Aboveground Biomass Production Research Articles

Promoting enhanced ecosystem services from cover crops using intra- and interspecific diversity

Farmers are increasingly looking to cover crops to provide ecosystem services to support yields, while reducing off-farm inputs. Research evidence in both unmanaged and agricultural ecosystems suggests that increased plant diversity can improve ecosystem service outcomes. The use of diverse cover crops as a practice to increase ecosystem service delivery has potential, though knowledge gaps remain regarding the types and levels of diversity that are most effective, and how environment may impact the desired outcomes. Using six species of legumes (hairy vetch, field pea, crimson clover) and of grasses (cereal rye, common wheat, ryegrass) along with multiple cultivars of each, we conducted an annual field experiment repeated twice during the winter fallow season. We tested the effect of a gradient of diversity in intraspecific mixtures, interspecific mixtures, and functional group (grass and legume) mixtures. We measured aboveground biomass production, weed biomass, soil-derived and fixed nitrogen in the shoots, and the C/N ratio of the aboveground biomass to evaluate corresponding ecosystem services relating to C and N cycling and weed suppression. Species mixtures, especially those composed of both grasses and legumes tended to have the most significant ecosystem service benefits suggesting that functional diversity is more significant than species richness. Where soil nutrients were less available, the diversity effect tended to be stronger, though this was significant in only two instances. These results lend some support to the stress-gradient hypothesis in that in more stressful conditions the diversity benefit was greater. Diverse mixtures may not consistently produce substantial service improvements, but there is little risk, and they may be most useful in marginal or depleted field conditions.

Lengthening single-stem rotation improves biomass yield and water use efficiency in black poplar genotype multi-stem rotation coppice plantations

Poplar short rotation coppice (SRC) plantations have great potential for supplying environmentally friendly bio-based industries. However, little research has focussed on the linkages between SRC management regimes and the consumption of water for biomass production in the Mediterranean environment. Therefore, we compared six hybrid clones and four native black poplar genotypes with an aim to examine how two different lengthening periods (3 vs. 5 years) of single-stem rotation affected growth performance in the following three years of multi-stem rotation coppice. To achieve this goal, we assessed the aboveground dry biomass production and variation in water use efficiency (WUE) of the genotypes annually. A longer single-stem rotation increased biomass productivity and WUE in the multi-stem rotation of the native black poplar, rather than that of the hybrid genotypes. In contrast, biomass and WUE performances did not diverge between the native and hybrid genotypes under the shorter single-stem phase. These findings underline the importance of lengthening the rotation of single-stem SRC plantations in hot and dry Mediterranean climates. Native black poplar genotypes managed in SRC should be strongly considered as environmentally compatible genetic resources both in protected areas and in areas where water supply constrains biomass production.

Contributions of individual cover crop species to rainfed maize production in semi-arid cropping systems

Cover crop (CC) species selection can contribute to reducing soil penetration resistance (brassica species), improved soil nitrogen (N) cycling (legume species), and suppression of weeds (grass species). However, one of the main concerns about including CCs in water-limited environments is soil water use and the consequences to subsequent crops. To determine the effects of individual CC species under water-limited environments, we evaluated fall and spring CC biomass produced, and soil water and N content, penetration resistance, weed density and biomass during the maize growing season, and maize grain yield. The experiment was conducted under a winter wheat-maize-fallow rotation at two locations (North Platte and Grant, NE) during 2016−2017 and 2017−2018 (four site-years). Treatments consisted of seven popular CC species plus a control (fallow), planted after winter wheat harvest. Spring oats, Siberian kale, and purple top turnip produced greater fall biomass, while cereal rye produced the greatest amount of spring biomass. However, cereal rye reduced soil volumetric water content in North Platte 2016−2017 and increased soil penetration resistance from 20–30 cm soil depth across site-years likely due to soil water use. Spring cover crop growth suppressed weeds early in the maize growing season. Due to its aboveground biomass production, cereal rye decreased weed density and biomass by 80 and 88 %, respectively, compared to the fallow treatment. On the other hand, except for brassicas, CCs decreased N levels in the soil during maize growing season, and all CC species reduced maize grain yield up to 30 % compared to fallow (except spring oats). Spring oats can be an alternative to cereal rye as CC species for semi-arid regions. However, since CCs did not promote any maize yield gain, our findings suggest that producers should use caution when incorporating CCs in their cropping systems in water-limited environments. This research provides valuable information on the potential impact of CCs on rainfed maize production, as well as help producers and agronomists develop better CC management programs for cropping systems in semi-arid regions.

