Low Soil Moisture Content Research Articles

Direct seeding of Oreomunnea mexicana, a threatened tree species from Southeastern Mexico

Compared to enrichment planting techniques, direct seeding may represent a viable low-cost method to ensure the conservation and recovery of forest ecosystems. However, it is necessary to identify the environmental factors that affect seed germination and seedling establishment in order to improve the success of this technique. It has been suggested that the establishment of Oreomunnea mexicana (Juglandaceae), a threatened tropical montane cloud forest tree species, is associated with microsites of high soil moisture. We assessed seedling emergence in O. mexicana through direct seeding in a secondary forest and characterized the microenvironmental conditions of the sowing microsite. We also assessed the effect of seed hydration on seedling emergence and evaluated the effect of soil moisture content and seed hydration in O. mexicana seed germination and seedling emergence under laboratory conditions. Seedling emergence was lower in the field than in the laboratory (37 vs. 42 %, respectively). At microsite level, seedling emergence correlated positively with soil moisture content but negatively with vegetation cover. After 11 months, 52 % of the emerged seedlings still survived. Under laboratory conditions, seedling emergence did not differ significantly between hydrated and non-hydrated seeds (43.2 ± 0.52 vs. 40.3 ± 0.51 %, respectively), but did between high and low soil moisture contents (80 ± 0.18 vs. 3.5 ± 0.085 %, respectively). With appropriate soil moisture and vegetation cover conditions, O. mexicana seed introduction into secondary forest is a reliable technique. However, the method could be improved by protecting the seedlings from physical damage.

Avaliação do sensor óptico de vegetação OptRx® na monitorização da variabilidade espacial e temporal de pastagens

The estimation of pasture productivity is an important step for the farmer in terms of planning animal stocking, organizing animal lots and determining supplementary feeding needs throughout the year. The main objective of this work was to evaluate a active optical sensor (OptRx®, which measures NDVI, Normalised Difference Vegetation Index) for monitoring aspects related to pasture variability and support to decision making for the farmer. The results showed the potential of NDVI for monitoring the evolution of spatial and temporal patterns of the vegetative state of biodiverse pasture. The higher NDVI were registered as pasture approached its greatest vegetative vigor, with a significan fall in the measured NDVI at the end of Spring, when the pasture began to dry due to the combination of higher temperatures and lower soil moisture content. This index was also effective for identifying different plant species (grasses/legumes) and variability in pasture yield. Furthermore, it was possible to develop calibration equations between the NDVI and pasture green and dry matter yield (kg/ha). Finally, an inverse relationship was obtained between NDVI and the pasture dry matter content (in %) in Alentejo dry-land farming systems.

Transcriptome analysis revealed the drought-responsive genes in Tibetan hulless barley.

BackgroundHulless barley, also called naked barley, is an important cereal crop worldwide, serving as a healthy food both for human consumption and animal feed. Nevertheless, it often suffered from drought stress during its growth and development, resulting in a drastic reduction in barley yields. Therefore, study on molecular mechanism of hulless barley drought-tolerance is very important for increasing barley production. To investigate molecular mechanism of barley drought-resistance, this study examined co-regulated mRNAs that show a change in expression pattern under early well water, later water deficit and finally water recovery treatments, and to identify mRNAs specific to water limiting conditions.ResultsTotal of 853 differentially expressed genes (DEGs) were detected and categorized into nine clusters, in which VI and VIII were apparently up-regulated under low relative soil moisture content (RSMC) level. The majority of genes in these two clusters was relevant to abiotic stress responses in abscisic acid (ABA) dependent and independent signaling pathway, including NCED, PYR/PYL/RCAR, SnRK2, ABF, MYB/MYC, AP2/ERF family, LEA and DHN. In contrast, genes within clusters II and IV were generally down-regulated under water stress; cluster IX genes were up-regulated during water recovery response to both low and high RSMC levels. Genes in implicated in tetrapyrrole binding, photosystem and photosynthetic membrane were the most affected in cluster IX.ConclusionTaken together, our findings indicate that the responses of hulless barley to drought stress shows differences in the pathways and genes activated. Furthermore, all these genes displayed different sensitivities to soil water deficit and might be profitable for future drought tolerance improvement in barley and other crops.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2685-3) contains supplementary material, which is available to authorized users.

