Water relations of Lithops plants embedded into the soil and exposed to free air

Transpiration and water uptake by Lithops lesliei N.E.Br. and L. karasmontana (Dint. et Schwant.) N.E.Br. were measured by means of a potometer in a plant growth chamber under controlled environmental conditions in order to determine whether the embedding of the leaf cones into the soil prevents excessive water loss or not. Plants without embedding increased the transpirational water loss by the cone mantle with decreasing relative humidity of the surrounding air; the diurnal water loss by transpiration was not balanced by the water uptake during the same time. The balance between transpiration and water uptake was maintained during the whole day and was independent of the relative humidity of the free air if the plants were embedded in the soil.     

Shoot temperatures and thermal tolerances for succulent species of Haworthia and Lithops

Abstract. Temperatures of small succulent plants, such as species in the genera Haworthia and Lithops , are highly influenced by temperatures of the surrounding soil. Indeed, the minimum and the maximum temperatures of the upper leaf epidermis of Haworthia retusa. H. turgida. Lithops leslei , and L. turbiniformis were generally within 1°C of the accompanying soil surface temperatures. An energybudget model closely predicted such soil-to-plant temperature differences as well as the effect of the greater convective exchange for the protruding Haworthia species compared with the Lithops species, which were flush with the soil surface. Although a lower shortwave absorptance would reduce maximum shoot temperatures, the shortwave absorptances of all four species were similar to those of the soil in their respective native habitats in South Africa. Tolerances of the four species to low and to high temperatures at three different day/night air temperatures (15°C/5°C, 30°C/20°C, and 45°C/35°C) were analysed using cellular accumulation of a vital stain, neutral red. Chlorenchyma cells were slightly more tolerant of extreme temperatures than were cells of the water-storage parenchyma. In this regard, H. retusa survived low and high temperatures that killed the water-storage parenchyma but not the chlorenchyma. Acclimation to low temperatures and to high temperatures, which was exhibited by all four species, led to estimated tolerances to 1 h at −16°C and 68°C. Although the low temperature tolerance is not particularly noteworthy, very few vascular plants are reportedly able to tolerate such high temperatures.     

Vertical gradient in soil temperature stimulates development and increases biomass accumulation in barley

We have detailed knowledge from controlled environment studies on the influence of root temperature on plant performance, growth and morphology. However, in all studies root temperature was kept spatially uniform, which motivated us to test whether a vertical gradient in soil temperature affected development and biomass production. Roots of barley seedlings were exposed to three uniform temperature treatments (10, 15 or 20°C) or to a vertical gradient (20-10°C from top to bottom). Substantial differences in plant performance, biomass production and root architecture occurred in the 30-day-old plants. Shoot and root biomass of plants exposed to vertical temperature gradient increased by 144 respectively, 297%, compared with plants grown at uniform root temperature of 20°C. Additionally the root system was concentrated in the upper 10cm of the soil substrate (98% of total root biomass) in contrast to plants grown at uniform soil temperature of 20°C (86% of total root biomass). N and C concentrations in plant roots grown in the gradient were significantly lower than under uniform growth conditions. These results are important for the transferability of 'normal' greenhouse experiments where generally soil temperature is not controlled or monitored and open a new path to better understand and experimentally assess root-shoot interactions.     

The dependence of methane transport in rice plants on the root zone temperature

Large diurnal and seasonal variations in methane flux from rice paddies have been found in many studies. Although these variations are considered to result from changes in methane formation rates in the soil and the transport capacity (e.g. biomass, physiological activities, and so on) of rice plants, the real reasons for such variations are as yet unclear. This study was conducted to clarify the effects of temperature on the rate of methane transport from the root zone to the atmosphere using hydroponically grown rice plants. Methane emission rates from the top of the rice plants whose roots were soaked in a solution with a high methane concentration were measured using a flow-through chamber method with the top or root of the rice plants being kept at various temperatures. The methane emission rates and methane concentrations in solution were analyzed using a diffusion model which assumes that the methane emission from a rice paddy is driven by molecular diffusion through rice plants by a concentration gradient. In the experiment where the temperature around the root was changed, the conductance for methane diffusion was typically 2.0-2.2 times larger when the solution temperature was changed from 15 to 30 °C. When the air temperature surrounding the top of the rice plant was changed, the change in conductance was much less. In addition, from measurements of methane flux and methane concentration in soil water in a lysimeter rice paddy during the 2 growing seasons of rice, it was found that the conductance for methane transport was correlated with the soil temperature at 5 cm depth. These results suggest that the temperature around the root greatly affects the methane transport process in rice plants, and that the process of passing through the root is important in determining the rate of methane transport through rice plants.     

