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Cacti segments were clipped from two different species of cactus: Opuntia chlorotica (pancake prickly pear) and Cylindropuntia acanthocarpa (buckhorn cholla). The 48 clipped segments were taken to the laboratory in plastic clam shell containers, where initial weights of the entire cactus segments were recorded. Three 1.3-cm diameter cores, totaling approx. 2.5-5 g total wet weight, were taken from each segment for measurement of initial water content and chemistry. The core weight was subtracted from the overall segment weight to represent the initial wet weight of each segment for the onset of the experiment. Three days after collection, the cactus segments were then placed in the field on February 20, 2017. Litter cages (23 × 23 cm) were constructed with 10-cm tall sides made out of 2-mm carbon fiber window mesh, zip-tied around four nails in the ground to make a square perimeter, with an extra 2.5 cm flap nailed flush with the ground to avoid the sides lifting. Cages were topped with a nylon 4.5×5 cm mesh lid; the larger mesh was to prevent shading that could decrease natural amounts of photodegradation. Each cage contained one cactus segment from either species, placed directly in the center of the cage, and the area around the cactus weeded to avoid shading. The cages were arranged in four replicate blocks, with each block containing 12 cages: 6 cages with O. chlorotica and 6 with C. acanthocarpa. The cages were placed approximately 30 cm apart from each other on bare soil. Throughout the first month of the experiment, the cages were checked regularly, and any attempts at root generation were removed from the segments to ensure they died and decomposed. Germinating plants were removed from the cages as necessary. Decomposing cactus segments were collected on 5 different dates spanning 1 year: 39 d, 65 d, 119 d, 221 d, and 354 d. At each collection date, one segment of each species was randomly chosen from each replicate block, totaling 8 samples per collection date (four of each species). During the summer drought periods, some of the prickly pear segments were partially consumed by very persistent herbivores (presumably jackrabbits, Lepus californicus) who chewed through the cages, and if the randomly selected cactus had large portions missing with characteristic bite marks, we chose the nearest neighbor that was not. However, at 119-354 d, partially eaten segments were unavoidable for some replicate blocks. These replicates were not used in analyses of mass remaining but were included for plant chemistry. Segments were returned to the lab in their same plastic clam shell from original collection. In the lab, the entire fresh mass of each cactus segment was recorded. Cores of 1.3-cm diameter, totaling approx. 2.5 g, were taken from each segment. The cores and the remainder of the cactus segments were dried at 60 degrees C for 72 h and reweighed (the sum of which was the total dry weight of the entire segment). Cactus water content was calculated as the % of the fresh core mass that was lost during drying. The dried cactus cores were ground to a fine powder using a ball-mill grinder (SPEX Sample Prep Mixer/Mill 8000D). Total P, Na, Mn, Mg, K, and Ca were measured on the cactus samples using the dry ash acid method digestion, by which the cacti samples were ashed in a muffle oven that was gradually brought to 475 degrees C over 1.5 hours, held at 475 degrees C for 4 hours, then dropped to 105 degrees C. Then the cactus ash was weighed for calculation of ash-free dry mass (AFDM), then digested in 5 mL of 35% HNO3. The samples were then centrifuged for 10 minutes, and the supernatant diluted to 5% HNO3 for measurement via inductively coupled plasma optical emissions spectroscopy (ICP-OES; Thermo iCAP6300, Hudson NH). Total C and N were measured using an elemental analyzer (Perkin Elmer PE2400, Wattham MA). Other metabolic and structural compounds were analyzed using pyrolysis-gas chromatography and mass spectrometry (py-GCMS). Samples were first pyrolysed on a CDS Pyroprobe 5150 pyrolyzer at 600 degrees C for 20 s (CDS Analytical, Inc., Oxford, PA, USA). Pyrolysis products were then transferred automatically to a Thermo Trace GC Ultra gas chromatograph (Thermo Fisher Scientific, Austin, TX, USA) and Polaris Q ion trap mass spectrometer (Thermo Fisher Scientific). Mass spectra were analysed using Automated Mass Spectral Deconvolution and Identification System, (AMDIS, V 2.65) and the National Institute of Standards and Technology (NIST) compound library. Compound relative abundances calculated relative to the total ion signal from all detected and identified peaks. Individual compounds were analyzed separately and also arranged into the following functional groups: lignin, aromatic, phenols, polysaccharides, proteins, other nitrogen-bearing compounds, lipids, and compounds of unknown functional origin. Given the time and labor expenses of py-GCMS, samples were only run at specific sampling periods (days 0, 39, and 119) representing 100%, 75%, and 50% mass remaining.