Productivity Of Terrestrial Ecosystems Research Articles

Consumer adaptation mediates top-down regulation across a productivity gradient.

Humans have artificially enhanced the productivity of terrestrial and aquatic ecosystems on a global scale by increasing nutrient loading. While the consequences of eutrophication are well known (e.g., harmful algal blooms and toxic cyanobacteria), most studies tend to examine short-term responses relative to the time scales of heritable adaptive change. Thus, the potential role of adaptation by organisms in stabilizing the response of ecological systems to such perturbations is largely unknown. We tested the hypothesis that adaptation by a generalist consumer (Daphnia pulicaria) to toxic prey (cyanobacteria) mediates the response of plankton communities to nutrient enrichment. Overall, the strength of Daphnia's top-down effect on primary producer biomass increased with productivity. However, these effects were contingent on prey traits (e.g., rare vs. common toxic cyanobacteria) and consumer genotype (i.e., tolerant vs sensitive to toxic cyanobacteria). Tolerant Daphnia strongly suppressed toxic cyanobacteria in nutrient-rich ponds, but sensitive Daphnia did not. In contrast, both tolerant and sensitive Daphnia genotypes had comparable effects on producer biomass when toxic cyanobacteria were absent. Our results demonstrate that organismal adaptation is critical for understanding and predicting ecosystem-level consequences of anthropogenic environmental perturbations.

Soil bacterial diversity is positively associated with air temperature in the maritime Antarctic

Terrestrial ecosystems in the maritime Antarctic experienced rapid warming during the latter half of the 20th century. While warming ceased at the turn of the millennium, significant increases in air temperature are expected later this century, with predicted positive effects on soil fungal diversity, plant growth and ecosystem productivity. Here, by sequencing 16S ribosomal RNA genes in 40 soils sampled from along a 1,650 km climatic gradient through the maritime Antarctic, we determine whether rising air temperatures might similarly influence the diversity of soil bacteria. Of 22 environmental factors, mean annual surface air temperature was the strongest and most consistent predictor of soil bacterial diversity. Significant, but weaker, associations between bacterial diversity and soil moisture content, C:N ratio, and Ca, Mg, PO43− and dissolved organic C concentrations were also detected. These findings indicate that further rises in air temperature in the maritime Antarctic may enhance terrestrial ecosystem productivity through positive effects on soil bacterial diversity.

Altered trends in carbon uptake in China's terrestrial ecosystems under the enhanced summer monsoon and warming hiatus.

The carbon budgets in terrestrial ecosystems in China are strongly coupled with climate changes. Over the past decade, China has experienced dramatic climate changes characterized by enhanced summer monsoon and decelerated warming. However, the changes in the trends of terrestrial net ecosystem production (NEP) in China under climate changes are not well documented. Here, we used three ecosystem models to simulate the spatiotemporal variations in China's NEP during 1982–2010 and quantify the contribution of the strengthened summer monsoon and warming hiatus to the NEP variations in four distinct climatic regions of the country. Our results revealed a decadal-scale shift in NEP from a downtrend of –5.95 Tg C/yr2 (reduced sink) during 1982–2000 to an uptrend of 14.22 Tg C/yr2 (enhanced sink) during 2000–10. This shift was essentially induced by the strengthened summer monsoon, which stimulated carbon uptake, and the warming hiatus, which lessened the decrease in the NEP trend. Compared to the contribution of 56.3% by the climate effect, atmospheric CO2 concentration and nitrogen deposition had relatively small contributions (8.6 and 11.3%, respectively) to the shift. In conclusion, within the context of the global-warming hiatus, the strengthening of the summer monsoon is a critical climate factor that enhances carbon uptake in China due to the asymmetric response of photosynthesis and respiration. Our study not only revealed the shift in ecosystem carbon sequestration in China in recent decades, but also provides some insight for understanding ecosystem carbon dynamics in other monsoonal areas.

