Higher Soil Water Content Research Articles

干旱条件下接种AM真菌对小马鞍羊蹄甲幼苗根系的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 干旱条件下接种AM真菌对小马鞍羊蹄甲幼苗根系的影响 DOI: 10.5846/stxb201601280209 作者: 作者单位: 中国科学院生态环境研究中心,中国科学院生态环境研究中心,中国科学院生态环境研究中心 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（31170581） Inoculation with arbuscular mycorrhizal fungi enhances the root system of Bauhinia faberi var. microphylla seedlings under drought stress conditions Author: Affiliation: Research center for Eco-Environmental Sciences,Chinese Academy of Sciences,Research center for Eco-Environmental Sciences,Chinese Academy of Sciences,Research center for Eco-Environmental Sciences,Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了探讨岷江干旱河谷丛枝菌根真菌（AMF）对寄主植物幼苗根系的影响，通过接种购买的AMF摩西球囊霉菌（Funneliformis mosseae）到优势乡土灌木小马鞍羊蹄甲（Bauhinia faberi var. microphylla）幼苗，在重度、中度和轻度干旱条件下培养3个月，研究不同干旱条件下AMF对幼苗根系形态特征、结构特征、功能性状的影响。方差分析结果表明：（1）3种干旱胁迫条件下，接菌均显著增加了幼苗的根总长、根表面积、根分枝数、根尖数（P < 0.001），在中度胁迫和轻度胁迫下，接菌显著促进根鲜重、根体积的增加（P < 0.001），轻度胁迫条件下接菌幼苗的根鲜重、根总长、根表面积、根体积、根尖数最高并显著高于其它处理，但接菌与未接菌的根平均直径之间没有显著差异；（2）接菌幼苗根系趋向于叉状分支结构，在重度胁迫时，叉状分支趋势更显著（P < 0.001）；（3）接菌幼苗的根比例都显著小于未接菌的，但幼苗比根长不存在显著差异。相关分析结果表明：菌根侵染率与根鲜重、根总长、根表面积、根体积、根分枝数、根尖数呈极显著正相关（P < 0.001），与拓扑指数、根比例呈极显著负相关（P < 0.001）。研究表明，在干旱条件下，AMF虽然没有提高生长初期的根系的吸收效率，但接种AMF显著影响幼苗根系形态特征和结构特征，更利于植物适应干旱环境，并且AMF对幼苗根系的促生作用随着干旱胁迫程度减轻而提高。 Abstract:Arbuscular mycorrhizal fungi (AMF) can develop a symbiotic relationship with the roots of most terrestrial plants, which can improve the drought tolerance of the host plants. Based on our previous studies, AMF play a critical role in promoting native plant growth in the arid valley of the Minjiang River, China. Furthermore, the effects of AMF on root growth are as important as their effects on aboverground growth. To understand how plant roots respond to AMF under different drought stress conditions, we designed a completely randomized full factorial pot experiment in a greenhouse in the arid valley of the Minjiang River. We added one common AMF (Funneliformis mosseae, FM) to the roots of seedlings from a dominant native shrub (Bauhinia faberi var. microphylla), using three different drought stress conditions. Continuous drought stress was induced by watering the seedlings with distilled water at one-day intervals for three months at low (40%), medium (60%), and high levels (80%) of the field capacity. At the end of the experiment, we harvested the seedlings, and cleaned their roots with distilled water. We subsequently measured the root fresh weight, scanned the roots with a root scanner (EPSON 11000XL), and obtained variables such as root length, root surface area, root volume, root forks, and number of root tips with WinRhizo. We subsequently analyzed the root architecture and the functional characteristics of the B. faberi seedlings to address the relationship between root development and AMF presence under different levels of drought stress. We used one-way ANOVAs, two-way ANOVAs, LSD fitting methods, and Pearson's correlations for our statistical analyses. Inoculation of FM significantly increased the total root length, root surface area, root forks, and the number of root tips under all three drought stress conditions (P < 0.001). In addition, under medium and high soil water content, it significantly increased root fresh weight and root volume (P < 0.001). More specifically, high soil water conditions resulted in the significantly highest root fresh weight, total root length, root surface area, root volume, and number of root tips after FM addition. Nonetheless, there was no significant difference in average root diameter between inoculated and non-inoculated seedlings. Inoculated seedlings tended to develop a dichotomous branching style, which was more profound at low (40% of field capacity) soil water content (P < 0.001). Furthermore, the root fractions of inoculated seedlings were significantly smaller than the non-inoculated seedlings (P < 0.001). However, there was no significant difference in specific root length among all the treatments. Root fresh weight, root length, root surface area, root volume, root forks, and number of root tips correlated significantly and positively with colonization rate (P < 0.001). In contrast, topological index and root fraction were significantly and negatively correlated with colonization rate (P < 0.001). Overall, we found that, although AMF did not improve the root absorption efficiency in the initial growth period of B. faberi, AMF presence significantly affected seedling root morphology and root functional characteristics. These latter effects enhanced B. faberi seedling growth, which allowed the plants to adapt to drought conditions. Finally, the positive effects of AMF on root growth increased with improving water conditions. 参考文献 相似文献 引证文献

