Kai Yue

Stimulation of terrestrial ecosystem carbon storage by nitrogen addition: a meta-analysis

Elevated nitrogen (N) deposition alters the terrestrial carbon (C) cycle, which is likely to feed back to further climate change. However, how the overall terrestrial ecosystem C pools and fluxes respond to N addition remains unclear. By synthesizing data from multiple terrestrial ecosystems, we quantified the response of C pools and fluxes to experimental N addition using a comprehensive meta-analysis method. Our results showed that N addition significantly stimulated soil total C storage by 5.82% ([2.47%, 9.27%], 95% CI, the same below) and increased the C contents of the above- and below-ground parts of plants by 25.65% [11.07%, 42.12%] and 15.93% [6.80%, 25.85%], respectively. Furthermore, N addition significantly increased aboveground net primary production by 52.38% [40.58%, 65.19%] and litterfall by 14.67% [9.24%, 20.38%] at a global scale. However, the C influx from the plant litter to the soil through litter decomposition and the efflux from the soil due to microbial respiration and soil respiration showed insignificant responses to N addition. Overall, our meta-analysis suggested that N addition will increase soil C storage and plant C in both above- and below-ground parts, indicating that terrestrial ecosystems might act to strengthen as a C sink under increasing N deposition.

Influence of multiple global change drivers on terrestrial carbon storage: additive effects are common

The interactive effects of multiple global change drivers on terrestrial carbon (C) storage remain poorly understood. Here, we synthesise data from 633 published studies to show how the interactive effects of multiple drivers are generally additive (i.e. not differing from the sum of their individual effects) rather than synergistic or antagonistic. We further show that (1) elevated CO2 , warming, N addition, P addition and increased rainfall, all exerted positive individual effects on plant C pools at both single-plant and plant-community levels; (2) plant C pool responses to individual or combined effects of multiple drivers are seldom scale-dependent (i.e. not differing from single-plant to plant-community levels) and (3) soil and microbial biomass C pools are significantly less sensitive than plant C pools to individual or combined effects. We provide a quantitative basis for integrating additive effects of multiple global change drivers into future assessments of the C storage ability of terrestrial ecosystems.

Foliar litter decomposition in an alpine forest meta-ecosystem on the eastern Tibetan Plateau

Litter decomposition is a biological process fundamental to element cycling and a main nutrient source within forest meta-ecosystems, but few studies have looked into this process simultaneously in individual ecosystems, where environmental factors can vary substantially. A two-year field study conducted in an alpine forest meta-ecosystem with four litter species (i.e., willow: Salix paraplesia, azalea: Rhododendron lapponicum, cypress: Sabina saltuaria, and larch: Larix mastersiana) that varied widely in chemical traits showed that both litter species and ecosystem type (i.e., forest floor, stream and riparian zone) are important factors affecting litter decomposition, and their effects can be moderated by local-scale environmental factors such as temperature and nutrient availability. Litter decomposed fastest in the streams followed by the riparian zone and forest floor regardless of species. For a given litter species, both the k value and limit value varied significantly among ecosystems, indicating that the litter decomposition rate and extent (i.e., reaching a limit value) can be substantially affected by ecosystem type and the local-scale environmental factors. Apart from litter initial acid unhydrolyzable residue (AUR) concentration and its ratio to nitrogen concentration (i.e., AUR/N ratio), the initial nutrient concentrations of phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) were also important litter traits that affected decomposition depending on the ecosystem type.

Chromium, Cadmium, and Lead Dynamics During Winter Foliar Litter Decomposition in an Alpine Forest River

ABSTRACT Little information is currently available about heavy metal dynamics during litter decomposition in areas receiving few inputs of exotic metals. A field litter decomposition experiment was conducted during the winter in an alpine forest river on the eastern Tibetan Plateau. Concentrations, release rates, and release rate per day of chromium (Cr), cadmium (Cd), and lead (Pb) were investigated in the foliar litter of willow (Salix paraplesia), azalea (Rhododendron lapponicum), cypress (Sabina saltuaria), and larch (Larix mastersiana) during the prefreezing, freezing, and thawing periods. Concentrations of Cr in willow, cypress, and larch; Cd in all foliar litter types; and Pb in azalea foliar litter increased following incubation over an entire winter. Both Cr and Pb showed patterns of accumulation during the prefreezing period and patterns of release in the freezing and thawing periods, but Cd showed accumulation in all three periods. Water temperature, pH, flow velocity, conductivity, and nutrient availability in the river were significantly related to the dynamics of these heavy metals in the decomposing foliar litter. The heavy metal accumulation pattern in running water suggested an absolute increase in metal mass, indicating that litter may act as an efficient metal “cleaner” and contribute to an ecosystems capacity for self-purification.

