The Infection Process of Pestalotiopsis Longisetula Leaf Spot on Strawberry Leaves

Pestalotia leaf spot, caused by the fungus Pestalotiopsis longisetula Guba, has become the major disease affecting strawberry production in Brazil. Strawberry seedlings with 4–5 leaves were inoculated with a conidial suspension of P. longisetula (2 × 10⁵ conidia/ml), and leaf samples were collected at 48, 72, 96 and 144 h after inoculation (hai) for observation in the scanning electron microscope. Conidia germinated within 48 hai. At 72 hai, conidia had formed very long germ tubes over the epidermal cells without any evidence of appressorial formation nor direct penetration. At 96 hai, fungal hyphae grew inter‐ and intracellularly in the lacunous parenchyma and also through tracheary elements. Pycnidia were first observed on the leaf surface at 96 hai. At 144 hai, conidia of P. longisetula were first liberated from the pycnidia. This study adds new information to better understand of the infection process of P. longisetula that may help in developing more effective disease control strategies.     

Calonectria leaf blight of Eucalyptus: A global review

Calonectria (= Cylindrocladium), an internationally recognised fungal ascomycete genus, causes significant diseases on numerous crops of forestry, horticultural and agricultural interest. Eucalyptus, an economically important multipurpose plantation forestry species, is severely threatened by Calonectria leaf blight (CLB) disease in Brazil, Australia, China, Indonesia, Vietnam and India. The disease causes serious mortality in the nurseries/plantations and yield losses due to defoliation. Since the first report of Calonectria in 1867, efforts have been made for the identification and characterisation of this vastly diverse hypocrealean genus. Currently, the genus Calonectria harbours 131 species grouped within 11 species complexes, and broadly categorised into the Prolate and Sphaero-Naviculate groups. Globally, 35 Calonectria species distributed in seven species complexes cause CLB of Eucalyptus, out of which 29 belong to the Prolate group and five to the Sphaero-Naviculate group. Likewise, 28 Calonectria species distributed in eight species complexes have been reported in association with infected Eucalyptus tissues and plantation soil, however, their pathogenicity remains to be determined. Given the importance of CLB of Eucalyptus, this review compiles its global impact, shifts in taxonomy and nomenclature of Calonectria, pathogenesis mechanism, defence response of Eucalyptus upon infection and disease management. This study identifies and provides direction to crucial areas of future research on CLB which is severely impacting Eucalyptus plantations globally.     

Effects of forest types on leaf functional traits and their interrelationships of Pinus massoniana coniferous and broad‐leaved mixed forests in the subtropical mountain,Southeastern China

Leaf functional traits are widely used to detect and explain adaptations that enable plants to live under various environmental conditions. This study aims to determine the difference in leaf functional traits among four forest types of Pinus massoniana coniferous and broad‐leaved mixed forests by leaf morphological, nutrients, and stoichiometric traits in the subtropical mountain, Southeastern China. Our study indicated that the evergreen conifer species of P. massoniana had higher leaf dry matter content (LDMC), leaf C content, C/N and C/P ratios, while the three deciduous broad‐leaved species of L. formosana, Q. tissima, and P. strobilacea had higher specific leaf area (SLA), leaf N, leaf P nutrient contents, and N/P ratio in the three mixed forest types. The results showed that the species of P. massoniana has adapted to the nutrient‐poor environment by increasing their leaf dry matter for higher construction costs thereby reducing water loss and reflects a resource conservation strategy. In contrast, the three species of L. formosana, Q. tissima, and P. strobilacea exhibited an optimized resource acquisition strategy rather than resource conservation strategy in the subtropical mountain of southeastern China. Regarding the four forest types, the three mixed forest types displayed increased plant leaf nutrient contents when compared to the pure P. massoniana forest, especially the P. massoniana–L. formosana mixed forest type (PLM). Overall, variation in leaf functional traits among different forest types may play an adaptive role in the successful survival of plants under diverse environments because leaf functional traits can lead to significant effects on leaf function, especially for their acquisition of nutrients and use of light. The results of this study are beneficial to reveal the changes in plant leaf functional traits at the regional scale, which will provide a foundation for predicting changes in leaf traits and adaptation in the future environment.     