Effects of Water Saving Practices on Winter Wheat and Summer Maize Yields in South Loess Plateau of Northwest China

A field experiment, laid out in Randomized Complete Block Design (RCBD) with split plot arrangement having four replications, was conducted at the south edge of loess plateau, Shaanxi, China to evaluate the responses of winter wheat and summer maize to different water saving management practices involving four mulching and irrigation treatments, i.e., plastic mulch ridge and straw mulch furrow combined with deficit irrigation (RF+DI), straw mulch combined with deficit irrigation (SM+DI), Deficit Irrigation (DI), and Conventional Flood Irrigation (CFI). Soil temperature and moisture during the crop growth were monitored in two years. RF+DI treatment significantly increased maize yield, and it also had higher wheat yield than SM+DI treatment. SM+DI treatment increased maize yield; however, it did not increase winter wheat yield. Soil water content in RF+DI and SM+DI treatments was significantly higher than those of CFI or DI treatments. Compared with RF+DI treatment, SM+DI treatment had higher soil water content (0-20 cm); however, it had the lowest heat 741 Degree Days of Soil (DDs) among the four treatments. The low soil temperature in SM+DI plots, especially in early spring, delayed winter wheat growth stages and development, thus reduced grain yield compared with RF+DI treatment. The positive effects of ridge-furrow system on both wheat and maize yield could be explained by harmonizing soil moisture and temperature by this treatment.

Effects of water-saving irrigation on weed infestation and diversity in paddy fields in East China

The purpose of the article is to investigate the effects of water-saving irrigation on weed infestation and diversity in paddy fields; a two-year field experiment was conducted in Gaoyou Irrigation District, China. The responses of two irrigation treatments, controlled irrigation (CI) and traditional irrigation (TI), were observed and compared. The irrigation water use, yield, weed density, coverage ratio, height, species richness, density, dominant species, Shannon–Wiener index, and Pielou index were examined to analyze the water productivity, weed infestation, and diversity in paddy fields under the two treatments. The results showed that the water conditions were similar before the late tillering stage, and thereafter the CI fields were alternatively dry and wet with shallow standing water and low soil water content, while the TI fields were mostly continuously flooded by deep standing water and high soil water content. Irrigation water use for CI was 46.8% lower than TI. The CI treatment reduced weed density by 38.0%, decreased coverage ratio by 13.8%, and resulted in a 39.0% increase in weed height. Fewer species were found in CI fields than TI fields. The Shannon–Wiener index decreased by 11.5%, and the Pielou index increased by 3.2%. The changed water regime under CI not only impeded the growth of dominant species but also placed the whole weed community at a relatively stable level with reduced weed density. Meanwhile, aquatic weeds were well controlled; however, semi-aquatic weeds became the dominant species. In general, CI effectively reduced the risk of weed outbreaks, and weed diversity also decreased when it reduced irrigation water use.

Impacts of grass removal on wetting and actual water repellency in a sandy soil

Abstract Soil water content and actual water repellency were assessed for soil profiles at two sites in a bare and grasscovered plot of a sand pasture, to investigate the impact of the grass removal on both properties. The soil of the plots was sampled six times in vertical transects to a depth of 33 cm between 23 May and 7 October 2002. On each sampling date the soil water contents were measured and the persistence of actual water repellency was determined of field-moist samples. Considerably higher soil water contents were found in the bare versus the grass-covered plots. These alterations are caused by differences between evaporation and transpiration rates across the plots. Noteworthy are the often excessive differences in soil water content at depths of 10 to 30 cm between the bare and grass-covered plots. These differences are a consequence of water uptake by the roots in the grass-covered plots. The water storage in the upper 19 cm of the bare soil was at least two times greater than in the grass-covered soil during dry periods. A major part of the soil profile in the grass-covered plots exhibited extreme water repellency to a depth of 19 cm on all sampling dates, while the soil profile of the bare plots was completely wettable on eight of the twelve sampling dates. Significant differences in persistence of actual water repellency were found between the grass-covered and bare plots.

