Minimal Plant Responsiveness to Summer Water Pulses: Ecophysiological Constraints of Three Species of Semiarid Patagonia |
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| Authors: | Rodolfo A Golluscio Valeria Sigal Escalada Juliana Pérez |
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| Institution: | 1. Department of Geography, State University of New York at Buffalo, 105 Wilkeson Quadrangle, Buffalo, NY 14261, USA;2. Department of Botany, University of Wyoming, 1000 E. University Avenue, Laramie, WY 82071, USA;3. Program in Ecology, University of Wyoming, 1000 E. University Avenue, Laramie, WY 82071, USA;4. Hawkesbury Institute for the Environment, University of Western Sydney, Australia;1. Department of Obstetrics and Gynecology, Ospedale San Gionvanni di Dio, University of Cagliari, Cagliari, Italy;2. Department of Radiology, Azienda Ospedaliero Universitaria di Cagliari – Polo di Monserrato, Cagliari, Italy;3. Department of Obstetrics and Gynecology, Clínica Universidad de Navarra, University of Navarra, Spain;1. Unidade Acadêmica Especializada em Ciências Agrárias, Universidade Federal do Rio Grande do Norte, Natal, RN, Brazil;2. Laboratório de Metabolismo de Plantas, Departamento de Bioquímica e Biologia Molecular, Universidade Federal do Ceará, Campus do Pici, CP 6020, CEP 60451-970, Fortaleza, Ceará, Brazil;3. Departamento de Engenharia Florestal, Universidade Federal de Campina Grande, CEP: 58.700-970, Patos, Paraíba, Brazil;4. Laboratório de Biomoléculas, Departamento de Bioquímica e Biologia Molecular, Universidade Federal do Ceará, Campus do Pici, CP 6020, CEP 60451-970, Fortaleza, Ceará, Brazil;5. Faculdade de Educação, Ciências e Letras do Sertão, Central Universidade Estadual do Ceará, CEP 63900-000, Quixadá, Ceará, Brazil;6. Faculdade Leão Sampaio Av. Padre Cicero, n° 2830 - Triangulo -Juazeiro do Norte, CE, Brazil;1. Department of Plant Ecology, University of Bayreuth, Bayreuth D-95447 (Germany);2. Department of Plant Sciences, Madurai Kamaraj University, Madurai 625021 (India);3. Institute for Genomic Biology, University of Illinois, Urbana, IL 61820 (USA) |
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| Abstract: | In arid ecosystems, a few large summer rains frequently differentiate wet years from dry ones. However, use of this additional water by plants has limited experimental evidence. We applied a 16-mm summer water pulse (12% of mean annual precipitation) to two plant communities of the Patagonian steppe, and compared responses of three dominant species, which can be ordered by decreasing xerophytism and increasing rooting depth and summer activity: 1) colapiche, evergreen dwarf shrub (Nassauvia glomerulosa Lag.] Don); 2) coirón amargo, evergreen grass (Stipa speciosa Trin. et Rupr.); and 3) neneo, drought deciduous shrub (Mulinum spinosum Cav.] Pers.). Shallow-rooted species (S. speciosa and N. glomerulosa), which use water from dry soil layers, showed a greater leaf water potential response to watering than deep-rooted species (M. spinosum). Leaf water potential response was greater and quicker in xerophytic species than in mesophytic ones (N. glomerulosa > S. speciosa > M. spinosum). However, this response only translated into leaf conductance and transpiration responses for coirón amargo, probably because the species with winter phenological cycle (N. glomerulosa) is less able to utilize summer water inputs than species with a summer phenological cycle (S. speciosa). The lack of response of deep-rooted M. spinosum in leaf conductance, transpiration, and photosynthesis may have been due to the high leaf water potential of control plants. Instead, in S. speciosa and N. glomerulosa net photosynthesis decreased below zero following watering, suggesting the start of growth pulses. The complex chain of plant processes triggered by rainfall, and the constraints imposed to different species by rooting depth, phenology, and xerophytism, could explain the frequent low response to both large rainfall events and above-average rainfall years in this arid community. Our results suggest that, paradoxically, water may be suboptimally used at local scales in arid rangeland ecosystems. |
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