黄土丘陵区植被类型与土壤微生物区系及生物量的关系

以陕西延安黄土丘陵区5种不同植被类型(人工刺槐林、天然侧柏林、天然辽东栎林、灌丛和裸地)为研究对象,分析了土壤微生物生物量碳、氮含量、细菌和真菌的丰度变化规律及其与土壤基本化学性质的关系。结果表明:(1)4种植被类型的土壤质量较之裸地都有不同程度的改善,总体趋势:天然林地人工林地裸地;(2)土壤微生物生物量碳、氮的总体趋势:天然林地最高,人工林次之,裸地最低,且与土壤有机碳(SOC)、全氮(TN)和速效磷(AP)极显著正相关(P0.01);(3)裸地土壤的细菌丰度最低,人工刺槐林真菌含量显著低于天然辽东栎林。细菌丰度与土壤营养状况呈显著正相关(P0.05),而真菌与土壤营养无明显相关性,只与土壤pH负相关。说明在该研究区域,植被类型与土壤质量对微生物资源都具有不同程度的作用。

Relationship among vegetation types and soil microbial biomass in the Loess Hilly region of China

To remedy adverse impacts on ecological environments, vegetation restoration has been completed on the Loess Hilly region of China, thus yielding changes in vegetation types, and secondary forests and exotic vegetation have reclaimed most of this area. Vegetation type plays an important role in soil quality, and similar land-use types usually possess similar soil properties and, most likely, similar microbial communities. To assess the effects of vegetation type on soil development, we measured the basic physicochemical properties, microbial biomass carbon (MBC) and nitrogen (MBN), and the number of bacteria and fungi of soils from areas with five different vegetation types, including a secondary natural oak forest, a non-typical natural forest of oriental arborvitae, a natural shrub land, a planted forest of black locust, and a plot of unforested bare land. We found that (1) soil properties improved with the presence of vegetation, compared with the abandoned bare land, and that there were differences in the physicochemical properties of soil from the different land-use types. Soils from the bare land and black locust forest yielded higher pH values than the natural forests, and the overall trend of soil quality was: natural forest > plantation > bare land. This indicated that vegetation coverage, especially natural types, has a beneficial effect on soil nutrient conditions and soil pH. (2) Similar to the trend of the other soil parameters, both MBC and MBN were highest in the oak forest and shrub land and lowest in the bare land and black locust forest. These two indices (MBC and MBN) were also strongly correlated with specific soil properties (soil organic carbon, r² = 0.725, total nitrogen, r² = 0.736, and phosphorus, r² = 0.775; P < 0.001), suggesting that vegetation type and soil properties influence microbial biomass. Thus, microbial biomass can be used to assess soil trophic status and which lower in oligotrophic soils on the Loess Plateau of China. In our study area, the soil was alkaline (pH 8.18-8.48), and the MBC/MBN ratio was ~6, indicating that actinomycetes were dominant, possibly facilitated by the alkaline soil conditions. (3) Bare land harbored the lowest abundance of bacteria, and the abundance of fungi in the black locust was lower than that of the oak forest. The abundance of bacteria exhibited a strong relationship with specific soil properties and was positively correlated with C/N ratio (r² = 0.754, P < 0.001), soil organic carbon (r² = 0.636, P < 0.05), total nitrogen (r² = 0.611, P < 0.05), and phosphorus (r² = 0.775, P < 0.05), and negatively correlated with pH (r² = 0.761, P < 0.001). In contrast, the abundance of fungi was only correlated with soil pH, thus confirming previous reports that bacteria and fungi respond to different environmental factors. This discrepancy may result from the different functions of bacteria and fungi. Fungi are primarily responsible for the decomposition of recalcitrant soil organic matter in forest soils. Thus, the overall trend of soil characteristic was: natural forest > plantation > bare land, indicating that the recovery of soil quality differed among plots with different vegetation types, and both soil microorganisms and soil microbial biomass, to a certain extent, can be used as an important index of soil fertility.