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Fine roots play a key role in carbon, nutrient, and water biogeochemical cycles in forest ecosystems. However, inter-annual dynamics of fine root production, mortality, and turnover on the basis of long-term measurement have been less studied. Here, field scanning rhizotrons were employed for tracking fine root by branch order over a 6years period in a larch plantation. For total fine roots, from the first- to the fifth-order roots, annual root length production, length mortality, standing crops, and turnover rate varied up to 3.4, 2.3, 1.5, and 2.3-folds during the study period, respectively. The inter-annual variability of those roots indices in the first-order and the second-order roots were greater than that of the higher order (third- to fifth-order) roots. The turnover rate was markedly larger for the first-order roots than for the higher order roots, showing the greatest variability up to 20times. Seasonal dynamics of root length production followed a general concentrated pattern with peak typically occurring in June or July, whereas root length mortality followed a general bimodal mortality pattern with the dominant peak in May and the secondary peak in August or October. Furthermore, the seasonal patterns of root length production and mortality were similar across years, especially for the first-order and the second-order roots. These results from long-term observation were beneficial for reducing uncertainty of characterizing fine root demography in consideration of large variation among years. Our findings highlight it is important for better understanding of fine root dynamics and determining root demography through distinguishing observation years and root branch orders.

The PL emission and carrier relaxation of CuInP2S6 vary greatly with temperature under phase transition, while the two-photon absorption changes slightly with temperature.

Rhizosphere effects (REs) play important roles in regulating carbon (C) and nutrient cycling in terrestrial ecosystems. However, little is known about the REs of mature trees in the field, especially at the ecosystem scale. This study aimed to explore the variation and patterns of REs in natural ecosystems. Here, combining soil monoliths with an adhering soil (shaking fine roots) method was adopted to sample paired rhizosphere soil and bulk soil along an altitudinal gradient. Based on the relative REs and the percentage of rhizosphere soil mass, the REs on soil C and net nitrogen mineralization rates (Cmin and net Nmin) at the ecosystem scale were estimated. Our results showed that the REs on soil processes, soil microbial biomass C and extracellular enzyme activities (β-glucosidase and N-acetyl-glucosaminidase activities), and soil chemical properties (total C, total N, inorganic N, extractable P, K, Ca, Mg, Fe, and Mn) were significantly positive across altitudinal sites, while soil pH was significantly negative. Although the relative REs on investigated variables varied significantly among altitudes, the relative REs did not show a clear trend with the increased altitudes. Across altitudes, the mean magnitude of ecosystem-level REs on Cmin and net Nmin were 19% (ranging from 4% to 48%) and 16% (ranging from 3% to 34%), respectively. Furthermore, the magnitude of ecosystem-level rhizosphere effects increased linearly with the increased altitudes. The altitudinal patterns of ecosystem-level RE mainly depend on the percentage of rhizosphere soil mass. In conclusion, our results provided a set of new evidence for the REs, and highlighted the need to incorporate REs into land C and N models.

Aims Rhizosphere is a hotspot for soil C and N biogeochemical cycling in terrestrial ecosystems. Our understanding of interaction between C and N mineralization mainly comes from the bulk soils, yet it is unknown the interaction in the rhizosphere soils. The study aimed to identify interactions between soil C and N mineralization in paired rhizosphere soils and bulk soils. Methods We used the “soil adhering to fine roots after shaking” method to collect paired rhizosphere soils and bulk soils along an altitudinal forest gradient. Soil C mineralization rates (Cmin) and net N mineralization rates (Nmin) were determined with laboratory incubation. Results We found a strong positive relationship between Cmin and Nmin in the rhizosphere soils across sites, whereas Cmin was not correlated with Nmin in the bulk soils. Furthermore, soil properties, microbial biomass C (MBC) and extracellular enzyme activities showed substantial paths affecting Cmin and Nmin using structural equation model. The coupling of Cmin and Nmin in rhizosphere soils could be triggered by root-soil interactions, resulting in the higher level of MBC, soil total C, soil total N, extracellular enzyme activities and specific microbial community structure. By contrast, the decoupling of Cmin and Nmin in the bulk soils might be attributed to the lower level of MBC and extracellular enzyme activities. Conclusions Our results demonstrated that soil C and N mineralization coupled in the rhizosphere rather than the bulk soils. These results highlight the need to distinguish rhizosphere from bulk soils for simulating soil C and N cycling in terrestrial ecosystems.

