Forest soils play an important role in controlling global warming by reducing atmospheric methane (CH
) concentrations. However, little attention has been paid to how nitrogen (N) deposition may ...alter microorganism communities that are related to the CH
cycle or CH
oxidation in subtropical forest soils. We investigated the effects of N addition (0, 30, 60, or 90 kg N ha
yr
) on soil CH
flux and methanotroph and methanogen abundance, diversity, and community structure in a Moso bamboo (Phyllostachys edulis) forest in subtropical China. N addition significantly increased methanogen abundance but reduced both methanotroph and methanogen diversity. Methanotroph and methanogen community structures under the N deposition treatments were significantly different from those of the control. In N deposition treatments, the relative abundance of Methanoculleus was significantly lower than that in the control. Soil pH was the key factor regulating the changes in methanotroph and methanogen diversity and community structure. The CH
emission rate increased with N addition and was negatively correlated with both methanotroph and methanogen diversity but positively correlated with methanogen abundance. Overall, our results suggested that N deposition can suppress CH
uptake by altering methanotroph and methanogen abundance, diversity, and community structure in subtropical Moso bamboo forest soils.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Temperate- and high-latitude forests have been shown to contribute a carbon sink in the Northern Hemisphere, but fewer studies have addressed the carbon balance of the subtropical forests. In the ...present study, we integrated eddy covariance observations established in the 1990s and 2000s to show that East Asian monsoon subtropical forests between 20°N and 40°N represent an average net ecosystem productivity (NEP) of 362 ± 39 g C m ⁻² yr ⁻¹ (mean ± 1 SE). This average forest NEP value is higher than that of Asian tropical and temperate forests and is also higher than that of forests at the same latitudes in Europe–Africa and North America. East Asian monsoon subtropical forests have comparable NEP to that of subtropical forests of the southeastern United States and intensively managed Western European forests. The total NEP of East Asian monsoon subtropical forests was estimated to be 0.72 ± 0.08 Pg C yr ⁻¹, which accounts for 8% of the global forest NEP. This result indicates that the role of subtropical forests in the current global carbon cycle cannot be ignored and that the regional distributions of the Northern Hemisphere's terrestrial carbon sinks are needed to be reevaluated. The young stand ages and high nitrogen deposition, coupled with sufficient and synchronous water and heat availability, may be the primary reasons for the high NEP of this region, and further studies are needed to quantify the contribution of each underlying factor.
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Drought has been one of the most important limiting factors for crop production, which deleteriously affects food security worldwide. The main objective of the present study was to quantitatively ...assess the effect of drought on the agronomic traits (e.g., plant height, biomass, yield, and yield components) of rice and wheat in combination with several moderators (e.g., drought stress intensity, rooting environment, and growth stage) using a meta-analysis study. The database was created from 55 published studies on rice and 60 published studies on wheat. The results demonstrated that drought decreased the agronomic traits differently between rice and wheat among varying growth stages. Wheat and rice yields decreased by 27.5% and 25.4%, respectively. Wheat grown in pots showed greater decreases in agronomic traits than those grown in the field. Rice showed opposite growing patterns when compared to wheat in rooting environments. The effect of drought on rice increased with plant growth and drought had larger detrimental influences during the reproductive phase (e.g., blooming stage, filling stage, and maturity). However, an exception was found in wheat, which had similar decreased performance during the complete growth cycle. Based on these results, future droughts could produce lower yields of rice and wheat when compared to the current drought.
