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Mangrove plantations exhibit a high potential for biomass carbon sequestration, however, their effects on soil organic carbon (SOC) accumulation remains unclear. We examined the dynamics of community structure and ecosystem carbon accumulation along a chronosequence of Sonneratia apetala plantations on Qi’ao Island, China. To reveal the self-thinning pattern of S. apetala plantations, 114 quadrats were randomly established in the S. apetala plantations. Four quadrats were selected for soil sampling from differently-aged (4, 9, and 15 years) S. apetala plantations, a 15-year-old S. apetala + Bruguiera gymnorrhiza plantation and a 40-year-old mature Kandelia obovate community. We found that the self-thinning process happened in these S. apetala plantations. The vegetation biomass was found to significantly increase with forest age and the 15-year-old S. apetala and 15-year-old S. apetala + Bruguiera gymnorrhiza plantations had similar total biomass as the 40-year-old K. obovate community. Notably, SOC content and stocks only showed a minor increment along the chronosequence of S. apetala plantations, and SOC stock of the 15-year-old S. apetala community was less than 60% of that of the 40-year-old K. obovate community. The 15-year-old S. apetala + B. gymnorrhiza community had a similar biomass value as the 15-year-old S. apetala community, but the former community had a significant higher SOC stock than the latter. Biomass increment and SOC accumulation are unsynchronized with mangrove plantation development, and monospecific mangrove plantations may not be able to significantly accelerate SOC sequestration in the early plantation stage. Multi-specific plantations may facilitate SOC accumulation more than monospecific plantations.

Numerous studies have reported that treelines are moving to higher elevations and higher latitudes. Most treelines are temperature limited and warmer climate expands the area in which trees are capable of growing. Hence, climate change has been assumed to be the main driver behind this treeline movement. The latest review of treeline studies was published in 2009 by Harsch et al. Since then, a plethora of papers have been published studying local treeline migration. Here we bring together this knowledge through a review of 142 treeline related publications, including 477 study locations. We summarize the information known about factors limiting tree-growth at and near treelines. Treeline migration is not only dependent on favorable growing conditions but also requires seedling establishment and survival above the current treeline. These conditions appear to have become favorable at many locations, particularly so in recent years. The review revealed that at 66% of these treeline sites forest cover had increased in elevational or latitudinal extent. The physical form of treelines influences how likely they are to migrate and can be used as an indicator when predicting future treeline movements. Our analysis also revealed that while a greater percentage of elevational treelines are moving, the latitudinal treelines are capable of moving at greater horizontal speed. This can potentially have substantial impacts on ecosystem carbon storage. To conclude the review, we present the three main hypotheses as to whether ecosystem carbon budgets will be reduced, increased or remain the same due to treeline migration. While the answer still remains under debate, we believe that all three hypotheses are likely to apply depending on the encroached ecosystem. Concerningly, evidence is emerging on how treeline migration may turn tundra landscapes from net sinks to net sources of carbon dioxide in the future.

The ecosystem carbon (C) balance in permafrost regions, which has a global significance in understanding the terrestrial C-climate feedback, is significantly regulated by nitrogen (N) dynamics. However, our knowledge on temporal changes in vegetation N limitation (i.e., the supply of N relative to plant N demand) in permafrost ecosystems is still limited. Based on the combination of isotopic observations derived from a re-sampling campaign along a ~3000 km transect and simulations obtained from a process-based biogeochemical model, here we detect changes in ecosystem N cycle across the Tibetan alpine permafrost region over the past decade. We find that vegetation N limitation becomes stronger despite the increased available N production. The enhanced N limitation on vegetation growth is driven by the joint effects of elevated plant N demand and gaseous N loss. These findings suggest that N would constrain the future trajectory of ecosystem C cycle in this alpine permafrost region., Massive stores of carbon and nutrients in permafrost could be released by global warming. Here the authors show that though warming across the Tibetan alpine permafrost region accelerates nitrogen liberation, contrary to expectations the elevated nutrients do not alleviate plant nitrogen limitation.

The Beijing-Tianjin Sand Source Control Project (BTSSCP), a national ecological restoration project, was launched to construct an ecological protection system in the Beijing-Tianjin sand source areas to reduce dust hazards. The carbon sequestration dynamics can be used to assess the ecological effects of an ecological restoration project. Here, we conducted vegetation and soil study to assess the carbon sequestration in the plantations with 10 years old stands in Beijing-Tianjin sand source areas. The results at the site scales indicated that the average net increase of plantation ecosystem carbon stock was 33.8 Mg C ha−1, with an annual increase rate of 3.38 Mg C ha−1 yr−1. The average net increase of carbon varied among regions, vegetation types, and forest management activities. Soil bulk density in the top soil decreased slightly after 10-year implementation of the project. Coniferous forests and shrubs are suitable plant species for sand source areas. Natural restoration in the plantations is a practical and feasible and promising approach for enhancing ecosystem carbon sequestration potential.