Full-Season Cover Crops and Their Traits That Promote Agroecosystem Services

Non-marketable crops are increasingly being used as a tool to promote agroecosystem services and sustainable agriculture. Nevertheless, crops vary greatly in the traits by which they capture resources and influence the local ecosystem. Here we report on the traits and associated soil microbial communities that relate to aboveground biomass production, nutrient capture, weed suppression, erosion control and building particulate organic matter of 22 different full-season cover crops. All agroecosystem services were positively correlated with maximum canopy height and leaf area. Rooting density was positively associated with indices of bacterial diversity. While some legumes produced the greatest standing N and P in aboveground biomass, they were also poor at capturing soil nitrate and promoted high levels of potential plant fungal pathogens. Conversely, Brassicaceae crops had the lowest levels of potential plant fungal pathogens, but also suppressed saprophytic fungi and rhizobia. Thus, not all crops are equal in their ability to promote all agroecosystem services, and while some crops may be ideal for promoting a specific agroecosystem service, this could result in a trade-off with another. Nonetheless, our study demonstrates that plant functional traits are informative for the selection of crops for promoting agroecosystem services.

Physiological Responses of Contrasting Maize (Zea mays L.) Hybrids to Repeated Drought

Maize is the most important crop worldwide in terms of production and yield, but every year a considerable amount of yield is lost due to drought. The foreseen increase in the number of drought spells due to climate change raises the question whether the ability to recover quickly after a water pulse may be a relevant trait for overall drought resistance. We here address the following hypotheses: (i) different maize hybrids exhibit distinct physiological adaptive responses to drought stress and (ii) these responses affect the ability to recover from the stress. (iii) The relative biomass production of maize hybrids, which show severe drought symptoms but are able to recover quickly after a water pulse, is comparable to those hybrids, which invest more energy into tolerance mechanisms. The physiological responses of eight maize hybrids to repeated drought were elucidated employing physiological parameters such as electrolyte leakage, osmolality, relative water content, growth rate and gas-exchange measurements. Only one hybrid was able to maintain biomass production under drought conditions. Amongst the others, two hybrids with similar growth inhibition but contrasting physiological responses were identified by a PCA analysis. Both strategies, i.e. stabilization of leaf water content via resistance mechanisms versus high recovery potential were equally effective in maintaining aboveground biomass production in the scenario of a long drought intermitted by a water-pulse. However, each strategy might be advantageous under different drought stress scenarios. Overall, the recovery potential is underestimated in drought resistance under natural conditions, which includes periodic cycles of drought and rewatering, and should be considered in screening trials.

Gone and forgotten: facilitative effects of intercropping combinations did not carry over to affect barley performance in a follow-up crop rotation

AimIntercropping often leads to improved productivity of individual species compared to monocultures. We have practically little knowledge of facilitation effects in different intercropping systems and their importance in creating soil legacies that can indirectly affect the succeeding crop in a crop rotation through plant-soil feedback (PSF) effects.MethodsTo test this, we used a two-phased field experiment where we combined intercropping and crop rotation. During intercropping, we grew maize, faba bean, and lupine in monocultures or two-species crop combinations. The following season, we grew winter barley on the soil previously used for intercropping to test PSF effects under field conditions.ResultsWe found evidence for facilitative effects on aboveground biomass production that were species-specific with faba bean and maize biomass benefitting when intercropped compared to their expected biomasses in monocultures. Lupine, in contrast, performed best in monocultures. After the intercropping phase, total soil mineral nitrogen was higher in legume monocultures creating soil legacies but this did not affect soil microbial parameters and barley biomass production in the follow-up rotation phase.ConclusionsWe found support for species-specific positive and negative interactions in intercropping. Our results also demonstrated that soil legacies play no significant role under moderately high nutrient environments.

