Research into Wave Energy Characteristic Signal of Transition Rainfall in Summer Drought Period in Sichuan and Chongqing

2010 ◽  
Author(s):  
Tiangui Xiao ◽  
Minghuan Wang ◽  
Weibin Chen
Keyword(s):  
Wave Energy ◽  
Energy Characteristic ◽  
Summer Drought ◽  
Drought Period ◽  
Characteristic Signal

scholarly journals Drought reduced monoterpene emissions from the evergreen Mediterranean oak <i>Quercus ilex</i>: results from a throughfall displacement experiment

2009 ◽  
Vol 6 (7) ◽  
pp. 1167-1180 ◽  
Author(s):  
A.-V. Lavoir ◽  
M. Staudt ◽  
J. P. Schnitzler ◽  
D. Landais ◽  
F. Massol ◽  
...  
Keyword(s):  
Water Potential ◽  
Leaf Water Potential ◽  
Quercus Ilex ◽  
Photochemical Efficiency ◽  
Leaf Water ◽  
Control Treatment ◽  
Summer Drought ◽  
Drought Period ◽  
Significant Difference ◽  
Monoterpene Emission

Abstract. The effects of water limitations on the emission of biogenic volatile organic compounds are not well understood. Experimental approaches studying drought effects in natural conditions are still missing. To address this question, a throughfall displacement experiment was set up in a natural forest of Quercus ilex, an evergreen Mediterranean oak emitting monoterpenes. Mature trees were exposed in 2005 and 2006 either to an additional drought, to irrigation or to natural drought (untreated control). In both years, absolute monoterpene emission rates as well as the respective standard factors of the trees exposed to normal and additional drought strongly declined during the drought periods. Monoterpene emissions were lower in year 2006 than in year 2005 (factor 2) due to a more pronounced summer drought period in this respective year. We observed a significant difference between the irrigation and additional drought or control treatment: irrigated trees emitted 82% more monoterpenes during the drought period 2006 than the trees of the other treatments. However, no significant effect on monoterpene emission was observed between normal and additional drought treatments, despite a significant effect on leaf water potential and photochemical efficiency. During the development of drought, monoterpene emissions responded exponentially rather than linearly to decreasing leaf water potential. Emissions rapidly declined when the water potential dropped below −2 MPa and photosynthesis was persistently inhibited. Monoterpene synthase activities measured in vitro showed no clear reduction during the same period. From our results we conclude that drought significantly reduces monoterpene fluxes of Mediterranean Holm oak forest into the atmosphere due to a lack of primary substrates coming from photosynthetic processes.

scholarly journals Drought and rewetting events enhance nitrate leaching and seepage-mediated translocation of microbes from beech forest soils

2020 ◽  
Author(s):  
Markus Krüger ◽  
Karin Potthast ◽  
Beate Michalzik ◽  
Alexander Tischer ◽  
Kirsten Küsel ◽  
...  
Keyword(s):  
Forest Soils ◽  
Nitrate Leaching ◽  
Soil Depth ◽  
Groundwater Resources ◽  
Beech Forest ◽  
Summer Drought ◽  
Ammonia Oxidizing Bacteria ◽  
Litter Layer ◽  
Drought Period ◽  
Potential Nitrification

AbstractNitrification in forest soils is often associated with increased leaching of nitrate to deeper soil layers with potential impacts on groundwater resources, further enhanced under scenarios of anthropogenic atmospheric nitrogen deposition and predicted weather extremes. We aimed to disentangle the relationships between soil nitrification potential, seepage-mediated nitrate leaching and the vertical translocation of nitrifiers in soils of a temperate mixed beech forest in central Germany before, during and after the severe summer drought 2018. Leaching of nitrate assessed below the litter layer and in 4, 16 and 30 cm soil depth showed high temporal and vertical variation with maxima at 16 and 30 cm during and after the drought period. Maximum of soil potential nitrification activity of 4.4 mg N kg-1 d-1 only partially coincided with maximum nitrate leaching of 10.5 kg N ha-2. Both ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA) were subject to translocation by seepage, and AOB decreased at least by half and AOA increased by one to three orders of magnitude in their abundance in seepage with increasing soil depth. On the level of the total bacterial population, an increasing trend with depth was also observed for Cand. Patescibacteria while Bacteroidetes were strongly mobilized from the litter layer but poorly transported further down. Despite stable population densities in soil over time, abundances of AOA, AOB and total bacteria in seepage increased by one order of magnitude after the onset of autumn rewetting. Predicted future higher frequency of drought periods in temperate regions may result in more frequent seepage-mediated seasonal flushes of nitrate and bacteria from forest soils. Moreover, the observed translocation patterns point to taxon-specific differences in the susceptibility to mobilization, suggesting that only selected topsoil derived microbial groups are likely to affect subsoil or groundwater microbial communities and their functional potential.

