Aboveground Biomass Accumulation Research Articles

The metropolitan parks of Quito as important carbon sinks

Abstract Despite the importance of urban forests as important carbon sinks, studies in Ecuador have yet to assess their potential to store carbon. We assessed the carbon stored in the aboveground biomass (AGB) and annual rates of AGB accumulation in the Guangüiltagua Metropolitan Park (GMP) and the Southern Metropolitan Park (SMP). We installed 11 plots per park of 0.063 ha, where we surveyed all stems with a diameter at breast height (DBH) ≥2.5 cm. To estimate annual increments in AGB, we installed dendrometer bands on 10% of the total stems recorded in each plot (only in stems with ≥10 cm DBH). We measured the dendrometer band segment increase every 4 months from September 2019 to October 2020. Our results show that the GMP stores 171 ± 96 Mg C ha−1, significantly higher than the amount of carbon storage recorded in the SMP (100 ± 41 Mg C ha−1). In contrast, the GMP sequestered 3.30 ± 1.71 Mg C ha year−1, while the SMP sequestered an average of 4.45 ± 2.63 Mg C ha year−1. At the landscape scale, the SMP contains 0.072 Tg C (0.058–0.091, 95% CI), while the GMP contains a reservoir of 0.096 Tg C (0.067–0.13, 95% CI). Likewise, the AGB in the SMP 3,165 Mg C year−1 (2209–4297, 95% CI), while that in the GMP sequestered 1859 Mg year−1 (1361–2430, 95% CI). Our results show that the metropolitan parks of Quito are important carbon sinks and constitute essential elements in mitigating climate change in urban spaces.

Incorporating small‐scale disturbances in models of forest structure and aboveground biomass of tropical mountains

AbstractSeveral efforts have been made to model forest structure and estimate global aboveground biomass (AGB) magnitude and distribution. However, AGB models still show large uncertainties, especially over tropical mountains that are difficult to survey and understudied. Although forest disturbance and land use greatly influence forest structure and AGB accumulation, they are rarely considered in forest structure and AGB models. Including the effect of forest disturbance and land use could improve model performance. In this study, we used Landsat time series analysis and forest inventory data to assess and model the effect of small‐scale disturbance and land use on tropical montane forest structure and AGB. We explored two approaches: abrupt forest change detection, using the algorithm Breaks For Additive Seasonal Trend (BFAST), and gradual vegetation change by calculating the variation of remote sensing vegetation indices over time. We found that tropical montane landscapes are very dynamic and heterogenous. Out of the 284 forest plots analyzed, 27% had abrupt disturbances at least once between 1993 and 2014, and some of them showed abrupt disturbances several times. Forest plots with abrupt disturbances exhibit statistically significant lower basal area, tree height, and AGB than plots without abrupt disturbances. Using linear mixed‐effects models, we found that the number of breakpoints, annual Normalized Difference Vegetation Index SD, and Normalized Difference Water Index minimum values over time were the most informative variables for predicting forest structure, particularly basal area (adjusted R2 = 0.61). These variables are easy to calculate and could add significant power to forest structure and AGB models. In conclusion, incorporating small‐scale disturbance to model forest structure and AGB at regional scales is feasible through the identification of recent abrupt and gradual forest change using remote sensing time series. Including recent forest disturbance variables as predictors in forest structure models can greatly improve biomass predictability and mapping in dynamic landscapes.

Tropical dry forest response to nutrient fertilization: a model validation and sensitivity analysis

Abstract. Soil nutrients, especially nitrogen (N) and phosphorus (P), regulate plant growth and hence influence carbon fluxes between the land surface and atmosphere. However, how forests adjust biomass partitioning to leaves, wood, and fine roots in response to N and/or P fertilization remains puzzling. Recent work in tropical forests suggests that trees increase fine root production under P fertilization, but it is unclear whether mechanistic models can reproduce this dynamic. In order to better understand mechanisms governing nutrient effects on plant allocation and improve models, we used the nutrient-enabled ED2 model to simulate a fertilization experiment being conducted in a secondary tropical dry forest in Costa Rica. We evaluated how different allocation parameterizations affected model performance. These parameterizations prescribed a linear relationship between relative allocation to fine roots and soil P concentrations. The slope of the linear relationship was allowed to be positive, negative, or zero. Some parameterizations realistically simulated leaf, wood, and fine root production, and these parameterizations all assumed a positive relationship between relative allocation to fine roots and soil P concentration. Model simulations of a 30-year timeframe indicated strong sensitivity to parameterization and fertilization treatment. Without P fertilization, the simulated aboveground biomass (AGB) accumulation was insensitive to the parameterization. With P fertilization, the model was highly sensitive to the parameterization and the greatest AGB accumulation occurred when relative allocation to fine roots was independent of soil P. Our study demonstrates the need for simultaneous measurements of leaf, wood, and fine root production in nutrient fertilization experiments and for longer-term experiments. Models that do not accurately represent allocation to fine roots may be highly biased in their simulations of AGB, especially on multi-decadal timescales.