Rice Resistance to Sheath Blight Mediated by Potassium

This study investigated the effect of potassium (K) on sheath blight (Rhizoctonia solani) development on rice plants from cultivars BR‐IRGA 409 and Labelle grown in nutrient solution containing 0, 50 and 100 mm of K. Sheath blight progress on inoculated sheaths was evaluated by measuring the relative lesion length at 48, 72, 96 and 120 h after inoculation (hai). Data were used to calculate the area under relative lesion length progress curve (AURLLPC). The foliar K concentration on leaf sheaths tissue increased by 61.48 and 116.05% to cultivars BR‐IRGA 409 and Labelle, respectively, as the K rates increased from 0 to 100 mm . A linear model best described the relationship between the AURLLPC and the K rates. The AURLLPC decreased by 29.2 and 21.3% for cultivars BR‐IRGA 409 and Labelle, respectively, as the K rates in the nutrient solution increased. It can be concluded that high K concentration on leaf sheaths tissue was important to decrease sheath blight symptoms on rice leaf sheaths.     

Litterfall deposition and leaf litter nutrient return in different locations at Northeastern Mexico

The aim of this study was to determine the litterfall production and macronutrient (Ca, K, Mg, N, and P) deposition through leaf litter in four sites with different types of vegetation. Site one (Bosque Escuela) was located at 1600 m a.s.l. in a pine forest mixed with deciduous trees, second site (Crucitas at 550 m a.s.l.) in the ecotone of a Quercus spp. forest and the Tamaulipan thornscrub and third and fourth sites (Campus at 350 m a.s.l. and Cascajoso at 300 m a.s.l., respectively) were in the Tamaulipan thornscrub. Litter constituents (leaves, reproductive structures, twigs, and miscellaneous residues) were collected at 15-day intervals from December 21, 2006, throughout December 20, 2007. Collections were carried out in ten litter traps (1.0 × 1.0 m) randomly situated at each site of approximately 2,500 m². Total annual litterfall deposition was 4407, 7397, 6304, and 6527 kg ha⁻¹ y⁻¹ for Bosque Escuela, Crucitas, Campus and Cascajoso, respectively. Of total annual litter production, leaves were higher varying from 74 (Bosque Escuela) to 86% (Cascajoso) followed by twigs from 4 (Cascajoso) to 14% (Crucitas), reproductive structures from 6 (Bosque Escuela) to 10% (Crucitas), and miscellaneous litterfall from <1 (Campus) to 12% (Bosque Escuela). The Ca annual deposition was significantly higher in Cascajoso (232.7 kg ha⁻¹ y⁻¹), followed by Campus (182.3), Crucitas (130.5) and Bosque Escuela (30.3). The K (37.5, 32.5, 24.8, 7.2, respectively), Mg (22.6, 17.7, 13.7, 4.5, respectively) followed the same pattern as Ca. However, N was higher in Campus (85.8) followed by Crucitas (85.1), Cascajoso (68.3), and Bosque Escuela (18.3). The P was higher in Campus and Crucitas (4.0) followed by Cascajoso (3.4) and Bosque Escuela (1.4). On an annual basis for all sites, the order of nutrient deposition through leaf litter was Ca > N> K > Mg > P, whereas on site basis of total nutrient deposition (Ca + N + K + Mg + P), the order was Cascajoso > Campus > Crucitas > Bosque Escuela. Ca, K, Mg, N, and P nutrient use efficiency values in leaf litter were higher in Bosque Escuela, while lower figures were acquired in Cascajoso and Crucitas sites. It seems that the highest litterfall deposition was found in the ecotone of a Quercus spp. forest and the Tamaulipan thornscrub; however, the Tamaulipan thornscrub vegetation alone had better leaf litter nutrient return.     

