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United States Department of Agriculture

Agricultural Research Service

Title: Extensive Summer Water Pulses Do Not Necessarily Lead to Canopy Growth of Great Basin and Northern Mojave Desert Shrubs

Authors
item Snyder, Keirith
item Donovan, L - UNIVERSITY OF GEORGIA
item James, J - UNIVERSITY OF CALIFORNIA
item Tiller, R - UNIVERSITY OF CALIFORNIA
item Richards, J - UNIVERSITY OF CALIFORNIA

Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 28, 2003
Publication Date: October 1, 2004
Citation: Snyder, K.A., Donovan, L.A., James, J.J., Tiller, R.L., Richards, J.H. 2004. Extensive summer water pulses do not necessarily lead to canopy growth of great basin and northern Mojave Desert shrubs. Oecologia. 141(2):325-334.

Interpretive Summary: This study examines how experimentally added growing season water affects the physiology and growth of dominant shrub species that occur in water-limited habitats of the Great Basin and northern Mojave Desert. There is a common assumption that in water-limited environments the addition of water during the growing season should result in improved plant physiological function and growth. Another inherent assumption is that improved plant physiological performance will lead to improved plant growth and thus alter competitive interactions that structure plant communities and determine potential responses to climate change. This study tests these assumptions by irrigating dominant species for 1 to 3 years in their natural habitats during the growing season. We assessed plant physiological responses and plant growth responses to large short-term growing season irrigations for: Chrysothamnus nauseosus, Sarcobatus vermiculatus, Atriplex confertifolia, and Atriplex parryi. We compared control and watered plants in nine case studies that encompassed adults of all four dominant shrub species, juveniles of three of the species, and two sites for two of the species. In every comparison, plants used additional summer water to improve plant water status or increase rates of functioning as indicated by other physiological measurements. However, use of additional summer water did not affect canopy growth in eight out of nine comparisons, despite the range of species, growth stages, and site conditions. The general lack of growth for these species might be due to close proximity of groundwater at these sites, co-limitation by nutrients, or inability to respond due to phenological canalization. An understanding of the connections between short-term physiological responses and plant growth is critical for determining the effect of additional growing season precipitation on plant community dynamics.

Technical Abstract: Plant species and functionally related species groups from arid and semiarid habitats vary in their capacity to take up summer precipitation, acquire nitrogen quickly after summer precipitation, and subsequently respond with ecophysiological changes (e.g., water and nitrogen relations, gas exchange). For species that respond ecophysiologically, the use of summer precipitation is generally assumed to affect long-term plant growth and, thus, alter competitive interactions that structure plant communities and determine potential responses to climate change. We assessed ecophysiological and growth responses to large, short-term irrigation pulses over one to three growing seasons for several widespread Great Basin and northern Mojave Desert shrub species: Chrysothamnus nauseosus, Sarcobatus vermiculatus, Atriplex confertifolia, and A. parryi. We compared control and watered plants in nine case studies that encompassed adults of all four species, juveniles for three of the species, and two sites for two of the species. In every comparison, plants used summer water pulses to improve plant water status or increase rates of functioning as indicated by other ecophysiological characters. Species and life history stage responses of ecophysiological parameters were consistent with several previous short-term studies. However, use of summer water pulses did not affect canopy growth in eight out of nine comparisons despite the range of species, growth stages, and site conditions. Summer water pulses affected canopy growth only for C. nauseosus adults. The general lack of growth effects for these species might be due to close proximity of groundwater at these sites, colimitation by nutrients, or inability to respond due to phenological canalization. An understanding of the connections between short-term ecophysiological responses and growth for different habitats and species is critical for determining the significance of summer precipitation for desert community dynamics.

Last Modified: 10/1/2014
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