Response of plant physiological parameters to soil water availability during prolonged drought is affected by soil texture

Soil water deficit is increasingly threatening the sustainable vegetation restoration and ecological construction on the Loess Plateau of China due to the climate warming and human activities. To determine the response thresholds of Amygdalus pedunculata (AP) and Salix psammophila (SP) to soil water availability under different textural soils, we measured the changes in net photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i), leaf water potential (ψ_w), water use efficiency (WUE) and daily transpiration rate (T_d) of the two plant species during soil water content (SWC) decreased from 100% field capacity (FC) to 20% FC in the sandy and loamy soils on the Loess Plateau in the growing season from June to August in 2018. Results showed that P_n, G_s, WUE and T_d of AP and SP remained relatively constant at the beginning of soil water deficit but decreased rapidly as plant available soil water content (PASWC) fell below the threshold values in both the sandy and loamy soils. The PASWC thresholds corresponding to P_n, G_s and C_i of AP in the loamy soil (0.61, 0.62 and 0.70, respectively) were lower than those in the sandy soil (0.70, 0.63 and 0.75, respectively), whereas the PASWC thresholds corresponding to P_n, G_s and C_i of SP in the loamy soil (0.63, 0.68 and 0.78, respectively) were higher than those in the sandy soil (0.58, 0.62 and 0.66, respectively). In addition, the PASWC thresholds in relation to T_d and WUE of AP (0.60 and 0.58, respectively) and SP (0.62 and 0.60, respectively) in the loamy soil were higher than the corresponding PASWC thresholds of AP (0.58 and 0.52, respectively) and SP (0.55 and 0.56, respectively) in the sandy soil. Furthermore, the PASWC thresholds for the instantaneous gas exchange parameters (e.g., P_n and G_s) at the transient scale were higher than the thresholds for the parameters (e.g., T_d) at the daily scale. Our study demonstrates that different plant species and/or different physiological parameters exhibit different thresholds of PASWC and that the thresholds are affected by soil texture. The result can provide guidance for the rational allocation and sustainable management of reforestation species under different soil conditions in the loess regions.     

沙地樟子松人工林土壤氮矿化特征

土壤氮(N)的有效性是沙地林生态系统生产力和稳定性的关键限制因子。本研究以科尔沁沙地樟子松人工林为研究对象，分析测定了10~60 a林龄土壤NH₄⁺-N、NO₃^--N和矿质N含量、氨化速率、硝化速率和N矿化速率的变化规律。结果表明：樟子松人工林土壤NH₄⁺-N、NO₃^--N和矿质N含量，随着不同林龄在10~60 a内表现出增加的趋势，其中10~30 a增幅较小，40~60 a显著提高；随着土层深度增加而减小，主要集中在0~20 cm，呈现出表聚性。不同林龄樟子松人工林土壤氨化速率、硝化速率和矿化速率均随林龄增加而增加，随土层深度的增加而降低，其中0~40 cm土层明显大于40~100 cm。通过双因素方差分析，得出林龄与土层对各矿化指标影响显著。土壤矿化指标与人工林地上樟子松株高、胸径、冠幅以及土壤有机碳、全氮、碱解氮有显著的正相关关系。通过冗余分析(RDA)表明，影响不同林龄土壤矿化指标的主要环境因子为全氮、全磷、有机碳；影响不同土层土壤矿化指标的主要环境因子为全氮、碱解氮、有机碳。因此，樟子松人工林能够改善沙地土壤N的有效性，幼龄林和中龄林改善效果较小，近成熟林和成熟林改善效果明显；对表层土的改善效果优于深层土；土壤肥力是影响土壤矿化指标的主要环境因子。     

三唑酮对木霉根际竞争定殖的影响

 在粘壤土中施用4~12μg/g土三唑酮能提高耐药木霉菌株在西瓜根尖4~1cm处根际土中的种群密度。4μg三唑酮处理的木霉根际竞争定殖指数、以及在4~8cm和10~14cm根段的根际木霉种群密度均高于不施药对照。土壤接种量为1×10³cfu/g土时木霉菌在西瓜根际增殖的比例较接种量为1×10⁶cfu/g土时大,2种接种量下三唑酮处理的根际木霉种群密度分别高于相应的不加药对照。在质地较好、C/N比值较高的粘壤土中木霉菌在西瓜根际的种群密度较砂壤土和粘土大,三唑酮对木霉在西瓜根际的增殖作用也较明显。     

