Origin of annual laminations in tufa deposits, southwest Japan

Laminated tufas and a tufa-depositing stream in SW Japan (Shirokawa, Ehime Prefecture) were studied monthly over a 3-yr period. A series of samples from the tufa clearly reveals the pattern of annual laminations. The annual layering pattern was primarily controlled by changes in the rate of calcite precipitation, as calculated from water chemistry. The concentration of dissolved CaCO₃, which correlates with the precipitation rate, was high in summer-autumn and low in winter-spring, owing to changes in the partial pressure of CO₂ in underground air. Regular seasonal changes in underground PCO₂ probably resulted from two temperature-dependent processes, the diffusion of soil CO₂ and the ventilation of underground air. These changes, in addition to water temperature changes, altered the precipitation rate, which has a clear seasonal pattern, especially in the lower stream. The seasonal precipitation rate was high in summer-autumn and low in winter-spring, which is consistent with the seasonal lamination pattern seen in the tufas. The textures of collected samples show that the laminations consist of densely calcified summer-autumn (June-October) laminae and lightly calcified winter-spring (November-May) laminae. We infer that the increased precipitation rate stimulated thick calcite encrustation on cyanobacterial filaments to produce the dense textures. This interpretation is supported by the lowered organic/inorganic carbon-production ratio in summer-autumn. Seasonal variations in cyanobacterial assemblages are present, but do not reflect the seasonal lamination pattern. Because the relevant processes are temperature dependent, the seasonal lamination pattern at Shirokawa is thought to generally apply to other laminated tufas deposited in temperate climates. However, a reversed pattern can result from local and climatic circumstances. Dense laminae were deposited in winter near the source of the spring at Shirokawa, because calcite precipitation was high owing to low underground PCO₂ in winter. Reversed patterns reported from northwestern Europe were probably influenced by seasonal rainfall, which is reflected in hydrological conditions.     

Factors controlling the timing of root elongation intensity in a mature upland oak stand

We examined the timing of root elongation intensity (REI) – the production of newly elongating roots measured in length per unit soil volume per unit time – in a mature white oak-chestnut oak forest in Tennessee, USA, over a 4-year period. We used a network of minirhizotrons to (1) examine environmental control of soil moisture and temperature over REI, (2) evaluate the control of phenology over REI (3) develop a multivariate regression equation using the variables of soil temperature, soil water potential and phenology to predict REI, and (4) delineate soil water potentials that were optimum for growth. Fifteen minirhizotron tubes were installed on the upper slope of an upland oak stand on Walker Branch Watershed in Oak Ridge, Tennessee. Measurements of REI were examined over three growing seasons in the upper 30 cm of the soil profile. Composited sets of data on REI, soil water potential, soil temperature and phenology were analyzed to determine the strength of relationships between the latter three variables and REI. There was no statistically significant relationship between REI and soil temperature during the growing season (March–November). The highly significant (p < 0.0001) relationship between soil water potential and REI was best described as log linear, using log₁₀ (-) vs. log₁₀ (REI). The correlation between a phenology index and REI was also highly significant (p < 0.0001), as the 24 highest REI levels occurred between late April and early August. Whereas soil water potential played a major role in controlling REI, our data indicate that at times phenologically related factors appeared to override environmental variables. The fact that REI generally peaked every year following completion of leaf expansion is congruent with the fixed shoot growth pattern of many temperate-zone deciduous tree species. In an attempt to explain the importance of phenology in controlling REI, we refer to the concept of `phenological programming'. This concept contrasts with more environmentally determinant explanations of the timing of root growth. Those theories cannot explain either our data or that of others, wherein, during late summer and early autumn, REI does not return to early summer rates, even though soil moisture and temperature conditions are equally, if not more, favorable. The particular type of `phenological programming' hypothesized in this study may be limited to mature deciduous trees exhibiting a fixed growth pattern of shoot expansion and growing in a temperate climate with a mid-summer drought period.     

