浙江南部亚热带森林土壤植硅体碳的研究

STUDY ON PHYTOLITH-OCCLUDED ORGANIC CARBON IN SOIL OF SUBTROPICAL FOREST OF SOUTHERN ZHEJIANG

植硅体封存有机碳（Phytolith—occluded organic carbon，PhytOC）是一种稳定的有机碳形态。它由植物自身硅化作用产生，在植物死亡或凋落后归还于土壤，从而影响森林生态系统稳定性碳库的储量。本文以浙江庆元县5种不同亚热带典型森林立地土壤为研究对象，利用不同土层深度（0～10cm、10～30cm、30—60cm和60～100cm）土壤样品，分析土壤植硅体含量和植硅体碳含量，并估算土壤中植硅体碳储量。结果表明，毛竹林、杉木林、针阔混交林、阔叶林和马尾松林土壤植硅体含量（土壤剖面平均值）变化范围在8．14～19．74gkg-1，其中毛竹林土壤植硅体含量最高。而植硅体中PhytOC平均含量最高的为马尾松林（24．31gkg-1），最低的为针阔混交林（13．06gkg-1）。土壤PhytOC／TOC比值随土层深度增加而急剧增加。统计分析表明，不同林分下土壤硅含量与土壤植硅体含量呈极显著相关关系（P〈0．01），与土壤PhytOC含量之间呈显著的正相关关系（P〈0．05）。我国亚热带毛竹林、杉木林、马尾松林、阔叶林和针阔混交林1m土体PhytOC总储量分别为1．988×107、4．025×107、2．575×107、2．542×107和0．340×107t。

Phytolith-occluded organic carbon （PhytOC） is a stable form of organic carbon. PhytOC is a product of silicification of a plant per se and goes back into the soil after the plant dies or withers, thus affecting storage of the stable carbon pool in the forest eco-system. Soil samples were collected from four different soil layers （ 0 ~ 10 cm, 10 ~ 30 cm, 30 ~ 60 cm and 60 - 100 cm ） in soil profile under five different stands of typical subtropical forestin Qingyuan County, Zhejiang Province for analysis of effects of the forest stands on content of soil phytolith and PhytOC and distribution of PhytOC, and for estimation of total storage of soil PhytOC in these forest soils, separately. In this study phytolith in soil samples was isolated using the microwave digestion method, and complete removal of peripheral organic carbon from phytolith was validated with the Walkley-Black method. The isolated phytoliths were put into a centrifuge tube with a known mass and dried in a forced air oven at 75℃ for 24 h. After cooling down the sample was weighed to determine mass of the phytoliths. Determination of PhytOC was performed using the Alkali Dissolution-Spectrophotometry. At the same time, a portion of standard soil sample （ GBW07405 ） was added to verify accuracy of the measurement. Results show that the content of phytoliths varied with the type of forest soil and the mean content of PhytOC in phytoliths did, too. The content of Phytoliths in the soil was 19.73 g kg-1 under bamboo groves, 8.14 g kg-1 under Masson pine forest and 12.24 g kg-1 under broad-leaved forest, showing sharp difference between the three. The mean content of PhytOC in soil phytoliths was 24.31 g kg-1 under Masson pine forest and 13.06 g kg-1 under conifer forest, also displaying sharp difference. The content of soil PhytOC under the same forest stand varied with depth in soil profile and the variation trends differed from stand to stand. The content of soil PhytOC decreased with soil depth under Moso bamboo groves and Chinese fir forest and did in a certain degree, too, under the other forest stands. PhytOC/TOC in the soil increased dramatically with soil depth under all the forest stands, except for the stand of Masson pine. The total storage of PhytOC in the soil under Moso bamboo groves, Chinese fir forest, Masson pine forest, broadleaf forest and mixed conifer-broadleaf forest was 1.988 × 107, 4.025 × 107, 2.575 ×107, 2.542 × 107 and 0.340 × 107 t. To sum up, soil phytoliths under the five different stands of forest vary in the range between 8.14 and 19.73 g kg-1, and the content of soil phytoliths is significantly higher under bamboo groves than under the other four stands of forests. The content of PhytOC in phytoliths varies between 13.06 - 24.31 g kg-1, and is the highest under the Masson pine forest..The content of soil silicon is positively related to content of soil PhytOC, suggesting that to raise the content of soil silicon is conducive to the content of soil phytoliths and soil PhytOC.The content decreases with so obvious in the soi of Phytoliths decreases with soil depth and on the whole, the content of soil PhytOC il depth along a soil profile, while PhytOC/TOC rises dramatically with soil depth but not so 1 layers of 10 ~ 30 cm and 30 - 60 cm under Chinese fir forest and broadleaf forest.