Silicon increases the phosphorus availability of Arctic soils

Phosphorus availability in soils is an important parameter influencing primary production in terrestrial ecosystems. Phosphorus limitation exists in many soils since a high proportion of soil phosphorus is stored in unavailable forms for plants, such as bound to iron minerals or stabilized organic matter. This is in spite of soils having a high amount of total soil phosphorus. The feasibility of silicon to mobilize phosphorus from strong binding sites of iron minerals has been shown for marine sediments but is less well studied in soils. Here we tested the effect of silicon on phosphorus mobilization for 143 Artic soils (representing contrasting soil characteristics), which have not been affected by agriculture or other anthropogenic management practices. In agreement with marine studies, silicon availabilities were significantly positive correlated to phosphorus mobilization in these soils. Laboratory experiments confirmed that silicon addition significantly increases phosphorus mobilization, by mobilizing Fe(II)-P phases from mineral surfaces. Silicon addition increased also soil respiration in phosphorus deficient soils. We conclude that silicon is a key component regulating mobilization of phosphorous in Arctic soils, suggesting that this may also be important for sustainable management of phosphorus availability in soils in general.

A threefold difference in plant growth response to nitrogen addition between the laboratory and field experiments

AbstractQuantifying the magnitude of plant response to nitrogen (N) addition is critical in improving our understanding of vegetation productivity in terrestrial ecosystems. Numerous studies under both the laboratory (hereafter lab) and field conditions have shown significant increases in plant growth by N addition. However, differences exist when we integrate or compare the results between N‐addition experiments under the lab and field conditions. Here, we performed a meta‐analysis on observations from 139 field and 127 lab experiments to identify their differences and similarities in the N response of plant growth. Overall, there was a threefold difference in the N effect on plant biomass between the lab (+63.1%) and field (+22.2%) experiments. The magnitude of the lab–field difference varied among plant categories and plant tissues. For example, the larger N effect in the lab than field conditions was about twofold for the herbaceous plant but fourfold for the woody species. Furthermore, the N‐induced increase in biomass was allocated more to above‐ground parts in the field but equally to above‐ and below‐ground parts under the lab conditions. We further showed that these differences were jointly attributed to the differential abiotic (i.e., environmental condition and N application methods) and biotic (i.e., interspecific interaction, age, and functional types) factors under these two experimental conditions. These findings highlight more attention should be paid when the results from the lab experiments are translated to understand the N response of the natural plants.

Interannual variability of terrestrial net ecosystem productivity over China: regional contributions and climate attribution

China’s terrestrial ecosystems play an important role in the global carbon cycle. Regional contributions to the interannual variation (IAV) of China’s terrestrial carbon sink and the attributions to climate variations are not well understood. Here we have investigated how terrestrial ecosystems in the four climate zones with various climate variabilities contribute to the IAV in China’s terrestrial net ecosystem productivity (NEP) using modeled carbon fluxes data from six ecosystems models. Model results show that the monsoonal region of China dominates national NEP IAV with a contribution of 86% (69%–96%) on average. Yearly national NEP changes are mostly driven by gross primary productivity IAV and half of the annual variation results from NEP changes in summer. Regional contributions to NEP IAV in China are consistent with their contributions to the magnitude of national NEP. Rainfall variability dominates the NEP annual variability in China. Precipitation in the temperate monsoon climate zone makes the largest contribution (23%) to the IAV of NEP in China because of both the high sensitivity of terrestrial ecosystem carbon uptake to rainfall and the large fluctuation in the precipitation caused by the East Asian summer monsoon anomalies. Our results suggest that NEP IAV can be mainly attributed to ecosystems with larger productivity and response to precipitation, and highlight the importance of monsoon climate systems with high seasonal and interannual variability in driving internannual variation in the land carbon sink.

Plant litter decomposition in a semiarid rangeland of Argentina: species and defoliation effects

