Components Of Net Primary Productivity Research Articles

Modeling the carbon costs of plant phosphorus acquisition in Amazonian forests

Plants growing in low phosphorus (P) soils, such as in the predominant soils of Amazonia, are believed to devote more energy to acquiring P through absorptive root production, symbionts, and root exudates than plants in more fertile soils. Accounting for these energy costs in vegetation models is essential, as underestimating carbon (C) allocation to nutrient acquisition may lead to overestimating plant biomass growth. We developed a quantitative model to test a theoretical framework of C costs of P acquisition across soil P gradients. The model considers four strategies: P foraging via absorptive roots and arbuscular mycorrhizal fungi and P mining via root exudation of phosphatases and organic acids. We used field observations (i.e., soil data, plant biomass production, and stoichiometry of different organs) from ten sites across Amazonia to calibrate the model and explore different scenarios of (i) experimental soil P addition and (ii) elevated atmospheric CO2 concentrations (eCO2). Our model reproduced expected trends in P-acquisition strategies, with plants increasingly investing in foraging strategies as soil soluble inorganic P (Pi) increases and increasingly investing in mining strategies as total P and less available P forms decrease. Relative investment in P acquisition was within observed ranges. Plants, on average and across all sites, invested the equivalent of 20.5% of their estimated total net primary production (NPP) in P acquisition. On average, plants allocated 15.3% of their NPP to P acquisition in the three most fertile sites, compared to 29.0% in the least fertile sites. C allocation to arbuscular mycorrhizas, phosphatases, and organic acids, which are not commonly measured components of total NPP, was up to 25.8% (16.9% on average) of the total NPP. We highlight the need for quantitative data on plant C allocation to P acquisition from the soil to strengthen further model development and future model projections.

Spatial and temporal variation of vegetation NPP and analysis of influencing factors in Heilongjiang Province, China

Vegetation net primary productivity (NPP) plays an important role in investigating carbon cycle and NPP provided by forest constitutes the main component of terrestrial vegetation NPP. Since late 1990s, a series of policies for protecting forest have been implemented in Heilongjiang Province, China, directly leading to the continuous change of forest area and growth environment. As a result, analysis of spatiotemporal characteristics of NPP after the implementation of protection policies was conducted in this study, and influencing factors leading to the distribution and spatiotemporal heterogeneity of NPP was also compared quantitatively, aiming to reveal the changing characteristics and influencing factors of NPP in a large area over a longer time span. In this study, multi-source data including MOD17A3 NPP product, meteorological data, topographic data and land-use data was selected, and then the spatiotemporal characteristics of NPP from 2001 to 2020 were analyzed through commonly-used spatiotemporal analysis indices and methods. Finally, influencing factors leading to the distribution and spatiotemporal heterogeneity of NPP in the study area were quantitatively compared and analyzed. Results show that the total amount of NPP in Heilongjiang Province has a fluctuating trend with an increasing rate of 23.47% over the past twenty years, and the increase/decrease scenarios of NPP usually can be found in forest regions with high forest coverage and urban regions experiencing dramatic urbanization processes, respectively. Meanwhile, this study also finds that there is no absolute dominant factor can be responsible for the difference in spatial distribution of NPP, but the conversion between forest and other land-use types are the main factors leading to the spatiotemporal heterogeneity of NPP in the study area. The conclusions in this study may provide guiding significance for formulating forestry protection policies in forest regions and designing land-use plans in the future, aiming to achieve the balance between ecological protection and urban development.

Competition-based mortality and tree losses. An essential component of net primary productivity