Effects of perennial biomass yield energy grasses and fertilization on soil characteristics and nutrient balances

AbstractBesides its bioenergy potential, perennial grasses can also have positive impacts on soil quality. However, responses of soil organic carbon (SOC) and total nitrogen (TN) depend on multiple factors, including grass species selection and N and P addition. We investigated the effect of four N and P fertility treatments (control = 0 kg N + 0 kg P ha–1 [N0P0]; 100 kg N + 0 kg P ha–1 [N1P0]; 0 kg N + 100 kg P ha–1 [N0P1]; 100 kg N + 100 kg P ha–1 [N1P1] applied annually] across 9 yr in Uruguay on soil nutrient balances, C and N pools, and biomass yields of elephantgrass (EG) (Pennisetum purpureum Schum.), giant reed (GR) (Arundo donax L.), and switchgrass (SW) (Panicum virgatum L.). Across years, EG had the highest biomass yield, followed by GR and SW (18.9, 16.3, and 14.1 Mg ha–1 yr–1, respectively). Across species, aboveground biomass increased by 46% with N addition. Yield response to P fertilization was lower (+11%). Elephantgrass had the highest N and P negative balance. Soil organic C and TN concentration were affected by species but not by fertilizer treatments. Giant reed had the highest SOC content gain in the first 0–40 cm (540 kg C ha– yr–1), and was the only species maintaining TN content from the beginning of the study. Giant reed could be an excellent option as a bioenergy crop due to its high aboveground biomass production, and its positive impacts on SOC and TN pools.

Warming reduces the production of a major annual forage crop on the Tibetan Plateau

Climate warming has been proposed to increase primary production of natural grasslands in cold regions. However, how climate warming affects the production of artificial pastures in cold regions remains unknown. To address this question, we used open-top chambers to simulate warming in a major artificial pasture (forage oat) on the cold Tibetan Plateau for three consecutive years. Surprisingly, climate warming decreased aboveground and belowground biomass production by 23.1%–44.8% and 35.0%–46.5%, respectively, without a significant impact on their ratio. The adverse effects on biomass production could be attributed to the adverse effects of high-temperatures on leaf photosynthesis through increases in water vapor pressure deficit (by 0.05–0.10 kPa), damages to the leaf oxidant system, as indicated by a 46.6% increase in leaf malondialdehyde content, as well as reductions in growth duration (by 4.7–6.7 days). The adverse effects were also related to exacerbated phosphorus limitation, as indicated by decreases in soil available phosphorus and plant phosphorus concentrations by 31.9%–40.7% and 14.3%–49.4%, respectively, and increases in the plant nitrogen: phosphorus ratio by 19.2%–108.3%. The decrease in soil available phosphorus concentration could be attributed to reductions in soil phosphatase activities (by 9.6%–18.5%). The findings of this study suggest an urgent need to advance agronomic techniques and cultivate more resilient forage genotypes to meet the increasing demand of forage for feeding livestock and to reduce grazing damage to natural grasslands on the warming-sensitive Tibetan Plateau.

New Forest Aboveground Biomass Maps of China Integrating Multiple Datasets

Mapping the spatial variation of forest aboveground biomass (AGB) at the national or regional scale is important for estimating carbon emissions and removals and contributing to global stocktake and balancing the carbon budget. Recently, several gridded forest AGB products have been produced for China by integrating remote sensing data and field measurements, yet significant discrepancies remain among these products in their estimated AGB carbon, varying from 5.04 to 9.81 Pg C. To reduce this uncertainty, here, we first compiled independent, high-quality field measurements of AGB using a systematic and consistent protocol across China from 2011 to 2015. We applied two different approaches, an optimal weighting technique (WT) and a random forest regression method (RF), to develop two observationally constrained hybrid forest AGB products in China by integrating five existing AGB products. The WT method uses a linear combination of the five existing AGB products with weightings that minimize biases with respect to the field measurements, and the RF method uses decision trees to predict a hybrid AGB map by minimizing the bias and variance with respect to the field measurements. The forest AGB stock in China was 7.73 Pg C for the WT estimates and 8.13 Pg C for the RF estimates. Evaluation with the field measurements showed that the two hybrid AGB products had a lower RMSE (29.6 and 24.3 Mg/ha) and bias (−4.6 and −3.8 Mg/ha) than all five participating AGB datasets. Our study demonstrated both the WT and RF methods can be used to harmonize existing AGB maps with field measurements to improve the spatial variability and reduce the uncertainty of carbon stocks. The new spatial AGB maps of China can be used to improve estimates of carbon emissions and removals at the national and subnational scales.