Plant litter decomposition is critical for terrestrial ecosystem productivity. Poa ligularis Nees ex Steud and Nassella tenuis (Phil.) Barkworth are native, desirable perennial grasses in central Argentina’s rangelands. Amelichloa ambigua (Speg.) Arriaga & Barkworth is only consumed when a better forage is unavailable. Litter traps were used to collect aboveground litter during two years. In March 2012, six bags, each one containing either leaf blade (three bags, one per species) or root litter (three bags, one per species) of the three species were located below the canopy of each replicate plant of the studied species (hereafter referred to as ‘location’). Blade litter bags were located on the soil surface, and root litter bags buried at 10cm soil depth. This allowed evaluation of the effects of defoliation, the different species canopies and the microbial community activity around their roots on decomposition of above- and belowground litter. For each species, twenty plants were either defoliated twice (5cm stubble height) or remained undefoliated during the growing season. Litter bags were collected after 2, 7, 13 and 24 months incubation. The study was repeated in 2013, with additional bags were placed for N content determination on leaf blade and root litters. Aboveground litter production was highest in P. ligularis; however, no differences were observed among species when the effect of plant size was eliminated. Aboveground litter of desirable species had higher N content and decomposed faster than that of A. ambigua. The opposite was recorded for root litter. Defoliation had no effect on litter decomposition, but location effects were detected after one year of incubation. Desirable perennial grasses promoted organic matter loss from litter, a key factor in increasing soil fertility in this semiarid ecosystem.

A dataset of primary production, respiration and net production in Chinese typical terrestrial ecosystems based on literature integration

A dataset of primary production, respiration and net production in Chinese typical terrestrial ecosystems based on literature integration

Enhanced peak growth of global vegetation and its key mechanisms.

The annual peak growth of vegetation is critical in characterizing the capacity of terrestrial ecosystem productivity and shaping the seasonality of atmospheric CO2 concentrations. The recent greening of global lands suggests an increasing trend of terrestrial vegetation growth, but whether or not the peak growth has been globally enhanced still remains unclear. Here, we use two global datasets of gross primary productivity (GPP) and a satellite-derived Normalized Difference Vegetation Index (NDVI) to characterize recent changes in annual peak vegetation growth (that is, GPPmax and NDVImax). We demonstrate that the peak in the growth of global vegetation has been linearly increasing during the past three decades. About 65% of the NDVImax variation is evenly explained by expanding croplands (21%), rising CO2 (22%) and intensifying nitrogen deposition (22%). The contribution of expanding croplands to the peak growth trend is substantiated by measurements from eddy-flux towers, sun-induced chlorophyll fluorescence and a global database of plant traits, all of which demonstrate that croplands have a higher photosynthetic capacity than other vegetation types. The large contribution of CO2 is also supported by a meta-analysis of 466 manipulative experiments and 15 terrestrial biosphere models. Furthermore, we show that the contribution of GPPmax to the change in annual GPP is less in the tropics than in other regions. These multiple lines of evidence reveal an increasing trend in the peak growth of global vegetation. The findings highlight the important roles of agricultural intensification and atmospheric changes in reshaping the seasonality of global vegetation growth.

Plant organic N uptake maintains species dominance under long-term warming

There is ample experimental evidence for shifts in plant community composition under climate warming. To date, however, the underlying mechanisms driving these compositional shifts remain poorly understood. The amount and form of nitrogen (N) available to plants are among the primary factors limiting productivity and plant coexistence in terrestrial ecosystems. We conducted a short-term 15N tracer experiment in a ten-year warming and grazing experiment in an alpine grassland to investigate the effects of warming and grazing on plant uptake of NO3−-N, NH4+-N, and glycine-N. Four dominant plant species (Kobresia humilis, Potentilla anseria, Elymus nutans, Poa annua) were selected. Results We found that 10-years of warming decreased plant uptake of inorganic N by up to 80% in all species. In contrast, warming increased the uptake of organic N in K. humilis, P. anseria, and E. nutans but not in P. annua. Results showed that plant relative biomass increased hyperbolically with the ratio of the plant species total uptake of available N and plant community uptake of available N. And a significant positive correlation between plant species uptake of soil glycine-N and the uptake of total available N. The stable relative biomass of plant species is largely dependent on organic N uptake by plants. We conclude that plant organic N uptake maintains species dominance under long-term warming.

