Foliar Nutrient Concentrations Research Articles

The Effects of Agronomic Herbaceous Plants on the Soil Structure of Gold Mine Tailings and the Establishment of Boreal Forest Tree Seedlings

In Canada, low-grade ore mines generate large amounts of mineral waste, such as mine tailings. To control erosion of the fine-grained tailings particles as quickly as possible, it is common practice for the mining industry to revegetate the mine tailings with agronomic herbaceous plants. However, it is unclear whether this practice is consequential to the natural establishment of boreal species. The first objective of this study was to evaluate which families of agronomic herbaceous plants (legumes or grasses) result in the most favorable physical and chemical soil properties for the establishment of boreal species. The second objective was to determine the effect of the agronomic herbaceous plants on the growth and foliar nutrient concentration on three indigenous boreal forest seedlings; jack pine (Pinus banksiana Lambert), tamarack (Larix laricina Du Roi), paper birch (Betula papyrifera Marshall), and a willow cultivar (Salix miyabeana Seemen). In 2013, a 1-ha in situ experimental surface of mine tailings was set up on the gold mine site in Malartic, Abitibi-Témiscamingue, Quebec. The experimental site was subdivided into three blocks, each further divided in 5 plots. Each plot was randomly seeded as follows: 100% grass, 100% legumes, a mixture of both, topsoil, and a control (tailings only, no seeding). In the 2015 spring season, thirty seedlings of the three boreal tree species and cuttings of the willow cultivars were planted in each treatment plot. Seedling height and root biomass were measured at the end of the 2016 growing season. Soil sample analyses indicated significant differences for bulk density, wilting point, and organic matter content between the topsoil and the different agronomic herbaceous and control treatments; however, no significant differences were found between the different herbaceous treatments and the control for soil pH, bulk density, wilting point, macroporosity, and organic matter content. The mortality rate of jack pine, tamarack, and paper birch seedlings was higher in the control plots compared to all other treatments. Root biomass and height of the willow cultivar were significantly higher in the legumes compared with topsoil treatment. Among the four pioneer tree seedlings studied, this research indicates that the combination of the willow cultivar with the legumes treatment produces the best seedling growth and survival in the highly abiotic and stressful environments inherent to mine tailings.

Verification of our empirical understanding of the physiology and ecology of two contrasting plantation species using a trait database.

The effects of climate change on forest ecosystems take on increasing importance more than ever. Information on plant traits is a powerful predictor of ecosystem dynamics and functioning. We reviewed the major ecological traits, such as foliar gas exchange and nutrients, xylem morphology and drought tolerance, of Cryptomeria japonica and Chamaecyparis obtusa, which are major timber species in East Asia, especially in Japan, by using a recently developed functional trait database for both species (SugiHinokiDB). Empirically, C. obtusa has been planted under drier conditions, whereas C. japonica, which grows faster but thought to be less drought tolerant, has been planted under wetter conditions. Our analysis generally support the empirical knowledge: The maximum photosynthetic rate, stomatal conductance, foliar nutrient content and soil-to-foliage hydraulic conductance were higher in C. japonica than in C. obtusa. In contrast, the foliar turgor loss point and xylem pressure corresponding to 50% conductivity, which indicate drought tolerance, were lower in C. obtusa and are consistent with the drier habitat of C. obtusa. Ontogenetic shifts were also observed; as the age and height of the trees increased, foliar nutrient concentrations, foliar minimum midday water potential and specific leaf area decreased in C. japonica, suggesting that nutrient and water limitation occurs with the growth. In C. obtusa, the ontogenetic shits of these foliar traits were less pronounced. Among the Cupressaceae worldwide, the drought tolerance of C. obtusa, as well as C. japonica, was not as high. This may be related to the fact that the Japanese archipelago has historically not been subjected to strong dryness. The maximum photosynthetic rate showed intermediate values within the family, indicating that C. japonica and C. obtusa exhibit relatively high growth rates in the Cupressaceae family, and this is thought to be the reason why they have been selected as economically suitable timber species in Japanese forestry. This study clearly demonstrated that the plant trait database provides us a promising opportunity to verify out empirical knowledge of plantation management and helps us to understand effect of climate change on plantation forests by using trait-based modelling.