Production of kale seedlings on substrates containing proportions of organic compost

One of the difficulties in the kale seedlings production in containers is to ensure the production of aboveground biomass with a limited portion of roots, restricted to a small volume of substrate. Thus, we investigated whether substrates with organic compost added to it associated with kale cultivars interfere in the quality of seedlings produced in a greenhouse. Here, we studied two kale cultivars and five substrates. The experiment was designed in randomized blocks, with treatments arranged in a bifactorial scheme (2 x 5), with three replications. We carried out the physical and chemical characterization of the substrates and evaluated attributes of the aerial part and root system of the kale seedlings. The results showed that the substrate with the highest water retention was the one without the addition of organic compost. The greater the proportion of organic compound added to the substrate, the higher the nitrogen, phosphorus and organic carbon values. Seedlings produced in the substrate with greater water retention capacity had better performance in relation to the morphology of the aerial part and the morphology of the root system. We conclude that seedlings of kale cultivars associated with substrates with higher water retention have better quality. Seedlings of the ‘Gaudina’ cultivar stand out for their better phytometric morphology, while seedlings of the ‘Manteiga’ cultivar have higher quality of root biomass.

Water Use, Efficiency, and Stomatal Sensitivity in Eastern Cottonwood and Hybrid Poplar Varietals on Contrasting Sites in the Southeastern United States

The southeastern United States has wide-scale potential to achieve high productivity from elite eastern cottonwood and hybrid poplar varietals to produce renewable bioenergy and bioproducts. In order to determine how environmental drivers impact water use and growth so that individuals can maintain growth during drought periods, varietals that use water efficiently, and/or tolerate water stress conditions, are needed to make planting recommendations across a variety of sites. Additionally, inoculation with nitrogen-fixing endophytic bacteria may improve water stress tolerance. The goals of this research were (1) to determine water use strategies using measurements of diurnal sapflow and differences in leaf retention for three eastern cottonwood (Populus deltoides, ST66, S7C8, and 110412) and three hybrid poplar (two P. deltoides × Populus maximowiczii, 6329 and 8019, and one Populus trichocarpa × P. deltoides, 5077) varietals on contrasting field sites, (2) determine the physiological impact of endophyte inoculation, and (3) determine which physiological parameters were most highly correlated with aboveground biomass. We found that whole-tree water use efficiency (WUE) was similar across varietals at 5.2 g biomass per kg water used and that water use scaled with tree size. We found that water use strategies in terms of scaled stomatal sensitivity to vapor pressure deficit converged across varietals under stressful soil water conditions at both sites, but that varietals 8019 and 110412 tended to exhibit the highest plasticity in stomatal sensitivity exhibiting the largest range in scaled stomatal sensitivity under different soil moisture conditions. Endophyte inoculation increased growth and stomatal sensitivity at the nitrogen-limited site. Leaf area, whole-tree WUE, and plasticity in stomatal sensitivity were correlated with aboveground biomass production across sites and varietals. Overall, these data can be used to model hydrologic impacts of large-scale Populus biofuel production as well as recommend varietals with efficient water use and stomatal sensitivity under a range of soil and atmospheric moisture stress factors.

Variability of stem solidness among miscanthus genotypes and its role on mechanical properties of polypropylene composites

AbstractMiscanthus (Miscanthus Andersson) is a perennial grass that is attracting growing interest from the biomaterial industry. Our aim was to compare miscanthus genotypes varying in stem solidness, a measure of degree to which pith fills cavity between the outer walls of the stem, and analyze whether this trait influences the mechanical properties of polypropylene composites reinforced with miscanthus particles. Six contrasting genotypes were chosen from a Miscanthus sinensis population to determine morphological variables, stem solidness, and mechanical properties of polypropylene composites including 30% of milled miscanthus particles of two sizes of 100 < × < 200 μm and 200 < × < 300 μm. Although aboveground biomass of miscanthus was closely related to the aboveground volume of the plant, namely stand volume, a few genotypes showed contrasting aboveground biomass production for similar stand volumes. This generated contrasting ratio between aboveground biomass and stand volume, namely plant‐specific weights, for similar plant volumes. A principal component analysis showed that fully pith‐filled stems, namely solid stems, were explained by a large stand volume and plant‐specific weights as well as small stem cross‐sections. Genotypes showing partially filled stems were taller with larger stem cross‐sections but smaller plant‐specific weights. They revealed high lignin and p‐coumaric acid contents. Compared to neat‐polypropylene, Young's modulus increased significantly by 139% and 134% and tensile strength by 39% and 36% for genotypes with partially filled stems compared to genotypes with fully pith‐filled stems, respectively. This difference in reinforcing capacity was similar to that of two particle sizes (139% and 134% for Young's modulus, 41% and 34% for tensile strength, respectively). A good tensile strength was obtained with large cross‐stem section, plant height and lignin and p‐coumaric acid contents. It decreased with plant‐specific weight, hemicellulose and ferulic acid contents. Wider morphological variations in other progenies or Miscanthus species should be explored further using the techniques reported here.