Air humidity as key determinant of morphogenesis and productivity of the rare temperate woodland fern Polystichum braunii

(1) Most ferns are restricted to moist and shady habitats, but it is not known whether soil moisture or atmospheric water status are decisive limiting factors, or if both are equally important. (2) Using the rare temperate woodland fern Polystichum braunii, we conducted a three‐factorial climate chamber experiment (soil moisture (SM) × air humidity (RH) × air temperature (T)) to test the hypotheses that: (i) atmospheric water status (RH) exerts a similarly large influence on the fern's biology as soil moisture, and (ii) both a reduction in RH and an increase in air temperature reduce vigour and growth. (3) Nine of 11 morphological, physiological and growth‐related traits were significantly influenced by an increase in RH from 65% to 95%, leading to higher leaf conductance, increased above‐ and belowground productivity, higher fertility, more epidermal trichomes and fewer leaf deformities under high air humidity. In contrast, soil moisture variation (from 66% to 70% in the moist to ca. 42% in the dry treatment) influenced only one trait (specific leaf area), and temperature variation (15 °C versus 19 °C during daytime) only three traits (leaf conductance, root/shoot ratio, specific leaf area); RH was the only factor affecting productivity. (4) This study is the first experimental proof for a soil moisture‐independent air humidity effect on the growth of terrestrial woodland ferns. P. braunii appears to be an air humidity hygrophyte that, whithin the range of realistic environmental conditions set in this study, suffers more from a reduction in RH than in soil moisture. A climate warming‐related increase in summer temperatures, however, seems not to directly threaten this endangered species.     

Leaf growth and population dynamics of intertidal Zostera japonica on the western coast of Korea

Leaf production and population dynamics of Zostera japonica were examined at three elevations of an intertidal transect in Seungbongdo Island on the western coast of Korea. Morphometrics, shoot density, biomass, leaf production, reproductive effort and environmental factors were monitored from October 2001 to October 2002. Z. japonica grew well in the lower intertidal zone from 0.2 to 1.0 m above mean chart datum. The upper station (St. 1) exhibited a finer sediment grain size and richer organic content than the middle (St. 2) and lower stations (St. 3). The size of shoots and leaves was significantly greater at St. 1 than at St. 3, whereas the rhizome internodes were longer at St. 3. Despite differences in morphological characteristics among three stations, seagrass biomass and shoot density were not significantly different among study sites. Shoot density, biomass, morphometrics and leaf productivity exhibited clear seasonal variations, which varied along with seasonal changes of water and air temperature. Leaf productivity measured by the clip and reharvest method was highest in September (4.3 g DW m⁻² d⁻¹) and lowest in February (0.2 g DW m⁻² d⁻¹). Reproductive shoots rapidly increased to maximum density along with the high water temperature in July to September. In the intertidal zone, Z. japonica exhibited faster vegetative growth on muddy sand than on sand, probably due to the difference in nutrient supply. The seasonal changes of water and air temperature were considered to play an important role in the seasonal leaf growth of Z. japonica.     

Leaf growth and population dynamics of intertidal Zostera japonica on the western coast of Korea

Leaf production and population dynamics of Zostera japonica were examined at three elevations of an intertidal transect in Seungbongdo Island on the western coast of Korea. Morphometrics, shoot density, biomass, leaf production, reproductive effort and environmental factors were monitored from October 2001 to October 2002. Z. japonica grew well in the lower intertidal zone from 0.2 to 1.0 m above mean chart datum. The upper station (St. 1) exhibited a finer sediment grain size and richer organic content than the middle (St. 2) and lower stations (St. 3). The size of shoots and leaves was significantly greater at St. 1 than at St. 3, whereas the rhizome internodes were longer at St. 3. Despite differences in morphological characteristics among three stations, seagrass biomass and shoot density were not significantly different among study sites. Shoot density, biomass, morphometrics and leaf productivity exhibited clear seasonal variations, which varied along with seasonal changes of water and air temperature. Leaf productivity measured by the clip and reharvest method was highest in September (4.3 g DW m⁻² d⁻¹) and lowest in February (0.2 g DW m⁻² d⁻¹). Reproductive shoots rapidly increased to maximum density along with the high water temperature in July to September. In the intertidal zone, Z. japonica exhibited faster vegetative growth on muddy sand than on sand, probably due to the difference in nutrient supply. The seasonal changes of water and air temperature were considered to play an important role in the seasonal leaf growth of Z. japonica.     