Seasonal variation in AMF colonisation, soil and plant nutrient content in gypsum specialist and generalist species growing in P-poor soils

AimsGypsum soils are P-limited atypical soils that harbour a rich endemic flora. These singular soils are usually found in drylands, where plant activity and soil nutrient availability are seasonal. No previous studies have analysed the seasonality of P nutrition and its interaction with the arbuscular mycorrhiza fungi (AMF) colonisation in gypsum plants. Our aim was to evaluate the seasonal changes in plant nutrient status, AMF colonisation and rhizospheric soil nutrient availability in gypsum specialist and generalist species.MethodsWe evaluated seasonal variation in the proportion of root length colonised by AMF structures (hyphae, vesicules and arbuscules), plant nutrient status (leaf C, N and P and fine root C and N) and rhizospheric soil content (P, organic matter, nitrate and ammonium) of three gypsum specialists and two generalists throughout a year.ResultsAll species showed arbuscules within roots, including species of Caryophyllaceae and Brassicaceae. Root colonisation by arbuscules (AC) was higher in spring than in other seasons, when plants showed high leaf P-requirements. Higher AC was decoupled from inorganic N and P availability in rhizospheric soil, and foliar nutrient content. Generalists showed higher AC than specialists, but only in spring.ConclusionsSeasonality was found in AMF colonisation, rhizospheric soil content and plant nutrient status. The mutualism between plants and AMF was highest in spring, when P-requirements are higher for plants, especially in generalists. However, AMF decoupled from plant demands in autumn, when nutrient availability increases in rhizospheric soil.

Response of foliar mineral nutrients to long‐term nitrogen and phosphorus addition in a tropical forest

Abstract Mineral nutrients play a pivotal role in plant growth, development and reproduction. The uptake and distribution of nutrients are generally limited by soil nutrient availability, affected by global change. However, the responses of foliar mineral nutrient concentrations to changes in soil nutrient availability remain largely untested in tropical forests. We used a field‐based experiment with nitrogen (N) and phosphorus (P) addition in a tropical forest in southern China to investigate the effect of N and P fertilization on exchangeable soil and foliar mineral nutrients of five understorey species. Our results show that N addition did not change soil pH, but reduced exchangeable soil Ca2+, Mg2+, Zn2+, Fe3+ and Mn2+ concentrations. In contrast, P addition increased soil pH, while it had no effects on exchangeable cations. Nitrogen addition significantly decreased foliar [Ca], [Mg] and [Mn], while P addition markedly reduced foliar [Cu] for most of the studied species. Foliar [K] and [Fe] were not affected by fertilization. The results indicate that long‐term N addition reduced the concentrations of several mineral nutrients in leaves, and we did not observe any adaptive mechanisms (e.g. increased transpiration to take up mobile soil nutrients) in the studied species to maintain foliar nutrient concentrations at high N supply. Synthesis. The responses of other foliar nutrient concentrations to N and P co‐addition were more complicated than those of N and/or P, and the specific decreases in mineral nutrient concentrations following long‐term N addition may influence key physiological process in the studied tropical understorey species, and ultimately reduce their fitness and survival under high N deposition. A free Plain Language Summary can be found within the Supporting Information of this article.

