Soil Minimum Temperatures Research Articles

Low winter temperatures and divergent freezing resistance set the cold range limit of widespread alpine graminoids

AbstractAim“Where and why does a species exist” is a fundamental question in ecology. However, the actual range limits of alpine plant species are largely unexplored and unexplained. We aim at identifying the cold range limits of the two most abundant alpine graminoid species on acidic soils that intermingle in mosaics of high‐elevation habitats across the European Alps.LocationAlpine grasslands in the Swiss Alps.TaxonCarex curvula (Cyperaceae) and Nardus stricta (Poaceae).MethodsWe assessed temperature 3 cm below ground, closest to the plant meristems, year‐round as well as snow cover duration, soil chemistry and vegetation characteristics at high spatio‐temporal resolution at 115 microsites. Field data were combined with various freezing resistance analyses in plant individuals at 38 microsites by employing mixed regression models.ResultsCarex and Nardus segregated across different microsites. Season length, growing degree hours and soil chemistry did not demarcate the two species' ranges, while their distribution was strongly affected by soil minimum temperature in winter. Carex occurred at sites with and without protecting snow cover and resisted low soil temperatures (−13°C). Nardus was absent at microsites with snow cover duration < 5 months and soil minimum temperatures below −5°C. During the growing season Carex had a higher leaf/shoot freezing resistance (lethal temperature for 50% of the leaf tissue LT50: −16.1°C) than Nardus (−13.3°C). Shoot apices tolerated lowest temperatures: Carex −30°C, Nardus −24°C. Though, a vital shoot apex alone did not ensure regrowth after winter, but intact vessels and roots were required, all less freezing tolerant than apical meristems and young leaves.Main conclusionsThe cold range limits of these widespread alpine graminoids are evidently set by thermal extremes in winter. Microtopography, thus snow distribution pattern, in concert with the species' freezing resistance explains the cold edge of the fundamental niche of these two species.

Nutrient Characteristics and Redox Potential Changes as Affected by Water Management in Rice Paddy Weighing Lysimeter

This study was designed to assess the nutrients characteristics and redox potential changes as affected by water management condition in rice paddy weighing lysimeter. Rice was grown from June to October 2015, and the water management was consisted of two methods: continuously flooding (CF) and alternate wetting and drying (AWD). Under the CF condition, the redox potential (Eh) of 5 cm topsoil began to decrease rapidly and maintained around -260 to -200 mV. The AWD showed the oxidation condition. The changes of soil pH in CF and AWD ranged from 6.0 to 7.0 and 5.7 to 7.1, respectively. Soil pH in the AWD condition indicated up and down patterns by irrigation. In changes in nutrient contents of the soil solutions, nitrate nitrogen (NO3-N) was initially 12.2 to 26.6 mg L-1 at the highest concentration, and the concentration of ammonia nitrogen (NH4-N) and phosphate (PO43-) appeared to be lower than 1 mg L-1 during rice cultivation. The grain yield of rice was significantly higher in the CF than in the AWD. Nitrogen and magnesium content in both rice grain and straw were not significantly different between the water management conditions. Phosphorous, potassium, and calcium content in the rice grain were not statistically different between CF and AWD conditions. However, the nutrient contents in rice straw were higher in the CF, compared with that in the AWD. Although the iron content in rice straw was higher in the CF than in the AWD, the manganese content showed an opposite tendency. Interestingly, soil maximum temperature at the daytime was significantly higher in the AWD than in the CF, whereas the soil minimum temperature at the night time was 0.5-0.9℃ lower in the AWD, compared with that of the CF. Therefore, these results suggest that the decrease in rice yield in AWD condition can be linked to the inhibition of phosphate absorption into rice plants under oxidized-soil condition and/or high temperature difference between day and night in the soil. Changes in the redox potential (Eh) of (A) 5, (B) 10, and (C) 15 cm soil depth under water management conditions of the continuously flooding (CF) and alternate wetting and drying (AWD).

