Jianping Tao, Juan Zuo, Ze He, Yuping Wang, Jinchun Liu, Wendan Liu, Johannes H.C. Cornelissen
Soil acidity has been considered a major driver of plant community composition and ecosystem function. Soil pH may affect decomposition rates of dead matter (litter) directly by effects on decomposers and indirectly by effects on the plant species and the quality of the dead leaves they shed. Leaf pH may be an important aspect of this quality. Understanding the consequences of differences in soil pH and leaf pH of different species for litter decomposition rates could provide useful information on the mechanism of carbon cycling processes. To unravel these factors, we set up a garden experiment in subtropical China in which we reconstructed soil and litter layer profiles representing acidic sandstone (low pH) and limestone (neutral pH) forest, respectively, and incubated dead leaves of many species from both these forest types in each of these soil types.
We found that leaf (litter) quality of different species and plant functional types was the strongest driver of variation in litter decomposition rates. These effects were determined by the physical structure and pH of the dead leaves of different species. However, while these effects were very strong among species collected from the same soil acidity conditions, there was no overall difference in litter decomposition rate between the species collected from the acidic versus limestone soil conditions. The strong difference in pH of soil substrate plus litter layer from the acidic sandstone forest versus the limestone forest did not directly affect leaf litter decomposition rates.
We conclude that leaf quality (including leaf pH) is a more important determinant of the decomposition rate of dead leaves than soil chemistry. These findings are important for understanding better how the acidity of both soil and plant material can affect the carbon cycle.