Ecological and evolutionary responses of an arctic plant to variation in microclimate and soil

The arctic and alpine regions are predicted to experience some of the highest rates of climate change, and the arctic vegetation is expected to be especially sensitive to such changes. Understanding the ecological and evolutionary responses of arctic plant species to changes in climate is therefore a key objective. Geothermal areas, where natural temperature gradients occur over small spatial scales, and without many of the confounding environmental factors present in latitudinal and other gradient studies, provide a natural experimental setting in which to examine the response of arctic–alpine plants to increasing temperatures. To test the ecological and evolutionary response of the circumpolar alpine bistort Persicaria vivipara to temperature, we collected plant material and soil from areas with low, intermediate and high soil temperatures and grew them at three different temperatures in a three-factorial growth chamber experiment. At higher experimental soil temperatures, sprouting was earlier and plants had more leaves. Sprouting was earlier in soil originating from intermediate temperature and plants had more leaves when grown in soil originating from low temperatures. We did not find evidence of local adaptation or genetic variation in reaction norms among plants originating from areas with low, intermediate and high soil temperature. Our findings suggest that the alpine bistort has a strong plastic response to warming, but that differences in soil temperature have not resulted in genetic differentiation. The lack of an observed evolutionary response may, for example, be due to the absence of temperature-mediated selection on P. vivipara, the low rate of sexual recombination, or high levels of gene flow balancing differences in selection. When placed within the context of other studies, we conclude that arctic–alpine plant species often show strong plastic responses to spring warming, while evidence of evolutionary responses varies among species.     

Effects of Temperature,Plant Age,Soil Texture,and Meloidogyne incognita on Early Growth of Soybean

A digitizer-microcomputer combination was utilized to determine soybean seedling response to population densities of M. incognita (Mi) under varied environmental conditions. Plant age, temperature, soil texture, and initial Mi inoculum (Pi) influenced the pattern of shoot and root growth. Effects of Mi on plant top growth were evident on plants inoculated 2 days after seeding, but generally were not noticeable on those receiving Mi after 4, 6, or 8 days (observations limited to 6 days after inoculation). The greatest Pi of Mi (16,700 juveniles/plant) suppressed root growth on plants inoculated at 2 or 4 days after seeding. Mi had no impact on root growth at 22 C on plants inoculated 6 or 8 days after seeding at any temperature used (22, 26, 30 C). New root initiation was inhibited on soybeans inoculated 2 days after seeding at the highest Pi at all three temperatures, but only at 30 C for a Pi of 1,670 juveniles/plant. Growth of first order lateral roots and general root length were suppressed by Mi on the youngest (2-day) plants. However, a low Pi (167 juveniles/ plant) resulted in root proliferation on 4-day-old plants at 26 C. Mi was most damaging in a low clay-content soil mixture.     

Ecophysiological observations on Drosophyllum lusitanicum

The carnivorous plant Drosophyllum lusitanicum inhabits heathland and ruderal sites in Portugal, Spain and Morocco. In the literature, various theories have been discussed concerning the ability of Drosophyllum to survive the annual dry period in summer. In August 2004, we examined: (1) the microclimate, (2) soil parameters and (3) the physiological conditions of the plants on two sites in Portugal and Spain. First, during the day, plants are exposed to very high air and soil temperatures and very low air humidity. The climatic extremes are not significantly softened by the population, only the wind speed is drastically decreased. During the night, on the other hand, very high air humidity and dew formation could be observed. The harsh climate is accompanied by stressful soil conditions. Second, the soil is completely dry, poor in fine earth, calcium and nutrients and more or less acid. Third, in spite of these climatic and edaphic extremes, all plants were green, produced trapping mucilage and caught numerous animals. Far from being affected by these conditions, Drosophyllum showed even better growth and reproduction on more extreme sites. We analysed the root system and found living fine roots missing. The osmotic value of the plants is rather low and water storage organs are absent. Therefore we conclude that in summer Drosophyllum is nourished by the dew at night.     

