Drylands cover well over one third of the Earth’s land and are an important part of the global carbon cycle. Despite this, most models underestimate carbon turnover in arid and semi-arid systems, limiting our ability to predict how they will respond to changing climates. This is partly because many models are driven by rainfall, assuming little to no decay between precipitation events. Unlike in many wetter systems though, plant litter decomposition in drylands is largely controlled by non-rainfall processes including photodegradation and biotic decomposition supported by non-rainfall moisture (fog, dew, and water vapor; “NRM”). Despite their importance however, few studies have examined how these drivers interact with one another and with fungal communities to influence carbon turnover. In this dissertation, I demonstrate how photodegradation, NRM, and fungal decomposers interact to accelerate carbon turnover in drylands. To do this, I leveraged a natural gradient of NRM frequency in the Namib Desert that receives intense solar radiation. In one study, I used a reciprocal transplant design to show that moisture regime exerts a strong influence on litter-associated fungal communities and show that the relationship between NRM and litter decay rates depends on the composition of the decomposer community. In another study, I manipulated solar radiation for three years and found that photodegradation of the plant cuticle allows litter to absorb more water during NRM events, accelerating biotic decomposition. By examining litter-associated fungal communities under these same radiation treatments, I also show that fungi are largely insensitive to radiation stress and that photodegradation mainly affects decomposition rates in this system through photochemical changes in litter that increase subsequent biotic decomposition. Finally, to quantify the relationship between NRM and carbon turnover on multi-year timescales, I measured mass loss for 30 months along a moisture gradient spanning an order of magnitude of NRM frequency. By coupling these data with continuous meteorological measurements over the same period, I show that accounting for NRM and temperature sensitivity substantially improves the performance of a simple exponential litter decay model. These findings build on previous work demonstrating the importance of solar radiation and NRM as crucial drivers of litter decomposition and point a way forward for future studies to examine how these two processes may interact under future climate scenarios. Drylands are undergoing significant changes from anthropogenic climate change and understanding the drivers of litter decomposition allows us to better predict how these ecosystems are responding to global change.
Read