Soil water extraction by a mixed eucalypt forest during a drought period

Soil Research ◽  
1986 ◽  
Vol 24 (1) ◽  
pp. 25 ◽  
Author(s):  
T Talsma ◽  
EA Gardner
Keyword(s):  
Soil Water ◽  
Water Use ◽  
Water Table ◽  
Unsaturated Flow ◽  
Growth Ring ◽  
Soil Water Potential ◽  
Water Extraction ◽  
Depth Interval ◽  
Summer Drought ◽  
Drought Period

Eucalypt trees growing on deep soils, with a water table at about 8 m depth, showed no apparent drought effects during the 1982-83 dry period in south-east Australia when gross precipitation was only 388 mm. At the end of the drought, soil water to 4 m depth was depleted to a soil water potential of -0.5 MPa and under these conditions unsaturated flow from the water table to the lower root zone was calculated to be 0.17 mm day-1. Water extraction over the depth interval from 0 to 6 m in the drought year was 533 mm, some 200 mm in excess of that used during a year of average rainfall. The contribution to tree water use from unsaturated flow from the water table was calculated to be small (15 mm) even in a drought year, and in most years water movement would be towards the water table to yield a deep drainage term estimated between 40 and 100 mm. Growth ring studies indicated that the lower water use, estimated at 2.6 mm day-1 during the spring-summer drought, did not affect the slowly growing E. radiata species, but reduced stem diameter growth of the faster growing E. dalrympleana and E. pauciflora species.

scholarly journals The impact of drought on total ozone flux in a mountain Norway spruce forest

2020 ◽  
Vol 66 (No. 7) ◽  
pp. 280-278 ◽  
Author(s):  
Thomas Agyei ◽  
Stanislav Juráň ◽  
Kojo Kwakye Ofori-Amanfo ◽  
Ladislav Šigut ◽  
Otmar Urban ◽  
...  
Keyword(s):  
Norway Spruce ◽  
Stomatal Closure ◽  
Severe Drought ◽  
Summer Drought ◽  
Spruce Forest ◽  
Soil Humidity ◽  
Drought Period ◽  
The Impact ◽  
Mild Drought ◽  
Norway Spruce Forest

In order to understand the impact of summer drought on dry deposition of tropospheric ozone (O<sub>3</sub>), we compared severe and mild drought periods of summer 2018 in a mountain Norway spruce forest at Bílý Kříž, Beskydy Mts. An eddy covariance technique was applied to measure diurnal courses of the ecosystem O<sub>3</sub> and CO<sub>2</sub> fluxes. Low O<sub>3</sub> deposition was recorded in the morning and evening, while the highest CO<sub>2</sub> and O<sub><sup>3</sup></sub> fluxes were recorded during the central hours of the day. Total O<sub>3</sub> deposition during severe drought (soil humidity 13%) was significantly higher than the deposition during the mild drought period (soil humidity 19%). Our data indicate that high vapour pressure deficit and low soil humidity during severe drought led to the stomatal closure, while non-stomatal O<sub>3</sub> deposition, associated with chemical reactions of O<sub>3</sub> with NO and volatile organic compounds, are responsible for higher total O<sub>3</sub> deposition during the severe drought period. Therefore, we assume that under severe drought stomatal O<sub>3</sub> uptake decreases but non-stomatal depositions to forest ecosystems substantially increase.