露水对植物的作用效应研究进展

概述了国内外露水对植物作用效应争议的两个方面,一是露水有利于促进植物生长,二是露水对植物生长具有负效应。前者主要包括干旱胁迫下植物生长重要的水资源、调节植物体内水分、改善土壤水分平衡、调节森林植物生长环境、有利于农作物管理及其病虫害防治等生态效益;后者包括导致植物发病、降低植物产量和质量等。文章还指出了露水对植物作用效应研究存在的问题,并提出了今后研究的方向：（1）露水对植物作用效应的机理研究;（2）干扰条件下露水对植物作用效应研究包括酸露对植物作用效应研究和城市热岛条件下露水对植物作用效应研究;（3）露水对植物多样性的影响研究;（4）露水在生物防治中的应用研究。     

Tundra plant structure and production in relation to the environment

The alpine and polar climatic limit for growth of woody plants is very much dependent on the mean temperatures of the warmest three or four summer months. Tundra plants with perennating buds close to the ground are sheltered by insulating snow cover. Many tundra plants can grow at temperatures 5–10°C below 0°C and also have low optimum temperatures. Total net production of tundra plants may be as high as 900 g/m²/yr as dry weight in moist and eutrophic low alpine shrub tundra and in antarctic moss mats. The variation in tundra plant production is often observed to be greater between different stands (communities) within one locality than between localities, because of very important variation in soil moisture and nutrients between the stands. On a global scale the biomass of vascular plants increases by an order of magnitude from the climatic severe polar desert to semidesert and again from there to moist shrub tundra. The cryptogam biomass increases only 2–10 fold from polar desert to low arctic shrub tundra. To a certain limit unfavourable climatic conditions are worse to above- than to belowground plant parts. Highest root biomass compared to top (up to 20 times higher) is observed in wet monocotyledonous polar and alpine communities. In polar desert root biomass is small again, as compared to tops and also in lower latitudes and altitudes of temperate regions.Presented at he Eighth International Congress of Biometeorology, 9–14 September 1979, Shefayim, Israel.     

Effects of phosphate and nitrate supply on productivity,agar content and physical properties of agar ofGracilaria strain G-16S

Gracilaria strain G-16S was cultured in various phosphorus (P) supply rates with low or high nitrogen (N) supply to determine the effects of nutrient supply on its productivity, agar content and physical properties of the agar. Productivity was reduced after four weeks of growth in zero P supply as plants reached 0.07% P tissue content (critical level), with fragmentation of these plants by six weeks (0.05% P; minimum viable level). Native agar content was higher in low P and high N, or low N conditions. Agar content appeared to increase with decreasing P under high N supply. This increase was not apparent with alkali treatment prior to extraction. Agar gel strength was greatly increased by alkali treatment. The highest gel strengths were obtained under high N supply at all P supply rates except zero P, and under low N supply at 12 M P week^–1. Native agar gel strengths showed a similar pattern on a lower scale. Melting temperatures were higher in agars with higher gel strengths. Dynamic gelling temperatures were generally high for alkali-treated agar, with agar from plants grown in zero P supply showing a slightly elevated gelling temperature. Melting and gelling temperatures of native agars with the highest gel strengths were in the same range as bacteriological agar. These results show that P and N supply affects productivity, agar content and agar physical properties, but the tradeoffs between a slightly higher agar quantity under nutrient limitation and higher agar quality under nutrient-replete conditions seem to favor the latter.     