Does human intervention modulate the above-ground carbon biomass of agroforestry systems? A study of homegardens in Jaffna peninsula, Sri Lanka

CONTEXTAccumulating above-ground biomass (AGB) and conservation of biodiversity are two major services provided by any ecosystem and homegardens are no exceptions. The permanent structure of a homegarden is owing to its perennial tree-community which steadily builds up and maintains the tree diversity and AGB accumulation. Being a manmade agroforestry system, humans play a vital role in mediating each component of homegarden ecosystem including its carbon stock and biodiversity through management of the tree community. OBJECTIVEThe objectives of this study were to compute the tree diversity and AGB and human interventions in homegarden ecosystem in Jaffna peninsula and to identify the most prominent factors affecting the AGB. METHODSA primary survey was conducted capturing 135 homegardens from two agro-ecological regions (DL3 and DL4) in Jaffna peninsula (Northern province, Sri Lanka), where homegardens are observed as the primary tree-based vegetation. Data on floral composition, livestock and, household-interventions in homegardens were gathered through a structured questionnaire. Tree diversity and AGB were computed using Shannon-Wiener index (SWI) and carbon stock respectively. A multiple linear regression model was estimated to determine the effects of pre-defined interventions on AGB of homegardens. RESULTS AND CONCLUSIONSThe study sample consisted of 122 small-scale (<0.2 ha), 11 medium-scale (0.2–0.8 ha) and 02 large-scale (>0.8 ha) homegardens. The mean tree diversity as estimated by SWI was 1.1 ± 0.6 with 38 perennial species and 1286 trees; 32 genera and 17 families. An average homegarden is estimated to store 23.8 ± 20.9 Mg C/ha as AGB. Homegardens which reared livestock animals, had a significantly lower SWI value, yet, a higher AGB stock, compared to the opposed group (p < 0.05). The SWI, time allocation (hours) for homegarden/week/ha, technical knowledge on farming and non-timber usage within homegarden have significantly (p < 0.05) contributed to the AGB of homegardens, with regression-coefficients of 6.12, 0.02, 1.38 and 7.91, respectively. The results indicate that up-keeping the commitment of households in managing their homegardens contribute to environmental sustainability. SIGNIFICANCEThe results revealed a significant contribution of human interactions on the size of the AGB of homegardens in Jaffna peninsula. This contribution was not adequately discussed in previously literature and the findings suggest the need to manage human interactions in homegarden agroforestry systems to optimize carbon stock in traditional homegardens.

The effects of geomorphology, soil and climate on the trajectory of aboveground biomass accumulation of beech (Fagus sylvatica L.) at the southern range margin

Forest ecosystems are among the most important carbon sinks in the terrestrial biomes. Therefore, the estimation of aboveground biomass accumulation is of fundamental importance for understanding the contribution of forest stands to the global carbon budget. In this study, we proposed a modelling approach to estimate aboveground biomass of beech forests in the Central Apennine based on stand age, climatic variables, topographic features and soil parameters. Using forest inventory data from the local forest management plans, international databases, and mixed-effect linear model, we identified stand age as a major driver of beech forests aboveground biomass. Climatic variables had generally higher influence than soil and topographic features, probably as a consequence of the homogeneous calcareous substrate which favoured the development of soils which are highly suitable for the growth of beech. Temperature range and seasonality were the most important climatic variables. Interestingly, we found that the aboveground biomass in Apennine beech forests is strongly site-specific. Different management approaches during the past centuries, i.e. presence or absence of conversion interventions of the analysed stands, are probably responsible for the growing site's significant influence. By highlighting the ideal locations for allocating the functions of forest production or evaluating the value of ecosystem services that regulate the climate, this study will help to improve both the precision of carbon budget modelling and decision-making in nature conservation and forest management.

