Changes in rainfall impact the release of metal elements in the litter of a subtropical mixed forest

Abstract

The release of metal elements from litter decomposition in forest ecosystems is crucial for material cycling and ecosystem health, but the impact of future variations in rainfall due to climatic fluctuations on this release is unknown. This study conducted an outdoor rainfall variability simulation and an in situ litter decomposition experiment in a subtropical location, with a focus on pure Pinus massoniana (PM) and 4 p.m. mixed stands (PM+Bretschneidera sinensis, PM+Cercidiphyllum japonicum, PM+Taxus wallichiana, and PM+Nageia nagi). We studied the release of metal elements from litter after one year of decomposition under different rainfall conditions (30% increase, natural, and 30% decrease) and calculated the mixing effect on the litter. The results showed that K, Mg, Mn, Cu and Zn were released and Na, Ca and Fe were enriched after one year of litter decomposition. Increased rainfall promoted K, Na, Mg, Mn, and Zn release, reduced Fe and Cu release, enhanced the synergistic effect of Na and Mn release, and exacerbated the antagonistic effect of Cu. Decreased rainfall reduced the synergistic effect of mixed litter on the release of Na, Ca, Mg, and Fe, while enhancing the synergistic effect of Mn and Zn. The lower degree of metal element release from single PM litter resulted in the enrichment of metal elements in the litter of apoplasts. The effect of rainfall variability on metal element release was more significant compared to tree species characteristics. Overall, decreased rainfall inhibited metal element release and slowed down element cycling; increased rainfall promoted Na and Mn release and accelerated Cu enrichment. It is noteworthy that mixed litter effectively mitigated the effects of rainfall changes on metal element release by regulating elemental cycling. The findings of this study add to a better understanding of nutrient dynamics in forest ecosystems and offer techniques and insights for addressing future climate change.