Dry weight partitioning and hydraulic traits in young Pinus taeda trees fertilized with nitrogen and phosphorus in a subtropical area

Divergent role of nutrient availability in determining drought responses of sessile oak and Scots pine seedlings: evidence from 13C and 15N dual labeling

Increased soil nutrient availability can promote tree growth while drought impairs metabolic functioning and induces tree mortality. However, limited information is available about the role of nutrients in the drought responses of trees. A greenhouse experiment was conducted with sessile oak (Quercus petraea (Matt.) Liebl) and Scots pine (Pinus sylvestris L.) seedlings, which were subjected to three fertilization treatments in the first year and two water regimes in the second year. Old and newly fixed carbon (C) and nitrogen (N) allocation were traced by dual labeling with 13C and 15N tracers, respectively, at two time points. Leaf gas exchange, biomass, as well as N and nonstructural carbohydrate (NSC) concentrations of all organs were measured. Fertilization predisposed sessile oak to drought-induced mortality, mainly by prioritizing aboveground growth, C and N allocation, reducing root NSC concentrations and decreasing old C contribution to new growth of leaves. In contrast, fertilization did not additionally predispose Scots pine to drought, with minor effects of fertilization and drought on newly fixed and old C allocation, tissues N and NSC concentrations. The role of nutrients for drought responses of trees seems to be species-specific. Therefore, we suggest nutrient availability and species identity to be considered in the framework of physiological mechanisms affecting drought-induced mortality.

Differential responses of contrasting low phosphorus tolerant cotton genotypes under low phosphorus and drought stress

BACKGROUND

Drought is one of the main reasons for low phosphorus (P) solubility and availability.

AIMS

The use of low P tolerant cotton genotypes might be a possible option to grow in drought conditions.

METHODS

This study investigates the tolerance to drought stress in contrasting low P-tolerant cotton genotypes (Jimian169; strong tolerant to low P and DES926; weak tolerant to low P). In hydroponic culture, the drought was artificially induced with 10% PEG in both cotton genotypes followed by low (0.01 mM KH₂PO₄) and normal (1 mM KH₂PO₄) P application.

RESULTS

The results showed that under low P, PEG-induced drought greatly inhibited growth, dry matter production, photosynthesis, P use efficiency, and led to oxidative stress from excessive malondialdehyde (MDA) and higher accumulation of reactive oxygen species (ROS), and these effects were more in DES926 than Jimian169. Moreover, Jimian169 alleviated oxidative damage by improving the antioxidant system, photosynthetic activities, and an increase in the levels of osmoprotectants like free amino acids, total soluble proteins, total soluble sugars, and proline.

CONCLUSIONS

The present study suggests that the low P-tolerant cotton genotype can tolerate drought conditions through high photosynthesis, antioxidant capacity, and osmotic adjustment.

Comprehensive sequence and expression profile analysis of the phosphate transporter gene family in soybean

The family of phosphate transporters (PHTs) mediates the uptake and translocation of Pi inside the plants. However, little is known about transporters in soybean. Therefore, Searched the Genome Database for Soybean, 57 GmPHTs family members were identified in soybean, Phylogenetic analysis suggested that members of the PHTs gene family can be divided into six clades. Collinearity analysis revealed that most of the GmPHT genes shared syntenic relationships with PHTs members in Arabidopsis thaliana and that large segment duplication played a major driving force for GmPHTs evolution in addition to tandem duplication. Further analysis of the promoter revealed that light-responsive elements and abiotic stress-responsive elements were widely distributed within the promoter regions of GmPHT genes. Based on RNA-seq data, GmPHTs showed different expression patterns in roots and leaves of soybean treated with long-term low phosphorus and short-term low phosphorus, in addition, the expression levels of GmPHT genes can be regulated by drought stresses, it was implied that the induced expression of GmPHTs could promote phosphorus uptake and transport in soybean and thus adapt to low phosphorus and drought stress, which is the first step dissection of Pi transport system and probably refers to new roles of PHTs genes in soybean.

Phosphorous Supplementation Alleviates Drought-Induced Physio-Biochemical Damages in Calligonum mongolicum

Calligonum mongolicum is a phreatophyte playing an important role in sand dune fixation, but little is known about its responses to drought and P fertilization. In the present study, we performed a pot experiment to investigate the effects of P fertilization under drought or well-watered conditions on multiple morpho-physio-biochemical attributes of C. mongolicum seedlings. Drought stress leads to a higher production of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), leading to impaired growth and metabolism. However, C. mongolicum exhibited effective drought tolerance strategies, including a higher accumulation of soluble sugars, starch, soluble protein, proline, and significantly higheractivities of peroxidase (POD) and catalase (CAT) enzymes. P fertilization increased the productivity of drought-stressed seedlings by increasing their growth, assimilative shoots relative water content, photosynthetic pigments, osmolytes accumulation, mineral nutrition, N assimilation, and reduced lipid peroxidation. Our findings suggest the presence of soil high P depletion and C. mongolicum high P requirements during the initial growth stage. Thus, P can be utilized as a fertilizer to enhance the growth and productivity of Calligonum vegetation and to reduce the fragility of the hyper-arid desert of Taklamakan in the context of future climate change.