Assessment of aboveground biomass and carbon accumulation in natural cenoses on the terraces of the northern slope of Khoysko‐the Makazhoy (Cheberloy) basin

Carbon exists as carbon dioxide in the atmosphere and makes up about 0.04% of the atmosphere. In the recent past, it has attracted a lot of attention as a greenhouse gas because it can influence the climate model of the world. Anthropogenic activities such as industrialization, deforestation, forest degradation and the burning of fossil fuels have caused an increase in atmospheric carbon levels and disrupted the global carbon cycle. The Climate Change Expert Group has identified five carbon pools of the terrestrial ecosystem that include biomass, namely aboveground biomass, underground biomass, debris, woody debris and soil organic matter. Among all carbon pools, aboveground biomass constitutes the major part of the carbon pool.

Влияние питательного субстрата на рост и распределение биомассы сеянцев Picea obovata Ledeb. в Северной Монголии

The development of seedling production technology and methods of establishing highyielding plantations of Picea obovata Ledeb. on a scientific basis is one of the urgent problems of forestry in Mongolia. In this study, we aimed to solve the following problems: to conduct a comparative analysis of the seedling growth parameters and biomass accumulation grown on different nutrient substrates; to assess the relationship between seedling growth, biomass accumulation and soil properties; to determine the most optimal nutrient substrates for seedling production of Siberian spruce in greenhouse conditions in Northern Mongolia. Six formulations of nutrient substrates (T1, Т2, Т3, Т4, Т5, Т6) were used for the seedling production of Picea obovata Ledeb. in greenhouses equipped with a sprinkler system. Nutrient substrates were prepared using black soil, manure, compost, peat, sawdust, sand in different composition ratios. During the 4-year-observation period height, root collar diameter, root length and aboveground and belowground biomass of seedlings were measured at the end of each growing season. We divided the biomass of seedlings into several structural elements. We found that all tested nutrient substrates, except the control substrate, had a positive effect on seedling growth in height and diameter. Comparative analyses showed that different ratio and composition of black soil, compost, manure, sawdust, and sand in the nutrient substrate had different effects on seedling growth (p &gt; 0.001) and biomass accumulation (p &gt; 0.001). Among the proposed nutrient substrates, the treatments T2 (50 % black soil + 20 % sand + 20 % peat + 10 % compost) and T6 (60 % black soil + 20 % sand + 10 % peat + 10 % compost) were selected as the most effective soil substrate that are suitable for further seedling production of Siberian spruce under greenhouse conditions in Mongolia. There fore, it was observed that good root system development was a determinant of seedling growth in height, diameter, and aboveground biomass accumulation especially from 3–4 years of age. Spruce seedling growth was positively correlated not only with humus content (r = 0.46), but also with soil acidity (r = 0.43) and available phosphorus (r = 0.48). The results of this investigation made an important contribution to the development of production technology for growing standard and large-sized seedlings of Picea obovata in greenhouse complexes in Northern Mongolia. For citation: Jagdag D., Batsaikhan G., Baatarbileg N., Lobanov A.I., Gerelbaatar S. Effect of Nutrient Substrate on Seedling Growth and Biomass Allocation of Picea obovata Ledeb. in Northern Mongolia. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 6, pp. 57–69. (In Russ.). https://doi.org/10.37482/0536-1036-2023-6-57-69

Increasing diversity gradient in lentil mixtures for intercropping with wheat reveals an increase in lentil biomass with minimal impact on mycorrhizal activity

