FluxLetter The Newsletter of FLUXNET Vol. 2 No. 4, December, 2009 Highlight FLUXNET site Highlighting Site: Santa Rita Creosotebush Santa Rita Creosotebush by Shirley A. (Kurc) Papuga Compared to other areas which in the timing, frequency and tridentata (hereafter referred to In This Issue: receive greater annual precipita- magnitude of precipitation as Larrea) already inhabited the tion, dryland carbon uptake is events will have important eco- southwestern United States by highly sensitive to precipitation hydrological consequences. the Last Glacial Maximum inputs (Huxman et al., 2004). Critical to predicting and under- (Duran et al., 2005). Now, Lar- FLUXNET site: The amount of precipitation in standing the implications of these rea is pervasive in three North Santa Rita Creosotebush Papuga (Kurc) S……...……...Pages 1-4 drylands is small; therefore, climatic changes is a better un- American deserts: the Mojave, dryland ecosystems depend on derstanding how dryland vegeta- the Sonoran, and the Chihua- Correspondence: pulses of moisture, i.e. small tion responds to and uses water huan, even though they differ in New Investments in the Austra- resources. topography, climate, and histori- pulses that primarily trigger lian Flux Network microbial activity and evapora- cal background. While Larrea Eamus D……………………Page 5-7 tion or large pulses that provide Introduction to Larrea triden- typically forms extensive mono- tata. typic stands, they are greatest in moisture to support photosyn- FLUXNET young scientist: thesis and transpiration. Most In the arid to semiarid areas of density in the Chihuahuan De- Aline Jaimes …………….….Pages 8-9 global climate models predict North America, a drought toler- sert with decreasing density to changes in the intra-annual vari- ant plant Larrea tridentata domi- the west (Barbour, 1969). A Research: ability of precipitation (Knapp et nates the landscape, extending ploidy gradient also occurs in Semiarid ECohydrological al., 2008). Given the average from Nevada, United States this species from east to west: Array – SECA (“creosotebush”) to Hidalgo, generally speaking, the Chihua- Scott RL, Jenerette GD, Huxman TE annual precipitation in drylands ………………..……....….Pages 10-12 globally is expected to decline Mexico (“gobernadora” or huan populations are diploid, the (e.g. Seager et al., 2007), changes “hediondilla”) (Figure 1). Larrea Sonoran populations are Lateral versus vertical car- tetraploid, and Mojave popula- bon fluxes in Baja California, tions are hexaploid; higher ploidy Mexico races are believed to be an adap- Escoto-Rodriguez M, Smith SV, Bullock SH………………..Pages 13-15 tation to increased aridity and/or higher temperature (Hunter et al., 2001). This unusual poly- CO2 fluxes in semi-arid sites on carbonate substrates ploidy is likely to have been a located in southeast Spain major factor in expansion in Serrano-Ortiz P, Pérez Sánchez-Cañete range of Larrea throughout the E, Domingo F, Were A, Villagarcía L, and Kowalski AS………...............Pages 16-18 20th century (Duran et al., 2005). Larrea is a repeat-blooming, New Mexico elevation gradi- ent evergreen shrub, with a C3 pho- Litvak M, and Fox, A…......Pages 19-21 tosynthetic pathway. With no defined trunk, it typically reaches heights of 1 to 1.5 m, but has been found to stretch as high as Figure 1: Distribution of creosotebush in North America and the location of the Santa Rita 4 m. Both inverted-cone and Creosotebush tower site at the northern boundary of the Santa Rita Experimental Range in southeastern Arizona. Image by Michelle Cavanaugh. Page 2 Santa Rita Creosotebush of Larrea were to change, would all depths) with no caliche layer, a reduction in cover and subse- to at least 1 m. Long term quent exposure of soil records from the SRER archives strengthen feedback to local (http://ag.arizona.edu/SRER/ and regional climate? data.html) suggest that the SRC flux station area receives aver- Site Description. age annual precipitation of 330 As of February 2010, a full two mm, half occurring in July years of flux observations will through September with mon- have been made at the Santa soon rains and the other half Rita Creosotebush (SRC) occurring from December tower site (Figure 3) located through February with winter about 30 miles south of Tucson and spring rains. within the boundaries of the Unique long-term measure- Santa Rita Experimental Range ments at the SRC tower site Figure 2: Close up view of Larrea leaves and flowers. Photo by Shirley Papuga. (SRER) in southeastern Arizona, include continuous measure- United States (Figure 1). The ments of soil moisture at multi- hemispherical canopies have illustrating the drought tolerant SRER is bounded at its southern ple depths in multiple profiles been identified, the architecture shrub provides a dependable and eastern borders by the all down to 1 m. Additionally, suggested to facilitate functional resource in an unpredictable Santa Rita