Plant Nutrition: An Effective Way to Alleviate Abiotic Stress in Agricultural Crops

By the year 2050, the world’s population is predicted to have grown to around 9–10 billion people. The food demand in many countries continues to increase with population growth. Various abiotic stresses such as temperature, soil salinity and moisture all have an impact on plant growth and development at all levels of plant growth, including the overall plant, tissue cell, and even sub-cellular level. These abiotic stresses directly harm plants by causing protein denaturation and aggregation as well as increased fluidity of membrane lipids. In addition to direct effects, indirect damage also includes protein synthesis inhibition, protein breakdown, and membranous loss in chloroplasts and mitochondria. Abiotic stress during the reproductive stage results in flower drop, pollen sterility, pollen tube deformation, ovule abortion, and reduced yield. Plant nutrition is one of the most effective ways of reducing abiotic stress in agricultural crops. In this paper, we have discussed the effectiveness of different nutrients for alleviating abiotic stress. The roles of primary nutrients (nitrogen, phosphorous and potassium), secondary nutrients (calcium, magnesium and sulphur), micronutrients (zinc, boron, iron and copper), and beneficial nutrients (cobalt, selenium and silicon) in alleviating abiotic stress in crop plants are discussed.

Improving Drought Stress Tolerance in Ramie (Boehmeria nivea L.) Using Molecular Techniques

Ramie is one of the most significant fiber crops and contributes to good quality fiber. Drought stress (DS) is one of the most devastating abiotic factors which is accountable for a substantial loss in crop growth and production and disturbing sustainable crop production. DS impairs growth, plant water relation, and nutrient uptake. Ramie has evolved a series of defense responses to cope with DS. There are numerous genes regulating the drought tolerance (DT) mechanism in ramie. The morphological and physiological mechanism of DT is well-studied; however, modified methods would be more effective. The use of novel genome editing tools like clustered regularly interspaced short palindromic repeats (CRISPR) is being used to edit the recessive genes in crops to modify their function. The transgenic approaches are used to develop several drought-tolerant varieties in ramie, and further identification of tolerant genes is needed for an effective breeding plan. Quantitative trait loci (QTLs) mapping, transcription factors (TFs) and speed breeding are highly studied techniques, and these would lead to the development of drought-resilient ramie cultivars. The use of hormones in enhancing crop growth and development under water scarcity circumstances is critical; however, using different concentrations and testing genotypes in changing environments would be helpful to sort the tolerant genotypes. Since plants use various ways to counter DS, investigating mechanisms of DT in plants will lead to improved DT in ramie. This critical review summarized the recent advancements on DT in ramie using novel molecular techniques. This information would help ramie breeders to conduct research studies and develop drought tolerant ramie cultivars.

Effects of nitrogen addition and increased precipitation on xylem growth of Quercus acutissima Caruth. in central China

Atmospheric nitrogen (N) deposition and increasing precipitation affect carbon sequestration in terrestrial ecosystems, but how these two concurrent global change variables affect xylem growth in trees (i.e., independently or interactively) remains unclear. We conducted novel experiments in central China to monitor the xylem growth in a dominant species (Quercus acutissima Caruth.) in response to N addition (CN), supplemental precipitation (CW) or both treatments (CNW), compared with untreated controls (C). Measurements were made at weekly intervals during 2014-15. We found that supplemental precipitation significantly enhanced xylem growth in the dry spring of 2015, indicating a time-varying effect of increased precipitation on intra-annual xylem growth. Elevated N had no significant effect on xylem increment, xylem growth rate, and lumen diameters and potential hydraulic conductivity (Ks) of earlywood vessels, but Ks with elevated N was significantly negatively related to xylem increment. The combination of additional N and supplemental precipitation suppressed the positive effect of supplemental precipitation on xylem increment in the dry spring of 2015. These findings indicated that xylem width was more responsive to supplemental precipitation than to increasing N in a dry early growing season; the positive effect of supplemental precipitation on xylem growth could be offset by elevated N resources. The negative interactive effect of N addition and supplemental precipitation also suggested that increasing N deposition and precipitation in the future might potentially affect carbon sequestration of Q. acutissima during the early growing season in central China. The effects of N addition and supplemental precipitation on tree growth are complex and might vary depending on the growth period and local climatic conditions. Therefore, future models of tree growth need to consider multiple-time scales and local climatic conditions when simulating and projecting global change.

Addressing Gender Inequities in Forest Science and Research

Forest research and professional workforces continue to be dominated by men, particularly at senior and management levels. In this review, we identify some of the historical and ongoing barriers to improved gender inclusion and suggest some solutions. We showcase a selection of women in forestry from different disciplines and parts of the globe to highlight a range of research being conducted by women in forests. Boosting gender equity in forest disciplines requires a variety of approaches across local, regional and global scales. It is also important to include intersectional analyses when identifying barriers for women in forestry, but enhanced equity, diversity and inclusion will improve outcomes for forest ecosystems and social values of forests, with potential additional economic benefits.