The stimulation of plant growth and biomass accumulation by elevated CO2 may be limited by soil nitrogen (N) availability. However, our understanding of the response of soil N cycling to elevated CO2 and when progressive N limitation occurs remains limited. Here, we used an open top chamber experiment to examine the effects of 10 years of elevated CO2 on ecosystem carbon (C) and N dynamics in a Quercus mongolica (oak) dominated system in northeastern China. Elevated CO2 increased oak biomass, C and N stocks and C/N by 26.4, 26.2, 16.5 and 8.6% respectively, which suggests increased plant N demand. Soil gross N mineralization, re-mineralization of microbial N and nitrification were accelerated likely due to increased photosynthesis (by 34.9%) and microbial biomass (by 24.2%) under elevated CO2. Thus, the supply of soil available N can sustain the tree growth stimulated by elevated CO2, and to date progressive N limitation has not happened. Nevertheless, both the annual increase of oak biomass, C and N stocks and C/N ratio and the seasonal variations of soil available N and microbial N concentrations, and net N transformation rates indicated that gradual N deficiency may be occurring and the CO2 fertilization effect has weakened with increasing treatment duration.

Intermittent drainage of rice fields alters soil redox potential and contributes to the reduction of CH4 emission and thus may reduce net global warming potential (GWP) during rice cultivation. Incorporation of green biomass helps maintaining soil organic matter, but may increase CH4 emission. We investigated net ecosystem carbon budget (NECB) and net GWP under two water management regimes—continuous flooding and intermittent drainage—having four biomass incorporation levels (0, 3, 6 and 12 Mg ha−1). Water management and biomass incorporation level demonstrated significant (P

In the last few decades, the Loess Plateau had experienced an extensive vegetation restoration to reduce soil erosion and to improve the degraded ecosystems. However, the dynamics of ecosystem carbon stocks with vegetation restoration in this region are poorly understood. This study examined the changes of carbon stocks in mineral soil (0–100 cm), plant biomass and the ecosystem (plant and soil) following vegetation restoration with different models and ages. Our results indicated that cultivated land returned to native vegetation (natural restoration) or artificial forest increased ecosystem carbon sequestration. Tree plantation sequestered more carbon than natural vegetation succession over decades scale due to the rapid increase in biomass carbon pool. Restoration ages had different effects on the dynamics of biomass and soil carbon stocks. Biomass carbon stocks increased with vegetation restoration age, while the dynamics of soil carbon stocks were affected by sampling depth. Ecosystem carbon stocks consistently increased after tree plantation regardless of the soil depth; but an initial decrease and then increase trend was observed in natural restoration chronosequences with the soil sampling depth of 0–100 cm. Moreover, there was a time lag of about 15–30 years between biomass production and soil carbon sequestration in 0–100 cm, which indicated a long-term effect of vegetation restoration on deeper soil carbon sequestration.

The response of terrestrial ecosystems to climate change remains a large source of uncertainty in the global carbon budget. Now results from a ten-year ecological manipulation experiment in the Mojave Desert provide direct evidence that CO2 fertilization can substantially increase ecosystem carbon storage in arid ecosystems.

Phenology is critical to ecosystem carbon quantification, and yet has not been well modeled considering both aboveground and belowground environmental variables. This is especially true for alpine and pan-arctic regions where soil physical conditions play a significant role in determining the timing of phenology. Here we examine how the spatiotemporal pattern of satellite-derived phenology is related to soil physical conditions simulated with a soil physical model on the Tibetan Plateau for the period 1989-2008. Our results show that spatial patterns and temporal trends of phenology are parallel with the corresponding soil physical conditions for different study periods. On average, 1 °C increase in soil temperature advances the start of growing season (SOS) by 4.6 to 9.9 days among