Implementation of non-local boundary layer schemes in the Regional Atmospheric Modeling System and its impact on simulated mesoscale circulations

This paper proposes the implementation of different non-local Planetary Boundary Layer schemes within the Regional Atmospheric Modeling System (RAMS) model. The two selected PBL parameterizations are the Medium-Range Forecast (MRF) PBL and its updated version, known as the Yonsei University (YSU) PBL. YSU is a first-order scheme that uses non-local eddy diffusivity coefficients to compute turbulent fluxes. It is based on the MRF, and improves it with an explicit treatment of the entrainment. With the aim of evaluating the RAMS results for these PBL parameterizations, a series of numerical simulations have been performed and contrasted with the results obtained using the Mellor and Yamada (MY) scheme, also widely used, and the standard PBL scheme in the RAMS model. The numerical study carried out here is focused on mesoscale circulation events during the summer, as these meteorological situations dominate this season of the year in the Western Mediterranean coast. In addition, the sensitivity of these PBL parameterizations to the initial soil moisture content is also evaluated. The results show a warmer and moister PBL for the YSU scheme compared to both MRF and MY. The model presents as well a tendency to overestimate the observed temperature and to underestimate the observed humidity, considering all PBL schemes and a low initial soil moisture content. In addition, the bias between the model and the observations is significantly reduced moistening the initial soil moisture of the corresponding run. Thus, varying this parameter has a positive effect and improves the simulated results in relation to the observations. However, there is still a significant overestimation of the wind speed over flatter terrain, independently of the PBL scheme and the initial soil moisture used, even though a different degree of accuracy is reproduced by RAMS taking into account the different sensitivity tests.

Effect of Eucalyptus forests on understory vegetation and soil quality

Eucalyptus forest plantations are normally devoid of understory vegetation that is often assumed to be associated with Eucalyptus allelopathic effects. The objective of this study was to determine the influence of high soil compaction and low soil moisture content on inhibition of the germination of understory seeds in Eucalyptus forests and thus would result in the scarcity of understory vegetation. The soil water content above the depth of 1 m of six major understory vegetation types was analyzed to determine if there was a correlation between soil water content and understory vegetation. The effects of soil treatment (soil-loosening vs. no soil-loosening) and water supply amount (2500, 2000, 1500, 1000, 500, 250, or 0 ml of water per day) on the seed germination rate of Stylosanthes sp. were explored using an artificial climate chamber experiment. Influence of soil source (five Eucalyptus forest soils vs. two non-Eucalyptus forest soils) and water supply (0, 50, 150, 200, or 400 ml of water every day) on the germination rate of five types of seed were assessed using a three-factor analysis of variance (ANOVA). Soil-loosening and water supply significantly (P < 0.05) increased seed germination rate with the contribution rates of 26.14 and 42.93 %, respectively. Analysis of variance for three-factor experiments revealed a significant (P < 0.05) effect of water supply and vegetation seed type on the germination rate of plant seeds. No significant effect of soil type was observed on germination rate, indicating that germination rate was not affected by soils in Eucalyptus forest. The conservation of soil characteristics, such as water content and compaction, during the development of a Eucalyptus forest plantation may be an effective strategy for encouraging the growth of understory vegetation. This study highlights the importance that in dry areas or areas prone to long-term drought, it would be preferable to retain native vegetation.

Evaluation of the Weather Research and Forecasting Model in the Durance Valley Complex Terrain during the KASCADE Field Campaign

AbstractIn the winter of 2012/13, the Katabatic Winds and Stability over Cadarache for the Dispersion of Effluents (KASCADE) observational campaign was carried out in southeastern France to characterize the wind and thermodynamic structure of the (stable) planetary boundary layer (PBL). Data were collected with two micrometeorological towers, a sodar, a tethered balloon, and radiosoundings. Here, this dataset is used to evaluate the representation of the boundary layer in the Weather Research and Forecasting (WRF) Model. In general, it is found that diurnal temperature range (DTR) is largely underestimated, there is a strong negative bias in both longwave radiation components, and evapotranspiration is overestimated. An illustrative case is subjected to a thorough model-physics evaluation. First, five PBL parameterization schemes and two land surface schemes are employed. A marginal sensitivity to PBL parameterization is found, and the sophisticated Noah land surface model represents the extremes in skin temperature better than does a more simple thermal diffusion scheme. In a second stage, sensitivity tests for land surface–atmosphere coupling (through parameterization of z0h/z0m), initial soil moisture content, and radiation parameterization were performed. Relatively strong surface coupling and low soil moisture content result in a larger sensible heat flux, deeper PBL, and larger DTR. The larger sensible heat flux is not supported by the observations, however. It turns out that, for the selected case, a combination of subsidence and warm-air advection is not accurately simulated, but this inaccuracy cannot fully explain the discrepancies found in the WRF simulations. The results of the sensitivity analysis reiterate the important role of initial soil moisture values.