Root carbon and nutrient homeostasis determines downy oak sapling survival and recovery from drought

The role of carbon (C) and nutrient uptake, allocation, storage and especially their interactions in survival and recovery of trees under increased frequencies and intensities of drought events is not well understood. A full factorial experiment with four soil water content regimes ranging from extreme drought to well-watered conditions and two fertilization levels was carried out. We aimed to investigate whether nutrient addition mitigates drought effects on downy oak (Quercus pubescens Willd.) and whether storage pools of non-structural carbohydrates (NSC) are modified to enhance survival after 2.5 years of drought and recovery after drought relief. Physiological traits, such as photosynthesis, predawn leaf water potential as well as tissue biomass together with pools and dynamics of NSC and nutrients at the whole-tree level were investigated. Our results showed that fertilization played a minor role in saplings' physiological processes to cope with drought and drought relief, but reduced sapling mortality during extreme drought. Irrespective of nutrient supply, Q. pubescens showed increased soluble sugar concentration in all tissues with increasing drought intensity, mostly because of starch degradation. After 28 days of drought relief, tissue sugar concentrations decreased, reaching comparable values to those of well-watered plants. Only during the recovery process from extreme drought, root NSC concentration strongly declined, leading to an almost complete NSC depletion after 28 days of rewetting, simultaneously with new leaves flushing. These findings suggest that extreme drought can lead to root C exhaustion. After drought relief, the repair and regrowth of organs can even exacerbate the root C depletion. We concluded that under future climate conditions with repeated drought events, the insufficient and lagged C replenishment in roots might eventually lead to C starvation and further mortality.

Expression dynamics indicate the role of Jasmonic acid biosynthesis pathway in regulating macronutrient (N, P and K+) deficiency tolerance in rice (Oryza sativa L.)

Expression pattern indicates that JA biosynthesis pathway via regulating JA levels might control root system architecture to improve nutrient use efficiency (NUE) and N, P, K⁺ deficiency tolerance in rice. Deficiencies of macronutrients (N, P and K⁺) and consequent excessive use of fertilizers have dramatically reduced soil fertility. It calls for development of nutrient use efficient plants. Plants combat nutrient deficiencies by altering their root system architecture (RSA) to enhance the acquisition of nutrients from the soil. Amongst various phytohormones, Jasmonic acid (JA) is known to regulate plant root growth and modulate RSA. Therefore, to understand the role of JA in macronutrient deficiency in rice, expression pattern of JA biosynthesis genes was analyzed under N, P and K⁺ deficiencies. Several members belonging to different families of JA biosynthesis genes (PLA1, LOX, AOS, AOC, OPR, ACX and JAR1) showed differential expression exclusively in one nutrient deficiency or in multiple nutrient deficiencies. Expression analysis during developmental stages showed that several genes expressed significantly in vegetative tissues, particularly in root. In addition, JA biosynthesis genes were found to have significant expression under the treatment of different phytohormones, including Auxin, cytokinin, gibberellic acid (GA), abscisic acid (ABA), JA and abiotic stresses, such as drought, salinity and cold. Analysis of promoters of these genes revealed various cis-regulatory elements associated with hormone response, plant development and abiotic stresses. These findings suggest that JA biosynthesis pathway by regulating the level of JA might control the RSA thus, it may help rice plant in combating macronutrient deficiency.

Predication of Photosynthetic Leaf Gas Exchange of Sugarcane (Saccharum spp) Leaves in Response to Leaf Positions to Foliar Spray of Potassium Salt of Active Phosphorus under Limited Water Irrigation

Sufficient water and fertilizer inputs in agriculture play a major role in crop growth, production, and quality. In this study, the response of sugarcane to limited water irrigation and foliar application of potassium salt of active phosphorus (PSAP) for photosynthetic responses were examined, and PSAP's role in limited water irrigation management was assessed. Sugarcane plants were subjected to limited irrigation (95-90 and 45-40% FC) after three months of germination, followed by a foliar spray (0, 2, 4, 6, and 10 M) of PSAP. The obtained results indicated that limited water irrigation negatively affected sugarcane growth and reduced leaf gas exchange activities. However, the application of PSAP increased the photosynthetic activities by protecting the photosynthetic machinery during unfavorable conditions. Mathematical modeling, a Skewed model, was developed and compared with the existing Gaussian model to describe the photosynthetic responses of sugarcane leaves under the limited irrigation with and without PSAP application. The models fitted well with the observed values, and the predicted photosynthetic parameters were in close relationship with the obtained results. The Skewed model was found to be better than the Gaussian model in describing the photosynthetic parameters of plant leaves positioned over a stem of limited water irrigation and applied PSAP application and is recommended for further application.