Drought effects on montane grasslands nullify benefits of advanced flowering phenology due to warming

AbstractWarming due to climate change is generally expected to lengthen the growing season in areas of seasonal climate and to advance plant phenology, particularly the onset of leafing and flowering. However, a reduction in aboveground biomass production and reproductive output may occur when warming is accompanied by drought that crosses critical water deficit thresholds. Tracking warmer temperatures has been shown to be species‐specific with unknown impacts on community composition and productivity. The variability in species’ ability to leverage earlier leaf unfolding and flowering into increased aboveground net primary production (ANPP) or increased investments into reproductive organs has heretofore been poorly explored. We tested whether phenological sensitivity to temperature, as a result of experimental warming, directly translated into increased plant performance, as measured by ANPP and flower abundance. In order to experimentally simulate climate warming, we translocated a total of 45 intact soil–plant communities downslope along an elevational gradient of 900 m within the European Alps from 1260 to 350 m asl and weekly recorded flower abundance and total green cover as well as cumulative biomass production at peak growing season. We found that advanced phenology at lower elevations was related to increased reproductive performance and conditional on whether they experienced drought stress. While a temperature increase of +1K had positive effects on the amount of reproductive organs for species with accelerated phenology, temperature increase going along with drier conditions resulted in plants being unable to sustain early investment in reproduction as measured by flower abundance. This finding highlights that the interaction of two climate change drivers, warming and drought, can push communities’ past resistance thresholds. Moreover, we detected biotic competition mechanisms and shifts toward forb‐depressed states with graminoids best taking advantage of experimentally altered increased temperature and reduced precipitation. Our results suggest that while species may track warmer future climates, concurrent drought events post a high risk for failure of temperature‐driven improvement of reproductive performance and biomass production in the European Alps.

Cultivars of popular restoration grass developed for drought do not have higher drought resistance and do not differ in drought‐related traits from other accessions

Numerous functional traits have been identified as key contributors to plant performance under drought. However, many of these traits, specifically root traits, are rarely considered in the development of native plant cultivars. In this study, we assessed whether cultivars of the perennial grass Elymus trachycaulus (Slender wheatgrass) developed for drought differ in (a) drought resistance (i.e. a plant's ability to maintain aboveground biomass productivity under water deficit), (b) aboveground and belowground traits, and (c) trait responses to drought from other accessions (i.e. other cultivars, wild accessions). We also evaluated trait plasticity, assessed whether multivariate trait relationships varied between control and drought conditions, and determined which suites of traits are related to drought resistance. We worked with seedlings at two developmental stages to assess whether patterns vary ontogenetically. E. trachycaulus cultivars developed for drought did not differ from other accessions in drought resistance or traits related to drought‐coping strategies. The effects of drought and accession on drought resistance, traits, and trait plasticity varied by developmental stage, but relationships among traits varied little between the two developmental stages. A primary axis of functional variation related to resource acquisition (plant height, root length, root tips) was consistently associated with drought resistance. However, which secondary axes were related to drought resistance varied by developmental stage and moisture condition. Our results suggest that traits and performance of commonly used cultivars ought to be reexamined to determine whether they are actually the best candidates for revegetation projects in specific contexts.

Rhizobia and endophytic bacteria isolated from rainforest fragments within an iron ore mining site of the Eastern Brazilian Amazon.