The management of arbuscular mycorrhizal fungi (AMF) is crucial for sustainable agricultural systems, given its beneficial impacts on soil health and crop productivity. This study aimed to assess the effect of lentil (Lens culinaris Medik.) mixtures for intercropping with durum wheat (Triticum durum Desf.) on mycorrhiza and investigate the role of legume intraspecific diversity in mycorrhizal development and crop biomass production. Since both intraspecific and interspecific diversity (i.e., cultivar mixtures and intercropping) have an effect in shaping soil microbiota in the rhizosphere, we hypothesised that increasing the level of diversification in the system enhances the provision of services (e.g., aboveground biomass accumulation), due to enhanced microbial activity and diversity. Specifically, increasing diversity within lentil cultivar mixtures strengthens the affinity of wheat for mycorrhiza, thereby influencing wheat mycorrhization in wheat-lentil intercrops. To test our hypothesis, we designed three lentil cultivar mixtures with increasing diversity levels using a trait-based approach, drawing from a pool of Italian lentil landraces characterised in a previous study. As an additional factor, we intercropped lentil mixtures with wheat and compared it with sole wheat and sole lentil commercial cultivar. In both experimental years, intercropping lentil mixtures with wheat consistently yielded higher soil mycorrhization levels (46% in 2021 and 52% in 2022) compared to sole wheat cultivation (23% in 2021 and 34 % in 2022). Nevertheless, AMF colonisation in lentil roots was significantly higher in sole crops (55% in 2021 and 70% in 2022, except for the commercial cultivar) compared to intercrops (35% in 2021 and 60% in 2022). This difference could be attributed to the presence of wheat, which might have suppressed the capacity of lentils to establish successful symbiosis with mycorrhiza. On the other hand, AMF colonisation of wheat roots in 2022 was significantly higher (52%) when intercropped with lentils than when cultivated as sole wheat (40%). Concerning biomass production in lentil mixtures in 2022, we observed a positive correlation between lentil biomass and the number of functional groups in the mixtures, both as pure stands (R2 = 0.19, p = 0.06) and intercrops (R2 = 0.29, p = 0.01). Additionally, in 2022, the total biomass of the intercropped system increased with the increase in diversity. Further experiments, incorporating microbial genetic analysis, are necessary to uncover potential associations between functional mixtures and AMF composition.

Plant biotype interacting grazing activity shapes grassland ecosystem functions

AbstractGrasslands play an essential role in maintaining the health of planet Earth, but many grasslands have lost their ecosystem services due to unsustainable management practices, such as overgrazing. Little is known about how grazing activity interacts with plant biotypes, impacting grassland ecosystem services. Here, we (1) assessed the relative performance of five plant biotypes in response to grazing activities and (2) determined the effectiveness of grazing exclusion in enhancing soil physiochemical properties in grasslands. The synthesis of 39,214 observations on plant‐, soil‐, and anthropogeny‐related factors from 88 published studies revealed that grazing exclusion increased aboveground plant biomass accumulation by 100.4% (±4.2 SE), belowground biomass by 70.2% (±25.7), total soil C content by 21.4% (±1.7), and soil organic carbon (SOC) concentration by 14.3% (±0.8), on average, as compared to moderate‐to‐heavy (MtH) grazing. Plant biotypes responded to grazing activities differently; alpine meadows increased total soil C content by 107.2%, alpine steppes increased SOC by 52.2%, but desert steppes decreased total C content by 21.8% under the grazing exclusion. All plant biotypes reduced soil bulk density by 6.4%–19.4% under grazing exclusion. Soil microbial community diversity responded to grazing activities inconsistently, ranging from an 18% decrease to a 26% increase in soil microbial diversity compared to MtH grazing. We conclude that selecting appropriate plant biotypes alongside improved grazing management will enhance grassland ecosystem functions and services as plant biotypes affect aboveground and belowground biomass and interface with soil physiochemical properties.

Recovery of aboveground biomass, soil carbon stocks and species diversity in tropical montane secondary forests of East Africa

Tropical montane forests are fragile ecosystems that provide a wide range of ecosystem services including hydrological services, biodiversity protection and storing carbon in the above and belowground and soils contributing to climate change mitigation. The world’s tropical montane forests are increasingly exposed to degradation and their recovery after disturbance has not been adequately quantified. Here, using information from 47 plots in three blocks of the Mau Forest Complex of Kenya, we assessed the changes in aboveground biomass (AGB), tree species diversity, soil carbon and nitrogen stocks following forest clearance. AGB recovered at an annual rate of 6.42 Mg ha−1 yr−1 in the first 20 years, the rate then slowed down to 4.46–4.67 Mg ha−1 yr−1 at around 25–30 years. Around 25 years after disturbance, AGB in recovering forests was 70 % (198.32 ± 78.11 Mg ha−1) of the AGB in the old secondary forest (OSF) (282.86 ± 71.64 Mg ha−1) and was statistically indistinguishable. Stem density, species diversity and richness indices did not show significant differences across recovery classes. There was no significant difference in soil carbon and nitrogen stocks across classes with the soil carbon (184.1 ± 41 Mg ha−1) of the young secondary forest (<10 years) being 84.5 % of that of the OSF (217.9 ± 51.8 Mg ha−1). This study reports a rapid rate of AGB and carbon accumulation within 20 years of disturbance, and high levels of species richness in these previously disturbed fragments of tropical montane forests of East Africa.

