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Gibson RK, Bradstock RA, Penman T, Keith DA, Driscoll DA. Determinants of growth of the flammable grass,
Triodia scariosa
: Consequences for fuel dynamics under climate change in the Mediterranean region of South Eastern Australia. AUSTRAL ECOL 2016. [DOI: 10.1111/aec.12348] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- Rebecca K. Gibson
- Centre for Environmental Risk Management of Bushfires, Institute for Conservation Biology and Environmental Management University of Wollongong Wollongong Australia
| | - Ross A. Bradstock
- Centre for Environmental Risk Management of Bushfires, Institute for Conservation Biology and Environmental Management University of Wollongong Wollongong Australia
| | - Trent Penman
- Centre for Environmental Risk Management of Bushfires, Institute for Conservation Biology and Environmental Management University of Wollongong Wollongong Australia
| | - David A. Keith
- NSW Office of Environment and Heritage Hurstville Australia
- Australian Wetlands, Rivers and Landscapes Centre University of New South Wales Sydney New South Wales Australia
- Long Term Ecological Research Network Terrestrial Ecosystem Research Network Australia
| | - Don A. Driscoll
- ARC Centre of Excellence for Environmental Decisions the NERP Environmental Decisions Hub Fenner School of Environment and Society Australian National University Canberra Australian Capital Territory Australia
- Fenner School of Environment and Society Australian National University Canberra Australian Capital Territory Australia
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Below-ground interspecific competition for water in a rubber agroforestry system may enhance water utilization in plants. Sci Rep 2016; 6:19502. [PMID: 26781071 PMCID: PMC4726060 DOI: 10.1038/srep19502] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2015] [Accepted: 12/14/2015] [Indexed: 11/22/2022] Open
Abstract
Rubber-based (Hevea brasiliensis) agroforestry systems are regarded as the best way to improve the sustainability of rubber monocultures, but few reports have examined water use in such systems. Accordingly, we tested whether interplanting facilitates water utilization of rubber trees using stable isotope (δD, δ18O, and δ13C) methods and by measuring soil water content (SWC), shoot potential, and leaf C and N concentrations in a Hevea-Flemingia agroforestry system in Xishuangbanna, southwestern China. We detected a big difference in the utilization of different soil layer water between both species in this agroforestry system, as evidenced by the opposite seasonal fluctuations in both δD and δ18O in stem water. However, similar predawn shoot potential of rubber trees at both sites demonstrating that the interplanted species did not affect the water requirements of rubber trees greatly. Rubber trees with higher δ13C and more stable physiological indexes in this agroforestry system showed higher water use efficiency (WUE) and tolerance ability, and the SWC results suggested this agroforestry is conductive to water conservation. Our results clearly indicated that intercropping legume plants with rubber trees can benefit rubber trees own higher N supply, increase their WUE and better utilize soil water of each soil layer.
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Wu H, Li XY, Jiang Z, Chen H, Zhang C, Xiao X. Contrasting water use pattern of introduced and native plants in an alpine desert ecosystem, Northeast Qinghai-Tibet Plateau, China. THE SCIENCE OF THE TOTAL ENVIRONMENT 2016; 542:182-191. [PMID: 26519579 DOI: 10.1016/j.scitotenv.2015.10.121] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2015] [Revised: 10/10/2015] [Accepted: 10/24/2015] [Indexed: 06/05/2023]
Abstract
Plant water use patterns reflect the complex interactions between different functional types and environmental conditions in water-limited ecosystems. However, the mechanisms underlying the water use patterns of plants in the alpine desert of the Qinghai-Tibet Plateau remain poorly understood. This study investigated seasonal variations in the water sources of herbs (Carex moorcroftii, Astragalus adsurgens) and shrubs (Artemisia oxycephala, Hippophae rhamnoides) using stable oxygen-18 isotope methods. The results indicated that the native herbs (C. moorcroftii, A. adsurgens) and one of the shrubs (A. oxycephala) mainly relied on water from the shallow layer (0-30 cm) throughout the growing season, while the introduced shrub (H. rhamnoides) showed plasticity in switching between water from shallow and deep soil layers depending on soil water availability. All studied plants primarily depended on water from shallow soil layers early in the season. The differences of water use patterns between the introduced and native plants are closely linked with the range of active root zones when competing for water. Our findings will facilitate the mechanistic understanding of plant-soil-water relations in alpine desert ecosystems and provide information for screening introduced species for sand fixation.
