农田改为农林(草)复合系统对红壤CO2和N2O排放的影响

以鄂南玉米地、紫穗槐/玉米地、香根草/玉米地、紫穗槐林地、香根草草地与撂荒地6种土地利用类型为研究对象,利用静态箱法,对夏玉米生长期间土壤CO2和N2O通量及影响因子进行了测定,研究我国北亚热带丘陵红壤区农田改变为林(草)地和农林(草)复合系统后土壤CO2和N2O排放特征。研究结果表明:(1)土地利用方式改变后,撂荒地土壤CO2排放量明显低于其他5种土地利用类型,但紫穗槐/玉米地、单作玉米地、香根草/玉米地、紫穗槐林地、香根草草地5种土地利用类型之间土壤CO2排放量差异不显著。(2)玉米生长期间,6种不同土地利用方式下,土壤N2O排放总量从高到低依次为紫穗槐/玉米地(508 g·hm-2·a-1)、紫穗槐林地(470 g·hm-2·a-1)、撂荒地(390 g·hm-2·a-1)、香根草/玉米地(373 g·hm-2·a-1)、香根草草地(372 g·hm-2·a-1)、单作玉米地(285 g·hm-2·a-1)。(3)土壤CO2通量与土壤有机碳、土壤微生物生物量碳和土壤含水量无显著相关关系;土壤N2O通量与土壤氮素净矿化率呈显著线性相关,但与土壤无机氮和土壤含水量无显著相关关系。农田改变为农林(草)复合系统可能潜在地增加土壤CO2和N2O排放;农田改变为林(草)地可能潜在地减少土壤CO2排放,增加土壤N2O排放。

CO2 and N2O emissions in the red soils of agro-forestry (grass) systems conversed from cropland in subtropical hilly region of China

Not much information exists on soil respiration and nitrous oxide emissions in soils under different terrestrial ecosystems in subtropical China. Field experiments were conducted in static chambers to investigate the effects of soil environmental conditions on CO₂ and N₂O fluxes from red soils under six different land use types. The investigated land use types included maize land, Amorpha fruticosa plantation, Vetiveria zizanioides plantation, A. fruticosa + maize and V. zizanioides + maize agro-forestry (grass) systems, and wasteland. Also variations in soil greenhouse gases, water, nitrogen, organic carbon, microbial biomass carbon and net nitrogen mineralization were determined. The results were as follows: 1) during maize growth season, CO₂ flux in wasteland was lower than that in A. fruticosa + maize agro-forestry system, sole maize, V. zizanioides + maize agro-grass system, A. fruticosa plantation and V. zizanioides plantation, in that order. However, no significant differences in CO₂ flux were noted among five land use types. 2) N₂O fluxes were 508 g·hm^-2·a^-1, 470 g·hm^-2·a^-1, 390 g·hm^-2·a^-1, 373 g·hm^-2·a^-1, 372 g·hm^-2·a^-1 and 285 g·hm^-2·a^-1 for A. fruticosa + maize agro-forestry system, A. fruticosa plantation, wasteland, V. zizanioides + maize agro-grass system, V. zizanioides plantation and sole maize, respectively. 3) No significant relationships existed between CO₂ fluxes and soil organic carbon, microbial biomass carbon or water content. Significant positive linear relationship was, however, observed between N₂O flux and soil mineralization. The study suggested that land conversion from cropland to agro-forestry potentially increased soil CO₂ and N₂O release. While land conversion from cropland to forestland and/or grassland potentially decreased soil CO₂ emission, it increased N₂O emission.