缙云山土地利用方式对土壤轻组及颗粒态有机碳氮的影响

选取缙云山阳坡同一海拔处亚热带常绿阔叶林(以下简称林地)、果园、坡耕地和撂荒地这4种不同土地利用类型,在0~60 cm深度内每隔10 cm采集一个土样,测定土壤轻组有机碳氮(LFOC、LFON)和颗粒态有机碳氮(POC、PON)含量,并计算其分配比例和碳氮比.结果表明,在0~60 cm土壤深度范围内,林地转变为坡耕地后,LFOC及LFON含量分别降低了71.42%和38.46%(P0.05),转变为果园后变化不明显,坡耕地撂荒后其含量分别升高了3.77倍和1.38倍(P0.05);林地转变为坡耕地或果园后,POC及PON含量均无明显变化,而坡耕地撂荒后其含量分别增加了4.12和1.25倍(P0.05).林地转变为坡耕地后土壤LFOC及LFON分配比例显著降低,转变为果园后则明显升高,而POC及PON分配比例变化均不明显;坡耕地撂荒后,LFOC、LFON、POC、PON分配比例均显著增加.土壤SOC/TN为撂荒地(12.93)林地(8.53)果园(7.52)坡耕地(4.40),LFOC/LFON为撂荒地(16.32)林地(14.29)果园(11.32)坡耕地(7.60),POC/PON为撂荒地(23.41)坡耕地(13.85)林地(10.30)果园(9.64).以上研究结果表明林地开垦为果园或坡耕地后容易导致土壤轻组有机碳氮的损失,而坡耕地撂荒则有利于土壤活性有机碳氮的积累;林地转变为坡耕地减弱了土壤有机碳氮的活性,而林地转变为果园以及坡耕地撂荒均使土壤有机碳氮活性增强;林地转变为坡耕地和果园加剧了土壤有机质的矿化,相对而言,坡耕地撂荒后有利于土壤有机质的固定.

Impacts of Land Use Changes on Soil Light Fraction and Particulate Organic Carbon and Nitrogen in Jinyun Mountain

Four land types including the subtropical evergreen broad-leaved forest, sloping farmland,orchard and abandoned land were selected to collect soil samples from 0 to 60 cm depth at the same altitude of sunny slope in the Jinyun Mountain in this study. Soil light fraction organic carbon and nitrogen (LFOC and LFON), and particulate organic carbon and nitrogen (POC and PON) were determined,and the distribution ratios and C/N ratios were calculated. The results showed that the contents of LFOC and LFON decreased significantly by 71.42% and 38.46% after the forest was changed into sloping farmland (P<0.05) but the change was not significant when it was changed into orchard (P >0.05), while the contents of LFOC and LFON increased significantly by 3.77 and 1.38 times after the sloping farmland was changed into abandoned land (P<0.05). The contents of POC and PON did not vary markedly after the forest was converted into orchard or sloping farmland, while the POC and PON contents increased markedly by 4.12 and 1.25 times after the sloping farmland was abandoned. Those above results indicated that abandoned land was easy for active organic carbon and nitrogen accumulation; on the contrary, sloping farmland was easy to lose soil labile carbon and nitrogen. The LFOC and LFON distribution ratios were significantly reduced by 31.20% and 30.08%, respectively after the forest was changed into the sloping farmland, and increased by 18.74% and 20.33% respectively after the forest was changed into the orchard. Nevertheless, the distribution ratios of LFOC and LFON were changed little by converting the forest into the sloping farmland and orchard. The distribution ratios of LFOC, LFON, POC and PON all increased significantly after the farmland was abandoned (P<0.05). Those results showed that the activity of soil organic carbon and nitrogen was enhanced after forest reclamation, while reduced after the sloping farmland was abandoned. The ratios of carbon to nitrogen in soil organic matter, light fraction organic matter and particulate organic matter were in the order of abandoned land (12.93)> forest (8.53)> orchard (7.52)> sloping farmland (4.40), abandoned land(16.32)> forest (14.29)> orchard (11.32)> sloping farmland (7.60), abandoned land (23.41)> sloping farmland (13.85)> forest (10.30)> orchard (9.64), which indicated that the degree of organic nitrogen mineralization was higher after forest cultivation and lower after the sloping farmland was abandoned.