Accumulation of Lead and Nutrients in Soybean and Sorghum Cultivated in Lead-Affected Tropical Soils

Lead is a potentially toxic chemical element, being responsible for many deleterious effects in living organisms. Therefore, understanding its dynamics and influence on plant growth is relevant for food security. The influence of Pb doses on nutrient accumulation in sorghum and soybean in two tropical soils with different buffering capacities was tested in a greenhouse study with four independent experiments (one per species/soil combination). The hypothesis was that the presence of Pb in soil decreases the accumulation of nutrients in soybean and sorghum plants. Soybean cultivated in a Typic Hapludox (TH) and sorghum, cultivated in both a Rhodic Acrudox (RA) and a TH, received 0, 200, 400, 800, 1200, 1600, 2200, and 2800 mg/kg of Pb, while soybean cultivated in RA received 0, 200, 400, 800, and 1600 mg/kg of Pb. Seeds were sown 24 h after application of Pb. Plants were harvested 21 days after the emergence of at least 50% of plants from the control treatment (approximately 30 days in total). Lead, macro, and micronutrient contents were determined in the shoot dry matter (SDM), and bioavailable Pb in soil was assessed by Mehlich-1. In general, TH allowed greater Pb uptake by plants, due to its lower buffering capacity. Soybean was the most affected crop with decreasing concentrations of N, K, Mg, and Ca, the latter was especially affected, with deficiency symptoms being observed. Effects on a longer time-scale are unknown, since significant decreases in nutrient contents were observed.

铅（Lead）是一种具有潜在毒性的化学元素，可对生物体产生多种有害效应。因此，阐明其环境动态及其对植物生长的影响，对于保障粮食安全具有重要意义。本研究针对两种缓冲能力各异的热带土壤，开展温室盆栽实验，设置4组独立实验（每组对应一个物种-土壤组合），以探究铅（Pb）施用量对高粱与大豆植株养分累积特征的影响。实验假说为：土壤中铅的存在会降低大豆及高粱植株的养分累积量。种植于典型强发育湿润老成土（Typic Hapludox，TH）的大豆，以及分别种植于红化湿润弱发育老成土（Rhodic Acrudox，RA）和典型强发育湿润老成土（TH）的高粱，分别施加0、200、400、800、1200、1600、2200及2800 mg/kg的铅；而种植于红化湿润弱发育老成土（RA）的大豆，仅施加0、200、400、800及1600 mg/kg的铅。铅施入土壤24小时后进行播种。待对照组中至少50%的植株出苗后，于出苗后21天收获植株（整个实验周期总计约30天）。对植株地上部干物质（shoot dry matter，SDM）中的铅、大量元素及微量元素含量进行测定；采用Mehlich-1浸提法评估土壤中生物有效性铅的含量。总体而言，典型强发育湿润老成土（TH）的缓冲能力更低，植株对铅的吸收量更高。受影响最为显著的作物为大豆，其植株内氮（Nitrogen，N）、钾（Potassium，K）、镁（Magnesium，Mg）及钙（Calcium，Ca）的浓度均出现下降，其中钙受影响尤为突出，甚至观测到了缺素症状。鉴于已观测到植株养分含量出现显著降低，更长时间尺度下的影响目前尚不明确。