From facilitative to competitive interactions between woody plants and plants with crassulacean acid metabolism (CAM): The role of hydraulic descent

AbstractWoody plants may facilitate the establishment of seedlings with crassulacean acid metabolism (CAM) by ameliorating the abiotic environment through an increase in soil water availability. Because of the low transpiration rate in shallow‐rooted CAM plants and the consequently high soil water contents in the shallow soil, deep‐rooted trees in tree–CAM associations could perform hydraulic descent transporting water from wetter shallow soil to drier deep soil in arid environments. It remains unclear, however, whether a high rate of hydraulic descent can turn the facilitation of CAM plants by woody plants into competition. In this study, we develop a mechanistic model to investigate the facilitation of shallow‐rooted CAM plants by deep‐rooted woody plants in the access to soil water resources along a rainfall gradient. The model results show that in the case of low‐to‐moderate root overlap woody plants could facilitate CAM plants in access to soil water; this effect is mainly induced by the reduction in evaporation from the soil surface due to shading. Both shading and hydraulic descent decrease (or hydraulic lift increases) along a rainfall gradient, thereby favoring facilitation. Investment in deep roots by woody plants is usually thought to increase niche differentiation with shallow‐rooted plants, thereby reducing the competition and promoting species coexistence. This study indicates that deep root development could also favor competition through the mechanism of hydraulic descent, thereby changing our understanding of the role of root depth in niche differentiation between shallow and deep‐rooted plants.

Effects of Maize Residue Quality and Soil Water Content on Soil Labile Organic Carbon Fractions and Microbial Properties

Investigating the effects of residue chemical composition on soil labile organic carbon (LOC) will improve our understanding of soil carbon sequestration. The effects of maize residue chemical composition and soil water content on soil LOC fractions and microbial properties were investigated in a laboratory incubation experiment. Maize shoot and root residues were incorporated into soil at 40% and 70% field capacity. The soils were incubated at 20 °C for 150 d and destructive sampling was conducted after 15, 75, and 150 d. Respiration, dissolved organic carbon (DOC), hot-water extractable organic carbon (HEOC), and microbial biomass carbon (MBC) were recorded, along with cellulase and β-glucosidase activities and community-level physiological profiles. The results showed that the cumulative respiration was lower in root-amended soils than in shoot-amended soils, indicating that root amendment may be beneficial to C retention in soil. No significant differences in the contents of DOC, HEOC and MBC, enzyme activities, and microbial functional diversity were observed between shoot- and root-amended soils. The high soil water content treatment significantly increased the cumulative respiration, DOC and HEOC contents, and enzyme activities compared to the low soil water content treatment. However, the soil water content treatments had little influence on the MBC content and microbial functional diversity. There were significantly positive correlations between LOC fractions and soil microbial properties. These results indicated that the chemical composition of maize residues had little influence on the DOC, HEOC, and MBC contents, enzyme activities, and microbial functional diversity, while soil water content could significantly influence DOC and HEOC contents and enzyme activities.

Stress transmission coefficient: A soil stress transmission property for a loading process

Predicting soil stress with analytical models requires proper selection of the models’ concentration factor. But due to the insufficient knowledge about the effects of soil conditions on stress transmission, little is known about how the concentration factor varies with soil states and loading conditions. Thus there is a need to supply specifically defined parameters with clearer physical meanings for soil stress transmission while easily being measured with simple laboratory setups. The function of the concentration factor was transformed and a dimensionless factor standing for soil-induced attenuation on the stress transmission between two points, (σ0-σz)/σ0, was derived, which complement, σz/σ0, is the soil stress transmission coefficient and is denoted as STC. Since soil stress transmission property is affected by soil states and loading conditions, a modified oedometer testing setup with a soil stress sensor was used to evaluate controlled soil properties on STCs. Totally 15 soil states were tested by controlling 5 soil water contents and 3 bulk densities. Correlation analysis were performed between measured STCs and soil state parameters, i.e. water content, bulk density and soil strength. The concentration factor was then back-calculated from the acquired STCs.The highly linear correlation between soil stress and applied surface stress indicates a stable STC for each particular soil state, suggesting that the theoretically derived STC could be used as a specific mechanical property to quantify soil stress transmission. In general, a high soil water content leads to an increased STC, meaning that wetter soils are more effective in transmitting the stress to deeper places. STC was also found both linearly decreased with dry bulk density and precompression stress. A higher soil strength imposes an improved shielding effect on soil stress transmission. The back-calculation of concentration factor from measured STCs illustrates that the proposed solution for soil stress transmission provides a means to define concentration factor for each soil state with measured result. Concentration factor varied from 2.64 to 12.39, being in agreement with the past reports. But the detail of how the concentration factor is affected by the changed states of soils is provided.