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Affiliation(s)
- Huawu Wu
- State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University, Beijing 100875, China; College of Resources Science and Technology, Beijing Normal University, Beijing 100875, China.
| | - Xiao-Yan Li
- State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University, Beijing 100875, China; College of Resources Science and Technology, Beijing Normal University, Beijing 100875, China.
| | - Zhiyun Jiang
- College of Resources Science and Technology, Beijing Normal University, Beijing 100875, China
| | - Huiying Chen
- College of Resources Science and Technology, Beijing Normal University, Beijing 100875, China
| | - Cicheng Zhang
- College of Resources Science and Technology, Beijing Normal University, Beijing 100875, China
| | - Xiong Xiao
- College of Resources Science and Technology, Beijing Normal University, Beijing 100875, China
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Kellner E, Hubbart JA. A comparison of the spatial distribution of vadose zone water in forested and agricultural floodplains a century after harvest. THE SCIENCE OF THE TOTAL ENVIRONMENT 2016; 542:153-61. [PMID: 26519576 DOI: 10.1016/j.scitotenv.2015.10.080] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Revised: 10/15/2015] [Accepted: 10/15/2015] [Indexed: 05/07/2023]
Abstract
To improve quantitative understanding of the long-term impact of historic forest removal on floodplain vadose zone water regime, a study was implemented in fall 2010, in the Hinkson Creek Watershed, Missouri, USA. Automated, continuously logging capacitance-frequency probes were installed in a grid-like formation (n=6) and at depths of 15, 30, 50, 75, and 100 cm within a historic agricultural field (Ag) and a remnant bottomland hardwood forest (BHF). Data were logged at thirty minute intervals for the duration of the 2011, 2012, and 2013 hydrologic years. Results showed volumetric water content (VWC) to be significantly different between sites (p<0.01) during the study, with site averages of 33.1 and 32.8% at the Ag and BHF sites, respectively. Semi-variogram analyses indicate the presence of strong (<25%) horizontal and vertical spatial correlation of VWC at the Ag site, and a relatively short-range (25 cm) vertical spatial correlation at the BHF, but only indicate horizontal VWC spatial correlation in the top 30 cm of the BHF profile. Likely mechanisms contributing to patterns of observed differences are contrasting rates and depths of plant water use, and the presence of preferential flow paths in the below ground BHF. Results suggest historic forest removal and cultivation of the Ag site lead to an effective homogenization of the upper soil profile, and facilitated the development of strong VWC spatial dependency. Conversely, higher hydraulic conductivity of the more heterogeneous BHF subsurface likely results in a wetting of the deeper profile (75 cm) during climatically wet periods, and thus a more effective processing of hydrologic inputs. Collective results highlight the greater extent and degree to which forest vegetation impacts subsurface hydrology, relative to grassland/agricultural systems, and point to the value of reestablishing floodplain forests for fresh water routing, water quality, and flood mitigation in mixed-land-use watersheds.
