Cyperaceae species are mainly found in the regions of south-western Australia where soil phosphorus content is very low. The soils in this region are severely impoverished of nitrogen and phosphorus. It is for this reason that Cyperaceae plants have their roots modified in structure and function. The adaptive response ensures that the external nutrients are acquired maximally while the internal nutrients are maximally allocated. Instead of developing the largely known mycorrhizal and root nodules symbiosis for nutrient-poor soils, the south-western Australia Cyperaceae have a different root adaptation. In specific, these plants produce “cluster and dauciform roots” (Miller, 2005, p. 655) which increase the capability of mobilizing nutrients from the poor nutrient-containing soils. The soils of South Africa also have very low phosphorus levels and hence they are also predominantly inhabited by non-mycorrhizal plants such as Cyperaceae species. The cluster roots that develop on these plants release citrate into the scarcely available particles of phosphorus in the soil, leading to the release of the phosphorus for plant use (White & Hammond, 2008).
Cyperaceae species have their dauciform roots mainly composed of carrot-like structures which attain a lateral swelling. These carrot-like modifications are further characterized by “rather ephemeral, dense clusters of long root hairs” (Miller, 2005, p. 655). Dauciform root modifications are known to thrive in soils that have a low supply of phosphorus. In fact, low phosphorus and nitrogen supply in soils initiates the formation of these structures; with increase in supply of phosphorus and nitrogen leading to suppression in dauciform root formation. The Rhynchosporeae tribe of the Cyperaceae is particularly known to adapt to low phosphorus and nitrogen soils by forming dauciform roots. With the long and dense root hairs (which are also fine in nature), these plants are able to scavenge for the scarce soil phosphorus thus suitably adapting Cyperaceae to phosphorus-poor soils.
It is important to note that in phosphorus impoverished soils, phosphorus is hidden within the soil particles and hence there is need for a mechanism that can “mine” the scarce phosphorous in an effective way. Cluster roots in Cyperaceae are well suited in their structure for this function as the roots exude enough carboxylates for this function. This act is synonymous to the “scavenging” strategy employed by mycorrhizal plants (Lambers et al., 2008). It is notable that growth of root clusters of the Cyperaceae become stimulated once these plants sense low phosphorus supply in the soil. The life of these modified roots is very short; nevertheless, they are able to exude carboxylates at a very fast rate (compared to roots that are not specialized for this function) in the root development process.
Plants that are found in phosphorus-malnourished soils are incapable of having a symbiotic association with the fungi of mycorrhizal type, thus the plants result into having root clusters (Lambers & Shane, 2006). Caustis blakei is one of the Cyperaceae species that has been studied to show dauciform root formation in phosphorus-deficient soils. According to Playsted et al. (2006), growth of C. blakei in phosphorus-starved conditions has been characterized by formation of dauciform roots, and the mass of the roots is inversely proportional to phosphorus availability. In a nutshell, dauciform roots in Cyperaceae are highly prolific and widely distributed in phosphorus deficient soils. This leads to an increase in release of carboxylates as well as increasing chances of acquiring the scarce phosphorus.
References
Lambers, H. & Shane, M. W. (2006). Role of root clusters in phosphorus acquisition and increasing biological diversity in agriculture. Wageningen UR Frontis Series, 21. Scale and Complexity in Plant Systems Research: Gene-Plant-Crop Relations.
Lambers, H., Chapin (III.), F. S., Chapin, F. S. and Pons, T. L. (2008). Plant physiological ecology, second edition. New York, NY: Springer.
Miller, M. R. (2005). The nonmycorrhizal root- a strategy for survival in nutrient-impoverished soils. New Phytologist, 165: 655-658
Playsted, C. W. S., Johnston, M. E., Ramage, C. M., Edwards, D. G., Cawthray, G. R. & Lamber, H. (2006). Functional significance of dauciform roots: exudation of carboxylates and acid phosphatase under phosphorus deficiency in Caustis blakei (Cyperaceae). New Phytologist, 170: 491-500.
White, P. J. & Hammond, J. (2008). The ecophysiology of plant-phosphorus interactions. New York, NY: Springer.