Water Availability Treatments Research Articles

Drought and simulated deer herbivory reduce growth in Atlantic white cedar seedlings

White-tailed deer are overabundant in much of eastern North America and may be suppressing regeneration in some tree species. Herbivory initially reduces plant biomass, but it has the potential to stimulate compensatory growth. However, stressful environmental conditions may reduce recovery from herbivory. Seedlings of Atlantic white cedar, Chamaecyparis thyoides (L.) Britton, Sterns & Poggenb., are frequently browsed by white-tailed deer and also experience both flooded and dry soils in natural habitats. We conducted a growth chamber experiment to test for a potential interaction between simulated deer browsing and water availability treatments on seedling height, stem diameter, and above- and belowground biomass. Of the 180 study plants, half were subjected to an initial clipping treatment, and all plants were then exposed to high, intermediate, or low water availability for 90 days. We found that, over the short term, seedlings in favorable growing conditions could not compensate for lost biomass after simulated browsing. Drought reduced shoot biomass, and flooded soils reduced root but not shoot growth. Water stress and herbivory did not interact to reduce growth more than the effect of each treatment separately. In general, the effect of water stress on plant size was greater than the effect of simulated herbivory.

Impact of genetic variation and long-term limited water availability on the ecophysiology of young Sitka spruce (Picea sitchensis (Bong.) Carr.).

Future limited water availability may reduce the potential of tree improvement to increase timber yields. We investigated ecophysiological variation between full-sibling families of Sitka spruce (Picea sitchensis (Bong.) Carr.) growing under contrasting water availability conditions: control (optimal) water availability and limited water availability. One-year-old seedlings of nine improved families plus an unimproved seed lot were grown in pots in a greenhouse and the two water availability treatments imposed via drip irrigation. Whole-plant water use varied between families. Stomatal conductance and the light-saturated quantum yield of photosystem II at times differed between families, but not consistently. Certain families showed considerably greater increases in electron transport rate with increasing photosynthetically active radiation. Limited water availability resulted in reduced branch water potential, leaf stomatal conductance and transpiration per unit leaf area, and increased whole-plant water-use efficiency, in all genetic material. The responses of plant water use and leaf carbon isotope composition to water limitation, were, however, initially influenced by variation in vigour between families-with conservative growth in some material slowing the decline in substrate moisture content. As the duration of water deficit extended, these variables showed a more uniform response across families. Between-family variation in physiological mechanisms of drought tolerance was not detected. Thus, for Sitka spruce, assessing juvenile material may not allow selection to prevent reductions in productivity associated with long-term sub-optimal growing conditions, but screening for conservative growth (within families as well as between families) may be beneficial where survival of relatively short-term water limitation is the primary concern.

Latitudinal and longitudinal clines of phenotypic plasticity in the invasive herb Solidago canadensis in China.

Phenotypic plasticity is thought to be important for plants in variable environments. The climatic variability hypothesis poses that populations at higher latitudes, due to the stronger variation in temperature, there should be more plastic in response to temperature than populations at lower latitudes. Similarly, populations at locations with stronger precipitation fluctuations should be more plastic in response to water availability than populations at locations with less variable precipitation. We sampled seven and nine populations of Solidago canadensis, a North American native that is invasive in China, along a latitudinal (temperature variability) and a longitudinal (precipitation variability) gradient, respectively, in China, and grew them under two temperature treatments and two water-availability treatments, respectively. Among the four traits with significant variation in plasticity among populations in response to temperature, plasticity of leaf length-to-width ratio was significantly positively correlated with latitude and temperature seasonality of the populations. In addition, root/shoot ratio and water-use efficiency showed significant variation in plasticity among populations in response to water availability, and plasticities of these two traits were significantly negatively correlated with longitude and positively correlated with precipitation seasonality. The observed geographic clines in plasticity suggest that phenotypic plasticity of S. canadensis may have evolved rapidly in regions with different climatic conditions, and this may have contributed to the spread of this invasive species.