喀斯特地区野生毛葡萄的钙组分特征及其对高钙环境的适应性分析北大核心CSCD

为了探究喀斯特地区野生毛葡萄(Vitis quinquangularis Rehd.)器官的钙含量、组分及其分布特征,揭示野生毛葡萄的需钙特性及其对高钙土壤的适应机制。该研究以贵州喀斯特地区野生毛葡萄为材料,取样测定了40个样地的野生毛葡萄立地土壤的pH值、交换性钙含量及其根、茎、叶中钙和镁及其钙组分含量,分析土壤交换性钙含量与不同钙组分间的关系,并观察野生毛葡萄叶片表面及根、茎、叶中的钙晶体。结果表明:(1)喀斯特地区野生毛葡萄总钙含量在器官中的分布表现为叶>根>茎,其分布特征与喜钙植物类似。(2)野生毛葡萄根、茎、叶中主要钙组分含量由高到低依次基本为草酸钙、果胶酸钙、水溶性钙、磷酸钙+碳酸钙、硝酸钙+氯化钙、硅酸钙(茎中稍有不同),根、茎、叶中草酸钙占所有钙组分总量和总钙含量的比例均最高,其次是果胶酸钙。(3)各样地野生毛葡萄叶片中Ca+Mg的含量范围在1.30%~4.07%之间,绝大多数在3.0%~4.0%范围内,表现出喜钙植物叶中高Ca+Mg含量的特性。(4)在喀斯特地区的野生毛葡萄体内,多种钙组分含量与土壤中的钙含量呈显著或极显著的正相关关系。(5)扫描电镜观察发现,野生毛葡萄叶片和根中储存有大量的草酸钙晶体,叶片中的草酸钙可通过气孔排出体外。研究发现,喀斯特地区野生毛葡萄属于喜钙植物,对喀斯特高钙环境的适应性强,叶片中钙的富集量大,有大量的草酸钙和果胶酸钙储存于体内,这种储钙特性和气孔的排钙行为对野生毛葡萄适应高钙环境具有重要作用。     

Seasonal drought and dry‐season irrigation influence leaf‐litter nutrients and soil enzymes in a moist,lowland forest in Panama

Abstract Climatic conditions should not hinder nutrient release from decomposing leaf‐litter (mineralization) in the humid tropics, even though many tropical forests experience drought lasting from several weeks to months. We used a dry‐season irrigation experiment to examine the effect of seasonal drought on nutrient concentrations in leaf‐fall and in decomposing leaf‐litter. In the experiment, soil in two 2.25‐ha plots of old‐growth lowland moist forest on Barro Colorado Island, Republic of Panama, was watered to maintain soil water potential at or above field capacity throughout the 4‐month dry season. Wet‐season leaf‐fall had greater concentrations of nitrogen (N, 13.5 mg g^?1) and calcium (Ca, 15.6 mg g^?1) and lower concentrations of sulfur (S, 2.51 mg g^?1) and potassium (K, 3.03 mg g^?1) than dry‐season leaf‐fall (N = 11.6 mg g^?1, Ca = 13.6 mg g^?1, S = 2.98 mg g^?1, K = 5.70 mg g^?1). Irrigation did not affect nutrient concentrations or nutrient return from forest trees to the forest floor annually (N = 18 g m^?2, phosphorus (P) = 1.06 g m^?2, S = 3.5 g m^?2, Ca = 18.9 g m^?2, magnesium = 6.5 g m^?2, K = 5.7 g m^?2). Nutrient mineralization rates were much greater during the wet season than the dry season, except for K, which did not vary seasonally. Nutrient residence times in forest‐floor material were longer in control plots than in irrigated plots, with values approximately equal to that for organic matter (210 in control plots vs 160 in irrigated plots). Calcium had the longest residence time. Forest‐floor material collected at the transition between seasons and incubated with or without leaching in the laboratory did not display large pulses in nutrient availability. Rather, microorganisms immobilized nutrients primarily during the wet season, unlike observations in tropical forests with longer dry seasons. Large amounts of P moved among different pools in forest‐floor material, apparently mediated by microorganisms. Arylsulfatase and phosphatase enzymes, which mineralize organically bound nutrients, had high activity throughout the dry season. Low soil moisture levels do not hinder nutrient cycling in this moist lowland forest.     