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Affiliation(s)
- Elliott Kellner
- School of Natural Resources, University of Missouri, Columbia, MO 65211, USA.
| | - Jason A Hubbart
- School of Natural Resources, Water Resources Program, University of Missouri, Columbia, MO 65211, USA
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Voltas J, Lucabaugh D, Chambel MR, Ferrio JP. Intraspecific variation in the use of water sources by the circum-Mediterranean conifer Pinus halepensis. THE NEW PHYTOLOGIST 2015; 208:1031-41. [PMID: 26193768 DOI: 10.1111/nph.13569] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Accepted: 06/13/2015] [Indexed: 05/13/2023]
Abstract
The relevance of interspecific variation in the use of plant water sources has been recognized in drought-prone environments. By contrast, the characterization of intraspecific differences in water uptake patterns remains elusive, although preferential access to particular soil layers may be an important adaptive response for species along aridity gradients. Stable water isotopes were analysed in soil and xylem samples of 56 populations of the drought-avoidant conifer Pinus halepensis grown in a common garden test. We found that most populations reverted to deep soil layers as the main plant water source during seasonal summer droughts. More specifically, we detected a clear geographical differentiation among populations in water uptake patterns even under relatively mild drought conditions (early autumn), with populations originating from more arid regions taking up more water from deep soil layers. However, the preferential access to deep soil water was largely independent of aboveground growth. Our findings highlight the high plasticity and adaptive relevance of the differential access to soil water pools among Aleppo pine populations. The observed ecotypic patterns point to the adaptive relevance of resource investment in deep roots as a strategy towards securing a source of water in dry environments for P. halepensis.
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Affiliation(s)
- Jordi Voltas
- Department of Crop and Forest Sciences - AGROTECNIO Center, University of Lleida, Rovira Roure 191, Lleida, E-25198, Spain
| | - Devon Lucabaugh
- Department of Crop and Forest Sciences - AGROTECNIO Center, University of Lleida, Rovira Roure 191, Lleida, E-25198, Spain
| | | | - Juan Pedro Ferrio
- Department of Crop and Forest Sciences - AGROTECNIO Center, University of Lleida, Rovira Roure 191, Lleida, E-25198, Spain
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56
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Evaristo J, Jasechko S, McDonnell JJ. Global separation of plant transpiration from groundwater and streamflow. Nature 2015; 525:91-4. [PMID: 26333467 DOI: 10.1038/nature14983] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2014] [Accepted: 07/14/2015] [Indexed: 11/09/2022]
Abstract
Current land surface models assume that groundwater, streamflow and plant transpiration are all sourced and mediated by the same well mixed water reservoir--the soil. However, recent work in Oregon and Mexico has shown evidence of ecohydrological separation, whereby different subsurface compartmentalized pools of water supply either plant transpiration fluxes or the combined fluxes of groundwater and streamflow. These findings have not yet been widely tested. Here we use hydrogen and oxygen isotopic data ((2)H/(1)H (δ(2)H) and (18)O/(16)O (δ(18)O)) from 47 globally distributed sites to show that ecohydrological separation is widespread across different biomes. Precipitation, stream water and groundwater from each site plot approximately along the δ(2)H/δ(18)O slope of local precipitation inputs. But soil and plant xylem waters extracted from the 47 sites all plot below the local stream water and groundwater on the meteoric water line, suggesting that plants use soil water that does not itself contribute to groundwater recharge or streamflow. Our results further show that, at 80% of the sites, the precipitation that supplies groundwater recharge and streamflow is different from the water that supplies parts of soil water recharge and plant transpiration. The ubiquity of subsurface water compartmentalization found here, and the segregation of storm types relative to hydrological and ecological fluxes, may be used to improve numerical simulations of runoff generation, stream water transit time and evaporation-transpiration partitioning. Future land surface model parameterizations should be closely examined for how vegetation, groundwater recharge and streamflow are assumed to be coupled.
