| Forest litters were the products of metabolism in the growth and developmental stages of forest plants, and they played an important part in maintaining the cycle of nutrient and energy in forest ecological system. Based on the litter of natural evergreen broadleaved forest(natural forest), Metasequoia glyptostroboides plantation, and Cryptomeria fortunei plantations in southern Sichuan province, using filed tests and indoor simulation experiment, we studied that litter production, nutrient content, microbial biomass, microbe quantity, enzyme activity, mineralization characterstics and the responses of the simulated N deposition in the decomposition course of the different litter layers were investigated. The results were as follows:(1) The natural water content of litter was natural forest> Metasequoia glyptostroboides plantation> Cryptomeria fortunei plantations. In all three forests water content in layer Y (decomposed layer) was the highest, and the layer Y played an important role in water and soil conservation. After artificial regeneration, the stock of litter in natural evergreen broadleaved forest was significantly decreased, which was1.53times of Metasequoia glyptostroboides plantation, and was10.32times of Cryptomeria fortunei plantations.The stock of litter in different litter layers was L (un-decomposed layer)<F (semi-decompose layer)<H (decomposed layer).(2) The content of nutrient elements in litter was natural forest> Metasequoia glyptostroboides plantation> Cryptomeria fortunei plantations. The content of N was highest in all nuteient, the order was N>K>P. With the deepening of decomposition, the content of N increased at first, and then which reduced, the order was F>L>H. The variation of the conten of K was the same as P, which was L<F<H. The content of C was Cryptomeria fortunei plantations> Metasequoia glyptostroboides plantation> natural forest. The litter nutrient content was natural evergreen broadleaved forest>Metasequoia glyptostroboides plantation> Cryptomeria fortunei plantations, and L<F<H in litter layers.(3) During the immersion test, the content of water soluble nutrient was natural forest> Metasequoia glyptostroboides plantation> Cryptomeria fortunei plantations, which was increased with the increasing time of immersed in water. The content of dissolved ammonium nitrogen and dissolved nitrate nitrogen was F>L>H, while the content of dissolved total phosphorus, available phosphorus, organic phosphorus, organic nitrogen, organic carbon, total potassium all were L>F>H.(4) Microbial biomass, microbe quantity and enzyme activity of litters were reduced after natural evergreen broadleaved forest artificially regenerationed, and showed a tendency of natural forest> Metasequoia glyptostroboides plantation> Cryptomeria fortunei plantations. Microbial biomass, microbe quantity and enzyme activity in different litter were F>L>H. Microbial biomass, microbe quantity and enzyme activity of litter were significantly correlated with each other, which means the biochemical characteristics and nutrient had a closed relationship.(5) Under different temperature tests, the mineralization rate of C, N, P, K were increased with the rise of temperature. The amount of CO2and NH3released decreased after natural evergreen broadleaved forest artificially regenerationded, which was natural forest> Metasequoia glyptostroboides plantation> Cryptomeria fortunei plantations, and L>F>H in litter layers.(6)In the research of responses of litter decomposition course to simulated N deposition,(NO:0kg N/(hm2·a), N1:60kg N/(hm2·a), N2:120kg N/(hm2·a), N3:240kg N/(hm2·a), the decomposition rate was natural forest> Metasequoia glyptostroboides plantation>Cryptomeria fortunei plantations, and N1>N0>N2>N3in natural forest; N2>N1>N0>N3in Metasequoia glyptostroboides plantation; N2>N1>NO>N3in Cryptomeria fortunei plantations. Different concentration level had different effects on the decomposition rate, which was both active and inhibitive on the decomposition rate of forest litter.The results of the study showed that microbial biomass, microbe quantity, enzyme activity and decomposition rate of litter were reduced after natural forest artificial regeneration, which was bad for the nutrient and energy cycle in forest ecological system. Protecting natural forest is very importantl to maintain the amount of litter, nutrient and the biochemical characteristic. The results could supply some references in the vegetation restoration and tree slection when converting farmland to forestland. |
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