Effect of climate warming on seedling growth and biomass accumulation of Acacia modesta and Olea ferruginea in a subtropical scrub forest of Pakistan

ABSTRACT This study investigated the short-term impacts of projected climate warming on two dominant tree species of the Hayat-ul-Mir subtropical scrub forest of Pakistan. Seedlings of Acacia modesta and Olea ferruginea were exposed to ambient (To) and warming temperature (To + 2.3°C and To + 4.5°C) with control (M15%) and elevated (M20%) soil moisture in plant growth chamber for 90 days. To + 4.5°C induced detrimental effects on both species inhibiting seed germination and reducing their growth rate, biomass accumulation and allocation, however promoted development of root nodules (12 ± 4,0 nodules/root) in A. modesta. To + 2.3°C with M20% was beneficial for O. ferruginea with significant increase in stem height (4.8 ± 1.4 cm), elongated roots (31.2 ± 3.4 cm), branch development (9 ± 1.7), biomass accumulation (8.69 ± 0.4 g) and higher foliar nutrient concentration but for A. modesta it only promoted root elongation (16.5 ± 1.3 cm) and biomass accumulation in stem (1.05 ± 0.1 g) and foliage (0.08 ± 0.001 g). A. modesta grew better under To with significantly high germination and survival rate. A future 2.3°C warming could be ecologically significant to induce shifts in the structure and function of the Hayat-ul-Mir forest.

Climate condition affects foliar nutrition in main European tree species

Foliar nutrient concentrations, contents, and ratios are important indicators for the nutritional status of trees. They depend on the availability of nutrients and the uptake capacities of the trees, which are controlled by forest structure, soil and climate condition. Consequently, accounting for climate conditions can aid the interpretation of foliar chemistry measurements.We applied a moving-window approach to identify the effects of atmospheric temperature and precipitation on tree nutrition at different time intervals based on data collected by institutions of the German Federal States within the ICP Forests Level II network. We studied the main nutrients N, P, K, Ca, and Mg as well as foliar mass for the main temperate tree species (European beech, temperate oaks, Norway spruce, Scots pine).Results show that foliar traits of all main tree species are affected by either current and/or lagged climate condition. Nutrient concentrations are generally less sensitive to climate condition than foliar mass and nutrient contents. Nutrient contents show the same response direction to climate condition as foliar mass, while nutrient concentrations mostly show an opposite response, potentially indicating the existence of dilution effects. Only Ca content in spruce shows weak effects of climate as changes in foliar mass are entirely counterbalanced by opposing changes in Ca concentrations.For spruce, pine, and oak significant climate effects on nutrient ratios were found. In general, N:P, N:K, and P:K are less sensitive to climate variations than ratios including Mg or Ca. In beech, all nutrient concentrations show a similar response to climate condition. Nutrient ratios in beech are thus relatively robust against climate condition compared to concentrations and contents.Our results highlight that intervals of less than three month provide a good indication of the climatic impact on tree nutrition. Longer periods, or means over several years, are less suitable as indicators. Defined periods show, however, a significant role of climate beside soil factors and species on foliar nutrition and should therefore be considered for the interpretation of tree nutrition.

Effects of wood ash and N fertilization on soil chemical properties and growth of Zelkova serrata across soil types

Wood ash generated as a by-product of biomass combustion can be a sustainable and reasonable approach to counteract acidification and correct nutrient deficiency in forest soils. We investigated the influence of wood ash (WA) and combined WA + N (nitrogen) on soil chemical properties, growth and foliar nutrients of Zelkova serrata and their potential as a soil amender across different soil types. We applied four levels of WA (0, 5, 10, and 20 Mg ha−1) and two levels of N fertilizer (0 and 150 kg ha−1) across three different soil types: landfill saline (LS) soil, forest infertile (FI) soil, and forest acidic (FA) soil. The WA generally improved soil pH, organic matter, available P, exchangeable cations (K+, Na+, Ca2+, and Mg2+), and EC of the three soils, but its ameliorating and neutralizing effects were predominant in FA soil. N fertilizer was more effective in improving plant growth, especially for biomass production in LS and FI soils. WA application significantly increased biomass production when it was applied over 5 Mg ha−1 in FA soil, but higher dose rate of WA (i.e. 20 Mg ha−1) seems to pose negative effects. Foliar P, K, and Ca concentrations also tended to increase with the increasing amount of WA. Therefore, lower dosage of WA without N can be applied as a soil amender to counteract forest soil acidity and improve plant growth and foliar nutrient concentration, whereas N fertilizer without WA can be added to correct nutrient soil deficiencies in landfill and infertile soils. This study should enhance our understanding of WA as a sustainable and reasonable approach to counteract acidification and correct nutrient deficiency in forest soils.

