Many endophytes have been found to be resistant to heavy metals and/or capable of degrading organic contaminants, and endophyte-assisted phytoremediation has been documented as a promising technology for in situ remediation of contaminated soils. During the phytoremediation of heavy metals, the heavy-metal-resistant endophytes can enhance plant growth, decrease metal phytotoxicity, and affect metal translocation and accumulation in plants. For the phytoremediation of organic contaminants, endophytes can produce various enzymes to degrade organic contaminants and reduce both the phytotoxicity and evapotranspiration of volatile contaminants. This paper reviews the diversity of contaminant-resistant/degrading endophytes and their role in phytoremediation and discusses some issues that have been raised surrounding this area of research.

The diversity and cold adaptation of endophytic fungi associated with five dominant plant species collected from the Baima Snow Mountain (altitude 4,000–4,300 m), Southwest China, were investigated. A total of 604 culturable endophytic fungi were isolated from 800 stems and leaf segments. The colonization rate of endophytic fungi in the five plant species ranged from 54% to 91%, and the colonization rate of endophytic fungi in the stems was significantly higher (87%) than that in the leaves (67%) (X ∼ 2 = 45.172, P < 0.001, chi-squared test). Based on the morphological characteristics and the ITS sequence analysis, the isolates were identified to 43 taxa, of which Cephalosporium, Sirococcus, Penicillium and Aspergillus were the dominant genera, and their relative frequencies were 14.06%, 12.58%, 9.44% and 7.95%, respectively. The Shannon-Weiner diversity indices and the Sorenson’s coefficient similarity indices of the endophytic fungi from the five plant species ranged from 1.25 to 2.70 and 0.53 to 0.67, respectively. Growth temperature tests indicated that 75% of the isolates from the Baima Snow Mountain were psychrotrophs and 14% were the transitional type between psychrotrophs and mesophiles, whereas all of the isolates from the Yuanjiang Dry-hot Valley were mesophiles, which suggested that the endophytes from the Baima Snow Mountain possess a remarkable ability to adapt to cold environments.

The diversity and plant growth-promoting ability of endophytic fungi associated with the five flower plant species growing in Yunnan, Southwest China, were investigated. A total of 357 culturable endophytic fungi were isolated from 1000 segments of healthy leaves and stems of the five plant species. Based on the morphological characteristics and the rDNA internal transcribed spacer (ITS) analysis, the isolates were identified to 24 taxa, of which Alternaria, Phomopsis, Cladosporium, and Colletotrichum were the dominant genera. The Sorenson's coefficient similarity indices of the endophytic fungi from the five flower plant species ranged from 0.36 to 0.80. It was found that the similarity index between two cultivated flowers (0.8) or the similarity index between two wild flowers (0.71–0.76) was higher than the similarity index between one cultivated flower and one wild flower (0.36–0.48). The Shannon indices (H) of the endophytic fungi from the five plant species ranged from 1.73 to 2.45, and the diversity indices of the wild flowers were higher than those of the cultivated flowers. The plant growth-promoting tests indicated that some isolates could improve the host plants' growth more efficiently when compared with the control (p < 0.05, least significant difference test).

The diversity and heavy metal (HM) tolerance of endophytic fungi (EF) associated with Dysphania ambrosioides, a hyperaccumulator from two Pb–Zn contaminated sites were investigated. A total of 237 culturable EF were isolated and identified to 43 taxa based on morphological characteristics and rDNA internal transcribed spacer analysis, of which 13 occurred as endophytes of both sites, while other taxa were only found in either site. The colonization rate, dominant genera, community structure of EF as well as the HM content in the plant from two sites were significantly different. We suggest that these differences may result from the difference in the soil HM content: lower HM content in the soil, more EF in the plant, which may enhance the plant HM accumulation and thus result higher HM in it. HM tolerance tests indicated that 50% of the isolates exhibited HM tolerance. Among them, two isolates exhibited better HM tolerance, of which FT2G59 could tolerate Pb, Zn, and Cd, and the minimum inhibitory concentration (MIC) of them were 30–50, > 680, 20–30 mmol/l, respectively. While, the isolate FT2G7 could tolerate Cd, and the MIC was 30–50 mmol/l. These isolates may have potential application in phytoremediation.