Soil compaction and water availability affect growth and survival of Quercus ilex subsp. ballota seedlings under different light environments

We examined the effect of abiotic characteristics (soil compaction, water availability and photosynthetic photon flux density (PPF) on the germination, emergence, growth and survival of Quercus ilex subsp. ballota seedlings. To determine the importance of these characteristics on the growth and development of the seedlings, we simulated two levels of water availability [650 mm year−1 (W650) and 1000 mm year−1 (W1000)], two levels of light [representing full (PPF100) and low sunlight (80 % reduction of sunlight, PPF20) conditions] and three soil compaction depths [soil compaction at depth 60 cm (C60), 25 cm (C25) and 10 cm (C10)]. Seedling emergence and survival were determined, along with various biometric characteristics. Emergence rate was only significantly affected by the water availability treatment, being significantly lower in W650. No differences were found in the other treatments. Seedlings grown under high PPF presented an increase in biomass. Seedlings grown in the deeper soils (C60) showed deeper and thinner roots. The results show increased survival of seedlings grown under low PPF and high water availability. Our results obtained in this greenhouse study support the hypothesis of facilitation, which considers that under drought conditions the promoting effect of water balance induced by the shade is more positive for the survival of the seedlings. We cannot say whether there are one or more independent factors that will limit or enhance the natural regeneration of Q. ilex, which implies that the effects of some can be mitigated, compensated for or amplified depending on the interaction with other elements. Knowledge of these interactions and the environmental variability of habitats at a smaller scale can be a powerful tool for promoting the growth of native vegetation and conservation of the Mediterranean area and dry environments.

Growth, biomass allocation and photosynthetic responses are related to intensity of root severance and soil moisture conditions in the plantation tree Cunninghamia lanceolata.

We employed the warm temperate conifer Cunninghamia lanceolata (Lamb.) Hook. as a model of plantation forest species to investigate ecophysiological responses to root treatments (control (0%), and ∼25, 50 or 75% of the initial root mass) under well-watered and water-limited conditions. Our results indicated that total root dry mass accumulation was negatively associated with the severity of root pruning, but there was evidence of multiple compensatory responses. The plants exhibited higher instantaneous and long-term (assessed by carbon isotope composition, δ(13)C) water-use efficiency in pruning treatments, especially under low water availability. Root pruning also increased the fine root/total root mass ratio, specific root length and fine root vitality in both water availability treatments. As a result of the compensatory responses, under well-watered conditions, height, stem dry mass accumulation, leaf/fine root biomass ratio (L/FR), transpiration rate, photosynthetic capacity and photosynthetic nitrogen-use efficiency (EN) were the highest under 25% pruning. Yet, all these traits except L/FR and foliage nitrogen content were severely reduced under 75% pruning. Drought negatively affected growth and leaf gas exchange rates, and there was a greater negative effect on growth, water potential, gas exchange and EN when >25% of total root biomass was removed. The stem/aboveground mass ratio was the highest under 25% pruning in both watering conditions. These results indicate that the responses to root severance are related to the excision intensity and soil moisture content. A moderate root pruning proved to be an effective means to improve stem dry mass accumulation.

Water stress and soil compaction impacts on clover growth and nutrient concentration

