Biodiversity is just one factor that contributes to the ability of ecosystems to simultaneously maintain multiple functions. However, the extent to which it affects multifunctionality has seldom been studied in drylands, an important ecosystem with many endemic plant and animal populations. To address this deficiency, Maestre et al. (2012) analyzed how the species richness of perennial vascular plants and key abiotic factors such as annual rainfall contributed to ecosystem functioning. They also analyzed their effects on carbon, nitrogen, and phosphorus cycling and storage. The results suggest that increased species richness has a positive relationship with ecosystem multifunctionality and that it may be particularly important in maintaining carbon and nitrogen cycles and helping resist desertification. With climate change expected to negatively impact species richness, dryland ecosystems may consequently suffer from decreases in functionality.–Katie Huang
Maestre, F.T., Quero, J.L., Gotelli, N.J., Escudero, A., Ochoa, V., Delgado-Baquerizo, M., García-Gómez, M., Bowker, M.A., Soliveres, S., Escolar, C., García-Palacios, P., Berdugo, M., Valencia, E., Gozalo, B., Gallardo, A., Aguilera, L., Arredondo, T., Julio, B., Boeken, B., Bran, D., Conceição, A.A., Cabrera, O., Chaeib, M., Derak, M., Eldridge, D.J., Espinosa, C.I., Florentino, A., Gaitán, J., Gatica, M.G., Ghiloufi, W., Gómez-González, S., Gutiérrez, J.R., Hernández, R.M., Huang, X., Huber-Sannwald, E., Jankju, J., Miriti, M., Monerris, J., Mau, R.L., Morici, E., Naseri, K., Ospina, A., Polo, V., Prina, A., Pucheta, E., Ramírez-Collantes, D.A., Romão, R., Tighe, M., Torrez-Díaz, C., Val, J., Veiga, J.P., Wang, D., Zaady, E., 2012. Plant species richness and ecosystem multifunctionality in drylands. Science 335: 214–218.
Maestre et al. sampled plots in 224 dryland ecosystems in all continents except Antarctica to create a global sample covering a wide range of available resources, abiotic factors, and species richness and composition. To measure multifunctionality, they identified 14 ecosystem functions related to carbon, nitrogen, and phosphorus cycling and storage that are important for ecosystem regulation and desertification identification. They standardized each of the processes and averaged those values to create an index for two different regression models. They also conducted separate analyses of how species richness affected the individual functions in each of the cycles. In addition, 255 other possible models were created to compare the effects of species richness with those of abiotic factors such as climate, slope, elevation, and soil texture. The best of these models were used to find the most important abiotic predictors of multifunctionality, mean rainfall and sand content of soil, and to compare their effects with those of species richness.
In both regression models, the authors found a positive relationship between species richness and multifunctionality. They speculate that this correlation may be due to plant species creating distinct niches in their usage of resources such as water, enabling more processes to function at the same time. Their results are consistent with experimental results on other ecosystems, suggesting a cause-and-effect linkage between species richness and multifunctionality. Of the seven abiotic factors they studied, the authors also found that the two most important predictors of multifunctionality were annual mean temperature and the sand content of the soil. When compared to species richness, all three factors were found to be similarly important to ecosystem processes, though species richness was even more important in the driest quarter of the year. Species richness was also consistently found to contribute to carbon and nitrogen processes, although it seems to have weaker effects on phosphorus-related functions, which depend more on abiotic factors such as elevation and rainfall. The authors suggest that plant species richness may be important for carbon sequestration and soil fertility, helping prevent desertification. With predicted climate change likely to reduce local species richness, it is possible that the loss of biodiversity may contribute negatively to ecosystem functionality in drylands.