冻融过程对荒漠短命植物种子萌发的影响

荒漠区冻融交替显著改变土壤温度和水分条件,并进一步影响荒漠植物种子萌发.为解析荒漠土壤冻融过程对植物种子萌发的影响,本研究以古尔班通古特沙漠4种典型短命植物[东方旱麦草(Eremopyrum orientale)、卵果鹤虱(Lappula patula)、尖喙拢牛儿苗(Erodiumoxyrrhychum)和条叶庭荠(...     

Can soil temperature direct the composition of high arctic plant communities?

Abstract. Low temperatures exert a primary constraint on the growth of high arctic vascular plants. However, investigations into the impact of temperature on high arctic plants rarely separate out the role of air and soil temperatures, and few data exist to indicate whether soil temperatures alone can significantly influence the growth of high arctic vascular plants in a manner that might direct community composition. We examined the response of high arctic plants of three functional types (grasses, sedges/rushes and non‐graminoids) to manipulated soil temperature under common air temperature conditions. Target plants, within intact soil cores, were placed in water baths at a range of temperatures between 4.9 and 15.3 °C for one growing season. Grasses responded most rapidly to increased soil temperature, with increased total live plant mass, above‐ground live mass and total below‐ground live mass, with non‐graminoids having the lowest, and sedges/rushes an intermediate degree of response. The ratio of above‐ground live mass to total live mass increased in all growth forms. Grasses, in particular, responded to enhanced soil temperatures by increasing shoot size rather than shoot number. In all growth forms the mass of root tissue beneath the moss layer increased significantly and to a similar extent with increasing soil temperature. These results clearly indicate that different growth forms, although collected from the same plant community, respond differently to changes in soil temperature. As a consequence, factors influencing soil temperature in high arctic ecosystems, such as global climate change or herbivory (which leads to reduced moss depth and increased soil temperatures), may also direct changes in vascular plant community composition.     

Elevated temperature shifts soil N cycling from microbial immobilization to enhanced mineralization,nitrification and denitrification across global terrestrial ecosystems

We assessed the response of soil microbial nitrogen (N) cycling and associated functional genes to elevated temperature at the global scale. A meta‐analysis of 1,270 observations from 134 publications indicated that elevated temperature decreased soil microbial biomass N and increased N mineralization rates, both in the presence and absence of plants. These findings infer that elevated temperature drives microbially mediated N cycling processes from dominance by anabolic to catabolic reaction processes. Elevated temperature increased soil nitrification and denitrification rates, leading to an increase in N₂O emissions of up to 227%, whether plants were present or not. Rates of N mineralization, denitrification and N₂O emission demonstrated significant positive relationships with rates of CO₂ emissions under elevated temperatures, suggesting that microbial N cycling processes were associated with enhanced microbial carbon (C) metabolism due to soil warming. The response in the abundance of relevant genes to elevated temperature was not always consistent with changes in N cycling processes. While elevated temperature increased the abundances of the nirS gene with plants and nosZ genes without plants, there was no effect on the abundances of the ammonia‐oxidizing archaea amoA gene, ammonia‐oxidizing bacteria amoA and nirK genes. This study provides the first global‐scale assessment demonstrating that elevated temperature shifts N cycling from microbial immobilization to enhanced mineralization, nitrification and denitrification in terrestrial ecosystems. These findings infer that elevated temperatures have a profound impact on global N cycling processes with implications of a positive feedback to global climate and emphasize the close linkage between soil microbial C and N cycling.     

Artificial neural networks for species identification by taxonomists

This paper is a study of the value of applying artificial neural networks (ANNs), specifically a multilayer perceptron (MLP), to identification of higher plants using morphological characters collected by conventional means. A practical methodology is thus demonstrated to enable botanical or zoological taxonomists to use ANNs as advisory tools for identification purposes. A comparison is made between the ability of the neural network and that of traditional methods for plant identification by means of a case study in the flowering plant genus Lithops N.E. Brown (Aizoaceae). In particular, a comparison is made with taxonomic keys generated by means of the DELTA system. The ANN is found to perform better than the DELTA key generator, for conditions where the available data is limited, and species relatively difficult to distinguish.     