Impacts of climate change on semi-natural alpine pastures productivity and floristic composition

Climate change impact on pasture floristic composition needs to be carefully assessed, given its key role for the resilience of pastoral systems and related ecosystem services. Nevertheless, variations in floristic composition are rarely taken into account in climate change impact studies. Here, we used the plant community model CoSMo to simulate future dynamics of biomass accumulation and floristic composition for high-altitude semi-natural alpine pastures. Dedicated multi-site field activities were conducted to collect data for model calibration. Simulations were run for four 20-year climate scenarios centered on 2040, resulting from the combination of two general circulation models (GISS-ES and HadGEM2) and two representative concentration pathways (RCP4.5 and RCP8.5). Results highlighted the capability of CoSMo to successfully reproduce the productivity and floristic composition of semi-natural pastures, modeling efficiency and R2 being higher than 0.90 for aboveground biomass accumulation and relative abundance of species. CoSMo simulated an overall positive effect of increasing temperatures on pasture productivity (+ 10.7% on average), due to higher biomass accumulation rates and longer growing seasons. However, these benefits were highly heterogeneous among the monitored pastures (ranging from − 2.5 to + 16.2%), because of differences in floristic composition and in species-specific thermal requirements that led to complex, non-linear reactions to climate variations. A negative impact of climate change was simulated for grazing value (− 11.1% on average), due to the higher suitability to future conditions of Nardus stricta, which has low grazing value compared to other species. Our results highlight that floristic composition should be explicitly considered while assessing climate change impacts on semi-natural pasture productivity and connected ecosystem services.

Sexual competition and light regimes interactively affect dimorphism and competitiveness of opposite sexes in Populus yunnanensis

Light, as the most important energy and environmental signal, exerts crucial impacts on plant-plant interactions and the composition of plant communities. However, little attention has been paid to understanding how females and males respond to sexual competition under different light conditions. In this study, we investigated morphological and physiological parameters between two sexes of Populus yunnanensis under intra- and intersexual competition in two light regimes, i.e., full light and shading conditions (equal to 55% full light). Under full-light conditions, males grown under intersexual competition exhibited greater above-ground biomass accumulation, specific leaf area (SLA), root-to-shoot ratio (R/S), non-structural carbohydrate (NSC) utilization efficiency, and a higher ability to maintain the balance of nitrogen (N) and phosphorus (P) content compared to females. These eco-physiological responses confer males with a competitive advantage over females under sufficient light conditions. In contrast, there were no significant sex-specific differences in biomass accumulation and relative competitive intensity (RCI) values under shade treatment. Under shading, the opposite sexes of P. yunnanensis exhibited mutual suppression of each other to varying degrees, showing similar competitive potential. These results demonstrate that the performance of plants in terms of morphology and physiology is strongly affected by patterns of sexual competition and light regimes. The asymmetry in sexual competition might be a crucial factor influencing the biased sex ratio of P. yunnanensis in natural habitats.

Estimating biomass of woody plants that grow in the different As-contaminated techno-soils in the ore-bearing provinces of Eastern Germany