Effects of three types of soil amendments on yield and soil nitrogen balance of maize-wheat rotation system in the Hetao Irrigation Area,China

Excessive fertilization combined with unreasonable irrigation in farmland of the Hetao Irrigation Area (HIR), China, has resulted in a large amount of nitrogen (N) losses and agricultural non-point source pollution. Application of soil amendments has become one of the important strategies for reducing N losses of farmland. However, there is still no systematic study on the effects of various soil amendments on N losses in the HIR. In this study, three types of soil amendments (biochar, bentonite and polyacrylamide) were applied in a maize-wheat rotation system in the HIR during 2015-2017. Yields of maize and wheat, soil NH₃ volatilization, N₂O emission and NO₃^- leaching were determined and soil N balance was estimated. The results showed that applications of biochar, bentonite and polyacrylamide significantly increased yields of maize by 9.2%, 14.3% and 13.3%, respectively, and wheat by 9.2%, 16.6% and 12.3%, respectively, compared with the control (fertilization alone). Applications of biochar, bentonite and polyacrylamide significantly reduced soil N leaching by 23.1%, 35.5% and 27.1%, soil NH₃-N volatilization by 34.8%, 52.7% and 37.8%, and soil N surplus by 23.9%, 37.4% and 30.6%, respectively. Applications of bentonite and polyacrylamide significantly reduced N₂O-N emissions from soil by 37.3% and 35.8%, respectively, compared with the control. Compared with application of biochar, applications of bentonite and polyacrylamide increased yields of maize and wheat by 5.1% and 3.5%, respectively. Our results suggest that soil amendments (bentonite and polyacrylamide) can play important roles in reducing N losses and increasing yield for the maize-wheat rotation system in the HIR, China.     

Spread of levan-positive populations of <Emphasis Type="Italic">Pseudomonas savastanoi</Emphasis> pv. <Emphasis Type="Italic">savastanoi</Emphasis>, the causal agent of olive knot,in central Italy

Mixtures of wet vegetable wastes (Brassica, carrot or onion) and dry onion waste were composted at 50 °C for 7 days. The incorporation of the raw or composted vegetable waste mixtures into sandy loam, silt and peat soils reduced the viability of sclerotia of S. cepivorum in glasshouse pot bioassays. The reduction in viability was dependent on waste type, rate of incorporation, duration of exposure and soil type. Onion waste was the most effective waste type in reducing sclerotia viability in all three soils. The Brassica and carrot wastes were as effective as the onion waste in silt soil but less effective in sandy loam and peat soil. A 50% w/w incorporation rate of the wastes gave the largest reduction in viability, with an increase in reduction over time. Composted onion waste reduced sclerotia viability under glasshouse and field conditions although the effect was smaller in the field. Composted onion waste incorporated into soil at 50% w/w reduced the incidence of Allium white rot on onion seedlings in glasshouse pot tests. Incidence and control of the disease differed with soil type. The most consistent control was achieved in peat soil whereas no control was observed in silt soil. Incorporation of the waste 2 months prior to sowing or transplanting reduced seedling emergence in sandy loam soil and growth in all three soil types. The potential for field application of composted vegetable wastes as a sustainable method for control of Allium white rot and waste disposal is discussed.     