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Affiliation(s)
- Jaivime Evaristo
- Global Institute for Water Security and School of Environment and Sustainability, University of Saskatchewan, Saskatoon, Saskatchewan S7N 3H5, Canada
| | - Scott Jasechko
- Department of Geography, University of Calgary, Calgary, Alberta T2N IN4, Canada
| | - Jeffrey J McDonnell
- Global Institute for Water Security and School of Environment and Sustainability, University of Saskatchewan, Saskatoon, Saskatchewan S7N 3H5, Canada.,School of Geosciences, University of Aberdeen, Aberdeen AB34 3FX, UK.,Department of Forest Engineering, Resources and Management, Oregon State University, Corvallis, Oregon 97331, USA
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57
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Zhou H, Zhao W, Zheng X, Li S. Root distribution of Nitraria sibirica with seasonally varying water sources in a desert habitat. JOURNAL OF PLANT RESEARCH 2015; 128:613-622. [PMID: 26003322 DOI: 10.1007/s10265-015-0728-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2014] [Accepted: 03/10/2015] [Indexed: 06/04/2023]
Abstract
In water-limited environments, the water sources used by desert shrubs are critical to understanding hydrological processes. Here we studied the oxygen stable isotope ratios (δ (18)O) of stem water of Nitraria sibirica as well as those of precipitation, groundwater and soil water from different layers to identify the possible water sources for the shrub. The results showed that the shrub used a mixture of soil water, recent precipitation and groundwater, with shallow lateral roots and deeply penetrating tap (sinker) roots, in different seasons. During the wet period (in spring), a large proportion of stem water in N. sibirica was from snow melt and recent precipitation, but use of these sources declined sharply with the decreasing summer rain at the site. At the height of summer, N. sibirica mainly utilized deep soil water from its tap roots, not only supporting the growth of shoots but also keeping the shallow lateral roots well-hydrated. This flexibility allowed the plants to maintain normal metabolic processes during prolonged periods when little precipitation occurs and upper soil layers become extremely dry. With the increase in precipitation that occurs as winter approaches, the percentage of water in the stem base of a plant derived from the tap roots (deep soil water or ground water) decreased again. These results suggested that the shrub's root distribution and morphology were the most important determinants of its ability to utilize different water sources, and that its adjustment to water availability was significant for acclimation to the desert habitat.
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Affiliation(s)
- Hai Zhou
- Linze Inland River Basin Research Station, Key Laboratory of Inland River Basin Ecohydrology, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, 320 Dong-gang West Road, Lanzhou, 730000, China
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58
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Barbeta A, Mejía-Chang M, Ogaya R, Voltas J, Dawson TE, Peñuelas J. The combined effects of a long-term experimental drought and an extreme drought on the use of plant-water sources in a Mediterranean forest. GLOBAL CHANGE BIOLOGY 2015; 21:1213-1225. [PMID: 25359123 DOI: 10.1111/gcb.12785] [Citation(s) in RCA: 82] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2014] [Accepted: 09/25/2014] [Indexed: 06/04/2023]
Abstract
Vegetation in water-limited ecosystems relies strongly on access to deep water reserves to withstand dry periods. Most of these ecosystems have shallow soils over deep groundwater reserves. Understanding the functioning and functional plasticity of species-specific root systems and the patterns of or differences in the use of water sources under more frequent or intense droughts is therefore necessary to properly predict the responses of seasonally dry ecosystems to future climate. We used stable isotopes to investigate the seasonal patterns of water uptake by a sclerophyll forest on sloped terrain with shallow soils. We assessed the effect of a long-term experimental drought (12 years) and the added impact of an extreme natural drought that produced widespread tree mortality and crown defoliation. The dominant species, Quercus ilex, Arbutus unedo and Phillyrea latifolia, all have dimorphic root systems enabling them to access different water sources in space and time. The plants extracted water mainly from the soil in the cold and wet seasons but increased their use of groundwater during the summer drought. Interestingly, the plants subjected to the long-term experimental drought shifted water uptake toward deeper (10-35 cm) soil layers during the wet season and reduced groundwater uptake in summer, indicating plasticity in the functional distribution of fine roots that dampened the effect of our experimental drought over the long term. An extreme drought in 2011, however, further reduced the contribution of deep soil layers and groundwater to transpiration, which resulted in greater crown defoliation in the drought-affected plants. This study suggests that extreme droughts aggravate moderate but persistent drier conditions (simulated by our manipulation) and may lead to the depletion of water from groundwater reservoirs and weathered bedrock, threatening the preservation of these Mediterranean ecosystems in their current structures and compositions.