Moso bamboo can rapidly complete its growth in both height and diameter within only 35-40 days after shoot emergence. However, the underlying mechanism for this "explosive growth" remains poorly ...understood. We investigated the dynamics of non-structural carbohydrates (NSCs) in shoots and attached mature bamboos over a 20-month period. The results showed that Moso bamboos rapidly completed their height and diameter growth within 38 days. At the same time, attached mature bamboos transferred almost all the NSCs of their leaves, branches, and especially trunks and rhizomes to the "explosively growing" shoots via underground rhizomes for the structural growth and metabolism of shoots. Approximately 4 months after shoot emergence, this transfer stopped when the leaves of the young bamboos could independently provide enough photoassimilates to meet the carbon demands of the young bamboos. During this period, the NSC content of the leaves, branches, trunks and rhizomes of mature bamboos declined by 1.5, 23, 28 and 5 fold, respectively. The trunk contributed the most NSCs to the shoots. Our findings provide new insight and a possible rational mechanism explaining the "explosive growth" of Moso bamboo and shed new light on understanding the role of NSCs in the rapid growth of Moso bamboo.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The Grain for Green Program (GGP), initiated in 1999, is the largest ecological restoration project in central and western China. Here, for the first time, we performed a meta-analysis and found that ...the GGP largely increased the soil organic carbon (SOC). The SOC was increased by 48.1%, 25.4%, and 25.5% at soil depths of 0-20 cm, 20-40 cm, and 40-60 cm, respectively. Moreover, this carbon accumulation has significantly increased over time since GGP implementation. The carbon accumulation showed a significantly more active response to the GGP in the top 20 cm of soil than in the deeper soil layers. Conversion of cropland to forest could lead to significantly greater SOC accumulation than would the conversion of cropland to grassland. Conversion from cropland to woodland could lead to greater SOC accumulation than would the conversion to either shrubland or orchard. Our results suggest that the GGP implementation caused SOC to accumulate and that there remains a large potential for further accumulation of carbon in the soil, which will help to mitigate climate change in the near future.
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Vegetation restoration on degraded lands has been encouraged worldwide due to its ecological services and function of controlling soil erosion and improving carbon (C) stocks in terrestrial ...ecosystems. Although the processes of runoff and sediment detachment and transport are well recognized, the effects of vegetation restoration on organic C loss through soil erosion are not fully understood within a given landscape. This study conducted a synthesis from 66 sites to evaluate the effects of vegetation restoration on annual C loss induced by soil erosion across the key areas of the ‘Grain for Green’ Program (GGP) in the Loess Plateau, China. The results showed that vegetation restoration has significantly reduced the annual C loss in sediment and from runoff. Since 2000, a total of 8.6 × 106 ha degraded land has been converted to forests, shrubs and grasslands under the GGP, which has reduced runoff by 1.5 × 109 m3 and is associated with 7.3 × 103 Mg C; furthermore, lost sediment has reduced by 348.7 Tg, which is associated with 1.8 Tg C per year, across the Loess Plateau. In the zone with a mean annual precipitation (MAP) < 550 mm, the degraded lands that have been converted to grasslands and shrubs have reduced more soil and water losses than have the lands that have been converted to forests; additionally, in the zone with a MAP >550 mm, the degraded lands that have been converted to forests have less soil erosion than do the lands that have been converted to grasslands and shrubs. Moreover, C loss induced by soil erosion was mainly affected by plant cover, soil porosity, slope, land-use change, and rainfall intensity on the Loess Plateau. This study suggests that optimal vegetation restoration measures should be adopted based on local conditions to reduce C loss induced by soil erosion.
•Vegetation restoration significantly reduced C loss in annual runoff and sediment.•Vegetation restoration driven by land-use changes could reduce the soil erosion.•Soil, topography, land uses and rainfall intensity affecting soil erosion induced C loss.•Optimal vegetation restoration measures should be adopted based on local conditions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Forest productivity may be determined not only by biodiversity but also by environmental factors and stand structure attributes. However, the relative importance of these factors in determining ...productivity is still controversial for subtropical forests.
Based on a large dataset from 600 permanent forest inventory plots across subtropical China, we examined the relationship between biodiversity and forest productivity and tested whether stand structural attributes (stand density in terms of trees per ha, age and tree size) and environmental factors (climate and site conditions) had larger effects on productivity. Furthermore, we quantified the relative importance of environmental factors, stand structure and diversity in determining forest productivity.
Diversity, together with stand structure and site conditions, regulated the variability in forest productivity. The relationship between diversity and forest productivity did not vary along environmental gradients. Stand density and age were more important modulators of forest productivity than diversity.
Synthesis. Diversity had significant and positive effects on productivity in species‐rich subtropical forests, but the effects of stand density and age were also important. Our work highlights that while biodiversity conservation is often important, the regulation of stand structure can be even more important to maintain high productivity in subtropical forests.