Soil compaction and insufficient water supply generally decrease crop performance. The effects of varying compaction and water availability levels on the growth of Berseem or Egyptian clover ( Trifolium alexandrimum L.), water use efficiency and nutrient concentration were investigated under greenhouse conditions. Treatments consisted of three soil compaction levels (bulk density of 1.2, 1.4 and 1.6 Mg m -3 ), and four water availability treatments (40%, 60%, 80% and 100% of soil field capacity) in a factorial combination. Soil compaction had a significant effect on water use efficiency with the highest (0.32 g l -1 ) at bulk density of 1.4 Mg m -3 and the lowest at the other bulk densities. Soil compaction had no significant effects on leaf area, shoot, root and total dry masses. Water stress resulted in lower leaf area (from 231 to 153 mm 2 pot -1 ), and the stem lengths were 7.6 cm and 4.3 cm for 80% and 60% of field capacity, respectively. Likewise, the highest (0.47 g pot -1 ) and lowest (0.33 g pot -1 ) total dry masses were observed at 80% and 60% field capacities. Water use efficiencies were 0.32 and 0.20 g l -1 for 100% and 60% field capacities, respectively. The accumulation of N, P and K per unit length of roots increased with soil compaction. As the water supply increased, the root and shoot dry weight and water use efficiency increased. Treatment of 100% field capacity resulted in the highest accumulation of N, P and K. Results indicated that the treatment of 80% field capacity and bulk density of 1.4 Mg m -3 provided the best conditions for clover performance, among the applied treatments. This study suggests that sufficient water supply can moderate the adverse effects of soil compaction on clover performance.

DETERMINAÇÃO DA MÁXIMA CAPACIDADE DE RETENÇÃO DE ÁGUA NO SUBSTRATO PARA PRODUÇÃO DE MUDAS DE EUCALIPTO EM VIVEIRO

A escassez de informações referentes ao consumo hídrico de mudas de espécies florestais freqüentemente dificulta o planejamento da irrigação em viveiros comerciais, levando muitas vezes, a adoção de medidas ineficientes de manejo, provocando perda no padrão de qualidade das mudas. Dessa forma, procurou-se neste trabalho investigar a máxima capacidade de retenção de água (MCRA) no substrato em que as mudas de eucalipto podem ser submetidas e determinar o coeficiente de cultivo (Kc) para o clone híbrido de E. urophylla x E. grandis. O estudo foi realizado em casa de vegetação, localizada na área experimental do Programa de Pós-Graduação em Ciências Florestais vinculado ao Centro de Ciências Agrárias da Universidade Federal do Espírito Santo (CCA-UFES) no município de Alegre, ES, montado num delineamento inteiramente casualizado, com cinco tratamentos de disponibilidade hídrica no substrato (90, 80, 70, 60 e 50% da MCRA), com quatro repetições. De acordo com os resultados obtidos, verificou-se que a disponibilidade hídrica no substrato de 70% da MCRA pode ser utilizada para a produção de mudas clonais de eucalipto, sem afetar o crescimento e o padrão de qualidade. O Kc estimado para as mudas de eucalipto em condições de viveiro foi de 1,25. AbstractDetermination of maximum capacity of water retention in substrate for production plants in Eucalyptus nursery. The scarcity of information regarding water consumption of seedlings of forest species often complicates the planning of irrigation in commercial nurseries, often leading the adoption of inefficient management measures, causing loss in the quality of seedlings. Thus, this study sought to investigate the capacity of water retention in the substrate in which the eucalyptus seedlings can be submitted and determine the crop coefficient (Kc) for the hybrid clone of E. urophylla x E . grandis. The study was conducted in a greenhouse located in the experimental area of the Post-Graduation of Forest Sciences bound to the Center for Agrarian Sciences, Federal University of Espírito Santo in the city of Alegre, ES, built in a completely randomized design with five treatments of water availability in the substrate (90, 80, 70, 60 and 50% of MCRA) and four replications. According to the results, it was found that water availability in the substrate MCRA of the 70% can be used for the production of minicutting, without affecting standards of growth and quality. The Kc for eucalyptus seedlings in nursery conditions was 1.25.Keywords: Coefficient of cultivation; irrigation management; Eucalyptus urophylla x E. grandis.

