and the soil water shortage degree can be studied through plant physiological response thresholds under soil drought stress. In this study, the lower-and-optimal limitation of SWA was evaluated with pots along the soil water gradient by quantifying plant gas exchange parameters. These parameters showed a strong cubic relationship with the relative soil water content (RWC) in four forage species. The lower limitation of RWC was obtained for Onobrychis viciifolia (4.0%–20.2%), followed by Astragalus adsurgens (15.5%–25.5%), Elymus nutans (16.1%–27.2%), and Lolium multiflorum (24.6%–35.8%). The average RWC was of 74.83%, and the water saturation point of water use efficiency (WSPWUE) showed a similar critical scope in the four species: Onobrychis viciifolia (71.2%–82.8%), Astragalus adsurgens (72.1%–84.2%), Elymus nutans (79.3%–85.1%), and Lolium multiflorum (76.7%–85.6%). The highest productivity with the highest availability of water (HPHAW) for Onobrychis viciifolia, Astragalus adsurgens, Elymus nutans and Lolium multiflorum was of 71.2%–82.8%, 72.1%–84.2%, 79.3%–85.1% and 76.7%–85.6%, respectively. The lower limitation of RWC, the maximum water use efficiency (WUEmax) and HPHAW in legumes were lower than those values obtained in gramineae, suggesting that legumes were more susceptible to soil drought stress. We concluded that plant gas exchange parameters acted as indicators for SWA under drought conditions, and represented a valuable tool for identifying SWA threshold response in environmental changes.

Plastic-Covered Ridge-Furrow Planting Combined with Supplemental Irrigation Based on Measuring Soil Moisture Promotes Wheat Grain Yield and Irrigation Water Use Efficiency in Irrigated Fields on the Loess Plateau, China

The purpose of this study was to investigate whether combining plastic-covered ridge and furrow planting (RF) and supplemental irrigation based on measuring soil moisture (SIMSM) can increase the grain yield and water use efficiency (WUE) of wheat (Triticum aestivum L.) in irrigated fields of Loess Plateau, China. In 2016–2018, the experiment was conducted at Doukou experimental farm (34°36′ N, 108°52′ E) with two plant systems (RF and traditional planting (TF)) and three irrigation treatments (S1 and S2: SIMSM with a target relative soil water content of 85% and 100%, respectively). The results suggest that under the TF system, SIMSM decreased the grain yield and nitrogen utilization. The reason for this may be the local low precipitation. However, the combination of RF and S2 significantly increased the WUE, protein and wet gluten concentration in the grain. In addition, the grain yield of the RF plus S2 treatment was not significantly different than that of the traditional irrigation method. These results suggest that combining RF and SIMSM with a target relative soil water content of 100% is beneficial to the synergistic improvement of the wheat yield, the wheat quality, and the water and fertilizer use efficiency in irrigated fields on the Loess Plateau.

Tandem mass tag-based (TMT) quantitative proteomics analysis reveals the response of fine roots to drought stress in cotton (Gossypium hirsutum L.)

BackgroundCotton (Gossypium hirsutum L.) is one of the most important cash crops worldwide. Fine roots are the central part of the root system that contributes to plant water and nutrient uptake. However, the mechanisms underlying the response of cotton fine roots to soil drought remains unclear. To elucidate the proteomic changes in fine roots of cotton plants under drought stress, 70–75% and 40–45% soil relative water content treatments were imposed on control (CK) and drought stress (DS) groups, respectively. Then, tandem mass tags (TMT) technology was used to determine the proteome profiles of fine root tissue samples.ResultsDrought significantly decreased the value of average root diameter of cotton seedlings, whereas the total root length and the activities of antioxidases were increased. To study the molecular mechanisms underlying drought response further, the proteome differences between tissues under CK and DS treatments were compared pairwise at 0, 30, and 45 DAD (days after drought stress). In total, 118 differentially expressed proteins (DEPs) were up-regulated and 105 were down-regulated in the ‘DS30 versus CK30’ comparison; 662 DEPs were up-regulated, and 611 were down-regulated in the ‘DS45 versus CK45’ comparison. The functions of these DEPs were classified according to their pathways. Under early stage drought (30 DAD), some DEPs involved in the ‘Cutin, suberin, and wax synthesis’ pathway were up-regulated, while the down-regulated DEPs were mainly enriched within the ‘Monoterpenoid biosynthesis’ pathway. Forty-five days of soil drought had a greater impact on DEPs involved in metabolism. Many proteins involving ‘Carbohydrate metabolism,’ ‘Energy metabolism,’ ‘Fatty acid metabolism,’ ‘Amino acid metabolism,’ and ‘Secondary metabolite biosynthesis’ were identified as DEPs. Additionally, proteins related to ion transport, stress/defense, and phytohormones were also shown to play roles in determining the fine root growth of cotton plants under drought stress.ConclusionsOur study identified potential biological pathways and drought-responsive proteins related to stress/defense responses and plant hormone metabolism under drought stress. Collectively, our results provide new insights for further improving drought tolerance in cotton and other crops.

