The drought treatment was not initiated until at the base, and 1. The existing branch- day 20 of the study to allow for the initial d e v e l o p m e n t es were r e m o v e d from each post to c o n f o r m with c o m - of roots and leaves.
Droughted posts were watered m o n planting practices. Prior to planting, the posts with ml applied as one dose on e v e r y fourth were kept in a cold dark storage area with the bottom day o f the study.
Each treatment consisted o f eight half placed in moist commercial soil mixture. The time replicate posts for a total o f 40 posts. The study was lag between cutting and planting was 4 days.
Pots 1. The field soil was Sharkey Clay Series collected f r o m the main floodplain o f the M e a s u r e m e n t s o f Eh, taken at 15, 30, 60, and 90 Mississippi River in D y e r County, Tennessee. Caps c m below the soil surface were conducted daily using were glued to the bottom of each pot, and holes were platinum-tipped electrodes, a millivoltmeter, and a cal- drilled on the side to allow control of water regime.
Soil p H was recorded w e e k l y at The study was conducted in an air-conditioned green- c m depth using a pH m e t e r and a p H electrode in all house with an average daily low temperature of Temperatures ranged f r o m a daily low o f R o o t porosity, a the top of plant canopy during sunny days.
Posts were measure o f the percent air space within a root, was maintained under well-watered and well-drained con- measured on posts at the conclusion of the study. Root ditions for 7 days before treatments were begun. Posts samples weighing between 0. Root porosity was m e a s u r e d using 50 m L pyc- willow posts to soil moisture regimes.
The treatments nometers as described b y Jensen et al. The represented a range of soil moisture regimes and soil p y c n o m e t e r was first filled with water and weighed. The root was then ex- were carefully r e m o v e d f r o m the pots and soil was tracted and ground to a paste with mortar and pestle. Posts were divided into above- The ground root was returned to the p y c n o m e t e r and and below-ground biomass components.
The above- weighed. The numbers of live and dead branches were also Gas Exchange and Water Relations recorded for each post. B e l o w - g r o u n d b i o m a s s was Stomatal conductance gw and net photosynthesis separated into live and dead root b i o m a s s between 0 - Pn were measured using a portable photosynthetic 15, , 3 0 - 6 0 , 6 0 - 9 0 , and 9 0 - 1 1 7 c m b e l o w the system CIRAS 1, PP Systems, England.
The gas ex- soil surface. At each depth interval, the n u m b e r o f lat- change m e a s u r e m e n t s were conducted periodically on eral roots originated f r o m the post was also counted. PAR and air temperature tween 9 0 - 1 1 7 c m were not counted due to the diffi- were also m e a s u r e d during each sampling period.
Gas culty o f obtaining accurate data. Roots at that depth exchange was measured on five posts one fully ex- had grown into fine mesh placed in the pots to keep panded leaf per post per treatment on days 16, 18, the soil f r o m washing through the side holes during 27, 35, 37, 49, 60, 68, and Pre-dawn water poten- watering.
No dead roots were found on the study posts tial was quantified using a portable pressure chamber. T h e above- and below- Measurements of pre-dawn water potential provide an ground portions o f each post without leaves, branch- estimate of plant water status and soil moisture avail- es, and roots were air-dried for three w e e k s in a green- ability Kozlowski et al. Pre-dawn water poten- house.
To examine sample leaf f r o m each post per treatment excluding the root biomass relationship with soil Eh, root bio- intermittently flooded posts on days 67, 74, and L e a f area was then regressed b y d r y Repeated measures analysis was used to test differ- weight. T h e m o d e l used to calculate l e a f area was ences in means of gas exchange data SAS L e a f samples weighing between 0. A spectrophotom- Soil Measurements eter was then used to record absorbance at and nm.
Chlorophyll concentration was calculated ac- M e a n soil p H ranged b e t w e e n 7. The entire soil profile in control and in the drained zone of the PF pots 0 - 4 5 c m depth r e m a i n e d well-aerated Biomass throughout the study as shown by Eh data Figure 1A. Posts were weighed to obtain initial biomass before In contrast, soil Eh at all depth classes in the C F treat- planting.
Since posts were collected during dormancy, ment, in the continuously-flooded portion o f the IF the initial biomass for leaf, branches and root com- treatment 6 0 - 1 2 0 cm , and in the flooded portion ponents was zero. In the 1F pots, breaking bud. Weekly mean soil redox potential Eh at various levels below the soil surface cm for control A , intermittently flooded B , partially flooded C , and continuously flooded D treatments.
Each point is the mean for 14 measurements. Bars represent standard error. N o n e of the posts in level was raised or lowered, respectively Figure 1B. Posts in other treatments displayed no stress symptoms. Mortality was not o b s e r v e d in the Plant Responses other treatments.