POPULATION DYNAMIC OF APHIDS AND THRIPS ON CERTAIN BREAD WHEAT CULTIVARS IN RELATION TO YIELD, GENOTYPIC PREFERENCE AND FACTORS REGULATING THEIR FLUCTUATION UNDER DROUGHT AND IRRIGATION CONDITIONS

<p>The study was conducted during (2015/2016 and 2016/2017) on bread wheat cultivars: Sahel1, Seds4, Gemaza9, Giza168, and Misr2 in Plant Protec. Dept. farm, Fac. of Agric., Assiut Univ., Assiut, Egypt to determine the separate effect of some abiotic and biotic factors on the population dynamics of aphid species: <em>Mayzus persicae</em>; <em>Brivecoryne brassicae</em>; <em>Rhopalosiphum padi</em>, and onion thrips, <em>Thrips tabaci</em> Lindeman under drought and irrigation conditions. The considered abiotic factors: plant age, chlorophyll AB; climatic factors: Daily Maximum Temperature (DMxT), Daily Minimum Temperature (DMnT), Soil Daily Maximum Temperature (SMxT) and Soil Minimum Temperature (SMnT) at 3 to 5 cm depth from soil surface, beside the biotic factors which presented in natural enemies (N.E.) to clarify which cultivar is suitable to be planted under drought or irrigation conditions under free insecticides use for both pests with references to cultivars yields. The infestations of both pests started in February during 1<sup>st</sup> season and January for 2<sup>nd</sup> season in all replicates with a high mean numbers of pests on cultivars under irrigation conditions than drought conditions. The peaks of aphids recorded from the middle of the 2<sup>nd</sup> month to the 3<sup>rd</sup> month; and thrips in the 2<sup>nd</sup> month to the half of 3<sup>rd</sup> month from sampling date under both conditions. The most important factors regulated the fluctuation of pests under drought conditions were arranged according to their efficiency as (DMnT= 26.70), (DMxT= 16.91), and (N.E= 16.40); respectively out of (66.50 %). Under irrigation conditions,<em> </em>fluctuations were determined by the efficiency of (N.E.= 38.17), (Chlorophyll AB= 14.97), and plant age (9.96); respectively out of (83.19 %) with positive significant correlations on all selected cultivars. Top yields were gained from Giza186, Misr2, and Sahel1; respectively during seasons of the study under both conditions, except Gemeza9 under irrigation condition in 1<sup>st</sup> season ranked the 3<sup>rd</sup> yield.</p>

Role of Free and Bound Phenols with Certain Field Factors in the Population Density of Aphid Species and Onion Thrips Attacking Bread Wheat Cultivars under Drought Conditions

The experiment of five of bread wheat cultivars (Sahel 1, Seds 4, Gemaza 9, Giza 168, and Misr 2) were investigated during (2015- 2016 and 2016- 2017) at the farm of Faculty of Agriculture, Assiut University, Assiut, Egypt. The considered field factors were represented in the climatic factors of daily maximum and minimum temperatures (°C), soil temperatures at 5 cm depth (°C), and the prevailed natural enemies with an estimation of phenolic contents (free and bound phenols) in the selected wheat cultivars. To investigate the efficiency of all considered factors together and each factor separately on the population fluctuation of onion thrips, Thrips tabaci Lindeman and aphid species (Mayzus persicae Sulz., Brivecoryne brassicae Linnaeus, and Rhopalosiphum padi Linnaeus) on the selected wheat cultivars under drought and field conditions in relation to the yields of cultivars. The mean numbers of thrips were higher than aphid species on most of the selected cultivars during the two studies seasons. The individuals of both insect pests were observed in the 15th of February, 2015 for the 1st season, while in the second season the infestations started in the 15th of January, 2016 on all of cultivars. The 1st season peaks by aphids were showed from the 15th of March to the 30th of April, 2016 on all cultivars, while two peaks of thrips population were observed on Sahel 1 and Seds 4, and three outbreaks on the rest of cultivars. The number of the peaks during the 2nd season by aphids and thrips were reached to two peaks for each pest during the 28th of April and the 15th of March, 2016. The efficiency (R2 x100) of all experimental considered factors were (72.98, 64.07, and 80.03%; respectively for aphids, thrips, and pests total grand). The considered factors were regulated the populations of pests during the studied seasons according to their efficiency in the following order for aphids: the natural enemies, the min. temperatures, the soil minimum temperatures were mainly participated with (20.847, 15.003, and 11.265 out of 72.98%; respectively for on all the cultivars), while The bound phenols were the least efficient factor (0.994 out of 72.98%). For thrips and the pests grand totals, the soil minimum temperature, the maximum temperature, and the minimum temperature were affected the population density by (22.099, 27.757; 12.914, 20.473; and 9.053, 11.377 out of 64.07 and 77.76%; respectively for thrips and the grand totals of pests) and the least efficient factor for thrips was free phenol contents (0.655 out of 77.76%, r= -1.082), and for the grand totals of pests were the natural enemies (0.169 out of 77.76%, r= 0.633). In both seasons, the greatest yield were obtained from from Giza 186 (178.33 and162.39 GY/10 plants; respectively in the 1st and the 2nd season). Meanwhile, the lowest one was recorded from Gemaza 9 (81.66 and 95.13 GY/10 plants; respectively in the 1st and the 2nd season).

