Fuzhong Wu

Cadmium accumulation and growth responses of a poplar (Populus deltoids × Populus nigra) in cadmium contaminated purple soil and alluvial soil

To characterize the phytoextraction efficiency of a hybrid poplar (Populus deltoidsxPopulus nigra) in cadmium contaminated purple soil and alluvial soil, a pot experiment in field was carried out in Sichuan basin, western China. After one growing period, the poplar accumulated the highest of 541.98+/-19.22 and 576.75+/-40.55 microg cadmium per plant with 110.77+/-12.68 and 202.54+/-19.12 g dry mass in these contaminated purple soil and alluvial soil, respectively. Higher phytoextraction efficiency with higher cadmium concentration in tissues was observed in poplar growing in purple soil than that in alluvial soil at relative lower soil cadmium concentration. The poplar growing in alluvial soil had relative higher tolerance ability with lower reduction rates of morphological and growth characters than that in purple soil, suggesting that the poplar growing in alluvial soil might display the higher phytoextraction ability when cadmium contamination level increased. Even so, the poplars exhibited obvious cadmium transport from root to shoot in both soils regardless of cadmium contamination levels. It implies that this examined poplar can extract more cadmium than some hyperaccumulators. The results indicated that metal phytoextraction using the poplar can be applied to clean up soils moderately contaminated by cadmium in these purple soil and alluvial soil.

Decomposition of Abies faxoniana litter varies with freeze-thaw stages and altitudes in subalpine/alpine forests of southwest China

Abstract Freeze–thaw events in winter may affect litter decomposition in cold biomes but few reports are available. We characterized the fir (Abies faxoniana) litter decomposition over a whole winter (November 2008 to April 2009) during the late autumn, deep winter, and early spring stages. The mass loss, nutrient release, and quality change of fir litter were determined using the litterbag method at 2700, 3000, 3300, and 3600 m altitude in southwest China. Over the winter an average of 18% mass, 27% C, 50% N, 40% P, 36% K, 30% cellulose, and 14% lignin were lost. Of these total losses, a majority loss of mass (70%), C (65%), N (50%), P (58%), K (42%), cellulose (70%), and lignin (68%) occurred during the deep winter stage. The highest loss rate of mass (19.2%) and lignin (16.4%) but the lowest N loss (47.9%) was at the highest 3600 m altitude. Soil freeze–thaw cycle resulted in significant losses of mass, while mass loss rate did not increase under the higher mean soil temperature during each stage. Our results confirmed that the physical process seemed to be the most important process for cold season decomposition in the cold biome.

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.

The dynamics pattern of soil carbon and nutrients as soil thawing proceeded in the alpine/subalpine forest

Abstract Little attention has been given to the dynamics of soil C and nutrients during the soil thawing period in subalpine/alpine forests. To understand the ecological linkages between the non-growing and growing seasons, soil C and nutrients were measured in the primary fir (Abies faxoniana) forest, fir and birch (Betula albosinensis) mixed forest and secondary fir forest in the subalpine/alpine regions of western China. Soils were sampled as soil thawing proceeded from 5 March, 15 March, 25 March, 5 April and 15 April to 25 April 2009, based on monitored soil temperatures. Frequencies of temperature fluctuations (below and above 0 °C) during the soil thawing period depended on the altitude. The soil organic layer showed higher contents and stocks of C, N and P compared with the mineral soil layer. Since the soil organic layer was more directly exposed to environmental changes, the variations of soil C and nutrients in the soil organic layer were more apparent than those in the mineral soil layer. The fluctuations of soil C and nutrients varied with the altitude during soil thawing period. Soil C and nutrient concentrations decreased sharply at the beginning of soil thawing, and thereafter increased in the mixed and secondary forest, which were different to the changes in the primary forest. Soil available nutrients, except for −N in the primary forest, showed an increasing tendency in the early stage of the thawing period, but soil available N and P decreased in the later stage of the thawing period. The increasing soil temperature had little effect on soil nutrient availability during the thawing period. The results indicated that soil carbon and nutrients were significantly affected by the length of freeze–thaw period, which is beneficial towards understanding the interactions between wintertime and the growing season.

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.

The responses of early foliar litter humification to reduced snow cover during winter in an alpine forest

Ni, X., Yang, W., Li, H., Xu, L., He, J., Tan, B. and Wu, F. 2014. The responses of early foliar litter humification to reduced snow cover during winter in an alpine forest. Can. J. Soil Sci. 94: 453-461. Snow cover can be reduced by ongoing winter warming in alpine biomes, affecting foliar litter humification, but few reports are available. To quantitatively clarify how early foliar litter humification responds to reduced snow cover in winter, a field litterbag experiment was conducted in an alpine forest in southwestern China. Mass losses, ΔlogK, E4/E6, degrees of humification and humification rates of six typical local foliar litters were investigated at the snow formation, snow cover and snow melt stage under snowpack levels differing in depth (deep snowpack, medium snowpack, thin snowpack, no snowpack) from November 2012 to April 2013. The results indicated that 14-15% of willow (Salix paraplesia), 8-9% of fir (Abies faxoniana), 6-7% of birch (Betula albo-sinensis), 5-8% of cypress (Sabina saltuaria), larch (Larix mastersiana) and azalea (Rhododendron lapponicum) foliar litter was humified, which was about 50% of what decomposed during the first winter. Moreover, the early humification of foliar litter (except for fir and birch) responded positively to the reduced snow cover, but mass loss exhibited negative responses. Such results suggest that reduced snow cover in winter would increase soil carbon or other material sequestration in the scenario of climate change.