Flooded posts developed hypertrophied lenticels, water roots roots initiated and developed f r o m the Gas Exchange and Water Relations. Stomatal con- portion of each post located under water , and dis- ductance gw of posts in all treatments r e m a i n e d low- played enhanced root porosity. However, root porosity er than that o f control posts throughout the study with was significantly greater only in CF posts Figure 2 the exception o f IF posts Figure 3A.
Standard error is shown following mean in. The response was in accord with the lowest gw, significantly l o w e r than all other treat- changes in water level i m p o s e d on the root s y s t e m by ments Figure 4A. Such shifts in ure 3 B. E a r l y during the r e m a i n e d ]ower than control posts throughout the study, Pn in P F posts s h o w e d the m o s t sensitivity Fig- study Figure 3A. F o r instance, mean gw was signifi- p h i e d lenticels and water roots u n d e r this treatment as cantly lower in posts under PF and C F treatments as c o m p a r e d to other flooded treatments.
Posts subjected c o m p a r e d to control Figure 4A. In addition, the m e a n gw of controls. Posts in the drought treatment posts in the drought t r e a t m e n t h a d significantly l o w e r m e a n Pn c o m p a r e d to all other treatments Figure 4B. L i m i t e d soil watering under d r o u g h t treat- treatments. Values represent average over the experimental ment resulted in d e v e l o p m e n t of soil water deficits that period.
Bars above means represent standard error. Different letters represent significant differences among treatments at in turn induced water stress in posts. Abbreviations: Control C , intermittently also s h o w e d significantly l o w e r more negative pre- flooded IF , partially flooded PF , continuously flooded dawn water potential than controls, w h i l e posts in the CF , drought D.
Mean stomatal conductance A and net photo- 0 synthesis B for black willow posts under various treat- i 4 i" I 0 14 2 56 70 ments. Values represent average over the experimental pe- Days riod. Different letters represent significant differences among treatments at Figure 3.
Values represent av- CF , drought D. Journal of Climate. Sections Abstract 1. Introduction 2. SLAM description and evaluation a. Model description b. Model evaluation 3. Synthetic forcing a. Forcing description b. Synthetic summers 4. Evaporation and soil moisture a. The source of regime behavior b. Impact of insolation on evaporative cooling c. Evaporative cooling and summertime temperature variability 5. Summary and conclusions Model Derivation and Equations a.
Enthalpy equations b. Moisture budget and enthalpy closure c. Soil moisture flux d. Soil heat flux e. Surface sensible heat flux and evapotranspiration f. Turbulent heat and moisture fluxes within the atmosphere g. Longwave radiation h. A note on numerical methods. Export References. Crossref Barriopedro , D. Crossref Berg , A. Crossref Best , M. Crossref Byrne , M. Crossref Collatz , G. Crossref Dee , D.
Crossref DeVries , D. Crossref Diffenbaugh , N. Crossref Dirmeyer , P. Crossref Donat , M. Crossref Eagleson , P. Crossref Ermold , B. Crossref Fischer , E. Crossref Franssen , H. Crossref Gentine , P. Crossref Hirsch , A. Crossref Jackson , R. Crossref Katz , R. Crossref Koster , R. Crossref Libardi , P. Crossref Long , C. Crossref Ma , H. Crossref McCoy , R. Crossref Merrifield , A. Crossref Morcrette , C.
Crossref Mueller , B. Crossref Nitao , J. Crossref Papalexiou , S. Crossref Previdi , M. Crossref Rawls , W. Crossref Riihimaki , L. Crossref Robine , J. Crossref Sauvageot , H. CO;2 false. Crossref Sellers , P. Crossref Seneviratne , S. Crossref Teuling , A. Crossref Tingley , M. Crossref Tong , B. Crossref Troyan , D.
Crossref van Heerwaarden , C. Crossref Vidale , P. Crossref Wei , Z. Crossref Xie , S. Export Figures View in gallery Multimodel-mean percentage change in standard deviation of 2-m air temperature between the —99 and —14 periods across an ensemble of CMIP5 model simulations of the RCP8.
View in gallery Schematic representation of the connection between evaporation efficiency and soil moisture, originally proposed by Budyko View in gallery a A schematic of the SLAM showing temperature and moisture variables in each model layer along with the boundary conditions. View in gallery Scatterplots of monthly averaged latent heat flux LHF as a function of a — d monthly averaged surface saturation X and e — h monthly averaged net insolation R.
View in gallery Box-and-whisker plots for a daily average near surface temperature T 3 and b daily average surface saturation X across the four column soil moisture initialization experiments. Close View raw image Multimodel-mean percentage change in standard deviation of 2-m air temperature between the —99 and —14 periods across an ensemble of CMIP5 model simulations of the RCP8. View raw image Schematic representation of the connection between evaporation efficiency and soil moisture, originally proposed by Budyko View raw image a A schematic of the SLAM showing temperature and moisture variables in each model layer along with the boundary conditions.
