Weed Interference in Soybean Crop Affects Soil Microbial Activity and Biomass

ABSTRACT: Weeds and microorganisms interacting with their rhizosphere may influence nutrient absorption, which is an important factor for plant competition. The purpose of this study was to evaluate the microbiological activity, inorganic phosphorus solubilization (Pi) and acid phosphatase in the cultivated soil, in a combination of soybean (Glycine max) plants and weeds. Soybeans were cultivated in monoculture and in competition with Bidens pilosa, Brachiaria decumbens (Syn. Urochloa decumbens) and Eleusine indica, under two conditions: a) plants competing without contact between the roots b) plants competing with contact between the roots. A nylon screen with a 50 µm mesh was added to prevent contact between the roots of the species in competition so that the substratum could be separated in the vase. The experiment was conducted in randomized blocks, with four replications. The soybeans in competition with weeds led to lower oxidation of organic matter per unit of microbial biomass, resulting in a lower metabolic quotient, compared with the soybean monoculture. The contact between soybean roots and B. pilosa, B. decumbens and E. indica maintained a strong influence, raising the solubilization of Pi, respectively valued at 51, 39 and 31% in relation to the cultivation of each species with a nylon screen. Microbiological activity, inorganic phosphorus solubilization and acid phosphatase were altered by plant species, combinations of weeds and soybean plants in competition; by root contact in some cases. Thus, the microbiological activity of the soil can influence competition strategies and plant development.

摘要：杂草与其根际（rhizosphere）微生物的互作可影响养分吸收，而养分吸收是植物竞争的重要影响因素。本研究旨在评估大豆（Glycine max）与杂草共生体系下耕作土壤的微生物活性、无机磷溶解能力（Pi）及酸性磷酸酶（acid phosphatase）活性。实验在两种条件下开展：大豆分别以单作模式，以及与三叶鬼针草（Bidens pilosa）、臂形草（Brachiaria decumbens，异名Urochloa decumbens）、牛筋草（Eleusine indica）竞争的模式进行种植，两种条件分别为：a）植物间无根系接触的竞争模式；b）植物间存在根系接触的竞争模式。实验中使用孔径为50 µm的尼龙网分隔竞争物种的根系，以实现培养容器内基质的分离。本实验采用随机区组设计（randomized blocks），设置4次重复。与大豆单作组相比，与杂草竞争的大豆其单位微生物生物量的有机质氧化量更低，因此代谢商（metabolic quotient）也更低。大豆根系与三叶鬼针草、臂形草及牛筋草的根系接触，会显著提升无机磷溶解能力，相较于各物种单独种植且使用尼龙网分隔的处理，其无机磷溶解率分别提升51%、39%和31%。植物物种、大豆与杂草的竞争组合以及部分情况下的根系接触，均会改变土壤微生物活性、无机磷溶解能力及酸性磷酸酶活性。由此可见，土壤微生物活性可影响植物的竞争策略与生长发育。