Insight into the carbon turnover in soil aggregates and density fractions is essential for reducing the uncertainty in estimating carbon pools on the Tibetan Plateau, and how they vary with land use type is unclear.  In this study, the effect of land use type on carbon storage and fractionation was quantified based on organic carbon and its ¹³C abundance at the microscale of soil aggregates and density fractions in Tibetan alpine ecosystems.  The sequence of soil aggregate destruction in the land use types of plantation (13.1%)<shrubland (32.7%)<grassland (47.9%)<farmland (61.8%) shows that plantations strengthen the soil structure.  Plantation land had a greater contribution of light fraction organic carbon (28.3%) but a lower contribution of mineral-associated organic carbon (40.6%) to the carbon stock compared to farmland (13.5 and 70.3%).  Interestingly, plantation land enhanced the aggregational differentiation of organic carbon and ¹³C in each density fraction, whereas no such phenomenon existed in the soil organic carbon.  Carbon isotope analyses revealed that carbon transfer in the plantation land occurred from the light fraction in macroaggregates (–24.9‰) to the mineral-associated fraction in microaggregates (–19.9‰).  When compared to the other three land use types, the low transferability of carbon in aggregates and density fractions in plantation land provides a stable carbon pool for the Tibetan Plateau.  This study shows that plantations can mitigate global climate change by slowing carbon transfer and increasing carbon storage at the microscale of aggregates and density fractions in alpine regions.

Tobacco (Nicotiana tabacum) and tomato (Solanum lycopersicum) are two major economic crops in China.  Tobacco mosaic virus (TMV; genus Tobamovirus) is the most prevalent virus infecting both crops.  Currently, some widely cultivated tobacco and tomato cultivars are susceptible to TMV and there is no effective strategy to control this virus.  Cross-protection can be a safe and environmentally friendly strategy to prevent viral diseases.  However, stable attenuated TMV mutants are scarce.  In this study, we found that the substitutions in the replicase p126, arginine at position 196 (R¹⁹⁶) with aspartic acid (D), glutamic acid at position 614 (E⁶¹⁴) with glycine (G), serine at position 643 (S⁶⁴³) with phenylalanine (F), or D at position 730 (D⁷³⁰) with S, significantly reduced the virulence and replication of TMV.  However, only the mutation of S⁶⁴³ to F reduced the RNA silencing suppression activity of TMV p126.  A double-mutant TMV-E614G-S643F induced no visible symptom and was genetically stable through six successive passages in tobacco plants.  Furthermore, our results showed that TMV-E614G-S643F double-mutant could provide effective protection against the wild-type TMV infection in tobacco and tomato plants.  This study reports a promising mild mutant for cross-protection to control TMV in tobacco and tomato plants.