View raw image Scatterplots of monthly averaged latent heat flux LHF as a function of a — d monthly averaged surface saturation X and e — h monthly averaged net insolation R.
View raw image Box-and-whisker plots for a daily average near surface temperature T 3 and b daily average surface saturation X across the four column soil moisture initialization experiments. Author: Frank L. Authors: Michael S. Dinniman and John M.
Authors: P. Thorne and R. Author: Ralph J. Donaldson Jr. Previous Article Next Article. Editorial Type: Article. Lucas R. Vargas Zeppetello 1 , David S. Battisti 1 , and Marcia B. Baker 1. Article History. Download PDF. Full access. Corresponding author : Lucas R. Vargas Zeppetello, lvz7 uw. Introduction As the climate warms, the impacts of increasing summertime temperatures are becoming more evident.
Table 1. Model description Figure 3a shows a schematic of the SLAM where all model layers and thermodynamic variables are labeled. All model layers have a temperature K and moisture variable that are assumed to be homogenous within the layer. The volumetric soil water content is defined as the volume occupied by liquid water in a unit volume of soil.
In Eq. In the Budyko framework, this coupling term is nonlinear see Fig. Model evaluation The SLAM needs time series of net absorbed shortwave radiation R , precipitation P , and cloud fraction c f as well as temperature and humidity boundary conditions T Top and q Top to generate output.
Table 2. Synthetic forcing The skill of the SLAM to reproduce the SGP observations for one summer motivates us to use it to understand the processes that control summertime temperatures and temperature variability more generally. Power spectra of ERA-Interim reanalysis output demonstrate that net surface insolation, hPa temperature, and hPa specific humidity are a combination of red noise and a diurnal cycle during the summer Dee et al.
Once we have the radiation time series [Eq. Synthetic summers Using the equations from section 4a , we create an ensemble of forcing time series for SLAM experiments to investigate the impact of soil moisture on summertime temperature variability. Table 3. As soil moisture increases, the tight grouping of the green lines compared to the brown lines in Fig.
We assume that an increment dE in evaporation rate produces a proportional change in evaporative cooling dT E. Therefore, a Taylor series expansion of Eq. Substituting this assumption into Eq. Impact of insolation on evaporative cooling In the real world, evaporation is not the only source of temperature anomalies.
If we combine Eqs. So far, we have argued that a negative feedback exists between soil moisture, evaporative cooling, and vapor pressure deficit.
Table 4. Evaporative cooling and summertime temperature variability We now investigate summertime temperature variability generated by SLAM in the synthetic forcing experiments. Table 5. Model Derivation and Equations a. To obtain model equations that allow us to integrate our state variables forward in time, we need enthalpy equations for the atmospheric and soil layers.
Moisture budget and enthalpy closure Since there are two unknowns T and m or T and q in each of the enthalpy tendency equations [Eqs. A2 and A9 ], we need two equations in each model layer to fully describe our system. Water must be conserved, so we can write water budgets for each layer in terms of model fluxes.
We can use the moisture fluxes shown in Fig. By combining the moisture budgets and enthalpy tendency equations, we can close our system and derive the temperature tendency equations for each layer. By summing Eqs.
In all were installed through the polyethylene sheet at an hedgerow system plots, three sets of wave-guides angle of In layers, respectively. Weekly rainfall during the phases of space as nested. During the — pair-wise comparison. There were some heavy rains in —14 May , covering the dry season 10 February and March yet with long phases without November —8 March , total soil water further rain.
To prevent tree roots from penetrating non- During the second phase of measurements 8 allocated area and neighbouring plots, hedgerow October —2 May , covering the dry sea- system plots were surrounded by trenches of 20 cm son 31 October —26 March , measure- width and 60 cm depth. The continuously water content between fallow systems were only cropped natural fallow and the alternately cropped found in the 0—20 cm depth layer Figure 3.
The alter- cropped hedgerow system-2 fallow. As from 21st hedgerows. In all cases, water content cropped hedgerow system-2 fallow and the con- under the G. The same the L. Water content in the 20—40 cm layer between 14th October and 14th May under Leucaena leucocephala and Gliricidia sepium hedgerows and in the middle between hedgerows in the 2 years crop; 2 years hedgerow fallow systems, Yaounde, southern Cameroon.
Water content mm in the 40—60 cm layer between 8th October and 2nd May , under Leucaena leucocephala and Gliricidia sepium hedgerows and in the middle between hedgerows in the 2 years crop; 2 years hedgerow fallow systems Yaounde, southern Cameroon. In the 20—40 cm layer, water A key concept in the development of hedgerow content was generally the highest under G. A major process in this shown.
