Schmidt Inger K, Michelsen Anders, Jonasson Sven
Botanical Institute, Department of Plant Ecology, University of Copenhagen, Øster Farimagsgade 2D, DK-1353 Copenhagen K, Denmark Fax: +45 35 32 23 21; e-mail:
Oecologia. 1997 Nov;112(4):557-565. doi: 10.1007/s004420050345.
We measured partitioning of N and P uptake between soil microorganisms and potted Festuca vivipara in soil from a subarctic heath in response to factorial addition of three levels of labile carbon (glucose) combined with two levels of inorganic N and P. The glucose was added to either non-sterilized or sterilized (autoclaved) soils in quantities which were within the range of reported, naturally occurring amounts of C released periodically from the plant canopy. The aims were, firstly, to examine whether the glucose stimulated microbial nutrient uptake to the extent of reducing plant nutrient uptake. This is expected in nutrient-deficient soils if microbes and plants compete for the same nutrients. Secondly, we wanted to test our earlier␣interpretation that growth reduction observed in graminoids after addition of leaf extracts could be caused directly by labile carbon addition, rather than by phytotoxins in the extracts. Addition of high amounts of N did not affect the microbial N pool, whereas high amounts of added P significantly increased the microbial P pool, indicating a luxury P uptake in the microbes. Both plant N and in particular P uptake increased strongly in response to soil sterilization and to addition of extra N or P. The increased␣uptake led to enhanced plant growth when both elements were applied in high amounts, but only led to increased tissue concentrations without growth responses when the nutrients were added separately. Glucose had strong and contrasting effects on plant and microbial N and P uptake. Microbial N and P uptake increased, soil inorganic N and P concentrations were reduced and plant N and P uptake declined when glucose was added. The responses were dose-dependent within the range of 0-450 μg C g soil added to the non-sterilized soil. The opposite responses of plants and microbes showed that plant acquisition of limiting nutrients is dependent on release of nutrients from the soil microbes, which is under strong regulation by the availability and microbial uptake of labile C. Hence, we conclude, firstly, that the microbial populations can compete efficiently with plants for nutrients to an extent of affecting plant growth when the microbial access to labile carbon is high in nutrient deficient soils. We also conclude that reduced growth of plants after addition of leaf extracts to soil can be caused by carbon-induced shifts in nutrient partitioning between plants and microbes, and not necessarily by phytotoxins added with the extracts as suggested by some experiments.
我们测量了北极苔原土壤中微生物与盆栽胎生羊茅之间氮和磷吸收的分配情况,以应对三种水平的易分解碳(葡萄糖)与两种水平的无机氮和磷的析因添加。葡萄糖被添加到未灭菌或灭菌(高压灭菌)的土壤中,添加量在报道的植物冠层定期释放的自然碳含量范围内。目的如下:首先,研究葡萄糖是否刺激微生物对养分的吸收,以至于降低植物对养分的吸收。如果微生物和植物竞争相同的养分,那么在养分缺乏的土壤中就会出现这种情况。其次,我们想检验我们之前的解释,即在添加叶提取物后禾本科植物生长减少可能是直接由添加易分解碳导致的,而不是由提取物中的植物毒素导致的。添加大量氮不会影响微生物氮库,而添加大量磷会显著增加微生物磷库,这表明微生物存在奢侈性磷吸收。土壤灭菌以及添加额外的氮或磷后,植物对氮尤其是磷的吸收均显著增加。当两种元素都大量添加时,吸收增加导致植物生长增强,但当分别添加养分时,仅导致组织浓度增加而无生长反应。葡萄糖对植物和微生物的氮和磷吸收有强烈且相反的影响。添加葡萄糖后,微生物对氮和磷的吸收增加,土壤无机氮和磷浓度降低,植物对氮和磷的吸收减少。在添加到未灭菌土壤中的0 - 450μg C g土壤范围内,这些反应呈剂量依赖性。植物和微生物的相反反应表明,植物对限制养分的获取取决于土壤微生物释放的养分,而这受到易分解碳的有效性和微生物吸收的强烈调节。因此,我们首先得出结论,当养分缺乏的土壤中微生物获得易分解碳的机会较高时,微生物种群可以在一定程度上与植物有效竞争养分,从而影响植物生长。我们还得出结论,向土壤中添加叶提取物后植物生长减少可能是由碳诱导的植物与微生物之间养分分配变化引起的,而不一定像一些实验所表明的那样是由提取物中添加的植物毒素导致的。