Functional Analysis of StPHT1;7, a Solanum tuberosum L. Phosphate Transporter Gene, in Growth and Drought Tolerance

PHT1 (phosphate transporter 1) family genes play important roles in regulating plant growth and responding to stress. However, there has been little research on the role of the PHT1 family in potatoes. In this study, using molecular and bioinformatic approaches, 8 PHT1 family genes were identified from the potato genome. StPHT1;7 was highly expressed in the whole potato plants. The overexpression and silence vectors of StPHT1;7 were constructed and transformed into the potato cultivar Desiree. Consequently, StPHT1;7 overexpression (with a relative expression 2-7-fold that in the control) and silence lines (with a relative expression of 0.3%-1% that in the control) were obtained. Their growth vigor was ranked in the order overexpression line > wild type > silence line. In the absence of phosphorus, the root length of the overexpression line was approximately 2.6 times that of the wild type, while the root length of the silence line was approximately 0.6 times that of the wild type. Furthermore, their tolerance to drought stress was ranked as wild type > overexpression line > silence line. These results suggest that StPHT1;7 affects growth and stress tolerance in potato plants.

Impact of phosphorus application on drought resistant responses of Eucalyptus grandis seedlings

Eucalyptus grandis is the most widely planted tree species worldwide and can face severe drought during the initial months after planting because the root system is developing. A complete randomized design was used to study the effects of two water regimes (well-watered and water-stressed) and phosphorus (P) applications (with and without P) on the morphological and physio-biochemical responses of E. grandis. Drought had negative effects on the growth and metabolism of E. grandis, as indicated by changes in morphological traits, decreased net photosynthetic rates (P_n ), pigment concentrations, leaf relative water contents (LRWCs), nitrogenous compounds, over-production of reactive oxygen species (ROS) and higher lipid peroxidation. However, E. grandis showed effective drought tolerance strategies, such as reduced leaf area and transpiration rate (E), higher accumulation of soluble sugars and proline and a strong antioxidative enzyme system. P fertilization had positive effects on well-watered seedlings due to improved growth and photosynthesis, which indicated the high P requirements during the initial E. grandis growth stage. In drought-stressed seedlings, P application had no effects on the morphological traits, but it significantly improved the LRWC, P_n , quantum efficiency of photosystem II (F_v /F_m ), chlorophyll pigments, nitrogenous compounds and reduced lipid peroxidation. P fertilization improved E. grandis seedling growth under well-watered conditions but also ameliorated some leaf physiological traits under drought conditions. The effects of P fertilization are mainly due to the enhancement of plant N nutrition. Therefore, P can be used as a fertilizer to improve growth and production in the face of future climate change.

Does fertilization explain the extraordinary hydraulic behaviour of apple trees?

Fertilization of woody plants plays a central role in agriculture and forestry, but little is known about how plant water relations are thereby affected. Here we investigated the impact of fertilization on tree hydraulics, and xylem and pit anatomy in the high-yield apple cultivars Golden and Red Delicious. In fertilized trees of Golden Delicious, specific hydraulic conductivity of branch xylem, hydraulic conductance of the root system, and maximum stomatal conductance increased considerably. In Red Delicious, differences between fertilized and control trees were less pronounced. In both cultivars, xylem embolism resistance of fertilized trees was significantly lower and stomatal closure occurred at lower water potentials. Furthermore, water potential at turgor loss point and osmotic potential at full saturation were higher and cell wall elasticity was lower in fertilized plants, suggesting reduced drought tolerance of leaves. Anatomical differences were observed regarding conduit diameters, cell wall reinforcement, pit membrane thickness, pit chamber depth, and stomatal pore length, with more pronounced differences in Golden Delicious. The findings reveal altered hydraulic behaviour in both apple cultivars upon fertilization. The increased vulnerability to hydraulic failure might pose a considerable risk for apple productivity under a changing climate, which should be considered for future cultivation and management practices.

Which Selective Logging Intensity is Most Suitable for the Maintenance of Soil Properties and the Promotion of Natural Regeneration in Highly Continental Scots Pine Forests?–Results 19 Years after Harvest Operations in Mongolia

Scots pine (Pinus sylvestris L.) forests are one of the main vegetation types in the Asian forest-steppe zone. However, over-harvesting currently threatens the natural regeneration and sustainability of these forests. In this study, we examine the long-term effects of different logging intensities on soil properties and natural regeneration in a natural Scots pine forest in the West Khentii Mountains (Mongolia), 19 years after selective logging. Our experimental design included five treatments: clear cut (CC), treatments with high (HI), medium (MI), low (LI) intensities, and a reference parcel with no logging impact at all (RE). We described and quantified the harvest events and applied ANOVA and LMM modeling to analyze and explain the long-term impacts of the logging intensities on soil properties and natural regeneration. We found that logging has a significant negative influence on the physical and chemical properties of the soil because it increases soil compaction and reduces soil nutrients. The most critical impacts of logging were on soil bulk density, total porosity, organic matter, and total nitrogen and phosphorus. The LMM modeling showed that organic matter (OgM), total nitrogen (TN), available K (AK) and pH values are especially impacted by logging. Our study revealed that the values for all of these variables show a linear decrease with increasing selective logging intensity and have a level of significance of p < 0.05. Another finding of this study is that selective logging with low and medium intensities can promote natural regeneration of Scots pine to numbers above those of the reference site (RE). High intensity logging and clear-cuts, however, limit the regeneration of Scots pine, reduce overall seedling numbers (p < 0.05), and create conditions that are suitable only for the regeneration of deciduous tree species. This underlines the risk of Scots pine forest degradation, either by replacement by broad-leaf trees or by conversion into non-forest ecosystems.