Drought resistance of ten ground cover seedling species during roof greening.

Roof greening is an important national policy for maintaining the hydrological balance in China; however, plant growth is limited by drought stress. This study aims to identify strong drought resistant plant species for roof greening from ten common species: Paeonia lactiflora, Hemerocallis dumortieri, Meehania urticifolia, Iris lactea var. chinensis, Hylotelephium erythrostictum, Sedum lineare, Iris germanica, Cosmos bipinnata, Hosta plantaginea, and Dianthus barbatus. By controlling the soil relative water content (RWC), we designed three treatments: moderate drought stress (40±2% < RWC < 45±2%), severe drought stress (RWC < 30±2%) and well-watered control (RWC > 75±2%). After the seedlings were provided different levels of water, their membrane permeability (MP), chlorophyll concentration (Chl), and superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX) activity were measured. Finally, the membership function method was used to assess the drought resistance of these species. The results showed that C. bipinnata and M. urticifolia were not suitable for moderate or severe drought stress and did not survive. The other species presented variations in physiological and biochemical parameters. The MP of He. dumortieri, I. lactea and Ho. plantaginea showed minor changes between the well-watered control and drought stress. Most of the species showed reduced SOD activity under moderate drought stress but increased activity under severe stress. All of the plant species showed decreases in the protective enzymes POD and APX with increasing drought stress. The membership function method was applied to calculate the plant species' drought resistance, and the following order of priority of the roof-greening plant species was suggested: He. dumortieri > I. germanica > I. lactea > D. barbatus > Hy. erythrostictum > S. lineare > Ho. plantaginea > P. lactiflora.

Photosynthetic CO&lt;sub&gt;2&lt;/sub&gt; response to soil water and its simulation using different models in leaves of two species

CO2 concentrations and soil moisture conditions are important factors in photosynthesis of trees. This study investigated the photosynthetic CO2 responses in the leaves of Prunus sibirica L. and Pinus tabulaeformis Carr. under eight soil water conditions in a semiarid loess hilly region. CO2-response curves and physiological parameters were fitted using a rectangular hyperbola model, nonrectangular hyperbola model, exponential equation, and modified rectangular hyperbola model. Results revealed the relative soil water content (RWCs) for P. sibirica required to maintain higher photosynthetic rate ranging from 46.5 to 81.6%, and that for P. tabulaeformis ranging from 35.4 to 84.5%. When RWCs exceeded these ranges, the net photosynthetic rate of both species decreased. CO2-response curves and three parameters, carboxylation efficiency, CO2-compensation point, and photorespiration rate, were well fitted by the four models when RWCs was appropriate for P. sibirica and P. tabulaeformis. When RWCs exceeded the optimal ranges, only the modified rectangular hyperbola model could precisely simulate the CO2-response curves and photosynthetic parameters of both species.

The Effects of Temperature and Humidity on a Field Population of Bradysia odoriphaga (Diptera: Sciaridae).

The production of Chinese chives is reduced throughout China due to a root-feeding dipteran pest Bradysia odoriphaga Yang et Zhang (Diptera: Sciaridae), therefore deciphering the conditions influencing its growth and development are important in developing ecological control strategies. A study was conducted from 2014 to 2017 to determine the relationship between the abundance of B. odoriphaga and temperature (atmospheric and soil), soil water content, and atmospheric humidity in a Chinese chive field in Beijing City, China. Numbers of adults peaked in March and October to November and were lowest in July to August and December to next February; numbers of larvae were highest in December to next February and lowest in July to August. From 2014 to 2017, the numbers of adults and larvae were significantly correlated with monthly mean atmospheric temperatures and soil temperatures, but were not significantly correlated with monthly mean atmospheric relative humidity and soil water content. However, for both adults and larvae, numbers were significantly greater with high soil water contents compared with drought treatment. The results of this study suggest that the very low soil water contents, high atmospheric temperatures, and high soil temperatures were critical for regulating field populations of B. odoriphaga.

Special issue in honour of Prof. Reto J. Strasser - Comparative analysis of drought stress response of maize genotypes using chlorophyll fluorescence measurements and leaf relative water content

The initial photochemical quantum efficiency of photosystem II (Fv/Fm) and performance index (PI), describing the ability of the photosynthetic apparatus to collect light energy, have been used to screen tolerance to drought stress by ten maize accessions, monitored by leaf relative water content (RWC) and soil water content (SWC). The Fv/Fm, PI, and RWC values were significantly reduced in drought-stressed plants. The analysis of chlorophyll a fluorescence induction rise from the basic dark-adapted fluorescence yield to the maximum (OJIP transient), distinguished accession Zea 1006 from Libya and Zea 612 from Italy, as the most tolerant and the least tolerant genotypes. The maize genotypes were classified using the Principal Component Analysis (PCA) and clustering methods, based on Fv/Fm and PI values, leaf RWC and SWC. Genotypes from Egypt and Libya were differentiated from genotypes from Europe, Russia and the USA.