Surface energy budget changes over Central Australia during the early 21st century drought

Satellite observations are used to investigate surface energy budget variability over central Australia during the early 21st century drought. Over a large expanse of open shrubland and savanna, surface albedo exhibits a multiyear increase of 0.06 during the drought followed by a sharp decline of 0.08 after heavy rainfall in 2010 broke the drought. The surface albedo variations are associated with increased normalized difference vegetation index (NDVI) during wet years before and after the drought and decreased NDVI during drought years. During the worst drought years (2002–2009), the surface albedo increase is most pronounced in the shortwave infrared region (wavelengths between 1 and 3 µm), implying soil moisture content variability is the likely cause of the albedo changes. At interannual timescales, surface albedo variability is associated with near-surface soil moisture, controlled by episodic precipitation events, whereas the multiyear increase in surface albedo is more closely linked with decreases in soil moisture in deeper surface layers. In addition to a higher surface albedo and lower soil moisture content during the drought, the observations show less evaporation, enhanced reflected shortwave radiation, increased upward emission of thermal infrared radiation, lower downwelling longwave (LW) radiation, reduced net total downward radiation, and higher sensible heating compared with the rainy period following the drought. Upward emission of thermal infrared radiation decreases sharply after the drought with increased surface evaporation. However, the surface energy budget changes during the worst drought years show a stronger relationship between upward emission of thermal radiation and reflected shortwave flux. During this period, evaporative fraction is extremely low and surface albedo is steadily increasing. In such extreme conditions, the surface albedo appears to modulate surface upward LW radiation, preventing it from getting too high. The change in upward LW radiation thus represents a negative feedback as it offsets further decreases in surface net radiation.

Ecophysiological leaf traits of native and exotic palm tree species under semi-arid conditions

AbstrA ct: The main goal of this study was to evaluate the performance of two palm species under semi-arid conditions during the rainy and dry periods: the semi-arid native Syagrus coronata and a native to tropical America, Acrocomia aculeata. The leaf water potential, gas exchange, leaf soluble sugars, starch, free amino acids, total soluble protein content and morphological traits were measured. The highest leaf water potential and CO 2 assimilation values in both species were achieved during the rainy period. In response to the low soil moisture content during the dry period, gas exchange decreased 72 and 92% in S. coronata and A. aculeata, respectively,

Spatial Variations of Soil Moisture under Caragana korshinskii Kom. from Different Precipitation Zones: Field Based Analysis in the Loess Plateau, China

Soil moisture scarcity has become the major limiting factor of vegetation restoration in the Loess Plateau of China. The aim of this study is: (i) to compare the spatial distribution of deep (up to 5 m) soil moisture content (SMC) beneath the introduced shrub Caragana korshinskii Kom. under different precipitation zones in the Loess Plateau and (ii) to investigate the impacts of environmental factors on soil moisture variability. Soil samples were taken under C. korshinskii from three precipitation zones (Semiarid-350, Semiarid-410, Semiarid-470). We found that the highest soil moisture value was in the 0–0.1 m layer with a large coefficient of variation. The soil water storage under different precipitation zones increased following the increase of precipitation (i.e., Semiarid-350 &lt; Semiarid-410 &lt; Semiarid-470), although the degree of SMC variation was different for different precipitation zones. The SMC in the Semiarid-350 zone initially increased with soil depth, and then decreased until it reached the depth of 2.8-m. The SMC in the Semiarid-410 zone showed a decreasing trend from the top soil to 4.2-m depth. The SMC in the Semiarid-470 zone firstly decreased with soil depth, increased, and then decreased until it reached 4.6-m depth. All SMC values then became relatively constant after reaching the 2.8-m, 4.2-m, and 4.6-m depths for Semiarid-350, Semiarid-410, and Semiarid-470, respectively. The low but similar SMC values at the stable layers across the precipitation gradient indicate widespread soil desiccation in this region. Our results suggested that water deficit occurred in all of the three precipitation zones with precipitation, latitude, field capacity, and bulk density as the main environmental variables affecting soil moisture. Considering the correlations between precipitation, SMC and vegetation, appropriate planting density and species selection should be taken into account for introduced vegetation management.

