| In this paper, the stand biomass, carbon storage, accumulation and distribution of nutrient, hydrological processes and ecological function were investigated in the forest ecosystem of Alnus cremaslogyne at stand age 5,8 and 14 respectively, to study the structure and functional process of Alnus cremastogyne forest ecosystem. So as to reveal the response and feedback to global climate change of forest ecosystem, and to provide data bases and reference for formulating management mode of regional forest ecosystem in the world. The results showed as followings:The stratum biomass of Alnus cremaslogyne plantation with trees of 5-year-old, 8-year-old and 14-year-old were 51.23 t·hm-2,73.05 t·hm-2, and 95.31 t·hm-2 separately. The above ground biomass accounted for 85.69%,82.36% and 88.18% of the total biomass separately. The proportion of trunk, branches and leaves increased with the tree age increase. The biomass of each component was ranked as:trunk>crown>roots. The spatial distribution of root biomass changes was:big roots>middle root>small roots> fine roots. The net productivity of stand increased with tree age increase, the average annual net productivity were 13.02,13.09 and 15.03 t·hm-2·a-1 respectively。The total length of different specific roots of 5 year-old Alnus cremastogyne plantation planted in Miluo ordered as:fine root>large root>coarse root. The specific root length (SRL) to total root length was ranked as fine root SRL>coarse root SRL> large root SRL. Root length density (RLD) showed decrease trends along the vertical direction of the roots; along the horizontal direction, RLD of big root decreased with the increase of distance away from the trunk. Good distribution range of Alnus cremastogyne root in three-phase were solid fraction38.5-54.5%, liquid fraction21～36.5%, gas 12.5～35.5%, and roots would not grow well enough outside those ranges.The biomass of a whole plantation ecosystem of Alnus cremastogyne increased with the stand age, biomass of 5,8,14-year-old alder ecosystems were 54.65,76.50,103.23 t·hm-2 respectively, the living ground cover in the ecosystem accounted for 3.18%,1.71% and 3.75% respectively, dead ground cover accounted for 3.07%,2.91% and 3.91% of the entire ecosystem biomass respectively.The arithmetic average carbon density of different organs of alder was 0.4788 gC·g-1 for the 5-year-old plantation,0.4857 gC·g-1 for the 8-year-old stand and 0.4958 gC·g-1 for the 14 year-old plantation, which increased with the stand age, and the variation coefficient ranged form 0.25% to 9.58%. The carbon densities of different organs varied in the following order:stems> branches> leaves> roots> bark. The change of carbon densities in different groups of under-storey of plants or the duff layer was not evident as the forest age increased. The carbon density of soil layer between 0 and 60cm increased along with the stands age of Alnus cremastogyne and declined with the soil depth. The carbon storage in different oranges was positively related to the biomass of corresponding organs. Superiority of carbon storage in the trees gradually increased as the forest stands aged, carbon storage of the trees had grown up from 25.88 t-hm 2 for the 5-year-old to 49.63 t·hm-2 for the 14-year-old plantation. The carbon stock of Alnus cremastogyne plantation ecosystem was mainly consisted of three sections, that was the trees, the litter and the soil, and the order of whose carbon stock could be ranked as follow:the soil>the trees>the litter. Carbon stock of Alnus cremastogyne plantation was 95.89 t·hm-2 at 5-year-old,122.12 t·hm-2 at 8-year-old and 130.75 t·hm-2 at 14-year-old. Carbon storage in forestlands soil layer (0～60 cm) accounted for more than 59.42% of that in the whole ecosystem, the ratio of carbon storage of aboveground to that of underground deceased along with growing age of the Alnus cremastogyne forest. The annual carbon fixation of the 5-year-old, the 8-year-old and the 14-year-old Alnus cremastogyne plantation was respectively 6.51,6.26 and 7.82 t·hm 2·a 1. Extant carbon storage of Alnus cremastogyne plantation in Hunan province was up to 2.8034×106t, accounting for 47.51% of its potential carbon storage.Nutrient content of Alnus cremastogyne leaves was relatively high, same change of nutrient content was found in branch as that in leaf of Alnus cremastogyne. N, P, K, Ca element in the dry wood reached their lowest concentration in spring. Seasonal variation of nutrient in bark was not evident. The highest nutrient content in leaves was N, while that of Ca in the bark, which should be the consequence of different physiological functions of various organs.Floor vegetation had relatively