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To quantify variations in the components of soil respiration (Rs), elucidate the impact of warming on heterotrophic respiration (Rh) in subalpine coniferous forest (LJ) and in subtropical evergreen broadleaf forest (ALS), and discern differences in the dominant regulating factors of soil respiration components between the two forest ecosystems. This study used multichannel automated soil efflux chambers with three treatments: control (CK), trenching (NR), and trenching with warming (NRW) in LJ and ALS in Southwest China. The results reveal that Rswas higher in ALS than in LJ, and the ratio of Rhto Rswas significantly higher in LJ than in ALS. Although soil temperature (ST) and soil moisture (SM) also identified the main controlling factors of Rs, Rh, Ra, and the warming effect of Rhwhen considering carbon cycle modeling, the sensitivity of Rsto temperature (Q10) was not significantly different between Rs, Rh, and Rafor both forests. The greater warming effect on Rhin LJ than in ALS is due to the combination of lower temperatures, recalcitrant organic matter, and slower litter decomposition in subalpine coniferous forests. This study confirmed that Rs, Rhand Rahad positive correlation with STand SMfor two ecosystems. This study has proven that the greater the warming effect of Rhis, the greater the contribution of Rhto Rsbecomes, and the lesser the contribution of Rato Rsin LJ becomes compared to that of ALS.

Grazing and over-grazing may drive changes in the diversity and functioning of below-ground meadow ecosystems. A field soil survey was conducted to compare microbial biomass carbon (Cmin) and soil fauna communities in the two main grassland management systems in subalpine regions of Yunnan Province, China: perennial grazing currently practiced due to increasing herd sizes and traditional seasonal grazing. A three-year exclosure experiment was then conducted to further compare the effects of different grazing practices, including treatments of no mowing, perennial grazing (NM + G), mowing followed by seasonal grazing (M + G), mowing and no grazing (M + NG), and no mowing or grazing (NM + NG). The comparative survey result revealed that Cminand total density of soil fauna were significantly lower at a perennially grazed site than at a seasonally grazed site. The experiment results showed that in comparison to non-grazing treatments (M + NG and NM + NG), grazing (NM + G and M + G) reduced total fauna density (by 150 individuals m−2) and the number of taxonomic groups present (by 0.32 taxa m−2). Mowing decreased Cmin(by 0.31 mg g−1). Furthermore, the NM + G treatment (perennial grazing) had the lowest density of Collembola (16.24 individuals m−2), one of the two most common taxonomic groups, although other taxonomic groups responded differently to the treatments. Treatment effects on soil fauna were consistent with those on above-ground grasses, in which C:N ratios were greatly reduced by grazing, with this effect being the greatest for the NM + G treatment. In contrast, different grazing treatments had little effect on C:N ratio of soil. Furthermore, the traditional grazing method (mowing followed by seasonal grazing) may have less severe effects on some taxonomic groups than perennial grazing. Therefore, an appropriate management should aim to protect soil fauna and microbes in this area from over-grazing and against further degradation.

Abstract: CO2 concentrations and related environmental factors were measured in an Asian tropical rainforest located in a small valley in Xishuangbanna, SW China, with the aim of investigating the CO2 pooling effect and its mechanism of formation. Pooling of CO2 was observed during the evening (1600–2200 hours local time); the accumulated CO2 subsequently flowed away after dusk. We consider that along-slope drainage flow, soil CO2 efflux, and temperature inversion contribute to the development of CO2 pooling. A new model is proposed to track the mechanism of the formation and dissipation of CO2 pooling (e.g., drainage flow, compensatory mechanisms). Given its influence on the storage term, we suggest that CO2 pooling and subsequent disappearance should be taken into account when calculating eddy covariance and other micrometeorological measurements of carbon flux for valley sites.

AbstractCO2concentrations and related environmental factors were measured in an Asian tropical rainforest located in a small valley in Xishuangbanna, SW China, with the aim of investigating the CO2pooling effect and its mechanism of formation. Pooling of CO2was observed during the evening (1600–2200 hours local time); the accumulated CO2subsequently flowed away after dusk. We consider that along-slope drainage flow, soil CO2efflux, and temperature inversion contribute to the development of CO2pooling. A new model is proposed to track the mechanism of the formation and dissipation of CO2pooling (e.g., drainage flow, compensatory mechanisms). Given its influence on the storage term, we suggest that CO2pooling and subsequent disappearance should be taken into account when calculating eddy covariance and other micrometeorological measurements of carbon flux for valley sites.

We examined plants growing in four tropical vegetation types (primary forest, secondary forest, limestone forest and a slash and burn field) in Xishuangbanna, southwest China for mycorrhizal associations. Of the 103 plant species examined (belonging to 47 families), 81 had arbuscular mycorrhizal (AM) associations, while three species possessed orchid mycorrhiza. AM colonization levels ranged between 6% and 91% and spore numbers ranged between 1.36 spores and 25.71 spores per 10 g soil. Mean AM colonization level was higher in primary and secondary forest species than in plant species from limestone forests and a slash and burn field. In contrast, mean AM fungal spore numbers of the primary and limestone forest were lower than in the secondary forest or the slash and burn field. AM fungal spores belonging to Glomus and Acaulospora were the most frequent in soils of Xishuangbanna. AM fungal colonization and spore numbers were significantly correlated to each other and were significantly influenced by vegetation type.