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ARS Home » Plains Area » Las Cruces, New Mexico » Range Management Research » Research » Publications at this Location » Publication #150427
Title: NUTRIENT RESORPTION IN SHRUBS GROWING BY DESIGN AND BY DEFAULT IN CHIHUAHUAN DESERT ARROYOS

Author
item KILLINGBECK, K - UNIV OF RHODE ISLAND
item WHITFORD, WALTER - NEW MEXICO STATE UNIV

Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2001
Publication Date: 8/1/2001
Citation: KILLINGBECK,K.T., WHITFORD,W.G. NUTRIENT RESORPTION IN SHRUBS GROWING BY DESIGN AND BY DEFAULT IN CHIHUAHUAN DESERT ARROYOS. OECOLOGIA. 2001. V. 128(3). P. 351-359.

Interpretive Summary: Ephemeral water-courses are important features of arid rangeland landscapes. The maintenance of channel integrity and functional relationships of ephemeral water-courses (arroyos) during flooding are dependent upon the vegetation along the channel margins and in the channel itself. Because arroyo sediments are coarse, most of the water entering arroyos percolates through the sediments (a process known as transmission loss). Arroyo sediments have extremely low concentrations of nitrogen and phosphorus. Plants found only in arroyos are obligate arroyo species; and, other species that grow along margins of arroyos and in arroyo sediments are facultative arroyo species. Obligate arroyo species (Brickellia laciniata and Chilopsis linearis) were more efficient and proficient in resorbing nitrogen from the leaves back into storage in the stem and roots than all six species of facultative arroyo margin species. The capacity to conserve nitrogen in the nitrogen poor environment of ephemeral stream channels is an important adaptation of obligate arroyo species.

Technical Abstract: In the northern stretches of the Chihuahuan Desert, the margins of ephemeral stream channels called arroyos support a unique vegetation dominated by a guild of winter-deciduous shrubs. To explore the dynamics of nutrient conservation in this assemblage of arroyo shrubs, we measured nitrogen (N) and phosphorus (P) resorption efficiency and proficiency in six species of shrubs growing in arroyos in southern New Mexico, USA. Collectively, these six species were no more efficient or proficient at resorbing N and P from senescing leaves than shrubs growing in other environments. Resorption efficiency averaged 53% and 50% for N and P, respectively, and resorption proficiency averaged 0.80% and 0.06% for N and P, respectively. However, resorption varied significantly between species specifically restricted in their distribution to riparian habitats (obligate riparian species) and those that were not. The two obligate riparian species combined (Brickellia laciniata, Chilopsis linearis) were significantly more efficient and proficient at resorbing N than the non-obligate riparian species combined (Fallugia paradoxa, Flourensia cernua, Prosopis glandulosa, Rhus microphylla). Additionally, both Brickellia and Chilopsis were individually significantly more proficient at resorbing N than any of the other four species. The dichotomy in resorption between obligate riparian species and those that were not may have been the result of the interplay between hydrology, geomorphology, and biology. Because arroyos move in space as the movement of water erodes banks and changes channel location, some plants are found along arroyos only because the arroyos have moved to them. These plants (plants growing by default) may be less well adapted to arroyo margins than obligate riparian species (plants growing by design). Significant differences in resorption between obligate and nonobligate riparian species suggested that evolutionary history and habitat specificity may be added to the list of factors known to influence resorption. Selected life history traits of the six species did not appear to be related to any measure of resorption, but leaf surface area, specific leaf mass, and nutrient concentrations in green leaves were all correlated with resorption efficiency or proficiency in one or more species. The only species capable of symbiotic N fixation, Prosopis glandulosa, retained at least 2.3 times more N in its senesced leaves than any other species. Patterns of resorption in arroyo shrubs strongly indicated that efficiency and proficiency are fundamentally different, complementary measures of resorption.