Partition of photosynthates between shoot and root in spring wheat (Triticum aestivum L.) as a function of soil water potential and root temperature

Low soil water potential and low or high root temperatures are important stresses affecting carbon allocation in plants. This study examines the effects of these stresses on carbon allocation from the perspective of whole plant mass balance. Sixteen-day old spring wheat seedlings were placed in a growth room under precisely controlled root temperatures and soil water potentials. Five soil water potential treatments, from −0.03 MPa to −0.25 MPa, and six root temperature treatments, from 12 to 32°C were used. A mathematical model based on mass balance considerations was used, in combination with experimental measurements of rate of net photosynthesis, leaf area, and shoot/root dry masses to determine photosynthate allocation between shoot and root. Partitioning of photosynthates to roots was the lowest at 22–27°C root temperature regardless soil water potential, and increased at both lower and higher root temperatures. Partitioning of photosynthates to the roots increased with decreasing soil water potential. Under the most favourable conditions, i.e. at −0.03 MPa soil water potential and 27°C root temperature, the largest fraction, 57%, of photosynthates was allocated to the shoots. Under the most stressed conditions, i.e. at −0.25 MPa soil water potential and 32°C root temperature, the largest fraction, more than 80%, of photosynthates was allocated to roots.     

Direct and indirect climate change effects on photosynthesis and transpiration

Climate change affects plants in many different ways. Increasing CO(2) concentration can increase photosynthetic rates. This is especially pronounced for C(3) plants, at high temperatures and under water-limited conditions. Increasing temperature also affects photosynthesis, but plants have a considerable ability to adapt to their growth conditions and can function even at extremely high temperatures, provided adequate water is available. Temperature optima differ between species and growth conditions, and are higher in elevated atmospheric CO(2). With increasing temperature, vapour pressure deficits of the air may increase, with a concomitant increase in the transpiration rate from plant canopies. However, if stomata close in response to increasing CO(2) concentration, or if there is a reduction in the diurnal temperature range, then transpiration rates may even decrease. Soil organic matter decomposition rates are likely to be stimulated by higher temperatures, so that nutrients can be more readily mineralised and made available to plants. This is likely to increase photosynthetic carbon gain in nutrient-limited systems. All the factors listed above interact strongly so that, for different combinations of increases in temperature and CO(2) concentration, and for systems in different climatic regions and primarily affected by water or nutrient limitations, photosynthesis must be expected to respond differently to the same climatic changes.     

The RustPuccinia abruptavar.partheniicola,a Potential Biocontrol Agent of Parthenium Weed: Environmental Requirements for Disease Progress

The rust fungusPuccinia abruptavar.partheniicola,a potential biological control agent of parthenium weed (Parthenium hysterophorus), was evaluated under controlled environmental conditions. A range of spore germination temperatures as well as dew period durations and temperatures were investigated to determine some of the environmental requirements for disease establishment and disease progress. Plants were inoculated with urediniospores and exposed to dew periods between 3 to 12 h at temperatures of 10, 15, or 20°C. For disease expression, the inoculated plants were then grown in a glasshouse at one of two temperature regimes (30/26°C or 18/13°C; day/night). Urediniospores germinated best at 12 ± 1°C, with lower germination rates at 5°C or above 20°C. No infection occurred when the plants were exposed to dew periods of ≤3 h, regardless of the incubation temperature. The disease progressed most rapidly when plants were inoculated and incubated for a dew period of at least 12 h at a temperature of 15 ± 1°C. The disease progressed most slowly following inoculation at dew periods of 6 h or less. Disease progress was more rapid when the plants were exposed to a cool-temperature regime (18/13°C) than when exposed to a warm-temperature regime (30/26°C). This suggests that good infection of parthenium weed could be obtained when the urediniospores arrive on the plants during the afternoon in the cooler months of the central Queensland autumn when relatively long dew periods are expected.     