Even-aged stands can regenerate with many thousand seedlings per hectare before the density declines to just a few hundred trees per hectare 100 years later; management practices can lead to even lower tree numbers due to quality selection and thinning. In other words, during the development of unmanaged stands, the majority of individuals die naturally due to competition. Despite the far-reaching consequences for structural and genetic diversity, dead wood and fuel wood accumulation, we have only limited quantitative knowledge about the continuous mortality of trees and the wood volume loss over longer timespans.For this study, we used a unique set of 476 unmanaged, monospecific experimental plots of Norway spruce (Picea abies (L.) H. Karst.), silver fir (Abies alba Mill.), Scots pine (Pinus sylvestris L.), European larch (Larix decidua Mill.), Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)), European beech (Fagus sylvatica L.), and oak (Quercus robur L. and Quercus petraea (Matt.) Liebl.) throughout Europe to analyze the competition-based mortality of trees and its dependency on age and site conditions.First, we show that the total stem volume production, standing stock, and mortality were continuously increasing until an age of 100–150 years. The accumulated competition-caused stem volume loss at that age amounted to 500–1000 m3 ha−1.Second, the net growth of the stands (share of the growth that is accumulated in the standing stock) strongly decreased with increasing age even when the gross growth was still high. The proportion of the net growth versus gross growth continuously decreased with increasing age regardless of site quality.Third, we show a degressive decrease of the annual relative tree number mortality rates from 0.05 to 0.20 in young down to 0.01–0.02 in mature stands. For some species, we found these rates to be site dependent with different directions of the site effect. The interplay of decreasing mortality rates and increasing average volume of the dead trees resulted in unimodal mortality curves over time of the annual mortality, peaking at 3–12 m3 ha−1 yr−1 at ages of about 75–150 years.Over the whole rotation, the average annual biomass loss from mortality ranged between 0.8 and 2.1 t ha−1 yr−1 with a carbon content of 0.4–1.1 t C ha−1 yr−1. We discuss the relevance of the results for measuring, understanding, modelling, and managing forest stands. Our results reveal that the withdrawal of forest management and setting aside (previously managed) forests over a rotation time of 100–150 years means that about one third of the total production in monospecific stands would flow to the debris pool rather than being exploited for carbon sequestration and related emission savings in harvested wood products. The mortality related loss fractions of above ground biomass we quantified in this study indicate the trade-off between wood production and setting aside forest to allow deadwood accumulation and associate changes in biodiversity.

Allometric relationships between above-ground biomass increment and stand characteristics for crimean pine in Taşköprü, Turkey

Background: Biomass increment, one of the main components of net primary production (NPP) in forest ecosystems, plays an important role as well as total biomass in the global carbon cycle. In this study, the changes of increments of the above-ground total, stem and branch biomasses depending on stand characteristics (i.e., stand age, stand density, and site index) were investigated, and these relations were modeled for Crimean pine (Pinus nigra J.F.Arnold subsp. pallasiana (Lamb.) Holmboe) stands in Taşköprü region of Türkiye. Data were obtained from 109 sample trees within 74 sample plots representing the wide range of possible stand characteristics. Results: The equations developed for above-ground total, stem and branch biomass increments have quite high coefficients of determination (R 2 =0.784, 0.684 and 0.780, respectively), whereas low root mean square errors (RMSE=0.749, 0.692 and 0.116, respectively). The results indicated that the biomass increment estimates from the allometric equations developed were decreasing with stand age and increasing with stand density and site index and also stand density is the strongest stand characteristic on biomass increment. Conclusion: The estimates are also consistent with the growth patterns, so the equations can be used for biomass increment estimations and also for carbon storage and NPP projections for Crimean pine stands of the region.

Biotic and climatic controls on the interannual variation in canopy litterfall of a deciduous broad-leaved forest

Canopy litterfall is an important component of net primary productivity (NPP) in forests, but the climatic and biotic controls on its interannual fluctuation remain poorly understood. In this study, we quantified the interannual variation in and the influencing factors of the canopy litterfall with 45 litter traps in nine plots for 12 years (2008 − 2019) in a temperate deciduous broad-leaved forest in Northeast China. The coefficients of interannual variation in the total (7.3%) and leaf (5.6%) litterfall were substantially lower than those in the basal area (BA) increment (21.0%) and gross primary productivity (10.2%). Climatic (i.e., air temperature, thermal time, precipitation, and radiation) and biotic (i.e., BA and species richness) factors jointly controlled the annual production of litterfall for individual plots and species. Significant climate legacy effects were detected in all components of the litterfall, with the strongest in woody tissue component that contributed to 58.9% of the total litterfall variability. The most important factor driving the variability of the total litterfall and its non-leaf components was climate legacy effect (67.2% to 86.6%), while those for the leaf litterfall were BA (40.4%) and species richness (38.3%). We conclude that high species richness of the deciduous forest increases the temporal stability of canopy productivity, and leaf productivity is much more stable than wood productivity as indicated by BA increament. These findings provide insight into spatiotemporal dynamics in the litterfall and canopy NPP in temperate deciduous forests.

