Infrared Thermal Imaging as a Rapid Tool for Identifying Water‐Stress Tolerant Maize Genotypes of Different Phenology

The main task of this research was to evaluate canopy temperature and Crop Water Stress Index (CWSI) by assessing genotype variability of maize performance for different water regimes. To that end, three hundred tropical and subtropical maize hybrids with different phenology in terms of date of anthesis were evaluated. The influence of phenology on the change in canopy temperatures and CWSI was not equal during the three dates of measurement. At the end of vegetative growth (82 days after sowing, DAS) and at the blister stage (DAS 97), a high significant difference in temperatures and CWSI (P < 0.001) were obtained between the early‐ and late‐maturity genotypes. During anthesis (DAS 89), phenology had a significant effect (P < 0.01) only for the well‐watered genotypes, while under water‐stress conditions, no differences were found between early and late genotypes in terms of canopy temperature and CWSI. High significant differences (P < 0.001) in stomatal conductance (g_s) between early and late genotypes for different treatments were observed. A relationship (R² = 0.62) between g_s and canopy temperature was obtained. Under a water‐stress canopy, temperature was measured at anthesis, which was negatively correlated with grain yield of the early (r = ?0.55)‐ and late (r = ?0.46)‐maturity genotypes in the water‐stressed condition.     

Effects of Increasing Salinity Stress and Decreasing Water Availability on Ecophysiological Traits of Quinoa (Chenopodium quinoa Willd.) Grown in a Mediterranean‐Type Agroecosystem

Quinoa is a native Andean crop for domestic consumption and market sale, widely investigated due to its nutritional composition and gluten‐free seeds. Leaf water potential (Ψ_leaf) and its components and stomatal conductance (g_s) of quinoa, cultivar Titicaca, were investigated in Southern Italy, in field trials (2009 and 2010). This alternative crop was subjected to irrigation treatments, with the restitution of 100 %, 50 % and 25 % of the water necessary to replenish field capacity, with well water (100 W, 50 W, 25 W) and saline water (100 WS, 50 WS, 25 WS) with an electrical conductivity (EC_w) of 22 dS m^?1. As water and salt stress developed and Ψ_leaf decreased, the leaf osmotic potential (Ψ_π) declined (below ?2.05 MPa) to maintain turgor. Stomatal conductance decreased with the reduction in Ψ_leaf (with a steep drop at Ψ_leaf between ?0.8 and 1.2 MPa) and Ψ_π (with a steep drop at Ψ_π between ?1.2 and ?1.4 MPa). Salt and drought stress, in both years, did not affect markedly the relationship between water potential components, RWC and g_s. Leaf water potentials and g_s were inversely related to water limitation and soil salinity experimentally imposed, showing exponential (Ψ_leaf and turgor pressure, Ψ_p, vs. g_s) or linear (Ψ_leaf and Ψ_p vs. SWC) functions. At the end of the experiment, salt‐irrigated plants showed a severe drop in Ψ_leaf (below ?2 MPa), resulting in stomatal closure through interactive effects of soil water availability and salt excess to control the loss of turgor in leaves. The effects of salinity and drought resulted in strict dependencies between RWC and water potential components, showing that regulating cellular water deficit and volume is a powerful mechanism for conserving cellular hydration under stress, resulting in osmotic adjustment at turgor loss. The extent of osmotic adjustment associated with drought was not reflected in Ψ_π at full turgor. As soil was drying, the association between Ψ_leaf and SWC reflected the ability of quinoa to explore soil volume to continue extracting available water from the soil. However, leaf ABA content did not vary under concomitant salinity and drought stress conditions in 2009, while differing between 100 W and 100 WS in 2010. Quinoa showed good resistance to water and salt stress through stomatal responses and osmotic adjustments that played a role in the maintenance of a leaf turgor favourable to plant growth and preserved crop yield in cropping systems similar to those of Southern Italy.     

高粉与低粉木薯品种叶片光合作用日变化及淀粉积累的研究

为了阐明高粉和低粉木薯叶片光合作用及淀粉累积的日变化规律,以高粉木薯品种‘辐选01’和低粉品种‘华南124’苗期叶片为对象,对叶片光合作用的日变化、叶片中的可溶性糖（葡萄糖、果糖、蔗糖）及总糖、淀粉含量、气孔密度等进行比较研究。结果表明：随着光强的增加,高粉品种‘辐选01’的光合速率较低粉品种‘华南124’高;且‘辐选01’叶片上表皮与下表皮的气孔密度都显著高于‘华南124’;2个木薯品种叶片中蔗糖、可溶性总糖含量在一天中是不断积累、逐渐增加的。在一天当中,木薯叶片中淀粉含量在18:00时达到最高。而高粉品种‘辐选01’的光合作用能力在一天当中与低粉品种‘华南124’存在较大差异,在8:00—14:00之间,‘辐选01’的光合作用能力与糖分积累较‘华南124’高,而在16:00—18:00之间,‘华南124’的光合作用能力与糖分积累较高,这可能与午后温室温度上升引起叶片温度过高,叶绿体活性与Rubisico活性降低、RuBP羧化酶再生能力降低导致了‘辐选01’的光合作用能力比‘华南124’的低。     