Response of Tropical Terrestrial Gross Primary Production to the Super El Niño Event in 2015

AbstractThe gross primary production (GPP) in tropical terrestrial ecosystems plays a critical role in the global carbon cycle and climate change. The strong 2015–2016 El Niño event offers a unique opportunity to investigate how GPP in the tropical terrestrial ecosystems responds to climatic forcing. This study uses two GPP products and concurrent climate data to investigate the GPP anomalies and their underlying causes. We find that both GPP products show an enhanced GPP in 2015 for the tropical terrestrial ecosystem as a whole relative to the multiyear mean of 2001–2015, and this enhancement is the net result of GPP increase in tropical forests and decrease in nonforests. We show that the increased GPP in tropical forests during the El Nino event is consistent with increased photosynthesis active radiation as a result of a reduction in clouds, while the decreased GPP in nonforests is consistent with increased water stress as a result of a reduction of precipitation and an increase of temperature. These results reveal the strong coupling of ecosystem and climate that is different in forest and nonforest ecosystems and provide a test case for carbon cycle parameterization and carbon‐climate feedback simulation in models.

Long-term Nutrient Fertilization Increased Soil Carbon Storage in California Grasslands

Elevated nutrient deposition often increases primary productivity in terrestrial ecosystems and thus has the potential to increase the flux of carbon (C) into soils. An important step toward greater understanding of nutrient effects on C storage involves assessing effects on different fractions of the soil C pool across a range of soil types. We quantified the combined effects of 8 years of nitrogen (N), phosphorus (P), potassium (K), and micronutrient fertilization on the C storage in bulk soil and in density fractions at four grassland sites in California. When averaged across sites, fertilization increased soil light fraction C by 64% relative to the control in the 0–10 cm depth. The increase in light fraction C likely resulted from the fertilization-induced increase in plant C input to soil, as aboveground net primary productivity also consistently increased with fertilization across sites. Effects of fertilization on heavy fraction C were highly site specific, having positive, negative, or no effect at individual sites. The response of heavy fraction C to fertilization appeared to be related to mean annual precipitation and soil bulk density. Overall, bulk soil C concentration showed a marginally significant increase of 6% with fertilization when averaged across sites (P = 0.07). Our results indicate that biomass production and soil light fraction are generally sensitive to fertilization across grasslands in California, likely contributing to increases in soil C storage. Responses of heavy fraction C, on the other hand, vary greatly among sites and may depend on climate and soil characteristics.

Modeling of soil phosphatase activity in land use ecosystems and topsoil layers in the Brazilian Cerrado

Soil phosphatase is a biochemical indicator of soil quality, and its activity plays a key role in the productivity of terrestrial ecosystems. Modeling the kinetic parameters of soil phosphatase is central to integrate ecological processes in tropical soils under different land use ecosystems. The goal of this study was to determine the kinetic parameters of soil acid phosphatase (APsoil) and assess the relationship between its kinetic parameters and soil quality indicators in two topsoil layers (at the 0–5 and 5–10 cm depths) from an Oxisol under the native Cerrado, pine, soya and sugarcane ecosystems. APsoil activity was assessed with different substrate concentrations (0, 0.75, 1.5, 3, 4.5, 6, 12 and 18 mmol L−1 of p-nitrophenol phosphate in buffer) at 37 °C, pH 6.5 and acetate buffer. The kinetic parameters (Km and Vmax) were estimated using the Michaelis-Menten (M-M) and Eadie-Hofstee (E-H) equations. Soil organic carbon (SOC), total nitrogen (TN), soil microbial respiration (SMR), microbial biomass carbon (MBC) and nitrogen (MBN), and dehydrogenase activity (DHA) were also measured. In both models, the highest Vmax and Km values were found in native Cerrado soil, followed by pine soil in two surface layers. Soya and sugarcane soils presented low Km values, showing a great substrate affinity of soil phosphatase in these ecosystems. The M-M model estimated higher Vmax and Km values than the E-H model. The M-M model did not show any difference in Km between the two layers of ecosystems, but the E-H model revealed significant differences between the layers with the lowest Km values at the 5–10 cm depth. The results revealed that Km has a significant correlation with SOC (r = 0.71), TN (r = 0.72), MBC (r = 0.75) and MBN (r = 0.75). The results also showed a greater correlation between the Km of the E-H model and soil quality indicators than the M-M model. Our study shows the importance of modeling the APsoil in the Brazilian Cerrado in relation to land use ecosystems, depths and the model applied.