Ecology of Nepenthes clipeata on Gunung Kelam, Indonesian Borneo

ABSTRACT Background Nepenthes clipeata is a Critically Endangered plant species with the population at its only location in the wild, Gunung (Mount) Kelam in Kalimantan, Indonesia, under threat – its nutrient relationships have not been studied. Aims To improve understanding of the autecology of N. clipeata by assessing the current population and providing information on its mineral nutrient relationships. Methods A survey was undertaken in 2019 when population numbers and habitat preferences of N. clipeata were recorded. Nutrient concentrations in soil, leaves and pitcher fluid were analysed and compared with those in other Nepenthes species. Results Eighteen individuals of N. clipeata were found on Gunung Kelam (only one of which was female). Seven other Nepenthes species were found and hybrids with two of these and N. clipeata were observed. Although the foliar nutrient concentrations (‘ionome’) of N. clipeata appeared distinct from that of other Nepenthes species, with N. clipeata having greater nutrient concentrations, particularly nitrogen, potassium and calcium, nitrogen limitation was still prevalent. Conclusions N. clipeata still persists in the wild but with very low numbers, indicating that conservation actions are required. Along with other species of Nepenthes, it is limited by soil nitrogen concentrations although it has a distinct ionome derived from high foliar nutrient concentrations.

Photosynthesis, Biomass Production, Nutritional Quality, and Flavor-Related Phytochemical Properties of Hydroponic-Grown Arugula (Eruca sativa Mill.) ‘Standard’ under Different Electrical Conductivities of Nutrient Solution

Arugula (Eruca sativa) is cultivated using hydroponic techniques in greenhouses to fulfill high year-round demand, but its nutrient management in hydroponic production has not yet been standardized, potentially leading to limited quality and productivity. Aiming to address this issue, we investigated the effect of electrical conductivity (EC) on yield, nutritional and phytochemical properties of arugula. The model cultivar arugula ‘Standard’ was grown at four different EC levels (1.2, 1.5, 1.8, and 2.1 dS·m−1). Our results indicated photosynthetic properties, SPAD, leaf area, yield and dry weight increased with increasing EC from 1.2 to 1.8 dS·m−1. Foliar nutrient content increased with higher EC, but nutrient solution with 2.1 dS·m−1 showed a significant decline in N, Ca and most of the micronutrients including Fe, Zn, Mo, Cu, B and Mn. Total glucosinolates, total chlorophyll and total carotenoids concentrations increased with increasing EC. In addition, total anthocyanin content was highest in plants grown in EC 1.2 and 2.1 dS·m−1, demonstrating a stress response when grown in extreme EC levels. Our results further indicated a rapid accumulation of nitrate with higher EC, potentially detrimental to human health. This research demonstrated the optimal EC range would be 1.5 to 1.8 dS·m−1 for arugula in hydroponic production systems based on yield, quality criteria and human health considerations.

High foliar K and P resorption efficiencies in old-growth tropical forests growing on nutrient-poor soils.

Resorption is the active withdrawal of nutrients before leaf abscission. This mechanism represents an important strategy to maintain efficient nutrient cycling; however, resorption is poorly characterized in old‐growth tropical forests growing in nutrient‐poor soils. We investigated nutrient resorption from leaves in 39 tree species in two tropical forests on the Guiana Shield, French Guiana, to investigate whether resorption efficiencies varied with soil nutrient, seasonality, and species traits. The stocks of P in leaves, litter, and soil were low at both sites, indicating potential P limitation of the forests. Accordingly, mean resorption efficiencies were higher for P (35.9%) and potassium (K; 44.6%) than for nitrogen (N; 10.3%). K resorption was higher in the wet (70.2%) than in the dry (41.7%) season. P resorption increased slightly with decreasing total soil P; and N and P resorptions were positively related to their foliar concentrations. We conclude that nutrient resorption is a key plant nutrition strategy in these old‐growth tropical forests, that trees with high foliar nutrient concentration reabsorb more nutrient, and that nutrients resorption in leaves, except P, are quite decoupled from nutrients in the soil. Seasonality and biochemical limitation played a role in the resorption of nutrients in leaves, but species‐specific requirements obscured general tendencies at stand and ecosystem level.

