Symbiotic Bacteria Enable Cacti to Colonize Bare Rock
New research has elucidated a remarkable symbiotic relationship that allows certain plant species, such as cacti, to thrive on seemingly inhospitable bare rock surfaces. Scientists have discovered that these plants host rock-dissolving bacteria within their roots, facilitating their growth in environments devoid of traditional soil.
A study conducted by Dr. Yoav Bashan and colleagues Dr. Esther Puente and Dr. Ching Li, based at the Northwestern Center for Biological Research in La Paz, Mexico, and in the US, investigated the Cardon cactus in the volcanic Baja California Sur mountain range. Their findings revealed the presence of endophytic bacteria capable of breaking down rock material. Notably, the cacti even transmit these "rock-busting" microorganisms to their offspring by incorporating them into their seeds.
Dr. Bashan noted their initial observation of healthy cacti flourishing on sheer rock formations, a habitat typically unsuitable for plant life due to the lack of essential minerals and accessible nitrogen, both bound within the rock. The researchers hypothesized that microorganisms were aiding the plants by fixing nitrogen and solubilizing minerals. Subsequent investigation confirmed the presence of these beneficial bacteria not only on the root surfaces but also within the root cells themselves.
Further analysis indicated that these endophytic bacteria are also present in the cactus fruit, enabling their transfer to seeds. These bacteria demonstrate the ability to weather rock, effectively reducing particle size. Dr. Bashan proposed that this represents a novel symbiotic interaction where the cactus provides carbon to the bacteria, while the bacteria indirectly supply crucial minerals and nitrogen to the plant.
This cooperative mechanism allows the cactus seed to establish itself on the rock surface as the bacteria initiate the dissolution process. The developing roots then penetrate the weakened rock, further fracturing it. Over time, this process can lead to the formation of small cavities beneath the plant where the dissolved rock has been washed away, leaving the roots partially exposed. Crucially, experiments revealed that cacti cannot survive without this bacterial association. The vertical transmission of the bacteria via seeds ensures that new generations possess the microbial partners necessary for pioneering colonization of barren rock environments, even when seeds are deposited in nutrient-poor substrates like bat and bird droppings.