Eucalyptus recruitment in degraded woodlands: no benefit from elevated soil fertility

Grasses and forbs compete heavily with young tree seedlings for available resources, greatly reducing tree seedling establishment success. Soil nutrient enrichment associated with agricultural intensification can increase the growth of both herbaceous and woody lifeforms growing in isolation, but may change the balance of competitive advantage when growing together. The effects of nitrogen and phosphorus enrichment on pasture biomass and competition with two Australian grassy woodland trees (Eucalyptus albens and Eucalyptus microcarpa) was investigated in a field plot trial. Soil nutrients increased pasture biomass, but had no measurable effect on tree growth in our experiment. Competition from pasture species, even at low levels, led to high tree seedling mortality and greatly reduced tree seedling growth compared with pasture-free plots. However, when pasture-free plots were excluded from the analysis, tree seedling leaf area was not strongly correlated with herbaceous biomass. Tree seedling establishment was severely restricted even at the lowest levels of pasture biomass. We conclude that increased soil fertility resulted in a competitive advantage to the pasture, and does not improve tree seedling establishment when grown either with or without exotic herbaceous pasture (grassy understorey) species.     

Mineral nutrient economy in competing species of Sphagnum mosses

Bog vegetation, which is dominated by Sphagnum mosses, depends exclusively on aerial deposition of mineral nutrients. We studied how the main mineral nutrients are distributed between intracellular and extracellular exchangeable fractions and along the vertical physiological gradient of shoot age in seven Sphagnum species occupying contrasting bog microhabitats. While the Sphagnum exchangeable cation content decreased generally in the order Ca²⁺ ≥ K⁺, Na⁺, Mg²⁺ > Al³⁺ > NH₄ ⁺, intracellular element content decreased in the order N > K > Na, Mg, P, Ca, Al. Calcium occurred mainly in the exchangeable form while Mg, Na and particularly K, Al and N occurred inside cells. Hummock species with a higher cation exchange capacity (CEC) accumulated more exchangeable Ca²⁺, while the hollow species with a lower CEC accumulated more exchangeable Na⁺, particularly in dead shoot segments. Intracellular N and P, but not metallic elements, were consistently lower in dead shoot segments, indicating the possibility of N and P reutilization from senescing segments. The greatest variation in tissue nutrient content and distribution was between species from contrasting microhabitats. The greatest variation within microhabitats was between the dissimilar species S. angustifolium and S. magellanicum. The latter species had the intracellular N content about 40% lower than other species, including even this species when grown alone. This indicates unequal competition for N, which can lead to outcompeting of S. magellanicum from mixed patches. We assume that efficient cation exchange enables Sphagnum vegetation to retain immediately the cationic nutrients from rainwater. This may represent an important mechanism of temporal extension of mineral nutrient availability to subsequent slow intracellular nutrient uptake.     

A comparative study of aluminium and nutrient concentrations in mistletoes on aluminium‐accumulating and non‐accumulating hosts

Mistletoes offer a unique model to study interactions among Al and nutrients in vascular plants, because they grow and reproduce on hosts with distinct Al uptake strategies. We investigated Al distribution and nutrient relations of mistletoes on Al‐accumulating and non‐accumulating hosts. We hypothesised that mistletoes would exhibit similar leaf nutrient and Al concentrations as their host plants, but a strong compartmentalisation of Al when growing on Al‐accumulators. We measured concentrations of N, P, K, Ca, Mg, Cu, Fe, Mn, Zn in leaves and Al in leaves, seeds and branches of Phthirusa ovata and Psittacanthus robustus infecting Miconia albicans, an Al‐accumulator, and Ph. ovata infecting Byrsonima verbascifolia, a non‐Al‐accumulator. High leaf concentrations of Al in Ph. ovata only occurred while parasitizing the Al‐accumulating host; there was no accumulation in branches or seeds. In P. robustus, large concentrations of Al were found in leaves, branches and seeds. Mistletoe seed viability and leaf nutrient concentrations were not affected by Al accumulation. Passive uptake of Al, Ca, Mg, Mn and Cu in mistletoes was evidenced by significant correlations between mistletoes and host leaf concentrations, but not of N, P and K. Al was retranslocated to different plant organs in P. robustus, whereas it was mostly restricted to leaves in Ph. ovata. We suggest that Al might have some specific function in P. robustus, which only parasitizes Al‐accumulator hosts, while the host generalist Ph. ovata can be considered a facultative Al‐accumulator.     

