Agricultural land-use change in a Mexican oligotrophic desert depletes ecosystem stability.
BACKGROUND
Global demand for food has led to increased land-use change, particularly in dry land ecosystems, which has caused several environmental problems due to the soil degradation. In the Cuatro Cienegas Basin (CCB), alfalfa production irrigated by flooding impacts strongly on the soil.


METHODS
In order to analyze the effect of such agricultural land-use change on soil nutrient dynamics and soil bacterial community composition, this work examined an agricultural gradient within the CCB which was comprised of a native desert grassland, a plot currently cultivated with alfalfa and a former agricultural field that had been abandoned for over 30 years. For each site, we analyzed C, N and P dynamic fractions, the activity of the enzyme phosphatase and the bacterial composition obtained using 16S rRNA clone libraries.


RESULTS
The results showed that the cultivated site presented a greater availability of water and dissolved organic carbon, these conditions promoted mineralization processes mediated by heterotrophic microorganisms, while the abandoned land was limited by water and dissolved organic nitrogen. The low amount of dissolved organic matter promoted nitrification, which is mediated by autotrophic microorganisms. The microbial N immobilization process and specific phosphatase activity were both favored in the native grassland. As expected, differences in bacterial taxonomical composition were observed among sites. The abandoned site exhibited similar compositions than native grassland, while the cultivated site differed.


CONCLUSIONS
The results suggest that the transformation of native grassland into agricultural land induces drastic changes in soil nutrient dynamics as well as in the bacterial community. However, with the absence of agricultural practices, some of the soil characteristics analyzed slowly recovers their natural state.
Laboratorio de biogeoquímica de suelos, Instituto de Investigaciones en Ecosistemas y Sustentabilidad, UNAM , Morelia , Michoacán , Mexico.
Natali
N
Hernández-Becerra
ENES Unidad Morelia, Universidad Nacional Autónoma de México , Morelia , Michoacán , Mexico.
Yunuen
Y
Tapia-Torres
Laboratorio de biogeoquímica de suelos, Instituto de Investigaciones en Ecosistemas y Sustentabilidad, UNAM , Morelia , Michoacán , Mexico.
Ofelia
O
Beltrán-Paz
Instituto de Ecología, Universidad Nacional Autónoma de México , Mexico.
Jazmín
J
Blaz
Instituto de Ecología, Universidad Nacional Autónoma de México , Mexico.
Valeria
V
Souza
Laboratorio de biogeoquímica de suelos, Instituto de Investigaciones en Ecosistemas y Sustentabilidad, UNAM , Morelia , Michoacán , Mexico.
Felipe
F
García-Oliva
Alfalfa; Bacteria community; Medicago sativa L.; Microbial activity; Resilience; Soil nutrients