Technical Note: A Rapid Method to Estimate Root Production in Grasslands, Shrublands, and Forests

Net primary production (NPP) is a critical ecosystem property that researchers and land managers attempt to quantify across ecosystems globally. Although the belowground NPP (BNPP) component of total NPP often contributes 50% or more to total NPP, it is infrequently measured due to the amount of labor involved. Here, I present a rapid method to estimate BNPP or fine root production in rangelands using sequential or root ingrowth cores and modifications to existing root-washing methods. The details provided should allow anyone to estimate BNPP in rangelands worldwide with minimal investment in materials and labor.

Ten-Year Estimation of Net Primary Productivity in a Mangrove Forest under a Tropical Monsoon Climate in Eastern Thailand: Significance of the Temperature Environment in the Dry Season

Mangrove forests play crucial roles in the coastal ecosystems of the tropics. Few studies have addressed long-term changes in the net primary productivity (NPP) of mangroves in relation to the tropical monsoon climate. We conducted a tree census from 2008 to 2018 in a permanent plot at a secondary mangrove forest under the tropical monsoon climate of Eastern Thailand. During this period, the mortality of fast-growing species and the increasing number of newly recruited trees revealed a temporal change in the plant composition and distribution. Total tree biomass linearly increased from 283.64 to 381.72 t·ha−1 during the study period. The NPP was calculated by using the summation method, which included fine root production. The NPP ranged from 21.19 to 29.04 t·ha−1·yr−1. The fluctuation in NPP and its components were analyzed in relation to climatic factors by the linear regression model. The NPP did not relate with the annual climatic factors, such as the mean temperature and annual rainfall. However, both increments in the basal area and living tree biomass, which is a major component of NPP, were negatively related with the maximum and mean monthly temperatures in the dry season. The annual mortality rate related positively with annual rainfall and the maximum monthly temperature in the dry season. Linear regression analyses showed that some major components of NPP were chiefly affected by the temperature environment in the dry season. These results indicated that the weather in the dry season was largely restricting the mangrove NPP due to effects on the saline water dynamics of the soils under the tropical monsoon climate, which were revealed by our recent study. It implies that the hot-dry season may lead to high mortality, long-term reduction in the increment of living-trees biomass, and thus lowered the ability to maintain high NPP of mangrove forests over the long-term.

Spatial and temporal variation of forest net primary productivity components on contrasting soils in northwestern Amazon

AbstractClimate is a strong determinant of tropical forest productivity; therefore, it is often assumed that Amazonian forest growing on the same local rainfall regime responds similarly to fluctuations in rainfall, independently of soil differences among them. We evaluated intra‐ and inter‐annual variation of net primary productivity (NPP) components, and forest dynamics during 2004–2012 yr in five forests on clay, clay‐loam, sandy‐clay‐loam, sandy‐loam and loamy‐sand soils, and the same local rainfall regime in northwestern Amazonia (Colombia). The questions were as follows: (1) Do NPP components and forest dynamics respond synchronously to temporal rainfall fluctuations? (2) Are the responses between above and belowground components and forest dynamics similar for different forest stands? A slight and complex synchronicity among different NPP components in their response to temporal rainfall fluctuations were found; few plots showed that aboveground biomass (AGB) and stem growth were susceptible to rainfall fluctuations, while belowground components (fine roots) showed correlation with one‐month lagged rainfall. Furthermore, despite that northwestern Amazonia is considered relatively aseasonal, litterfall showed high seasonality in the loam‐soil forest group, as well as the fine‐root mass, particularly during the 2005 drought. Litterfall correlation with rainfall of sandy‐loam terra‐firme forest was time lagged as well as fine‐root mass of the loamy‐sand forest. The correlation between mortality and rainfall was weak, except for the loamy‐sand forest (white‐sand forest, 77%). High mortality rates occurred in the non‐flooded forests for the censuses that included the dry years (2004–2005, 2005–2006). Interestingly, litterfall, AGB increment, and recruitment showed high correlation among forests, particularly within the loam‐soil forest group. Nonetheless, leaf area index (LAI) measured in the most contrasting forests (clay and loamy‐sand soil) was poorly correlated with rainfall, but highly correlated among them, which could be indicating a phenotypic response to the incident radiation in these sites; also, LAI did not reflect the differences in NPP components and their response to rainfall. Overall, the different temporal behavior of NPP components among forests in relation to rainfall fluctuations suggests the important role that soil exerts on the responses of plant species in each site, besides their effect on forest dynamics and community composition.