Sulcotrione soil persistence and mobility in summer maize and winter wheat crops

Sulcotrione soil persistence in spring maize ( Zea mays L.) crops grown on a sandy loam soil was greater at pH 5·5 and 6·0 (soil half-life T _1/2≈58 days) than at pH 7·1 ( T _1/2 = 44 days). Sulcotrione was also applied as recommended on a summer maize crop at the five- to six-leaf growth stage, grown on a sandy loam soil. Sulcotrione soil half-life was 44 days, and the herbicide remained mainly in the 0- to 5-cm surface soil layer during the cropping period, in spite of the high water solubility and the heavy rains at the end of August; lower sulcotrione concentrations (10–18% of the total during the 2-month period after sulcotrione application) were detected in the 5- to 10-cm surface soil layer. The herbicide was applied pre-emergence to winter wheat ( Triticum aestivum L.) at four sites that differed in their soil texture and composition: loamy sand, sandy loam, loam and clay loam. Persistence was greater in the soils containing more organic matter. In soils having similar organic matter contents, persistence was lower in the soil containing more sand relative to loam and clay. During the winter crops, sulcotrione moved down to the 10- to 15-cm soil layer, in spite of the fact that the rains were lower in winter than in summer. Sulcotrione most generally was not detected in the 15–20 cm soil layer of the maize and winter wheat crops.     

Grazing alters sandy soil greenhouse gas emissions in a sand-binding area of the Hobq Desert,China

Deserts are sensitive to environmental changes caused by human interference and are prone to degradation. Revegetation can promote the reversal of desertification and the subsequent formation of fixed sand. However, the effects of grazing, which can cause the ground-surface conditions of fixed sand to further deteriorate and result in re-desertification, on the greenhouse gas (GHG) fluxes from soils remain unknown. Herein, we investigated GHG fluxes in the Hobq Desert, Inner Mongolia Autonomous Region of China, at the mobile (desertified), fixed (vegetated), and grazed (re-desertified) sites from January 2018 to December 2019. We analyzed the response mechanism of GHG fluxes to micrometeorological factors and the variation in global warming potential (GWP). CO₂ was emitted at an average rate of 4.2, 3.7, and 1.1 mmol/(m²•h) and N₂O was emitted at an average rate of 0.19, 0.15, and 0.09 µmol/(m²•h) at the grazed, fixed, and mobile sites, respectively. Mean CH₄ consumption was as follows: fixed site (2.9 µmol/(m²•h))>grazed site (2.7 µmol/(m²•h))>mobile site (1.1 µmol/(m²•h)). GHG fluxes varied seasonally, and soil temperature (10 cm) and soil water content (30 cm) were the key micrometeorological factors affecting the fluxes. The changes in the plant and soil characteristics caused by grazing resulted in increased soil CO₂ and N₂O emissions and decreased CH₄ absorption. Grazing also significantly increased the GWP of the soil (P<0.05). This study demonstrates that grazing on revegetated sandy soil can cause re-desertification and significantly increase soil carbon and nitrogen leakage. These findings could be used to formulate informed policies on the management and utilization of desert ecosystems.     

石羊河下游不同立地类型黑果枸杞种群分布格局

在样地调查的基础上，结合相邻格子取样方法，采用扩散系数（C）、丛生指标（I）、负二项参数(K)、聚块性系数（C_a）、平均拥挤指标（m*）、聚集度指标（G）、Moristia指数（I_δ）、Green指数（I_G）等8个指标，对石羊河下游不同立地类型黑果枸杞种群分布格局、聚集强度进行了研究，结果表明：①沙地和盐碱地黑果枸杞个体数量较多，聚集程度相对较高，砾石和固定半固定沙地黑果枸杞的个体数量较少，聚集程度相对较低；②盐碱地和沙地黑果枸杞种群呈现聚集分布，固定半固定沙地和砾石样地相对于沙地和盐碱地的聚集程度有所减弱，有一定的随机趋势；③不同发育阶段的黑果枸杞种群格局类型总体呈现聚集分布的特点，随着龄级的增大，黑果枸杞种群分布格局表现出由聚集向均匀分布的变化趋势。     

基于HYDRUS-1D的不同质地土壤入渗过程数值模拟

基于HYDRUS-1D软件,对不同土质(淤泥、粉砂壤土、砂质粘壤土)的灌溉方案进行了系统的数值实验,模拟灌溉结束时及灌溉结束24 h之后的土壤剖面含水量和土壤湿润锋的变化情况。结果表明:在不产生径流的情况下,灌溉结束24 h后土壤的含水量分布和湿润深度只与土壤种类和灌溉量有关,与灌溉速度无关;对透水性较好的土质,灌溉水分重分布明显,以粉砂壤土灌溉速率0.7 cm·h~(-1)和灌溉时间3 h为例,灌溉结束时和灌溉24 h后土壤湿润深度分别为9.2 cm和20.6 cm,有55.3%的灌溉水参加了水分重分布;土壤湿润深度与灌溉量之间存在线性关系,拟合直线的斜率介于5.15(淤泥)和5.95(砂质黏壤土)之间。     