Establishing the role of woody species as an instrument for heavy metal bioaccumulation is a relevant issue today in the context of the development of the phytoremediation system. The article presents the results of studies on the influence of different Arsenic (As) concentrations in soil on the development of aboveground biomass in Betula pendula Roth. and Populus tremula L. stands under conditions of reclamation plantings. The studies were conducted in 30 locations of birch and poplar tree plantations within the ore-producing regions of Saxony (Eastern Germany) in soil with different levels of As contamination. The highest As content was noted in the technosoil of the Davidschacht site, where the metalloid content was 229.3 times greater compared with a value in a conditionally uncontaminated area (Großschirma). The values of leaf area index and aboveground biomass obtained in field measurements were presented. The aboveground biomass values in the investigated plantations ranged from 189.9 ±10.16 to 201.8 ± 19.09 t/ha, and leaf area index values ranged from 1.74 ± 0.29 to 2.05 ± 0.16 m2/m2. Sentinel-2A multispectral images were processed for the construction of a map of the aboveground biomass distribution within the region under study. The values of the spectral indices for leaf area index were obtained with subsequent construction of the regression dependence of the aboveground biomass in the plantings on this indicator. The RMSE value for the developed model of the dependence of aboveground biomass on the leaf area index was 17.84 t/ha, which could be considered as satisfactory and can serve as a basis for practical application of the model developed. The inverse trend in relation to locations with different levels of soil contamination with As was determined for the aboveground biomass indicator. Within the region under study, the highest value of aboveground biomass in the stands was found for the area with the lowest As level. The results showed that the correlation coefficient between the highest of the optimal spectral indices, the leaf area index, and the aboveground biomass in B. pendula and P. tremula plantings was statistically significant and approached the value of 0.7. The results presented can become a theoretical basis for monitoring the accumulation of aboveground biomass of tree stands in areas with different levels of soil contamination with As. In perspective, the presented model of biomass estimation based on spectral technologies can serve as an application basis for rapid assessment of the growth and development parameters of forest stands in As-contaminated areas.

Low predictability in aboveground biomass accumulation in Brazilian semi‐deciduous seasonal Atlantic Forest restoration sites

There are high expectations about the role of active reforestation in mitigating climate change, by means of carbon sequestration and storage, fueling the carbon credit market. Carbon credits are calculated in advance based on the number of planted trees or, at best, the expected size and wood density of planted trees. However, the contribution of tropical reforestations with native species for carbon sequestration in the long term is still unclear, since most sites being monitored are less than 20 years old, thus limiting the ability to make forecasts of what is a dynamic, multifactor restoration outcome. We used a chronosequence to analyze aboveground biomass (AGB) accumulation in 30 Brazilian semi‐deciduous seasonal Atlantic Forest restoration sites sharing the same climate, soil type, and restoration technique. We evaluated the entire age range of 1–19 years, and three age intervals, 1–3 years, 4–8 years, and over 9 years. AGB, basal area, and tree density increased considering all ages (1–19 years). Our results showed, however, that the AGB, tree density, and basal area can increase linearly from 1 to 3 years but present no significant trend after 4 years. Adjusted model r2 values decreased with time, suggesting that the controlled effects of active restoration are quickly replaced by other natural, uncontrolled, and, to some extent, unknown factors. Although continued efforts are needed to make more realistic predictions of long‐term carbon stocks based on tree planting, high levels of biomass estimates for time intervals as short as 20 years may never be achieved.

Above-ground biomass accumulation in Cerradão managed by the mass ratio

Background: Forests have a huge potential to mitigate global warming through CO2 accumulation in their living biomass. Thus, understanding the functioning of these ecosystems is crucial for revealing factors that drive biomass accumulation. Functional diversity helps us understand ecosystem services, including biomass accumulation. Within this context, this work aimed to investigate the role of functional diversity in biomass accumulation for woody vegetation of the Cerradão. Methods: We estimated above-ground biomass (AGB) of 50 Cerradão stands in Brazil and measured five different functional traits associated with tree species’ survival and growth. For each stand, we calculated five community-weighted means (CWMs), based on each functional trait, and three functional diversity metrics. We specifically explored the relationship between CWMs describing functional diversity metrics and AGB. After that, exponential regressions were adjusted, using the variables that presented significant correlation as independent variables and AGB as a dependent variable. Regressions with more than one independent variable were fitted in a way that avoided collinearity. Based on the strongest correlation coefficient (r) and the lowest Akaike value (AIC), we chose the best regression to explain the majority of the variance in AGB. Results: Our results showed the role of function in determining AGB. In particular, bivariate correlations show that four CWM functional traits and two functional diversity metrics are significantly associated with AGB production, with CWM showing AGB estimation variables. However, multiple regression analyses show that maximum height is the only trait significantly associated with AGB and it alone provides the best model fit. Conclusions: The accumulation of AGB in Cerradão is explained by the mass ratio theory, and this ecosystem services is directly related to the presence and abundance of species with greater potential tree height (Htmax).