Small-Scale Forest Structure Influences Spatial Variability of Belowground Carbon Fluxes in a Mature Mediterranean Beech Forest

The tree belowground compartment, especially fine roots, plays a relevant role in the forest ecosystem carbon (C) cycle, contributing largely to soil CO2 efflux (SR) and to net primary production (NPP). Beyond the well-known role of environmental drivers on fine root production (FRP) and SR, other determinants such as forest structure are still poorly understood. We investigated spatial variability of FRP, SR, forest structural traits, and their reciprocal interactions in a mature beech forest in the Mediterranean mountains. In the year of study, FRP resulted in the main component of NPP and explained about 70% of spatial variability of SR. Moreover, FRP was strictly driven by leaf area index (LAI) and soil water content (SWC). These results suggest a framework of close interactions between structural and functional forest features at the local scale to optimize C source–sink relationships under climate variability in a Mediterranean mature beech forest.

Spatial and Temporal Variations in Aboveground Woody Carbon Storage for Cerrado Forests and Woodlands of Mato Grosso, Brazil

AbstractTropical forests and savanna account for nearly 65% of the total global terrestrial net primary production (NPP); however, there are still large uncertainties in tropical forest NPP because of limited field measurements, especially in the structurally diverse Brazilian savanna (cerrado). To address this uncertainty, we measured patterns of aboveground wood C stocks (Cw) and rates of wood C storage (ΔCw) over a 7‐year period for cerrado forests and woodlands of southern Mato Grosso, Brazil, arrayed across hydrological and soil fertility gradients. We focused on ΔCw because it is an important component of NPP, and wood is a stable, long‐term, C storage reservoir. Annual rates of ΔCw were significantly affected by estimates of P and cation (K and Ca) availability, and analysis of covariance indicated that relationships between ΔCw and nutrient availability were independent of stand hydrology. Both upland and hyperseasonal stands exhibited a decline in ΔCw during the 2015–16 El Niño event, which was exceptionally warm and dry. A limited analysis of the uncertainty associated with the field measurements ranged from 7% for wood density to 24% for tree density, while the uncertainty associated with derived quantities ranged from 10% for tree height to 41% for Cw. Overall, these results suggest that soil fertility and annual precipitation are important drivers of ΔCw and that warming and drying associated with climate change will cause a decline in aboveground woody C storage for these, and similar, tropical forests and woodlands.

Increased litterfall contributes to carbon and nitrogen accumulation following cessation of anthropogenic disturbances in degraded forests

Litterfall production constitutes a significant component of net primary production and is a fundamental process in the global carbon and nutrient cycles of terrestrial ecosystems. Recent studies have demonstrated that the cessation of anthropogenic disturbances including selective harvesting, fuelwood collection, and grazing in degraded forests has led to increased forest cover and soil carbon and nitrogen. Despite the importance of litterfall in terrestrial ecosystems, the dynamics of litterfall production and its contribution to soil carbon and nitrogen following the cessation of anthropogenic disturbances in degraded forests remain poorly understood. We used a chronosequence to examine the litterfall dynamics since the cessation of anthropogenic disturbances in the subtropical forests of Eastern China. We found that annual litterfall production increased significantly from 2.5 Mg ha−1 year−1 in stands with recurring disturbances to 4.5 Mg ha−1 year−1 in stands after 31 years of cessation of disturbances, i.e., approximately 80% increase in litterfall production. The increased litterfall production resulted from increasing shrub cover and stand basal area and canopy succession following restoration. The increase in litterfall production contributed to the increased contents and stocks of soil organic matter, carbon, and nitrogen, which increased in the topsoil (0–10 cm) by 200%, 30%, and 150%, respectively, after 31 years of restoration. Our results show evidence for increased annual litterfall production due to the increased stand basal area and shrub cover and canopy succession from pioneer to late-successional species following the cessation of anthropogenic disturbances in the degraded forests. Our results suggest that the increased litterfall production contributed strongly to the accumulation of organic matter, carbon, and nitrogen in the soil following the cessation of anthropogenic disturbances.