Monitoring pasture variability: optical OptRx(®) crop sensor versus Grassmaster II capacitance probe.

Estimation of pasture productivity is an important step for the farmer in terms of planning animal stocking, organizing animal lots, and determining supplementary feeding needs throughout the year. The main objective of this work was to evaluate technologies which have potential for monitoring aspects related to spatial and temporal variability of pasture green and dry matter yield (respectively, GM and DM, in kg/ha) and support to decision making for the farmer. Two types of sensors were evaluated: an active optical sensor ("OptRx(®)," which measures the NDVI, "Normalized Difference Vegetation Index") and a capacitance probe ("GrassMaster II" which estimates plant mass). The results showed the potential of NDVI for monitoring the evolution of spatial and temporal patterns of vegetative growth of biodiverse pasture. Higher NDVI values were registered as pasture approached its greatest vegetative vigor, with a significant fall in the measured NDVI at the end of Spring, when the pasture began to dry due to the combination of higher temperatures and lower soil moisture content. This index was also effective for identifying different plant species (grasses/legumes) and variability in pasture yield. Furthermore, it was possible to develop calibration equations between the capacitance and the NDVI (R(2) = 0.757; p < 0.01), between capacitance and GM (R(2) = 0.799; p < 0.01), between capacitance and DM (R(2) =0.630; p < 0.01), between NDVI and GM (R(2) = 0.745; p < 0.01), and between capacitance and DM (R(2) = 0.524; p < 0.01). Finally, a direct relationship was obtained between NDVI and pasture moisture content (PMC, in %) and between capacitance and PMC (respectively, R(2) = 0.615; p < 0.01 and R(2) = 0.561; p < 0.01) in Alentejo dryland farming systems.

Coupled long-term summer warming and deeper snow alters species composition and stimulates gross primary productivity in tussock tundra.

Climate change is expected to increase summer temperature and winter precipitation throughout the Arctic. The long-term implications of these changes for plant species composition, plant function, and ecosystem processes are difficult to predict. We report on the influence of enhanced snow depth and warmer summer temperature following 20 years of an ITEX experimental manipulation at Toolik Lake, Alaska. Winter snow depth was increased using snow fences and warming was accomplished during summer using passive open-top chambers. One of the most important consequences of these experimental treatments was an increase in active layer depth and rate of thaw, which has led to deeper drainage and lower soil moisture content. Vegetation concomitantly shifted from a relatively wet system with high cover of the sedge Eriophorum vaginatum to a drier system, dominated by deciduous shrubs including Betula nana and Salix pulchra. At the individual plant level, we observed higher leaf nitrogen concentration associated with warmer temperatures and increased snow in S. pulchra and B. nana, but high leaf nitrogen concentration did not lead to higher rates of net photosynthesis. At the ecosystem level, we observed higher GPP and NEE in response to summer warming. Our results suggest that deeper snow has a cascading set of biophysical consequences that include a deeper active layer that leads to altered species composition, greater leaf nitrogen concentration, and higher ecosystem-level carbon uptake.