scholarly journals CH<sub>4</sub> and N<sub>2</sub>O dynamics in the boreal forest–mire ecotone

2015 ◽  
Vol 12 (2) ◽  
pp. 281-297 ◽  
Author(s):  
B. Tupek ◽  
K. Minkkinen ◽  
J. Pumpanen ◽  
T. Vesala ◽  
E. Nikinmaa
Keyword(s):  
Ground Water ◽  
N2o Emission ◽  
N2o Emissions ◽  
Summer Drought ◽  
Drought Period ◽  
Local Climate ◽  
N2o Fluxes ◽  
Ch4 And N2o ◽  
Water Saturated ◽  
Boreal Landscapes

Abstract. In spite of advances in greenhouse gas research, the spatiotemporal CH4 and N2O dynamics of boreal landscapes remain challenging, e.g., we need clarification of whether forest–mire transitions are occasional hotspots of landscape CH4 and N2O emissions during exceptionally high and low ground water level events. In our study, we tested the differences and drivers of CH4 and N2O dynamics of forest/mire types in field conditions along the soil moisture gradient of the forest–mire ecotone. Soils changed from Podzols to Histosols and ground water rose downslope from a depth of 10 m in upland sites to 0.1 m in mires. Yearly meteorological conditions changed from being exceptionally wet to typical and exceptionally dry for the local climate. The median fluxes measured with a static chamber technique varied from −51 to 586 μg m−2 h−1 for CH4 and from 0 to 6 μg m−2 h−1 for N2O between forest and mire types throughout the entire wet–dry period. In spite of the highly dynamic soil water fluctuations in carbon rich soils in forest–mire transitions, there were no large peak emissions in CH4 and N2O fluxes and the flux rates changed minimally between years. Methane uptake was significantly lower in poorly drained transitions than in the well-drained uplands. Water-saturated mires showed large CH4 emissions, which were reduced entirely during the exceptional summer drought period. Near-zero N2O fluxes did not differ significantly between the forest and mire types probably due to their low nitrification potential. When upscaling boreal landscapes, pristine forest–mire transitions should be regarded as CH4 sinks and minor N2O sources instead of CH4 and N2O emission hotspots.

Yield and stolon characteristics of white clover (Trifolium repens L.) cultivars in perennial pasture in Victoria

1997 ◽  
Vol 37 (2) ◽  
pp. 159 ◽  
Author(s):  
S. G. Clark ◽  
M. J. McFadden
Keyword(s):  
White Clover ◽  
Trifolium Repens ◽  
Leaf Size ◽  
Summer Drought ◽  
Sheep Grazing ◽  
Drought Period ◽  
Diverse Range ◽  
Herbage Yield ◽  
Seed Reserves ◽  
Trifolium Repens L

Summary. The herbage yield, stolon characteristics and soil seed reserves of a diverse range of white clover (Trifolium repens L.) cultivars were studied at Hamilton in south-western Victoria. The cultivars were sown with perennial grass (Phalaris aquatica L.) and the pasture was rotationally grazed by sheep. The aim of the study was to identify white clover types which would persist under sheep grazing. The widely used cultivar, Haifa, fails to persist in this environment. Cultivars were divided into 3 groups depending on leaf size (range 2.5–13.0 cm2). Large-leaved cultivars were the most productive in the first year of the experiment but by year 3 some of the intermediate leaf-size cultivars were the most productive. Haifa (large leaved) was particularly unproductive in the third year compared with other large and intermediate leaf-size cultivars. Stolon characteristics were measured in early spring 1987, mid summer 1988 and early autumn 1988. Total stolon yield on each occasion was 0.46–0.99, 0.65–1.68 and 0.05–0.25 t DM/ha respectively. Intermediate leaf- size cultivars tended to have the highest stolon yields on each occasion. Stolon yield declined at the same rate (mean 87%; range 81–92%) in all cultivars between the second and third sampling date indicating that there is no variation in the cultivars’ ability to survive the summer drought period. Although seed reserves for most cultivars were high at the end of the experiment (range 11–130 kg/ha) no seedling recruitment was observed and seed is thought to play no role in sward survival in this environment. Plant breeders developing white clover cultivars for this environment should concentrate on maximising stolon yield at the beginning and end of the summer drought period (January–mid March). Intermediate leaf-size genotypes are likely to provide the best combination of stolon and herbage yield. Grazing management should also aim to maximise stolon yield at these critical times. The use of large-leaved, non-stoloniferous cultivars should be discouraged by advisers as they are not suited to this marginal environment under sheep grazing.