Effect of freezing temperature and duration on winter survival and grain yield of winter wheat

Climate change has already increased the occurrence of extreme temperature events, which has restricted the production and development of winter wheat. To evaluate the effects of freezing temperature and duration on winter wheat survival and grain yield, two years of controlled freezing experiments were conducted under different freezing temperatures and durations. Three freezing temperatures (T1, T2 and T3) were implemented in these experiments, and soil minimum temperatures of −14 °C, −17 °C and −20 °C were designated for T1, T2 and T3, respectively. The freezing durations were designed as 2, 4, 6, 8 and 10 days under T1, 1, 2, 3, 5, 6, 7, 8 and 9 days under T2, and 1, 2, 3, 4, 5, 6 and 8 days under T3. The effects of freezing duration on the mortality of plants and tillers, as well as its effects on the grain yield per pot (GYPP), were much more serious under lower temperature. For every 1-day increase in freezing duration, GYPP decreased by 3.3% and 8.4% under T1 and T2, respectively, while the spike number per pot (SNPP) decreased by 4.4% and 21.6% under T1 and T2, respectively. When analyzing the combined effects of freezing temperature and duration, we introduced freezing degree days (FDD), which uses soil minimum temperatures below a threshold of −12 °C to represent the magnitude of the exposure to freezing temperature and duration. For every 1 °C·d increase in FDD, the mortality of plants and tillers increased by 1.0% and 1.4%, respectively. The interaction between freezing temperature and duration had a great effect on GYPP (0.5–1.2%/oC·d), while SNPP was more sensitive to freezing stress than GYPP and decreased at a rate of 2.3–2.9%/oC·d. An increasing trend in grain number per spike (GNPS) was clearly observed as FDD increased in 2014–2015, while freezing stress during the overwintering period had no direct influence on thousand-grain weight (TGW). The variation in GYPP was mainly caused by the grain number per pot (GNPP = SNPP × GNPS). The contribution of SNPP to the variation in GYPP was greater than that of GNPS or TGW under mild temperature, while GNPS contributed more under severe temperature. The results of this study provide data support for the improvement of crop models when simulating the effect of temperature stress on grain crops, and they can be consulted to predict freezing injury during winter wheat production.

Simulated root freezing in the nursery: effects on the growth and physiology of containerized boreal conifer seedlings after outplanting

The effects of induced root freezing injury on 2+0 white spruce (Picea glauca (Moench) Voss), black spruce (Picea mariana (Mill.) BSP), and jack pine (Pinus banksiana Lamb.) seedlings were studied. Hardened seedlings were exposed to freezing during the fall and cold stored until planting. Seedlings were planted in spring on two field sites with different soil moisture levels (wet or dry). Seedling morphology and physiology were measured periodically during the first growing season, and mortality was evaluated at the end of the season. With the exception of June measurements on the wet site, where daytime water potential fell as low as –2.0 MPa, root damage did not seriously affect shoot water potential. Generally, stomatal conductance decreased with increasing root damage. Net photosynthesis on both sites decreased between 22 and 39% with increasing root damage. Root damage did not affect the ratio of intercellular to ambient CO2concentration. As well, reductions in the nitrogen concentration of current-year foliage with increasing root damage were observed, suggesting that the observed reductions in net photosynthesis were caused by nonstomatal factors. Root growth was greater on the wet site than on the dry site, particularly between August and October, when mean soil minimum temperatures were lower on the dry site. On both sites, aerial dry mass was only slightly affected by root damage in July and August, but the effect of damage became more pronounced in October on the wet site. Black spruce and white spruce seedling mortality began being affected when approximately 50% of the root systems were damaged, while jack pine mortality was affected starting at 40% damage. Root damage levels of 50% caused 2.0 and 1.5 cm reductions in annual height increment of white spruce and black spruce, respectively, and 40% damage caused a reduction of 1.0 cm in annual height increment of jack pine.

