| Litter decomposition is an important process in energy flow and nutrient cycling. Exploring the effect of species and functional diversity on litter decomposition, not only can link two important level of species and ecosystems together, you can also verify the hypothesis (e.g. mass ratio hypotheses, niche separation hypothesis hypotheses) that the role of the species in the ecosystem function, it is essential to complete understand the relationship between biodiversity and ecosystem function.Leaf litter of 6 common woody species were selected from evergreen broadleaved forests located on Tiantong National Forest Park (29.45°N,121.97°E), Zhejiang Province:Schima superba, Celtis sinensis, Castanopsis fargesii, Aphananthe aspera, Cyclobalanopsis myrsinifolia, Liquidambar formosana. We investigated how species richness, species composition of leaf litter mixture affected leaf litter decomposition, and set 3 levels of species richness (1,2,3),7 species combination treatments (Schima superba, Castanopsis fargesii, Cyclobalanopsis myrsinifolia, Schima superba+Castanopsis fargesii, Castanopsis fargesii+Cyclobalanopsis myrsinifolia, Schima superba+Cyclobalanopsis myrsinifolia, Schima superba+ Castanopsis fargesii+Cyclobalanopsis myrsinifolia, respectively). Meanwhile, in order to explore the relationship between functional diversity and leaf litter decomposition, we set 5 levels of functional diversity. Then we analysed the mass loss rate and nutrient release rate of individual species and mixtures, discussed how species and functional diversity to affect leaf litter decomposition. The main results are as below:(1) Three species decomposed alone after one year, the decomposition rate of Schima superba significantly faster than Castanopsis fargesii and Cyclobalanopsis myrsinifolia(P<0.05), mass loss of Castanopsis fargesii and Cyclobalanopsis myrsinifolia was not significantly different (P> 0.05).Most of the month, TN release rate of Cyclobalanopsis myrsinifolia was significantly greater than Schima superba and Castanopsis fargesii (P<0.05). TP release rate of Schima superba was significantly greater than Castanopsis fargesii in in December, January and June, but only in January was significantly greater than Cyclobalanopsis myrsinifolia (P<0.05).However, phylogenetic signal results of mass loss and nutrient release rate showed that there was no phylogenetic signal of monocultures(P>0.05).(2) The results showed that, in addition to TP release rate (P<0.05), mass loss, TOC and TN release rate had no significantly affected by increasing species richness from one to three species (P>0.05). Moreover, P elements always were enriched in species richness 3, while the other two started enrichment in August. It showed that species richness only had significantly effect on TP release rate.(3) Results about the effect of species composition on leaf litter decomposition showed, when Schima superba decomposition alone, its mass loss ratio was significantly greater than Schima superba+Cyclobalanopsis myrsinifolia and Schima superba+Castanopsis fargesii+Cyclobalanopsis myrsinifolia (P< 0.05), and Schima superba+Cyclobalanopsis myrsinifolia was significantly greater than Castanopsis fargesii+Cyclobalanopsis myrsinifolia (P<0.05). However, TP release rate of Schima superba+Castanopsis fargesii+Cyclobalanopsis myrsinifolia was significantly greater than other species combination in Schima superba and its mixtures, Castanopsis fargesii and its mixtures, Cyclobalanopsis myrsinifolia and its mixtures. But different species combination was not significantly difference in TOC and TNrelease rate (P>0.05). The results showed that changes in species composition can significantly affect the mass loss rate and TP release rate of mixed leaf litter, but has no effect on TOC and TN release rate.(4) Mass loss was best predicted negatively by the CWM of TOC, LDMC, nitrogen:phosphorus ratios, leaf nitrogen content (P<0.001) and positively by the CWM of leaf phosphorus content, MLA, SLA, carbon:nitrogen (P<0.001). In contrast, TN and TP release rate were best predicted positively by the CWM of TOC, leaf nitrogen content, LDMC, nitrogen:phosphorus ratios and negatively by the CWM of leaf phosphorus content, MLA, SLA, carbon:nitrogen. Moreover, TOC release rate was not significantly predicted by the CWM of 8 leaf traits (P>0.05), and no significant relationship between the FDQ of 8 leaf traits and litter decomposition (P> 0.05). It showed that, compared to the " niche separation hypothesis hypotheses", "mass ratio hypotheses" is more suitable to explain mass loss ratio and nutrient release ratio of leaf litter, support for the "mass ratio hypothesis."In conclusion, this study showed that mass loss is positively affected by species composition, but there is no relationship between species richness and mass loss. The CWM of 8 leaf traits had significant relationship with mass loss, TN and TP release rate. So "mass ratio hypotheses" is more suitable to explain mass loss ratio and nutrient release ratio of leaf litter, support for the "mass ratio hypothesis."... |
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