Chemical curing of annual pastures in Southern Australia for beef cattle and sheep

1971 ◽  
Vol 22 (3) ◽  
pp. 401 ◽  
Author(s):  
AL Pullman ◽  
WG Allden
Keyword(s):  
Beef Cattle ◽  
Nutritive Value ◽  
South Australia ◽  
Indirect Evidence ◽  
Water Soluble ◽  
Soluble Carbohydrate ◽  
Summer Drought ◽  
Summer Period ◽  
Drought Period ◽  
Cattle And Sheep

A desiccant herbicide (paraquat) was used to kill an annual pasture during the late spring months when the digestibility of the dry matter (DM) was 75%. The nutritive value of this standing herbage during the summer drought period was compared in field and pen studies with pasture allowed to mature naturally in the Mediterranean environment of South Australia. The herbicide treatment resulted in a significant reduction of standing herbage at the beginning of the summer period (5766 v. 2791 kg DM/ha). The DM digestibility by beef cattle of treated and untreated herbage was similar (52.4 v. 53.0% respectively). There was no difference between the paraquat-treated and the naturally matured pasture in the content or the apparent digestibility of organic matter, water-soluble carbohydrate, cellulose, or lignin; but nitrogen content, digestibility, and retention were significantly higher for paraquat-treated herbage. Rainfall between spraying and the beginning of the summer period was 140 mm. Indirect evidence from a separate study indicates that the fall in digestibility of the herbage after paraquat treatment was influenced by both rainfall and the spraying treatment. The productivity of beef cattle and sheep grazing the treated and untreated pastures during the dry summer confirmed the results of the digestibility studies, there being no difference between treatments in weight change or wool production. After the commencement of the autumn rainfall season the proportion of grass . on the sprayed area was greatly reduced, and the growth of cattle was significantly impaired. Thus the overall effect of the paraquat treatment was to reduce cattle growth.

Contrasting functional strategies following severe drought in two Mediterranean oaks with different leaf habit: Quercus faginea and Quercus ilex subsp. rotundifolia

2020 ◽  
Author(s):  
David Alonso-Forn ◽  
José Javier Peguero-Pina ◽  
Juan Pedro Ferrio ◽  
Maurizio Mencuccini ◽  
Óscar Mendoza-Herrer ◽  
...  
Keyword(s):  
Life Span ◽  
Quercus Ilex ◽  
Soil Water Potential ◽  
Leaf Life Span ◽  
Severe Drought ◽  
Summer Drought ◽  
Drought Period ◽  
Quercus Faginea ◽  
Leaf Habit ◽  
Mediterranean Oaks

Abstract Nowadays, evergreen sclerophyllous and winter-deciduous malacophyllous oaks with different paleogeographical origins coexist under Mediterranean-type climates, such as the mixed forests of the evergreen Quercus ilex subsp. rotundifolia Lam. and the winter-deciduous Quercus faginea Lam. Both Mediterranean oaks constitute two examples of contrasting leaf habit, so it could be expected that they would have different functional strategies to cope with summer drought. In this study, we analysed photosynthetic, photochemical and hydraulic traits of different organs for Q. faginea and Q. ilex subsp. rotundifolia under well-watered conditions and subjected to very severe drought. The coordinated response between photosynthetic and hydraulic traits explained the higher photosynthetic capacity of Q. faginea under well-watered conditions, which compensated its shorter leaf life span at the expense of higher water consumption. The progressive imposition of water stress evidenced that both types of Mediterranean oaks displayed different functional strategies to cope with water limitations. Specifically, the decrease in mesophyll conductance associated with edaphic drought seems to be the main factor explaining the differences found in the dynamics of net CO2 assimilation throughout the drought period. The sharp decline in photosynthetic traits of Q. faginea was coupled with a strong decrease in shoot hydraulic conductance in response to drought. This fact probably avoided extensive xylem embolism in the stems (i.e., ‘vulnerability segmentation’), which enabled new leaf development after drought period in Q. faginea. By contrast, leaves of Q. ilex subsp. rotundifolia showed effective photoprotective mechanisms and high resistance to drought-induced cavitation, which would be related with the longer leaf life span of the evergreen Mediterranean oaks. The co-occurrence of both types of Mediterranean oaks could be related to edaphic conditions that ensure the maintenance of soil water potential above critical values for Q. faginea, which can be severely affected by soil degradation and climate change.

