An isopod, well-adapted to the harsh conditions of arid-lands, crawls on the desert floor in search of leaf litter. Image credit: Viraj R. Torsekar (CC BY 4.0).
In most ecosystems on land, it is largely small organisms such as microbes that break down dead plant material (known as plant litter) into nutrients that are recycled into the soil. Given that microbes need moisture to survive, scientists have long questioned how plant litter undergoes this decomposition in dry ecosystems.
Previous research focused primarily on how solar radiation and other environmental factors affect how quickly plant litter decomposes in these harsh conditions. However, another possibility is that larger decomposers, such as animals like beetles and termites that feed on dead plant material, are better adapted to arid conditions and may be more abundant in areas with low rainfall. As a result, plant litter in dry environments may decompose at similar rates to areas with higher rainfall.
Torsekar, Sagi et al. tested this idea by monitoring how quickly plant litter decomposed at seven sites with similar average temperatures but different rainfall levels. Dozens of baskets with different sized mesh – which excluded some or all animal decomposers based on size – were placed at each site and a technique called pitfall trapping was used to identify the decomposers at each site.
The experiments showed that plant litter broke down at similar rates across five of the seven sites, but decomposition was slower at extremely dry sites. In the winter, when rainfall is typically higher than at other times in the year, microbe decomposers played a bigger role in breaking down the leaf litter than in the (drier) summer months. On the other hand, animal decomposers were more abundant at sites with low rainfall than sites with higher rainfall. Furthermore, decomposition by animals at these arid sites during summer was just as fast as microbial decomposition at the wetter sites in winter.
The findings of Torsekar, Sagi et al. suggest that larger, animal decomposers compensate for the lower microbial decomposition of plant matter in ecosystems with little rainfall. In the future, a better understanding of how nutrients are recycled in dry areas will help predict how different ecosystems will respond to climate change.