Influence of intensified air pollution on the sunny diffuse radiation fraction in China

In recent years, air pollution has been getting increasingly serious in China—A cause of great concern for the government and general public. Research on air pollution has focused mainly on the environmental and climatic effects, such as the increasing number of haze days, reduction in visibility, human health impacts, suppression of global warming, extension of cloud life, restriction of light precipitation, and weakening of the East Asian monsoon. In fact, the exacerbation of air pollution might also affect the radiation balance of the surface-atmosphere system, with subsequent direct impacts in areas of socioeconomic concern like agricultural production. However, domestically, research in this area is currently lacking. Accordingly, the present study, based mainly on the sunny diffuse radiation fraction (SDRF—defined as the diffuse solar radiation divided by the total solar radiation in conditions of sunny weather) at 47 stations over China, combined with CO2 emissions data, aerosol optical depth (AOD) and sunshine duration data, analyzes the spatiotemporal variation of SDRF in China and the possible determining factors. The results provide a reference and basis for the accurate assessment of terrestrial ecosystem productivity and its carbon budget. Analysis of the SDRF distribution reveals clear regional characteristics in China, with relatively larger values distributed mainly in the Sichuan Basin and Central China. However, the values of SDRF in Yunnan, Xinjiang, Tibet and Northeast China are small. The majority of stations show an obvious upward trend in SDRF, especially in Eastern China, where the upward trend is more significant than in other regions. Therefore, after removal of the effects of cloud, aerosols should be considered a factor with important influence on the SDRF during the past 50 years. Analysis of the characteristics in each region shows that the increase in SDRF is more obvious in North China, East China and Central China than in South China, Northeast China, Northwest China and Southwest China. This indicates that, in regions where air pollution is more serious, the decline in SDRF is more significant. Sunshine duration in sunny weather is highly correlated with SDRF, with the correlation coefficient in East China, Central China and North China often exceeding −0.8 (statistically significant at the 99.9% confidence level). This result implies that an increase in the concentration of aerosol particles in the air has a significant impact on sunshine duration and SDRF over China.

The Importance of Aquatic Carbon Fluxes in Net Ecosystem Carbon Budgets: A Catchment-Scale Review

The growing importance of resolving ecosystem carbon budgets has resulted in more studies integrating terrestrial and aquatic carbon fluxes. Although recent estimates highlight the importance of inland waters in global carbon budgets, the extent to which aquatic pathways contribute to the net ecosystem carbon budget (NECB) of different ecosystems remains poorly understood. Here, we provide a cross-ecosystem review of annual carbon budgets integrating terrestrial and aquatic fluxes. Large variability in the proportion of aquatic carbon offset to terrestrial net ecosystem productivity (NEP) was observed, with aquatic offsets ranging from < 1% in a boreal forest to 590% in a freshwater marsh. The total aquatic carbon flux was positively correlated with terrestrial NEP, suggesting highly productive ecosystems will have greater aquatic carbon offsets. However, due to an order of magnitude difference in the range of terrestrial NEP (~ 1000 g C m−2 y−1) compared to aquatic fluxes (~ 100 g C m−2 y−1), ecosystems with small NEP’s had greater relative aquatic carbon offsets overall in their NECB’s. Northern hemisphere peatlands and forests represented 54% of all integrated carbon budget studies collected, indicating a severe ecosystem and spatial bias. Mangroves, agricultural, and disturbed ecosystems were the most underrepresented, yet had extreme ranges in terrestrial NEP and NECB (− 638 to 1170 g C m−2 y−1). To improve our mechanistic understanding of the role of aquatic pathways in NECB’s, more site-specific integrative studies need to be undertaken across a broader range of climatic regions and ecosystem types.

Global radiation, photosynthetically active radiation, and the diffuse component dataset of China, 1981–2010

Abstract. Solar radiation, especially photosynthetically active radiation (PAR), is the main energy source of plant photosynthesis, and the diffuse component can enhance canopy light use efficiency, thus increasing ecosystem productivity. In order to predict the terrestrial ecosystem productivity precisely, we not only need global radiation and PAR as driving variables, but also need to treat diffuse radiation and diffuse PAR explicitly in ecosystem models. Therefore, we generated a series of radiation datasets, including global radiation, diffuse radiation, PAR, and diffuse PAR of China from 1981 to 2010, based on the observations of the China Meteorology Administration (CMA) and the Chinese Ecosystem Research Network (CERN). The dataset should be useful for the analysis of the spatiotemporal variations of solar radiation in China and the impact of diffuse radiation on terrestrial ecosystem productivity based on ecosystem models. The dataset is freely available from Zenodo on the following website: https://zenodo.org/record/1198894#.Wx6–C_MwWo (https://doi.org/10.11922/sciencedb.555, Ren et al., 2018).