Effects of frost action on soil physical properties of plough pan

Undisturbed soil cores of loamy clay plough pan were subjected to the treatments of freezing and thawing in laboratory. The effects of frost action on its bulk density, porosity, and hydraulic conductivity were investigated. The results indicate that freezing and thawing significantly reduced the bulk density of plough pan and increased its porosity and hydraulic conductivity. The reduction in the bulk density was closely related to the average daily soil minimum temperature and soil water content.

A degree-day model for regional prediction of first occurrence of frit flies in oats in Sweden

A degree-day model for regional prediction of first occurrence of frit flies, Oscinella frit (L.), in oat fields in Sweden was developed. The model parameters were calibrated using water trap and temperature data from one province. Another set of data from the same and other provinces was used to validate the predictions of the model. Different methods of degree-day calculation, based on either air or soil minimum temperatures, were compared and the least variation of temperature sums associated with date of first occurrence was found using actual degree-days calculated from air temperature data. In the validation of the mode, median date of first occurrence could be predicted with an error of less than five days in 12 of 15 province-year combinations. The mean predictive errors differed between years and provinces and also, in one case, due to choice of weather station within region. Based on these results we conclude that the degree-day model predicts regional occurrence of frit flies with reasonably small errors and that it will be an important part in the development of a decision support system for control of frit flies.

ASPEN WOOD CHIP AND STONE MULCHES FOR ORNAMENTAL PLANTINGS IN INTERIOR, ALASKA

Five woody ornamentals Rosa rugosa, Cotoneaster acutifolia, Malus baccata, Picea glauca and Pinus contorta var. latifolia, were grown for 4 seasons mulched with one of five treatments: 2.5 cm or 5 cm of crushed basaltic quarry stone, 5 cm or 10 cm of quaking aspen wood chips, and an unmulched control. Maximum soil temperatures at the 10 cm depth on the wood chip plots were decreased by as much as 8°C over control plots, and soil moisture was increased. Stone mulch plots showed a slight increase in both temperature and moisture. Soil minimum temperatures were lower on the wood chip plots than the other treatments early in the season, but were slightly higher in September. Soil pH and available N, P and K did not differ among mulch treatments. Weed growth was suppressed by all mulch treatments but was best controlled on the wood chip plots followed by the 5 cm stone plots. Plant growth for all species except Rosa rugosa was greatest on the stone mulch plots. Roses growing on the stone mulch plots and the control were subject to significant dieback from winter injury and did not show any difference in total growth after 4 years when compared with the wood chip plots. Plants grown on the wood chip plots exhibited varying degrees of nitrogen deficiency which may be related to reduced nutrient uptake in cooler soils or to a significant amount of rooting in the mulch-soil interface.

ASPEN WOOD CHIP AND STONE MULCHES FOR ORNAMENTAL PLANTINGS IN INTERIOR, ALASKA

Five woody ornamentals Rosa rugosa, Cotoneaster acutifolia, Malus baccata, Picea glauca and Pinus contorta var. latifolia, were grown for 4 seasons mulched with one of five treatments: 2.5 cm or 5 cm of crushed basaltic quarry stone, 5 cm or 10 cm of quaking aspen wood chips, and an unmulched control. Maximum soil temperatures at the 10 cm depth on the wood chip plots were decreased by as much as 8°C over control plots, and soil moisture was increased. Stone mulch plots showed a slight increase in both temperature and moisture. Soil minimum temperatures were lower on the wood chip plots than the other treatments early in the season, but were slightly higher in September. Soil pH and available N, P and K did not differ among mulch treatments. Weed growth was suppressed by all mulch treatments but was best controlled on the wood chip plots followed by the 5 cm stone plots. Plant growth for all species except Rosa rugosa was greatest on the stone mulch plots. Roses growing on the stone mulch plots and the control were subject to significant dieback from winter injury and did not show any difference in total growth after 4 years when compared with the wood chip plots. Plants grown on the wood chip plots exhibited varying degrees of nitrogen deficiency which may be related to reduced nutrient uptake in cooler soils or to a significant amount of rooting in the mulch-soil interface.