Studies have shown that tropospheric ozone (O3) impacts trees in various ways, including growth reductions. To date, the landscape-level response of Canadian forests carbon (C) to O3 exposure has not been quantified. We used a modified version of the Carbon Budget Model of the Canadian Forest Sector and data from Aspen FACE to quantify the landscape-level impacts of different O3 exposure modelling experiments. The main strengths of our approach consisted of using the most complete empirical data available to estimate the amount and location of forest C across Canada, as well as explicitly simulating the consequences of fire, insect, and harvest disturbances on forest C dynamics. These disturbances lead to younger forests and, considering trees sensitivity to O3 exposure to decrease with age, thus result in higher landscape-level modelled impacts for the same O3 levels. Despite various sources of uncertainty, our results indicate that even under a modelling experiment where O3 increases continuously over four decades, the landscape-level impacts on the merchantable biomass and ecosystem C remain limited. Our results also suggest that the current direct impacts of O3 on Canadian forests are likely below detection at the landscape level.

An analysis suggests that the time taken for ecosystems to recover from drought increased during the twentieth century. If the frequency of drought events rises, some ecosystems might never have the chance to fully recover. See Letter Droughts affect ecosystem carbon storage, but the factors influencing ecosystem recovery from droughts remain poorly understood. This study finds that gross primary productivity recovery times from droughts are strongly associated with climate and carbon cycle dynamics and to a much lesser extent with biodiversity and carbon dioxide fertilization. The authors find that recovery time is longest in the tropics and high northern latitudes. They also observe that the area of ecosystems under active recovery and the length of recovery time have increased globally over the twentieth century. If future droughts become more frequent this may lead to a chronic state of incomplete recovery with adverse consequences for the land carbon sink.

The frequency of severe droughts is increasing in many regions around the world as a result of climate change(1-3). Droughts alter the structure and function of forests(4,5). Site- and region-specific studies suggest that large trees, which play keystone roles in forests(6) and can be disproportionately important to ecosystem carbon storage(7) and hydrology(8), exhibit greater sensitivity to drought than small trees(4,5,9,10). Here, we synthesize data on tree growth and mortality collected during 40 drought events in forests worldwide to see whether this size-dependent sensitivity to drought holds more widely. We find that droughts consistently had a more detrimental impact on the growth and mortality rates of larger trees. Moreover, drought-related mortality increased with tree size in 65% of the droughts examined, especially when community-wide mortality was high or when bark beetles were present. The more pronounced drought sensitivity of larger trees could be underpinned by greater inherent vulnerability to hydraulic stress(11-14), the higher radiation and evaporative demand experienced by exposed crowns(4,15), and the tendency for bark beetles to preferentially attack larger trees(16). We suggest that future droughts will have a more detrimental impact on the growth and mortality of larger trees, potentially exacerbating feedbacks to climate change.

An open-path eddy covariance system was set up in Damxung rangeland station to measure the carbon flux from July to October, 2003. The canopy quantum yield (alpha) of alpine meadow was calculated by the linear function between the net ecosystem carbon dioxide exchange (NEE) and the photosynthetic active radiation (PAR) under low light, and how it was influenced by the temperature was also discussed. Results showed that the canopy a decreased almost linearly with temperature, with the decrease in every 1 degrees C increase of temperature similar to those measured on leaf level of C-3 plant. At the beginning, the decrease of canopy a with temperature was 0.0005 Nmol CO2-mu mol(-1) PAR; while it increased to 0.0008 Nmol CO2.mu mol(-1) PAR in September, showing a rising trend with plant growing stages. Compared with the canopy a calculated with rectangular hyperbola function, the value in the paper was lower. However, the method advanced here has the advantages in examining the relationship between a and the key environmental factors, such as temperature.

Short- and long-term patterns of net ecosystem carbon balance (NECB) for small, relatively uniform forest stands have been examined in detail, but the same is not true for landscapes, especially those with heterogeneous disturbance histories. In this paper, we explore the effect of two contrasting types of disturbances (i.e., fire and tree harvest) on landscape level NECB by using an ecosystem process model that explicitly accounts for changes in carbon (C) stores as a function of disturbance regimes. The latter were defined by the average disturbance interval, the regularity of the disturbance interval (i.e., random, based on a Poisson frequency distribution, or regular), the amount of C removed by the disturbance (i.e., severity), and the relative abundance of stands in the landscape with unique disturbance histories. We used the model to create over 300 hypothetical landscapes, each with a different disturbance regime, by simulating up to 200 unique stand histories and averaging their total C stores. Mean NECB and its year-to-year variability was computed by calculating the difference in mean total C stores from one year to the next. Results indicated that landscape C stores were higher for random than for regular disturbance intervals, and increased as the mean disturbance interval increased and as the disturbance severity decreased. For example, C storage was reduced by 58% when the fire interval was shortened from 250 years to 100 years. Average landscape NECB was not significantly different than zero for any of the simulated landscapes. Year-to-year variability in landscape NECB, however, was related to the landscape disturbance regime; increasing with disturbance severity and frequency, and higher for random versus regular disturbance intervals. We conclude that landscape C stores of forest systems can be predicted using the concept of disturbance regimes, a result that may be a useful for adjusting estimates of C storage to broad scales that are solely based on physiological processes.