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Affiliation(s)
- Adrià Barbeta
- CSIC, Global Ecology Unit CREAF-CSIC-UAB, Cerdanyola del Vallès (Catalonia), E-08193, Spain; CREAF, Cerdanyola del Vallès (Catalonia), E-08193, Spain
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59
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Prechsl UE, Burri S, Gilgen AK, Kahmen A, Buchmann N. No shift to a deeper water uptake depth in response to summer drought of two lowland and sub-alpine C3-grasslands in Switzerland. Oecologia 2014; 177:97-111. [DOI: 10.1007/s00442-014-3092-6] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Accepted: 09/12/2014] [Indexed: 10/24/2022]
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Nippert JB, Ocheltree TW, Orozco GL, Ratajczak Z, Ling B, Skibbe AM. Evidence of physiological decoupling from grassland ecosystem drivers by an encroaching woody shrub. PLoS One 2013; 8:e81630. [PMID: 24339950 PMCID: PMC3855384 DOI: 10.1371/journal.pone.0081630] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Accepted: 10/23/2013] [Indexed: 11/18/2022] Open
Abstract
Shrub encroachment of grasslands is a transformative ecological process by which native woody species increase in cover and frequency and replace the herbaceous community. Mechanisms of encroachment are typically assessed using temporal data or experimental manipulations, with few large spatial assessments of shrub physiology. In a mesic grassland in North America, we measured inter- and intra-annual variability in leaf δ13C in Cornus drummondii across a grassland landscape with varying fire frequency, presence of large grazers and topographic variability. This assessment of changes in individual shrub physiology is the largest spatial and temporal assessment recorded to date. Despite a doubling of annual rainfall (in 2008 versus 2011), leaf δ13C was statistically similar among and within years from 2008-11 (range of −28 to −27‰). A topography*grazing interaction was present, with higher leaf δ13C in locations that typically have more bare soil and higher sensible heat in the growing season (upland topographic positions and grazed grasslands). Leaf δ13C from slopes varied among grazing contrasts, with upland and slope leaf δ13C more similar in ungrazed locations, while slopes and lowlands were more similar in grazed locations. In 2011, canopy greenness (normalized difference vegetation index – NDVI) was assessed at the centroid of individual shrubs using high-resolution hyperspectral imagery. Canopy greenness was highest mid-summer, likely reflecting temporal periods when C assimilation rates were highest. Similar to patterns seen in leaf δ13C, NDVI was highest in locations that typically experience lowest sensible heat (lowlands and ungrazed). The ability of Cornus drummondii to decouple leaf physiological responses from climate variability and fire frequency is a likely contributor to the increase in cover and frequency of this shrub species in mesic grassland and may be generalizable to other grasslands undergoing woody encroachment.
