转植酸酶玉米大田种植对根际土壤磷含量及组成的影响

转基因作物种植推广中的生态风险是广泛关注的焦点。转植酸酶玉米可以提高动物对玉米籽粒的磷素利用率,但是对土壤磷素的影响尚未见报道。本研究基于2011年开始的田间实验,通过2012年和2013年玉米生长季的动态采样,研究转植酸酶玉米种植对土壤磷含量和组成的影响。结果表明,与亲本相比,转植酸酶玉米对土壤磷的影响强烈依赖于采样时间和磷形态,2012年玉米播种前和2013年抽穗期土壤水溶态磷(H2O-Pi)、氢氧化钠提取态无机磷(NaOH-Pi)和氢氧化钠提取态有机磷(NaOH-Po)含量均显著低于对照;碳酸氢钠提取态有机磷(NaHCO3-Po)在2012年播种前和2013年成熟期显著低于对照,而微生物生物量磷(MBP)只在2013年成熟期有显著差异。种植转植酸酶玉米没有影响土壤全磷(TP)、稀盐酸提取态无机磷(Dil.HCl-Pi)、浓盐酸提取态无机磷(Conc.HCl-Pi)、浓盐酸提取态有机磷(Conc.HCl-Po)和残留态磷(Residual-P)含量。总之,连续3年种植转植酸酶玉米仅在某些采样期对土壤高活性和中等活性磷产生影响。转植酸酶玉米种植对土壤磷素影响的评价和影响机制研究需要结合植物和土壤,并在不同地点开展长期监测。

Effects of phytase transgenic corn on content and composition of phosphorus in rhizosphere soil under field conditions

Phosphorus (P) is one of the mineral elements essential to growth of all animals. However, corn as a major source of energy and feed to animals, is fairly low in content of P available to monogastric animals and about 80% of the phosphorus in corn is phytate-P. In monogastric animals, phytate-P is very low in utilization rate because the animals lack endogenous phytase. Therefore, inorganic P is routinely added to the feed of the animals to satisfy their requirement for P, As a result, a unutilized portion of the dietry P is excreted with faeces of the animals, thus polluting the soil and water sources. Moreover, phytic acid is also a kind of anti-nutritional factor that seriously affects animal uptake of Ca, Fe, Zn, and some other nutrient elements. Supplementation of exogenous phytase extracted from microbial fementation into feed has been considered to be one of the most effective ways to reduce P output. However, the extraction of phytase is rather costly, thus limiting its extensive commercial use. Phytase genes of Aspergillus niger were transferred into the endosperm of corn, turning out corn seeds that contain Aspergillus niger phytase. After generations of breeding and screening, obtained was a corn homozygous line of phytase transgenic corn (PTC) that is able to stably express phytase and inherite stably generation after generation. Feeding this kind of corn can improve P utilization rate of monogastric animals and reduce P content in their faeces, thus eliminating P pollution of the environment. Compared with conventional corn, PTC planted in the field may have some potential risks. However, phosphorus is a nutrient element essential to crops and an important pollutant as well deteriorating water environments. Commercial plantation of PTC has aroused ecological concerns with respect to potential effect on content and composition of soil P. On the one hand, PTC may directly affect soil P level through release of phytase into the soil, and on the other hand, the changes in chemical composition or quality of crop residues, like roots and straw left in the soil may have some effect on soil biological communities and biochemincal activity of the soil, thus in the end affecting the processes of fixation and mineralization-release of soil inorganic and organic P. Therefore, theoretically planting PTC will generate some effect on soil P transformation processes, and in turn further alter soil fertility of the field and quality of its surrounding water bodies. Nevertheless, to our knowledge, little has been reported on effects of planting PTC on soil P. A field experiment started in 2011, planting phytase transgenic corn (BVLA430101) and isogenic corn (Yingyu 35), separately, as Treatment PTC and Treatment CK, each of which has 5 replicates, making up a total of 10 plots. Soil samples were collected at different corn growing stages in 2012 and 2013 for analysis using the modified Hedley phosphorus fractionation method to investigate effects of planting PTC on content and compositions of soil P. Results show that the effects of PTC on soil P varied with timing of sampling and fraction of P. The soil in Treatment PTC was much lower than the soil in Treatment CK in content of water soluble P (H2O-Pi), NaOH extractable inorganic P (NaOH-Pi) and NaOH extractable organic P (NaOH-Po) before seeding in 2012 and at the heading stage in 2013, and in content of NaHCO3 extractable organic P (NaHCO3-Po) before seeding in 2012 and at the maturing stage in 2013. however, the two soils differed significantly in content of microbial biomass P (MBP) only at the maturing stage in 2013. Growing PTC had no significant effects on the contents of total P (TP), diluted HCl extractable inorganic P (Dil.HCl-Pi), concentrated HCl extractable inorganic P (Conc.HCl-Pi), concentrated HCl extractable organic P (Conc.HCl-Po) and Residual P (Residual-P). The soil in Treatment PTC was much higher than the soil in Treatment CK in phytase activity throughout the two corn growing seasons, and in alkaline phosphatase activity as well before seeding in 2012 and during the whole corn growing season in 2013. Anyway, growing PTC three years in row had some effects on contents of labile P and moderately labile P and activity of alkaline phosphatase in the soil only at certain growth stages, and significant effects on phytase activity during the two corn growing seasons. It is, therefore, necessary to take into account the crop and the soil related in evaluating effects of planting PTC on soil P and studying mechanisms of the effects, and what is more, to maintain long term monitoring at different sites.