Half-precision Self-walking Variable Fertilization Seeder Design

The half-precision fertilization seeder of rice and wheat is designed against the problems of large straw mulching quantity, high soil water content, the traditional rice and wheat seeder easily blocked and poor fertilization seeding uniformity in Jianghuai region. The machine uses the rotary tillage stubble cleaning way to actively block and improves the traditional furrowing fertilization seeding method easy to cause winding grass. Electric control mode is used to drive the seed fertilizer shaft for sowing and fertilizing, the machine can carry on the straw returning to field, applying fertilizer, sowing, covering earth, rolling and other operations at one time, and can achieve the goal of half-precision fertilization seeding rice and wheat. The test results show that the machine has good anti-blocking performance and high operation efficiency. It works stably and reliably, and the various technical indexes meet the requirements of precision and half-precision mechanization planting, suitable for rice and wheat.

High atmospheric demand for water can limit forest carbon uptake and transpiration as severely as dry soil

AbstractWhen stressed by low soil water content (SWC) or high vapor pressure deficit (VPD), plants close stomata, reducing transpiration and photosynthesis. However, it has historically been difficult to disentangle the magnitudes of VPD compared to SWC limitations on ecosystem‐scale fluxes. We used a 13 year record of eddy covariance measurements from a forest in south central Indiana, USA, to quantify how transpiration and photosynthesis respond to fluctuations in VPD versus SWC. High VPD and low SWC both explained reductions in photosynthesis relative to its long‐term mean, as well as reductions in transpiration relative to potential transpiration estimated with the Penman‐Monteith equation. Flux responses to typical fluctuations in SWC and VPD had similar magnitudes. Integrated over the year, VPD fluctuations accounted for significant reductions of GPP in both nondrought and drought years. Our results suggest that increasing VPD under climatic warming could reduce forest CO2 uptake regardless of changes in SWC.

Simulating N2O emissions under different tillage systems of irrigated corn using RZ-SHAW model

Nitrous oxide (N2O) is a potent greenhouse gas (GHG), and agriculture is a global source of N2O emissions from soil fertility management. Yet emissions vary by agronomic practices and environmental factors that govern soil moisture and temperature. Ecosystem models are important tools to estimate N2O emissions by accounting for such variables, and models can strengthen field research. The objective of this study was to test RZ-SHAW predictions of crop production and N2O emissions from conventional till (CT) and no-till (NT) systems at high (HN) rate and low nitrogen input (LN) treatments in an irrigated corn (Zea mays L.) field in Colorado from 2003 to 2006 growing seasons. The model was calibrated using the HN-CT, and other treatments were used as validations. Additionally, the SHAW model was run in conjunction with RZWQM2 to account for differences in soil surface temperatures. Simulated crop yields were within 0.7 and 0.9% of measured yield for HN-NT and CT treatments, and 32 and 3% of measured yield for LN-NT and CT treatments, respectively. Spring soil temperatures were cooler by 2°C in NT compared to CT, and were correctly simulated using RZ-SHAW coupled model. RZ-SHAW simulated N2O emissions were slightly under predicted by 0.10 (1.5%) and 0.56 (7.1%) kgNha−1 for HN-NT and HN-CT treatments, respectively. Results for LN treatments showed larger differences in simulated N2O emissions and were over predicted by 0.11 (16%) kgNha−1 in NT and under predicted by 0.29 (29%) gNha−1day−1 in CT. Annual emissions were in close agreement, with observed and simulated showing 12 and 10% lower N2O emissions from HN-NT than HN-CT, respectively. Cooler surface soil temperature and higher soil water content in the HN-NT treatment caused slower breakdown of crop residue and slightly more denitrification than HN-CT, resulting in lower N2O emissions in HN-NT. This is the first test of the newly added GHG component in RZ-SHAW under no-till management, and results suggest with some improvements the model could be applied to quantify N2O emissions from different management practices.

