Green leaf litter alters decomposition dynamics by enhancing the quantity and quality of plant biomass in the litter pool

Background/Question/Methods

Many animals create green leaf litter, or greenfall, as a byproduct of herbivory, reproductive strategy or habitat modification and thereby enhance the quality and quantity of plant biomass entering the litter pool. Greenfall makes higher quality litter because green leaves have not yet undergone nutrient resorption that occurs during leaf senescence. In the process of making greenfall, animals often transport green leaves to new microsites. Because litter decomposition can be strongly affected by microheterogeneity in environmental conditions, like solar radiation and soil-litter mixing, litter translocation may alter the quantity of litter reaching the soil and rate of transformation into soil organic matter via decomposition. These changes in litter pool and decomposition may influence carbon (C) and nutrient cycling dynamics. We investigated decomposition differences between greenfall and senesced litter of three common Chihuahuan Desert plants from which animals frequently generate greenfall. In a two-year litterbag study, we quantified differences in mass, C, and nitrogen (N) losses between greenfall and senesced litter by using green and recently senesced leaves to simulate phenological litter differences and placing litterbags in shrub intercanopy and subcanopy microsites to simulate litter translocation that may occur during greenfall generation. 

Results/Conclusions

We found significant differences in the initial quality of green and senesced leaves, with green leaves having roughly twice the N content of senesced leaves of the same species. Both litter quality (green or senesced) and microsite significantly affected decomposition rate (P < 0.001 and P < 0.01, respectively). Exponential decay regressions of litter percent mass remaining indicated that for two of the three species, greenfall decomposition was more rapid than senesced litter (greenfall: k = 0.34, 0.47; senesced: k = 0.19, 0.35); for the third species the opposite pattern was true (greenfall: k = 0.17; senesced: k = 0.25). For all three species, decomposition was more rapid in intercanopy than subcanopy microsites (intercanopy: k = 0.33, 0.64, 0.28; subcanopy: k = 0.20, 0.19, 0.14). These results support that the phenological modification of litter through the generation of greenfall increases litter quality, and that this increased litter quality in combination with microsite modification from greenfall translocation affect, generally positively, the overall rate of decomposition. These findings imply that the addition of greenfall to the litter pool may affect the quantity and rate of litter C and nutrient incorporation into the soil via decomposition.