Soil structure after 18 years of long-term different tillage systems and fertilisation in Haplic Luvisol

Soil structure is a key determinant of many soil environmental processes and is essential for supporting terrestrial ecosystem productivity. Management of arable soils plays a significant role in forming and maintaining their structure. Between 1994 and 2011, we studied the influence of soil tillage and fertilisation regimes on the stability of soil structure of loamy Haplic Luvisol in a replicated long-term field experiment in the Dolná Malanta locality (Slovakia). Soil samples were repeatedly collected from plots exposed to the following treatments: conventional tillage (CT) and minimum tillage (MT) combined with conventional (NPK) and crop residue-enhanced fertilisation (CR+NPK). MT resulted in an increase of critical soil organic matter content (St) by 7% in comparison with CT. Addition of crop residues and NPK fertilisers significantly increased St values (by 7%) in comparison with NPK-only treatments. Soil tillage and fertilisation did not have any significant impact on other parameters of soil structure such as dry sieving mean weight diameters (MWD), mean weight diameter of water-stable aggregates (MWD&lt;sub&gt;WSA&lt;/sub&gt;), vulnerability coefficient (Kv), stability index of water-stable aggregates (Sw), index of crusting (Ic), contents of water-stable macro- (WSA&lt;sub&gt;ma&lt;/sub&gt;) and micro-aggregates (WSA&lt;sub&gt;mi&lt;/sub&gt;). Ic was correlated with organic matter content in all combinations of treatments. Surprisingly, humus quality did not interact with soil management practices to affect soil structure parameters. Higher sums of base cations, CEC and base saturation (Bs) were linked to higher Sw values, however higher values of hydrolytic acidity (Ha) resulted in lower aggregate stability in CT treatments. Higher content of K&lt;sup&gt;+&lt;/sup&gt; was responsible for higher values of MWD&lt;sub&gt;WSA &lt;/sub&gt;and MWD in CT. In MT, contents of Ca&lt;sup&gt;2+&lt;/sup&gt;, Mg&lt;sup&gt;2+ &lt;/sup&gt;and Na&lt;sup&gt;+&lt;/sup&gt; were significantly correlated with contents of WSA&lt;sub&gt;mi &lt;/sub&gt;and WSA&lt;sub&gt;ma&lt;/sub&gt;. Higher contents of Na&lt;sup&gt;+&lt;/sup&gt; negatively affected St values and positive correlations were detected between Ca&lt;sup&gt;2+&lt;/sup&gt;, Mg&lt;sup&gt;2+ &lt;/sup&gt;and Na&lt;sup&gt;+&lt;/sup&gt; and Ic in NPK treatments.

Surrounding species diversity improves subtropical seedlings' carbon dynamics.