Fertilization and seasonality influence on the photochemical performance of tree legumes in forest plantation for area recovery in the Amazon.

N-fixing leguminous species can reach atmospheric dinitrogen gas (N2), having an advantage under N-limited degraded environments. These N-fixers are constantly used as facilitative species. Chlorophyll a fluorescence (ChF) acknowledges how different species take up and use light energy during photosynthesis. These techniques assess stress and performance responses to photosynthesis and are used for the selection of species with potential for reforestation. Six Fabaceae species were selected for this study: three nonfixing species (Cenostigma tocantinum, Senna reticulata and Dipteryx odorata) and three N-fixing species (Clitoria fairchildiana, Inga edulis and Acacia spp.). Variations in chlorophyll fluorescence under high vs. low water and nutrient conditions were studied. Multivariate analysis was performed to detect the effects of seasonality and fertilization on dark-adapted ChF two years after the experiment was established. The correlation among ChF variables and growth, photosynthesis and foliar nutrient concentrations was evaluated. Under high water- and nutrient-availability conditions, plants exhibited an enhanced performance index on absorption basis values correlated with electron transport fluxes. Under drought and nutrient-poor conditions, most species exhibit increased energy dissipation as photoprotection. High interspecific variation was found; therefore, species-specific responses should be considered in future ChF studies. Corroborating the ability to colonize high-light environments, N-fixers showed an increased performance index correlated with electron transport and Zn and N foliar concentrations. Negative correlations were found between photosynthesis and trapped fluxes. Diameter growth was positively correlated with electron transport fluxes. Given the different responses among species, ChF is an effective technique to screen for seasonality, fertilization and species effects and should be considered for use during forest restoration. Finally, the addition of fertilization treatments may facilitate tropical forest restoration due to the importance of nutrients in physiological processes. N-fixers showed high photochemical performance and tolerance to abiotic stress in degraded areas and therefore should be included to support ecosystem biomass restoration.

Soil compaction and organic matter removal effects on soil properties and tree growth in the Interior Douglas-fir zone of southern British Columbia

Silviculture systems and associated forest harvesting practices that affect the level of soil compaction and organic matter retained on a site will cause changes to soil properties and processes that may affect the growth of planted trees. We present results for soil conditions and tree growth after 15 years for 6 Long-term Soil Productivity Study (LTSP) installations in 2 distinct regions of the Interior Douglas-fir (IDF) biogeoclimatic zone in southern British Columbia (BC). In a 3 × 3 factorial design, three levels of compaction and organic matter removal were replicated in two distinct IDF regions that varied in parent material, but with similar climates. Each treatment was then split and planted with two different species, Douglas-fir and lodgepole pine. In each region, three unique sites (block), all within a radius of 50 km from one other, were installed with the same combination of treatment and species for a total of six replicates, three in each of two regions. Across IDF regions, tree heights on calcareous soils in the Rocky Mountains of south-eastern BC were 36% lower for Douglas-fir and 23% lower for lodgepole pine than on more acidic soils on the Thompson Plateau. There were varying differences across treatments in soil and foliar nutrient concentrations between IDF regions, primarily from regional parent material differences. However, nutrient deficiencies were apparent in both regions and may have limited growth, especially on the more calcareous sites. Increases to soil bulk density (27%) 1 year after compaction did not impact tree survival, height at Year-15, or chemical properties in foliar tissue or soil. Fewer growing season frost events and increased soil water availability during the seedling establishment period was a likely reason for a 25% increase in Douglas-fir survival at Year-15 with the whole tree + forest floor removal (OM3) treatment. However, whole tree + forest floor removal (OM3) also produced a 13–19% reduction in soil N, S, K, and mineralizable N when compared to both stem-only (OM1) and whole tree (OM2) harvesting treatments that kept the forest floor intact. Effects on forest productivity from soil compaction after 15 years appear to be overshadowed by the more prominent effect of organic matter removal treatments during stand establishment and early growth. Future work at these installations focusing on nutrient budget, forest health, and ecosystem carbon stock differences across treatments will provide valuable insight into silviculture and harvesting practices for different species and regions in the dry forests of southern BC.