红河干热河谷木棉种群的天然更新

PDF HTML阅读 XML下载 导出引用 引用提醒 红河干热河谷木棉种群的天然更新 DOI: 10.5846/stxb201407161446 作者: 作者单位: 西南林业大学国家林业局西南地区生物多样性保育重点实验室 昆明 650224,西南林业大学国家林业局西南地区生物多样性保育重点实验室 昆明 650224 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金(31260175); 云南省高校科技创新团队建设项目 Causes of difficulties with natural regeneration of a Bombax ceiba population in Hong-He dry-hot valleys (DHV) Author: Affiliation: Southwest Forestry University,Southwest Forestry University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:在以干热为显著特点的干热河谷,木棉成年树生长、开花良好。但其实生苗天然更新不良,其发生过程和影响因子至今尚不明确。通过对红河干热河谷木棉种群种子扩散特点、萌发策略和影响因素研究,在分析木棉实生天然更新困难影响因子的同时,对更新幼苗的发生进行了探讨。结果表明:单株木棉成年母树平均生产果实(358±46)个,单果和单株种子数分别为(274±45)粒和(98092±2540)粒,木棉种质资源丰富。种子的扩散范围广,而田间种子损失量大(损失比例为霉变54.0%、动物取食18.2%和搬运12.0%)。自然条件下种子活力在落种后10-35 d,种子含水量为2.1%-5.9%时为最佳,落种45 d后活力显著下降。干旱条件下木棉落种萌发成苗过程是天然更新的关键环节,其间水分因子起直接作用,连续数日20%-40%的土壤含水率能促进幼苗更新。适度覆土(1-2 cm)可起到改善落种的水分环境的作用,从而促进萌发。旱季降雨少,干旱持续时间长是阻碍更新幼苗向幼树转化的瓶颈。可见,地表种子存留量低、土壤含水量低、种子自然活力保存时间短、自然和人为干扰等环节限制了木棉种群成功的实生天然更新。 Abstract:Kapok trees (Bombax ceiba) grow well and have normal flowering and seeding capacity in Hong-He dry-hot valley (DHV), which is characterized by a dry and hot climate. The valley sees small rainfall and long duration of drought during the dry season. Kapok seeds have a normal germination potential, but their natural regeneration is very poor. Young trees or seedlings are seldom observed under a mature kapok tree. The causes of the difficulties with their natural regeneration and the related factors controlling the regeneration process remain unclear. To understand the process of seedling development and the causes of problems with natural regeneration, we measured seed production per tree, seed dispersal characteristics as well as the field and indoor seed germination potential in a kapok natural population in Hong-He DHV. The results showed that each mature kapok tree produced (98092±2540) seeds on average. The mean fruit number per tree and the mean seed number per fruit were 358 ± 46 and 274 ± 45, respectively. These findings indicated that the seed source was abundant. The seeds started to disperse by flying with kapok fiber after the fruit cracking from late April to early May. Most of the seeds (82.7%) dispersed within the distance 4-22 m around the parent tree. The area 14 m away from the parent tree was the concentrated seed dispersal zone, with seed density 1005 seeds/m2. The seed rain lasted for 15 days. The losses among the seeds falling on the ground were high. Approximately 30.2% of these seeds were taken by birds, ants, and mice, and 54.0% of the seeds perished because of mildew. Field germination tests showed that the germination rate for the treatment with 2 cm surface soil mulching was 60.3%, whereas the germination rate for the treatment without soil mulching ranged from 15.0% to 38.8%. The seeds did not germinate if the soil mulching depth was 6 cm. Apparently, the seeds falling onto the bare land without soil mulching or with excessively deep soil mulching have low germination rates. Additionally, the sterilization test with different disinfection treatments demonstrated that an infection reduced the germination rate by 40.8%. The seed viability was also influenced by seed moisture conditions. The seed moisture decreased with the increasing period after seed falling up to 40 days. Seeds at 10-35 days after maturation had moisture content of 2.1%-5.9% and showed the best seed viability, but the viability declined significantly 45 days after maturation. Soil moisture of 20%-40% was favorable for seedling development. This result indicated that both seed and soil moisture directly affected seed germination and the seedling development process. The seeds showed a wide span of tolerance to temperature changes. The seeds could germinate at a temperature between 10 and 50 ℃, showing the best germination rate at 30-35 ℃. In conclusion, weak precipitation and prolonged drought during the dry season in these dry-hot valleys lead to conditions that are inhospitable to germination and growth. These conditions reduce the number of remaining seeds, lower soil moisture content, and shorten the seed viability period. Therefore, weak rainfall and a long drought seem to be the bottleneck that restricts the progression from seedlings to young trees. Soil mulching (1-2 cm) can increase the seed germination rate by improving moisture conditions. 参考文献 相似文献 引证文献

Water use, root activity and deep drainage within a perennial legume-grass pasture: A case study in southern inland Queensland, Australia

Water use and depth of water extraction of leucaena ( Leucaena leucocephala ) and Rhodes grass ( Chloris gayana ) pasture, irrigated with desalinated coal seam water (a by-product of the coal seam gas industry), were monitored to provide background information on root activity, spatial and temporal water use and deep drainage over a 757-day period from August 2011 to August 2013. Methodology comprised measurement of soil water from surface to 4 m depth using 8 EnviroSCAN probes connected to dataloggers positioned within leucaena twin rows and within the Rhodes grass inter-row. Just over 581,000 individual moisture measurements were collated and are reported here. Water extraction (and by inference root activity) of leucaena and Rhodes grass showed marked seasonal fluctuation with deepest and highest water extraction occurring during the first growing season; water extraction was greatly diminished during the following drier and cooler seasons due to the negative influences of lower soil moisture contents, lower temperatures and increased defoliation on pasture growth. The highest values of deep drainage below 4 m depth occurred when high rainfall events corresponded with high soil water storage in the entire profile (0–4 m depth). Given that water usage by both leucaena and Rhodes grass was greatest in the upper layers of soil (<1.5 m), future research should focus on how the level of competitive interaction might be managed by choice of row spacing and frequency of irrigation. Further studies are needed, including: (a) physical sampling to determine the depth of active roots; (b) how defoliation affects rooting behaviours and water use of leucaena; and (c) modelling of the water and salt balances of leucaena and grass inter-row systems using data from this study, with various levels of irrigation, to investigate the risks of deep drainage over an extended climate sequence. Keywords: Active rooting depth, agroforestry, Chloris gayana , Leucaena leucocephala , water extraction. DOI: 10.17138/TGFT(4)129-138