Mountains. Since at three digital “game” cameras, water and nutrient accumulation environment (Minckley et al., least 1904 (Figure 4), Larrea has on a time-lapse setting, are below the shrub (DeSoyza et al., 2000). The spherical fruit, pea- been the dominant species near monitoring the daily phenologi- 1997; Whitford et al., 1997). sized and densely covered with the very northern boundary of cal activity of the Larrea, such as The bifoliolate leaves of Larrea fuzzy white hairs, eventually the SRER where the SRC tower green up and flowering, within are opposite, with two asymmet- splits into 5 pieces, each contain- site is located (UTM: 0515177, footprint of the flux tower. rical oblong leaflets joined at the ing a single seed. Moisture, 3530284) at an elevation of base, measuring about 1 cm long temperature, and soil conditions about 950 m. Some Research Highlights. and 3 to 4 mm wide (Figure 2). are all thought to play a role in Total canopy cover at the SRC We have seen that the depth of The odorous resin that coats the ability of Larrea seeds to tower site is 24% (14% Larrea moisture reservoirs is largely these leaves has been shown to germinate. and the other 10% a combina- associated with the nature of promote water use efficiency, Over the last century, the area tion of annual grasses, annual precipitation events in dryland deter herbivores, and screen dominated by Larrea in North herbaceous species, and cacti). ecosystems (Kurc and Small, ultra-violet radiation (Meinzer et America has increased, and is Soil crusts are also prevalent 2004; Kurc and Small, 2007). al., 1990). This resin, secreted associated with coincident land throughout the site. The height Soil moisture pulses at the by a glandular epidermis of the degradation during that time of the average Larrea is 1.7 m, surface follow most storms stipules, is a complex mixture of (Grover and Musick, 1990). with an average of 24 stems while deep soil moisture pulses phenolics, saponins, terpenoids, Therefore, the management of about 10 mm in diameter. are less frequent. In fact, sur- wax esters, partially o- cattle grazing and fire has been Thus, Larrea at the SRC tower face soil moisture decreases methylated flavones and fla- modified to minimize shrub en- site are larger than many en- rapidly following rainfall events; vonols (Gonzalez-Coloma et al., croachment. Yet, widespread countered in the southwestern the best fit exponential time 1994), which can be extracted Larrea offers a predictable re- United States. Additionally, constant is less than 3 days for medicinal and industrial uses source in an otherwise unpre- insect galls – potentially an (Kurc and Small, 2004). Likely, (Arteaga et al., 2005). Flowers dictable and harsh environment. indication of plants with mini- this surface moisture is only of Larrea are solitary, axillary, For better or for worse, climatic mal water stress (Waring and available to shallow rooted and perfect, about 2 cm wide changes that will temperature Price, 1990) – are common on plants, if they are able use the (Figure 2). More than 120 bee and precipitation patterns are the Larrea at this site. moisture before it is quickly species have been found on the likely affect the distribution of Soil at the SRC tower site is lost to evaporation. flowers of creosotebush, 21 of Larrea in the region. How resil- sandy loam (~ 65% sand, ~ 24% Because evaporation and respi- which are Larrea specialists; ient is Larrea? If the distribution silt, ~ 11% clay, averaged over ration should be more influ- Page 3 Santa Rita Creosotebush tion (E) and soil moisture at press). This digital image- A several depths. ET was best derived greenness showed that correlated with soil moisture at the green-up of creosotebush is 37.5 cm (deep soil moisture). driven by deep soil moisture, At this depth, T and soil mois- just as for transpiration and net ture were also most strongly carbon uptake. We also show correlated. On the other hand, that carbon uptake in Larrea E was best correlated with soil ecosystems is correlated with, moisture at 2.5 cm (surface soil and may be able to be predicted moisture). Given these statis- using, image-derived greenness, tics, undoubtedly large rainfall suggesting that this inexpensive events or closely spaced small tool has the potential to play a rainfall events are critical to the large role in developing a better healthy structure and function spatial understanding of the of these Larrea ecosystems. carbon dynamics of shrub- Finally, we recently processed a dominated drylands. year of images from our time- The dependence of Larrea on B lapse digital cameras to derive deep soil moisture is evident daily greenness at the SRC from our research. Still, more tower site (Kurc and Benton, in work is necessary to under- Figure 3: Side view of the Santa Rita Creosotebush tower site (a) Photo by Shirley Papuga. An overhead view of the Santa Rita Creosotebush tower site (b) Photo by Mark Heitlinger.