Impact of Seed Applied Rhizobacterial Inoculants on Growth of Wheat (Triticum aestivum) and Cowpea [Vigna unguiculata] and their Influence on Rhizospheric Microbial Diversity

Current study was planned to demonstrate (Experiment I), the impact of seed bacterization (inoculation dose—106, 108, 1010, 1012 CFU/ml) with two bacterial isolates Variovorax paradoxus RAA3 and M11 (Unidentified) on growth and foliar nutrient content (NPK) of wheat (var. H1105 and PBW660) and cowpea (var. PL-1 and PL-2) cultivars under glass house conditions. Strain RAA3 treated plants exhibited most promising results for shoot fresh weight (26.7%, 30.2%), shoot dry weight (44.4%, 63.3%) and chlorophyll content (66.8%, 66.9%) as compared to the control plants of respective varieties. This inoculant also caused significant changes in the foliar nitrogen (14.5%, 14.2%), phosphorus (36.4%, 46.7%) and potassium (20.1%, 65.9%) content in wheat and cowpea, respectively, as compared to the non-inoculated plants. Moreover, the inoculum dose of 108 of bacterial inoculum was found to be most effective and thus, considered as an optimum dose for the plant growth promotion. In another study (Experiment II), seed bacterization with RAA3 (108 CFU/ml) on nine different varieties of wheat was performed, and significant varietal and treatment effect were observed for many of growth parameters as compared to untreated control plants. Overall results showed maximum response at inoculum dose of 108, therefore this dose was taken to assess the influence of PGPR inoculation on rhizospheric microbial diversity of wheat and cowpea. We observed that RAA3 inoculation has led to a shift in microbial population in both wheat and cowpea varieties. Irrespective of varieties, RAA3 (inoculum dose of 108 CFU/ml) treated plants of wheat showed dominant microbial groups of siderophores producers, nitrogen fixers and actinomycetes, whereas, in RAA3 treated plants of cowpea the dominant microbial population of only siderophores producers was recorded.

Effects of Management Practices on Soil Properties and Plant Nutrition in Hay Meadows in Picos de Europa

Fertilization and mowing affects the physico-chemical properties of soils, as well as the characteristics of the plants growing on them. Changes in the management techniques are causing semi-natural grasslands to disappear all over Europe. These grasslands host a great amount of diversity, thus their conservation is a top priority. This work studies whether the kind of management has an influence on the soil properties and the foliar content in macronutrients in 25 hay meadows located in Picos de Europa (10 in Asturias, 10 in Castilla y León and 5 in Cantabria). Soils at a 0–20 cm depth showed a high content of organic matter and a low C/N ratio. Effective cation exchange capacity was adequate for a texture, which varied from sandy clay loam to loam, with an average clay content of 17%. Mean values of foliar nutrient concentrations showed a deficiency in K. In this study, management practices were shown to affect some properties of the soils, namely pH, sand percentage and exchangeable K and Ca, to different extents. The highest values of pH and exchangeable Ca were significantly correlated with the least intensive management.

Chicken manure as soil amendment: Effect on yield and foliar nutrient content of tanier, and on chemical properties of the soil.

