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Pratt RB, Tobin MF, Jacobsen AL, Traugh CA, De Guzman ME, Hayes CC, Toschi HS, MacKinnon ED, Percolla MI, Clem ME, Smith PT. Starch storage capacity of sapwood is related to dehydration avoidance during drought. Am J Bot 2021; 108:91-101. [PMID: 33349932 DOI: 10.1002/ajb2.1586] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Accepted: 09/22/2020] [Indexed: 05/26/2023]
Abstract
PREMISE The xylem tissue of plants performs three principal functions: transport of water, support of the plant body, and nutrient storage. Tradeoffs may arise because different structural requirements are associated with different functions or because suites of traits are under selection that relate to resource acquisition, use, and turnover. The structural and functional basis of xylem storage is not well established. We hypothesized that greater starch storage would be associated with greater sapwood parenchyma and reduced fibers, which would compromise resistance to xylem tensions during dehydration. METHODS We measured cavitation resistance, minimum water potential, starch content, and sapwood parenchyma and fiber area in 30 species of southern California chaparral shrubs (evergreen and deciduous). RESULTS We found that species storing greater starch within their xylem tended to avoid dehydration and were less cavitation resistant, and this was supported by phylogenetic independent contrasts. Greater sapwood starch was associated with greater parenchyma area and reduced fiber area. For species without living fibers, the associations with parenchyma were stronger, suggesting that living fibers may expand starch storage capacity while also contributing to the support function of the vascular tissue. Drought-deciduous species were associated with greater dehydration avoidance than evergreens. CONCLUSIONS Evolutionary forces have led to an association between starch storage and dehydration resistance as part of an adaptive suite of traits. We found evidence for a tradeoff between tissue mechanical traits and starch storage; moreover, the evolution of novel strategies, such as starch-storing living fibers, may mitigate the strength of this tradeoff.
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Affiliation(s)
- R Brandon Pratt
- California State University, Bakersfield, Department of Biology, Bakersfield, California, 93311, USA
| | - Michael F Tobin
- University of Houston-Downtown, Department of Natural Sciences, One Main Street, Houston, Texas, 77002, USA
| | - Anna L Jacobsen
- California State University, Bakersfield, Department of Biology, Bakersfield, California, 93311, USA
| | - Courtney A Traugh
- California State University, Bakersfield, Department of Biology, Bakersfield, California, 93311, USA
| | - Mark E De Guzman
- California State University, Bakersfield, Department of Biology, Bakersfield, California, 93311, USA
| | - Christine C Hayes
- California State University, Bakersfield, Department of Biology, Bakersfield, California, 93311, USA
| | - Hayden S Toschi
- California State University, Bakersfield, Department of Biology, Bakersfield, California, 93311, USA
| | - Evan D MacKinnon
- California State University, Bakersfield, Department of Biology, Bakersfield, California, 93311, USA
| | - Marta I Percolla
- California State University, Bakersfield, Department of Biology, Bakersfield, California, 93311, USA
| | - Michael E Clem
- California State University, Bakersfield, Department of Biology, Bakersfield, California, 93311, USA
| | - Paul T Smith
- California State University, Bakersfield, Department of Biology, Bakersfield, California, 93311, USA
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Venturas MD, MacKinnon ED, Dario HL, Jacobsen AL, Pratt RB, Davis SD. Chaparral Shrub Hydraulic Traits, Size, and Life History Types Relate to Species Mortality during California's Historic Drought of 2014. PLoS One 2016; 11:e0159145. [PMID: 27391489 PMCID: PMC4938587 DOI: 10.1371/journal.pone.0159145] [Citation(s) in RCA: 68] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Accepted: 06/28/2016] [Indexed: 11/21/2022] Open
Abstract
Chaparral is the most abundant vegetation type in California and current climate change models predict more frequent and severe droughts that could impact plant community structure. Understanding the factors related to species-specific drought mortality is essential to predict such changes. We predicted that life history type, hydraulic traits, and plant size would be related to the ability of species to survive drought. We evaluated the impact of these factors in a mature chaparral stand during the drought of 2014, which has been reported as the most severe in California in the last 1,200 years. We measured tissue water potential, native xylem specific conductivity, leaf specific conductivity, percentage loss in conductivity, and chlorophyll fluorescence for 11 species in February 2014, which was exceptionally dry following protracted drought. Mortality among the 11 dominant species ranged from 0 to 93%. Total stand density was reduced 63.4% and relative dominance of species shifted after the drought. Mortality was negatively correlated with water potential, native xylem specific conductivity, and chlorophyll fluorescence, but not with percent loss in hydraulic conductivity and leaf specific conductivity. The model that best explained mortality included species and plant size as main factors and indicated that larger plants had greater survival for 2 of the species. In general, species with greater resistance to water-stress induced cavitation showed greater mortality levels. Despite adult resprouters typically being more vulnerable to cavitation, results suggest that their more extensive root systems enable them to better access soil moisture and avoid harmful levels of dehydration. These results are consistent with the hypothesis that short-term high intensity droughts have the strongest effect on mature plants of shallow-rooted dehydration tolerant species, whereas deep-rooted dehydration avoiding species fare better in the short-term. Severe droughts can drive changes in chaparral structure as a result of the differential mortality among species.