Effects of compound growth regulators on the anatomy of Jujube Leaf and Fruit

Effects of three compound growth regulators formulated with hypersensitivity protein, spermidine, salicylic acid and DA-6 (diethyl aminoethanol hexanoate) were tested on Xinjiang Jun Jujube. The doses of compound growth regulators were named as A (Hypersensitivity protein + spermidine + salicylic acid at the rate of 30 mg/L, 0.1 mmol/L and 0.25 mmol/L, respectively), B (Hypersensitive protein + spermidine + DA-6 at the rate of 30 mg/L, 0.1 mmol/L and 30 mg/L, respectively) and C (Spermidine + salicylic acid + DA-6 at the rate of 0.1 mmol/L, 0.25 mmol/L and 30 mg/L, respectively) versus a control group CK (contained only water). Fruit anatomical structures were compared after spraying. The results indicated that after spraying, the thickness of the upper and lower epidermal cells and the stratum corneum were increased. However, the upper epidermal stratum corneum became significantly thicker than the lower epidermis. Spraying with A improved the thickness of upper and lower epidermal cells, stratum corneum, the central vein and mesophyll. The cumulative effects of all these changes in leaf and fruit anatomical structures provided the resistance of the experimental fruit plant to stress. While the B and C regulators had inhibitory effects. So, the results obtained after spraying A category were beneficial to improve the stress resistance of the fruits. The length and cell area of pericarp and sarcocarp cells in the treatment groups were not changed significantly. But the length, number of sarcocarp cells and number of gaps were lower than those in the CK. This study can provide new measures for improving plant resistance in jujube production.     

Effects of early-fruit removal on endogenous cytokinins and abscisic acid in relation to leaf senescence in cotton

Numerous studies have shown that early-fruit removal enhances vegetative growth and development of cotton (Gossypium hirsutum L.). However, few studies have examined changes in leaf senescence and endogenous hormones due to fruit removal. The objective of this study was to determine the correlation between some endogenous phytohormones, particularly the cytokinins and abscisic acid (ABA), and leaf senescence following fruit removal. Cotton was grown in pots and in the field during 2005 and 2006. Two early-fruiting branches were excised from plants at squaring to form the fruit removal treatment while the non-excised plants served as control. Plant biomass, seed cotton yield, cytokinins and ABA levels in main-stem leaves and xylem sap as well as main-stem leaf photosynthetic rate (Pn) and chlorophyll (Chl) concentration were determined after removal or at harvest. Fruit removals increased the leaf area, root and shoot dry weight and plant biomass at 35 days after removal (DAR), whether in potted or field-grown cotton; under field conditions, it also improved plant biomass and seed cotton yield at harvest. The Pn and Chl concentration in excised plants were significantly higher than in control plants from 5 to 35 DAR, suggesting that fruit removal considerably delayed leaf senescence. Fruit-excised plants contained more trans-zeatin and its riboside (t-Z + t-ZR), dihydrozeatin and its riboside (DHZ + DHZR), and isopentenyladenine and its riboside (iP + iPA) but less ABA in both main-stem leaves and xylem sap than control plants from 5 to 35 DAR. These results suggest that removal of early fruiting branches delays main-stem leaf senescence, which can be attributed to increased cytokinin and/or reduced ABA. Cytokinin and ABA are involved in leaf senescence following early fruit removal.     