Plant litter inputs can influence soil organic carbon (SOC) decomposition via the priming effect. However, our understanding of the priming effect and underlying mechanisms is primarily from studies with leaf litter addition, while little is known about root litter effects, particularly of woody plants. Here, using a13C natural tracer approach, we conducted a 12-week incubation experiment to investigate litter decomposition and priming effect of mature-tree root orders (1st to 5th) of Cunninghamia lanceolata (Lamb.) Hook. We explored how litter decomposition and the priming effect were related to microbial biomass of main groups, enzyme activities, and root tissue chemistry. Root litter decomposition rates increased with increasing root order, especially during the first 4 weeks, which was likely due to higher non-structural C and lower tannin concentrations for higher order roots. A negative priming effect occurred at this initial intensive stage when microbes may have preferred utilizing litter-derived labile C. Subsequently, the priming effect switched to positive, and showed larger priming effects for the higher order roots than the lower order ones. Higher order roots also showed higher fungi to bacteria ratios and enzyme activities than the lower order roots. These patterns of fungi to bacteria ratios and enzyme activities and thus the priming effect could be attributed to the difference in carbon:nitrogen ratio among root orders. Overall, we for the first time provide strong evidence for the effect of root order on the priming effect, and thus highlight that separating root litter based on root order is necessary for accurately evaluating its influence on SOC decomposition.

Rhizosphere priming is crucial for regulating soil carbon and nitrogen biogeochemical cycles. An appreciable number of studies have been conducted to quantify the rhizosphere priming effect (RPE), and have shown that the RPE is sensitive to changes of plant and soil conditions. These diverse results across individual studies offer us an opportunity to explore for potential general patterns and variability. In this study, we conducted a meta-analysis of RPE values taken from 31 publications. Our results showed that, on average, the RPE enhanced soil organic carbon mineralization rate by 59% across all studies. The magnitudes of the RPE significantly varied among plant types and soil texture. Within plant types, woody species showed the highest RPE followed by grasses while crops had the lowest level of the RPE, indicating that plant traits and physiology may exert important controls on the RPE. Soils with finer texture tended to produce stronger RPEs than soils with coarser texture, suggesting that interactions between the rhizosphere and the soil matrix may modulate the RPE. Furthermore, the level of the RPE is positively correlated with aboveground plant biomass, but surprisingly not with root biomass which is the commonly believed key variable for influencing the RPE. In addition, the RPE increased with the length of experimental duration, which implies that the RPE may persist much longer than previously believed because it impacts stabilized soil carbon more than labile carbon as the length of experimental duration increases. Overall, the results from this meta-analysis further illustrate several complex features of the RPE and call for future attentions to decipher this complexity.

Root turnover is a key process contributing to soil carbon storage, nutrient cycling, and other ecosystem functions. However, quantifying root turnover rates remains highly uncertain and methodologically challenging. Field rhizotrons were employed to quantify root turnover times using median longevities of five branching orders in a Larix gmelinii plantation. Root images were recorded by scanning the rhizotron windows at a monthly interval during four growing seasons. Root demographic data and branching orders were obtained by analyzing these images using Rootfly software coupled with manual mouse‐tracing of individual roots. Root longevities and turnover estimates were calculated using these data. Roots of different branching orders showed significantly different turnover times. The mean turnover times of the first‐order roots and second‐order roots were 284 and 994 d, respectively. Roots of higher branching orders (third to fifth orders) remained alive at the end of the 4‐yr experimental period, indicating much longer turnover times than the duration of the experiment. Root turnover times increased exponentially with branching orders. Further analysis of these data suggested that root branching orders combined with sampling biases, timing of root cohorts, and longevity distribution patterns crucially influenced root turnover times. The method of combining field glass rhizotrons with electronic scanning permits quantification of root turnover for five branching orders in a temperate forest. The overall result empirically demonstrates the crucial role of branching orders for accurately quantifying root turnover times.