Dynamics of multiple metallic elements during foliar litter decomposition in an alpine forest river

Key messageCompared with previously reported data, we found that plant litter decomposes faster in river ecosystem than on forest floor in a comparable period, but the dynamics of metallic elements during litter decomposition in river are likely to share common patterns with the corresponding ones in decomposing litter on forest floor.ContextLitter decomposition in terrestrial lotic ecosystem is one of the most important pathways for metallic elements cycling, while little information is currently available about the dynamics of metallic elements in the decomposing litter of lotic ecosystems.Aims and methodsThe concentrations and release rates of potassium (K), calcium (Ca), sodium (Na), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), and aluminium (Al) were investigated in the decomposing foliar litter of four dominant species in an alpine forest river.ResultsOver a 1-year period of decomposition, K, Ca, and Mg were released from virtually all types of litter, whereas Na, Fe, Mn, Zn, Cu, and Al were released from willow litter but accumulated in azalea, cypress, and larch litters during litter decomposition. Litter species, decomposition period, and river water characteristics (e.g., temperature, pH, flow velocity, and nutrient availability) were significantly related to the dynamics of these metallic elements in decomposing litter.ConclusionOur results suggested that the similarity between the dynamics of metallic elements in the decomposing litter of lotic ecosystems reported here and previously for forest floors indicates a general pattern for the cycling of metallic element across different ecosystem types, and the net accumulation patterns for elements such as Zn, Cu, and Al during litter decomposition suggested that some litter species may act as efficient “cleaner” for metal purification in future ecological engineering.

Study type and plant litter identity modulating the response of litter decomposition to warming, elevated CO2, and elevated O3: A meta‐analysis

Plant litter decomposition is one of the most important ecosystem carbon flux processes in terrestrial ecosystems and is usually regarded as sensitive to climate change. The goal of the present study was to examine the effects of changing climate variables on litter decomposition. By synthesizing data from multiple terrestrial ecosystems, we quantified the response of the litter decomposition rate to the independent effects of warming, elevated carbon dioxide (CO2), elevated ozone (O3), and the combined effects of elevated CO2 + elevated O3. Across all case studies, warming increased the litter decomposition rate significantly by 4.4%, but this effect could be reduced as a result of the negatively significant effects of elevated CO2 and elevated CO2 + elevated O3. The combined effects of elevated CO2 + elevated O3 decreased the litter decomposition rate significantly, and the magnitude appeared to be higher than that of the elevated CO2 per se. Moreover, the study type (field versus laboratory), ecosystem type, and plant litter identity and functional traits (growth form and litter form) were all important moderators regulating the response of litter decomposition to climate warming and elevated CO2 and O3. Although litter decomposition rate may show a moderate change as a result of the effects of multiple changing climate variables, the process of litter decomposition would be strongly altered due to the differing mechanisms of the effects of each climate change variable, suggesting that the global carbon cycle and biogeochemistry could be substantially affected.

Contribution of Soil Fauna to Foliar Litter-Mass Loss in Winter in an Ecotone between Dry Valley and Montane Forest in the Upper Reaches of the Minjiang River

Litter decomposition during winter can provide essential nutrients for plant growth in the subsequent growing season, which plays important role in preventing the expansion of dry areas and maintaining the stability of ecotone ecosystems. However, limited information is currently available on the contributions of soil fauna to litter decomposition during winter in such ecosystems. Therefore, a field experiment that included litterbags with two different mesh sizes (0.04 mm and 3 mm) was conducted to investigate the contribution of soil fauna to the loss of foliar litter mass in winter from November 2013 to April 2014 along the upper reaches of the Minjiang River. Two litter types of the dominant species were selected in each ecosystem: cypress (Cupressus chengiana) and oak (Quercus baronii) in ecotone; cypress (Cupressus chengiana) and clovershrub (Campylotropis macrocarpa) in dry valley; and fir (Abies faxoniana) and birch (Betula albosinensis) in montane forest. Over one winter incubation, foliar litter lost 6.0%-16.1%, 11.4%-26.0%, and 6.4%-8.5% of initial mass in the ecotone, dry valley and montane forest, respectively. Soil fauna showed obvious contributions to the loss of foliar litter mass in all of the ecosystems. The highest contribution (48.5%-56.8%) was observed in the ecotone, and the lowest contribution (0.4%-25.8%) was observed in the montane forest. Compared with other winter periods, thawing period exhibited higher soil fauna contributions to litter mass loss in ecotone and dry valley, but both thawing period and freezing period displayed higher soil fauna contributions in montane forest. Statistical analysis demonstrated that the contribution of soil fauna was significantly correlated with temperature and soil moisture during the winter-long incubation. These results suggest that temperature might be the primary control factor in foliar litter decomposition, but more active soil fauna in the ecotone could contribute more in litter decomposition and its related ecological processes in this region.