The aim of the present study was to isolate and evaluate the diversity of rhizobial and endophytic bacterial strains from undisturbed native rainforests within an iron ore mining site of the Serra Norte de Carajás in the Eastern Brazilian Amazon region to assess their biotechnological utility in reclamation of areas. Experiments were conducted to capture strains from samples of the soil of these forests at the sites Arenito II, Noroeste II, and Sul IV using Macroptilium atropurpureum and Mimosa acutistipula var. ferrea as trap host plants. Only M. atropurpureum nodulated, and the different bacterial strains were isolated from its nodules. There was no difference in the number of nodules among the areas, but the Arenito II bacterial community was the most efficient, indicated by the aboveground biomass production and suitable shoot mass/root mass ratio. Fifty-two (52) bacterial isolates were obtained, distributed in five groups, including nodulating and endophytic bacteria: 32 from Arenito II, 12 from Noroeste II, and 8 from Sul IV. The nodulating Bradyrhizobium genus was common to the three areas, whereas Paraburkholderia was found only in Arenito II. The nodD1 gene was amplified in all the strains of both nodulating genera. Strains of the nodulating genus Methylobacterium were also isolated from the three areas; however, they did not nodulate the host of origin, and their nodD1 gene was not amplified. Endophytic strains were also isolated from the genera Paenibacillus, Pantoea, and Leifsonia in Arenito II, Leifsonia in Noroeste I, and Paenibacillus in Sul IV. The greater nodulation and rhizobial and endophytic bacterial diversity observed in Arenito II were probably due to the more suitable edaphic properties of the area. The isolated strains were incorporated in the collection of the Department of Soil Science of UFLA and will be investigated in relation to their symbiotic characteristics with native host plants, as well as their ability to perform other biological processes.

Fungal endophytes increase biomass production in pale swallow-wort (Vincetoxicum rossicum (Kleopow) Barbar.)

Pale swallow-wort, Vincetoxicum rossicum (Kleopow) Barbar., is an invasive weed in the lower Great Lakes Basin of North America. We investigated the relationship between V. rossicum productivity and several environmental variables across 54 established V. rossicum populations in southern Ontario. Variables included climate measurements, soil characteristics (pH, texture, and nutrient status), habitat type, plant community, and the diversity of root-associated fungi. Vincetoxicum rossicum roots were collected at all 54 sites, and associated fungi were compared using terminal restriction fragment length polymorphism. Aboveground biomass of V. rossicum was measured at 23 sites with similar light regimes, allowing comparison between populations. Results suggested that abiotic soil variables, and habitat type have little effect on V. rossicum productivity. Aboveground biomass production was significantly correlated with precipitation, and the presence of fungal pathogens and dark septate endophytes. Annual precipitation and soil clay content were also positively correlated with the abundance of soil pathogens. Accumulation of these microbes may negatively affect co-occurring native plants and associated fungal partners. The presence of these fungal species in soil could be used as an indicator of site susceptibility to invasion by V. rossicum and assist in the development of management plans for this exotic vine.

Soil nutrients and crop yield response to conservation-effective management practices in the sub-humid highlands agro-ecologies of Kenya

Crop productivity in most smallholder farming systems in Sub-Saharan Africa experience low use of soil amendment resources, low and erratic rainfall, frequent dry spells, and droughts. Rain-fed agriculture has a high crop yield potential if rainfall and soil nutrient input resources are utilized effectively. Thus, in 2011, we set up an on-farm experiment in Meru South (sub-humid) and Mbeere South (marginal sub-humid) sub-counties in upper Eastern Kenya to assess conservation-effective management (CEM) practices effects on maize (Zea Mays L.) yields response and soil nutrients. The CEM practices were; tied ridging (TR), mulching (MC), and minimum tillage (MT), with conventional tillage (CT) as a control. There were frequent dry spells and droughts during the experimental period. The experiment ran for four seasons, from the long rains season of 2011 (LR11), short rains seasons of 2011 (SR11), long rains season of 2012 (LR12), short rains 2012 (SR12), and long rains season of 2013 (LR13). In Meru South, TR and MT treatments had significantly higher phosphorus content (100% and 66%, respectively) than the control. Also, in the same site, Cu and Zn were high in MT than in CT treatments. In the Mbeere South site, the aboveground biomass yield was significantly higher in TR treatment (by 71%) than CT during SR11, while in LR12 season, it significantly increased by 72% and 46% under MC and TR treatments, respectively, than the control. The TR treatment had significantly higher aboveground biomass than the control (84% and 115%) in the SR12 and LR13 seasons. In Meru South, MC treatment had significantly higher aboveground biomass, which was significantly higher, by 39%, during the SR11 season and 46% in TR treatment in SR12 season than the control. This study highlighted tied ridging as the best-fit practice for enhancing maize crop aboveground biomass production in rain-fed farming systems of marginal lands and sub-humid regions receiving unreliable rainfall. Further, we recommend longer-term experimentation to explore CEM effects on soil nutrients.