Leaf Primordium Initiation and Expanded Leaf Production are Co-ordinated through Similar Response to Air Temperature in Pea (Pisum sativumL.)

Accurate prediction of the timing of leaf area development isessential to analyse and predict the responses of crops to theenvironment. In this paper, we analyse the two processes determiningthe chronology of leaf development—initiation of leafprimordia by the shoot meristem and production of expanded leavesout of the shoot tip—in several pea (Pisum sativumL.)cultivars in response to air temperature and plant growth rate.Contrasting levels of air temperature and plant growth rateduring leaf development were induced by a wide range of sowingdates and plant densities in glasshouse or field experiments.Full leaf expansion was found to occur one phyllochron afterfull leaf unfolding, whatever the leaf nodal position. Primordiuminitiation and expanded leaf production rates presented similarquantitative responses to air temperature (linear response andcommonx-intercept), whatever the plant growth rate, cultivaror period of cycle. As a consequence, they were co-ordinatedand the numbers of initiated primordia or expanded leaves wereeasily deduced from simple visual observation of leaf unfolding.The change, over time, of the numbers of initiated leaf primordiaand fully expanded leaves correlated with cumulated degree-days,with stable relationships in a wide range of environmental conditions.Two phases, with different production rates, had to be considered.These results allowed us to predict accurately the beginningand the end of individual leaf development from daily mean airtemperatures. The relationships obtained here provide an effectiveway of analysing and predicting leaf development responses tothe environment. Pisum sativumL.; pea; number of leaf primordia; number of leaves; temperature; modelling     

Ecophysiological responses of two dominant grasses to altered temperature and precipitation regimes

Ecosystem responses to climate change will largely be driven by responses of the dominant species. However, if co-dominant species have traits that lead them to differential responses, then predicting how ecosystem structure and function will be altered is more challenging. We assessed differences in response to climate change factors for the two dominant C₄ grass species in tallgrass prairie, Andropogon gerardii and Sorghastrum nutans, by measuring changes in a suite of plant ecophysiological traits in response to experimentally elevated air temperatures and increased precipitation variability over two growing seasons. Maximum photosynthetic rates, stomatal conductance, water-use efficiency, chlorophyll fluorescence, and leaf water potential varied with leaf and canopy temperature as well as with volumetric soil water content (0–15 cm). Both species had similar responses to imposed changes in temperature and water availability, but when differences occurred, responses by A. gerardii were more closely linked with changes in air temperature whereas S. nutans was more sensitive to changes in water availability. Moreover, S. nutans was more responsive overall than A. gerardii to climate alterations. These results indicate both grass species are responsive to forecast changes in temperature and precipitation, but their differential sensitivity to temperature and water availability suggest that future population and community structure may vary based on the magnitude and scope of an altered climate.     

Fine root dynamics in Slovenian beech forests in relation to soil temperature and water availability

Key message

Fine root ingrowth and mortality of European beech are related to evapotranspiration, cumulative forest floor precipitation, soil temperature and water content, which are affected by forest management and gap creation.

Abstract

The ingrowth and mortality of European beech (Fagus sylvatica L.) fine roots (diameters <2 mm) were studied in relation to environmental variables describing temperature and water availability at four sites, covering a range in environmental conditions likely to be encountered in Slovenian beech forests. Minirhizotron images were used to determine fine root dynamics in a stand and gap in each of the sites for 12 periods during the 2007–2009 growing seasons. The environmental variables included air and soil temperatures, precipitation, forest floor precipitation, evapotranspiration and soil water contents. For data analysis, the daily mean values for each period for all variables were used. Fine root ingrowth and mortality were higher in the managed stand and gap compared to the old-growth stand and gap, but only significantly correlated with each other in the case of the managed stand. Forest floor precipitation and soil temperature were significant in explaining fine root ingrowth, whereas maximal evapotranspiration, soil temperature and soil water content were more important for fine root mortality. However, the correlations were weak and inconsistent among the four sites. By including site as predictor as well as environmental variables, R ² values of 0.49 and 0.55 for ingrowth and mortality, respectively, were achieved. Despite this, the relationships between the fine root dynamics and selected environmental factors appeared relatively weak and complex, especially for fine root ingrowth and might be partially related also to differences in successional stages of the forests under study.