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Affiliation(s)
- Jesse B. Nippert
- Division of Biology, Kansas State University, Manhattan, Kansas, United States of America
- * E-mail:
| | - Troy W. Ocheltree
- Division of Biology, Kansas State University, Manhattan, Kansas, United States of America
- Department of Forest and Rangeland Stewardship, Colorado State University, Fort Collins, Colorado, United States of America
| | - Graciela L. Orozco
- Division of Biology, Kansas State University, Manhattan, Kansas, United States of America
| | - Zak Ratajczak
- Division of Biology, Kansas State University, Manhattan, Kansas, United States of America
| | - Bohua Ling
- Department of Geography, Kansas State University, Manhattan, Kansas, United States of America
| | - Adam M. Skibbe
- Division of Biology, Kansas State University, Manhattan, Kansas, United States of America
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61
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Biohydrologic effects of eastern redcedar encroachment into grassland, Oklahoma, USA. Biologia (Bratisl) 2013. [DOI: 10.2478/s11756-013-0252-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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63
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Penna D, Oliviero O, Assendelft R, Zuecco G, Meerveld I(HJV, Anfodillo T, Carraro V, Borga M, Fontana GD. Tracing the Water Sources of Trees and Streams: Isotopic Analysis in a Small Pre-Alpine Catchment. ACTA ACUST UNITED AC 2013. [DOI: 10.1016/j.proenv.2013.06.012] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Ward D, Wiegand K, Getzin S. Walter's two-layer hypothesis revisited: back to the roots! Oecologia 2012; 172:617-30. [PMID: 23266712 PMCID: PMC3679411 DOI: 10.1007/s00442-012-2538-y] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2012] [Accepted: 11/16/2012] [Indexed: 11/26/2022]
Abstract
Walter (Jahrb Wiss Bot 87:750–860, 1939) proposed a two-layer hypothesis, an equilibrium explanation for coexistence of savanna trees and grasses. This hypothesis relies on vertical niche partitioning and assumed that grasses are more water-use efficient than trees and use subsurface water while trees also have access to deeper water sources. Thus, in open savannas, grasses were predicted to predominate because of their water use efficiency and access to subsurface water. This hypothesis has been a prominent part of the savanna literature since first proposed. We review the literature on Walter’s hypothesis and reconsider his original intentions. Walter intended this hypothesis to be restricted to dry savannas. In his opinion, mesic and humid savannas were controlled by biotic factors and disturbances. We surveyed the global savanna literature for records of vertical niche partitioning by grasses and trees. We find that, within the scope of Walter’s original intentions, this hypothesis works remarkably well, and in some cases is appropriate for deserts as well as for dry temperate systems and even some mesic savannas.
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Affiliation(s)
- David Ward
- School of Life Sciences, University of KwaZulu-Natal, Scottsville, South Africa.
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65
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Zegada-Lizarazu W, Wullschleger SD, Surendran Nair S, Monti A. Crop Physiology. GREEN ENERGY AND TECHNOLOGY 2012. [DOI: 10.1007/978-1-4471-2903-5_3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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66
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Response of dominant grass and shrub species to water manipulation: an ecophysiological basis for shrub invasion in a Chihuahuan Desert grassland. Oecologia 2011; 169:373-83. [PMID: 22159870 DOI: 10.1007/s00442-011-2217-4] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2010] [Accepted: 11/23/2011] [Indexed: 10/14/2022]
Abstract
Increases in woody vegetation and declines in grasses in arid and semi-arid ecosystems have occurred globally since the 1800s, but the mechanisms driving this major land-cover change remain uncertain and controversial. Working in a shrub-encroached grassland in the northern Chihuahuan Desert where grasses and shrubs typically differ in leaf-level nitrogen allocation, photosynthetic pathway, and root distribution, we asked if differences in leaf-level ecophysiology could help explain shrub proliferation. We predicted that the relative performance of grasses and shrubs would vary with soil moisture due to the different morphological and physiological characteristics of the two life-forms. In a 2-year experiment with ambient, reduced, and enhanced precipitation during the monsoon season, respectively, the encroaching C(3) shrub (honey mesquite Prosopis glandulosa) consistently and substantially outperformed the historically dominant C(4) grass (black grama Bouteloua eriopoda) in terms of photosynthetic rates while also maintaining a more favorable leaf water status. These differences persisted across a wide range of soil moisture conditions, across which mesquite photosynthesis was decoupled from leaf water status and moisture in the upper 50 cm of the soil profile. Mesquite's ability to maintain physiologically active leaves for a greater fraction of the growing season than black grama potentially amplifies and extends the importance of physiological differences. These physiological and phenological differences may help account for grass displacement by shrubs in drylands. Furthermore, the greater sensitivity of the grass to low soil moisture suggests that grasslands may be increasingly susceptible to shrub encroachment in the face of the predicted increases in drought intensity and frequency in the desert of the southwestern USA.