Integrative Effects of Vine Water Relations and Grape Ripeness Level of Vitis vinifera L. cv. Shiraz/Richter 99. I. Physiological Changes and Vegetative-Reproductive Growth Balances

The water relations and physiological status of the grapevine are critical for obtaining a quality product and for fully exploring vineyard and grape potential. The objective of this investigation was to determine the effect of grapevine water status (induced by means of two field water capacity-based irrigation levels, 75% and 100%, applied at single and combined vine developmental stages) on morphological and physiological changes in Vitis vinifera L. cv. Shiraz/Richter 99 grapevines and grapes (harvested at different soluble solid levels) under field conditions. The integrative effects of vine water relations and grape ripeness level, specifically in a Mediterranean high winter rainfall area, have not yet been investigated systematically. The terroir affected the reaction of the vines to treatments. The soil displayed high water-holding capacity and a buffer against favourable evapotranspiration conditions, even with a western aspect and being subjected to long and relatively dry seasons, with frequent occurrence of high temperatures and grapevines with fully developed canopies. The vines did not seem overly stressed – in line with the relatively high base soil water fractions of mostly more than 50% of field water capacity. Primary and secondary leaf water potential and stem water potential displayed similar patterns and the water potential of the primary and secondary leaves was similar. Despite relatively high base soil water contents that prevented excessively low plant water potential and classic leaf and berry behaviour to surface, the vines still responded in a noticeable way to volume and timing of irrigation in relation to the grape ripeness level status. Water relations, ripeness level and terroir conditions showed an integrated, steering impact on physiological, vegetative and reproductive behaviour. Post-veraison irrigated vines were expected to maintain relatively high water potential during the last weeks of the ripening period, but this seemed not to be the case. All vines seemed to have recuperated/stabilised during this time, maintaining their water balances. Physical, physiological and compositional changes in the berry during late ripening under field conditions were clarified further. New information was obtained on the relationships between the behaviour of the root system, canopy and grapes and the changing terroir conditions during the ripening period.

Drivers of changes in agricultural intensity in Europe

The global demand for agricultural products will increase in the 21st century, unless major transformations in consumptive behaviour occur. To a large extent, production increases in agriculture will depend on intensifying existing agricultural systems. Yet, our understanding of what determines the spatial patterns of agricultural intensity and changes therein is limited. Here, we analysed agricultural intensity changes in Europe focussing on yields and fertiliser application for six major crop-type groups for the period 1990–2007. We applied random effects panel regressions to analyse the spatial determinants of intensity changes using a suite of biophysical and socio-economic variables. We found that yields increased and mineral nitrogen application decreased by approximately 10%, suggesting a decoupling of changes in output and input intensity in Europe’s agricultural systems. Yields and nitrogen application across crop-type groups were particularly high in Western and Central Europe, whereas Eastern Europe was characterised by lower yields and nitrogen application. We also found strong sub-national variation in intensity levels in respect to crop-type groups and indicators. Higher yields were typically related to higher fertilisation, high soil quality, less growing degree days, and high labour productivity. Higher nitrogen application rates, in turn, were related to high soil water and carbon contents, and high labour productivity. Our study provides insights into broad-scale agricultural intensity patterns in Europe that allow for identifying trade-offs between agriculture and the environment, as well as entry points for regionalised, targeted policy making towards a more sustainable management of Europe land systems.

Soil hydraulic properties as influenced by prairie restoration

Prairie restoration has received increased public attention in recent years for its ecosystem services. The objective of this study was to evaluate effects of prairie restoration on soil hydraulic properties as compared to native prairie (NP), grass and row-crop management. Soil cores (76mm diam.×76mm long) from six replicate locations were sampled to a 60-cm depth at 10-cm intervals from two prairie treatments, a continuous no-till treatment (NT), a long-term timothy grass (Phleum pratense L.) treatment (TM) and a row-crop (RC) treatment. The NP has never been tilled and the restored prairie (RP) was established in 1993. All treatments have Mexico silt loam (fine, smectitic, mesic, Vertic Epiaqualfs) soil. Bulk density, saturated hydraulic conductivity (Ksat), soil water retention and pore size distribution were determined. In-situ Ksat was measured using a constant head permeameter with five replications. Bulk density was significantly lower for NP than all treatments. Bulk density was significantly lower for the 0 to 10cm depth for all treatments, and the 10 to 30cm depth recorded the highest values. The in-situ Ksat of RP was lower than other treatments. The first horizon had the highest value for this parameter for all treatments. NP had significantly higher laboratory measured Ksat, and it was almost four times higher than RP. The 0 to 10cm depth of all treatments had significantly higher values for laboratory Ksat than other depths and the 50 to 60cm showed the lowest Ksat. NP had the highest macroporosity and fine-mesoporosity, while RP had the highest microporosity. NP had significantly higher water retention at saturation while RP had the highest water retention for soil water pressures of −33kPa, −100kPa and −1500kPa. Soil water retention was significantly higher in NP for −0.4kPa to −10kPa soil water pressures; at −20kPa NP, RP and RC had significantly higher water retention. The NP treatment had higher soil water content than the other treatments for the 0 to 10cm, 10 to 20cm, 20 to 30cm and 50 to 60cm depths at soil water pressure of −20kPa. The 30 to 40cm and 40 to 50cm depths of RP had higher soil water content at all soil water pressures. Results imply that prairie restoration influences some hydraulic properties in claypan soils; however, it is unlikely to achieve the original prairie soil characteristics due to the prior erosion of the top soil.