     

Influence of different soil temperatures on water use,growth and internal water status of soybean

Studies on the effect of soil temperature on internal water relations of well watered soybean (Glycine max L.) at constant air temperature under controlled conditions were carried out. A specially designed thermogradient tank was used for obtaining a range of soil temperatures. Data on shoot height, shoot weight, root length, root weight, leaf area and leaf water potential were obtained at 41 days after sowing and the highest values of these parameters were recorded at 28.6°C. The air temperature during the course of these investigations was 25±1°C and it may be concluded that slightly warmer soil temperatures than air temperatures were optimal for soybean with regard to the above measured parameters.     

Resistance to Water Transport in Shoots of Vitis vinifera L. : Relation to Growth at Low Water Potential

Apparent resistances to water transport in the liquid phase were determined from measurements of soil, root, basal shoot internode, shoot apex, and leaf water potentials and water flux in Vitis vinifera (cv White Riesling) during soil drying. Predawn water potential differences (ΔΨ) in the shoots accounted for 20% of the total ΔΨ between the soil and the shoot apex when plants were well-watered but increased to about 90% when shoot growth ceased. The ΔΨ from soil to root was essentially constant during this period. At low water potential, the ΔΨ in the shoot was persistent when transpiration was low (predawn) or completely prevented (plant bagging). The apparent hydraulic resistance between the basal shoot internode and most rapidly expanding leaf (or shoot apex) increased several-fold when water was withheld. Leaf and internode expansion both exhibited high sensitivity to increasing hydraulic resistance. Measurements of pneumatic resistance to air flow through frozen internode segments indicated progressive vapor-filling of vessels as soil drying progressed. From these observations and others in the literature, it was suggested that embolization may be a common occurrence and play an important role in the inhibition of shoot growth at moderate water deficits.     

Glycine-Glomus-Bradyrhizobium Symbiosis : X. Relationships between Leaf Gas Exchange and Plant and Soil Water Status in Nodulated, Mycorrhizal Soybean under Drought Stress

Soybean (Glycine max [L.] Merr.) plants were colonized by the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (VAM plants) or fertilized with KH₂PO₄ (nonVAM plants) and grown for 50 days under controlled conditions. Plants were harvested over a 4-day period during which the soil was permitted to dry slowly. The harvest was terminated when leaf gas exchange was no longer measurable due to drought stress. Significantly different effects in shoot water content, but not in shoot water potential, were found in VAM and nonVAM plants in response to drought stress. Leaf conductances of the two treatments showed similar response patterns to changes in soil water and shoot water potential but were significantly different in magnitude and trend relative to shoot water content. The relationships between transpiration, CO₂ exchange and water-use efficiency (WUE) were the same in VAM and nonVAM plants in response to decreasing soil water and shoot water potential. As a function of shoot water content, however, WUE showed different response patterns in VAM and nonVAM plants.     

Warm spring temperatures induce persistent season-long changes in shoot development in grapevines

Background and Aims

The influence of temperature on the timing of budbreak in woody perennials is well known, but its effect on subsequent shoot growth and architecture has received little attention because it is understood that growth is determined by current temperature. Seasonal shoot development of grapevines (Vitis vinifera) was evaluated following differences in temperature near budbreak while minimizing the effects of other microclimatic variables.

Methods

Dormant buds and emerging shoots of field-grown grapevines were heated above or cooled below the temperature of ambient buds from before budbreak until individual flowers were visible on inflorescences, at which stage the shoots had four to eight unfolded leaves. Multiple treatments were imposed randomly on individual plants and replicated across plants. Shoot growth and development were monitored during two growing seasons.