Net primary production in plantations of Pinus taeda and Eucalyptus cloeziana compared with a mountain miombo woodland in Mozambique

Planting monocultures of fast-growing non-native (exotic) species is one way to slow or reverse deforestation and forest degradation in tropical zones. This study compared the effects on total net primary production (NPP) of first-rotation monoculture (34-year-old) plantations of Pinus taeda and Eucalyptus cloeziana and adjacent mountain miombo woodland in Mozambique. Total NPP was defined as the sum of annual carbon (C) sequestration in total aboveground tree biomass, belowground coarse root biomass, fine roots (≤2 mm) and fine litterfall.Field measurements were conducted over one year in three 30 m × 30 m permanent sampling plots for each forest type and involved monitoring litterfall and fine root production using in-growth cores and stem diameter growth. Carbon increment in aboveground tree biomass and belowground coarse root biomass was determined using allometric equations, for P. taeda, E. cloeziana, and root-to-shoot ratio, for miombo woodland.Major findings were that total NPP in P. taeda (14.1 Mg C ha−1 yr−1) and E. cloeziana (19.7 Mg C ha−1 yr−1) stands was significantly higher than in miombo woodland stands (5.9 Mg C ha−1 yr−1). These differences were largely attributable to lower basal area and presumably lower leaf biomass in miombo stands. There were several indications that the miombo stands studied had been degraded by selective cutting and other forms of use of forest resources. The difference in total NPP was also reflected in differences in patterns of C sequestration. Carbon in litterfall was the largest component of total NPP in miombo stands (41%), whereas C increment in aboveground tree biomass was the largest component of total NPP in plantation stands (44% in P. taeda and 51% in E. cloeziana).If the aim of forest management is to increase NPP and C sequestration in biomass of degraded miombo stands, our results indicate that replacement with plantations of P. taeda or E. cloeziana can be a useful management option, provided that the plantations are protected from anthropogenic disturbances, particularly fire. However, this aim needs to be balanced against other environmental aims and the socio-economic needs of local communities, since miombo woodland provides a wide range of unique economic, social and ecological benefits.

Logging disturbance shifts net primary productivity and its allocation in Bornean tropical forests.

Tropical forests play a major role in the carbon cycle of the terrestrial biosphere. Recent field studies have provided detailed descriptions of the carbon cycle of mature tropical forests, but logged or secondary forests have received much less attention. Here, we report the first measures of total net primary productivity (NPP) and its allocation along a disturbance gradient from old-growth forests to moderately and heavily logged forests in Malaysian Borneo. We measured the main NPP components (woody, fine root and canopy NPP) in old-growth (n=6) and logged (n=5) 1ha forest plots. Overall, the total NPP did not differ between old-growth and logged forest (13.5±0.5 and 15.7±1.5 Mg C ha-1 year-1 respectively). However, logged forests allocated significantly higher fraction into woody NPP at the expense of the canopy NPP (42% and 48% into woody and canopy NPP, respectively, in old-growth forest vs 66% and 23% in logged forest). When controlling for local stand structure, NPP in logged forest stands was 41% higher, and woody NPP was 150% higher than in old-growth stands with similar basal area, but this was offset by structure effects (higher gap frequency and absence of large trees in logged forest). This pattern was not driven by species turnover: the average woody NPP of all species groups within logged forest (pioneers, nonpioneers, species unique to logged plots and species shared with old-growth plots) was similar. Hence, below a threshold of very heavy disturbance, logged forests can exhibit higher NPP and higher allocation to wood; such shifts in carbon cycling persist for decades after the logging event. Given that the majority of tropical forest biome has experienced some degree of logging, our results demonstrate that logging can cause substantial shifts in carbon production and allocation in tropical forests.