Increasing biodiversity has been linked to higher primary productivity in terrestrial ecosystems. However, the underlying ecophysiological mechanisms remain poorly understood. We investigated the effects of surrounding species richness (monoculture, two‐ and four‐species mixtures) on the ecophysiology of Lithocarpus glaber seedlings in experimental plots in subtropical China. A natural rain event isotopically labelled both the water uptaken by the L. glaber seedlings and the carbon in new photoassimilates through changes of photosynthetic discrimination. We followed the labelled carbon (C) and oxygen (O) in the plant–soil–atmosphere continuum. We measured gas‐exchange variables (C assimilation, transpiration and above‐ and belowground respiration) and δ13C in leaf biomass, phloem, soil microbial biomass, leaf‐ and soil‐respired CO 2 as well as δ18O in leaf and xylem water. The 13C signal in phloem and respired CO 2 in L. glaber in monoculture lagged behind those in species mixture, showing a slower transport of new photoassimilates to and through the phloem in monoculture. Furthermore, leaf‐water 18O enrichment above the xylem water in L. glaber increased after the rain in lower diversity plots suggesting a lower ability to compensate for increased transpiration. Lithocarpus glaber in monoculture showed higher C assimilation rate and water‐use efficiency. However, these increased C resources did not translate in higher growth of L. glaber in monoculture suggesting the existence of larger nongrowth‐related C sinks in monoculture. These ecophysiological responses of L. glaber, in agreement with current understanding of phloem transport are consistent with a stronger competition for water resources in monoculture than in species mixtures. Therefore, increasing species diversity in the close vicinity of the studied plants appears to alleviate physiological stress induced by water competition and to counterbalance the negative effects of interspecific competition on assimilation rates for L. glaber by allowing a higher fraction of the C assimilated to be allocated to growth in species mixture than in monoculture.

Using imaging spectroscopy to detect variation in terrestrial ecosystem productivity across a water-stressed landscape.

A central challenge to understanding how climate anomalies, such as drought and heatwaves, impact the terrestrial carbon cycle, is quantification and scaling of spatial and temporal variation in ecosystem gross primary productivity (GPP). Existing empirical and model-based satellite broadband spectra-based products have been shown to miss critical variation in GPP. Here, we evaluate the potential of high spectral resolution (10nm) shortwave (400-2,500nm) imagery to better detect spatial and temporal variations in GPP across a range of ecosystems, including forests, grassland-savannas, wetlands, and shrublands in a water-stressed region. Estimates of GPP from eddy covariance observations were compared against airborne hyperspectral imagery, collected across California during the 2013-2014 HyspIRI airborne preparatory campaign. Observations from 19 flux towers across 23 flight campaigns (102 total image-flux tower pairs) showed GPP to be strongly correlated to a suite of spectral wavelengths and band ratios associated with foliar physiology and chemistry. A partial least squares regression (PLSR) modeling approach was then used to predict GPP with higher validation accuracy (adjusted R2 =0.71) and low bias (0.04) compared to existing broadband approaches (e.g., adjusted R2 =0.68 and bias=-5.71 with the Sims etal. model). Significant wavelengths contributing to the PLSR include those previously shown to coincide with Rubisco (wavelengths 1,680, 1,740, and 2,290nm) and Vcmax (wavelengths 1,680, 1,722, 1,732, 1,760, and 2,300nm). These results provide strong evidence that advances in satellite spectral resolution offer significant promise for improved satellite-based monitoring of GPP variability across a diverse range of terrestrial ecosystems.

Cross-scale controls on carbon emissions from boreal forest megafires.

Climate warming and drying is associated with increased wildfire disturbance and the emergence of megafires in North American boreal forests. Changes to the fire regime are expected to strongly increase combustion emissions of carbon (C) which could alter regional C balance and positively feedback to climate warming. In order to accurately estimate C emissions and thereby better predict future climate feedbacks, there is a need to understand the major sources of heterogeneity that impact C emissions at different scales. Here, we examined 211 field plots in boreal forests dominated by black spruce (Picea mariana) or jack pine (Pinus banksiana) of the Northwest Territories (NWT), Canada after an unprecedentedly large area burned in 2014. We assessed both aboveground and soil organic layer (SOL) combustion, with the goal of determining the major drivers in total C emissions, as well as to develop a high spatial resolution model to scale emissions in a relatively understudied region of the boreal forest. On average, 3.35kgCm-2 was combusted and almost 90% of this was from SOL combustion. Our results indicate that black spruce stands located at landscape positions with intermediate drainage contribute the most to C emissions. Indices associated with fire weather and date of burn did not impact emissions, which we attribute to the extreme fire weather over a short period of time. Using these results, we estimated a total of 94.3TgC emitted from 2.85Mha of burned area across the entire 2014 NWT fire complex, which offsets almost 50% of mean annual net ecosystem production in terrestrial ecosystems of Canada. Our study also highlights the need for fine-scale estimates of burned area that represent small water bodies and regionally specific calibrations of combustion that account for spatial heterogeneity in order to accurately model emissions at the continental scale.