美洲黑杨与大青杨杂种叶片气孔导度的红外热像测量方法研究

为了研究红外热像技术在测量叶片气孔导度的应用上的可行性,以美洲黑杨与大青杨杂种(Populus deltoids Bartr.×Populus ussuriensis Kom.)为材料,在正常灌溉和干旱胁迫的对比下,利用红外热像仪考察了叶片的气孔导度Gs的日变化,根据叶片能量平衡方程分析了气孔导度与温度之间的关系,并采用便携式光合测量系统验证了红外热像测量气孔导度的准确性。结果表明：在2种水分处理条件下,叶片的气孔导度值均呈双峰曲线,峰值出现在10:00和14:00,正常灌溉和干旱条件下的峰值分别为120 mmol/(m2?s)、70 mmol/(m2?s)和80 mmol/(m2?s)、40 mmol/(m2?s);气孔导度与温度的响应呈反比趋势;气孔导度的模型计算值与实际测量值之间的关系呈线性相关,正常灌溉和干旱状态下的相关系数分别为0.8678、0.8347;气孔导度相关指数IG和水分胁迫指数CWSI分别与测量得到的气孔导度呈正比、反比的趋势。总之,与传统的利用便携式光合仪测定气孔导度相比,利用红外热像技术测量更便捷、准确,且适用性更加广泛,本研究为今后利用红外热像测量气孔导度奠定了理论基础。     

遮荫条件下O_3胁迫对冬小麦气孔导度影响的模拟

为了探究在遮荫条件下地表O3浓度增加对冬小麦气孔导度的影响,开展了两种不同强度遮荫与开顶式气室（OTC）相结合的大田试验,设置3个处理组：O3浓度为（100±9）nL.L-1结合（60±5）%遮荫的处理组（T1）;O3浓度为（100±9）nL.L-1结合（20±5）%遮荫的处理组（T2）;O3浓度为（100±9）nL.L-1不作遮荫的处理组（CK）。利用SC-1型气孔导度仪测定了3个处理组冬小麦不同生育期的气孔导度值。综合分析了生育期和O3胁迫,以及水汽压差（VPD）、温度（T）、光照（PAR）环境因子的变化对冬小麦气孔导度的影响,采用修正后的Jarvis非线性气孔导度模型模拟了3个处理组的气孔导度值。结果表明：遮荫对大田环境因子均产生了影响,其中,T1、T2处理组8：00—16：00点的平均温度和水汽压差较CK相比分别下降了5.6℃、4.1℃和0.84kPa、0.74kPa;用该模型得到的气孔导度模拟值与观测值进行了比较,R2=0.88,表明模型模拟效果良好;同时,根据O3吸收通量模型计算出T1、T2和CK处理组在整个O3熏蒸时期,冬小麦O3累积吸收通量分别为14.92、15.52、16.23mmolO3.m-2,并由此建立了O3吸收通量（x）与干物质损失（y）的关系分别为：y=1.0-0.038x和y=1.0-0.022x,表明在相同O3胁迫条件下,遮荫导致了冬小麦O3累积吸收通量的差异,在60%和20%遮荫条件下,O3吸收通量增加10mmol.m-2,与CK相比,其干物质累积损失分别为38.0%和22.0%。     

若干阔叶树树冠各层叶气孔密度及光照条件对气孔密度的影响

４０种阔叶树树冠的外、中、内层同龄叶中，均以外层叶的气孔密度最高，其次为中层叶，内层叶气孔密度最低。新银合欢和马尖相思幼苗在高光照强度下所形成的叶气孔密度最高，中等光照者次之，低光照者最低。在蓝光照射下形成的叶气孔密度最高，其次为红光照射者，自然漫射光下最低。这说明光照强度和光波长对气孔密度有深刻影响。     

Analysis of the variations in dry matter yield and resource use efficiency of maize under different rates of nitrogen,phosphorous and water supply

Abstract

Increasing resources use efficiency in intensive cultivation systems of maize (Zea mays L.) can play an important role in increasing the production and sustainability of agricultural systems. The objectives of the present study were to evaluate DM yield and the efficiency of inputs uses under different levels of water, nitrogen (N) and phosphorus (P) in maize. Therefore, three levels of irrigation including 80 (ETc₈₀), 100 (ETc₁₀₀) and 120% (ETc₁₂₀) of crop evapotranspiration were considered as the main plots, and the factorial combination of three levels of zero (N₀), 200 (N₂₀₀) and 400 (N₄₀₀) kg N ha^?1 with three levels of zero (P₀), 100(P₁₀₀) and 200 (P₂₀₀) kg P ha^?1 was considered as the sub plots. The results showed that increasing the consumption of water and P was led to the reduction of N and P utilization efficiency, while RUE increased. WUE was also increased in response to application of N and P, but decreased when ET_C increased. DM yield under ETc₈₀ treatment reduced by 11 and 12%, respectively, compared to ETc₁₀₀ and ETc₁₂₀ which was due to reduction of cumulative absorbed radiation (R_abs(cum)) and RUE. Under these conditions, changes of stomatal conductance (gs) had little effect on DM yield. It was also found that N limitation caused 11 and 20% reduction in DM yield compared to N₂₀₀ and N₄₀₀, respectively. This yield reduction was mainly the result of decrease in RUE. By decreasing R_abs(cum), P deficiency also reduced DM yield by 5 and 9%, respectively, relative to P₁₀₀ and P₂₀₀ treatments.     