Exudation rates and δ13C signatures of tree root soluble organic carbon in a riparian forest

Tree root exudation (TRE) of water soluble organic carbon (WSOC) is an important but under-assessed component of net primary production, and is thought to strongly influence rhizosphere biogeochemistry. Riparian systems in particular are often viewed as biogeochemical hot spots fueled partially by root exudate WSOC. However, TRE rates have not been previously reported for these systems. The δ13C signatures of exudates may provide important insights into plant physiology and inform isotope-based methods to identify sources of soil CO2 fluxes, but this information is also generally lacking. In the present study, root exudate WSOC was collected in situ to assess both net exudation rates and exudate δ13C values in a temperate riparian forest. Net TRE rates were found to be most strongly related to a combination of tree species, root characteristics and net ecosystem exchange (Adj. R2 = 0.73; p < 0.001). In contrast, exudate δ13C values were correlated to time-lagged vapor pressure deficit (Adj. R2 = 0.21; p < 0.05) and air temperature (Adj. R2 = 0.43; p < 0.05), suggesting a rapid transfer of photosynthate from the canopy to the rhizosphere. Extrapolation of mean net TRE rates (13 µmol C g root−1 day−1) from a root mass basis to the entire sampling area suggests that TRE may account for as much as 3% of net annual C uptake and represents an important input of organic matter to riparian soils. Our findings of predictable TRE rates and exudate δ13C values in the present study suggest that future studies examining δ13C values of different plant components, soil organic matter and respired soil CO2 would benefit by accounting for the impact of root exudates.

Forest biomass, productivity and carbon cycling along a rainfall gradient in West Africa.

Net Primary Productivity (NPP) is one of the most important parameters in describing the functioning of any ecosystem and yet it arguably remains a poorly quantified and understood component of carbon cycling in tropical forests, especially outside of the Americas. We provide the first comprehensive analysis of NPP and its carbon allocation to woody, canopy and root growth components at contrasting lowland West African forests spanning a rainfall gradient. Using a standardized methodology to study evergreen (EF), semi-deciduous (SDF), dry forests (DF) and woody savanna (WS), we find that (i) climate is more closely related with above and belowground C stocks than with NPP (ii) total NPP is highest in the SDF site, then the EF followed by the DF and WS and that (iii) different forest types have distinct carbon allocation patterns whereby SDF allocate in excess of 50% to canopy production and the DF and WS sites allocate 40%-50% to woody production. Furthermore, we find that (iv) compared with canopy and root growth rates the woody growth rate of these forests is a poor proxy for their overall productivity and that (v) residence time is the primary driver in the productivity-allocation-turnover chain for the observed spatial differences in woody, leaf and root biomass across the rainfall gradient. Through a systematic assessment of forest productivity we demonstrate the importance of directly measuring the main components of above and belowground NPP and encourage the establishment of more permanent carbon intensive monitoring plots across the tropics.

What controls variation in carbon use efficiency among Amazonian tropical forests?

AbstractWhy do some forests produce biomass more efficiently than others? Variations in Carbon Use Efficiency (CUE: total Net Primary Production (NPP)/ Gross Primary Production (GPP)) may be due to changes in wood residence time (Biomass/NPPwood), temperature, or soil nutrient status. We tested these hypotheses in 14, one ha plots across Amazonian and Andean forests where we measured most key components of net primary production (NPP: wood, fine roots, and leaves) and autotrophic respiration (Ra; wood, rhizosphere, and leaf respiration). We found that lower fertility sites were less efficient at producing biomass and had higher rhizosphere respiration, indicating increased carbon allocation to belowground components. We then compared wood respiration to wood growth and rhizosphere respiration to fine root growth and found that forests with residence times &lt;40 yrs had significantly lower maintenance respiration for both wood and fine roots than forests with residence times &gt;40 yrs. A comparison of rhizosphere respiration to fine root growth showed that rhizosphere growth respiration was significantly greater at low fertility sites. Overall, we found that Amazonian forests produce biomass less efficiently in stands with residence times &gt;40 yrs and in stands with lower fertility, but changes to long‐term mean annual temperatures do not impact CUE.

