To better understand the soil carbon dynamics and cycling in terrestrial ecosystems in response to environmental changes, we studied soil respiration, litter decomposition, and their relations to soil temperature and soil water content for 18-months (Aug. 2010–Jan. 2012) in three different-aged Pinus massoniana forests in the Three Gorges Reservoir Area, China. Across the experimental period, the mean total soil respiration and litter respiration were 1.94 and 0.81, 2.00 and 0.60, 2.19 and 0.71 µmol CO₂ m⁻² s⁻¹, and the litter dry mass remaining was 57.6%, 56.2% and 61.3% in the 20-, 30-, and 46-year-old forests, respectively. We found that the temporal variations of soil respiration and litter decomposition rates can be well explained by soil temperature at 5 cm depth. Both the total soil respiration and litter respiration were significantly positively correlated with the litter decomposition rates. The mean contribution of the litter respiration to the total soil respiration was 31.0%–45.9% for the three different-aged forests. The present study found that the total soil respiration was not significantly affected by forest age when P. masonniana stands exceed a certain age (e.g. >20 years old), but it increased significantly with increased soil temperature. Hence, forest management strategies need to protect the understory vegetation to limit soil warming, in order to reduce the CO₂ emission under the currently rapid global warming. The contribution of litter decomposition to the total soil respiration varies across spatial and temporal scales. This indicates the need for separate consideration of soil and litter respiration when assessing the climate impacts on forest carbon cycling.

Both exotic and native plant invasions can have profound impacts on ecosystems. While many studies have examined the effects of exotic plant invasions on soil properties, relatively few have tested the effects of native plant invasions on soil microbial communities. Furthermore, we know little about the effects of native plant invasions on microbial communities in litter. In subtropical forests in southern China, we sampled litter at three decomposition stages and top soil in three forest sands representing three stages of the invasion (not invaded, moderately and heavily invaded) by the Moso bamboo (Phyllostachys edulis (Carriere) J. Houzeau), a native species in China. We measured chemical properties (concentrations of C, N, P, Mg, Al, K, Ca, Mn, Cu, and Zn, and concentrations of cellulose and lignin) and microbial communities in litter and/or soil. The bamboo invasion, in general, decreased the element concentrations in litter and soil and also decreased total microbial abundance and diversity. Considering bacteria and fungi separately, the bamboo invasion decreased fungal diversity in litter and soil, but had little impact on bacterial diversity, suggesting that fungi are more sensitive and vulnerable to the bamboo invasion than bacteria. We conclude that native Moso bamboo invasions into subtropical forests may lead to a complex biogeochemical process in the litter–soil system, which may threaten local forest ecosystems by affecting microbial communities and, thus, litter decomposition and nutrient cycling.

Phosphorus (P) is a nutrient limiting plant growth in subtropical regions. However, our understanding of how soil P responds to an increase in stand age is rather poor. In particular, little is known about how bioavailable P pools (soluble P, exchangeable P, hydrolyzable P, and ligand P) shift with a change in stand age. Moreover, the P cycle in rhizosphere soil has the most direct and significant influence on plants. The aim of the present study was to determine the concentrations of total P in various rhizosphere soil bioavailable P fractions in 5-, 9-, 19-, 29-, and 35-year-old stands of Pinus massoniana Lamb. According to the results, total P (TP) concentration and N:P ratio in rhizosphere soil first decreased, and then increased with an increase in stand age. Soluble P concentration decreased first, and then increased with an increase in stand age; exchangeable P and ligand P decreased first, and then tended to be stable with an increase in stand age, whereas hydrolyzable P increased first, and then decreased. Structural Equation Model results suggested that ligand P and soluble P were the major factor affecting the TP. In addition, soil microorganisms and acid phosphatase-driven hydrolyzable P play a crucial role in soil bioavailable P cycling. Overall, the results of our study provide a mechanistic understanding of soil bioavailable P cycling under low available P conditions, and a basis for an effective P management strategy for the sustainable development of P. massoniana plantations.

The root of Moso bamboo (Phyllostachys edulis (Carrière) J. Houz.) develops extremely rapidly at seedling phase and is highly sensitive to water content in soil, but its response patterns and adaptation strategies of its root to drought are little known. The aim of this study was to investigate the response of root morphology and architecture of Moso bamboo to drought at seedling phase and then to explore the drought adaptation strategies of its root. One-year-old potted seedlings of Moso bamboo were planted under three drought treatments (control, moderate drought and severe drought) for three months. Seedling growth, specific root length (SRL), root architecture (fractal dimension (FD), root branching angle (RBA) and root topological index (TI)) and non-structural carbohydrate (NSC) concentrations in roots were measured every month. The results are as follows: (i) The dry weight of root and shoot decreased significantly under drought stress. (ii) The SRL decreased under drought stress in the early duration (the first month), and then increased in the late duration (the third month). Both FD and RBA decreased, while TI and the concentrations of NSCs increased under drought stress. (iii) The NSC concentrations were positively correlated with SRL and TI, but exhibited an inverse relationship to FD and RBA. Our results indicated that Moso bamboo seedlings formed a “steeper, simpler, expensive (low SRL and high TI)” root architecture to adapt to a short-term drought (one month), and formed a “cheaper (high SRL)” root to adapt to a long-term drought (three months). Increase of NSC concentrations supported the root architecture plasticity to some extent.

The aim of this work was to study the changes in the BVOCs emission rates and physiological mechanistic response of Pinus massoniana saplings in response to drought stress. Drought stress significantly reduced the emission rates of total BVOCs, monoterpenes, and sesquiterpenes, but had no significant effect on the emission rate of isoprene, which slightly increased under drought stress. A significant negative relationship was observed between the emission rates of total BVOCs, monoterpenes, and sesquiterpenes and the content of chlorophylls, starch, and NSCs, and a positive relationship was observed between the isoprene emission rate and the content of chlorophylls, starch, and NSCs, indicating different control mechanism over the emission of the different components of BVOCs. Under drought stress, the emission trade-off between isoprene and other BVOCs components may be driven by the content of chlorophylls, starch, and NSCs. Considering the inconsistent responses of the different components of BVOCs to drought stress for different plant species, close attention should be paid to the effect of drought stress and global change on plant BVOCs emissions in the future.

Previous studies have shown that biochar fertilization has profound effects on plant and fine root growth, but there is a lack of studies on how changes in plant and soil stoichiometry by biochar fertilization influence plant growth and root morphology. We investigated the effects of biochar fertilization on biomass, root morphology, plant nutrient concentrations, and the stoichiometry of plants and soil in a greenhouse experiment with Pinus massoniana (Lamb.) (PM) and Cunninghamia lanceolata (Lamb.) Hook. (CL) throughout the 2017 growing season immediately following biochar fertilization application. Four levels of biochar treatment were used, i.e., addition rates of 0 (control), 5 (low biochar), 10 (medium biochar), and 20 t ha⁻¹ (high biochar). Biochar fertilization had no effect on biomass, fine root length, or fine root surface area. Biochar treatment, however, had significant effects on nutrient levels and their stoichiometry in both plants and soil. Detrended correspondence analysis suggested that increases in soil C:N, soil C:P, and soil N:P were associated with increases in plant nutrient levels, especially P concentration. Our results indicate that biochar fertilization prioritizes enhancing plant and soil nutrients over increasing height and diameter in the first growing season. A higher biochar fertilization dosage has a major influence on root morphology for PM and on P concentrations in the plant and soil for CL, probably through different growth characteristics and nutrient resorption rates. Further studies, particularly those considering long-term effects, are necessary before general recommendations regarding biochar application should be given.