Growth-promoting bacteria and natural regulators mitigate salt toxicity and improve rapeseed plant performance

Salinity is a major environmental stress that limits plant production and portraits a critical challenge to food security in the world. In this research, the impacts of plant growth–promoting bacteria (Pseudomonas RS-198 and Azospirillum brasilense RS-SP7) and foliar application of plant hormones (salicylic acid 1 mM and jasmonic acid 0.5 mM) on alleviating the harmful effects of salt stress in rapeseed plants (Brassica napus cv. okapi) were examined under greenhouse condition. Salt stress diminished rapeseed biomass, leaf area, water content, nitrogen, phosphorus, potassium, calcium, magnesium, and chlorophyll content, while it increased sodium content, endogenous salicylic and jasmonic acids, osmolyte production, H₂O₂ and O₂^•− generations, TBARS content, and antioxidant enzyme activities. Plant growth, nutrient content, leaf expansion, osmolyte production, and antioxidant enzyme activities were increased, but oxidative and osmotic stress indicators were decreased by bacteria inoculation + salicylic acid under salt stress. Antioxidant enzyme activities were amplified by jasmonic acid treatments under salt stress, although rapeseed growth was not generally affected by jasmonic acid. Bacterial + hormonal treatments were superior to individual treatments in reducing detrimental effects of salt stress. The best treatment in rectifying rapeseed growth under salt stress was combination of Pseudomonas and salicylic acid. This combination attenuated destructive salinity properties and subsequently amended rapeseed growth via enhancing endogenous salicylic acid content and some essential nutrients such as potassium, phosphorus, and magnesium.

     

Influence of Non-nitrogenous Soil Amendments on Soil CO2 Efflux and Fine Root Production in an N-Saturated Northern Hardwood Forest

Non-nitrogenous mineral nutrients may be an important constraint on forest productivity and belowground processes in many ecosystems. We measured responses of soil CO₂ efflux (FCO₂), fine root production, and root-free incubation soil respiration to experimental additions of non-nitrogenous mineral nutrients (phosphorus (P) + potassium (K) fertilizer, dolomitic lime, and P + K plus lime) over 2 years in a sugar-maple-dominated forest in central Ontario; this region receives some of the highest anthropogenic nitrogen (N) inputs in North America, and evidence exists for co-limitation by P, magnesium (Mg), and calcium (Ca) of the growth of dominant trees. Soil amendments, in particular P + K fertilization, reduced FCO₂, fine root production and microbial respiration, with decreases in FCO₂ of 28–51% in fertilized compared to control plots. Partial regression analyses indicated that soil available P had a negative effect on FCO₂, fine root production, and microbial respiration, but detected no significant effects of N, Ca, or Mg. Path analysis further suggested that available P reduced both fine root production and microbial respiration, and that these effects were largely responsible for reduced FCO₂. There was also a residual direct negative relationship between available P and FCO₂, which may represent reduced metabolic activity of roots. The study indicates that P is a critical nutrient dominating belowground processes in an N-saturated forest ecosystem, and suggests that additions of P may enhance C sink strength in managed forests in part through reductions in soil CO₂ efflux.     

Infection Process of Botrytis cinerea on Eucalypt Leaves

This study aimed to elucidate the infection process of Botrytis cinerea on eucalypt leaves. Tests were conducted to evaluate the influence of leaf side (adaxial or abaxial), leaf age and luminosity on conidial germination, appressorium formation and grey mould (GM) severity. The adaxial and abaxial surfaces of detached eucalypt leaves were inoculated with a conidial suspension of B. cinerea and kept under constant light or dark. Subsequently, the adaxial surface of young and old leaves was inoculated and kept in the dark. To evaluate the percentage of conidia germination and appressorium formation, leaf samples were collected 6 hours after inoculation (hai), clarified (alcohol and chloral hydrate) and evaluated under a light microscope. The severity of GM was assessed 10 days after inoculation. For scanning electron microscopy analysis, samples were collected from 2 to 168 hai. A higher percentage of conidia germination (92%) and GM severity (21%) occurred on the adaxial surfaces of leaves kept in the dark. There was no statistical difference between the surfaces of young and old leaves for conidia germination. No appressorium was formed by B. cinerea. The GM severity on young leaves (17.3%) was 34 times higher than on old leaves (0.5%). The micrographs showed germinating conidia emitting 1–4 germ tubes in samples at 4 hai. The fungus penetration occurred through intact leaf surfaces, and both extra‐ and intracellular colonization of the mesophyll cells by the hyphae of the pathogen were observed at 120 hai. Sporulation occurred on the adaxial and abaxial surfaces (macronematous conidiophores) and below the epidermis (micronematous conidiophores).     

