Evapotranspiration from an arid zone plant community

Sammis, T. W.; Gay, Lloyd W.

doi:10.1016/s0140-1963(18)31685-9

Cited by 58 publications

(10 citation statements)

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“…While Sala and Lauenroth (1982; showed that small rains (<5 mm) stimulate the growth of grasses in semi-arid regions and concluded that these small events may provide a shallow source of moisture for some plant FTs, others suggest that small rainfall events do not reach the roots of plants (Dougherty et al 1996;Nobel 1976;Weaver 1982). Indeed, the usefulness of small rainfall events (<5 mm) as determinants of plant growth would seem quite limited in warm deserts of the southwestern United States, given the very low numbers of roots in the top few centimeters of soil (Franco and Nobel 1991;MacMahon and Schimpf 1981;Rundel and Nobel 1991) and the high evaporation losses from the soil surface (Reynolds et al 2000b;Samis and Gay 1979). The resolution of this dilemma lies with a consideration of additional factors that influence the 'biological significance' of individual rainfall events: namely, antecedent soil moisture conditions and the chance of that rainfall event becoming part of a sequence of consecutive events.…”

Section: Discussionmentioning

confidence: 99%

Modifying the ‘pulse–reserve’ paradigm for deserts of North America: precipitation pulses, soil water, and plant responses

et al. 2004

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The 'pulse-reserve' conceptual model--arguably one of the most-cited paradigms in aridland ecology--depicts a simple, direct relationship between rainfall, which triggers pulses of plant growth, and reserves of carbon and energy. While the heuristics of 'pulses', 'triggers' and 'reserves' are intuitive and thus appealing, the value of the paradigm is limited, both as a conceptual model of how pulsed water inputs are translated into primary production and as a framework for developing quantitative models. To overcome these limitations, we propose a revision of the pulse-reserve model that emphasizes the following: (1) what explicitly constitutes a biologically significant 'rainfall pulse', (2) how do rainfall pulses translate into usable 'soil moisture pulses', and (3) how are soil moisture pulses differentially utilized by various plant functional types (FTs) in terms of growth? We explore these questions using the patch arid lands simulation (PALS) model for sites in the Mojave, Sonoran, and Chihuahuan deserts of North America. Our analyses indicate that rainfall variability is best understood in terms of sequences of rainfall events that produce biologically-significant 'pulses' of soil moisture recharge, as opposed to individual rain events. In the desert regions investigated, biologically significant pulses of soil moisture occur in either winter (October-March) or summer (July-September), as determined by the period of activity of the plant FTs. Nevertheless, it is difficult to make generalizations regarding specific growth responses to moisture pulses, because of the strong effects of and interactions between precipitation, antecedent soil moisture, and plant FT responses, all of which vary among deserts and seasons. Our results further suggest that, in most soil types and in most seasons, there is little separation of soil water with depth. Thus, coexistence of plant FTs in a single patch as examined in this PALS study is likely to be fostered by factors that promote: (1) separation of water use over time (seasonal differences in growth), (2) relative differences in the utilization of water in the upper soil layers, or (3) separation in the responses of plant FTs as a function of preceding conditions, i.e., the physiological and morphological readiness of the plant for water-uptake and growth. Finally, the high seasonal and annual variability in soil water recharge and plant growth, which result from the complex interactions that occur as a result of rainfall variability, antecedent soil moisture conditions, nutrient availability, and plant FT composition and cover, call into question the use of simplified vegetation models in forecasting potential impacts of climate change in the arid zones in North America.

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Section: Discussionmentioning

confidence: 99%

Modifying the ‘pulse–reserve’ paradigm for deserts of North America: precipitation pulses, soil water, and plant responses

et al. 2004

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“…The predicted transpiration fraction of water loss for this station was between 51% (SWB) and 61% (PALS-SW) of the total (Table 7). Experiments that study evaporation and transpiration in "isolation," such as measuring soil evaporation in a lysimeter devoid of roots [e.g., Sammis and Gay, 1979], are likely to reach erroneous conclusions because of the strong interdependency between these processes.…”