Water availability and formation of propagules of arbuscular mycorrhizal fungi associated with sorghum

Arbuscular mycorrhizal fungi (AMF) promote greater tolerance to the negative effects of water stress in their host plants, yet may also be influenced by the availability of water in the production of their infective propagules. The objective of this study was to assess the effect of water availability in the soil on the sporulation of Claroideoglomus etunicatum, Gigaspora albida and Scutellospora heterogama, and the influence of this condition on the infective potential and number of nuclei in glomerospores of these species. The reduction of water availability from 75 to 25% did not decrease significantly the sporulation of C. etunicatum, but resulted in decrease of sporulation of G. albida (600 to 7 glomerospores per 30g−1 soil) and S. heterogama (274 to 2 glomerospores per 30g−1 soil). The water availability at 75 and 71% promoted maximum sporulation of G. albida and S. heterogama, respectively. While G. albida and S. heterogama had greater sporulation than C. etunicatum, the infective potential of these species was lower, which may be related to the life-strategy and type of infective propagules of each species. The number of nuclei per glomerospore varied only among the species (p<0.05), with C. etunicatum and G. albida presenting the higher number of nuclei when compared to S. heterogama, but no differences were found among the treatments of water availability (p>0.05). These results suggest that AMF have distinct sporulation strategies and the amount of glomerospores is not directly related to the infectivity of the inoculum. Possibly, the differences in the life-strategies among the species were greater than the effects of water availability.

Expression of functional traits during seedling establishment in two populations of Pinus ponderosa from contrasting climates.

First-year tree seedlings represent a particularly vulnerable life stage and successful seedling establishment is crucial for forest regeneration. We investigated the extent to which Pinus ponderosa P. & C. Lawson populations from different climate zones exhibit differential expression of functional traits that may facilitate their establishment. Seeds from two populations from sites with contrasting precipitation and temperature regimes east (PIPO dry) and west (PIPO mesic) of the Oregon Cascade mountains were sown in a common garden experiment and grown under two water availability treatments (control and drought). Aboveground biomass accumulation, vegetative phenology, xylem anatomy, plant hydraulic architecture, foliar stable carbon isotope ratios (δ(13)C), gas exchange and leaf water relations characteristics were measured. No treatment or population-related differences in leaf water potential were detected. At the end of the first growing season, aboveground biomass was 74 and 44% greater in PIPO mesic in the control and drought treatments, respectively. By early October, 73% of PIPO dry seedlings had formed dormant buds compared with only 15% of PIPO mesic seedlings. Stem theoretical specific conductivity, calculated from tracheid dimensions and packing density, declined from June through September and was nearly twice as high in PIPO mesic during most of the growing season, consistent with measured values of specific conductivity. Intrinsic water-use efficiency based on δ(13)C values was higher in PIPO dry seedlings for both treatments across all sampling dates. There was a negative relationship between values of δ(13)C and leaf-specific hydraulic conductivity across populations and treatments, consistent with greater stomatal constraints on gas exchange with declining seedling hydraulic capacity. Integrated growing season assimilation and stomatal conductance estimated from foliar δ(13)C values and photosynthetic CO2-response curves were 6 and 28% lower, respectively, in PIPO dry seedlings. Leaf water potential at the turgor loss point was 0.33 MPa more negative in PIPO dry, independent of treatment. Overall, PIPO dry seedlings exhibited more conservative behavior, suggesting reduced growth is traded off for increased resistance to drought and extreme temperatures.

Environmental heterogeneity leads to higher plasticity in dry‐edge populations of a semi‐arid Chilean shrub: insights into climate change responses

Summary Interannual variability in climatic conditions should be taken into account in climate change studies in semi‐arid ecosystems. It may determine differentiation in phenotypic plasticity among populations, with populations experiencing higher environmental heterogeneity showing higher levels of plasticity. The ability of populations to evolve key functional traits and plasticity may determine the survival of plant populations under the drier and more variable climate expected for semi‐arid ecosystems. Working with populations of the semi‐arid Chilean shrub Senna candolleana along its entire distribution range, we assessed inter‐ and intra‐population variation in functional traits as well as in their plasticity in response to water availability. We measured morphological and physiological traits related to drought resistance in both field conditions and in a greenhouse experiment, where drought response was evaluated under two water availability treatments. All populations responded plastically, but higher precipitation heterogeneity in dry‐edge populations seemed to have selected for more plastic genotypes compared to populations growing at mesic sites and with more homogeneous environmental conditions. Synthesis. Our results suggest adaptive plasticity since higher levels of phenotypic plasticity were positively associated with plant performance. However, we did not find evidence for genetic variation for plasticity within populations. To the extent that phenotypic plasticity may play a key role in future persistence, populations at mesic sites may be more vulnerable to climate change due to their lower plasticity and their current limitations to evolve novel norms of reaction. Conversely, although Senna candolleana populations at the dry edge are exposed to higher levels of stress, they may be less susceptible to climate change in view of their greater plasticity. We highlight the need to consider population differentiation in both mean traits and their plasticity to model realistic scenarios of species distribution under climate change.