Alleviation of phosphorus deficiency stress by moderate salinity in the halophyte <Emphasis Type="Italic">Hordeum maritimum</Emphasis> L.

Hordeum maritimum (Poacea) is a facultative halophyte potentially useful for forage production in saline zones. Here, we assessed whether moderate NaCl-salinity can modify the plant response to phosphorus (P) shortage. Plants were cultivated for 55 days under low or sufficient P supply (5 or 60 μmol plant⁻¹ week⁻¹ KH₂PO₄, respectively), with or without 100 mM NaCl. When individually applied, salinity and P deficiency significantly restricted whole-plant growth, with a more marked effect of the latter stress. Plants subjected to P deficiency showed a significant increase in root growth (as length and dry weight) and root/shoot DW ratio. Enhanced root growth and elongation presumably correspond to the well-known root adaptive response to mineral deficiency. However, leaf relative water content, leaf P concentration, and leaf gas exchange parameters were significantly restricted. The interactive effects of salinity and P deficiency were not added one to another neither on whole plant biomass nor on plant nutrient uptake. Indeed, 100 mM NaCl-addition to P-deficient plants significantly restored the plant growth and improved CO₂ assimilation rate, root growth, K⁺/Na⁺ ratio and leaf proline and soluble sugar concentrations. It also significantly enhanced leaf total antioxidant capacity and leaf anthocyanin concentration. This was associated with significantly lower leaf osmotic potential, leaf Na⁺ and malondialdehyde (MDA) concentration. Taken together, these results suggest that mild salinity may mitigate the adverse effects of phosphorus deficiency on H. maritimum by notably improving the plant photosynthetic activity, the osmotic adjustment capacity, the selective absorption of K⁺ over Na⁺ and antioxidant defence.     

Latitudinal Patterns and Climatic Drivers of Leaf Litter Multiple Nutrients in Chinese Broad-Leaved Tree Species: Does Leaf Habit Matter?

Leaf litter nutrients play a key role in nutrient cycling in forest ecosystems, yet our current knowledge of the ways in which climate controls leaf litter nutrients remains uncertain, especially for broad-leaved tree species in China. We performed a meta-analysis of geographic patterns of leaf litter nutrients of Chinese broad-leaved tree species in relation to climatic variables and leaf habit (as a discrete classification of tree species). We found that mean leaf litter carbon (C), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were 458.36, 10.11, 0.72, 6.37, 14.22 and 2.59 mg^?1 g, respectively. Leaf litter nutrients did not diverge between leaf habits where they coexisted. These leaf litter nutrients displayed significant latitudinal trends, partly driven by climatic factors and a shift in leaf habit. Mean annual precipitation explained the largest amount of total variation in leaf litter C, N, P and K, and mean annual temperature was the most important predictor for leaf litter Mg, whereas leaf habit was the largest contributor to total variation in leaf litter Ca. We further found that the relationships between climate and leaf litter nutrients were distinguishable for evergreen and deciduous broad-leaved tree species. Collectively, our study differed from previous studies that evaluated leaf litter nutrients and only focused on N and P, and substantiated that leaf litter nutrients in forest ecosystems were affected by climate and leaf habit, but the strengths of the influences of these factors were strongly contingent on leaf litter nutrient identity. Therefore, alteration of climate would directly and indirectly (via a shift in species composition) affect latitudinal patterns of leaf litter nutrients and thus the associated nutrient flux and ecosystem functioning. Our study also underlined the need to include multiple nutrients to explore the influence of climate on leaf litter nutrient stoichiometry.     