Key Results

Higher bud temperatures advanced the date of budbreak and accelerated shoot growth and leaf area development. Differences were due to higher rates of shoot elongation, leaf appearance, leaf-area expansion and axillary-bud outgrowth. Although shoots arising from heated buds grew most vigorously, apical dominance in these shoots was reduced, as their axillary buds broke earlier and gave rise to more vigorous lateral shoots. In contrast, axillary-bud outgrowth was minimal on the slow-growing shoots emerging from buds cooled below ambient. Variation in shoot development persisted or increased during the growing season, well after temperature treatments were terminated and despite an imposed soil water deficit.

Conclusions

The data indicate that bud-level differences in budbreak temperature may lead to marked differences in shoot growth, shoot architecture and leaf-area development that are maintained or amplified during the growing season. Although growth rates commonly are understood to reflect current temperatures, these results demonstrate a persistent effect of early-season temperatures, which should be considered in future growth models.     

Impact of soil texture and water availability on the hydraulic control of plant and grape-berry development

Aims

All components of the soil-plant-atmosphere (s-p-a) continuum are known to control berry quality in grapevine (Vitis vinifera L.) via ecophysiological interactions between water uptake by roots and water loss by leaves. The scope of the present work was to explore how the main hydraulic components of grapevine influence fruit quality through changes in liquid- and gas-phase hydraulic conductance.

Methods

To reach our objectives, determinations of shoot growth, berry size and sugar content, leaf gas exchange, predawn leaf water potential (as a proxy of soil water potential), midday stem water potential and leaf water potential were performed in conjunction with anatomical measurements of shoot xylem. All measurements were conducted in two different cultivars (Cabernet franc and Merlot) and on three different soil types (clayey, gravelly, and sandy).

Results

Shoot xylem morphometric characteristics and whole-plant hydraulic conductance were influenced by cultivar and soil type. Differences in leaf gas exchange parameters and water potentials were determined by soil type significantly more than by cultivar. Between the two extremes (gravelly soil imposing drought conditions and sandy soil with easily accessible water) the clayey soil expressed an intermediate plant water consumption and highest sugar accumulation in berry.

Conclusions

Hydraulic and non hydraulic limitations to vine/berry interactions supported the conclusion that water availability in the soil overrides differences due to cultivar in determining the productive potential of the vineyard. Non hydraulic stomatal control was expected to be an important component on plants grown on the clayey soil, which experienced a moderate water stress. Possible links between hydraulic traits and berry development and quality are discussed.     

5-Aminolevulinic acid ameliorates salinity-induced metabolic, water-related and biochemical changes in Brassica napus L.

A number of studies have established that plant growth and development in oilseed rape (Brassica napus L.) are hampered by salinity stress. Nowadays, researchers have focused on the use of plant growth regulators to increase plant tolerance against salinity. An experiment was performed to evaluate the effects of 5-aminolevulinic acid (ALA, 30 mg l^?1) on Brassica napus L. (cv. ??ZS 758??) plants under NaCl (100, 200 mM) salinity. Data presented here were recorded on two different leaf positions (first and third) to have a better understanding of the ameliorative role of ALA on NaCl-stressed oilseed rape plants. Results have shown that increasing salinity imposed negative impact on relative growth rate (root and shoot) and leaf water relations (osmotic potential and relative water content), whereas enhanced the level of relative conductivity, malondialdehyde (MDA) content, osmolytes (soluble sugar, soluble protein, free amino acid and proline) concentration, reactive oxygen species (ROS), and enzymatic (ascorbate peroxidase, guaiacol peroxidase, catalase and superoxide dismutase) and non-enzymatic (reduced glutathione and ascorbate) antioxidants activity in two different leaf position samples. Foliar application of ALA improved relative growth rate (root and shoot) and leaf water relations (osmotic potential and relative water content), and also triggered the further accumulation of osmolytes (soluble sugar, soluble protein, free amino acid and proline) as well as enzymatic (ascorbate peroxidase, guaiacol peroxidase, catalase and superoxide dismutase) and non-enzymatic (reduced glutathione and ascorbate) antioxidants activity in both leaf samples, whereas decreased the membrane permeability, MDA content and ROS production. Our results also indicate that osmolytes are preferentially accumulated in younger tissues.     