Efectos de la fertilización del suelo sobre el crecimiento arbóreo en bosques pluviales tropicales del Chocó, Colombia

The tree diameter growth (CDA) is a fundamental component of net primary productivity (NPP) and carbon storage in forest ecosystems; therefore, it plays a key role in mitigating global climate change. It has been hypothesized that CDA in lowland tropical rain forests is limited by the availability of soil nutrients, yet little experimental evidence is available, especially in forest of high precipitation (&gt;5 000 mm per year). This study evaluated the effects of soil fertilization on CDA in tropical rainforests of the Colombian Pacific, one of the wettest areas of the world. Such effects were assessed at the level of localities, diametric categories, wood density, and functional groups. To do this, two arboreal inventories (2014 and 2015) were performed, five fertilization treatments (Nitrogen-N, Phosphorus-P, Potassium-K, NPK and Control) were applied, and the CDA was determined in five permanent plots of one hectare. We found that the application of N and NPK had little effect on CDA as compared to the control; while the addition of P and K produced significant reduction of the trees relative growth rate, with respect to the control at the level of localities, in small and medium sized trees, in all wood densities (low, medium and high), and in the group of dicotyledonous species. Although these results did not corroborate the hypothesis of nutrient limitation on CDA in the studied forests, it was found that during the early years of fertilization (mainly with P and K), different patterns of aboveground and belowground NPP occurred to maximize photosynthesis and soil nutrient acquisition.

Correction: Net Primary Productivity and Edaphic Fertility in Two Pluvial Tropical Forests in the Chocó Biogeographical Region of Colombia.

[This corrects the article DOI: 10.1371/journal.pone.0168211.].

Net Primary Productivity and Edaphic Fertility in Two Pluvial Tropical Forests in the Chocó Biogeographical Region of Colombia.

The net primary productivity (NPP) of tropical forests is a key process of the carbon cycle and therefore for the mitigation of global climate change. It has been proposed that NPP is limited by the availability of soil nutrients in lowland tropical forests and that belowground NPP decreases as edaphic fertility increases. This hypothesis was evaluated in two localities (Opogodó and Pacurita) of the Chocó Biogeographical region, one of the rainiest of the world, where the aboveground (litter and wood) and belowground (fine and coarse roots) components of NPP were measured. Fertility parameters (pH, nutrients, and texture) were also determined and related to NPP. Total NPP was similar between locations (23.7 vs. 24.2 t ha-1 year-1 for Opogodó and Pacurita, respectively). However, components of NPP showed differences: in Pacurita, with steeper topography, NPP of wood and coarse roots were higher; therefore, differences of topography and drainage between localities probably affected the NPP of wood. On the other hand, soils of Opogodó, where NPP of fine roots was higher, showed higher contents of sand, N+, and organic matter (OM). With the increase of pH, OM, N+, K, Mg, and sand, the NPP of leaves and fine roots as well as the percentage of NPP belowground also increased, which suggests NPP limitation by multiple nutrients. The increase of NPP belowground with the availability of edaphic nutrients evidenced a redistribution of the aboveground and belowground components of NPP with the increase of soil fertility in oligotrophic systems, probably as a mechanism to improve the capture of resources.

Relación entre la producción de hojarasca y las condiciones edáficas en bosques pluviales tropicales del Chocó Biogeográfico, Colombia

Litter production (NPP litterfall ) is one of the main components of net primary productivity (NPP) in forest ecosystems. Such NPP litterfall  is determined considerably by the soil conditions in tropical rainforests. To evaluate this hypothesis five 1-ha permanent plots were established in two forests of Choco (Opogodo and Pacurita) where NPP litterfall  was measured in 125 collectors, monthly-monitored for a year. In addition, basic soil-fertility parameters were measured and related to the NPP litterfall . It was observed that both forests exhibited nutrient-poor soils, but with higher sand content, total N and organic matter (OM) in Opogodo. The NPP litterfall  was similar in both forests (7.82 t ha -1  yr -1  in Opogodo, and 7.35 t ha -1  yr -1  in Pacurita). Also, the litter-fall components with greatest contribution were leaves (> 60%), stems (19%) and miscellaneous (14%). Total NPP litterfall  showed a weak negative correlation with the percentage of silt. Leaf litter production was positively associated with sand content, pH, O.M. and total nitrogen; whereas, it was negatively correlated with aluminum (Al), effective cation exchange capacity (ECEC) and silt. In general, correlations between NPP litterfall  and soil parameters were weak, apparently due to the small variation in soil fertility and low availability of some nutrients (phosphorus and calcium). Therefore, these results partially confirmed the hypothesis of soil-fertility limitation upon NPP in the forests of Choco.