Crawler phenology and generation development of the Florida wax scale,ceroplastes floridensis,on citrus planted in two soil types

Appearance of Florida wax scale (FWS) crawlers in citrus groves planted in sandy soil preceded that in groves planted in loam. The duration of crawler presence was longer on citrus in loam than in sandy soil. Mean age, as expressed by weighted developmental stage, yielded a linear regression with time. FWS develops two generations per year, which on sandy soil appear earlier and develop faster to the preovipositional stage than on loam. The size of ovipositing females was in direct correlation with the duration of development.     

The influence of tillage on the weed flora in a succession of winter wheat crops on a clay loam soil and a silt loam soil

Weed populations were monitored for 4 years on two experiments designed to compare the effect of different primary tillage treatments on winter wheat (Triticum aestivum L.) cropping. Ploughing was compared with deep and shallow tine cultivation and with no tillage on both a clay loam and a silt loam over chalk. Soil-acting residual herbicides were used to control weeds, especially Alopecurus myosuroides Huds. and Avena fatua L. Dicotyledonous weeds were uncommon on the clay loam but on the silt loam, in a year when no residual herbicide was used, they were most numerous where the soil was disturbed most. In other years there was little difference in the number emerging. Six species were reduced in number by reduced cultivation or no tillage, whilst four species, including two grasses, were increased. At both sites, A. myosuroides was more numerous on direct drilled and tine cultivated plots than on ploughed. Herbicides gave good control on the silt loam but failed to control the weed on the clay loam. On the clay loam, A. fatua was most numerous on tine cultivated plots and a combination of herbicides and roguing produced a decline in the population.     

三种拟除虫菊酯类农药在砂土和壤土中的淋溶行为

采用土柱淋溶法和气相色谱法研究了3种拟除虫菊酯类农药三氟氯氰菊酯、联苯菊酯和高效氯氰菊酯在热带地区主要土壤类型砂土和壤土中的淋溶特性。结果表明:3种拟除虫菊酯类农药在砂土和壤土中主要残留于第1段土壤 (0～5 cm) 中,且驻留量随土壤深度增大而减少。三氟氯氰菊酯、高效氯氰菊酯和联苯菊酯在砂土中的R_i值分别为52.86%、94.73%和83.19%,在壤土中的R_i值分别为54.70%、77.28%和55.33%,均大于50%。根据农药在土壤中的淋溶性等级划分标准,3种药剂均属于难淋溶农药,不易对地下水造成污染。本研究结果可为热带地区土壤和地下水中农药污染修复提供参考。     

吡虫啉和毒死蜱对尿素氮在土壤中转化的影响

为了考察杀虫剂施用对尿素态氮在土壤中转化过程的影响,采用室内培养法,通过测定土壤铵态氮和硝态氮质量分数以及反硝化损失的动态变化,研究了在施用尿素的土壤（有效氮含量为200 mg/kg）中分别添加不同剂量的吡虫啉和毒死蜱2种杀虫剂时,杀虫剂对尿素的水解、土壤氮的硝化及反硝化过程的影响。结果表明:吡虫啉和毒死蜱各剂量处理在第3天时对尿素水解具有显著的促进作用（PPPPP<0.01）,减少反硝化损失量39.69%。     

Ecological stoichiometry and biomass response of Agropyron michnoi Roshev. under simulated N deposition in a sandy grassland,China