Changes in henna (Lawsonia inermis L.) morphological traits under different deficit irrigations in the southern Tunisia

Henna plant belongs to continental oases where water shortage constitutes the essential limiting factors of its agricultural production. Lawsonia inermis L. (Lytraceae) is often exposed to severe drought stress in Gabes; a Tunisian arid region. The present study was carried out to evaluate the impact of water stress on the morphology of Tunisian henna plants. Thus, an experiment of four months was carried out under greenhouse at the Institute of Arid Region in Medenine, Tunisia. Henna was exposed to three different irrigation regimes, whereby the plants where irrigated to field capacity (control, T0), 50% of the control (moderate stress, T1) and 25% of the control (severe deficit irrigation, T2). Results showed that, leaf area (LA), leaf number and stem length of henna, decreased in response to the studied stress. The effect of water stress was clearly observed on those parameters. Moderate drought (T1) did not damage henna morphology, and the plants grew better than without water limitation (T0). Furthermore, the water stress-typical responses were shown as time and severity dependent in all the measured parameters. Indeed, lowest water availability treatment (T2) induced significant decrease in total number of leaves, as well as reductions in LA. Under this severe water stress (T2); LA was reduced by 65.79%, compared to control, at 60 days after the initiation of the bioassay. Stem length decreased significantly in the most severe water stress, this reduction was about 44%. Globally, we conclude that henna plant growth decreased progressively to long-term water limitation.

Effects of Glomus intraradices on the growth and reactive oxygen metabolism of foxtail millet under drought

Foxtail millet (Setaria italica L.) is an ancient domesticated crop grown in arid and semi-arid Africa and Eurasian continent. This study investigated the effects of arbuscular mycorrhizal (AM) fungi (Glomus intraradices) and water stress on the growth and reactive oxygen metabolism of foxtail millet under greenhouse pot conditions. After two soil water availability treatments [well-watered (WW) −0.11 MPa; water-stressed (WS) −0.68 MPa] for 31 days, G. intraradices could colonize well in the roots of foxtail millet. Water stress inhibited AM colonization, plant growth and crop yield, and also increased reactive oxygen metabolism and antioxidant enzyme activities of foxtail millet. G. intraradices-inoculated foxtail millet had greater plant height, collar diameter, panicle heigh, panicle weight and grain weight, higher enzyme activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and glutathione reductase (GR), and lower concentration of malondialdehyde (MDA) , H2O2, and O2 ·-, when compared with non-inoculated foxtail millet under both WW and WS conditions. Our results demonstrated that G. intraradices-inoculated foxtail millet showed higher drought-tolerance by improving their growth and productivity, reactive oxygen species (ROS) and antioxidant enzyme activities, compared with non-inoculated foxtail millet. This indicates that G. intraradices inoculation is a potential method for enhancing the performance of foxtail millet under drought conditions.