higher nutrient content comparied with that in ground litter and tree layer. N, P, K concentration in Alnus cremastogyne leaves were significantly higher than that in the ground litter while Ca was contrary.The order of macro element concentration of the 5 years,8 years and 14 years old Alnus cremastogyne forest tree layer and living ground cover were:N>Ca>K>Mg>P. By the tree age increasing, concentration of N also increased; but concentration of K was decreased with age increase. The order of macro element concentration of living ground cover was 8-year-old>14-year-old>5-year-old. Order of macro element concentration of dead litter was:N>Ca>Mg>K>P.Nutrient concentration in soil layer of Alnus cremastogyne forest ecosystem ordered as:K>Mg>N>P>Ca, nutrient accumulation was166046.23 kg·hm-2; total elements accumulated were 754.77 kg·hm-2, the amount of nutrient accumulation of each component arranged in the following order:leaves> branch> trunk> root> bark. Nutrient accumulation of ground cover was 154.83 kg·hm-2, litter layer nutrient accumulated for 99.21 kg·hm-2, total amount was 254.04 kg·hm-2, accounted for the entire ecosystem of 0.15%. Alnus cremastogyne plantation accumulated an annual amounts of 167809.80 kg·hm-2 nutrient, most of it contributed by the soil layers.12.516 kg nutrient was needed to produce It dry matter for Alnus cremastogyne.Throughfall, canopy interception and trunk runoff of Sichuan alder and Taiwan alder had significant relationship with atmospheric rainfall; they were linear relationship, exponential relationship and quadratic relationship respectively. The redistribution of atmospheric precipitation input by throughfall, canopy interception and trunk runoff of Sichuan alder plantation accounting for 78.21%,16.51%,5.28% of atmospheric rainfall respectively; for Taiwan alder plantations the values were 80.77%,15.03%,4.20% respectively.Nutrient element concentrations of throughfall of Sichuan and Taiwan alder plantation ranked as:Ca>K>Mg>NH4+-N>NO3-N>Mn>Fe>Cu; Ca>K>NH4+-N>Mg >NO3-N>Fe>Mn>Cu, where NH4+-N concentration was reduced more than 60% in throughfall compared with that in the rainfall outside the forest, NH4+-N concentration in the throughfall and trunk runoff first decreased then increased. K, Fe, Cu of throughfall and trunk runoff increased in Sichuan and Taiwan alder forest. Elements K in Sichuan alder plantation has a maximal increase from 2.010mg·L-1 to 10.461 mg·L-1 during precipitation.Sichuan, and Taiwan alder's canopy interception rates were 16.51% and 15.03% respectively, stem flow rate was 5.28% and 4.20% respectively. Alder plantation of Sichuan had higher effective water-holding capacity of 17.0 t·hm-2, while that of Taiwan alder plantation was smaller, which was 16.2 t·hm-2.Soak time and water retention time of shrub and herb layer had exponential relationship, the longer time the water soak, the smaller holding rate, saturation after 3h soak. Effective water-holding capacity of ground litter ordered as Sichuan alder plantation (1.70mm)>Taiwan alder plantation (1.62mm)> suitable afforestation land(0.13mm).Reservation of ground litter layer and non-decomposed layer of Alder forest increased with seasonal change, a gradual increase was found in semi-decomposed litter layer with seasonal change. Reservation amount of ground litter and non-decomposed layer were Sichuan alder plantation> Taiwan alder plantation, while moisture of semi-decomposed and ground litter layer was Taiwan alder>Sichuan alder, highest moisture content was found in non-decomposed litter layer of Sichuan alder. Ground litter biomass had a negative correlation with soil moisture; moisture content in all layers of ground litter and soil moisture were positively correlated.Moisture in 0-75cm soil layer increased with the increasing depth, the average water content were Sichuan alder (19.86%)>Taiwan alder (17.59%)>suitable afforestation land (17.18%). Within 30-75cm soil layer, regardless sub-levels, the water content of soil was always the Sichuan alder>Alnus alder>suitable afforestation land. Coefficient of variation of soil moisture gradually decreased with the soil depth.No significant correlation was found between rainfall and water content in the soil that deeper than 30cm below the ground; daily average temperature had no significant effect on soil moisture (p>0.05) in both Sichuan alder and Taiwan alder plantation; daily average relative humidity in Sichuan alder plantation has no significant effect on moisture content at all soil layers, however that had significant positive relationship with 0-75cm soil layer of Taiwan alder plantation. |
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