Effect of potassium on growth and nitrate reductase during water stress and recovery in maize

Abstract The effect of potassium (0,50, 100 and 200 mg/pot) was studied on growth characteristics and nitrate reductase activity in maize (Zea mays) seedlings during water stress and subsequent recovery. In irrigated plants K⁺ increased the rate of leaf area expansion, leading to increased leaf area per plant. Increased leaf area was associated with decreased chlorophyll content. Water stress (–15 bars) enhanced the stomatal resistance of leaves which was further accentuated by K⁺ application. Nitrate reductase activity rose in irrigated plants 24 h after K⁺ application. Subsequently, as water stress developed, K⁺ helped to maintain higher NR activity for the first two days. However, K⁺ had no effect on half life of NR in light or darkness. During recovery from stress K⁺ aided to maintain the higher leaf expansion rate, the chlorophyll content and the stomatal resistance. The results above are discussed in relation to the ability of K⁺ to maintain better growth under water stress.     

干热河谷区不同林龄赤桉叶中养分含量和再吸收率的比较及其线性回归分析

以种植于干热河谷区的赤桉(Eucalyptus camaldulensis Dehnh.)幼龄林、中龄林和成熟林为研究对象,分析了赤桉鲜叶和凋落叶中养分(包括N、P、K、Ca、Mg和Na)的含量和化学计量比,并计算各养分的再吸收率;在此基础上,对鲜叶和凋落叶中各养分的含量与再吸收率进行线性回归分析.结果表明:成熟林赤桉鲜叶和凋落叶的有机碳、全氮、全磷、全钾和全钠含量总体上高于幼龄林,而全钙和全镁含量则低于幼龄林;且鲜叶中的全氮、全磷、全钾、全钠和全镁含量总体上高于凋落叶,而有机碳和全钙含量则低于凋落叶.成熟林赤桉鲜叶和凋落叶的C:N比、鲜叶的N:P比和N:K比以及凋落叶的K:P比和Ca:Mg比均低于幼龄林,但其鲜叶的K:P比和Ca:Mg比及凋落叶的N:P比和N:K比则高于幼龄林;且不同林龄鲜叶的C:N比、K:P比和Ca:Mg比均低于凋落叶.各林龄赤桉叶的Ca再吸收率及幼龄林和中龄林叶的Na再吸收率均为负值,而其余养分的再吸收率均为正值;随林龄增长,N、K和Mg的再吸收率先升高后降低,而P、Ca和Na的再吸收率却先降低后升高;总体上看,赤桉叶中各养分的再吸收率从高到低依次为P、N、K、Mg、Na、Ca.线性回归分析结果表明:赤桉鲜叶的全钾和全钠含量分别与K和Na再吸收率呈极显著正相关(P<001),全钙含量与Ca再吸收率呈显著正相关(P<005);而凋落叶的全氮含量与N再吸收率呈极显著负相关,全镁含量与Mg再吸收率呈显著负相关.综合分析结果显示:林龄对赤桉叶的养分含量和再吸收率有明显影响,其保存养分的能力随林龄增长呈现先增强后减弱的趋势.     

Calcium plus magnesium indicates digestibility: the significance of the second major axis of plant chemical variation for ecological processes

Plant variation in nutrient concentrations encompasses two major axes. The first is connected to nitrogen (N) and phosphorus (P), reflects growth rate and has been designated as the leaf economics spectrum (LES) while the second follows the gradient in calcium (Ca) and magnesium (Mg) and mirrors cell structural differences. Here, we tested in grasslands whether the sum Ca + Mg concentrations is a better indicator of digestibility than LES constituents. Structural equation modelling revealed that the total effect size of N (0.30) on digestibility was much lower than that of Ca + Mg (0.58). The N effect originated predominantly from sampling date (biomass ageing), while the Ca + Mg effect largely from phylogenetic composition (proportion of monocots). Thus, plant variation in partially substitutable divalent cations seems to play a significant role in biomass digestion by ruminants. This finding contests, together with litter decomposition studies, the prominent role of the LES for understanding both fundamental ecological processes.