Comparative wood anatomy of Ficus cestrifolia (Moraceae) in two distinct soil conditions

Abstract Wood anatomical traits respond to environmental variables and among them, soil has a direct impact on secondary xylem. This study compares the wood anatomy of two populations of Ficus cestrifolia occurring in two lowland formations of Southern Brazil (MAQ and SJS) with similar climate but different soil conditions. Wood samples were collected at breast height and prepared according to standard wood anatomy techniques. Soil samples were collected and subjected to a nutrient analysis. Wood was described quali and quantitatively. The qualitative wood anatomical features of both populations were similar. Some quantitative differences were observed. In MAQ area, the levels of macro- and micronutrients were higher than in SJS. Its population presented higher vessel frequency, thicker-walled fibers, and lower vulnerability index. SJS's population had longer fibers, wider rays and a higher ray frequency, and higher vulnerability index. This suite of characters indicates that the MAQ population has a safer and more efficient xylem structure for water conduction. Under the influence of similar climate and soil type, differences regarding wood anatomical traits found between the two populations of Ficus cestrifolia can thus be regarded as an ecological response to the micro-environmental soils nutrients composition.

Phosphorous fertilization alleviates drought effects on Alnus cremastogyne by regulating its antioxidant and osmotic potential

Alnus cremastogyne, a broad-leaved tree endemic to south-western China, has both commercial and restoration importance. However, little is known of its morphological, physiological and biochemical responses to drought and phosphorous (P) application. A randomized experimental design was used to investigate how drought affected A. cremastogyne seedlings, and the role that P applications play in these responses. Drought had significant negative effects on A. cremastogyne growth and metabolism, as revealed by reduced biomass (leaf, shoot and root), leaf area, stem diameter, plant height, photosynthetic rate, leaf relative water content, and photosynthetic pigments, and a weakened antioxidative defence mechanism and high lipid peroxidation level. However, the reduced leaf area and enhanced osmolyte (proline and soluble sugars) accumulation suggests drought avoidance and tolerance strategies in this tree. Applying P significantly improved the leaf relative water content and photosynthetic rate of drought-stressed seedlings, which may reflect increased anti-oxidative enzyme (superoxide dismutase, catalase and peroxidase) activities, osmolyte accumulation, soluble proteins, and decreased lipid peroxidation levels. However, P had only a slight or negligible effect on the well-watered plants. A. cremastogyne is sensitive to drought stress, but P facilitates and improves its metabolism primarily via biochemical and physiological rather than morphological adjustments, regardless of water availability.

Arbuscular mycorrhizal fungi and foliar phosphorus inorganic supply alleviate salt stress effects in physiological attributes, but only arbuscular mycorrhizal fungi increase biomass in woody species of a semiarid environment

Salinity may limit plant growth especially in arid and semiarid regions. Arbuscular mycorrhizal fungi (AMF) and the supply of inorganic phosphorus (Pi) could alleviate the negative effects of such stress by improvement in stomatal conductance, photosynthesis and biomass. The aim of this study is to evaluate the ecophysiological performance of Cenostigma pyramidale (Tul.) E. Gagnon & G. P. Lewis (Fabaceae) in a greenhouse under salinity conditions in combination with the supply of AMF and leaf Pi. The experiment was conducted in a factorial design considering two levels of salinity (+NaCl and -NaCl), two levels of AMF (+AMF and -AMF) and two levels of leaf Pi supply (+Pi and -Pi). The variables gas exchange, leaf primary metabolism, dry biomass and nutrients were measured. Plants with AMF under non-saline conditions presented a high photosynthesis and biomass. In saline conditions, AMF promoted lower decrease in photosynthesis, high shoot dry matter and low content of leaf and root Na+ and Cl-. Plants treated with leaf Pi increased biomass and photosynthetic pigments under both conditions and accumulated more Cl- in shoots under salinity conditions. When combined, AMF * Pi increased photosynthesis only in non-saline conditions. Plants under salinity conditions without AMF and Pi had higher decreases in gas exchange and high content of Cl- in roots. Therefore, C. pyramidale plants improved their metabolism under both growth conditions in the presence of AMF, Pi or a combination of both. However, the greatest increases in growth and tolerance to salinity occurred in the isolated presence of AMF.