We can therefore as- hedgerow trees and crops. De- Stahr et al. The few tree control and hedgerow intercropping systems. Deep rooting food crops had a higher water short-lived in — Contrary to that, the and nutrient use than hedgerow intercropping grass dominated natural fallow maintained a lower systems in their study.
Hairiah et al. The data Ultisol. Consequently they challenged the appro- from this study do not support hypotheses 1 and 3. Kanmenge et al. Any system reducing water 60— and — cm in both dry seasons, contents to lower levels than another system will indicates that neither system had an advantage in create conditions under which leaching of nutri- extracting sub-soil water.
Therefore, hypothesis 2 ents will be delayed, because more rain is required cannot be accepted. In the 0—60 cm soil horizon, it is unlikely that either such cases soil solution remains accessible to crops system accesses or recovers more nutrients from for a longer period, increasing the probability of layers deeper than 60 cm during dry phases.
We nutrient uptake by food crops. Lehmann et al. The cover crop Cameroon and comparable situations in the Pueraria phaseoloides appeared to be most capable humid tropics. Grimme H. Knick, S. Studies in Avian Biology Vol. Knick and J. Lauenroth, W. Ecohydrology and the partitioning AET between transpiration and evaporation in a semiarid steppe. Ecosystems 9, — Maestas, J. Tapping soil survey information for rapid assessment of sagebrush ecosystem resilience and resistance.
Rangelands 38, — Manier, D. Geological Survey Open-File Report — Maurer, E. Fine-resolution climate projections enhance regional climate change impact studies.
Eos Transac. AGU Millar, C. Climate change and forests of the future: managing in the face of uncertainty. Miller, D. A conterminous united states multilayer soil characteristics dataset for regional climate and hydrology modeling. Earth Interact. Moss, R. The next generation of scenarios for climate change research and assessment. Noy-Meir, I. Desert ecosystems: environment and producers. Overpeck, J. The challenge of hot drought.
Palmquist, K. Mid-latitude shrub steppe plant communities: climate change consequences for soil water resources. Ecology 97, — Spatial and ecological variation in dryland ecohydrological responses to climate change: implications for management.
Paruelo, J. Relative abundance of plant functional types in grasslands and shrublands of North America. Petrie, M. A review of precipitation and temperature control on seedling emergence and establishment for ponderosa and lodgepole pine forest regeneration. R Core Team Rehfeldt, G. North American vegetation model for land-use planning in a changing climate: a solution to large classification problems. Reichstein, M. Climate extremes and the carbon cycle. Renne, R. Soil and stand structure explain shrub mortality patterns following global change type-drought and extreme precipitation.
Renwick, K. Multi-model comparison highlights consistency in predicted effect of warming on a semi-arid shrub. Roundy, B. Resilience and resistance in sagebrush ecosystems are associated with seasonal soil temperature and water availability.
Saha, S. The NCEP climate forecast system reanalysis. Schlaepfer, D. R package version 3. Climate change reduces extent of temperate drylands and intensifies drought in deep soils. Effects of ecohydrological variables on current and future ranges, local suitability patterns, and model accuracy in big sagebrush.
Ecography 35, — Natural regeneration processes in big sagebrush Artemisia tridentata. R package version 2. Seager, R. Greenhouse warming and the 21st century hydroclimate of southwestern North America. Seidl, R. REVIEW: searching for resilience: addressing the impacts of changing disturbance regimes on forest ecosystem services. Shriver, R. Adapting management to a changing world: warm temperatures, dry soil, and inter-annual variability limit restoration success of a dominant woody shrub in temperate drylands.
Smith, M. The ecological role of climate extremes: current understanding and future prospects. Snyder, K. Effects of changing climate on the hydrological cycle in cold desert ecosystems of the great Basin and Columbia Plateau. Soil Survey Staff Keys to Soil Taxonomy , 12th Edn.
Stein, B. National Wildlife Federation. Stocker, T. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change. Taylor, K. An overview of CMIP5 and the experiment design. Tietjen, B. Climate change-induced vegetation shifts lead to more ecological droughts despite projected rainfall increases in many global temperate drylands.
Tohver, I. Impacts of 21st-century climate change on hydrologic extremes in the pacific northwest region of North America. Water Resour. Ummenhofer, C. Extreme weather and climate events with ecological relevance: a review. National Centers for Environmental Prediction a. Dataset ds National Centers for Environmental Prediction b.
Vicente-Serrano, S. Response of vegetation to drought time-scales across global land biomes. Wang, L. Dryland ecohydrology and climate change: critical issues and technical advances. Earth Syst. West, N. Williams, M. Zhang, X. Attributing intensification of precipitation extremes to human influence. Keywords: aridification, big sagebrush ecosystems, cheatgrass, climate change, drought, ecological transformation, vulnerability.
The use, distribution or reproduction in other forums is permitted, provided the original author s and the copyright owner s are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Bradford, jbradford usgs. Chambers, jeanne.
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