Interannual climatic variability effects on yield, berry and wine quality indices in long-term deficit irrigated grapevines, determined by multivariate analysis

Interannual climatic variability effects on yield, berry and wine quality indices in long-term deficit irrigated grapevines, determined by multivariate analysis Pascual Romero,1 Jose Ignacio Fern&aacute;ndez-Fern&aacute;ndez,2 Pablo Bot&iacute;a1 1Department of Natural Resources, Irrigation Group and Physiology of Stress, 2Department of Viticulture, The Murcian Institute of Agri-Food Research and Development (IMIDA), Murcia, Spain Abstract: The effects of climatic factors on yield and berry and wine quality for long-term (7&nbsp;years) deficit-irrigated (DI) Monastrell wine grapes under the semiarid conditions of southeast Spain were analyzed. The relationships between climatic variables and the yield, and novel technological berry quality (QItechnologicalberry), phenolic berry quality (QIphenolicberry), overall berry quality (QIoverallberry), and wine quality (QIwine) indices confirmed that the most important climatic factors were rainfall, temperature, and radiation. Climate was more influential in determining yield, berry, and wine composition in some important physiological periods such as early season (budburst&ndash;fruit set) and ripening (v&eacute;raison&ndash;harvest). In general, climate had more influence on berry quality than on wine quality indices and greater QIoverallberry was also reflected in greater QIwine. According to the stepwise multiple regression, the best fitted models for the partial root-zone drying irrigation (PRI) system were less complex (with a lower number of climatic variables) than for the regulated deficit irrigation (RDI) system, suggesting that PRI is less influenced by climatic factors than RDI. For PRI, the models for yield, berry and wine quality were explained by three climatic factors (rainfall, T&ordf;, and radiation), whereas for RDI, more climatic factors came into play (number of hours of sunshine, evapotranspiration, and vapor pressure deficit). According to these models, in RDI, a sunny and drier pre-v&eacute;raison period followed by higher soil water availability and associated greater crop evapotranspiration during ripening favored final berry and wine quality. In contrast, in PRI, greater rainfall during the growing season and greater solar radiation during ripening were the main climatic factors that positively influenced the yield response, berry and wine quality. Besides, berry quality in PRI was more affected (negatively) by high temperatures (high T&ordf;max and T&ordf;min) during the growing season than in RDI and SDI, indicating that cooler and humid years may favor the PRI response more. These results suggest that years with a cool, wet winter followed by a mild, wet spring and early summer (April&ndash;June) and a mild fruit set&ndash;v&eacute;raison period (June&ndash;July), and then greater solar radiation during ripening (August&ndash;mid-September) provide adequate growth potential and increase the likelihood of higher berry and wine quality in PRI. Besides, more irrigated SDI vines were less sensitive to high temperatures and low soil water content during ripening than RDI and PRI vines. Keywords: berry quality indices, climatic factors, multivariate analysis, deficit irrigation techniques, wine quality index, yield

Conserved water use improves the yield performance of soybean (Glycine max (L.) Merr.) under drought

We evaluated the importance of conserved water use in drought adaptation in soybean [Glycine max (L.) Merr.], and identified the traits involved in this mechanism. Eight soybean genotypes, four landraces and four recent cultivars, were collected and yield performance in the field was determined and used in pot experiments to evaluate the yield performance and the water use pattern under three soil moisture treatments imposed from 40days after sowing: well-watered [WW, soil water content (SWC) maintained between 85%–100% field capacity (FC)]; water stress (WS, water withheld until SWC decreased to 30% FC, rewatered to 100% FC and water withheld again to 30% FC); and terminal water stress (TWS, water withheld until maturity). The recent cultivars all out-yielded the landraces in two different years in the field and under well-watered conditions in the pot experiment. Among the eight soybean genotypes, J19 and ZH – two recent cultivars with lower daily water use before flowering, but higher use after flowering – had the best yield performance in the WS and TWS treatments in the pot experiment and in the field. These two soybean genotypes and J19, another recent cultivar, had higher grain yield, hundred-grain weights and water use efficiency for grain yield (WUEG) in the WS treatments than the other genotypes, and higher hundred grain weights, higher WUEG, higher pod numbers and the only significant grain yield in the TWS treatment. J19 and ZH had low root length densities (RLD), low leaf areas at flowering, and transpiration decreased at high plant available soil water content under drought. Thus, we conclude that reducing RLD and restricting water loss contributed to conserved water use and improved yield performance and WUEG in water-limited conditions.