Section: Evapotranspirationmentioning

confidence: 99%

A comparative modeling study of soil water dynamics in a desert ecosystem

Kemp¹,

Reynolds²,

Pachepsky³

et al. 1997

Water Resources Research

109

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Abstract. We compared three different soil water models to evaluate t. he extent to which variation in plant growth form and cover and soil texture along a topographic gradient interact to affect relative rates of evaporation and transpiration under semiarid conditions. The models all incorporated one-dimensional distribution of water in the soil and had separate functions for loss. of water through transpiration and soil evaporation but differed in. the degree of mechanism and emphasis. PALS-SW (Patch Arid Lands Simulator-Soil Water) is a mechanistic model that includes soil water fluxes and emphasizes the physiological control of water loss by different plant life forms along the gradient. 2DSOIL is a mechanistic model that emphasizes the physical aspects of soil water fluxes. SWB (Soil Water Budget) is a simple water budget model that has no soil water redistribution and includes simplified schemes for soil evaporation and transpiration by different life forms. The model predictions were compared to observed soil water distributions at five positions along the gradient. All models predicted soil water distributions reasonably well and, for the most part, predicted similar trends along the transect in the fractions of water lost as soil evaporation versus transpiration. Transpiration was low.est (about 40% of total evapotranspiration (ET)) for the creosote bush community, which had the lowest plant cover (30% peak cover). The fraction of ET as transpiration increased with increasing plant cover, with 2DSOIL predictin. g the highest transpiration (60% of total ET) for the mixed vegetation community (60% peak cover) on relatively fine textured soil and PALS-SW predicting highest transpiration (69% of total ET) for the mixed vegetation community (70% peak cover) on relatively coarse textured soil. The community type had an effect on the amount of water lost as transpiration primarily via depth and di. stribution of roots. In this respect, PALS-SW predicted greatest differences amon. g stations as related to differences in plant community types. However, since PALS-SW did not provide as good of fit with the soil moisture data as did 2DSOIL, the differences in the morphology and physiology of the life-forms may be secondary to the overall control of water loss by the primary factors accounted for in 2DSOIL: vertical distribution of soil moisture, degree of canopy cover, and evaporative energy budget of the canopy. Soil texture interacted with the amount and type of plant cover to affect evaporation and transpiration, but the effect was relatively minor.

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“…Low soil-moisture likewise precludes much radiantenergy loss via evaporation, and in at least one instance (transpiration from Larrea tridentata in the Sonoran Desert) only a small percentage of total AET appears to be due to the transpiration process itself (Sammis & Gay, 1979). Rather little of this energy is absorbed, as it impinges on relatively dry soils and sparse vegetation.…”

Section: Climatementioning

confidence: 99%

Desert Ecosystems: Their Resources in Space and Time

Crawford

Gosz

1982

Envir. Conserv.

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The dynamics of desert ecosystems control levels of resources that are essential to the survival of desert biotas. Because precipitation is both low and relatively unpredictable in arid regions, the climates, topographies, and soils, of these areas present formidable constraints to resource availability in space and time. And for the same reason, the processes of production, consumption, decomposition, and nutrient-cycling in deserts are also highly irregular and difficult to predict with accuracy. For example, global models relating actual evapotranspiration to primary production and decomposition apply poorly in arid regions.Surprisingly great amounts of carbon are stored in desert soils, particularly in caliche deposits which represent a major ‘sink’ of carbon from the atmosphere. In Arizona desert soils, inorganic carbon exceeds organic carbon by a factor of > 10. Direct use of organic carbon is made principally by organisms that break down desert litter and simultaneously cause relatively high rates of nitrogen mineralization. While nitrogen is traditionally considered deficient in arid environments, its flux is considerable because of high rates of gain by fixation and loss by denitrification and volatilization. Nitrogen accumulates in ‘islands of fertility’ beneath desert shrubs where it becomes relatively available because of (i) its high concentration in plant litter, and (ii) reduced activity of any aromatic modifiers that retard decomposition.It is misleading in deserts to relate nutrient availability to yearly averages, as nutrients may become highly available following pulses of ‘effective’ precipitation. Moreover, mineralization and subsequent availability to plants of phosphorous, the ‘master element’ in nutrient cycling, are moderately independent of nitrogen mineralization and can proceed rapidly. Clearly, the case for nutrient deficiency in deserts may be overstated.Consumption of primary production has varying effects on rates of resource availability in desert ecosystems. Generally weak regulation of primary production is predicted for consumers of green vegetation, except occasionally during early drought. Carnivores should exert variable controls over their prey, while pollinators, seed-eaters, and detritivores—most of which are strongly soil-associated—should have the greatest impacts on primary production and nutrient cycling.

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Evapotranspiration from an arid zone plant community

Cited by 58 publications

References 9 publications

Modifying the ‘pulse–reserve’ paradigm for deserts of North America: precipitation pulses, soil water, and plant responses

Modifying the ‘pulse–reserve’ paradigm for deserts of North America: precipitation pulses, soil water, and plant responses

A comparative modeling study of soil water dynamics in a desert ecosystem

Desert Ecosystems: Their Resources in Space and Time

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