Phylogenetic signal in growth and reproductive traits and in their plasticity: theDescurainiaradiation in the Canary Islands

Despite the extensive use of phylogenetic methods in comparative plant biology, there is little information on how traits and their plastic responses can be affected by phylogenetic constraints (i.e. limitations in phenotypic expression resulting from the phylogenetic history of a lineage), particularly in plant radiations that may have occurred over a relatively short time period. In this study, we examined phylogenetic constraints in a monophyletic group of species of Descurainia (Brassicaceae) endemic to the Canary Islands. We measured growth and reproductive traits in a glasshouse experiment representing 17 populations of eight taxa previously analysed in a phylogenetic context. Two water availability treatments were used to assess the plasticity of the examined traits. Most of the traits did not show strong phylogenetic signal; only weak evidence for phylogenetic constraint was found in traits related to reproduction (total number of flowers, onset of flowering) and biomass allocation to roots. Substantial levels of plasticity were observed in all the examined traits, but plasticity showed little interaction between treatment and taxon, suggesting little divergence among taxa. Our study provides evidence that phylogenetic constraints in these quantitative traits, including their plastic expression, have not played a significant role in the pattern of phenotypic diversification of this island plant group. Phenotypic plasticity may thus have favoured adjustment to the habitats occupied by each species during the radiation process. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 384–398.

Fungal endophyte (Epichloë festucae) alters the nutrient content of Festuca rubra regardless of water availability.

Festuca rubra plants maintain associations with the vertically transmitted fungal endophyte Epichloë festucae. A high prevalence of infected host plants in semiarid grasslands suggests that this association could be mutualistic. We investigated if the Epichloë-endophyte affects the growth and nutrient content of F. rubra plants subjected to drought. Endophyte-infected (E+) and non-infected (E−) plants of two half-sib lines (PEN and RAB) were subjected to three water availability treatments. Shoot and root biomass, nutrient content, proline, phenolic compounds and fungal alkaloids were measured after the treatments. The effect of the endophyte on shoot and root biomass and dead leaves depended on the plant line. In the PEN line, E+ plants had a greater S:R ratio than E-, but the opposite occurred in RAB. In both plant lines and all water treatments, endophyte-infected plants had greater concentrations of N, P and Zn in shoots and Ca, Mg and Zn in roots than E- plants. On average, E+ plants contained in their shoots more P (62%), Zn (58%) and N (19%) than E- plants. While the proline in shoots increased in response to water stress, the endophyte did not affect this response. A multivariate analysis showed that endophyte status and plant line impose stronger differences in the performance of the plants than the water stress treatments. Furthermore, differences between PEN and RAB lines seemed to be greater in E- than in E+ plants, suggesting that E+ plants of both lines are more similar than those of their non-infected version. This is probably due to the endophyte producing a similar effect in both plant lines, such as the increase in N, P and Zn in shoots. The remarkable effect of the endophyte in the nutrient balance of the plants could help to explain the high prevalence of infected plants in natural grasslands.

Interactive effects of water supply and defoliation on photosynthesis, plant water status and growth of Eucalyptus globulus Labill

Increased climatic variability, including extended periods of drought stress, may compromise on the health of forest ecosystems. The effects of defoliating pests on plantations may also impact on forest productivity. Interactions between climate signals and pest activity are poorly understood. In this study, we examined the combined effects of reduced water availability and defoliation on maximum photosynthetic rate (A(sat)), stomatal conductance (g(s)), plant water status and growth of Eucalyptus globulus Labill. Field-grown plants were subjected to two water-availability regimes, rain-fed (W-) and irrigated (W+). In the summer of the second year of growth, leaves from 75% of crown length removed from trees in both watering treatments and physiological responses within the canopies were examined. We hypothesized that defoliation would result in improved plant water status providing a mechanistic insight into leaf- and canopy-scale gas-exchange responses. Defoliated trees in the W+ treatment exhibited higher A(sat) and g(s) compared with non-defoliated trees, but these responses were not observed in the W- treatment. In contrast, at the whole-plant scale, maximum rates of transpiration (E(max)) and canopy conductance (G(Cmax)) and soil-to-leaf hydraulic conductance (K(P)) increased in both treatments following defoliation. As a result, plant water status was unaffected by defoliation and trees in the defoliated treatments exhibited homeostasis in this respect. Whole-plant soil-to-leaf hydraulic conductance was strongly correlated with leaf scale g(s) and A(sat) following the defoliation, providing a mechanistic insight into compensatory up-regulation of photosynthesis. Above-ground height and diameter growth were unaffected by defoliation in both water availability treatments, suggesting that plants use a range of responses to compensate for the impacts of defoliation.