More effect of ephemeral plant species diversity on aboveground biomass than functional diversity and functional composition

AbstractThe quantification of plant diversity–productivity relationships is essential for accurate productivity assessments. Global change drivers are altering resource availability and biodiversity. However, the extent to which multiple attributes of diversity (species, functions) buffer community productivity in response to the resource availability changes and the potential driver mechanisms of the diversity‐productivity relationship still needs to be the consensus. We investigated the ephemeral plant diversity–productivity relationships of different attributes along a precipitation gradient in the Gurbantunggut Desert, China. To evaluate the potential mechanisms by which diversity and functional composition affect aboveground productivity (niche complementarity and selection effect). Our results showed that (1) the variance of species richness (SR), Rao's quadratic entropy (RaoQ), community‐weighted mean of height (CWMH), and community‐weighted mean of leaf phosphorus concentration (CWMP) was larger among sites (variation between different sites) than subplots (variation between different subplots). Among subplots, the variance of community‐weighted mean of specific leaf area (CWMSLA), community‐weighted mean of leaf carbon concentration (CWMC), and community‐weighted mean of leaf nitrogen concentration (CWMN) was larger than the sites. (2) SR, RaoQ, CWMC, CWMN, CWMH, pH, and mean annual precipitation (MAP) collectively influenced the accumulation of aboveground biomass (AGB). (3) Species diversity and MAP have strongly affected AGB and accounted for 50% and 42%. The study confirms that SR is the optimal predictor of biomass in ephemeral plants. Complementation effects may be the primary mechanism explaining the relationship between biodiversity and productivity in the Gurbantunggut Desert, and thus the effect of plant diversity cannot be downplayed.

Effects of the nitrate and ammonium ratio on plant characteristics and Erythropalum scandens Bl. substrates.

Erythropalum scandens Bl. is a woody vegetable with high nitrogen demand that inhabits southern China. Ammonium and nitrate are the two main forms of inorganic nitrogen that plants directly absorb. A pot experiment was performed to determine the growth, physiological responses, and preferences of 12-month-old E. scandens seedlings for ammonium and nitrate. Aboveground and underground growth indexes, biomass, physiological and biochemical indexes (chlorophyll [Chl], soluble sugar, soluble protein and free proline contents), and substrate pH and nitrogen contents were determined under different nitrate and ammonium ratios (0 NO3-: 100 NH4+, 25 NO3-: 75 NH4+, 50 NO3-: 50 NH4+, 75 NO3-: 25 NH4+, and 100 NO3-: 0 NH4+), and the control (0 NO3-: 0 NH4+). The results showed that ammonium and nitrate improved the growth and physiological status of E. scandens seedlings in most of the treatments compared to the control. The aboveground growth status and biomass accumulation of E. scandens seedlings were significantly better under the 0 NO3-: 100 NH4+ treatment during fertilization compared with all other treatments. However, the growth status of the underground parts was not significantly different among treatments. Significant differences in osmoregulator content, except for soluble sugars, and Chl content were observed. Soluble sugars and soluble proteins were highest under the 0 NO3-: 100 NH4+ treatment at the end of fertilization (day 175). However, free proline accumulated during fertilization and the increase in NO3- indicated that excessive use of NO3- had a negative effect on the E. scandens seedlings. The order of accumulating nitrogen content was leaves > roots > stems. The highest N accumulation occurred in the aboveground parts under the 0 NO3-: 100 NH4+ treatment, whereas the highest N accumulation occurred in the underground parts under the 50 NO3-: 50 NH4+ treatment. Substrate pH increased at the end of fertilization (day 175) compared with the middle stage (day 75), while total nitrogen, ammonium, and nitrate were highly significantly different among the treatments. Total nitrogen and NH4+ content were the highest under the 0 NO3-: 100 NH4+ treatment, while NO3- content was the highest under the 100 NO3-: 0 NH4+ treatment. In conclusion, 12-month-old E. scandens seedlings grew best, and had better physiological conditions in NH4+ than NO3-. The 0 NO3-:100 NH4+ treatment (ammonium chloride 3.82 g/plant) resulted in the best growth and physiological conditions. Most of the growth and physiological indexes were inhibited with the increase in nitrate.

Optimizing Grain Yield and Radiation Use Efficiency through Synergistic Applications of Nitrogen and Potassium Fertilizers in Super Hybrid Rice.