Effect of salinisation of soil on growth, water status and general nutrient accumulation in seedlings .of Delonix regia (Fabaceae)

Greenhouse experiments were conducted to assess the effect of salinisation of soil on emergence, growth, water content, proline content and mineral accumulation of seedlings of Delonix regia (Hook.) Raf. (Fabaceae). Sodium chloride (NaCl) was added to the soil and salinity was maintained at 0.3, 1.9, 3.9, 6.0 and 7.9 dS m^?1. A negative relationship between seedling emergence and salt concentration was obtained. Salinity caused reduction in water content and water potential of tissues (leaves, stems, tap roots and lateral roots) that resulted in internal water deficit to plants. Consequently, shoot and root elongation, leaf expansion and dry matter accumulation in leaves, stems, tap roots and lateral root tissues of seedlings significantly decreased in response to increasing concentration of salt. Proline content in tissues was very low. There were no effective mechanisms to control net uptake of Na on root plasma membrane and subsequently its transport to shoot tissues. Potassium content significantly decreased in tissues in response to salinisation of soil. This tree species is a moderate salt-tolerant glycophytic plant. Nitrogen and calcium content in tissues significantly decreased as soil salinity increased. Phosphors content in tissues exhibited a declining trend with increase in soil salinity. Changes in tissues and whole-plant accumulation pattern of other elements tested, as well as possible mechanisms for avoidance of Na toxicity in this tree species in response to salinisation, are discussed.     

Water relations of crok-oak (Quercus suber L.) under natural conditions

Daily and annual courses of leaf transpiration, stomatal conductance and shoot water potential of four Quercus suber individuals were compared in a semi-natural stand in southwest Portugal, from spring 1989 to early summer 1990.The trees investigated showed annual patterns typical of evergreen sclerophyllous species but varied in their range of stomatal operation. This appeared to be related to differences in hydraulic conductivity in the root-to-leaf pathway.Maximum stomatal conductance and transpiration rates occurred from March to June.Water stress was found to be moderate and winter cold stress due to low air and soil temperatures appeared to have an influence on plant water balance through their effects on flow resistances.Abbreviations g_sw stomatal conductance - g_max maximum stomatal conductance - PAR photosynthetically active radiation - RH relative humidity of the air - T leaf transpiration - Ta air temperature - TL leaf temperature - T_max maximum leaf transpiration - W air-to-leaf vapor pressure difference - shoot water potential - PD predawn shoot water potential - MIN minimum shoot water potential     

Willow water uptake and shoot extension growth in response to nutrient and moisture on a clay landfill cap soil

Extension growth of willow (Salix viminalis L.) and changes in soil water were measured in lysimeters containing clay and sandy loam soils with different amendment and watering treatments. No water uptake was found below 0.3 m in the nutritionally poor unamended clay; amendment with organic matter to 0.4 m depth resulted in water extraction down to 0.5 m depth whereas in the sandy loam, there was greater extraction from all depths down to 0.6 m. With water stress, wilting of plants occurred when the volumetric soil water content at 0.1 m was about 31% in the clay and 22% in the sandy loam. Compared with shoots on plants in the amended clay, those in the unamended treatment showed reduced extension growth, little increase in stem basal area (SBA) and a small shoot leaf area, resulting from a reduced number of leaves shoot⁻¹ and a small average area leaf⁻¹. Water stress also reduced shoot extension growth, SBA gain and the leaf area on extension growth. Shoot growth rates were significantly correlated with air temperature and base temperatures between 2.0 and 7.6 °C were indicated for the different treatments. These studies have helped to explain some of the large treatment effects described previously on biomass production and plant leaf area.     