Effects of two Glomus species on the growth and physiological performance of Sophora davidii seedlings under water stress

Sophora davidii is an important leguminous scrub that is widely used for revegetation in the semiarid Loess Plateau and other arid valley areas of China, where it usually suffers drought stress. This study investigated the effects of arbuscular mycorrhizal (AM) fungi (Glomus mosseae and Glomus constrictum) and water stress on the growth and physiological performance of S. davidii seedlings under greenhouse pot conditions. Two soil water availability treatments (well-watered (WW) −0.10 MPa; water-stressed (WS) −0.86 MPa) were applied for 61 days. At the end of this experiment, G. mosseae and G. constrictum had colonized the roots of S. davidii seedlings. Water stress inhibited AM colonization, plant growth, chlorophyll concentration, gas exchange and chlorophyll fluorescence of S. davidii seedlings. Mycorrhizal seedlings had greater shoot dry weight, root dry weight, plant height, root length, instantaneous water use efficiency (iWUE), net photosynthetic rate (Pn), stomatal conductance (gs), maximal photochemical efficiency of PSII photochemistry (Fv/Fm), lower intercellular CO2 concentration and photochemical quenching values (qP), when compared with non-mycorrhizal seedlings under both WW and WS conditions. Furthermore, G. constrictum was found to be more efficient at improving the shoot and root mass, plant height, iWUE, Pn, gs, qP, and ΦPSII of S. davidii seedlings, when compared with G. mosseae under both WW and WS conditions. Our results demonstrate that AM Glomus symbiosis enhanced S. davidii seedling resistance by improving its growth and physiological performance under water stress conditions. This suggests that Glomus inoculation is a potential tool for enhancing outplanting performance of S. davidii in semiarid areas of China.

Efeito simultâneo da deficiência hídrica e do alumínio tóxico no solo na cultivar IAC91-5155 de cana-de-açúcar

Sugarcane is a very important economic crop in Brazil. The effects of abiotic stresses cause negative reduction of the productivity in the sugarcane industry. In order to identify indicators of stresses tolerance, two physiological variables were evaluated, nitrate reductase activity and chlorophyll contents in young plants of sugarcane, cv. IAC91-5155. The simultaneous effect of abiotic stresses of high occurrence in Brazilian soils are, water deficiency and aluminum toxicity. The plants were submitted to three treatments of water availability (% field capacity, FC): no stress (70% FC), moderate stress (55% FC), and extreme stress (40% FC); and three acidity treatments in the soil (base saturation, V%): no acidity (V=55%), average acidity (V=33%), and high acidity (V=23%). The experiment was carried out in greenhouse, with 29.7±4.3ºC and 75±10% RH. The experimental design was in randomized blocks, in 3×3 factorial arrangement, with four replicates. After 60 days, nitrate reductase activity and chlorophyll contents were evaluated in the diagnostic leaf. The results demonstrate that the response of plants to a combination of drought and aluminum toxicity, similar to the conditions in many natural environments, is different from the response of plants to each of these stresses applied individually, as typically tested in the laboratory. The nitrate reductase activity can be used as a biochemical-physiological marker of water deficiency while chlorophyll contents can be used as a biochemical-physiological marker of both of them, water deficiency or aluminum toxicity in soil. Both parameters can not be as a biochemical-physiological marker for acclimation of young plants of sugarcane cv. IAC91-5155, under the combined stresses.

A Physiological Stimulating Factor of Water Intake during and after Dry Forage Feeding in Large-type Goats.