Effects of enclosure time on the community composition of methanotrophs in the soils of the Inner Mongolia grasslands

Despite the great number of studies about methane uptake and its response to grazing in the Inner Mongolia grasslands, only a few focused on the methanotrophic composition. This study aimed to investigate the methanotrophic community structure and abundance, then to analyze the abiotic driving factors of methanotrophic community structure in different enclosed times in this area. In this study we chose typical grasslands in the Xilin River Basin of Inner Mongolia, China to investigate methanotrophic community structure and abundance under different enclosure treatments as follows: 79E (grassland enclosed since 1979), 99E (grassland enclosed since 1999), and G (freely grazed grassland). A clone library was used to reveal the methanotroph community structure, and their relationships with abiotic factors were analyzed by redundancy analysis. Methanotroph abundance was determined by real-time PCR. The OTUs of the three treatments mainly belonged to Type I methanotrophs, probably caused by the high pH value. Among all OTUs, only OTU1 belonged to upland soil cluster γ (USC-γ), whose abundance was the largest in all OTUs, indicating the USC-γ cluster was the main one to oxidize CH4 in the Inner Mongolia grasslands. Methanotrophic abundance (represented by the pmoA gene copies per gram of dry weight soil) decreased with the enclosure time as G (4.5 × 107) > 99E (2.8 × 107) > 79E (2.0 × 107), mainly caused by the lower soil moisture content in G. Lower soil moisture content facilitates more CH4 and O2 diffusive into soil thus leading to the proliferation of methanotrophs. This study found a high abundance of methanotrophs in the soils of the Inner Mongolia grasslands, with the USC-γ cluster having the largest abundance, which may play a key role in oxidizing CH4 in the Inner Mongolia grasslands. Combined with those of previous studies, the results showed an obvious change of methanotrophic community composition with the increase of enclosure time.

Effect of vineyard floor management on water regime, growth response, yield and fruit quality in Cabernet Sauvignon

We investigated the effect of two different inter-row vineyard floor management practices. These were the permanently cultivated soil and the inter-row sward sawn with a mixture of regularly mown grasses. The experimental vineyard was planted with Cabernet Sauvignon and was located in the wine region of Central Serbia. The study was conducted during the 2011 and 2012 seasons, and the observed variables included soil and vine water status, growth, yield and fruit quality. Our results clearly indicate a lower soil moisture content in the grass sward treatment. The same treatment was also characterised with a lower stem water potential (Ψstem). The Ψstem values measured before and after veraison (from −0.6 to −0.8MPa) indicate a presence of mild to moderate water stress in grapevines under the inter-row sward treatment. The same treatment was also characterised with an increased accumulation of the fruit total soluble solids (TSS), amounting 24.8 °Brix in 2011. and 27.8 °Brix in 2012. Furthermore, the concentration of total polyphenols was increased in the same treatment (1124.63mgL−1 GEA in 2011 and 1170.38mgL−1 GEA in 2012). The concentration of anthocyanins in the berry skin was also increased in this treatment (9.83mgg−1 FW in 2011 and 13.45mgg−1 FW in 2012). The inter-row sward treatment was associated with a lower grapevine vigour, reduced by 36% in 2011 and 46% in 2012. In the same treatment, the grape yield, and cluster and berry weight were not significantly reduced. The seasonal meteorological conditions have exhibited a significant influence on the fruit phenolic composition. The seasonal effect was particularly evident in the content of gallocatehin, naringenin and vanillin, where the 2011 season had a larger content of these compounds within both experimental treatments. Moreover, the 5-O-caffeoylquinic acid, resveratrol, umbeliferone and apigenin were detected only in the samples from the 2011 season. The berry samples from the cultivated inter-row treatment were found to have a higher content of catechin, quercetin, and quercetin 3-O-galactoside in the berry skin. Maintaining the mown inter-row sward as a vineyard floor management practice had shown a significant influence on indicators of vegetative growth and thus it represents a powerful tool to control the vegetative growth in Cabernet Sauvignon, when grown in the conditions characterised by moderately continental climate with a low risk of drought in the flowering to anthesis period.