The controversy on how to measure fine root production of forests (P) most accurately continues. We applied four different approaches to determine annual rates of P in an old-growth temperate Fagus sylvatica–Quercus petraea stand: sequential soil coring with minimum–maximum calculation, sequential coring with compartmental flow calculation, the ingrowth core method, and a recently developed root chamber method for measuring the growth of individual fine roots in situ. The results of the four destructive approaches differed by an order of magnitude and, thus, are likely to introduce large errors in estimating P. The highest annual rates of P were obtained from the sequential coring approach with compartmental flow calculation, intermediate rates by sequential coring with minimum–maximum calculation, and low ones by both the root growth chamber and ingrowth core approaches. A carbon budget for the stand was set up based on a model of annual net carbon gain by the canopy and measurements on carbon sink strength (annual leaf, branch and stem growth). The budget implied that a maximum of 27% of the net carbon gain was available for allocation to fine root growth. When compared to the carbon budget data, the sequential coring/compartmental flow approach overestimated annual fine root production substantially; whereas the ingrowth core and root growth chamber approaches grossly underestimated P rates. With an overestimation of about 25% the sequential coring/minimum–maximum approach demonstrated the best agreement with the carbon budget data. It is concluded that the most reliable estimate of P in this temperate forest will be obtained by applying the sequential coring/minimum–maximum approach, conducted with a large number of replicate samples taken on a few dates per season, in conjunction with direct root growth observation by minirhizotrons.

Background Trends in Alaska ecosystem carbon fluxes were predicted from inputs of monthly MODerate resolution Imaging Spectroradiometer (MODIS) vegetation index time-series combined with the NASA-CASA (Carnegie Ames Stanford Approach) carbon cycle simulation model over the past decade. CASA simulates monthly net ecosystem production (NEP) as the difference in carbon fluxes between net primary production (NPP) and soil microbial respiration (Rh). Results Model results showed that NEP on a unit area basis was estimated to be highest (> +10 g C m-2 yr-1) on average over the period 2000 to 2010 within the Major Land Resource Areas (MRLAs) of the Interior Brooks Range Mountains, the Arctic Foothills, and the Western Brooks Range Mountains. The lowest (as negative land C source fluxes) mean NEP fluxes were predicted for the MLRAs of the Cook Inlet Lowlands, the Ahklun Mountains, and Bristol Bay-Northern Alaska Peninsula Lowlands. High levels of interannual variation in NEP were predicted for most MLRAs of Alaska. Conclusions The relatively warm and wet years of 2004 and 2007 resulted in the highest positive NEP flux totals across MLRAs in the northern and western coastal locations in the state (i.e., the Brooks Range Mountains and Arctic Foothills). The relatively cold and dry years of 2001 and 2006 were predicted with the lowest (negative) NEP flux totals for these MLRAs, and likewise across the Ahklun Mountains and the Yukon-Kuskokwim Highlands.

Increasing temperatures are expected to increase decomposition rates in soils, potentially reducing ecosystem carbon storage. Research now indicates that — in a tropical montane forest — soil carbon stocks are unaffected by higher temperatures despite substantially increased rates of CO2 release from the soil.

MUCH of the carbon assimilated by plants is allocated to fine root production1–5, and the amount of carbon and nutrients subsequently returned to the soil from fine root turnover equals or surpasses that returned through leaf litter in many forests6–9. Unfortunately, limitations in traditional methods of studying roots have prevented us from thoroughly understanding the dynamic nature of fine root mortality in most forests, and better measurements of fine root longevity are needed to quantify and model more accurately ecosystem carbon and nutrient budgets8–11. We used minirhizotrons12,13 to follow the mortality of contemporaneous fine root cohorts in two sugar maple (Acer saccharum Marsh.) forests located 80 km apart (north–south) during 1989 and 1990. We report here that roots in the northern forest consistently lived the longest, principally owing to greater rates of mortality early in the life of roots at the southern site. Differences in site factors suggest that warmer soil temperatures seem to be associated with the more rapid death of roots at the southern site.