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Sun SJ, Meng P, Zhang JS, Wan X. Variation in soil water uptake and its effect on plant water status in Juglans regia L. during dry and wet seasons. TREE PHYSIOLOGY 2011; 31:1378-1389. [PMID: 22116051 DOI: 10.1093/treephys/tpr116] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Temporal and spatial variations in the water status of walnut trees (Juglans regia L.) and the soil in which they were growing were traced by analyzing the differences in hydrogen isotopes during spring and summer in a 7-year-old walnut stand. Walnut root dynamics were measured in both dry and wet seasons. Walnut roots were mainly distributed in the upper soil (0-30 cm depth), with around 60% of the total root mass in upper soil layers and 40% in deep soil layers (30-80 cm depth). The upper soil layers contributed 68% of the total tree water requirement in the wet season, but only 47% in the dry season. In the wet season, total roots, living roots and new roots were all significantly more abundant than in the dry season. There were significant differences in pre-dawn branch percentage loss of hydraulic conductance (PLC), pre-dawn leaf water potential and transpiration between the dry and wet seasons. Water content in the upper soil layers remarkably influenced xylem water stable-hydrogen isotope (δD) values. Furthermore, there were linear relationships between the xylem water δD value and pre-dawn branch PLC, pre-dawn leaf water potential, transpiration rate and photosynthetic rate. In summary, J. regia was compelled to take a larger amount of water from the deep soil layers in the dry season, but this shift could not prevent water stress in the plant. The xylem water δD values could be used as an indicator to investigate the water stress of plants, besides probing profiles of soil water use.
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Affiliation(s)
- Shou-Jia Sun
- Institute of New Forest Technology, Chinese Academy of Forestry, Beijing 100091, PR China
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Bihmidine S, Bryan NM, Payne KR, Parde MR, Okalebo JA, Cooperstein SE, Awada T. Photosynthetic performance of invasive Pinus ponderosa and Juniperus virginiana seedlings under gradual soil water depletion. PLANT BIOLOGY (STUTTGART, GERMANY) 2010; 12:668-675. [PMID: 20636910 DOI: 10.1111/j.1438-8677.2009.00251.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Changes in climate, land management and fire regime have contributed to woody species expansion into grasslands and savannas worldwide. In the USA, Pinus ponderosa P.&C. Lawson and Juniperus virginiana L. are expanding into semiarid grasslands of Nebraska and other regions of the Great Plains. We examined P. ponderosa and J. virginiana seedling response to soil water content, one of the most important limiting factors in semiarid grasslands, to provide insight into their success in the region. Photosynthesis, stomatal conductance, maximum photochemical efficiency of PSII, maximum carboxylation velocity, maximum rate of electron transport, stomatal limitation to photosynthesis, water potential, root-to-shoot ratio, and needle nitrogen content were followed under gradual soil water depletion for 40 days. J. virginiana maintained lower L(s), higher A, g(s), and initial F(v)/F(m), and displayed a more gradual decline in V(cmax) and J(max) with increasing water deficit compared to P. ponderosa. J. virginiana also invested more in roots relative to shoots compared to P. ponderosa. F(v)/F(m) showed high PSII resistance to dehydration in both species. Photoinhibition was observed at approximately 30% of field capacity. Soil water content was a better predictor of A and g(s) than Psi, indicating that there are other growth factors controlling physiological processes under increased water stress. The two species followed different strategies to succeed in semiarid grasslands. P. ponderosa seedlings behaved like a drought-avoidant species with strong stomatal control, while J. virginiana was more of a drought-tolerant species, maintaining physiological activity at lower soil water content. Differences between the studied species and the ecological implications are discussed.
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Affiliation(s)
- S Bihmidine
- School of Natural Resources, University of Nebraska, Lincoln, NE, USA
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