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Affiliation(s)
- Martin D. Venturas
- Department of Biology, California State University, 9001 Stockdale Hwy, Bakersfield, CA 93311, United States of America
- Grupo de Investigación en Genética, Fisiología e Historia Forestal, Universidad Politécnica de Madrid, Avda. de las Moreras s/n, 28040, Madrid, Spain
- * E-mail:
| | - Evan D. MacKinnon
- Department of Biology, California State University, 9001 Stockdale Hwy, Bakersfield, CA 93311, United States of America
| | - Hannah L. Dario
- Natural Science Division, Pepperdine University, 24255 Pacific Coast Highway, Malibu, CA 90263, United States of America
| | - Anna L. Jacobsen
- Department of Biology, California State University, 9001 Stockdale Hwy, Bakersfield, CA 93311, United States of America
| | - R. Brandon Pratt
- Department of Biology, California State University, 9001 Stockdale Hwy, Bakersfield, CA 93311, United States of America
| | - Stephen D. Davis
- Natural Science Division, Pepperdine University, 24255 Pacific Coast Highway, Malibu, CA 90263, United States of America
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Pratt RB, MacKinnon ED, Venturas MD, Crous CJ, Jacobsen AL. Root resistance to cavitation is accurately measured using a centrifuge technique. Tree Physiol 2015; 35:185-196. [PMID: 25716876 DOI: 10.1093/treephys/tpv003] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Plants transport water under negative pressure and this makes their xylem vulnerable to cavitation. Among plant organs, root xylem is often highly vulnerable to cavitation due to water stress. The use of centrifuge methods to study organs, such as roots, that have long vessels are hypothesized to produce erroneous estimates of cavitation resistance due to the presence of open vessels through measured samples. The assumption that roots have long vessels may be premature since data for root vessel length are sparse; moreover, recent studies have not supported the existence of a long-vessel artifact for stems when a standard centrifuge technique was used. We examined resistance to cavitation estimated using a standard centrifuge technique and compared these values with native embolism measurements for roots of seven woody species grown in a common garden. For one species we also measured vulnerability using single-vessel air injection. We found excellent agreement between root native embolism and the levels of embolism measured using a centrifuge technique, and with air-seeding estimates from single-vessel injection. Estimates of cavitation resistance measured from centrifuge curves were biologically meaningful and were correlated with field minimum water potentials, vessel diameter (VD), maximum xylem-specific conductivity (Ksmax) and vessel length. Roots did not have unusually long vessels compared with stems; moreover, root vessel length was not correlated to VD or to the vessel length of stems. These results suggest that root cavitation resistance can be accurately and efficiently measured using a standard centrifuge method and that roots are highly vulnerable to cavitation. The role of root cavitation resistance in determining drought tolerance of woody species deserves further study, particularly in the context of climate change.
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Affiliation(s)
- R B Pratt
- Department of Biology, California State University, Bakersfield, 9001 Stockdale Hwy, Bakersfield, CA 93311, USA
| | - E D MacKinnon
- Department of Biology, California State University, Bakersfield, 9001 Stockdale Hwy, Bakersfield, CA 93311, USA
| | - M D Venturas
- Department of Biology, California State University, Bakersfield, 9001 Stockdale Hwy, Bakersfield, CA 93311, USA
| | - C J Crous
- Forestry and Agricultural Biotechnology Institute, University of Pretoria, Pretoria 0002, South Africa
| | - A L Jacobsen
- Department of Biology, California State University, Bakersfield, 9001 Stockdale Hwy, Bakersfield, CA 93311, USA
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Hacke UG, Venturas MD, MacKinnon ED, Jacobsen AL, Sperry JS, Pratt RB. The standard centrifuge method accurately measures vulnerability curves of long-vesselled olive stems. New Phytol 2015; 205:116-27. [PMID: 25229841 DOI: 10.1111/nph.13017] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Accepted: 08/01/2014] [Indexed: 05/02/2023]
Abstract
The standard centrifuge method has been frequently used to measure vulnerability to xylem cavitation. This method has recently been questioned. It was hypothesized that open vessels lead to exponential vulnerability curves, which were thought to be indicative of measurement artifact. We tested this hypothesis in stems of olive (Olea europea) because its long vessels were recently claimed to produce a centrifuge artifact. We evaluated three predictions that followed from the open vessel artifact hypothesis: shorter stems, with more open vessels, would be more vulnerable than longer stems; standard centrifuge-based curves would be more vulnerable than dehydration-based curves; and open vessels would cause an exponential shape of centrifuge-based curves. Experimental evidence did not support these predictions. Centrifuge curves did not vary when the proportion of open vessels was altered. Centrifuge and dehydration curves were similar. At highly negative xylem pressure, centrifuge-based curves slightly overestimated vulnerability compared to the dehydration curve. This divergence was eliminated by centrifuging each stem only once. The standard centrifuge method produced accurate curves of samples containing open vessels, supporting the validity of this technique and confirming its utility in understanding plant hydraulics. Seven recommendations for avoiding artefacts and standardizing vulnerability curve methodology are provided.
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Affiliation(s)
- Uwe G Hacke
- Department of Renewable Resources, University of Alberta, Edmonton, AB, T6G 2E3, Canada
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