Early growth,dry matter allocation and water use efficiency of two sympatric Populus species as affected by water stress

We exposed cuttings of two sympatric species of Sect. Tacamahaca Spach, Populus cathayana Rehder and Populus przewalskii Maximowicz, to two watering regimes in a greenhouse. In the semi-controlled environmental study, two watering treatments which were watered to 100 and 25% of field capacity were used, respectively. The effects of water deficit on early growth, biomass allocation and water use efficiency (WUE) were investigated. We found that there were significant interspecific differences in early growth, dry matter allocation and water use efficiency between two sympatric Populus species. Compared with P. cathayana, P. przewalskii showed higher shoot height, dry matter accumulation, number of leaves, total leaf area, fine root mass, fine root/total root ratio and water use efficiency under both well-watered and water-stressed treatments. On the other hand, P. przewalskii also showed higher root mass/foliage area ratio, root/shoot ratio and carbon isotope composition than P. cathayana under water-stressed treatment. The results suggested that there were different water-use strategies between two sympatric Populus species, P. przewalskii with higher drought tolerance may employ a conservative water-use strategy, whereas P. cathayana with lower drought tolerance may employ a prodigal water-use strategy. The findings confirm the existence of interspecific genetic differences in early growth, dry matter allocation and water use efficiency as affected by water stress, these variations in drought responses may be used as criteria for species selection and tree improvement.     

Litter decomposition of woody species in shrublands of NW Patagonia: how much do functional groups and microsite conditions influence decomposition?

The study examined the effects of leaf traits, soil microsite, and microclimate characteristics on litter decomposition of the dominant species in two functional groups (FG), deciduous and evergreen, in shrublands in NW Patagonia, Argentina. Leaf traits considered were nutrient concentration (C, N, P, C/N, and N/P) and physical characteristics (area, strength, specific leaf area, and dry matter content). Soil microsite characteristics measured were pH, C, N, P, C/N and water retention capacity, while soil microclimate characteristics recorded were soil and air, temperature and moisture, and solar radiation. Five evergreen and five deciduous woody shrub species were selected. During 1 year, litter and microsite properties were measured below canopy: (i) senescent leaf chemical and physical properties, and the quantity as well as field decomposition of litter and (ii) soil chemistry, and soil and air physical properties. The factors controlling litter decomposition were different for each FG. In deciduous species, C/N ratio had a negative effect on decomposition. In evergreen species, decomposition was affected negatively by leaf carbon and dry matter content. Litter decomposition depended exclusively on the inherent senescent leaves traits. The common decomposition pattern between species of both FG could be attributed to similar leaf traits and the correlation between variables that control decomposition in both groups. Plant nutrient inputs associated with the litter decomposition process did not explain the soil nutrient content. These results suggest that other organic matter sources (roots, branches, and fruits) are more important than leaves on soil fertility.     

Effects of silicon on Zea mays plants exposed to water and oxygen deficiency

Effects of shoot and root supplementation with silicon on the response of Zea mays L. plants to matric water potential (Ψ_m) and oxygen deficiency (waterlogging) stresses were studied. The soil water limitation (Ψ_m) and oxygen deprivation significantly reduced shoot dry weight, chlorophyll (Chl) content, ascorbic acid content, as well as leaf relative water content. Both soil drying and waterlogging caused a significant increase in the leaf membrane injury by heat (51°C) and dehydration (40% PEG) stresses. The levels of lipid peroxidation (POL) and hydrogen peroxide (H₂O₂) content were increased by excess soil drying and oxygen deficiency. Supplementary silicon at 1.0 mM significantly increased Chl content and improved water status. Concentrations of H₂O₂, MDA, and proline and leaf membrane injury were significantly reduced by Si application. The reverse helds true for ascorbic acid. The results of this study indicate that application of silicon might improve growth attributes, effectively mitigate the adverse effect of drought and waterlogging, and increase tolerance of maize plants. The silicon-induced improvement of drought and anoxia tolerance was associated with the increase in oxidative defense abilities.