| Forest litterfall is a vital part of forest ecosystems, which plays a very important role in maintaining ecosystem productivity, the net carbon storage, soil organic matter and community succession, etc. Karst region is one of the most fragile ecosystems in the world, and its ecological functions of litter layers is critical. Through the Nonggang 15ha PLOT litter monitoring, in order to study the composition and quantity of litter, the dynamics of each component of litter, the seasonal variation of six dominant species’nutrient concentration, and nutrient return and utilization efficiency, master the dynamic changes in Nonggang karst seasonal rainforest litter, deeply understand the structure and function of Nonggang karst seasonal rainforest ecosystems, biogeochemical processes in karst areas, explore the material cycle for elucidating the mechanism of karst forests maintain biodiversity and ecosystem reconstruction to provide a scientific basis. The results are as follows:1) The amount leaf litter range from 340.24 g·m-2 to 495.56 g·m-2 in 2012-2014. The total amount of litter collected in 2014 was 465.08 g·m-2, which account for the annual amount of 92.41%. However, the falling branches, flowers, fruits and debris are extremely low.17 leaves litter of the dominant species account for 69.75% in total falling leaves. And 11 kinds evergreen species accounted the amount leaf litter for 43.75%, another 5 kinds deciduous trees accounted for 26.00%. These dominant species greatly affects the dynamics of the pattern of the total amount of litter. According to their characteristics, they can be divided into four categories litter: Litter peak occurs in the spring and autumn of evergreen trees, litter peak occurs in autumn or winter of deciduous trees, evergreen trees litter the dynamic emerges multiple peaks, litter peak occurs in the spring and fall of deciduous trees.2) Using PCA analysis found that the amount of leaf litter by slope, abundance, bumpiness and aspect cosine (South and North Slope) is a positive correlation, and by aspect sine value (East and West Slope) is a negative correlation; the number of species is positive correlation by the number tree species and unevenness, and negative correlation by the aspect cosine (South and North Slope) and elevation. Reflecting the amount of litter and species composition variation have a significant correlation with topographical factors and biological factors.3) The leaf litter nutrient concentrations of a few dominant species Cleistanthus sumatranus, Hainania trichosperma, Vitex kwangsiensia, Sterculia monosperma and Saraca dives, Archidendron guangxiensis, are various in different seasons and species. N and Ca annual average concentration of each species is highest, K and Mg is middle, and P is lowest, except for C. These results indicate that the nutrient concentration of the litter are affected by seasonal variation.Nutrient return of each element in different species have differences and the dynamics of the litter nutrient return is broadly consistent with litter seasonal dynamics in different seasons. The return of the amount of each nutrient species in 2014 are as follows:Cleistanthus sumatranus is 335.148 kg·ha-1, Hainania trichosperma is 243.549 kg·ha-1, Vitex kwangsiensia is 270.737 kg·ha-1, Sterculia monosperma is 261.513 kg·ha-1, Saraca dives is 74.279 kg·ha-1 and Archidendron guangxiensis is 58.320 kg·ha-1, repectively, reflecting the different nutrient return among different species.Each species of annual nutrient return order as follows:Cleistanthus sumatranus, Sterculia monosperma and Saraca dives are both C>Ca> N> K> Mg> P; Hainania trichosperma is C> Ca> N> Mg> K> P; Vitex kwangsiensia and Archidendron guangxiensis are C>N> Ca> K> Mg> P. Obviously, each species’return of P is lowest, it is likely to be constrained Nonggang karst seasonal rainforest vegetation growth factor.A few dominant species nutrient utilization efficiency of each element in different seasons show some differences. The same annual species nutrient utilization efficiency(NUE) of each element order as follows:Cleistanthus sumatranus, Sterculia monosperma and Saraca dives are P> Mg> K> N> Ca> C; Hainania trichosperma is P> K> Mg> N> Ca> C; Vitex kwangsiensia and Archidendron guangxiensis are P> Mg> K> Ca> N> C. Each species P utilization efficiency (NUEp), followed by the Mg utilization efficiency (NUEMg), and the utilization efficiency of C (NUEc) is minimum. Once again it shows the P is likely to restrict Nonggang karst seasonal rainforest vegetation growth factor. Another, C utilization efficiency and P, Ca, Mg utilization efficiency among different species exist a significant positive correlation. Besides, efficiency and utilization efficiency of P and K are also significant positive correlation. Nutrient utilization efficiency of various elements reflects that the nutrients in plants have the interaction. |
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