During two consecutive years, chicken manure effects on yield and foliar nutrient content of tanier, and on chemical properties of the soil were evaluated. Treatments were 0, 25 and 50 t/ha of chicken manure incorporated into the soil prior to planting the first year. No significant differences in yield were found among the chicken manure treatments. This lack of differences was attributed to the high coefficient of variation found in the experiment. Nevertheless, with the application of 25 t/ha we observed a 17% and 122% increase in yield on the first and second year of the experiment, respectively, compared to yield in the check treatment. This increase in yield could be related to the ample benefit of applied organic matter, especially in low fertility soil. Only foliar nitrogen content showed a significant increase with the chicken manure application in both years, whereas potassium content increased with manure application during the second year. The application of chicken manure caused an increase of organic matter, electric conductivity and N, P, K and Mg content in the soil during the first year.

African Rhino plantain clone (Musa AAB) behavior when using chicken manure as soil amendment and nematicides.

The effects of chicken manure as a soil amendment and the application of nematicides on plant characteristics, yield and foliar nutrient content of the African Rhino plantain clone were evaluated. Chemical properties of the soil were monitored after chicken manure application. Chicken manure, at a rate of 25 t/ha, was incorporated during soil preparation. The nematicide treatment Included the use of etoprop at planting, followed by oxamyl at six and 12 months after planting. The application of chicken manure significantly increased the height and diameter of the pseudostem, reduced the number of days from planting to shooting, and increased bunch weight, and yield per hectare. With the use of chicken manure a yield of 34,242 kg/ha was obtained. This yield represents a 33% increase over that of the treatment without chicken manure. The use of nematicides significantly diminished the number of collapsed plants and Increased plantain yield. The use of chicken manure Increased the foliar content of N and Ca whereas the use of nematicide had no effect on any of the nutrient foliar content. The chemical properties of the soil (pH; organic matter; electric conductivity; N, P, K, Ca and Mg content) were not affected by the use of chicken manure.

Nutrient availability predicts multiple stem frequency, an indicator of species resprouting capacity in tropical forests

Abstract Resprouting capacity is a key component of plant life history. While resprouting requires substantial nutrient reserves to support new growth, the influence of soil fertility on resprouting is largely unknown. We tested whether the frequency of multi‐stemmed trees, a potential indicator of resprouting history, is associated with low soil fertility, reflecting selection for conservative life histories that enhance survival, or with high fertility, reflecting greater resource availability to support regrowth. Data from the Barro Colorado Island (BCI) 50‐ha plot in Panama showed that multi‐stemmed trees are more likely to resprout during their lifetime than single‐stemmed trees, and that multiple stem frequency has a strong taxonomic signal for adult trees. To test how multiple stem frequency varies with demographic rates and nutrient allocation strategies, we compiled functional trait datasets for 71 species from lowland forest on BCI and 43 species from lower montane forest in western Panama. We also assessed environmental correlates of community‐wide multiple stem frequency in thirty‐seven 1‐ha lowland plots in the Panama Canal watershed and twelve 1‐ha montane plots in western Panama, spanning gradients of rainfall and soil fertility. Multiple stem frequency was not correlated with species demographic rates or wood density, suggesting that resprouting is unrelated to classical ‘persistence’ traits in neotropical tree species. Multiple stem frequency of tree species occurring on BCI was weakly but significantly positively correlated with regional soil phosphorus associations, but unrelated to foliar nutrient concentrations. Multiple stem frequency covaried strongly with soil and tissue nutrient status across fertility gradients. It was significantly positively correlated with nutrient allocation traits, including foliar phosphorus and wood nitrogen and phosphorus, among species sampled across soil habitats in western Panama. At the community level, the proportion of woody stems >10 cm DBH with at least one multiple stem increased with plant available soil phosphorus. Synthesis. These results suggest a novel mechanism by which soil phosphorus availability influences tree recruitment and forest dynamics by facilitating resprouting. Future experiments should seek to understand whether soil fertility mediates resprouting frequency through nutrient supply directly, or via the formation of enhanced wood nutrient reserves.