The architecture and morphology of absorptive roots show substantial plasticity in response to forest management practices. These traits are known to play important roles in the acquisition of soil resources by trees. However, the effects of nutrient addition, thinning and pruning on absorptive root traits and their feedback to root foraging strategies remain unclear. We investigated the values and plasticity of traits related to nutrient foraging (root architecture, growth and morphology) for first- and second-order roots (absorptive roots) following nitrogen (N) addition, phosphorous (P) addition, thinning and pruning treatments in a young Chinese fir ( Cunninghamia lanceolata ) plantation. We measured twelve traits of absorptive roots under the five treatments (control, N addition, P addition, thinning and pruning) and determined relationships between the values and plasticity of root traits and stem growth rate. We demonstrated clear patterns of root traits and their plasticity in response to the treatments. N and P addition increased root biomass (B) and root tissue density (RTD). Thinning and pruning led to larger specific root length (SRL) and root nitrogen concentrations (N), but resulted in lower root length (L) and root length density (RLD). Principal component analysis of the measured traits and plasticity provided evidence for two suites of traits related to resource acquisition and conservation strategies among treatments. The trait syndromes exhibiting resource acquisition strategy (SRL and N) is arrayed well along the positive part of the first axis, whereas the opposite trait syndromes with resource conservation strategy (root diameter and RTD) is along the negative part of the first axis. The first axis also separates nutrient-induced treatments (N and P addition) from light-mediated treatments (pruning and thinning). Furthermore, first-order root exhibited higher foraging sensitivity and precision (expressed as relative fine root length difference) in response to P addition than to the other treatments. The foraging sensitivity and precision, plus B, L and RLD showed that first-order roots are more responsive to environment than second-order roots across the treatments. Stem growth rate was correlated positively with absorptive root traits (biomass, root surface area index, root length density, and root tip number) after thinning, but negatively with these traits after N and P addition. These findings demonstrate that C . lanceolata finely tuned root foraging strategies between first- and second-order root traits and their plasticity at the intraspecific level in response to forest management practices. Further studies may explore nutrient-induced and light-mediated foraging strategies between absorptive roots across root branch orders in mature Chinese fir plantation.

Increases in carbon (C) inputs to soil can replenish soil organic C (SOC) through various mechanisms. However, recent studies have suggested that the increased C input can also stimulate the decomposition of old SOC via priming. Whether the loss of old SOC by priming can override C replenishment has not been rigorously examined. Here we show, through data–model synthesis, that the magnitude of replenishment is greater than that of priming, resulting in a net increase in SOC by a mean of 32% of the added new C. The magnitude of the net increase in SOC is positively correlated with the nitrogen-to-C ratio of the added substrates. Additionally, model evaluation indicates that a two-pool interactive model is a parsimonious model to represent the SOC decomposition with priming and replenishment. Our findings suggest that increasing C input to soils likely promote SOC accumulation despite the enhanced decomposition of old C via priming., The magnitudes of replenishment and priming, two important but opposing fluxes in soil organic carbon (SOC) dynamics, have not been compared. Here the authors show that the magnitude of replenishment is greater than that of priming, resulting in a net SOC accumulation after additional carbon input to soils.

Forest gap models are important tools for assessing the impact of global climate change on forest dynamics of tree species composition and size structure. In this study, the FAREAST gap model was used to examine the response of forest dynamics on Gongga Mountain, which is located on the southeastern fringe of the Tibetan Plateau, under three climate change scenarios. The simulated results showed that the climax community of the deglaciation slash would be mixed species of Picea brachytyla, Tsuga chinensis, and Pinus densata under climate change scenarios, as opposed to the pure Abies fabri forest under the current climate. Climate change also drove replacement of Populus purdomiis by Betula utilis, which became the most abundant pioneer tree species on the deglaciation slash. Under scenarios of climate change, three responses of the four typical forests distributed between 2200 and 3580 m above sea level are observed, such as dieback of today’s forest at 2200 and 3150 m, gradual change of the species composition at 2780 m, and afforestation at 3580 m. It is worth noting that the scenarios of climatic change are of inherent uncertainty, in the same way as the formulation of the ecological factors used in the models. It is suggested that simulations not be interpreted as predictions of the future development of the forest, but as a means of assessing their sensitivity to climate change. It is concluded that mountainous forests are quite sensitive to climate change.