Sandy grassland in northern China is a fragile ecosystem with poor soil fertility. Exploring how plant species regulate growth and nutrient absorption under the background of nitrogen (N) deposition is crucial for the management of the sandy grassland ecosystem. We carried out a field experiment with six N levels in the Hulunbuir Sandy Land of China from 2014 to 2016 and explored the Agropyron michnoi Roshev. responses of both aboveground and belowground biomasses and carbon (C), N and phosphorus (P) concentrations in the plant tissues and soil. With increasing N addition, both aboveground and belowground biomasses and C, N and P concentrations in the plant tissues increased and exhibited a single-peak curve. C:N and C:P ratios of the plant tissues first decreased but then increased, while the trend for N:P ratio was opposite. The peak values of aboveground biomass, belowground biomass and C concentration in the plant tissues occurred at the level of 20 g N/(m²·a), while those of N and P concentrations in the plant tissues occurred at the level of 15 g N/(m²·a). The maximum growth percentages of aboveground and belowground biomasses were 324.2% and 75.9%, respectively, and the root to shoot ratio (RSR) decreased with the addition of N. N and P concentrations in the plant tissues were ranked in the order of leaves>roots>stems, while C concentration was ranked as roots>leaves>stems. The increase in N concentration in the plant tissues was the largest (from 34% to 162%), followed by the increase in P (from 10% to 33%) and C (from 8% to 24%) concentrations. The aboveground biomass was positively and linearly correlated with leaf C, N and P, and soil C and N concentrations, while the belowground biomass was positively and linearly correlated with leaf N and soil C concentrations. These results showed that the accumulation of N and P in the leaves caused the increase in the aboveground biomass, while the accumulation of leaf N resulted in the increase in the belowground biomass. N deposition can alter the allocation of C, N and P stoichiometry in the plant tissues and has a high potential for increasing plant biomass, which is conducive to the restoration of sandy grassland.     

Uptake and residues of aldicarb in sugarbeet leaves

The breakdown of aldicarb and its oxidation products (the sulphoxide and the sulphone, aldoxycarb), under field conditions in 1976, were studied on three different types of soil (a sandy loam, a silt loam and a sandy clay loam that were normally cropped with sugarbeet). Residues were determined in leaves, stems, roots and soil, and related to aphid counts. Higher doses were needed on heavy soils in order to obtain a sufficient concentration in the leaves and thus provide an efficient treatment for aphid control. Weather conditions, especially rainfall, also affected the residue content. At harvest, the sugar beet tops used for fodder can contain residues which vary widely, depending on dosage, soil type and climatic conditions.     

土壤棉黄萎病菌选择性培养基——棉选一号

 棉花黄萎病的发生发展与土壤中微菌核的数量有着密切关系.本文介绍一种用于检验土壤内棉黄萎病菌的选择性培养基——棉选一号.其成份为:NaNO₃ 2g、MgSO₄·7H₂O 0.5g、K₂HPO₄ 1g、Fe₂（SO₄）₃·XH₂O 0.01g.KCl 0.5g、蔗糖5g、琼脂15g、蒸馏水1000ml、氯霉素300mg、井岗霉素2.5ppm、五氯硝基苯350ppm、克菌丹0.5ppm.这种培养基能有效地分离自然土壤中黄萎病菌的微菌核,而极少受其他微生物的干扰,由于培养基上菌落大、黑色、微菌核呈放射状,故易用肉跟计数微菌核的数量.     

西甜瓜果斑病菌avrRxo1同源基因激发玉米Rxo1抗性产生的研究

生物信息学分析发现西(甜)瓜果斑病菌(Acidovorax citrulli,Ac)基因组中存在水稻条斑病菌(Xanthomonas oryzae pv.oryzicola,Xoc)avrRxo1的同源基因avrRxo1_(Ac)。为了揭示avrRxo1_(Ac)是否能够激发玉米R基因Rxo1介导的过敏反应(Hypersensitive response,HR),本研究克隆了avrRxo1_(Ac)基因;氨基酸同源性分析结果显示:AvrRxo1_(Ac)与AvrRxo1的同源性为53.16%。将avrRxo1_(Ac)置于Xoc的avrRxo1突变体中,发现其不能恢复该突变体在含有Rxo1玉米上激发HR反应的能力;借助农杆菌瞬时表达体系发现AvrRxo1A,也不能在Rxo1玉米上激发HR反应。这些结果表明avrRxo1_(Ac)-Rxo1互作不表现为基因-对-基因关系,暗示Rxo1抗病基因转入西甜瓜中,将不能起到抗西(甜)瓜细菌性果斑病的作用。     