The remarkable yield performance of super hybrid rice has played a crucial role in ensuring global food security. However, there is a scarcity of studies investigating the contribution of radiation use efficiency (RUE) to hybrid rice yields under different nitrogen and potassium treatments. In this three-year field experiment, we aimed to evaluate the impact of two hybrid rice varieties (Y-liangyou 900: YLY900 and Quanyouhuazhan: QYHZ) under varying nitrogen regimes (N90: 90 kg N ha-1, N120: 120 kg N ha-1, N180: 180 kg N ha-1) and potassium regimes (K120: 120 kg K2O ha-1, K160: 160 kg K2O ha-1, K210: 210 kg K2O ha-1) on grain yield and its physiological determinants, including RUE, intercepted photosynthetically active radiation (IPAR), aboveground biomass production, and harvest index (HI). Our results revealed that both rice varieties exhibited significantly higher yields when coupled with nitrogen and potassium fertilization. Compared to the N90 × K120 treatment, the N120 × K160 and N180 × K210 combinations resulted in substantial increases in grain yield (12.0% and 21.1%, respectively) and RUE (11.9% and 21.4%, respectively). The YLY900 variety showed notable yield improvement due to enhanced aboveground biomass production resulting from increased IPAR and RUE. In contrast, the QYHZ variety's aboveground biomass accumulation was primarily influenced by RUE rather than IPAR, resulting in higher RUE and grain yields of 9.2% and 5.3%, respectively, compared to YLY900. Importantly, fertilization led to significant increases in yield, biomass, and RUE, while HI remained relatively constant. Both varieties demonstrated a positive relationship between grain yield and IPAR and RUE. Multiple regression analysis indicated that increasing RUE was the primary driver of yield improvement in hybrid rice varieties. By promoting sustainable agriculture and enhancing fertilizer management, elevating nitrogen and potassium levels from a low base would synergistically enhance rice yield and RUE, emphasizing the critical importance of RUE in hybrid rice productivity compared to HI.

Responses of Ephemeral Plants to Precipitation Changes and Their Effects on Community in Central Asia Cold Desert.

In the context of global climate change, changes in precipitation patterns will have profound effects on desert plants, particularly on shallow-rooted plants, such as ephemeral plants. Therefore, we conducted an experiment on artificial control of precipitation for four dominant ephemeral plants, Erodium oxyrhinchum, Alyssum linifolium, Malcolmia scorpioides, and Hyalea pulchella, in the southern edge of Gurbantunggut Desert. We measured the importance value and some growth parameters of the four species under increased or decreased precipitation and constructed trait correlation networks for each of the four species. We also compared the response of increased or decreased precipitation to vegetation coverage. The results show that drought significantly reduced the survival rate, seed production and weight, and aboveground biomass accumulation of ephemeral plants. The four ephemeral plants showed different tolerance and response strategies to precipitation changes. E. oxyrhinchum and M. scorpioides can avoid drought by accelerating life history, and E. oxyrhinchum, A. linifolium, and H. pulchella can alleviate the negative effects of drought by adjusting leaf traits. However, the response of different species to the wet treatment was not consistent. Based on the results of the trait correlation network, we consider A. linifolium belongs to the ruderal plant, E. oxyrhinchum and M. scorpioides belong to the competitive plants, and H. pulchella belongs to the stress-tolerant plant. The outstanding trait coordination ability of E. oxyrhinchum makes it show absolute dominance in the community. This indicate that ephemeral plants can adapt to precipitation changes to a certain extent, and that distinct competitive advantages in growth or reproduction enabled species coexistence in the same ecological niche. Nevertheless, drought significantly reduces their community cover and the ecological value of ephemeral plants. These findings established the basis to predict vegetation dynamics in arid areas under precipitation changes.

Simulation of stand dynamics for miombo woodlands in Kitulangalo Forest Reserve, Morogoro, Tanzania

ABSTRACT Miombo woodlands constitute the most extensive type of forest cover within South and East Africa, Tanzania in particular, and they are seriously threatened by intensive degradation and deforestation. The dynamics of miombo stands were examined in this study using a simple simulation system applied to experimental stands at the Kitulangalo Forest Reserve (KFR) in Tanzania. Prediction of tree-level diameter increment, mortality, and ingrowth across species groups with empirical models based on data from experimental sites constituted the essential elements of the simulation system. Diameter distribution, stand basal area, volume yield, and above-ground biomass accumulation were assessed in three harvesting alternatives across three species groups. The results indicate a high degree of positive response to careful selective harvesting in lightly degraded, recovering miombo forests. Simulation systems compiled from experimentally based models seem promising as tools for research on stand dynamics and sustainable management alternatives in miombo woodlands.