Organic matter, nutrient content and biological activity in burned and unburned soils of a Mediterranean maquis area of southern Italy

2005 ◽  
Vol 14 (4) ◽  
pp. 365 ◽  
Author(s):  
Anna De Marco ◽  
Anna Elisa Gentile ◽  
Carmen Arena ◽  
Amalia Virzo De Santo
Keyword(s):  
Organic Matter ◽  
Organic Matter Content ◽  
Nutrient Content ◽  
Matter Content ◽  
Summer Drought ◽  
Drought Period ◽  
Soil Organic Matter Content ◽  
Microbial Carbon ◽  
Mediterranean Maquis ◽  
Phillyrea Angustifolia

Experimental fires were performed during the summer-drought period in a Mediterranean maquis in the Castel Volturno Nature Reserve in south-western Italy. The two different fuel loads applied (4 kg m−2 and 2 kg m−2) resulted in complete and partial combustion of the vegetation, respectively. Soil organic matter content (SOM), total and available element concentrations (K, Mg, Na, Mn, Fe, Cu, Pb, Cd), microbial carbon, respiration, metabolic quotient (qCO2), and the coefficient of endogenous mineralization (CEM) were measured at intervals in the dry and wet seasons over a period of about 3 years, in burned and adjacent unburned soils. Soil samples (0–5 cm depth) were collected under the cover of Phillyrea angustifolia L., a dominant species in the study area. Both fires induced long-lasting increases in SOM. As indicated by the increase in CEM, part of the accumulated SOM was mineralized in the first 3 months after fire whereas part of the accumulated SOM was instead stable. Both fires increased the total and available fractions of nutrients and trace elements. During the first 3 months after fire, microbial biomass and qCO2 were higher in the burned soils, which were richer in nutrients, but were characterized by harsher environmental conditions compared to unburned soils.

scholarly journals Modeling the forest dynamics of the Sierra Nevada under climate change using SORTIE-ND

2021 ◽  
Vol 78 (3) ◽  
Author(s):  
Emily V. Moran ◽  
Nikole Vannest ◽  
Mélaine Aubry-Kientz
Keyword(s):  
Climate Change ◽  
Sierra Nevada ◽  
Forest Dynamics ◽  
Model Simulation ◽  
Basal Area ◽  
Stem Density ◽  
Summer Drought ◽  
Drought Period ◽  
Drought Tolerant ◽  
Tolerant Species

Abstract Key message Model simulation results suggest that forests in the Sierra Nevada mountains of California will tend to increase in density and basal area in the absence of fire over the next century, and that climate change will favor increases in drought-tolerant species. Context Climate change is projected to intensify the natural summer drought period for Mediterranean-climate forests. Such changes may increase tree mortality, change species interactions and composition, and impact ecosystem services. Aims To parameterize SORTIE-ND, an individual-based, spatially explicit forest model, for forests in the Sierra Nevada, and to model forest responses to climate change. Methods We use 3 downscaled GCM projections (RCP 8.5) to project forest dynamics for 7 sites at different elevations. Results Basal area and stem density tended to increase in the absence of fire. Climate change effects differed by species, with more drought-tolerant species such as Jeffrey pine (Pinus jeffreyi A.Murray bis) and black oak (Quercus kelloggii Newb.) exhibiting increases in basal area and/or density. Conclusion Increasing forest density may favor carbon sequestration but could increase the risk of high-severity fires. Future analyses should include improved parameterization of reproduction and interactions of disturbance with climate effects.

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