Paludification reduces black spruce growth rate but does not alter tree water use efficiency in Canadian boreal forested peatlands

BackgroundBlack spruce (Picea mariana (Mill.) BSP)-forested peatlands are widespread ecosystems in boreal North America in which peat accumulation, known as the paludification process, has been shown to induce forest growth decline. The continuously evolving environmental conditions (e.g., water table rise, increasing peat thickness) in paludified forests may require tree growth mechanism adjustments over time. In this study, we investigate tree ecophysiological mechanisms along a paludification gradient in a boreal forested peatland of eastern Canada by combining peat-based and tree-ring analyses. Carbon and oxygen stable isotopes in tree rings are used to document changes in carbon assimilation rates, stomatal conductance, and water use efficiency. In addition, paleohydrological analyses are performed to evaluate the dynamical ecophysiological adjustments of black spruce trees to site-specific water table variations.ResultsIncreasing peat accumulation considerably impacts forest growth, but no significant differences in tree water use efficiency (iWUE) are found between the study sites. Tree-ring isotopic analysis indicates no iWUE decrease over the last 100 years, but rather an important increase at each site up to the 1980s, before iWUE stabilized. Surprisingly, inferred basal area increments do not reflect such trends. Therefore, iWUE variations do not reflect tree ecophysiological adjustments required by changes in growing conditions. Local water table variations induce no changes in ecophysiological mechanisms, but a synchronous shift in iWUE is observed at all sites in the mid-1980s.ConclusionsOur study shows that paludification induces black spruce growth decline without altering tree water use efficiency in boreal forested peatlands. These findings highlight that failing to account for paludification-related carbon use and allocation could result in the overestimation of aboveground biomass production in paludified sites. Further research on carbon allocation strategies is of utmost importance to understand the carbon sink capacity of these widespread ecosystems in the context of climate change, and to make appropriate forest management decisions in the boreal biome.

Influence of burning and defoliation on Festuca costata (Nees) in the Drakensberg

Fire occurs naturally in grasslands and savannas and it is commonly used as a management tool to influence structure and composition. The ability of a grass plant to recover from fire may be influenced by the fire frequency and intensity (influenced by seasonal weather conditions and fuel load), defoliation and competition from neighbouring plants. This study sought to investigate factors influencing the fire and herbivore dynamics of an evergreen C3 grass, Festuca costata, in a high-altitude C4 dominated grassland in the Drakensberg Mountains of South Africa. We experimentally examined the effect of fire frequency, defoliation and competition from neighbours on the growth dynamics of F. costata. Annual burning significantly decreased aboveground biomass production, number of tillers and tuft circumference of F. costata. Defoliation similarly reduced aboveground biomass production, number of tillers, tuft circumference and specific leaf area of F. costata. Competition from neighbouring plants reduced aboveground biomass production, number of tillers and tuft circumference of F. costata. Given the expected variable impacts of increasing CO2 levels and temperature on C3 and C4 grasses, these results provide insights for managing the matrix of C3 and C4 grasses in the Drakensberg grasslands in a changing climate.

Biochar application rate does not improve plant water availability in soybean under drought stress

Biochar, a form of porous pyrogenic carbon, has been shown to influence soil physicochemical properties and increase crop yield. However, it is unclear whether biochar application at different rates will improve crop performance in a clay soil under drought conditions through increasing plant water uptake. Here, we examined performance of soybean after amendment with biochar (pyrolysed at ~400 °C for 5 h) at four application rates (0, 25, 50 and 100 t ha−1) and grown under three moisture regimes (40%, 60% and 80% of field capacity). The instantaneous plant water content was determined periodically by recording relative water content, water retention capacity, and water uptake capacity in leaves while the cumulative water stress and water use efficiency (WUE) were determined from aboveground δ13C signatures and amount of water applied, respectively. The yield and yield attributes were also recorded. Results showed that across all drought treatments, biochar application significantly enhanced crop growth rate and increased total biomass production with a doubling in yield in the 100 t ha−1 biochar application. However, the seed yield did not increase with biochar application. Although biochar application improved WUE (biomass produced per unit of water applied), it most likely did not improve plant water uptake, since none of the measured plant water status indicators were affected by biochar. Instead, the enhanced biomass production may have been caused by an improvement in plant nutrition. Possibly, biochar application increased N acquisition through biological nitrogen fixation as there was a significant relationship between nitrogen (N) concentration in aboveground biomass and total biomass production. Moreover, application of biochar increased soil available potassium (K), and enhanced K uptake may have increased stress tolerance in soybean. Therefore, our findings show that biochar could improve plant performance in a clay soil by improving nutrient supply rather than by increasing water uptake.