The influence of waterlogging at different temperatures on penetration depth and porosity of roots and on stomatal diffusive resistance of pea and maize seedlings

The 8 days old seedlings of pea (cv. Ilowiecki) and maize (cv. Alma F1) were subjected to differentiated aeration conditions (control — with pore water tension about 15 kPa and flooded treatment) for 12 days at three soil temperatures (7, 15 and 25 °C). The shoots were grown at 25 °C while the soil temperature was differentiated by keeping the cylinders with the soil in thermostated water bath of the appropriate temperature. Lowering the root temperature with respect to the shoot temperature caused under control (oxic) conditions a decrease of the root penetration depth, their mass and porosity as well as a decrease of shoot height, their mass and chlorophyll content; the changes being more pronounced in maize as compared to the pea plants. Flooding the soil diminished the effect of temperature on the investigated parameters; the temperature effect remaining significant only in the case of shoot biomass and root porosity of pea plants. Root porosity of pea plants ranged from 2 to 4 % and that of maize plants — from 4 to 6 % of the root volume. Flooding the soil caused an increase in the root porosity of the pea plants in the entire temperature range and in maize roots at lower temperatures by about 1 % of the root volume. Flooding the soil caused a decrease of root mass and penetration depth as well as a decrease of plant height, biomass and leaf chlorophyll content.     

Predicted global warming scenarios impact on the mother plant to alter seed dormancy and germination behaviour in Arabidopsis

Abstract Seed characteristics are key components of plant fitness that are influenced by temperature in their maternal environment, and temperature will change with global warming. To study the effect of such temperature changes, Arabidopsis thaliana plants were grown to produce seeds along a uniquely designed polyethylene tunnel having a thermal gradient reflecting local global warming predictions. Plants therefore experienced the same variations in temperature and light conditions but different mean temperatures. A range of seed‐related plant fitness estimates were measured. There were dramatic non‐linear temperature effects on the germination behaviour in two contrasting ecotypes. Maternal temperatures lower than 15–16 °C resulted in significantly greater primary dormancy. In addition, the impact of nitrate in the growing media on dormancy was shown only by seeds produced below 15–16 °C. However, there were no consistent effects on seed yield, number, or size. Effects on germination behaviour were shown to be a species characteristic responding to temperature and not time of year. Elevating temperature above this critical value during seed development has the potential to dramatically alter the timing of subsequent seed germination and the proportion entering the soil seed bank. This has potential consequences for the whole plant life cycle and species fitness.     

Developmental changes in shoot N dynamics of lucerne (Medicago sativa L.) in relation to leaf growth dynamics as a function of plant density and hierarchical position within the canopy

Shoot N concentration in plants decreases as they get bigger, due to the fact that N accumulates less rapidly than dry matter in plants during the plant growth process, leading to an allometric relationship between shoot N content (N(sh)) and shoot mass (W(sh)): N(sh)=a(W(sh))b. The results obtained on lucerne plants growing either under controlled low density conditions or in dense stands under field conditions show that the value of the allometric coefficient b that represents the ratio between the relative N accumulation rate in shoots [dN(sh)/(N(sh)dt)] and the relative growth rate [dW(sh)/(W(sh)dt)], decreases from 0.88 for a low plant density to 0.72 for a dense stand. Therefore, the fractional increase of shoot N per unit of shoot dry matter is lower when plants are in competition for light in dense canopies. This decrease can be entirely explained by the parallel decline in the leaf area per unit of shoot mass. Thus, a remarkably constant linear relationship can be established between N(sh) and leaf area (LA): N(sh)=1.7 g m(-2) LA, regardless of the conditions (low versus high density, controlled versus field conditions). Moreover, in a field dense stand, the comparison of plants with contrasting positions between the top and the bottom of the canopy (dominant, intermediate or suppressed plants), also shows that the difference in N(sh) at similar shoot mass is explained by the proportion of leaf mass to shoot mass. These data support the idea that leaf growth drives the dynamics of shoot N accumulation. These results also indicate that competition for light among individual plants within a dense canopy induces developmental changes in plant morphology (leaf:stem ratio) that explain the differences observed in shoot N concentration. This last observation could be extrapolated to multi-specific plant stands. Therefore, the sharing of N resources among plant species could partially be the result of the sharing of light within the canopy.