Individual and combined effects of multiple global change drivers on terrestrial phosphorus pools: A meta-analysis

Human activity-induced global change drivers have dramatically changed terrestrial phosphorus (P) dynamics. However, our understanding of the interactive effects of multiple global change drivers on terrestrial P pools remains elusive, limiting their incorporation into ecological and biogeochemical models. We conducted a meta-analysis using 1751 observations extracted from 283 published articles to evaluate the individual, combined, and interactive effects of elevated CO2, warming, N addition, P addition, increased rainfall, and drought on P pools of plant (at both single-plant and plant-community levels), soil and microbial biomass. Our results suggested that (1) terrestrial P pools showed the most sensitive responses to the individual effects of warming and P addition; (2) P pools were consistently stimulated by P addition alone or in combination with simultaneous N addition; (3) environmental and experimental setting factors such as ecosystem type, climate, and latitude could significantly influence both the individual and combined effects; and (4) the interactive effects of two-driver pairs across multiple global change drivers are more likely to be additive rather than synergistic or antagonistic. Our findings highlighting the importance of additive interactive effects among multiple global change drivers on terrestrial P pools would be useful for incorporating P as controls on ecological processes such as photosynthesis and plant growth into ecosystem models used to analyze effects of multiple drivers under future global change.

Assessing the temporal dynamics of aquatic and terrestrial litter decomposition in an alpine forest

1. Litter decomposition supplies nutrients and energy within and among aquatic and terrestrial ecosystems. It is driven by several biotic and abiotic factors, the relative importance of which may change during litter decay. However, to date, very few studies have addressed the temporal dynamics of such factors across aquatic and terrestrial ecosystems, which limits our understanding of litter decomposition process. 2. To assess the temporal dynamics of major abiotic and biotic litter decomposition drivers, we conducted a 2-year field experiment to evaluate the losses of foliar litter carbon (C) and nitrogen (N) in alpine streams, riparian zones and forest floors. Environmental (soil, water and climatic) factors were continuously monitored, and incubated plant litter was sampled over time to assess temporal changes in litter chemistry and microbial diversity. 3. We analysed sequential litter decomposition stages based on mass-loss intervals and used structural equation modelling to disentangle the relative importance of each biotic and abiotic driver. 4. Our results suggested that across the aquatic and terrestrial ecosystems, litter C and N loss was generally controlled by a common hierarchy of drivers: (a) Environment and initial litter quality regulated C and N loss via both direct and indirect effects, and their total effects were mainly significant in the early and late decomposition stages, respectively; (b) changes in litter chemistry significantly influenced litter decomposition throughout the decomposition process, mainly via direct effects; and (c) microbial diversity per se showed minimal effects on litter C and N loss. 5. The identified common hierarchy of biotic and abiotic drivers and their direct and indirect effects on C and N loss at different decomposition stages across aquatic and terrestrial ecosystems indicates the possibility of integrating aquatic and terrestrial decomposition into a single framework for future construction of models accounting for temporal dynamics of litter decomposition.

Different Responses of Terrestrial C, N, and P Pools and C/N/P Ratios to P, NP, and NPK Addition: a Meta-Analysis

Although phosphorus (P) enrichment alone or in combination with other nutrients such as nitrogen (N) and potassium (K) due to anthropogenic activities may modify the nutrient pools and nutrient elemental ratios of terrestrial ecosystems, few studies have revealed the global effects of P alone or in combination with N and K enrichment on terrestrial ecosystems. In this study, we conducted a meta-analysis of the impacts of P addition alone or in combination with N and K on the C, N, and P pools and C/N/P ratios of plants, soils, and microbial biomass in terrestrial ecosystems. The results suggest that the following changes occurred: (1) P addition resulted in a significantly larger plant C pool, which was further enhanced when extra N and K were added. (2) The soil and microbial biomass C pools and the plant, soil, and microbial biomass N pools were minimally affected by P addition at the global scale but were noticeably affected when N and K were simultaneously added. (3) The P pools of the plants, soil, and microbial biomass were significantly and consistently enhanced by the addition of P, NP, and NPK. (4) The plant C/N, N/P, and C/P ratios were significantly reduced when P was added, while the C/N/P ratios in the soil and microbial biomass were minimally affected. These results, which show the inconsistent responses of plant, soil, and microbial biomass nutrient pools and elemental ratios to P, NP, and NPK addition, improve our understanding of terrestrial ecosystem functions under global change scenarios.