Diversity had significant and positive effects on productivity in species‐rich subtropical forests, but the effects of stand density and age were also important. Our work highlights that while biodiversity conservation is often important, the regulation of stand structure can be even more important to maintain high productivity in subtropical forests.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
With a pace of about twice the observed rate of global warming, the temperature on the Qinghai‐Tibetan Plateau (Earth's ‘third pole’) has increased by 0.2 °C per decade over the past 50 years, which ...results in significant permafrost thawing and glacier retreat. Our review suggested that warming enhanced net primary production and soil respiration, decreased methane (CH4) emissions from wetlands and increased CH4 consumption of meadows, but might increase CH4 emissions from lakes. Warming‐induced permafrost thawing and glaciers melting would also result in substantial emission of old carbon dioxide (CO2) and CH4. Nitrous oxide (N2O) emission was not stimulated by warming itself, but might be slightly enhanced by wetting. However, there are many uncertainties in such biogeochemical cycles under climate change. Human activities (e.g. grazing, land cover changes) further modified the biogeochemical cycles and amplified such uncertainties on the plateau. If the projected warming and wetting continues, the future biogeochemical cycles will be more complicated. So facing research in this field is an ongoing challenge of integrating field observations with process‐based ecosystem models to predict the impacts of future climate change and human activities at various temporal and spatial scales. To reduce the uncertainties and to improve the precision of the predictions of the impacts of climate change and human activities on biogeochemical cycles, efforts should focus on conducting more field observation studies, integrating data within improved models, and developing new knowledge about coupling among carbon, nitrogen, and phosphorus biogeochemical cycles as well as about the role of microbes in these cycles.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Soil fauna are crucial decomposers in terrestrial ecosystems, but how the role of soil fauna varies among climatic conditions and litter substrates remains poorly understood. Here, we conducted a ...four-year litter decomposition experiment along an elevational gradient (453 m, 945 m, 3058 m and 3582 m) in southwestern China. Two dominant tree species with contrasting leaf traits (coniferous vs. broadleaf) were used for field incubation at each site. Litterbags with two mesh sizes (3 vs. 0.04 mm) were used to permit and exclude the presence of soil fauna. The changes in elevation caused corresponding shifts in temperature and precipitation but did not affect the abundance and diversity of soil fauna communities. Soil fauna increased annual decomposition rates (
k
) by 14.5–28.7% across all litter types. Our structural equation models indicated that increasing temperature reduced while increasing moisture increased soil fauna effects on decomposition. Moreover, temperature and moisture modulated the contribution of soil fauna to litter decomposition via different mechanisms: (1) the reduced soil fauna contribution was driven by the increased temperature through increasing the litter C/N and fauna density (possibly because higher densities were associated with smaller organisms) and (2) the increased soil fauna effects were driven by increased moisture that increased the diversity of soil fauna. These results demonstrate that the effects of soil fauna are sensitive to changes in climate and litter quality across elevation gradients, and environment factors (i.e., temperature and moisture) may mediate the contribution of soil fauna to litter decomposition in opposite directions.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
To investigate N metabolism of two contrasting Populus species in acclimation to low N availability, saplings of slow-growing species (Populus popularis, Pp) and a fast-growing species (Populus alba ...× Populus glandulosa, Pg) were exposed to 10, 100, or 1000 μM NH4NO3. Despite greater root biomass and fine root surface area in Pp, lower net influxes of NH4 + and NO3 – at the root surface were detected in Pp compared to those in Pg, corresponding well to lower NH4 + and NO3 – content and total N concentration in Pp roots. Meanwhile, higher stable N isotope composition (δ15N) in roots and stronger responsiveness of transcriptional regulation of 18 genes involved in N metabolism were found in roots and leaves of Pp compared to those of Pg. These results indicate that the N metabolism of Pp is more sensitive to decreasing N availability than that of Pg. In both species, low N treatments decreased net influxes of NH4 + and NO3 –, root NH4 + and foliar NO3 – content, root NR activities, total N concentration in roots and leaves, and transcript levels of most ammonium (AMTs) and nitrate (NRTs) transporter genes in leaves and genes involved in N assimilation in roots and leaves. Low N availability increased fine root surface area, foliar starch concentration, δ15N in roots and leaves, and transcript abundance of several AMTs (e.g. AMT1;2) and NRTs (e.g. NRT1;2 and NRT2;4B) in roots of both species. These data indicate that poplar species slow down processes of N acquisition and assimilation in acclimation to limiting N supply.
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