When ruminants consume dry forage, they also drink large volumes of water. The objective of this study was to clarify which factor produced when feed boluses enter the rumen is mainly responsible for the marked increase in water intake in the second hour of the 2 h feeding period in large-type goats fed on dry forage for 2 h twice daily. Six large-type male esophageal- and ruminal-fistulated goats (crossbred Japanese Saanen/Nubian, aged 2 to 6 years, weighing 85.1±4.89 kg) were used in two experiments. In experiment 1, the water deprivation (WD) control and the water availability (WA) treatment were conducted to compare changes in water intake during and after dry forage feeding. In experiment 2, a normal feeding conditions (NFC) control and a feed bolus removal (FBR) treatment were carried out to investigate whether decrease in circulating plasma volume or increase in plasma osmolality is mainly responsible for the marked increase in water intake in the second hour of the 2 h feeding period. The results of experiment 1 showed that in the WA treatment, small amounts of water were consumed during the first hour of feeding while the majority of water intake was observed during the second hour of the 2 h feeding period. Therefore, the amounts of water consumed in the second hour of the 2 h feeding period accounted for 82.8% of the total water intake. The results of experiment 2 indicated that in comparison with the NFC control, decrease in plasma volume in the FBR treatment, which was indicated by increase in hematocrit and plasma total protein concentrations, was higher (p<0.05) in the second hour of the 2 h feeding period. However, plasma osmolality in the FBR treatment was lower (p<0.05) than compared to the NFC control from 30 min after the start of feeding. Therefore, thirst level in the FBR treatment was 82.7% less (p<0.01) compared with that in the NFC control upon conclusion of the 30 min drinking period. The results of the study indicate that the increased plasma osmolality in the second hour of the 2 h feeding period is the main physiological stimulating factor of water intake during and after dry forage feeding in large-type goats.

Atividade da enzima redutase do nitrato e teores de prolina livre em raízes de cana-de-açúcar sob os estresses hídrico e ácido no solo

The aim of this work was evaluate the physiological indicators of association between water deficiency and soil acidity, by determining the nitrate reductase activity, the levels of free proline and initial growth of the root system of seedlings of sugarcane cv. IAC91-5155. After 30 days, the seedlings were transferred to plastic pots with 12 dm 3 of dystrophic alic Red Latosol (Oxisol) and submitted to association of three treatments of water availability: no stress (70%), moderate stress (55%) and severe stress (40%), in according with field capacity and three acidity treatments: no stress (55%), moderate stress (33%) and severe stress (23%), considering the base saturation. The experimental design was that of random blocks under factorial scheme of 3x3, with four replicates. After 60 days under the stress association, the levels of free proline, the nitrate reductase activity and the growth of the sugarcane roots system were evaluated in seedlings of sugarcane. The nitrate reductase enzyme activity can be considered a physiological indicator of the effect of the association of acid and water stress in moderate conditions in soil, while the free proline can be considered physiological indicator to both stress in severe conditions. Water deficiency increasing reduced growth of sugarcane roots.

Nutrient and water availability alter belowground patterns of biomass allocation, carbon partitioning, and ectomycorrhizal abundance in Betula nigra

In managed settings, seedlings are often fertilized with the objective of enhancing establishment, growth, and survival. However, responses of seedlings to fertilization can increase their susceptibility to abiotic stresses such as drought. Seedlings acclimate to variation in soil resources by reallocating carbon among different physiological processes and compartments, such as above versus belowground growth, secondary metabolism, and support of ectomycorrhizal fungi (EMF). We examined the effects of nutrient and water availability on carbon allocation to above and belowground growth of river birch (Betula nigra), as well as partitioning among root sugars, starch, phenolics, lignin, and EMF abundance. As nutrient availability increased, total plant biomass and total leaf area increased, while percent root biomass decreased. Root sugars, total root phenolics and EMF abundance responded quadratically to nutrient availability, being lowest at intermediate fertility levels. Decreased water availability reduced total leaf area and root phenolics relative to well-watered controls. No interactions between nutrient and water availability treatments were detected, which may have been due to the moderate degree of drought stress imposed in the low water treatment. Our results indicate that nutrient and water availability significantly alter patterns of carbon allocation and partitioning in roots of Betula nigra seedlings. The potential effects of these responses on stress tolerance are discussed.