Global warming potentially alters the terrestrial carbon (C) cycle, likely feeding back to further climate warming. However, how the ecosystem C cycle responds and feeds back to warming remains unclear. Here we used a meta-analysis approach to quantify the response ratios of 18 variables of the ecosystem C cycle to experimental warming and evaluated ecosystem C-cycle feedback to climate warming. Our results showed that warming stimulated gross ecosystem photosynthesis (GEP) by 15.7%, net primary production (NPP) by 4.4%, and plant C pools from above- and belowground parts by 6.8% and 7.0%, respectively. Experimental warming accelerated litter mass loss by 6.8%, soil respiration by 9.0%, and dissolved organic C leaching by 12.1%. In addition, the responses of some of those variables to experimental warming differed among the ecosystem types. Our results demonstrated that the stimulation of plant-derived C influx basically offset the increase in warming-induced efflux and resulted in insignificant changes in litter and soil C content, indicating that climate warming may not trigger strong positive C-climate feedback from terrestrial ecosystems. Moreover, the increase in plant C storage together with the slight but not statistically significant decrease of net ecosystem exchange (NEE) across ecosystems suggests that terrestrial ecosystems might be a weak C sink rather than a C source under global climate warming. Our results are also potentially useful for parameterizing and benchmarking land surface models in terms of C cycle responses to climate warming.

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Biotic interactions involving exotic plants in their introduced ranges may differ from those of co‐occurring plant species and from interactions in their native ranges. When interactions are less negative, or more positive compared to native plant species, this may increase invasion success, and differences among ranges may cause changes in exotic plant traits. Here, we investigated arbuscular mycorrhizae (AM) associated with Triadica sebifera seedlings from populations in native (China) and introduced ranges (US) and with seedlings from US and China species within three co‐occurring genera (Liquidambar, Ulmus, Celtis) grown in multiple common gardens in both ranges. No general pattern of higher or lower AM colonization was found in the introduced range for China and US Celtis, Liquidambar, or Ulmus species. However, AM colonization was significantly higher for Triadica than for other genera, particularly in the introduced range, suggesting AM may improve Triadica's invasion success. Triadica AM colonization was higher in US than China gardens, decreased with increasing soil nitrogen in China, but was independent of soil nitrogen in the US. This might reflect a different effect of soil fertility on this mutualism among ranges. Introduced Triadica populations had higher AM colonization than native populations, particularly in US gardens, implying a possible advantage from greater AM association in the introduced range. This is the first field study demonstrating post‐introduction changes in mycorrhizal colonization of an invasive species. It indicates that there are ecological and evolutionary components to the effect of positive interactions on plant invasions.

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Exotic plant species may exhibit abiotic niche expansions that enable them to persist in a greater variety of habitat types in their introduced ranges than in their native ranges. This may reflect variation in limitation by different abiotic niche dimensions (realized niche shift) or phenotypic effects of biotic interactions that vary among ranges (realized niche expansion). Novel abiotic and biotic environments in the introduced range may also lead to genetic changes in exotic plant traits that enhance their abiotic stress tolerance (fundamental niche expansion). Here, we investigated how biotic interactions (aboveground herbivory and soil organisms) affect plant salinity tolerance using the invasive species Triadica sebifera from China (native range) and US (introduced range) populations grown in common gardens in both ranges. Simulated herbivory significantly reduced survival in saline treatments with reductions especially large at low salinity. Soil sterilization had a negative effect on survival at low salinity in China but had a positive effect on survival at low salinity in the US. Triadica survival and biomass were higher for US populations than for China populations, particularly in China but salinity tolerance did not depend on population origin. On average, arbuscular mycorrhizal (AM) colonization was higher for US populations, US soils and low salinity. These factors had a significant, positive, non‐additive interaction so that clipped seedlings from US populations in low saline US soils had high levels of AM colonization. Overall, our results show that phenotypic biotic interactions shape Triadica's salinity tolerance. Positive and negative biotic interactions together affected plant performance at intermediate stress levels. However, only aboveground damage consistently affected salinity tolerance, suggesting an important role for enemy release in expanding stress tolerance.

Background and aims Exotic plant species experience conditions in their introduced ranges that differ from those in their native range. Exotic plants may experience genetic changes in traits related to resource use, abiotic stress tolerance, and biotic interactions in response to such novel biotic and abiotic environments. Methods We conducted a pot experiment in the native range to investigate how soil fertility, soil salinity and soil sterilization together determine the performances of native (China) and invasive (US) populations of the tree Triadica sebifera. Results Salinity decreased plant growth, and increased AMF colonization and root:shoot. Fertilization or an unsterilized soil biota reduced the negative effects of salinity on plant survival. Fertilization decreased AMFcolonization and root:shoot ratio. Biomass was positively related to AMF colonization in unfertilized soils only. Seedlings from invasive populations grew faster and had higher AMF colonization. Conclusions Our results suggest that this invasive plant is able to persist in more saline environments when soil fertility is high or suitable AMF is present. The importance of the soil biota appears to be greater on low fertility soils where AMF provides significant benefits. The greater AMF association of plants from invasive populations suggests that resources, abiotic stress, and biotic interactions all may play a role in successful plant invasions.

Biomass allocation is an important plant trait that responds plastically to environmental heterogeneities. However, the effects on this trait of pollutants owing to human activities remain largely unknown. In this study, we investigated the response of biomass allocation of Phragmites australis to petroleum pollution by a 13 CO 2 pulse-labelling technique. Our data show that plant biomass significantly decreased under petroleum pollution, but the root–shoot ratio for both plant biomass and 13 C increased with increasing petroleum concentration, suggesting that plants could increase biomass allocation to roots in petroleum-polluted soil. Furthermore, assimilated 13 C was found to be significantly higher in soil, microbial biomass and soil respiration after soils were polluted by petroleum. These results suggested that the carbon released from roots is rapidly turned over by soil microbes under petroleum pollution. This study found that plants can modulate biomass allocation in response to petroleum pollution.