水田改果园后土壤性质的变化及其特征

近年来,水田改作经济林地,在我国南方地区非常普遍。为深入了解这一转变对土壤质量的影响,以浙江省典型水稻土(青粉泥田)及其改果园不同年限的系列表层土壤(0—15 cm)为研究对象,应用磷脂脂肪酸生物标记等方法,研究了水田改果园后土壤理化性质和微生物群落结构等性质的变化以及它们之间的关系。结果表明,水田改果园后,土壤中大于0.25 mm水稳定性团聚体、盐基饱和度、p H值、有机质、全氮和碱解氮等随着改果园年限的延长而显著降低(P0.05)。土壤微生物生物量碳氮、微生物商和土壤呼吸强度随改果园年限增加而显著下降(P0.01)。土壤微生物群落结构也发生明显变化:磷脂脂肪酸总量显著降低(P0.01),微生物种类减少,原生动物在土壤微生物中所占比例增加,革兰氏阴性细菌与革兰氏阳性细菌比值降低(P0.01),好氧细菌/厌氧细菌和甲烷氧化菌/细菌增加(P0.01),表征养分胁迫的环丙基脂肪酸/前体物和异式脂肪酸/反异支链脂肪酸显著增加(P0.01)。冗余分析表明,土壤含水率、有机质和碱解氮是决定水田和果园土壤微生物群落结构差异的最重要因子(P0.01);改果园后,土壤微生物群落结构发生了阶段性变化,不同利用方式对微生物群落结构的影响程度要大于同一利用方式耕作不同年限对微生物群落结构的影响。研究表明,水田改果园后土壤理化性质以及生物学性质发生退化,土壤质量下降;而水田中微生物数量和种类都比较丰富,因而认为水田是土壤(地)可持续利用的一种有效方式。

Effects of land-use change from paddy field to orchard farm on soil property shift processes and their characteristics

Studies of the effects of land-use change on soil physicochemical properties, microbial community structure and other biological properties are important for understanding changes in soil quality in agricultural soils. A diverse soil microbial community is an important measure of sustainable land use, and soil microbial community structure and diversity are sensitive indicators of soil quality. In recent years, land-use change from paddy field to economic forest land has been very common in the south of China. In order to recognize the effects of this land-use change on soil quality, a study was conducted, in Zhejiang province, on paddy and orchard surface soil (0-15 cm). Multivariate analyses including phospholipid Fatty Acids (PLFAs) were employed to determine the changes in soil environmental factors, microbial community structure and their relationships after land-use change from paddy fields to orchard farms. Water-stable aggregates (>0.25 mm), pH, organic matter (OM), base saturation (BS), total nitrogen (TN), Alkali-hydrolysable nitrogen (AHN) decreased after land-use change from paddy to orchard soils, and they had significant negative correlations with orchard age (P < 0.05). Enhancement of organic carbon mineralization and reductions in plant residues in the soil caused the decline in soil organic matter content which resulted in a reduction in water-stable aggregates (>0.25 mm) and total nitrogen. The increase in nitrification also led to a reduction in alkali hydrolyisable nitrogen. The extensive application of acidic fertilizer and enhancement of nitrification increased soil acidification (caused by H⁺). Microbial biomass carbon (MBC), microbial quotient (qMB) and soil respiration (Resp) decreased, and had significant negative correlations with orchard ages (P < 0.01). The changes in biological properties could be due to decreased soil moisture, OM and other soil characteristics. During the change from paddy field to orchard farm, soil microbial community structure changed: total phospholipid fatty acids (TPLFAs), PLFAs of bacteria, fungi, actinomycetes, protozoa, and specific microbial lipids decreased. Possibly because of enhancement of soil aeration, the ratio of protozoa to bacteria slightly increased. The ratios of Gram positive bacteria to Gram negative bacteria decreased significantly (P < 0.01). In contrast, aerobic bacteria to anaerobic bacteria and methanotrophic bacteria to total bacterial ratios increased significantly (P < 0.01). The ratios of fatty acids Iso to Anteiso and fatty acids cyclo to precurso increased significantly (P < 0.01), which implied that nutrient stress on soil microorganisms enhanced. Redundancy analysis (RDA) showed that the first 4 axes explained 95.6% of the cumulative variation of soil microbial community structure, which indicated that the 11 kinds of soil environmental factors were the main factors affecting the structure of the soil microbial community. Soil moisture, OM and AHN were the most important environmental factors to determine the differences in soil microbial community structure between paddy and orchard soils (P < 0.01). The analysis also indicated that land-use change had a greater effect on soil microbial community structure than orchard age. Our study concludes that after land-use change from paddy fields to orchard farms, soil physicochemical and biological properties degraded, and thus soil quality decreased. In contrast, a diverse soil microbial community was achieved and maintained in paddy soil systems, hence we predict that paddy fields are an effective way to maintain soil sustainability.