Nighttime stomatal conductance differs with nutrient availability in two temperate floodplain tree species

Nighttime water flow varies between plant species and is a phenomenon for which the magnitude, purpose and consequences are widely discussed. A potential benefit of nighttime stomata opening may be increased nutrient availability during the night since transpiration affects the mass flow of soil water towards plant roots. We investigated how nitrogen (N) and phosphorus (P) fertilization, and short-term drought affected stomatal conductance of Fraxinus excelsior L. and Ulmus laevis Pallas during the day (gs) and night (gn), and how these factors affected growth for a period of 18 weeks. Both species were found to open their stomata during the night, and gn responded to nutrients and water in a different manner than gs. Under N-deficiency, F. excelsior had higher gn, especially when P was sufficient, and lower pre-dawn leaf water potential (Ψpd), supporting our assumption that nutrient limitation leads to increases in nighttime water uptake. Under P-deficiency, F. excelsior had higher relative root production and, thus, adjusted its biomass allocation under P shortage, while sufficient N but not P contributed to overall higher biomasses. In contrast, U. laevis had higher gn and lower root:shoot ratio under high nutrient (especially N) availability, whereas both sufficient N and P produced higher biomasses. Compared with well-watered trees, the drought treatment did not affect any growth parameter but it resulted in lower gn, minimum stomatal conductance and Ψpd of F. excelsior. For U. laevis, only gs during July was lower when drought-treated. In summary, the responses of gs and gn to nutrients and drought depended on the species and its nutrient uptake strategy, and also the timing of measurement during the growing season. Eutrophication of floodplain forests dominated by F. excelsior and U. laevis may, therefore, considerably change nighttime transpiration rates, leading to ecosystem-level changes in plant-water dynamics. Such changes may have more severe consequences in the future as a higher frequency of drought events is predicted under climate change.

Early fruiting in Synsepalum dulcificum (Schumach. & Thonn.) Daniell juveniles induced by water and inorganic nutrient management

Background. The miracle plant, Synsepalum dulcificum (Schumach. & Thonn.) Daniell is a native African orphan crop species that has recently received increased attention due to its promise as a sweetener and source of antioxidants in both the food and pharmaceutical industries. However, a major obstacle to the species' widespread utilization is its relatively slow growth rate and prolonged juvenile period. Method. In this study, we tested twelve treatments made up of various watering regimes and exogenous nutrient application (nitrogen, phosphorus and potassium, at varying dosages) on the relative survival, growth, and reproductive development of 15-months-old S. dulcificum juveniles. Results. While the plants survived under most tested growing conditions, nitrogen application at doses higher than 1.5 g [seedling] ^-1 was found to be highly detrimental, reducing survival to 0%. The treatment was found to affect all growth traits, and juveniles that received a combination of nitrogen, phosphorus, and potassium (each at a rate of 1.5 g [seedling] ^-1), in addition to daily watering, exhibited the most vegetative growth. The simple daily provision of adequate water was found to greatly accelerate the transition to reproductive maturity in the species (from >36 months to an average of 23 months), whereas nutrient application affected the length of the reproductive phase within a season, as well as the fruiting intensity. Conclusions. This study highlights the beneficial effect of water supply and fertilization on both vegetative and reproductive growth in S. dulcificum. Water supply appeared to be the most important factor unlocking flowering in the species, while the combination of nitrogen, phosphorus and potassium at the dose of 1.5 g (for all) consistently exhibited the highest performance for all growth and yield traits. These findings will help intensify S. dulcificum's breeding and horticultural development.

Phosphorous Application Improves Drought Tolerance of Phoebe zhennan

Phoebe zhennan (Gold Phoebe) is a threatened tree species in China and a valuable and important source of wood and bioactive compounds used in medicine. Apart from anthropogenic disturbances, several biotic constraints currently restrict its growth and development. However, little attention has been given to building adaptive strategies for its conservation by examining its morphological and physio-biochemical responses to drought stress, and the role of fertilizers on these responses. A randomized experimental design was used to investigate the effects of two levels of irrigation (well-watered and drought-stressed) and phosphorous (P) fertilization treatment (with and without P) to assess the morphological and physio-biochemical responses of P. zhennan seedlings to drought stress. In addition, we evaluated whether P application could mitigate the negative impacts of drought on plant growth and metabolism. Drought stress had a significant negative effect on the growth and metabolic processes of P. zhennan. Despite this, reduced leaf area, limited stomatal conductance, reduced transpiration rate, increased water use efficiency, enhanced antioxidant enzymes activities, and osmolytes accumulation suggested that the species has good adaptive strategies for tolerating drought stress. Application of P had a significant positive effect on root biomass, signifying its improved water extracting capacity from the soil. Moreover, P fertilization significantly increased leaf relative water content, net photosynthetic rate, and maximal quantum efficiency of PSII under drought stress conditions. This may be attributable to several factors, such as enhanced root biomass, decreased malondialdehyde content, and the up-regulation of chloroplast pigments, osmolytes, and nitrogenous compounds. However, P application had only a slight or negligible effect on the growth and metabolism of well-watered plants. In conclusion, P. zhennan has a strong capability for drought resistance, while P application facilitates and improves drought tolerance mostly through physio-biochemical adjustments, regardless of water availability. It is imperative to explore the underlying metabolic mechanisms and effects of different levels of P fertilization on P. zhennan under drought conditions in order to design appropriate conservation and management strategies for this species, which is at risk of extinction.

