集约化农业生产的土壤中含有丰富的AM真菌种类和孢子数目。以往的研究表明，在低磷条件下AM真菌能够提高作物的磷吸收，但在高磷土壤中AM真菌是否依然发挥着作用并不清楚。在本文中，我们原位研究了长期高磷肥投入的农田中，土著AM真菌是否对P的利用依然有贡献。我们设计了菌丝室装置，通过在PVC管两端分别密封不同孔径的膜（30 或 0.45 µm），允许或阻止菌丝穿透尼龙膜，进入菌丝室，并阻止棉花根系的进入。我们用土壤速效磷（Olsen-P）的耗竭来表征土著AMF对磷的吸收。结果表明，土著AMF能够介导磷的耗竭和微生物量磷（MBP）的周转，并且在高磷条件下（Olsen-P: 78.29 mg kg^-1），速效磷的耗竭和MBP的周转率最大；不同施肥处理的棉花根内定殖着特有的AM真菌群落，且Glomus 和 Paraglomus占主导地位，暗示了长期的施肥能够驯化AM真菌群落。在本研究结果中，我们得出了即使在高磷条件下，土著AM真菌在土壤磷的耗竭和周转中依然发挥着重要作用。

Soil organic carbon (SOC), soil microbial biomass carbon (SMBC) and SMBC quotient (SMBC/SOC, qSMBC) are key indexes of soil biological fertility because of the relationship to soil nutrition supply capacity. Yet it remains unknown how these three indexes change, which limits our understanding about how soil respond to different fertilization practices. Based on a 22-yr (1990-2011) long-term fertilization experiment in northwest China, we investigated the dynamics of SMBC and qSMBC during the growing period of winter wheat, the relationships between the SMBC, qSMBC, soil organic carbon (SOC) concentrations, the carbon input and grain yield of wheat as well. Fertilization treatments were 1) nonfertilization (control); 2) chemical nitrogen plus phosphate plus potassium (NPK); 3) NPK plus animal manure (NPKM); 4) double NPKM (hNPKM) and 5) NPK plus straw (NPKS). Results showed that the SMBC and qSMBC were significantly different among returning, jointing, flowering and harvest stages of wheat under long-term fertilization. And the largest values were observed in the flowering stage. Values for SMBC and qSMBC ranged from 37.5 to 106.0 mg kg-1 and 0.41 to 0.61%, respectively. The mean value rank of SMBC during the whole growing period of wheat was hNPKM>NPKM>NPKS>CK>NPK. But there were no statistically significant differences between hNPKM and NPKM, or between CK and NPK. The order for qSMBC was NPKS>NPKM>CK>hNPKM>NPK. These results indicated that NPKS significantly increased the ratio of SMBC to SOC, i.e., qSMBC, compared with NPK fertilizer or other two NPKM fertilizations. Significant linear relationships were observed between the annual carbon input and SOC (P<0.01) or SMBC (P<0.05), and between the relative grain yield of wheat and the SOC content as well (P<0.05). But the qSMBC was not correlated with the annual carbon input. It is thus obvious that the combination of manure, straw with mineral fertilizer may be benefit to increase SOC and improve soil quality than using only mineral fertilizer.