The Crucial Role of Soil Organic Matter in Satisfying the Phosphorus Requirements of Olive Trees (Olea europaea L.)

Under high organic matter content, even under low extractable soil P concentrations, sufficient or over-sufficient foliar P levels may be found. This multi-year study aimed at examining the effects of organic matter content and irrigation management on (a) soil fertility, (b) P-cycle related soil enzymes (acid and alkaline phosphatase, pyrophosphatase) and (c) foliar nutrient concentrations. Irrigated and non-irrigated groves of fully productive trees of the cultivar “Chondrolia Chalkidikis” with low organic matter (LOM < 1.5%), medium organic matter (1.5% < MOM < 2.5%) and high organic matter (HOM > 2.5%) were selected for the experimentation. It was hypothesized that olive groves receiving high inorganic fertilization and irrigation inputs (usually with medium to relatively low organic matter content) would show higher soil and foliar P concentrations compared to the non-irrigated groves with higher organic matter content receiving manure applications. Most of the soil variables (including the three enzymes’ activities) were affected by differences in organic matter content. However, organic matter content did not show a significant influence on foliar nutrient concentrations. Olive trees, especially those cultivated in soils with high organic matter content (receiving organic fertilization), can over-satisfy their P nutritional needs, even though soil analyses show low soil extractable P concentrations, probably due to the high enzymatic activity of acid and alkaline phosphatases. The practical conclusion of this study is that P fertilizer recommendations should be primarily based on foliar P rather than on extractable soil P.

Altitude and management affect soil fertility, leaf nutrient status and Xanthomonas wilt prevalence in enset gardens

Abstract. Enset (Ensete ventricosum) is a productive, drought-tolerant and multipurpose food security crop grown in the densely populated Ethiopian highlands. It is a so-called orphan crop, and its production suffers from a lack of information on proper soil fertility management and its interaction with bacterial wilt disease caused by the pathogen Xanthomonas campestris pv. musacearum. The aim of this study was therefore to assess soil–plant nutrient variation within enset home gardens at three altitudes (ranging from 2000 to 3000 m above sea level – a.s.l.) in the Gamo highlands and investigate whether this variation affects disease prevalence. Altitude in the rift valley covaries with soil leaching, and plant available P, Ca and Mg in soils significantly raised with decreasing altitude. Soil carbon and most nutrients reached very high levels in the gardens, whereas the more distant outfields were severely nutrient deprived. Differences in management intensity within the garden caused soil pH, conductivity, total organic carbon, total N and available P, K, Ca, Mg, Mn and Fe levels to significantly decline with distance from the house; yet, this decrease in soil nutrients was not mirrored in a response of foliar nutrient content, except for N. Hence, over-fertilization is likely, and establishing evidence-based nutrient recommendations for enset would benefit soil quality and productivity both in the gardens and in the outfields. Disease prevalence was high in the study area, with one-third of the farms affected in the recent past. Although more experimental work is needed to exclude confounding factors, our data indicate that the effects of altitude, P fertilization, micronutrients and K-Ca-Mg balance are promising avenues for further investigation into Xanthomonas wilt disease susceptibility.

Empirical support for the biogeochemical niche hypothesis in forest trees.

The possibility of using the elemental compositions of species as a tool to identify species/genotype niche remains to be tested at a global scale. We investigated relationships between the foliar elemental compositions (elementomes) of trees at a global scale with phylogeny, climate, N deposition and soil traits. We analysed foliar N, P, K, Ca, Mg and S concentrations in 23,962 trees of 227 species. Shared ancestry explained 60-94% of the total variance in foliar nutrient concentrations and ratios whereas current climate, atmospheric N deposition and soil type together explained 1-7%, consistent with the biogeochemical niche hypothesis which predicts that each species will have a specific need for and use of each bio-element. The remaining variance was explained by the avoidance of nutritional competition with other species and natural variability within species. The biogeochemical niche hypothesis is thus able to quantify species-specific tree niches and their shifts in response to environmental changes.