Soil respiration in poplar plantations in northern China at different forest ages

Aims

This study aims to test the effects of forest age on soil respiration in poplar ecosystems in northern China and to separate the contributions of root respiration (Rr) and soil microbes to the total soil respiration (Rs).

Methods

Rs in three poplar forests (5, 10, and 15?years old) were measured using an LI-6400-09 soil chamber connected to an LI-6400 portable infrared gas analyzer during the growing seasons in 2007 and 2008. Root respiration was measured using the root excision method. The soil micro-organisms were quantified using the dilution-plate method.

Results

The results show that Rs was the highest in the 5-year-old forest and lowest in 15-year-old forest. The contribution of Rr to Rs ranged from 29.4 to 81.0%. Rr/Rs tended to be significantly higher in the 15-year-old forest than that in the younger forests; but Rr was the highest in the 5-year-old forest. Temporal variation in Rs can be largely accounted by fine-root biomass (R?=?0.718), while soil N was significantly negatively correlated with Rs (R?=?-0.646).

Conclusions

Rs, Rr and Rr/Rs vary significantly with the forest age. The lower Rs in the older forests increased their carbon use efficiency. Underground factors, dominated by fine-root biomass, affect Rs, Rr and Rr/Rs substantially. Soil microbial community structure is a particularly important underground factor.     

Species-specific COI primers for rapid identification of Bemisia tabaci Mediterranean (MED) species

Bemisia tabaci (Gennadius) is a rapidly evolving species complex, and is small in size and difficult to identify quickly and accurately. For the accurate identification and effective prevention of this species, the specific PCR method based on the mitochondrial DNA cytochrome oxidase subunit I (mt DNA COI) gene was used in the present study to evaluate rapid molecular detection technological applications for Mediterranean (MED) species. The MED was targeted and whitefly species from different regions were used as references. Fragments of the mt DNA COI gene of the MED and other closely related species were amplified with universal primers. Species-specific mitochondrial DNA cytochrome oxidase subunit I (SS-COI) primers BQLF/BQLR and BQJF/BQJR were designed from variable sites of MED and other whitefly species partial COI gene sequences. Subsequently, the lengths of target fragments were amplified by two pairs of SS-COI primers. Meanwhile, the accuracy, specificity and sensitivity of SS-COI primers were determined using various life stages of the MED and other related species collected from different locations. The primer pairs BQLF/BQLR and BQJF/BQJR generated 334 bp and 483 bp amplified fragment length respectively. Accuracy test results showed that primers can detect the MED single-head adults and also accurately detect single-egg and first instar, second instar and third instar nymphs, MED pupae, etc. Specific detection results demonstrated that the primers were able to amplify the MED but not the following species/populations: Middle East-Asia Minor 1 (MEAM1), Asia I, Asia II 1, Asia II 6 and Asia II 7, Aleurocanthus spiniferus (Quaintanca), A. camelliae, Siphoninus phillyreae, Aleuroclava rhododendri, A. thysanospermi, Aleurolobus taonabae, Dialeurodes citri and Trialeurodes vaporariorum (Westwood) in different areas. Sensitivity detection results showed that primers can detect the minimum threshold of 2,160 pg/μl and 1.38 pg/μl, respectively (equivalent to 1/1280 and 1/2000000 adult). This technique solves the problem that MED cannot be identified based on morphology. This method simultaneously adopted SS-COI PCR technological applications that improved detection accuracy and saved detection time.