Soil N2O fluxes along an elevation gradient of tropical montane forests under experimental nitrogen and phosphorus addition

Nutrient deposition to tropical forests is increasing, which could affect soil fluxes of nitrous oxide (N2O), a powerful greenhouse gas. We assessed the effects of 35-56 months of moderate nitrogen (N) and phosphorus (P) additions on soil N2O fluxes and net soil N-cycling rates, and quantified the relative contributions of nitrification and denitrification to N2O fluxes. In 2008, a nutrient manipulation experiment was established along an elevation gradient (1000, 2000 and 3000 m) of montane forests in southern Ecuador. Treatments included control, N, P and N+P addition (with additions of 50 kg N ha−1 yr-1 and 10 kg P ha−1 yr-1). Nitrous oxide fluxes were measured using static, vented chambers and N cycling was determined using the buried bag method. Measurements showed that denitrification was the main N2O source at all elevations, but that annual N2O emissions from control plots were low, and decreased along the elevation gradient (0.57 ± 0.26 to 0.05 ± 0.04 kg N2O-N ha-1 yr-1). We attributed the low fluxes to our sites’ conservative soil N cycling as well as gaseous N losses possibly being dominated by N2. Contrary to the first 21 months of the experiment, N addition did not affect N2O fluxes during the 35-56 month period, possibly due to low soil moisture contents during this time. With P addition, N2O fluxes and mineral N concentrations decreased during Months 35-56, presumably because plant P limitations were alleviated, increasing plant N uptake. Nitrogen plus phosphorus addition showed similar trends to N addition, but less pronounced given the counteracting effects of P addition. The combined results from this study (Months 1-21 and 35-56) showed that effects of N and P addition on soil N2O fluxes were not linear with time of exposure, highlighting the importance of long-term studies.

Long-term water stress leads to acclimation of drought sensitivity of photosynthetic capacity in xeric but not riparian Eucalyptus species.

Experimental drought is well documented to induce a decline in photosynthetic capacity. However, if given time to acclimate to low water availability, the photosynthetic responses of plants to low soil moisture content may differ from those found in short-term experiments. This study aims to test whether plants acclimate to long-term water stress by modifying the functional relationships between photosynthetic traits and water stress, and whether species of contrasting habitat differ in their degree of acclimation. Three Eucalyptus taxa from xeric and riparian habitats were compared with regard to their gas exchange responses under short- and long-term drought. Photosynthetic parameters were measured after 2 and 4 months of watering treatments, namely field capacity or partial drought. At 4 months, all plants were watered to field capacity, then watering was stopped. Further measurements were made during the subsequent 'drying-down', continuing until stomata were closed. Two months of partial drought consistently reduced assimilation rate, stomatal sensitivity parameters (g1), apparent maximum Rubisco activity (V'(cmax)) and maximum electron transport rate (J'(max)). Eucalyptus occidentalis from the xeric habitat showed the smallest decline in V'(cmax) and J'(max); however, after 4 months, V'(cmax) and J'(max) had recovered. Species differed in their degree of V'(cmax) acclimation. Eucalyptus occidentalis showed significant acclimation of the pre-dawn leaf water potential at which the V'(cmax) and 'true' V(cmax) (accounting for mesophyll conductance) declined most steeply during drying-down. The findings indicate carbon loss under prolonged drought could be over-estimated without accounting for acclimation. In particular, (1) species from contrasting habitats differed in the magnitude of V'(cmax) reduction in short-term drought; (2) long-term drought allowed the possibility of acclimation, such that V'(cmax) reduction was mitigated; (3) xeric species showed a greater degree of V'(cmax) acclimation; and (4) photosynthetic acclimation involves hydraulic adjustments to reduce water loss while maintaining photosynthesis.