Symbiosis with AMF and leaf Pi supply increases water deficit tolerance of woody species from seasonal dry tropical forest

In seasonal dry tropical forests, plants are subjected to severe water deficit, and the arbuscular mycorrhizal fungi (AMF) or inorganic phosphorus supply (P_i) can mitigate the effects of water deficit. This study aimed to assess the physiological performance of Poincianella pyramidalis subjected to water deficit in combination with arbuscular mycorrhizal fungi (AMF) and leaf inorganic phosphorus (P_i) supply. The experiment was conducted in a factorial arrangement of 2 water levels (+H₂O and -H₂O), 2 AMF levels (+AMF and -AMF) and 2P_i levels (+P_i and -P_i). Leaf primary metabolism, dry shoot biomass and leaf mineral nutrients were evaluated. Inoculated AMF plants under well-watered and drought conditions had higher photosynthesis and higher shoot biomass. Under drought, AMF, P_i or AMF+P_i plants showed metabolic improvements in photosynthesis, leaf biochemistry and higher biomass compared to the plants under water deficit without AMF or P_i. After rehydration, those plants submitted to drought with AMF, P_i or AMF+P_i showed a faster recovery of photosynthesis compared to treatment under water deficit without AMF or P_i. However, plants under the drought condition with AMF showed a higher net photosynthesis rate. These findings suggest that AMF, P_i or AMF+P_i increase the drought tolerance in P. pyramidalis, and AMF associations under well-watered conditions increase shoot biomass and, under drought, promoted faster recovery of photosynthesis.

Molecular cloning and functional analysis of two phosphate transporter genes from Rhizopogon luteolus and Leucocortinarius bulbiger, two ectomycorrhizal fungi of Pinus tabulaeformis

Inorganic phosphorus (Pi) is essential for plant growth, and phosphate (P) deficiency is a primary limiting factor in Pinus tabulaeformis development in northern China. P acquisition in mycorrhizal plants is highly dependent on the activities of phosphate transporters of their root-associated fungi. In the current study, two phosphate transporter genes, RlPT and LbPT, were isolated from Rhizopogon luteolus and Leucocortinarius bulbiger, respectively, two ectomycorrhizal fungi forming symbiotic interactions with the P. tabulaeformis. Phylogenetic analysis suggested that the sequence of the phosphate transporter of L. bulbiger is most closely related to a phosphate transporter of Hebeloma cylindrosporum, whereas the phosphate transporter of R. luteolus is most closely related to that of Piloderma croceum. The subcellular localization indicated that RlPT and LbPT were expressed in the plasma membrane. The complementation assay in yeast indicated that both RlPT and LbPT partially compensated for the absence of phosphate transporter activity in the MB192 yeast strain, with a K m value of 57.90 μmol/L Pi for RlPT and 35.87 μmol/L Pi for LbPT. qPCR analysis revealed that RlPT and LbPT were significantly up-regulated at lower P availability, which may enhance P uptake and transport under Pi starvation. Our results suggest that RlPT and LbPT presumably play a key role in Pi acquisition by P. tabulaeformis via ectomycorrhizal fungi.

Fast-growing Acer rubrum differs from slow-growing Quercus alba in leaf, xylem and hydraulic trait coordination responses to simulated acid rain

We investigated the effects of historic soil chemistry changes associated with acid rain, i.e., reduced soil pH and a shift from nitrogen (N)- to phosphorus (P)-limitation, on the coordination of leaf water demand and xylem hydraulic supply traits in two co-occurring temperate tree species differing in growth rate. Using a full-factorial design (N × P × pH), we measured leaf nutrient content, water relations, leaf-level and canopy-level gas exchange, total biomass and allocation, as well as stem xylem anatomy and hydraulic function for greenhouse-grown saplings of fast-growing Acer rubrum (L.) and slow-growing Quercus alba (L.). We used principle component analysis to characterize trait coordination. We found that N-limitation, but not P-limitation, had a significant impact on plant water relations and hydraulic coordination of both species. Fast-growing A. rubrum made hydraulic adjustments in response to N-limitation, but trait coordination was variable within treatments and did not fully compensate for changing allocation across N-availability. For slow-growing Q. alba, N-limitation engendered more strict coordination of leaf and xylem traits, resulting in similar leaf water content and hydraulic function across all treatments. Finally, low pH reduced the propensity of both species to adjust leaf water relations and xylem anatomical traits in response to nutrient manipulations. Our data suggest that a shift from N- to P-limitation has had a negative impact on the water relations and hydraulic function of A. rubrum to a greater extent than for Q. alba We suggest that current expansion of A. rubrum populations could be tempered by acidic N-deposition, which may restrict it to more mesic microsites. The disruption of hydraulic acclimation and coordination at low pH is emphasized as an interesting area of future study.