Foliar Litter Nitrogen Dynamics as Affected by Forest Gap in the Alpine Forest of Eastern Tibet Plateau

There is increasing attention on the effects of seasonal snowpack on wintertime litter decomposition, as well as the processes following it, in cold biomes. However, little information is available on how litter nitrogen (N) dynamics vary with snowpack variations created by tree crown canopies in alpine forests. Therefore, to understand the effects of seasonal snowpack on litter N dynamics during different critical stages, litterbags with fir (Abies faxoniana), birch (Betula albo-sinensis), larch (Larix mastersiana) and cypress (Sabina saltuaria) foliar litter were placed on the forest floor beneath snowpack created by forest gaps in the eastern Tibet Plateau. The litterbags were sampled at the onset of freezing, deep freezing, thawing and growing stages from October 2010 to October 2012. Mass loss and N concentrations in litter were measured. Over two years of decomposition, N release occurred mainly during the first year, especially during the first winter. Litter N release rates (both in the first year and during the entire two-year decomposition study period) were higher in the center of canopy gaps than under closed canopy, regardless of species. Litter N release rates in winter were also highest in the center of canopy gaps and lowest under closed canopy, regardless of species, however the reverse was found during the growing season. Compared with broadleaf litter, needle litter N release comparisons of gap center to closed canopy showed much stronger responses to the changes in snow cover in winter and availability of sunshine during the growing season. As the decomposition proceeded, decomposing litter quality, microbial biomass and environmental temperature were important factors related to litter N release rate. This suggests that if winter warm with climate change, reduced snow cover in winter might slow down litter N release in alpine forest.

Effects of afforestation with Eucalyptus grandis on soil physicochemical and microbiological properties

It is generally believed that plantations of Eucalyptus bring about a decrease in soil fertility. Soil physicochemical and microbiological properties were measured across a range of E. grandis plantation ages (1–10 years) in south-western China to determine whether and how eucalypt afforestation of agricultural land affected the soil fertility. The results indicate that afforestation with E. grandis caused changes in soil properties with soil depth, and the changes were dependent on the stand age. Soil bulk density decreased significantly, but water-holding capacity increased significantly with time. Soil organic matter content, C : N ratio, and soil microbial biomass C and N concentrations showed an initial phase of decline and then increased significantly over time in the upper soil layers of E. grandis plantations aged from 1 to 4 or 5 years. Soil pH in E. grandis plantations did not change significantly with stand age or soil layer. Cation exchange capacity in the upper soil layer of E. grandis plantations increased significantly over time. Total exchangeable bases and base saturation in the soil decreased significantly with depth and with increasing plantation age. Furthermore, E. grandis afforestation of arable soils had no significant effects on total N, total P, and available P contents. The requirements of the trees, understory microenvironmental conditions, and allelopathic effects might play important roles in the dynamic changes of soil physicochemical and microbiological properties. The results demonstrate the progressive development of processes that lead to the restoration of soil fertility following E. grandis afforestation of arable soils. However, most of the properties measured for the afforested soils resembled the properties of arable soils and did not resemble those of the soil of control forests. Thus, reversion of soil properties in the study plantations is likely to require a considerable period of time. Long-term research is needed to understand changes in the soil properties resulting from afforestation with Eucalyptus and to predict future trends.

Changes in soil microbial biomass and bacterial diversity during the transition from winter to growing season in the subalpine/alpine forests

Changes in microbial community from winter to growing season are helpful to understand their selfadaptations in the high-frigid ecosystem. A field experiment was conducted to investigate soil microbial biomass and bacterial diversity by PCR-DGGE in the primary fir (Abies faxoniana) forest (PF), fir and birch (Betula albosinensis) mixed forest (MF) and secondary fir forest (SF) in western China. Soil samples were collected in March, April, May and August, 2009. The microbial biomass C (MBC) in soil organic layer (OL) increased from winter to growing season, but insignificant changes were observed in soil thawing period (April and May). In contrast, MBC in soil mineral layer (ML) displayed an obvious decrease at the end of soil thawing (May) and then increased. Rich DGGE bands indicating rich bacteria populations have been detected even under completely soil frozen condition. The richness of bacteria community significantly decreased during soil thawing period and then increased to growing season, except for which in OL of MF. The similarity of bacterial communities implied significant community changes during the transition, showing more sensitivity to temperature than forest type and soil layer. The results here are of ecological significance in explaining the adaptation of microorganisms in the high-frigid areas.