Comparison And Study On Phosphorus Cycle In Different Ages Of Rubber Plantation

The phosphorus element is one of the primary productive forces of the forest growth and net primary productivity of the forest ecosystem. The phosphorus element is one of the main control factors of the forest growth and forest ecosystem due to the low availability of the phosphorus element in the soil of the tropics. For the past two decades, the importance of the phosphorus element circulation in controlling the land ecosystem has gained more and more attention. Therefore, it is important to conduct research on the forest ecosystem phosphorus circulation. The author chooses different age of rubber plantations as its research subject, and conducts both field experiments and laboratory experiments to study the phosphorus of input (precipitation) and output (runoff), the phosphorus element of accumulation and distribution in rubber plantation ecosystem, and the return and decomposition of litter in the open county. The dissertation examines the relationship between the phosphorus element of biological cycle and biogeochemistry circulation in three different ages of rubber plantation ecosystem, which had provided basis theory and data for improving the way of rational fertilization, and increasing the fertilizer using efficiency in rubber plantation. The dissertation also provides theoretical basis for the sustainable development of the rubber plantation. The research indicates that,(1) The tree biomass in different ages of the rubber plantation has a positive correlation with the tree age. The stem is the largest component of the tree biomass, occupying 45.44～47.46% of the total biomass in a the rubber tree, and the distributing sequence of biomass is:stem> branch> bark> root> leaf (16a/22a), But the distributing sequence of biomass in 10 age of rubber plantation is stem> branch> bark>leaf> root.In the different ages of rubber plantation, the phosphorus content in various organs demonstrates similarity in the changes with monthly variation. And due to the physical and biological characteristics of various organs, the content of phosphorus element in different organs shows significant difference, which is ranked in the following order:leaf> root> branch> stem> bark.(2) The annual average litter accumulation in litter layer is 6078.8～6823.4 kg/hm2, and in the different ages of rubber plantation, the litter accumulation has a positive correlation with the tree age:22a>16a>10a. The components of litter are mainly leaf, branch, fruit and flower, and leaf is accounted for 75.6～80.3% in the total amount of litter. The change in the quantity of the phosphorus element contained in the decomposing process of both leaves and branches during wither and fall shows a concentrates-release pattern, and the ratio of phosphorus released in the decomposing process of leaves is lager than branches.(3) In the rubber plantation ecosystem, the content of available phosphorus, organic phosphorus and total phosphorus in soil rank in the following order:0～20cm> 20～40cm> 40～60cm. The phosphorus of enrichment coefficient in leaves, stems and roots of rubber in different ages has a positive correlation with the tree age.(4) The mean total accumulation of phosphorus in rubber plantation ecosystem is 2411.86 kg/hm2, and the accumulation of the soil layer, plant layer and litter layer respectively is 2341.4kg/hm2 (96.86%),67.3kg/hm2 (3.00%), and 3.1 kg/hm2(0.14%). The rank of the phosphorus storage in the theses layers is as follows:soil layer> plant layer>litter layer. The phosphorus storages in the plant layer changed with forest ages shows an increasing trend, but the phosphorus storages changed with forest ages shows a declining trend.The phosphorus element input from the atmospheric precipitation is rare, only 0.0082 kg/(hm2 a), and through the canopy and trunk after the rain leaching of phosphorus, the content is 27 times as much the content in the rainfall. The data shows that forest precipitation and stem flow increase the phosphorus circulation in the rubber plantation ecosystem.(5) In the different ages of the rubber plantation, the order of the phosphorus absorption is 22a> 16a> 10a, the order of the annual phosphorus retention is 22a> 10a> 16a, and the order of the phosphorus return through litter-fall and eluviation is 22a> 10a> 16a. Meanwhile, the average modulus of the total phosphorus of absorption, retention and return in rubber plantation ecosystem are respectively 0.01, 0.59 and 0.28.(6) In the different ages of the rubber plantation ecosystem, the magnitude of the difference in the quantities of the phosphorus element between the annual input and annual output is to a great extent related to the age of rubber plantation. The quantity of the phosphorus element of the annual input is tested to be more than the annual output in the 10 age of rubber plantation ecosystem, which shows that phosphorus element is on the state of accumulation; and the quantity of the phosphorus element of the annual input is tested to be less than the annual output in the 16 and 22 age of rubber plantation ecosystem, which shows that the phosphorus element is on the state of accumulated deficit. The order of the phosphorus deficit within the system is 22a> 16a.