Physiological Response of Multiple Contrasting Rice (Oryza sativa L.) Cultivars to Suboptimal Temperatures

The physiological response of multiple rice cultivars, eighteen initially and eight cultivars later on, to suboptimal temperatures (ST) conditions was investigated in laboratory and outdoor experimental conditions. Treatment with ST decreased growth in different extents according to the cultivar and affected the PSII performance, determined by chlorophyll fluorescence fast‐transient test, and stomatal conductance, regardless the experimental condition. Two groups of cultivars could be distinguished on the base of their growth and physiological parameters. The group of cultivars presenting higher growths displayed optimal JIP values, and higher instantaneous water use efficiency (WUE_i), due to a lower Gs under ST, unlike cultivars showing lower growth values, which presented worse JIP values and could not adjust their Gs and hence their WUE_i. In this work, we detected at least two cultivars with superior tolerance to ST than the cold tolerant referent Koshihikari. These cultivars could be used as parents or tolerance donors in breeding for new crop varieties. On other hand, positive and significant correlations between data obtained from laboratory and outdoor experiments suggest that laboratory measurements of most of the above mentioned parameters would be useful to predict the response of rice cultivars to ST outdoor.     

Supply of tree-holes limits nest density of cavity-nesting birds in primary and logged subtropical Atlantic forest

Tree cavities are proposed to limit populations and structure communities of cavity-nesting birds. Although the greatest diversity of cavity-nesting birds is found in tropical and subtropical moist forests, little is known about how tropical logging affects the abundance of cavities or cavity-nesting birds. We compared the abundance of cavities and cavity nests between primary and selectively-logged subtropical moist Atlantic forest in Argentina, and conducted the first before-after controlled nest-box addition experiment to determine whether nest sites limit the breeding density of cavity-nesting birds in tropical or subtropical moist forest. Visual inspection of 86 cavities identified through ground-surveys revealed that only 19% were suitable for nesting birds, suggesting that cavity abundance may be overestimated in the literature on tropical forests. Suitable cavities were found in fewer than 1% of 1156 trees <60 cm dbh but 20% of 20 trees >100 cm dbh. Logged forest had half the basal area of primary forest, one third the density of large trees, nine times fewer cavities suitable for nesting birds, and 17 times fewer active nests. When we added nest boxes, nesting density increased on treatment plots but not on control plots in both logged and primary forest, suggesting that cavity supply can limit nest density even in relatively undisturbed forest. This is the first experiment to show how reduced cavity supply in logged tropical forest can limit breeding density of cavity-nesting birds. International initiatives such as forest certification should promote tropical timber management strategies that conserve large live cavity-bearing trees.     

Optimization of an oxygen-based approach for community-level physiological profiling of soils

Current approaches for rapid assessment of carbon source utilization by whole soil communities (i.e., community-level physiological profiling or CLPP) provide a limited, biased view of microbial communities with little connection to in situ activities. We developed an alternative CLPP approach based upon fluorometric detection of dissolved oxygen consumption in a microtiter platform which offers flexible manipulation of experimental factors. In the attempt to reduce oxygen re-dissolution, the wells were filled with liquid to very near the top and sealed. We found that filling the wells with 240 vs. 150 μl of sample improved the sensitivity of the system to discern both the response to a substrate amendment as low as 10 mg l⁻¹ and un-amended, endogenous respiration. The preparation of a soil slurry facilitates inoculation into the microplate. Disruption of soil samples had a limited effect on the endogenous respiration in comparison to intact soil microbags in a 24-well microplate. Storage time (up to 33 days) reduced the level of activity in intact soil microbags but not in disrupted samples. A microcosm fertilization experiment was set to study the effects of N availability on the respiratory response in the plates. The use of soil organic carbon (SOC) and amended C-substrates (50 mg l⁻¹) was increased by the addition of nitrogen (N) in the plate, and appeared N-limited shortly after microcosm fertilization. The addition of the eukaryotic inhibitor cycloheximide delayed the initial increase in fluorescence (time to minimum response) of several C sources (casein, acetate, asparagine, coumaric acid), varying among soils, which could be explained by the fungal use of these compounds. However, the extent of the inhibition caused by cycloheximide did not increase at higher fungal to bacteria ratios as estimated by PLFA analysis, indicating that the direct estimation of the fungal biomass from cycloheximide addition is not feasible. This paper provides an optimized, standardized protocol for soil analysis, and sets the basis for further validation studies that will continue to define the underlying capabilities/biases of this approach.