Interface Shear Strengths Between Geosynthetics and Clayey Soils

Interface shear behavior between geosynthetics and clayey soil was investigated by large scale direct shear tests. The interfaces investigated are geomembrane (GM) and clayey soil; GM and geotextile (GT); and GT encased geosynthetics clay liner (GCL) and clayey soil. For GM/clayey soil interfaces, a softer GM resulted in a higher apparent adhesion, and higher water content of the soil yielded lower interface strength. A GM/bentonite interface had a small friction angle of 3 –4° only. For all cases tested, the interface shear strength (τ f) was lower than the shear strength of the corresponding soil (τ fs), and the lowest τ f /τ fs ratio was about 0.55. For GM/GT interfaces, the stiffer a GM, the lower the interface shear strength. Also a GT with a woven slit film layer, which is smoother than a randomly aligned nonwoven fiber surface, had a lower interface shear strength. The moisture content of a cover silty soil layer also had a considerable effect on the interface shear strength. Higher water content of the cover soil promoted soil particles entering the openings of the GT and increased the strength. For GCL/clayey soil interfaces, increase the water content of the bentonite in the GCL, reduced the interface friction angle, but increased apparent adhesion. The ratios of τ f /τ fs was about 0.8–1.0, and it reduced with the increase of the water content of the bentonite and overburden pressure possibly due to migration of water from the GCL to the interface.

Irrigation management for spring maize grown on saline soil based on SWAP model

Soil salinization and water quality deterioration severely limit the development of irrigation agriculture in arid areas. Transient numerical models such as the agro-hydrological Soil-Water-Atmosphere-Plant (SWAP) model have played an important role in agricultural irrigation management. In order to find the optimal irrigation practices for spring maize grown on saline soil in Shiyang River Basin, the SWAP model was calibrated and validated to simulate water-salt transport and relative yield based on field experiments in 2008 and 2009. The average annual precipitation in this area is about 164mm. Experimental observations of soil water content, soil salinity and maize growth were made in lysimeters filled with disturbed loam soil having saturation extract water salinity (ECe) around 5.76dSm−1. Six irrigation treatments altogether including three levels of irrigation water amount: 100%, 67% and 50% ETc (evapotranspiration, 510mm) and two levels of irrigation water salinity: 0.65 and 3.2dSm−1 were arranged, each treatment with 3 replications for each treatment. The acceptable root mean square error (RMSE), mean relative error (MRE), the Nash and Sutcliffe model efficiency (NSE), the coefficient of determination (R2) between simulation and observation of soil water content, salt concentration and relative yield demonstrated that the calibrated SWAP model was applicable to irrigation management evaluation for maize grown on saline soil. Based on the analysis of simulated water and salt balance, relative yield and relative water use efficiency, the optimal irrigation schedule of maize grown on the saline soil for 50% hydrologic year was irrigation amount of 460mm with four times, for both fresh water 0.65dSm−1 (80Fr) and slight saline water 3.2dSm−1 (80Sal3). Compared to fresh irrigation treatment, higher soil water content and salt concentration, and lower relative yield and relative water use efficiency were obtained by saline irrigation treatment. However, for the maize grown on saline soil, the effect of irrigation amount at high level on relative yield and water use efficiency was unobvious with the difference less than 4%. Relative yield with 0.74 and 0.63 can be obtained by 80Fr and 80Sal3 every year after soil water-salt reached balance.