Responses of hydraulics at the whole-plant level to simulated nitrogen deposition of different levels in Fraxinus mandshurica

Nitrogen (N) deposition is expected to have great impact on forest ecosystems by affecting many aspects of plant-environmental interactions, one of which involves its influences on plant water relations through modifications of plant hydraulic architecture. However, there is a surprising lack of integrative study on tree hydraulic architecture responses to N deposition, especially at the whole-plant level. In the present study, we used a 5-year N addition experiment to simulate the effects of six different levels of N deposition (20-120 kg ha(-1) year(-1)) on growth and whole-plant hydraulic conductance of a dominant tree species (Fraxinus mandshurica Rupr.) from the typical temperate forest of NE China. The results showed that alleviation of N limitation by moderate concentrations of fertilization (20-80 kg ha(-1) year(-1)) promoted plant growth, but further N additions on top of the threshold level showed negative effects on plant growth. Growth responses of F. mandshurica seedlings to N addition of different concentrations were accompanied by corresponding changes in whole-plant hydraulic conductance; higher growth rate was accompanied by reduced whole-plant hydraulic conductance (Kplant) and higher leaf water-use efficiency. A detailed analysis on hydraulic conductance of different components of the whole-plant water transport pathway revealed that changes in root and leaf hydraulic conductance, rather than that of the stem, were responsible for Kplant responses to N fertilization. Both plant growth and hydraulic architecture responses to increasing levels of N addition were not linear, i.e., the correlation between measured parameters and N availability exhibited bell-shaped curves with peak values observed at medium levels of N fertilization. Changes in hydraulic architecture in response to fertilization found in the present study may represent an important underlying mechanism for the commonly observed changes in water-related tree performances in response to N deposition.

Balancing the risks of hydraulic failure and carbon starvation: a twig scale analysis in declining Scots pine

Understanding physiological processes involved in drought-induced mortality is important for predicting the future of forests and for modelling the carbon and water cycles. Recent research has highlighted the variable risks of carbon starvation and hydraulic failure in drought-exposed trees. However, little is known about the specific responses of leaves and supporting twigs, despite their critical role in balancing carbon acquisition and water loss. Comparing healthy (non-defoliated) and unhealthy (defoliated) Scots pine at the same site, we measured the physiological variables involved in regulating carbon and water resources. Defoliated trees showed different responses to summer drought compared with non-defoliated trees. Defoliated trees maintained gas exchange while non-defoliated trees reduced photosynthesis and transpiration during the drought period. At the branch scale, very few differences were observed in non-structural carbohydrate concentrations between health classes. However, defoliated trees tended to have lower water potentials and smaller hydraulic safety margins. While non-defoliated trees showed a typical response to drought for an isohydric species, the physiology appears to be driven in defoliated trees by the need to maintain carbon resources in twigs. These responses put defoliated trees at higher risk of branch hydraulic failure and help explain the interaction between carbon starvation and hydraulic failure in dying trees.

Fertilization with urea, ammonium and nitrate produce different effects on growth, hydraulic traits and drought tolerance in Pinus taeda seedlings

Urea fertilization decreases Pinus taeda L. growth in clay soils of subtropical areas. The negative effect of urea is related to changes in some hydraulic traits, similar to those observed in plants growing under drought. The aims of this work were (i) to determine whether different sources of nitrogen applied as fertilizers produce similar changes in growth and hydraulic traits to those observed by urea fertilization and (ii) to analyze the impact of those changes in plant drought tolerance. Plants fertilized with urea, nitrate [Formula: see text] or ammonium [Formula: see text] were grown well watered or with reduced water supply. Urea and [Formula: see text] fertilization reduced plant growth and increased root hydraulic conductance scaled by root dry weight (DW). [Formula: see text] fertilization did not reduce plant growth and increased shoot hydraulic conductance and stem hydraulic conductivity. We conclude that [Formula: see text] is the ion involved in the changes linked to the negative effect of urea fertilization on P. taeda growth. [Formula: see text] fertilization does not change drought susceptibility and it produces changes in shoot hydraulic traits, therefore plants avoid the depressive effect of fertilization. Urea and [Formula: see text] fertilizers induce changes in DW and root hydraulic conductance and consequently plants are less affected by drought.

Different mechanisms drive the performance of native and invasive woody species in response to leaf phosphorus supply during periods of drought stress and recovery

The effects of drought stress and leaf phosphorus (Pi) supply on photosynthetic metabolism in woody tropical species are not known, and given the recent global environmental change models that forecast lower precipitation rates and periods of prolonged drought in tropical areas, this type of study is increasingly important. The effects of controlled drought stress and Pi supply on potted young plants of two woody species, Anadenanthera colubrina (native) and Prosopis juliflora (invasive), were determined by analyzing leaf photosynthetic metabolism, biochemical properties and water potential. In the maximum stress, both species showed higher leaf water potential (Ψl) in the treatment drought +Pi when compared with the respective control -Pi. The native species showed higher gas exchange under drought +Pi than under drought -Pi conditions, while the invasive species showed the same values between drought +Pi and -Pi. Drought affected the photochemical part of photosynthetic machinery more in the invasive species than in the native species. The invasive species showed higher leaf amino acid content and a lower leaf total protein content in both Pi treatments with drought. The two species showed different responses to the leaf Pi supply under water stress for several variables measured. In addition, the strong resilience of leaf gas exchange in the invasive species compared to the native species during the recovery period may be the result of higher efficiency of Pi use. The implications of this behavior for the success of this invasive species in semiarid environments are discussed.