Topographic controls on the depth distribution of soil CO2 in a small temperate watershed

Accurate measurements of soil CO2 concentrations (pCO2) are important for understanding carbonic acid reaction pathways for continental weathering and the global carbon (C) cycle. While there have been many studies of soil pCO2, most sample or model only one, or at most a few, landscape positions and therefore do not account for complex topography. Here, we test the hypothesis that soil pCO2 distribution can predictably vary with topographic position. We measured soil pCO2 at the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO), Pennsylvania, where controls on soil pCO2 (e.g., depth, texture, porosity, and moisture) vary from ridge tops down to the valley floor, between planar slopes and slopes with convergent flow (i.e., swales), and between north and south-facing aspects. We quantified pCO2 generally at 0.1–0.2 m depth intervals down to bedrock from 2008 to 2010 and in 2013. Of the variables tested, topographic position along catenas was the best predictor of soil pCO2 because it controls soil depth, texture, porosity, and moisture, which govern soil CO2 diffusive fluxes. The highest pCO2 values were observed in the valley floor and swales where soils are deep (≥0.7 m) and wet, resulting in low CO2 diffusion through soil profiles. In contrast, the ridge top and planar slope soils have lower pCO2 because they are shallower (≤0.6 m) and drier, resulting in high CO2 diffusion through soil profiles. Aspect was a minor predictor of soil pCO2: the north (i.e., south-facing) swale generally had lower soil moisture content and pCO2 than its south (i.e., north-facing) counterpart. Seasonally, we observed that while the timing of peak soil pCO2 was similar across the watershed, the amplitude of the pCO2 peak was higher in the deep soils due to more variable moisture content. The high pCO2 observed in the deeper, wetter topographic positions could lower soil porewater pH by up to 1 pH unit compared to porewaters equilibrated with atmospheric CO2 alone. CO2 is generally the dominant acid driving weathering in soils: based on our observations, models of chemical weathering and CO2 dynamics would be improved by including landscape controls on soil pCO2.

Salinization during salt-marsh restoration after managed realignment

Salt marshes provide an important and unique habitat for plants and animals. To restore salt marshes, numerous coastal realignment projects have been carried out, but restored marshes often show persistent ecological differences from natural marshes. We evaluate the effects of elevation and marsh topography, which are in turn affected by drainage and livestock grazing, on soil salinity after de-embankment. Salinity in the topsoil was monitored during the first 10 years after de-embankment and compared with salinity in an adjacent reference marsh. Additionally, salinity at greater depths (down to 1.2 m below the marsh surface) was monitored during the first 4 years by measuring the electrical conductivity of the groundwater. Chloride concentration in the top soil strongly decreased with increasing elevation; however, it was not affected by marsh topography, i.e. distance to creek or breach. Chloride concentrations higher than 2 g Cl−/litre were found at elevations below 0.6 m + MHT. Salinization of the groundwater, however, took several years. At low marsh elevations, the salinity of the deep groundwater (at 1.2 m depth) increased slowly throughout the full 4-year period of monitoring but did not reach the level of seawater. Compared to the ungrazed treatment, the grazed treatment led to lower accretion rates, lower soil-moisture content and higher chloride content of soil moisture. The de-embankment of the agricultural grasslands resulted in a rapid increase of soil salinity, although deeper ground-water levels showed a much slower response. Elevation accounted for most of the variation in the salinization of the soil. Grazing may enhance salinity of the top soil.

Impacts of soil moisture content on simulated mesoscale circulations during the summer over eastern Spain

The Regional Atmospheric Modeling System (RAMS) version 6.0 has been used to investigate the impact and influence of initial soil moisture distributions on mesoscale circulations. To do this, two different events have been selected from the 2011 summer season: one at the beginning of the season (June) and the other one at the end of the season (August). For each of these mesoscale frameworks a total of five distinct simulations were performed varying the initial soil moisture content: a control run and four additional sensitivity tests. The control run, corresponding to a low soil moisture content, is the one used within the real-time weather forecasting system implemented in the Valencia Region. In the corresponding sensitivity simulations this low value has been progressively increased in different steps until the original soil moisture content doubled. It has been found that high soil moisture is associated with colder near-surface temperature, a moister relative humidity and a slightly lower near-surface wind speed, whereas a drier soil resulted in a dryer relative humidity, warmer temperature and a slight low-level wind. In general, the highest soil moisture contents are required to reproduce the near-surface daily cycles of temperature and relative humidity through higher values of latent heat flux and lower values of sensible heat flux. In this regard, moistening the soil improves the previous results obtained using the RAMS configuration used within the operational forecasting system. However, the wind speed is not quite sensitive to changes in the soil moisture content over flatter terrain. Finally, although a warming and dryer mixing layer is obtained with the lowest soil moisture content, the mixing layer height remains practically unchanged when using the distinct configurations over flat terrain. These differences are enhanced over more complex terrain.