Leaching of aldicarb and thiofanox,and their uptake in soils by sugarbeet plants

The leaching of aldicarb and thiofanox in soils (sandy loam, silt loam and sandy clay loam), and their uptake by sugarbeet plants were studied. Three irrigation levels were maintained: half, normal and double dose. The residues were determined as the sum of the insecticidal metabolites (parent compound + sulphoxide+ sulphone) for both pesticides. Leaching was greatly influenced by the amount of water added and the soil type. Under normal conditions, leaching seemed to proceed very slowly, keeping the chemicals available for uptake by the root systems for a long time. The concentration of insecticide in the leaves was highest in beets grown on sandy loam and lowest in those grown on sandy clay loam. The quantity of irrigation did not influence the residue concentration in the leaves greatly, although its influence was obvious on the total residue present (μg per plant). Increasing the water dose always resulted in a higher total residue, and a greater plant weight. The breakdown in the soils was directly related to the water dose. The experiments show that thiofanox was more stable than aldicarb and was taken up by sugarbeet to a greater extent.     

Persistence and movement of ethofumesate in soil*

Persistence of ethofumesate [(±)2-ethoxy-2.3-dihydro-3,3-dimethylbenzofuran-5-yl-methansulphonate] in soil was associated with soil temperature. Ethofumesate applied at 4.5 kg/ha in November persisted about twice as long in soil as that applied the following March. In another field study, 88–91% of the herbicide had dissipated after 24 weeks in sandy loam soil, compared to 72–77% in loam soil when it was applied at rates of 2.2, 3.4, 4.5, and 9.0 kg/ha. The rate of degradation was independent of the initial rate of chemical applied. The time required for 50% of the herbicide to dissipate in sandy loam and loam soils was 7.7 and 12.6 weeks, respectively. The movement of ethofumesate in these two soils over a 24-weeks sampling period was confined mainly to the upper 7.5 cm of the soil profile.     

Effects of water stress on growth phenology photosynthesis and leaf water potential in Stipagrostis ciliata (Desf.) De Winter in North Africa

Stipagrostis ciliata (Desf.) De Winter is a pastoral C₄ grass grown in arid regions. This research work focused on assessing the growth of S. ciliata accessions derived from two different climate regions (a wet arid region in the Bou Hedma National Park in the central and southern part of Tunisia (coded as WA), and a dry arid region from the Matmata Mountain in the south of Tunisia (coded as DA)) under water stress conditions. Specifically, the study aimed to investigate the phenological and physiological responses of potted S. ciliata seedlings under different water treatments: T₁ (200 mm/a), T₂ (150 mm/a), T₃ (100 mm/a) and T₄ (50 mm/a). Growth phenology, net photosynthesis (P_n), stomatal conductance (g_s), midday leaf water potential (Ψ_md), predawn leaf water potential (Ψ_pd), soil water content (SWC) and soil water potential (Ψ_s) were observed during the water stress cycle (from December 2016 to November 2017). The obtained results showed that the highest growth potential of the two accessions (WA and DA) was recorded under treatment T₁. The two accessions responded differently and significantly to water stress. Photosynthetic parameters, such as P_n and g_s, decreased sharply under treatments T₂, T₃ and T₄ compared to treatment T₁. The higher water stress increased the R/S ratio (the ratio of root dry biomass to shoot dry biomass), with values of 1.29 and 2.74 under treatment T₄ for accessions WA and DA, respectively. Principal component analysis (PCA) was applied, and the separation of S. ciliata accessions on the first two axes of PCA (PC1 and PC2) suggested that accession DA was detected in the negative extremity of PC1 and PC2 under treatments T₁ and T₂. This accession was characterized by a high number of spikes. For treatments T₃ and T₄, both accessions were detected in the negative extremity of PC1 and PC2. They were characterized by a high root dry biomass. Therefore, S. ciliata accessions responded to water stress by displaying significant changes in their behaviours. Accession WA from the Bou Hedma National Park (wet arid region) showed higher drought tolerance than accession DA from the Matmata Mountain (dry arid region). S. ciliata exhibits a significant adaptation capacity for water limitation and may be an important species for ecosystem restoration.