Soil water dynamics and availability for citrus and peanut along a hillslope at the Sunjia Red Soil Critical Zone Observatory (CZO)

The hillslopes of red soils (Ultisols) in southern China are intensively cultivated for cash crops and fruit trees. During the rainy monsoon, soil erosion is prevalent, whereas a summer/autumn dry season induces drought stress. Crops respond differently to these stresses, and have different effects on soil water regime. This study used a combination of field observation and HYDRUS-2D modeling to assess the soil water dynamics and plant available water for peanut (Arachis hypogaea) and citrus (Citrus sinensis) at Sunjia Red Soil Critical Zone Observatory (CZO). Between April 1, 2012 and March 31, 2014, surface runoff and moisture content at 5, 20, 40, and 80cm depths in the soil under both land uses were monitored at up, middle and foot slope positions along a hillslope. Results indicate that the citrus plot had higher soil water content at 5cm depth during the dry season, and lower at 20, 40 and 80cm depths throughout the year than the peanut plot. As expected, the soil water content was higher at foot slope, compared to up slope, and in deeper soil than near surface. We observed limited soil water availability to peanut during mid-July to August, and to citrus from mid-July to mid-November. Compared to the peanut plot, the citrus plot generally showed 12–28% greater evapotranspiration, 3–4 times less runoff, and 2–57% greater deep drainage. These differences were greater at the up slope position. Our data and HYDRUS-2D simulation suggest that the deep-rooted citrus reduced runoff during the rainy season by increasing macropore flow and canopy interception, and minimized the soil water stress during the dry season by utilizing water from deeper soil. Thus, we recommend trench planting of citrus along with peanut intercropping on hilly red soils as sustainable agricultural practices.

Spatial heterogeneity of CO2 efflux and optimization of the number of measurement positions

CO2 efflux from a soil surface is usually highly heterogeneous. This can make difficulties in its estimation for the whole investigated site. Therefore, the aims of this study were to determine the spatial heterogeneity of CO2 efflux in four different ecosystems, and to determine the minimum sample size required to effectively estimate CO2 efflux from the studied area.CO2 efflux was measured at 30 to 64 positions in a spruce forest, a beech forest, a grassland and a wetland during several campaigns. Mean CO2 efflux normalized for temperature of 10 °C ranged between 1.37 and 3.57 μmolCO2 m−2 s−1, while the highest values were observed for the spruce forest and the lowest for the wetland, where soil respiration processes were reduced by high soil water content. The spatial heterogeneity of CO2 efflux ranged between 15 and 57%, with lowest values for the grassland ecosystem and the highest for the wetland. We found a decrease in CO2 efflux with increasing soil moisture at the forest sites and the wetland. At the forest sites this effect was not caused by oxygen limitation or high soil water content, but can be attributed to other soil properties co-varying with soil water content. At the grassland site, the heterogeneity of CO2 efflux was mainly affected by grass height. The minimum number of measurement positions was determined by calculating the SD of a thousand random selections for different numbers of sample positions (n = 5–55). The minimum number of positions was the n value which displayed a SD that was ≤5% of the mean R10 from the whole data set. The minimum number of positions ranged from between 9 and 35 and it increased with increasing heterogeneity. This relationship was fit by a sigmoid regression.

Long-term thinning alters ponderosa pine reproduction in northern Arizona

The future of ponderosa pine (Pinus ponderosa var. scopulorum) forests in the southwestern United States is uncertain because climate-change-induced stresses are expected to increase tree mortality and place greater constraints on regeneration. Silvicultural treatments, which include thinning, are increasingly being used to address forest health concerns by restoring ponderosa pine forests to more open conditions representative of historical forest structure. In light of the greater use of thinning and mounting concerns about the future of the species at the southern edge of its range, further investigations about impacts of thinning on ponderosa pine regeneration and underlying mechanisms are needed. We used a long-term (>50years) experiment in northern Arizona to investigate impacts of repeated stand thinning that maintained different growing stock basal areas (0, 7, 14, 23, 34, 66m2ha−1) on early seedling survival, growth, and microenvironment. Seedling survival for the first two years after germination (2013–2015), which had above-average precipitation, was higher than reported in several earlier studies and ranged between 4 and 21% among all basal areas. Seedling density exhibited a negative quadratic relationship with basal area and was positively associated with litter cover. Growing stock levels that fostered the highest seedling survival and density were those with a low density of overstory trees, low canopy cover, high cone production, coverage of soil by a thin layer of litter, and high soil water content at a depth of 15–30cm. Overstory basal area was positively associated with seedling height but negatively associated with seedling diameter. During this relatively wet period, all basal area treatments supported higher average seedling densities than those previously recommended to produce a multi-aged stand or presettlement structure in the southwestern United States. Our results show that long-term maintenance of low to intermediate basal areas (7–23m2ha−1) by thinning over the last 50years led to a favorable microenvironment for early seedling establishment of ponderosa pine.