Functional evenness of N-to-P ratios of evergreen-deciduous mixtures predicts positive non-additive effect on leaf litter decomposition
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The effects of litter diversity on litter decomposition remain debated. We tested to what extent the community-weighted means (CWM; functional composition) versus Rao’s dissimilarity of litter nitrogen (N)-to-phosphorus (P) ratios explain the non-additive mixture effect on decomposition rate (k) and associated N release.
We carried out a one-year field decomposition experiment with a range of five litter types ranging from three evergreens only (high N/P and low specific leaf area, SLA) to three deciduous species only (low-N/P and high-SLA), with 30:70, 50:50 and 70:30% mixtures of these two extremes in between, in subtropical forest of China.
There were tight hump-backed relationships of absolute k-values and N release, respectively, with the CWMSLA. The mixtures with the highest functional evenness in terms of CWMN/P caused the highest positive non-additivity on decomposition (R2 = 0.72) and N release (R2 = 0.95) rates. In contrast, the mixing effect on k or N release was weakly positively correlated with Rao’s dissimilarity of N/P (R2 = 0.38 and 0.27 respectively).
Our results provide a strong framework for predicting litter decomposition rates and associated N release versus immobilization in mixtures of deciduous versus evergreen species based on their differences in initial stoichiometry.
KeywordsBiogeochemical cycling Evergreen broadleaf forest Functional diversity and composition Leaf traits Species diversity Stoichiometry
We thank Professor Han Y. H. Chen and Dong He for their help with the data analysis. We also thank Mingshan Xu, Liuli Zhou, Yantao Zhao, Yanjun Song, Junyang Chen and Danni Zhu for their help in the field and laboratory. This study was supported by the National Natural Science Foundation of China (Grant Nos. 31770467 and 31670438).
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